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Electronics => Metrology => Topic started by: zlymex on September 28, 2016, 09:39:32 pm

Title: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on September 28, 2016, 09:39:32 pm
Brief facts
 - 2DW23x series is a Chinese brand temperature compensated Zener reference
 - There are two identical zener diodes connected in back to back manner in a 3-lead TO-39 package.
(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=258770;image)
 - Norminal voltage 6.0V t0 6.5V
 - Norminal zero-TC current ranges from 5mA to 15mA depending on types.
 - Datasheet(in Chinese) http://www.chinaeds.com/zl/%E5%B8%B8%E7%94%A8IC%5C2%5C2D%5C2DW230.pdf (http://www.chinaeds.com/zl/%E5%B8%B8%E7%94%A8IC%5C2%5C2D%5C2DW230.pdf)

Why 2DW23x
These 2DW23x series(2DW232, 2DW233, 2DW234, 2DW235) has been around for many year and was probably the only 'reference grade' zener in China. Previously known as 2DW7C and changed name about ten years ago. There were/are many manufacturers making these devices and I have tons of them. The performance varies according to makers very much and generally are poor (aging rate, tempco, noise). I've never use them in my designs/circuits.

However, people discovered that there is this Shanghai 17th Radio Factory making this particular Diamond brand(there is a diamond symbol on face of each device) with exceptional low noise, even lower than that of LTZ1000. I didn't believed, but there are a lot of buying/teardown/discuss about it:
http://bbs.38hot.net/forum.php?mod=viewthread&tid=49306 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=49306)
http://bbs.38hot.net/forum.php?mod=viewthread&tid=84620 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=84620)
http://bbs.38hot.net/forum.php?mod=viewthread&tid=119921 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=119921)
http://bbs.38hot.net/forum.php?mod=viewthread&tid=120264 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=120264)
http://bbs.38hot.net/forum.php?mod=viewthread&tid=120731 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=120731)

So, I built my own noise meter recently and bought some samples. At first, the noise tested is not good, 1.2uVp-p, same or slightly inferior to LTZ1000. However, some one soon pointed out that the power supply might be the problem. After I changed the power source to batteries, I got even better result than others: 0.4uVp-p at 5mA, which is one third of LTZ1000. I swapped devices, altered current, measured my other LTZ1000 based voltages(4910, 732A, 732B etc) as reference, and I bought more 2DW23x from other e-stores, they all show this ultra-low noise characteristic.


Availability
I bought about 200 unit of 2DW233 from here: https://item.taobao.com/item.htm?spm=a1z09.2.0.0.gpf2Zk&id=35815633601 (https://item.taobao.com/item.htm?spm=a1z09.2.0.0.gpf2Zk&id=35815633601)
(https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/?action=dlattach;attach=224337;image)
Then I bought 550 unit of 2DW234 from another seller.

There are many sellers at Aliexpress selling these cheaply but only buy those with diamond mark on the top such as
http://www.aliexpress.com/item/Free-shipping-2DW233-DIP3/32433963421.html (http://www.aliexpress.com/item/Free-shipping-2DW233-DIP3/32433963421.html)
http://www.aliexpress.com/item/hot-spot-10pcs-2DW232-new-original-in-stock/32637084815.html (http://www.aliexpress.com/item/hot-spot-10pcs-2DW232-new-original-in-stock/32637084815.html)
https://www.aliexpress.com/item/High-quality-10Pcs-2DW234-2DW235-2DW236-New/32527935820.html (https://www.aliexpress.com/item/High-quality-10Pcs-2DW234-2DW235-2DW236-New/32527935820.html)
Be warned, I got these links by searching only. Someone was buying one of the entries and did not receive the package in 75 days.


My plan to test/use
1. A very simple circuit(batteries+resistor) to test/verify noise, done.

2. A simple circuit to test/seek the zero-TC point, partially done.
For a given device at given zener current, there is a convex shape of voltage-temperature curve and there is a peak voltage which is the zero-TC point for temperature.
(https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=258879;image)
Because of this, for a given device at given temp, there is a convex shape of voltage-current curve and there is a peak voltage which is the zero-TC point for zener current.
The type number(2DW232, 2DW233) indicating different nominal zener current for this zero-TC point. For instance, the zero-TC current of 2DW232 is 5mA, the zero-TC current of 2DW233 is 7.5mA, the zero-TC current of 2DW234 is 10mA, and so on.
But in reality,  there is not much difference. A device of any type may show zero-TC current at any value ranging from 4mA to 20mA, therefore, there is need to test every device for it's zero-TC current.

3. Accelerate aging
Boil at 100 degree C and freeze at -15 degree C, repeat the cycle many times.

4. A circuit to test aging rate etc.
 - build many to test simultaneously
 - characterize TC
 - test by continuous power up, power down/up, mild thermal shock, mechanical shock
(https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=259031;image)
The zener current(5mA to 10mA) is supplied by an foil resistor R1 from the final 10V. The current should be stable to 25ppm annually.
R2 and R3 are foil divider pair, the exact value is no very important but this 10V should be stable to 15ppm annually(assuming 2DW233 is stable).
I'll use AD707AH because I have a lot of them and the noise is not too bad(0.23uVpp, 14pAp-p).

5. Others
I've built one prototype but the noise is not as low as expected probably because there is no heat sink/thermal lag.
(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=258768;image)


Reference
There is a Chinese military standard SJ 50033/150-2002 on 2DW230-2DW236.
http://doc.mbalib.com/view/7ff38949056ec076fcf871d4e67ec0f4.html (http://doc.mbalib.com/view/7ff38949056ec076fcf871d4e67ec0f4.html)
(https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=258881;image)

More datasheet from the industry
http://doc.mbalib.com/view/1a1945b2dcc8911e2a82b0f5ff52fc0f.html (http://doc.mbalib.com/view/1a1945b2dcc8911e2a82b0f5ff52fc0f.html)

I also found an old article(dated 1986, attached but in Chinese), the author were obviously from Shanghai 17th radio factory describing this 'superb' zener of Diamond brand.
He said, from 1982, the factory began a profound revolutionary change of the process structure of the 2DW230-2DW236 series making it rival similar products abroad in term of low noise and low drift. There are some test results in the article but the author did not tell anything about their new process. There was someone who tested an 2DW234 dated 1987 and got 3.2uVp-p noise, compatible with what have described in the article(http://bbs.38hot.net/forum.php?mod=viewthread&tid=120264 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=120264)). He also tested another 2DW234 dated 2013 and got 0.57uVp-p noise. This means that there must be another change of the process structure in Shanghai 17th radio factory between 1987 to 2013. One thing for certain is that they changed the internal connection of two zener from common anode(as can be seen from above two internal diagrams) to common cathode.

I took apart one(of 2DW234), here is the photo by my card camera plus a magnifier
(https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/?action=dlattach;attach=226642;image)
Someone at 38hot(archwang) took a much better inside photo of 2DW234 dated 2013(see attached)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on September 28, 2016, 09:42:44 pm
Low frequency noise test
By my DIY noise meter(https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/ (https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/)), I tested some 2DW233.
(https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/?action=dlattach;attach=224382;image)
(https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/?action=dlattach;attach=224457;image)

For a given zener, the LF noise is inverse proportional to the square root of applied current. I plotted the curve for some well known zeners with 2DW23x which shows 2DW232 is about 2.54 times better noise wise or 6.5 times better current wise.
(https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/?action=dlattach;attach=225203;image)


T.C. test



Aging test
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on September 29, 2016, 01:29:06 am
With the two references in one case one could use the second zener as a normal diode to sene the chip temperature.

Form the internal pictures shown in one of the links, it looks like the chip itself is covered in a drop if transparent glue (e.g. epoxy). So heating to more than 100-120 C (and the speed of cooling from there) might have an influence on the glue and thus performance / aging.

With the relatively high power, there can be temperature fluctuation due to turbulent air flow - this might look very much like 1/f noise. Often one covers sensitve circuits with a kind of foam / fiber.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on September 29, 2016, 01:52:27 am
With the two references in one case one could use the second zener as a normal diode to sene the chip temperature.

Form the internal pictures shown in one of the links, it looks like the chip itself is covered in a drop if transparent glue (e.g. epoxy). So heating to more than 100-120 C (and the speed of cooling from there) might have an influence on the glue and thus performance / aging.

With the relatively high power, there can be temperature fluctuation due to turbulent air flow - this might look very much like 1/f noise. Often one covers sensitve circuits with a kind of foam / fiber.

I think you are absolutely correct on these points. I'm going to design an temperature oven by using the forward biased diode. I also boiled 200 pieces for high temperature cycle but not higher.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on September 29, 2016, 07:14:20 am
All very interesting, thanks for posting this.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: quarks on September 29, 2016, 06:00:21 pm
Bookmark!
Thanks a lot for sharing.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on September 29, 2016, 07:18:23 pm
+1
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: retrolefty on September 29, 2016, 09:54:38 pm
Bookmark!
Thanks a lot for sharing.

Ditto  :-+
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: WN1X on September 30, 2016, 12:42:37 am
I also boiled 200 pieces for high temperature cycle but not higher.

Zener diode soup...my favorite  :-DD

Very interesting thread...I look forward to future updates  :-+
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Theboel on October 06, 2016, 03:20:56 pm
Try to contact some seller who offer this Zener but no luck, perhaps some else luckier than me can share information
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 07, 2016, 03:04:22 am
Try to contact some seller who offer this Zener but no luck, perhaps some else luckier than me can share information
1st Oct. to 7th Oct. is a Holiday in China.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on October 07, 2016, 07:57:58 pm
I'll let this next few days pass, because of the back orders that the sellers might have, and next week I'll try to buy some 10 to 30 units and try to make 2 or 3 boards and test over time for drift.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Theboel on October 08, 2016, 12:10:00 am
@ Zlymex,
Thank You for the information. but still if anybody outside china can buy it online I like to know the information.

btw, I like to use this zener for discrete ADC/DAC in audio freq range application anyone has experience about that ?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: blueskull on October 08, 2016, 12:20:20 am
2DW family... Classic Chinese part numbering, dates back to the 60s/70s. Probably you can build an OPAMP for your new reference with 3AX/3DG transistors >:D, that will be cool, very cool vintage tech porn.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: ali_asadzadeh on October 14, 2016, 03:57:13 am
Zlymex how do you compare 2DW232 with LTZ1000A when you are measuring them with the gears that use LTZ1000A as their reference and claiming that they are better than LTZ1000A also I have another question, how they characterized the LTZ1000A against what beast?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Squantor on October 14, 2016, 06:08:11 pm
@ Zlymex,
Thank You for the information. but still if anybody outside china can buy it online I like to know the information.

btw, I like to use this zener for discrete ADC/DAC in audio freq range application anyone has experience about that ?

I ordered at this store: https://www.aliexpress.com/item/2DW230-2DW231-2DW232-2DW233-2DW234/966304921.html (https://www.aliexpress.com/item/2DW230-2DW231-2DW232-2DW233-2DW234/966304921.html)

It is still underway to me, hopefully they are the "diamond" brand zeners, a lot of people are using the same pictures. I will report back as soon as I get them. One thing to notice with this vendor is that you need to send him a message with what type you want to buy.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on October 22, 2016, 04:25:26 am
I ordered 30 pcs from the below link. Only 10 pcs arrived

https://www.aliexpress.com/item/High-quality-10Pcs-2DW234-2DW235-2DW236-New/32527935820.html?spm=2114.13010608.0.0.lA0Mcy (https://www.aliexpress.com/item/High-quality-10Pcs-2DW234-2DW235-2DW236-New/32527935820.html?spm=2114.13010608.0.0.lA0Mcy)

The parts arrived but they do not have the diamond mark on top. There is no mark on top. The part number is written in blue on the side with no visible production date. The logo in blue is mostly a blur and not readable.

I have contacted the seller and asked for a refund. I paid $20 for 30 pcs to be sent to me. My guess is that most of these sellers are selling garbage parts with a picture of the good stuff on their page.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: JS on October 22, 2016, 06:03:35 am
I ordered 30 pcs from the below link. Only 10 pcs arrived

https://www.aliexpress.com/item/High-quality-10Pcs-2DW234-2DW235-2DW236-New/32527935820.html?spm=2114.13010608.0.0.lA0Mcy (https://www.aliexpress.com/item/High-quality-10Pcs-2DW234-2DW235-2DW236-New/32527935820.html?spm=2114.13010608.0.0.lA0Mcy)

The parts arrived but they do not have the diamond mark on top. There is no mark on top. The part number is written in blue on the side with no visible production date. The logo in blue is mostly a blur and not readable.

I have contacted the seller and asked for a refund. I paid $20 for 30 pcs to be sent to me. My guess is that most of these sellers are selling garbage parts with a picture of the good stuff on their page.

Even if they are doing that makes no sense to not send the specified quantity...

JS
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on October 22, 2016, 08:16:43 am
I ordered 30 pcs from the below link. Only 10 pcs arrived

https://www.aliexpress.com/item/High-quality-10Pcs-2DW234-2DW235-2DW236-New/32527935820.html?spm=2114.13010608.0.0.lA0Mcy (https://www.aliexpress.com/item/High-quality-10Pcs-2DW234-2DW235-2DW236-New/32527935820.html?spm=2114.13010608.0.0.lA0Mcy)

The parts arrived but they do not have the diamond mark on top. There is no mark on top. The part number is written in blue on the side with no visible production date. The logo in blue is mostly a blur and not readable.

I have contacted the seller and asked for a refund. I paid $20 for 30 pcs to be sent to me. My guess is that most of these sellers are selling garbage parts with a picture of the good stuff on their page.

Even if they are doing that makes no sense to not send the specified quantity...

JS

I stand corrected. The other 20 pcs were balled up in what looked like filler packing. So they did send all 30 but these are not what is pictured. Many of the sellers of these have the same picture posted.

I picked a different seller and sent an email asking if the parts are exactly as pictured. We shall see what happens. No big deal one way or the other. It would be good to get 20 to 30 of these and let a batch cook for a while.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 22, 2016, 01:08:13 pm
That's very unfortunate @VintageNut. Anyway, only the diamond brand has low noise property, others are just garbage.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: martinr33 on October 22, 2016, 05:31:18 pm
I have managed to get some via TaoBao. They look genuine.  I'll see if I can persuade my wife to put them up for sale on her web site.


(https://lh3.googleusercontent.com/vcqFwOrE_rUTYmUUnHLhcjAienJXS_2F8-RInTpr69mdNNdKdRmWtkQWL8uY82qhawpjdrR3GAGwhah_379jleq1Vawakm9vAWkNy7B4YUwbMpuPWcUimQ0u-kazfv1Z1zn7IqX29kc6fsCvGaNN1qf8t19OgO9cydwlz37KjleJH22OpbCqBFG2oT2YmUtUDu1PNRNBw9EcdBCSG3vHtjEi7fMpeRmgzdg432bWiKz3TrFHLKTBh8Z3JfwLa2V566lZve9KsCiu18ImZVI8_8uiIobP0ognSoEQnzHzVG90DlQaAB9V4NaFSlf48yQq7UgTV8oXGbv9_H3Hnda3U6RTEEJ79hU7d53NubqCzVTi77I0_F7XcYEPbs_KCePfqrfCxZlLuucV02viTzDATYOS7iyoGUn6s4Q1d2jSFVCzzEpBit12I87_kWPf9P3Icq1I-sypd2AgkfXRVYr62kOqvOEdfHtN_STL5wIeZRKJxEGgw-JaYar7oACqs-tXktu7xYimVg3Q0qKlyEZEuXFyFX1oCXirK02Ft9a_TTlFeo2cm7F0UGSHUh33Xn2eROH-F-hjhyyDDekN_1c-ql3T8EtvlMVX7B9knC0GwtCD5OtGaA=w1449-h1951-no)

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on October 22, 2016, 06:39:46 pm
Are there data on how good those references are in respect to drift. The kind of glue on top of the chip is not that promising, as it might age, especially at higher temperature.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: janode on October 22, 2016, 09:13:29 pm
I tried my luck with "AIX ELECTROINC CO.,LTD":
https://www.aliexpress.com/item/2DW233-DIP3/32354191799.html (https://www.aliexpress.com/item/2DW233-DIP3/32354191799.html)

Oh well, not so surprisingly the components don't look the same as in the picture. There's poor quality blue printing on the side, not the top, of the components. Leads are gold colour.. actually very close to colour of my 21K gold ring. Weird if they bothered to waste actual gold on those  :-DD. I would love to add here the head banging smiley, because it's so great, but I'm not really disappointed.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on October 22, 2016, 10:28:30 pm
I have managed to get some via TaoBao. They look genuine.  I'll see if I can persuade my wife to put them up for sale on her web site.


That would be cool and very helpful.
How did you purchase via Taobao? I could not get the website to be usable in english.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SeanB on October 22, 2016, 10:57:10 pm
I tried my luck with "AIX ELECTROINC CO.,LTD":
https://www.aliexpress.com/item/2DW233-DIP3/32354191799.html (https://www.aliexpress.com/item/2DW233-DIP3/32354191799.html)

Oh well, not so surprisingly the components don't look the same as in the picture. There's poor quality blue printing on the side, not the top, of the components. Leads are gold colour.. actually very close to colour of my 21K gold ring. Weird if they bothered to waste actual gold on those  :-DD. I would love to add here the head banging smiley, because it's so great, but I'm not really disappointed.

My bet is they simplt relabelled old stock transistors and sold them. Try them for gain, it might be a Germanium PNP transistor with a badge job.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on October 22, 2016, 11:03:46 pm
For those interested in the 2DW2xx, maybe zlymex can help out, since he has access to tabao and know's what could be real, we could buy them for the ones that want them, and send them out, if he want to get this kind of trouble. :-)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 23, 2016, 01:17:20 am
For those interested in the 2DW2xx, maybe zlymex can help out, since he has access to tabao and know's what could be real, we could buy them for the ones that want them, and send them out, if he want to get this kind of trouble. :-)

Yes. I can buy a batch and mail it to one oversea location at my own expense, and the one who receive the package will responsible for distribution to who ever needed and agreed in certain term.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on October 23, 2016, 02:45:28 am
Hello Zlymex

That would be a "group buy" as we say in the USA.

I am willing to host the logistics in the USA. I can receive the parts and send out the parts to the participants in the USA.

For myself, I do not require hundreds of parts. I only need 20 to 30 pcs of each of 2dW233, 2dw234.

Do the higher current parts have lower noise? For example does the 2DW234 have lower noise than the DW233? If so, is the 2DW236 the lowest noise part?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on October 23, 2016, 03:53:52 am
Is there any particular place in Europe that would be advantageous from a postal costs point of view to use as a hub for the European leg of this? I ask as I'm quite happy to volunteer as the hub of the European leg of this, but UK postal rates to other European countries have always traditionally been one of the higher.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 23, 2016, 03:51:24 pm
Ok. may be I will buy 200pcs(or more?) and mail them to VintageNut/USA, and VintageNut will mail 100pcs to Cerebus/Europe, or may be the other way round. I'll check which way is better(available postal, custom, pricing) tomorrow.

From my tests, 2DW232 or 2DW233 will do, the difference with others(2DW235, 2DW234) is only the nominal zero TC current, but I saw not very much actual difference, and the zero TC current of 2DW232 or 2DW233 are usually higher than nominal. The manufacture seems to mark the brand randomly.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: JS on October 23, 2016, 04:17:50 pm
  You do want zero TC, if it's at higher current it would usually be a good thing, as it means lower noise, unless you are after long term stability instead of low noise, in which case you wouldn't be using the 2DW233 I guess.

JS
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on October 23, 2016, 08:09:47 pm
Even the 2DW233 has the zero TC at already quite a high current level and thus low noise. High currents also cause more self heating and thus require a higher temperature. So I don't think it really helps to go above 5 mA. If than one could still use 2 units in parallel for lower noise - usually 2 units at 5 mA should give a lower noise than 1 at 10 mA, not for the higher frequency part, but for the 1/f part. With the relatively low price it is a very real option to use 2 or even more refs combined.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on October 23, 2016, 09:54:42 pm
This would be a good project to buy some 30 of the 2DW2xx, select 14 of them and make an stable 100V, but probably the PSU's would have to be separate for each, this could be better than buffering the LM399/LTZ to 100V.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Theboel on October 23, 2016, 10:33:34 pm
count me for 20pcs, EU or USA doesnt matter  8)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on October 23, 2016, 11:27:31 pm
Hello Zlymex

The lowest cost will be China Post to United States Postal Service.

I have bought several $20 items from eBay and AliExpress that incur no customs fee to the USA. There is ePacket China Post shipping which is used by eBay that is very low cost.

If you ship to UK or Eu first , there will probably be Value Added Tax.

If it is not too much trouble, maybe ship one package to USA and one package to UK?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 24, 2016, 12:36:15 am
Ok, the item I plan to buy is here: https://item.taobao.com/item.htm?spm=a230r.1.14.17.q4TxU1&id=35862405041
I've already bought from the entry before and proofed to be genuine(low noised). I've just online talked to the seller that they still have the same batch as I bought for at least 300pcs, which is dated 14-4.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: eliocor on October 24, 2016, 12:45:09 am
I would be interested in about 30/50 pieces...
I live in Europe (Italy)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on October 24, 2016, 12:55:12 am
If you ship to UK or Eu first , there will probably be Value Added Tax.

Here till 22€ we don't pay nothing, but if the package is small and the value is higher, and the declared value is low e.g. $5 there is no problem.
The prices here for the shipping for all EEC are 4€ till 500g, I can post here the shipping cost for the various weights.
 
If it is not too much trouble, maybe ship one package to USA and one package to UK?

That would be best, since from the US to EU, you can add another week at least.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on October 24, 2016, 12:58:39 am
Hi, I would be interested in some in the USA.  Somewhere in the 25-250 range I suppose depending on what the overall pricing looks like.

EDIT: Hi zlymex, thank you for all of the good information you have shared about these models of references as well as noise measurement circuits, and for being willing to facilitate a group buy.
And thank you VintageNut, thank you for your interest to also facilitate a group buy.
I am wondering what the price discount versus quantity of parts purchsed is?  I think I saw that zlymex may have previously been buying hundreds of such parts, (550pcs, 200pcs,...) at once, and maybe that is at the best price per lot level or maybe it is better at some other possible level that is achievable in the group purchase?

Also I apologize for the basic question but I wonder if from the research you all have done if there is any indication as to the likely magnitude of the long term drift of these devices, and also the unit to unit variation of characteristics in a batch, and whether some factors like humidity change, mechanical stress, or vibration would likely be a significant concern in integrating these into a circuit?

In response to VintageNut's comment about a temperature controller, as well as to generalize about making some open HW that could be useful to the users of this part, I would be glad (*as long as I can spare any time in the coming days/weeks) to contribute my effort to design a temperature controller or other accessory PCB / circuit design for this sort of purpose. 

I do not have access to any especially good temperature measurement hardware (beyond basic NTC thermistors, a couple of IC digital sensors, some K thermocouples, and 2N3904 junctions that could be measured), and not at all any premade environmental controlled test / calibration system, though, but I could make a custom firmware + data acquisition based controller design and come up with some ideas for use of either printed foil heaters, discrete resistor heaters, or similar simple concepts.  I suppose that should easily be enough to look for non-absolute temperature correlated short term variations in particular spots of maybe under 0.1C.  I might be able to get a basic RTD to look for smaller fluctuations and have something more closely correlated to absolute temperature.

 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: pmcouto on October 24, 2016, 01:01:24 am
I would be interested in about 50 pcs.

Regards,
Pedro
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Squantor on October 24, 2016, 01:48:46 am
I would be interested in 20 pieces or more depending on pricing. I live in the Netherlands.

I have actually ordered a bunch from aliexpress. Hopefully they are diamond brand but I don't count on it.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: JS on October 24, 2016, 02:08:46 am
This would be a good project to buy some 30 of the 2DW2xx, select 14 of them and make an stable 100V, but probably the PSU's would have to be separate for each, this could be better than buffering the LM399/LTZ to 100V.

You could do it with a single supply, provided you find the zero TC current for all the devices together.

Even the 2DW233 has the zero TC at already quite a high current level and thus low noise. High currents also cause more self heating and thus require a higher temperature. So I don't think it really helps to go above 5 mA. If than one could still use 2 units in parallel for lower noise - usually 2 units at 5 mA should give a lower noise than 1 at 10 mA, not for the higher frequency part, but for the 1/f part. With the relatively low price it is a very real option to use 2 or even more refs combined.

Ok, when you said require a higher temp are you talking about an oven or just that it will go higher? I should double check the levels, I didn't know it was already that high.

JS
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on October 24, 2016, 03:16:13 am
Ok, the item I plan to buy is here: https://item.taobao.com/item.htm?spm=a230r.1.14.17.q4TxU1&id=35862405041
I've already bought from the entry before and proofed to be genuine(low noised). I've just online talked to the seller that they still have the same batch as I bought for at least 300pcs, which is dated 14-4.

Hello Zlymex

If you buy 300 pcs, you can ship 150 pcs to USA and 150 pcs to Eu. I can handle sending out envelopes from USA.

My thought is to make 25 pcs available to 5 people from the USA. I will keep 25 pcs for my project(s).

The seller's price at Taobao looks like USD $0.25 each so the 150 pcs will be USD $37.50 plus shipping to Zlymex in China and shipping from China to USA and any customs that the US Customs charges. We shall see.

Zlymex, I can send you payment from Paypal if you want. Just let me know. There is no hurry for me.

My intention is to make one "group reference". Sort of a poor man's bank of Fluke 732B. It would be good to find a way to make an ovenized PCB that can be kept at 30 deg C or maybe even a little higher.

Thank you for sharing your China low noise zener source!
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: pelule on October 24, 2016, 03:53:02 am
I would have interest in 30 pieces for me as one of the European batch receivers.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: MatteoX on October 24, 2016, 04:23:30 am
Hi, I would also be interested for 25 pcs or more for the USA group buy.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on October 24, 2016, 04:29:42 am

The prices here for the shipping for all EEC are 4€ till 500g, I can post here the shipping cost for the various weights.


As I suspected, that rules out the UK as the European hub. The cheapest from here to Portugal for 250-500g is over £5 GBP - even with the low £ that's still nearly 50%  higher shipping costs.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on October 24, 2016, 04:55:23 am
We've also the express mail, that is from 100g - 250g = 4.70€ and from 250g - 500g = 6.40€ for EU.

The normal mail is 100g - 250g = 2.35€ and from from 250g - 500g = 4€ for EU.

And 0.65€ for an bubble bag, so if the 25x 2DW23x are from 100g - 250g, that will be 2.35€ + 0.65€ = 3.00€ + 23% VAT = 3.69€ if my math is correct, and I'm looking at this the correct way.

Let's see how many are need for EU & US.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on October 24, 2016, 05:28:46 am
We've also the express mail, that is from 100g - 250g = 4.70€ and from 250g - 500g = 6.40€ for EU.

The normal mail is 100g - 250g = 2.35€ and from from 250g - 500g = 4€ for EU.

And 0.65€ for an bubble bag, so if the 25x 2DW23x are from 100g - 250g, that will be 2.35€ + 0.65€ = 3.00€ + 23% VAT = 3.69€ if my math is correct, and I'm looking at this the correct way.

Let's see how many are need for EU & US.

The nearest part, mechanically, I have here is in a TO-72 case and that weighs in at 0.91gm. So 25 off would be in the close region of 25gm + the weight of packaging.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on October 24, 2016, 05:34:28 am
Ok so new prices for normal mail;

20g - 50g = 1.20€
50g - 100g = 1.40€

For express mail;

20g - 50g = 3.10€
50g - 100g = 3.60€

Plus the above package and VAT.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on October 24, 2016, 06:25:37 am
From the picture it looks like these may (just a guess since they could just be side by side die) be monolithic.
Does anyone know from a tear down or thermal analysis if this is one monolitic die, or two physicaly different die side by side?

Has anyone done a thermal analysis to see what the temperature coupling response is from one zener to the next?

If they are either monolithic or side by side independent die but likely from the same wafer I wonder how good the parametric matching is from one zener to the next in the same package?
 
It seems like one could
(a) make a dual reference of course + and - 6.xV
(b) use the second zener as a forward biased diode junction temperature sensor  to sense temperature of the other zener (as has been mentioned here)
(c) maybe use one zener with a variable curent through it as a heater to heat the adjacent unit and help control its temperature over a small range (and perhaps also as a temperature sensor).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: orin on October 24, 2016, 06:39:21 am
Count me in for 20 in the USA.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on October 24, 2016, 07:38:08 am
I'm interested in 30 pieces too. Germany/Europe
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: hammy on October 24, 2016, 07:48:06 am
I would also be interested for 30 pcs for the EU/Germany group buy.

Thank you!  :-+
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on October 24, 2016, 08:22:25 am
The price from the link that @zlymex post from tabao shows $0.24 each, plus shipping from @zlymex to both US & EU host's.
The shipping from @zlymex to each host (1 in US, 1 in EU) would be divided by all in each group.
Then each one in that group (US & EU) would pay the shipping from the host to is address to the host.
Also from my point of view makes more sense after @zlymex give the shipping price for each host, and we've close the numbers of the buy, that all should pay directly to @zlymex, leaving that way only the last shipment to pay to the host.

From what I get till now, here are some numbers;

Europe:
@Theboel - 20
@eliocor - 30 (Buy Limit)
@pmcouto - 30 (Buy Limit)
@Squantor - 30 (Buy Limit)
@pelule - 30
@branadic - 30
@hammy - 30
@ Nuno_pt - 30
@Cerebus - 20
@manganin - 30 (Buy Limit)
@2N3055 - 20
@MosherIV - 3
@janode - 20
@Alex Nikitin - 30 (Buy Limit)
@babysitter - 30
@plesa - 30



US:
@evb149 - 30 (Buy Limit)
@MatteoX - 30 (Buy Limit)
@orin - 20
@VintageNut - 25
@Galaxyrise - 20

Asia - 20


Anyone missing?

Updated & Buy Limit impose to 30 for person, because of the explanation below given by @zlymex, after this there could be organize another group buy for those that need more parts, but this propose is to try the 2DW23x series for drift beside the LM399/LTZ1k.

Updated
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on October 24, 2016, 08:48:45 am
Put me down for 20 or whatever turns out to be the nearest convenient quantity.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: manganin on October 24, 2016, 08:51:42 am
200 pcs / EU
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: 2N3055 on October 24, 2016, 09:19:45 am
Can I have 20 pcs/EU please?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: martinr33 on October 24, 2016, 09:54:04 am
Mine came from here:

https://world.taobao.com/item/35862405041.htm?fromSite=main

I think that is the same supplier. The ones I have have a colored dot on the side, and a black diamond logo, part number and date code on the top. One batch is 2016, the others are 2015.

I opened a couple up, they have a white silicone seal not an epoxy seal. I'll try to get the silicone off, get some pictures.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 24, 2016, 10:36:49 am
Well, that amount(summarized by Nuno_pt) certainly exceed my expectation.
Like I said, I'll buy 200-300 pcs and ship to one oversea location(USA) at my own expense.
The purpose of the 'group buy' from my point of view is for test for EEVBLOG members, therefore I hope not exceed 20-30 pcs each.
The reason for the limit is the availability from one seller, also because of the customs here which may have very strict rule for random packages.
Again, This zener has the best noise property I've ever tested, but the T.C. is just average, and drift is a question mark.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: blueskull on October 24, 2016, 10:41:16 am
also because of the customs here which may have very strict rule for random packages.

I think customs only cares about incoming packages, not outgoing packages.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 24, 2016, 11:01:50 am
The price from the link that @zlymex post from tabao shows $0.24 each, plus shipping from @zlymex to both US & EU host's.
The shipping from @zlymex to each host (1 in US, 1 in EU) would be divided by all in each group.
Then each one in that group (US & EU) would pay the shipping from the host to is address to the host.
Also from my point of view makes more sense after @zlymex give the shipping price for each host, and we've close the numbers of the buy, that all should pay directly to @zlymex, leaving that way only the last shipment to pay to the host.

From what I get till now, here are some numbers;

Europe:
@Theboel - 20
@eliocor - 30 to 50
@pmcouto - 50
@Squantor - 20 or more
@pelule - 30
@branadic - 30
@hammy - 30
@ Nuno_pt - 30
@Cerebus - 20
@manganin - 200


US:
evb149 - 25 to 250
MatteoX - 25 or more
orin - 20


Anyone missing?
Thanks very much for the plan and summery. One reason(the expense on me) is that I have difficulty in receiving money from where I reside.
There is no worry thought for this zener to sold out even the group test results are positive because the zener is in production.
The there one slight worry though, the quality may vary among batches. The taobao link I posted is the one which I've tested and proofed to have low noise.

The reason I bought 550pcs of 2DW234 from another seller is because one of my friends bought some samples before and tested to have narrow distribution of zero TC current. The seller got 1100 pcs and we bought them all. These 2DW234 were dated 13-2(Feb 2013) and we cannot find any others seller selling the same thing. New devices, although low in noise, they tends to have large(but similar) distribution of zero TC current, regardless of the part number.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: blueskull on October 24, 2016, 11:07:25 am
One reason(the expense on me) is that I have difficulty in receiving money from where I reside.

Or they can pay me to my PayPal or WellsFargo account, then I can transfer money to you in CNY from my SPDB account.
I live in US and I have both US and Chinese bank accounts.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on October 24, 2016, 11:54:43 am
also because of the customs here which may have very strict rule for random packages.

I think customs only cares about incoming packages, not outgoing packages.

Not Chinese customs. They clear outbound packages too. When I order things from China that come with tracking codes I often explicitly see the step in the tracking details. For example, from an order that's currently in transit:

09-Oct-2016 09:41   Departure export customs   SHENZHEN

For the most part they seem to go into export customs and come straight out again, but I've had orders that have sat in Chinese export customs for several days.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on October 24, 2016, 11:56:57 am
One reason(the expense on me) is that I have difficulty in receiving money from where I reside.

Or they can pay me to my PayPal or WellsFargo account, then I can transfer money to you in CNY from my SPDB account.
I live in US and I have both US and Chinese bank accounts.

This is how people end up in 'extended screening' at the air port. The NSA connect you to a series of payments that take a circuitous route via a Chinese bank account...  ;)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: blueskull on October 24, 2016, 11:57:49 am
Not Chinese customs. They clear outbound packages too. When I order things from China that come with tracking codes I often explicitly see the step in the tracking details. For example, from an order that's currently in transit:

09-Oct-2016 09:41   Departure export customs   SHENZHEN

For the most part they seem to go into export customs and come straight out again, but I've had orders that have sat in Chinese export customs for several days.

I meant Chinese customs does not seize or check outgoing packages, but of course, a package will have to go through customs before entering or leaving China.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on October 24, 2016, 12:04:12 pm
Thanks zlymex, I appreciate all the information you have shared on your noise reference experiments and noise tester circuit. 

I did not intend to ask for too many pieces for convenience of a group buy.  I had just assumed that after seeing your talks of ordering 550 and hundreds more that those were usual lot quantities and perhaps also were less expensive in such quantities as well.

I think some number from a few up to 30 is good for testing for me as you've suggested. 
I was interested in Nuno_pt's idea to use more than 14 in series to achieve a 100V low noise reference, or the idea others have mentioned to use several in parallel to reduce random noise by square root (number) or similar ideas so I thought I could eventually use more than 100 if they worked at least reasonably well.  But I have no urgent short term need to do more than testing with less quantities.

A particular concern to me about finding that a small number of these are good (low noise even if drift is more than TI/Analog/Linear/Maxim similar high grade references) is that it may be hard to order the Shanghai 17th Radio Factory's "good model" part since mostly resellers seem to sell the "junk" versions even accompanied with pictures and specifications of the "good model" part.  So there is temptation to "get the right one while it is clear how to do so".

Another concern is to find that there is some quality of a particular batch of them that is good and not being able to find similar units in the future or from different suppliers so therefore the characterization work could be much harder if trying to characterize different batches ordered over time vs. one batch that may be more consistent.  Though I see that you say that it is not your recent experience that the recently available batches are very consistent in parametric spreads anyway.  But at least we know that the model is good if not the characteristics as tight as the best 2013 batch you found.

And of course that it is hard (so I have seen from others comments, this would be my first try if I should attempt it for this) and maybe expensive depending on the seller's desire to ship internationally in some way to buy from Taobao directly and get the items shipped to the USA for a non-Chinese speaking customer.  But I saw another comment from a different thread that maybe it is easier than it once was to order internationally from Taobao.  If it is not so hard / costly then I and I suppose others would not mind to just order individually if wanting more quantities.
I will see what I can learn about using Taobao.  If the "e packet" low cost shipping service is available easily for US customers and there are no significant other problems/costs for ordering/shipping per order then maybe USA customers could order without causing inconvenience to you.
https://www.eevblog.com/forum/chat/why-use-taobao/msg953114/#msg953114 (https://www.eevblog.com/forum/chat/why-use-taobao/msg953114/#msg953114)
https://www.eevblog.com/forum/chat/why-use-taobao/msg953118/#msg953118 (https://www.eevblog.com/forum/chat/why-use-taobao/msg953118/#msg953118)
 
I guess that it is not known that the Shanghai 17th Radio Factory sells these parts "directly" through Taobao / similar markets in low (hundreds) quantities directly to consumers if this particular Taobao seller might not be expected to have such quantities of stock and perhaps could even eventually substitute other factories / models of parts if they run out of this batch?  It seems like they might do some good business with US and European customers if they somehow sold easily via paypal / ebay / whatever.  My own interest is as an aspiring novice volt-nutter but I'd guess it'd be popular for audio enthusiasts and such.

I also noticed that some people (who I have never done any business with so I just mention the messages I have seen in searching for keyword taobao here for my own education about buying from it) say they routinely export items from China to sell through eBay so if demand exceeds what is convenient to arrange for a small group buy I guess someone who routinely sells through ebay might agree to carry this part in their ebay store if they can source the "good version" from the Shanghai 17th Radio Factory or other acceptably certain reseller.  Franky, Tayda, maybe even someplace like Adafruit, Sparkfun, or similar might source / sell such a thing.
https://www.eevblog.com/forum/chat/what-site-to-use-for-puchasing-china-stuff-at-eu/msg176762/#msg176762 (https://www.eevblog.com/forum/chat/what-site-to-use-for-puchasing-china-stuff-at-eu/msg176762/#msg176762)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on October 24, 2016, 12:08:01 pm
The price from the link that @zlymex post from tabao shows $0.24 each, plus shipping from @zlymex to both US & EU host's.
The shipping from @zlymex to each host (1 in US, 1 in EU) would be divided by all in each group.
Then each one in that group (US & EU) would pay the shipping from the host to is address to the host.
Also from my point of view makes more sense after @zlymex give the shipping price for each host, and we've close the numbers of the buy, that all should pay directly to @zlymex, leaving that way only the last shipment to pay to the host.

From what I get till now, here are some numbers;

Europe:
@Theboel - 20
@eliocor - 30 to 50
@pmcouto - 50
@Squantor - 20 or more
@pelule - 30
@branadic - 30
@hammy - 30
@ Nuno_pt - 30
@Cerebus - 20
@manganin - 200


US:
evb149 - 25 to 250
MatteoX - 25 or more
orin - 20


Anyone missing?


25 pcs for me. If Zlymex ships to me, I will ship to the other people in the US. I can also ship USPS to Indonesia. I have Paypal and I can receive the shipping fees. I have participated in sharing components on Diyaudio.com  These parts will go fast.

If Zlymex can only get 300 pcs, there will not be an ability to send 200 pcs to anyone. Everybody be realistic about how many of these parts are available.

The idea is for people to try these Zeners to see if they are lower noise and can work as a reference for DIY metrology at home.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: blueskull on October 24, 2016, 12:12:46 pm
This is how people end up in 'extended screening' at the air port. The NSA connect you to a series of payments that take a circuitous route via a Chinese bank account...  ;)

I have my PhD work in a sensitive field, high density power packaging, which is ITAR controlled, and I receive funding from USDOE plus my lab has connection with USDOD/LMCO. Needless to say, I should have already been tagged.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: MosherIV on October 24, 2016, 05:52:24 pm
Hi

Can I have 2 or 3 peices please?

Thanks
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 24, 2016, 06:15:51 pm
Thank everyone for the info/suggestions/comments.

Initially in this post, I just share some information, providing aliexpress.com(same boss as taobo) links, because I know many people buy electric parts there even with free shipment. Then I heard some bad news that they didn't ship or wrong parts, plus Nuno_pt suggest me to help, that's when I came in.

I've just asked our company's postal office that there is only one postal company to mail to USA, which is EMS China, although the price is high(240 RMB for 500g), I can cope with that. I've never heard ePacket, may be I've never mail anything abroad, may be that service is not available to my area, may be I didn't ask other places.

I'm buying 2DW232 from taobao now, the data code is 15-4, for which I've bought and tested before.

If everything is Ok(my spot check, postal, tests by recipients), and anyone need large quantity, a real group buy can be start later. But if that is still by me/taobao, I will again buy small samples first.

Again, this is a trial at my expense, I don't have any connections with the seller at taobao or the 17th radio factory. If anyone need some piece of 2DW232 for test, leave your comments here, my intention is to get more people involved in testing. For those who have said needing more than 30 pcs, lets see if there are something left.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: blueskull on October 24, 2016, 06:23:00 pm
I've never heard ePacket, may be I've never mail anything abroad, may be that service is not available to my area, may be I didn't ask other places.

ePacket is China Post's special service only offered to professional exporters. For instance, if you constantly ship abroad with an export license, you can get an ePacket account.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on October 24, 2016, 09:11:53 pm
Post with quantities updated above, because of this Zener is still in production and can be bought in another group buy with the help from @zlymex, and also because of what @zlymex explain above, the limit will 30 pieces for each person, at a later stage another group buy can be organize and the ones that want more can buy on the second round.

This small quantities of 30 is to choose the best's and to make some PCB's, and look at the comparison about drift in relation to the more use Zeners like LM399/LTZ1k, and see if they can be use also for references in a home lab.

240RMB is 33€ at today exchange, for the EU group with the current committed members the shipping cost from @zlymex to the EU host is 33€/11 members = 3€ each members + ~0.24€ each Zener + shipping from the EU host to each one.

So for 30 pieces that will be 0.24€ each x 30 pieces = 7.20€ + 3€ shipping from @zlymex to EU = 10.20€, plus the shipping from the host to each.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: manganin on October 24, 2016, 09:20:28 pm
200 pcs / EU

My new 100 input scanner will be ready soon. Or actually two of them.

The seller's price at Taobao looks like USD $0.25 each

Cheap enough for a statistical experiment. If available in large quantity...
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on October 24, 2016, 09:48:34 pm
Count me in for 50 pieces.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: janode on October 25, 2016, 02:42:43 am
Anyone missing?

Me too!  20 pcs.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: babysitter on October 25, 2016, 03:03:02 am
If not too late, i will take 30 pcs too.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: BravoV on October 25, 2016, 03:06:42 am
Me 20
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: janode on October 25, 2016, 03:07:13 am
My bet is they simplt relabelled old stock transistors and sold them. Try them for gain, it might be a Germanium PNP transistor with a badge job.

I'm too young for germanium transistors  :-DD I measured Vf 0.7V so silicon. Vz ~5.6V @ 5mA. It would have been more fun to find out they were something weird rebadged, but no..
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on October 25, 2016, 03:12:57 am
I'm too young for germanium transistors  :-DD I measured Vf 0.7V so silicon. Vz ~5.6V @ 5mA. It would have been more fun to find out they were something weird rebadged, but no..

I'm old enough to remember scraping the paint off the outside of glass encapsulated OC71s to convert them into phototransistors.  :(
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Echo88 on October 25, 2016, 05:21:42 am
Can someone tell me, how all of you are gonna make use of the low noise while maintaing extremely low drift? Wouldnt it be more reasonable to just stick together a few LTZ1000 to get sqrt(n) noise reduction, while having a very low drift, backed by decades of experience?  ???
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on October 25, 2016, 05:22:34 am
Update, just missing @BravoV since I can't see is flag.

For now:

383 for EU.
115 for US.
20 for Asia.


Let's see how many @zlymex was able to buy,  and then figure a way to split them if enough for all at same time, or we've to buy the rest on the second round.

For now also if put only 30 pieces for each one, base on the 300 units that @zlymex told.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on October 25, 2016, 05:33:21 am
Can someone tell me, how all of you are gonna make use of the low noise while maintaing extremely low drift? Wouldnt it be more reasonable to just stick together a few LTZ1000 to get sqrt(n) noise reduction, while having a very low drift, backed by decades of experience?  ???

On the first page @zlymex show that the 2DW23x has lower noise then the LTZ, but what we'll see is the long time drift, if it's something like the LTZ with can be good since for let's say 4 modules it cost around $1 plus shipping, while the same 4 LTZ it's $200 plus shipping.

For me will be an experiment about long time drift.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: plesa on October 25, 2016, 05:36:32 am
Count me in, please. 30pcs (buy limit)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: TiN on October 25, 2016, 05:40:28 am
Subbed  :popcorn:
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Galaxyrise on October 25, 2016, 08:04:47 am
I'd like to be in for 20.  Very much appreciate the efforts of those members making this possible, even if I'm in too late for this time around.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on October 25, 2016, 12:41:15 pm
I couldn't get the translate to work for my browser on Taobao last night and I didn't see any indication of Shanghai 17th radio factory online by any searching that I thought could lead to something like a direct alibaba or ebay or tmall store of theirs if they had one.

So for the moment I will be content with whatever quantity is possible to make available in this small group purchase and if there is in the near future another another group buy with larger quantities I would probably still be interested in 100-200 additional pieces of the part discussed here.

If the noise is as good as has been suggested by others' experiences then that to me is good enough to be useful.  If the long term drift is also reasonably low then that is even better.  But for many applications just a somewhat stable but low noise and inexpensive source could be useful for short term measurements.  At 1/200th the cost of a LTZ1000 it would be tempting to use it for dozens of applications where I wouldn't use a much higher cost reference simply due to cost.
And if you need low noise and low drift you can always combine a stable reference with this low noise reference in the same system if you can correct for the drift of this reference via a digitally applied offset from the measured value of the stable reference.

 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 25, 2016, 02:43:39 pm
I bought 9 bags, 450pcs(50pcs in a bag). I have to open at least one bag to check when arrived today or tomorrow.
The weight of one bag is 52.5g, so 9 bags is 473g. Plus package, it may exceed the 500g limit, so I may have to ship 400pcs.

I've just search "2DW232" and "Shanghai 17th Radio Factory"(in Chinese) and got 7 entries, all the sellers are in Shanghai.
The 1st is the one I bought(having bought 5 times), The 2nd have been bought 1 time.

I've once try to put Chinese here but it won't allowed by the forum, but here I try again for Shanghai 17th Radio Factory:
????????

Edit: the above two faces plus two "?" were in Chinese but showed incorrectly.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: TiN on October 25, 2016, 02:46:57 pm
This forum does not support non-western symbols. Same with cyrillics :)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: BravoV on October 25, 2016, 02:50:49 pm
Update, just missing @BravoV since I can't see is flag.

For now:

383 for EU.
115 for US.

Let's see how many @zlymex was able to buy,  and then figure a way to split them if enough for all at same time, or we've to buy the rest on the second round.

For now also if put only 30 pieces for each one, base on the 300 units that @zlymex told.

Check your PM.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: blueskull on October 25, 2016, 03:02:39 pm
I've once try to put Chinese here but it won't allowed by the forum, but here I try again for Shanghai 17th Radio Factory:
????????

Put the search URL into a URL shortener, then post the shortened URL.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on October 25, 2016, 08:07:20 pm
Hello Zlymex

Can you ship 300 pcs to EU and 150 pcs to USA? There are more people in EU who want these parts.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on October 25, 2016, 08:58:40 pm
I've once try to put Chinese here but it won't allowed by the forum, but here I try again for Shanghai 17th Radio Factory:
????????

Edit: the above two faces plus two "?" were in Chinese but showed incorrectly.

The forum software is weird. It manages character encodings correctly up to and including previewing your own comments but then seems to completely stuff the encoding when you actually post the message.

For example, I'll type "?" here, and what's in the quote marks as, I see them, is a Greek omega. I'll hit 'preview' and, it still looks like an omega to me, now I'll hit 'post' and, based on past experience, it'll turn into "?".

Editted to add: And sure enough, that's exactly what happened. It makes the 'preview' feature half useless.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: quarks on October 25, 2016, 09:54:05 pm
seems to be to late, but I would be interested to know if I can still join and buy 30 of it
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 26, 2016, 02:58:25 am
- Norminal zero-TC current ranges from 5mA to 15mA depending on types.
These 2DW23x series(2DW232, 2DW233, 2DW234, 2DW235) has been around for many year and ....

were you able to try the diff in noise between the xx2 (5mA) vs the xx5(12.5mA)?
Every device I tested follows the inverse square root rule
Noises were all similar at given current
Zero TC current are different among xx2
Zero TC current are the same between xx2 and xx5
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 26, 2016, 03:08:25 am
Package arrived today, will test tomorrow.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: janode on October 26, 2016, 03:21:00 am
Can someone tell me, how all of you are gonna make use of the low noise while maintaing extremely low drift? Wouldnt it be more reasonable to just stick together a few LTZ1000 to get sqrt(n) noise reduction, while having a very low drift, backed by decades of experience?  ???

While low noise and low drift enable many experiments, so does also low cost :) I guess most are hoping this offers a combination of low cost and low noise.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on October 26, 2016, 12:14:28 pm
Thank you very much, zlymex.  It looks good.  Good luck with your tests.
The package seems to have arrived very quickly to you.
 
Package arrived today, will test tomorrow.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: simon51 on October 26, 2016, 02:37:28 pm
Package arrived today, will test tomorrow.
I also bought 50pcs 2DW232 from the same seller,looking forward your test methods and results. :clap:
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 26, 2016, 06:31:15 pm
Package arrived today, will test tomorrow.
I also bought 50pcs 2DW232 from the same seller,looking forward your test methods and results. :clap:

I've just finished testing 10, powered by three lithium cells in series(12.4V noise free) and series 1k precision resistor with the test zener to get about 6.3mA test current.
(https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/?action=dlattach;attach=224466;image)

The terminal marked red(may be other color) is negative, center terminal is positive, the other terminal(connected to the case) open.

Because the noise is very small, and also the TC is not tuned, the device is very sensitive to air turbulence, I covered it with a lot of tissues (wrapped around the device and legs).

The result is positive, 9 is very typical but one is a bit above average. I plotted these on the original chart with added green dots. Some dots are overlapping.
(https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=265131;image)
I've packed 430pcs up and ready to ship to VintageNut/USA tomorrow.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on October 26, 2016, 11:51:54 pm
Hello Zlymex

Thank you for buying these parts for the Metrology community here.
I will coordinate with the other interested people to distribute the parts.
I think we should start a group buy thread and take that discussion off of this thread.

Please let me know if there is a way to compensate you for buying the parts. If you cannot receive an electronic payment, is there something you want to acquire from the USA that I can send to you via USPS/China Post that is the same value? Maybe something that is difficult for you to acquire in China but costs about the same as what you paid for these parts?

The science behind your personal metrology projects is impressive. Building your own microvolt DIY noise meter is one example. For sure, I will want some help on this thread building up a set of 4 references like the Fluke 732B .

best regards,

VintageNut
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on October 27, 2016, 01:48:35 am
I think we should start a group buy thread and take that discussion off of this thread.

Seconded. The thanks are also seconded.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on October 27, 2016, 10:59:12 am
Thank you zlymex.
The results are good to see and interesting.

I've just finished testing 10, powered by three lithium cells in series(12.4V noise free) and series 1k precision resistor with the test zener to get about 6.3mA test current.
(https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/?action=dlattach;attach=224466;image)

The terminal marked red(may be other color) is negative, center terminal is positive, the other terminal(connected to the case) open.

Because the noise is very small, and also the TC is not tuned, the device is very sensitive to air turbulence, I covered it with a lot of tissues (wrapped around the device and legs).

The result is positive, 9 is very typical but one is a bit above average. I plotted these on the original chart with added green dots. Some dots are overlapping.
(https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=265131;image)
I've packed 430pcs up and ready to ship to VintageNut/USA tomorrow.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: hammy on October 27, 2016, 11:26:37 am
I've packed 430pcs up and ready to ship to VintageNut/USA tomorrow.

How is the shipping/distribution now organized?

Thank you zylmex!
hammy
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: simon51 on October 27, 2016, 02:00:33 pm
zlymex,thank you!
I do a simple test for 2dw233 compare with ltflu-1.The circuit is same with the fluke5440a REF board that series two sza263(ltflu-1)  then buffer output 13v.I replace ltflu-1 with 2dw233 and series 1.8k(1k should be better) foil resistor with 2dw233 to get current about 3.6mA,then test the output noise(0.1~10Hz),the ltflu-1x2 is about 1.8uV(vpp),the 2dw233x2 is about 1uV(vpp). :-+The problem is the 2dw233x2 output voltage is not stable, The matter needs to bo resolved.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 27, 2016, 02:01:22 pm
I've packed 430pcs up and ready to ship to VintageNut/USA tomorrow.

How is the shipping/distribution now organized?

Thank you zylmex!
hammy
I've just sent a PM to VintageNut, the shipping company(EMS) requires the telephone number of the receiver.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 27, 2016, 02:11:28 pm
zlymex,thank you!
I do a simple test for 2dw233 compare with ltflu-1.The circuit is same with the fluke5440a REF board that series two sza263(ltflu-1)  then buffer output 13v.I replace ltflu-1 with 2dw233 and series 1.8k(1k should be better) foil resistor with 2dw233 to get current about 3.6mA,then test the output noise(0.1~10Hz),the ltflu-1x2 is about 1.8uV(vpp),the 2dw233x2 is about 1uV(vpp). :-+The problem is the 2dw233x2 output voltage is not stable, The matter needs to bo resolved.

Nice work.
It seems to be some 50Hz noise on the photo of the oscilloscope.
The instability of  2DW233 may result from the air flow around the TO-39 case which can be minimized by fillers of soft and insulated material around 2DW233 and the pins on both side of the PCB. Try tissue first.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on October 27, 2016, 04:37:17 pm
I've packed 430pcs up and ready to ship to VintageNut/USA tomorrow.

How is the shipping/distribution now organized?

Thank you zylmex!
hammy
I've just sent a PM to VintageNut, the shipping company(EMS) requires the telephone number of the receiver.

I sent a PM with my phone number. Thank you very much for doing this very kind thing!
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on October 27, 2016, 04:48:59 pm
I've packed 430pcs up and ready to ship to VintageNut/USA tomorrow.

How is the shipping/distribution now organized?

Thank you zylmex!
hammy

We will start a new thread for the group buy if the 2DX233 parts that Zlymex has kindly purchased for the group here on this thread.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 27, 2016, 04:54:31 pm
I've packed 430pcs up and ready to ship to VintageNut/USA tomorrow.

How is the shipping/distribution now organized?

Thank you zylmex!
hammy
I've just sent a PM to VintageNut, the shipping company(EMS) requires the telephone number of the receiver.

I sent a PM with my phone number. Thank you very much for doing this very kind thing!
Received and the package is shipped.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: BravoV on October 27, 2016, 06:32:03 pm
Zlymex, pls read your PM, regarding zones, I'm alone in my region.  :'(
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on October 27, 2016, 06:50:46 pm
Zlymex, pls read your PM, regarding zones, I'm alone in my region.  :'(
I read your PM but I'm not sure what you need apart from request 20 samples of 2DW232 for which you can contact VintageNut. I'm here only responsible for shipping to one oversea location(USA).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: babysitter on October 28, 2016, 06:39:09 pm
Look what a member of my local Makerspace has drawn for me, will be printed next week and hopefully fits 2DW23X and also TO-99 (LTZ1000). At the club we print with PLA which is not suitable for high temperature, ABS can be printed but it seems to need tighter parameter control or something, so no one there likes to print it. Mounting holes are M2. Will publish STL file. The thick wall will be flled with a air chamber structure by the slicing software, giving better isolation than solid material.

Best regards
Hendrik.


 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on October 29, 2016, 12:06:23 am
I have access to a DLP printer (layer thickness 25µm - 150µm, window size 70 x 40mm² with 1920x1080px, maximum part size  400 x 330 x 200mm³).

I printed a LTZ1000 spacer some months ago using a material called PLASTCure Rigid 10500, but a material called PLASTCure Clear 100 (transparen) is available too.
If there is a bigger interest I could offer such caps for small budget by printing a complete batch of such caps.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: quarks on October 29, 2016, 01:11:13 am
Hello branadic,

will these caps fit to the HP3458A A9 LTZ1000 Reference Board?

thanks
quarks
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: babysitter on October 29, 2016, 02:19:35 am
@Branadic: If you tell me the hole distance and the location of the nose relative to the holes, I can ask this guy to apply it to his drawing. But i have defined relatively thick walls as I can have some air filled closed holes in the wall then.

We have only a prusa I3 filament printer at the club, dont ask for details, I dont know it - yet.

br
hendrik
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on October 29, 2016, 03:45:51 am
I guess it was TiN how published a copy of a LTZ1000 cap, a while ago. Maybe someone wants to check wether this one matches the original used in 3458A?
Otherwise we can use any other design, as long as everyone is fine with the it.
The good think about the printed material is, that you can also cut a thread into the material.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Nuno_pt on October 29, 2016, 03:50:50 am
Maybe we can arrange a cap that fits the LTZ/LM399/2DW23x, they should be pretty close in terms of dimensions.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: pelule on October 29, 2016, 05:02:46 am
I would add myself to the list of buyers of that cap-print-group, if that fit at least to LTZ1000 and 2DW2xx (thus also to LMx99 - not the H package).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: babysitter on October 29, 2016, 05:21:52 am
Hey, great response! I guess we can make some of them at the club. But first I'd like to check the measures, try the 2DW when they arrive, my LTZ in the finished reference source is already under a (vacuum port) cap. Distribution is easy with STL files, everyone who wants one only has to find someone to print.



Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: pelule on October 29, 2016, 06:37:19 am
Hi Flinstone,
use that link below to add yourself to the list (but read hints/instruction first, you'll find, if you scroll up on that page a bit )
See link:
https://www.eevblog.com/forum/metrology/group-buy-of-2dw233-ultra-low-noise-zener-reference/msg1057877/#msg1057877 (https://www.eevblog.com/forum/metrology/group-buy-of-2dw233-ultra-low-noise-zener-reference/msg1057877/#msg1057877)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on November 01, 2016, 05:38:25 am
Quote
@Branadic: If you tell me the hole distance and the location of the nose relative to the holes, I can ask this guy to apply it to his drawing. But i have defined relatively thick walls as I can have some air filled closed holes in the wall then.

Could find the CAD files from TiN:

https://xdevs.com/doc/HP_Agilent_Keysight/3458A/cad/a9_cap_top.STEP
https://xdevs.com/doc/HP_Agilent_Keysight/3458A/cad/a9_cap_bot.STEP

There you can find the hole distance.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 01, 2016, 06:08:17 am
The cap will be only a minor detail, and usually different from the one for an LTZ1000, as the zener has no internal heater. So the zener will consume less power and good insulation may not be a good thing.
The more important point might be choosing the circuit. The simple version is something like the one used with a LM399 or LM329: scale to a higher voltage (e.g. 10 V) and than use a resistor to set the current.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on November 01, 2016, 02:11:30 pm
The cap will be only a minor detail, and usually different from the one for an LTZ1000, as the zener has no internal heater. So the zener will consume less power and good insulation may not be a good thing.
The more important point might be choosing the circuit. The simple version is something like the one used with a LM399 or LM329: scale to a higher voltage (e.g. 10 V) and than use a resistor to set the current.

And because if it, a more 'useful' zener current of 8mA or >12mA can be applied to achieve even lower noise per device than LTZ1000 for which the data sheet only recommend 4mA.

The cap or tissue are useful only to stop the air flow around the device/legs, not for thermal insulation. However, these two are often closely related. One good example is the one used by Datron/Wavetek in their 49xx voltage reference where they use black form plus a metal outer case.

As for the step-up to 10V, yes, there is this circuit of "scale to a higher voltage (e.g. 10 V) and than use a resistor to set the current." on the first page of the thread.
(https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=259031;image)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 02, 2016, 06:01:59 am
To take really advantage of the low noise of this reference type, one might want to use a lower noise than the AD707 - even though the AD707 is already quite good. As input bias / current noise is not that critical, something like an OP27 / LT1007 should be OK.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on November 02, 2016, 06:14:59 am
It would be good to have the second diode directly in use, maybe for some servo temperature controller.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on November 06, 2016, 08:12:42 pm
What about using the second zener to reduce noise instead?  Feeding it to a separate opamp and then combining reduces the noise by a factor of 1/sqrt(2). While not much this would give an easy improvement for the price of an extra opamp.

Using it just for temp sensing seems a sacrilege.. that could be easily done by gluing a thermistor on top of it.

-BK
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 06, 2016, 09:22:04 pm
Even with just one diode used, the noise is already really low - e.g. better than an OP07, OP177 or AD707 which are typical candidates for scaling the voltage. The current to get a low TC is already quite high (e.g 5 mA range) - more current is more of a problem it you don't want the chip to heat up too much.

Having a temperature sensor directly on the chip can really help to stabilize or just measure the temperature.  So I would consider this the more practical use for the second diode.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Tazz on November 06, 2016, 09:31:06 pm
Kleinstein, I second you for the use of the second diode
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on November 06, 2016, 10:47:02 pm
Zlymex:

Isnt the 2nd diode already used forward biased as temperature compensation diode?
I cannot get this clear from your description.
In this case you do not need to think about further noise reduction.

Or are there 2 temperature compensated diodes (2 zeners + 2 diodes) in one package?
In this case you cannot read the temperature. (because the zener voltage is in series to the compensation diode).

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: plesa on November 06, 2016, 11:33:37 pm
Zlymex:

Isnt the 2nd diode already used forward biased as temperature compensation diode?
I cannot get this clear from your description.
In this case you do not need to think about further noise reduction.

Or are there 2 temperature compensated diodes (2 zeners + 2 diodes) in one package?
In this case you cannot read the temperature. (because the zener voltage is in series to the compensation diode).

with best regards

Andreas

There are only two zeners, back to back and common anode connected to package.
So there is first order temperature compensation - zener avalanche  diode.
On first piece I will have I'm going to remove epoxy and check it under microscope.
https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/ (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/)
It is the same like used in zeners like 1N82x.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on November 06, 2016, 11:52:16 pm
The 1N82x has a normal diode in series to the zener.

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: plesa on November 06, 2016, 11:59:06 pm
The 1N82x has a normal diode in series to the zener.

with best regards

Andreas

OK, and do you thin that doping level will make noticeable difference in tempco of forward biased diode?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on November 07, 2016, 12:18:28 am
I suggest a flexible arrangement to use the second diode --
(a) To be able to use it forward biased to measure temperature. 
(b) Perhaps it could even be used in forward or reverse to help control temperature as well (small addition to local temperature as controlled)?
(c) In reverse as a voltage reference.

When used in reverse as a second voltage reference one could
(d) Get a negative reference voltage to match the positive which could be useful for miscellaneous purposes.
(e) Ger a negative reference voltage to match the positive one and so the back to back series voltage could be measured like a null measurement to look for differential drift of the two diodes.  This could be useful for stability tracking of the voltage outputs.
(f) The pair of voltages could be assessed independently for noise and drift so one could get two measurements from one unit. 
(g) It could be determined how good the matching of characteristics are between the two diodes which may or may not be monolithic adjacent pads on the same wafer or which could be two different die which are likely from the same wafer and may or may not generally be from adjacent sites. In any case knowing the matching of the two devices that ought to be as similar as possible could indicate the stability of performance of either / both over time and use.
(h) If one device is noisy the other one could be used as a primary reference output.   
(i) and of course be bringing out the signal forward / reverse tempco measurement can be made for use in analysis & R&D of subsequent uses / circuits whether for purposes of reference or temperature controller.

If for practical circuit uses there is to be any use cases of using the dual diodes to make bipolar references then it should be characterized as such with a constant current flowing through both diodes to see how that use case could perform.
 
What about using the second zener to reduce noise instead?  Feeding it to a separate opamp and then combining reduces the noise by a factor of 1/sqrt(2). While not much this would give an easy improvement for the price of an extra opamp.

Using it just for temp sensing seems a sacrilege.. that could be easily done by gluing a thermistor on top of it.

-BK
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 07, 2016, 12:25:40 am
Has anyone managed to find a more comprehensive datasheet for these parts? I successfully downloaded the one that zlymex linked in his first post (the 2 page Shen Xin one) but didn't have any success downloading the ones he linked later.

I've attached one pdf datasheet that I found (SJ brand), it appears to include lots of environmental test requirents but is mostly incomprehensible to me. I guess one from the 17th Radio Factory itself would be the holy grail. It, or a translation, might help answer some of the questions that are coming up.

Chris

(Edit: typo)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 07, 2016, 12:49:57 am
It is a good question whether the two zeners are just normal zener diodes (like 6.2 V reference diodes) or they are supposed to used as a pair in series as a 7 V reference more like the 1N829 or similar.

There are both ways to get a low TC reference diode at the right current: either just a suitable zener diode at about 5-6 V or a compensated version with a zener and normal diode in series like in the 1N829, usually in the 7 V range or higher.

As the voltage is only 6.2 V, I would expect a relatively normal zener. We don't really know much about the internal details - at least they seem to be much lower noise than normal zener diodes. So there is like a more or less secret detail that makes these diodes so special.

Normally the TC of a silicon diode in forward direction is not depending on details of the diode: usually one has a linear temperature dependence that extrapolates to 1.2 V at 0 K. Higher current gives a higher voltage and thus lower TC. Thus a diode with 600 mV forward drop at 300 K will have a -2 mV/K slope.

As the diodes are connected common anode, there is no way to use them in series as a 12.4 V ref. One might be able to use the second diode as a backup to check for drift - but this would likely be better with a completely separate one.

With no detailed DS one might want to do a few measurements, e.g. voltage as a function of current an temperature to get TC and differential resistance. To really get the best working conditions one might need these data for the individual units anyway.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on November 07, 2016, 01:26:34 am
It is a good question whether the two zeners are just normal zener diodes (like 6.2 V reference diodes) or they are supposed to used as a pair in series as a 7 V reference more like the 1N829 or similar.

There are both ways to get a low TC reference diode at the right current: either just a suitable zener diode at about 5-6 V or a compensated version with a zener and normal diode in series like in the 1N829, usually in the 7 V range or higher.

As the voltage is only 6.2 V, I would expect a relatively normal zener. We don't really know much about the internal details - at least they seem to be much lower noise than normal zener diodes. So there is like a more or less secret detail that makes these diodes so special.

Hello,

I think you have never had a 1N829 in hand.
The 1N829 has around 6.4V. (one of the usual voltages of temperature compensated zeners).
It is a normal diode 0.7V (-2mV/K) and a Zener (around 5.7 so +2mV/K) in series.
If you measure the 1N829 zener in "forward direction" you will find the breakdown voltage of the normal diode.
(which is beyond 15 V).

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 07, 2016, 02:47:26 am
I happened to measure a few 1N827 to 829 a few days ago, they were in the 6.2-6.3V range. The highest was a very old ex Solartron 1N829A which came out at 6.37V iirc, all at 7.5mA. It's only LM399, LTZ etc that are in the 6.95V range.

If that is in the same range as the 2DW233 then it is either a zener+series diode or a higher voltage zener with unsusual TC characteristics.  If it is a zener + diode combo then that will exclude using the second one as a sense diode... 1N82x don't conduct backwards (forwards in the conventional sense), the series diode is reverse biased.  :-\

This is the sort of thing a more comprehensive (and comprehensible?) datasheet would tell us.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on November 07, 2016, 03:01:42 am
Hello,

in the 1N82x series there are also some back to back zeners available (1N824) (but without center tap)
in this case both directions will have the 5.9-6.5 V zener voltage.
http://www.microsemi.com/document-portal/doc_download/10940-sa6-3-pdf (http://www.microsemi.com/document-portal/doc_download/10940-sa6-3-pdf)

The trick of having a forward biased diode and a zener diode is that there will be a "zero TC" current
where the diode and zener TC are compensated to near zero over a small temperature range.

with best regards

Andreas


Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on November 07, 2016, 04:19:06 am
Someone claimed that the 1N823 also has superior noise characteristics, though I don't have any to test and there are not specific details.
http://www.diyaudio.com/forums/parts/35821-some-noise-measurements-leds-zener-diodes-12.html#post960894 (http://www.diyaudio.com/forums/parts/35821-some-noise-measurements-leds-zener-diodes-12.html#post960894)
"By chance I found that the noise of an 1N823 (6.2V temperature compensated) is dramatically less than that of ordinary zeners, even when you need more than one for getting the required voltage."

If I recall correctly I think I saw that the noise of a zener is related to its area and current density which makes sense if a larger area is like putting more devices in parallel.  If that is the case then perhaps part of the lower noise of such devices could simply be that they are larger area devices?

Hello,

in the 1N82x series there are also some back to back zeners available (1N824) (but without center tap)
in this case both directions will have the 5.9-6.5 V zener voltage.
http://www.microsemi.com/document-portal/doc_download/10940-sa6-3-pdf (http://www.microsemi.com/document-portal/doc_download/10940-sa6-3-pdf)

The trick of having a forward biased diode and a zener diode is that there will be a "zero TC" current
where the diode and zener TC are compensated to near zero over a small temperature range.

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on November 07, 2016, 05:22:53 am
Hello,

my measurements on several 1N829A (which are only specified for lesser T.C. (at 7.5mA) than 1N823) range from 2uVpp to 22uVpp 1/f noise (0.1 .. 10Hz).
This depends much on manufacturer.
I do not know if the quality nowadays is still the same...

The lesser noise (compared to higher voltage zeners in the link) might result from lower dynamic resistance.
Which is below 10 Ohms for around 6V compared to around 100 Ohms or more for higher voltage zeners.

With best regards

Andreas

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on November 07, 2016, 04:10:05 pm
Hello, thank you very much, that is interesting and good information about your findings with these parts.

Hello,

my measurements on several 1N829A (which are only specified for lesser T.C. (at 7.5mA) than 1N823) range from 2uVpp to 22uVpp 1/f noise (0.1 .. 10Hz).
This depends much on manufacturer.
I do not know if the quality nowadays is still the same...

The lesser noise (compared to higher voltage zeners in the link) might result from lower dynamic resistance.
Which is below 10 Ohms for around 6V compared to around 100 Ohms or more for higher voltage zeners.

With best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 07, 2016, 04:31:12 pm
I have talked with factory that originally made those 2DW233's, Shanghai No. 17 Radio Factory, and I can order them for you fresh from the factory if you want to.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on November 07, 2016, 04:44:35 pm

If I recall correctly I think I saw that the noise of a zener is related to its area and current density which makes sense if a larger area is like putting more devices in parallel.  If that is the case then perhaps part of the lower noise of such devices could simply be that they are larger area devices?

That is not the case. If we parallel four identical devices and run the same current, the noise would be the same.
Parallel four devices and the noise is halved, this only happens if the total current is quadrupled. but this is equivalent to running the larger current on a single device.
The advantage of large area is the ability to run at larger current.
"2DW232 has much better noise than LTZ1000", this is compared at the same zener current.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: 2N3055 on November 07, 2016, 06:36:16 pm
You can consider that large crystal is equivalent of many small crystals connected in parallel. All stochastic noise related events combine same as they would from dozens of separate parallel connected diodes..
Of course,  if  you run it as same current density as with separate diodes...
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on November 08, 2016, 12:57:49 pm
Thank you very much, technix!

What information did you receive about prices for various quantity ranges?

I would be interested to order some, maybe others here will also be so.

I have talked with factory that originally made those 2DW233's, Shanghai No. 17 Radio Factory, and I can order them for you fresh from the factory if you want to.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on November 08, 2016, 01:01:21 pm
Thank you very much, zlymex, and 2N3055, your explanations are logical.
 

That is not the case. If we parallel four identical devices and run the same current, the noise would be the same.
Parallel four devices and the noise is halved, this only happens if the total current is quadrupled. but this is equivalent to running the larger current on a single device.
The advantage of large area is the ability to run at larger current.
"2DW232 has much better noise than LTZ1000", this is compared at the same zener current.

You can consider that large crystal is equivalent of many small crystals connected in parallel. All stochastic noise related events combine same as they would from dozens of separate parallel connected diodes..
Of course,  if  you run it as same current density as with separate diodes...
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 08, 2016, 03:07:46 pm
Thank you very much, technix!

What information did you receive about prices for various quantity ranges?

I would be interested to order some, maybe others here will also be so.

I have talked with factory that originally made those 2DW233's, Shanghai No. 17 Radio Factory, and I can order them for you fresh from the factory if you want to.

They gave me a solid 75 US cents each regardless of amount, and for order more than 50 (a whole pack) they will pay for the shipping from their factory to my home. When I send it on the shipping cost would be $5 for less than 2kg.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 08, 2016, 03:33:26 pm
Here is the test circuit I am going to use when selecting the 2DW233 for you.

ADC is the built-in 10-bit unit inside ATmega328P, while DAC is TLC5615 (8-bit) referenced from ADR03B. The microcontroller will perform a search to find the best approximate of the zero TC point in the range of 0mA to about 50mA.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on November 08, 2016, 10:33:32 pm
Here is the test circuit I am going to use when selecting the 2DW233 for you.

ADC is the built-in 10-bit unit inside ATmega328P, while DAC is TLC5615 (8-bit) referenced from ADR03B. The microcontroller will perform a search to find the best approximate of the zero TC point in the range of 0mA to about 50mA.
2DW232 is very sensitive to the supply current, therefore I suspect the short term stabllity of the current mirror unless they are paired and thermally bonded.

Theoritically, to test the zero T.C. points(there are many for one device), there is the need both for varying the current and the temperature.
Practically, a step current can be used, then monitor the voltage variation direction to determin whether the current is Ok.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 08, 2016, 11:40:45 pm
Here is the test circuit I am going to use when selecting the 2DW233 for you.

ADC is the built-in 10-bit unit inside ATmega328P, while DAC is TLC5615 (8-bit) referenced from ADR03B. The microcontroller will perform a search to find the best approximate of the zero TC point in the range of 0mA to about 50mA.
2DW232 is very sensitive to the supply current, therefore I suspect the short term stabllity of the current mirror unless they are paired and thermally bonded.

Theoritically, to test the zero T.C. points(there are many for one device), there is the need both for varying the current and the temperature.
Practically, a step current can be used, then monitor the voltage variation direction to determin whether the current is Ok.

In practise I am using the BCV62 for the current mirror - the two PNPs are built on the same piece of silicon and are factory matched. I have already breadboarded the setup and tests on my stock of 1N4728 and 1N4734 are showing the correct behavior. I can scan through 0 to 25mA (I ended up using a 199.7 ohm resistor instead of 100 ohm one as the current sense resistor) at about 0.1mA step and measure the voltage with this automated jig.

I will implement a faster search algorithm that can find the optimal current on the MCU and a component insert sense feature, so when the parts arrive I can bulk test them very rapidly.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 09, 2016, 12:02:29 am
To measure the voltage change one should use a way more capable ADC / DMM or maybe measure only difference towards a fixed voltage close by. For a 10 ppm/K TC and 10 K Temperature step, one has only bout a .6 mV change. So something like a 14 Bit resolution would be the minimum - better more.

Changing the current can also change the internal temperature - though at least the temperature increase should be about proportional to current and reproducible.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 09, 2016, 01:29:52 am
To measure the voltage change one should use a way more capable ADC / DMM or maybe measure only difference towards a fixed voltage close by. For a 10 ppm/K TC and 10 K Temperature step, one has only bout a .6 mV change. So something like a 14 Bit resolution would be the minimum - better more.

Changing the current can also change the internal temperature - though at least the temperature increase should be about proportional to current and reproducible.

I was searching for the Iz with maximum Vz. Maybe I do need a better ADC though, but otherwise my rig is fully automated and can detect the insert of DUT and can search for that Iz point.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on November 09, 2016, 03:36:12 am
To measure the voltage change one should use a way more capable ADC / DMM or maybe measure only difference towards a fixed voltage close by. For a 10 ppm/K TC and 10 K Temperature step, one has only bout a .6 mV change. So something like a 14 Bit resolution would be the minimum - better more.

Changing the current can also change the internal temperature - though at least the temperature increase should be about proportional to current and reproducible.

I was searching for the Iz with maximum Vz. Maybe I do need a better ADC though, but otherwise my rig is fully automated and can detect the insert of DUT and can search for that Iz point.

If you measure differentially against a stable voltage source that's close to the expected zener voltage and then add a bit of gain you'll get much better sensitivity. I'm concerned that you've looking for effects that are on a very close order to the LSB step of the ATMega's ADC. You could derive your stable voltage from the same reference you use for the ADC. You might even gain a tiny advantage from this giving you a ratiometric measurement vs your voltage reference.

I don't exactly know what the expected spread of voltage with individual part variations and temperature is, but if we say for argument sake it is +/-300mV and your original measurement range was 0-10V that would give a resolution improvement of 17 times for the cost of an op amp and a few resistors. That's an LSB of 585 uV versus your original LSB of 9.76 mV. I think you need this and at least a couple more bits on the ADC. The latter would give you a ~125 uV LSB.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 09, 2016, 03:59:34 am
One is not looking for the current with maximum Vz. The Voltage should go up with current over the full range - unless the temperature rise is to much. This point is not what one is looking for. The interesting point is the current at which the voltage is not temperature dependent in linear approximation for the right temperature range, e.g. with 30 C environment or a higher temperature like 50-60C when used with temperature stabilization.

So one would really need to resolve small changes (like 10 µV) in the voltage. So the test rig would be a little more complicated. More like using a commercial DMM (or high resolution ADC) to measure the voltage. The µC internal ADC is more like good enough to read the temperature from the other diode.
If you really want to go with the µC internal (10 Bit) ADC one might be able to only measure the difference to a second reference and use the ADC only for a maybe +-50-100 mV.

So the procedure could be:
0) at RT measure the forward voltage of the second diode, to calibrate it as a thermometer.
1) set test current for a first try
2) Adjust the second ref. voltage so that the difference to the DUT is small (e.g. < 50  mV)
3) Put a relatively high current (e.g. 10-20 mA) through the second diode in the chip, to cause some heat up
4) Change the current to the second diode to a small one in forward direction to use it for temperature measurement
5) do a fast measurement of voltage difference and temperature during cooling (e.g. 5-30 seconds). Temperature measurement is not that critical - decay curve should be similar for the devices.
It more to get the average temperature and an estimate for the order of magnitude.
6) calculate / estimate TC for the given test current and temperature range
7) adjust the current to get lower TC   (e.g. interpolate / extrapolate form older points and maybe typical curve).
8) Repeat if needed (TC to large).

For just a few parts one could do this also by hand - reading the drop on a DMM.
If you really need to automate, I would look for a better external ADC (e.g. 16-24 Bits).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 09, 2016, 04:49:04 am
Or just use a SMU......
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 09, 2016, 05:20:39 am
So how do you guys think about this idea:

On the board I have an ADR03B that is used by the constant current generator. I can wire up the resistive divider so the divided buffered output from 2DW233 is also close to the output voltage of ADR03B. Then I can use the built-in differential PGA of the ATmega to measure the ratiometric difference of 2DW233 and ADR03B with a relatively high gain.

Rinse and repeat in a fridge or on top of a boiling kettle.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 09, 2016, 05:38:40 am
So how do you guys think about this idea:

On the board I have an ADR03B that is used by the constant current generator. I can wire up the resistive divider so the divided buffered output from 2DW233 is also close to the output voltage of ADR03B. Then I can use the built-in differential PGA of the ATmega to measure the ratiometric difference of 2DW233 and ADR03B with a relatively high gain.

Rinse and repeat in a fridge or on top of a boiling kettle.

For low noise high stability applications mostly the performance in a reasonably narrow temperature range (say, 20C-50C) is important. I would use a temperature cycling device made out of a small Peltier cooler and a local heater for the zener, so the temperature swing can be arranged by just switching the heater on/off (as Peltier modules do not like switching polarity quickly) and the optimum current will be found for the smallest voltage change from cold to warm and back.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 09, 2016, 05:47:30 am
I don't know what kind of power element should be used to heat it up. Scanning the entire current range takes about 2.5 seconds using my fully automated design but things can be cooled down quite a bit by then. If I can digitally control the temperature even only with 8 bit resolution I can still characterize those diodes fairly well and can fully automate it (so you just plug in the component and wait until a full report is spit out from the AVR.)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 09, 2016, 06:01:33 am
The amplifier inside the AVRs is not really good, but in principle it could work with the difference.
With a gain of 200 the signal range would be somewhere in the 12 mV range and resolution at about 10 µV. With a divider to about half to third - this is 20-30 µV resolution for the reference.

The reference (ADR03) might need some noise filtering. Due to noise (e.g. amplifier) it may also take some averaging to get good enough data.
The divider needs individual adjustment (but still really stable) for each diode to bring it in the range. It might limit the current range used in one go.

The interesting temperatures would be more like normal room temperature or a little up, maybe up to 50 C environment. No real need for data below room temperature. Getting data on TC versus current at near room temperature (only self heating, maybe increased from the second diode) is already an important part. The optimum current should not be that much temperature dependent.

If you want a real characterization you would need a better ADC, to get the full resolution and thus also get direct data, so no adjustable divider. This is something a SMU is made for - if you have one.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 09, 2016, 06:18:17 am
The amplifier inside the AVRs is not really good, but in principle it could work with the difference.
With a gain of 200 the signal range would be somewhere in the 12 mV range and resolution at about 10 µV. With a divider to about half to third - this is 20-30 µV resolution for the reference.

The reference (ADR03) might need some noise filtering. Due to noise (e.g. amplifier) it may also take some averaging to get good enough data.
The divider needs individual adjustment (but still really stable) for each diode to bring it in the range. It might limit the current range used in one go.

The interesting temperatures would be more like normal room temperature or a little up, maybe up to 50 C environment. No real need for data below room temperature. Getting data on TC versus current at near room temperature (only self heating, maybe increased from the second diode) is already an important part. The optimum current should not be that much temperature dependent.

If you want a real characterization you would need a better ADC, to get the full resolution and thus also get direct data, so no adjustable divider. This is something a SMU is made for - if you have one.
I don't have a SMU but I do have MCP3911, a dual channel 24-bit ADC with internal 1.7V reference and differential inputs. Maybe I can use that?

And still how do I control the temperature of the diodes? If I heat up the chip using one of the two diodes, will PWM work?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 09, 2016, 07:02:39 am
Using the MCP3911 could work to build a higher resolution measurement system. Only the low voltage range (like +-600 mV) might be a little inconvenient and need some care against thermal EMF. So it is possible, but not very easy and more like a separate project first.

The resolution is good enough to eliminate the subtraction. And stability should be good enough to measure Vz versus current at different temperatures instead of changes in Vz on fast modulated temperature. Though you still have the option to measure fast.  Later you can than sort the data towards  voltage versus temperature for the different current settings.

For heating the chip PWM on the second diode could work. The downside is that you can only measure well when the heating current is off, as they share a common pin. So one would have a heating phase and one for measuring the zener ref. and the other diode as a temperature sensor with a much lower current (e.g 100 µA) in the other direction. This could work for more moderate temperatures (e.g. 10-40 K temperature rise). The internal heater is fast, but limited power. PWM on the second diode could also introduce thermal gradients and thus mechanical stress, so this would not be the most accurate way.

For higher temperature or very accurate data an external heater would be needed. The external heater might be controlled by PWM. One might not need to have a control loop, but could do the measurements during slow heat-up and cool-down. The second diode could be used as a temperature sensor.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 11, 2016, 01:43:24 pm
I mounted one of the 2DW232 parts on to a banana plug, plugged it into a KE2461 forcing 5mA. I am monitoring voltage with a DMM7510.

The voltage is 6.02xxxx and wanders about 600uV p-p, 166 uV standard deviation.

I traded some PMs with chuckb. He tried forcing current into a 2DW23X part with a calibrator and saw the voltage wandering as well.

My opinion is that the instruments that can force current are not ppm stable and cannot be relied upon to maintain stable enough current for a zener reference device.

Any other opinions?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Vgkid on November 11, 2016, 02:38:53 pm
What about making a precision current source? You have precision resistors, right.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 11, 2016, 04:11:39 pm
I mounted one of the 2DW232 parts on to a banana plug, plugged it into a KE2461 forcing 5mA. I am monitoring voltage with a DMM7510.

The voltage is 6.02xxxx and wanders about 600uV p-p, 166 uV standard deviation.

I traded some PMs with chuckb. He tried forcing current into a 2DW23X part with a calibrator and saw the voltage wandering as well.

My opinion is that the instruments that can force current are not ppm stable and cannot be relied upon to maintain stable enough current for a zener reference device.

Any other opinions?

You need a more stable source to compare it against, for example LM399.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 11, 2016, 08:38:22 pm
I mounted one of the 2DW232 parts on to a banana plug, plugged it into a KE2461 forcing 5mA. I am monitoring voltage with a DMM7510.

The voltage is 6.02xxxx and wanders about 600uV p-p, 166 uV standard deviation.

I traded some PMs with chuckb. He tried forcing current into a 2DW23X part with a calibrator and saw the voltage wandering as well.

My opinion is that the instruments that can force current are not ppm stable and cannot be relied upon to maintain stable enough current for a zener reference device.

Any other opinions?

You need a more stable source to compare it against, for example LM399.

Have you watched Dave's teardown of the DMM7510? the DMM7510 has an ovenized LTFLU as its reference. This same ovenized LTFLU is what provides the Fluke 5700A DC volts reference .

The DMM7510 can measure the 3ppm daily drift of my Fluke 731B (two of them) in my lab/office.The 731B drifts 1 ppm for every 2 or 3 degrees F.

The LM399 is what is inside my calibrated KE2000 and it is a very stable and it agrees with my DMM7510. The DMM7510 has 10X resolution measuring the daily drift of the 731B compared to the KE2000.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 11, 2016, 08:41:04 pm
What about making a precision current source? You have precision resistors, right.

I do have some precision resistors. They would probably require tempco tweaking to make a better current source than what is in the KE2461. Its a good idea. That will have to go on the long list of future projects.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 11, 2016, 09:20:53 pm
If would also suspect the current source, though this should not be that bad. Also EMI could be a problem, when using an external unit.
There is also a chance that there is quite some temperature effect, as the TC is low only for a suitable current and this current can be vary quite a lot from device to device. Having one with 6.0x V suggest this could be one of the more extreme ones. So if possible I would also monitor the temperature via the second diode.

The normal test circuit would be similar to the one right at the beginning of the thread.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 11, 2016, 10:29:56 pm
If would also suspect the current source, though this should not be that bad. Also EMI could be a problem, when using an external unit.
There is also a chance that there is quite some temperature effect, as the TC is low only for a suitable current and this current can be vary quite a lot from device to device. Having one with 6.0x V suggest this could be one of the more extreme ones. So if possible I would also monitor the temperature via the second diode.

The normal test circuit would be similar to the one right at the beginning of the thread.

I think that the SMU is not the largest contributor to the 100+ uV wander of the zener.

I just changed the forced current to 10mA and the average wander is now 6 uV instead of 100+ uV at 5mA.

It looks like an automated measurement will be required to characterize all 10 pcs of the 2DW232 that I will be using.

The 2DW232 mounted on the banana plug is wrapped in 3 tissues tied with a twist tie.

Another thing to mention here is that it takes 30+ minutes for the 2DW232 to stabilize. In open air, it never stabilizes.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: TiN on November 11, 2016, 10:54:29 pm
I can test with my SMUs (K2400 and HP 4142) and try automate tempco finding, once I get few of these little wonders too.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 11, 2016, 11:05:55 pm
If would also suspect the current source, though this should not be that bad. Also EMI could be a problem, when using an external unit.
There is also a chance that there is quite some temperature effect, as the TC is low only for a suitable current and this current can be vary quite a lot from device to device. Having one with 6.0x V suggest this could be one of the more extreme ones. So if possible I would also monitor the temperature via the second diode.

The normal test circuit would be similar to the one right at the beginning of the thread.

I think that the SMU is not the largest contributor to the 100+ uV wander of the zener.

I just changed the forced current to 10mA and the average wander is now 6 uV instead of 100+ uV at 5mA.

It looks like an automated measurement will be required to characterize all 10 pcs of the 2DW232 that I will be using.

The 2DW232 mounted on the banana plug is wrapped in 3 tissues tied with a twist tie.

Another thing to mention here is that it takes 30+ minutes for the 2DW232 to stabilize. In open air, it never stabilizes.

To find the optimal current for minimum tempco you have to do a temperature change, for example heating the zener with a power resistor, letting it to cool down (with a several seconds repetition time), and adjust the current for a minimal change in voltage. It is also would be interesting to see if the minimum tempco would be for one zener only or for a zener in series with the second half working as a diode (which I suspect might be the case).

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 11, 2016, 11:18:15 pm
For manual finding the optimum current, one could look an the stabilization curve (the first 10-20 seconds or so) after turning the current on. For too low a current, the voltage should drift down on settling and for to high a current the settling should be upwards.
Of cause one can do the same with the SMU and PC as well.

As heater one could use the second zener as well, so the observed voltage will stay about the same and one could use an AC coupled amplifier to watch small changes.

The much better performance at 10 mA suggests that the wandering / drift was due to thermal effects and 10 mA being much closer to the point of zero TC. Only 6 µV suggests this is already rather close - e.g. a TC of a few ppm / K at most. Final performance can also depend slightly on the resistor to set the current and the environment temperature range.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 11, 2016, 11:46:12 pm
For manual finding the optimum current, one could look an the stabilization curve (the first 10-20 seconds or so) after turning the current on. For too low a current, the voltage should drift down on settling and for to high a current the settling should be upwards.
Of cause one can do the same with the SMU and PC as well.

As heater one could use the second zener as well, so the observed voltage will stay about the same and one could use an AC coupled amplifier to watch small changes.

The much better performance at 10 mA suggests that the wandering / drift was due to thermal effects and 10 mA being much closer to the point of zero TC. Only 6 µV suggests this is already rather close - e.g. a TC of a few ppm / K at most. Final performance can also depend slightly on the resistor to set the current and the environment temperature range.

Short answer: the voltage never settles upwards.

The datasheet that Zlymex posted has max power at 200mW and current of 30mA.

I have tested one sample at 5mA, 10mA, 15mA, 20mA, 25mA and 30mA. The device is wrapped in three layers of tissue to kill any air current.

The voltage always decreases for many minutes until a stable voltage is reached.

The particular device in-hand operates at 6.19xxxx volts at 30 mA. I will let this device run at 30mA until it settles and report +/- deviation.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 12, 2016, 12:01:11 am
Short answer: the voltage never settles upwards.

And what happens if you connect both sides (one as a zener, one as a diode in series with zener)?

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 12, 2016, 12:37:41 am
Short answer: the voltage never settles upwards.

And what happens if you connect both sides (one as a zener, one as a diode in series with zener)?

Cheers

Alex

I am not sure what you are asking to try. Maybe draw it out by hand and post the drawing(s)?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 12, 2016, 12:43:31 am
Here is a screen capture of the statistics of the DMM7510 measuring voltage .

Keep in mind that the voltage measure cables are unshielded  24" long each. I will use shielded BNC cable eventually when I have a 2DW232 on a pcb in an enclosure.


RMS noise (standard deviation) is less than 1/2 uV.


Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 12, 2016, 01:12:33 am
Short answer: the voltage never settles upwards.

And what happens if you connect both sides (one as a zener, one as a diode in series with zener)?

Cheers

Alex

I am not sure what you are asking to try. Maybe draw it out by hand and post the drawing(s)?

Like that:

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 12, 2016, 02:00:48 am
Short answer: the voltage never settles upwards.

And what happens if you connect both sides (one as a zener, one as a diode in series with zener)?

Cheers

Alex

I am not sure what you are asking to try. Maybe draw it out by hand and post the drawing(s)?

Like that:

Cheers

Alex

I believe that is how it is connected and is how it is intended to be used. Pin 1 is the red dot which is the output. Pin 2 is grounded. Pin 3 is the case is ignored.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 12, 2016, 02:07:11 am
I believe that is how it is connected and is how it is intended to be used. Pin 1 is the red dot which is the output. Pin 2 is grounded. Pin 3 is the case is ignored.

OK, thanks, that was my understanding as well, however from the discussion in this thread it was not quite clear.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 12, 2016, 03:58:29 am
For manual finding the optimum current, one could look an the stabilization curve (the first 10-20 seconds or so) after turning the current on. For too low a current, the voltage should drift down on settling and for to high a current the settling should be upwards.
Of cause one can do the same with the SMU and PC as well.

As heater one could use the second zener as well, so the observed voltage will stay about the same and one could use an AC coupled amplifier to watch small changes.

The much better performance at 10 mA suggests that the wandering / drift was due to thermal effects and 10 mA being much closer to the point of zero TC. Only 6 µV suggests this is already rather close - e.g. a TC of a few ppm / K at most. Final performance can also depend slightly on the resistor to set the current and the environment temperature range.

It appears to be the opposite of your hypothesis.
For too-high current, the voltage drifts down. For too-low current, the voltage drifts up.

Now that that is sorted out, the zero T-C current for this device is between 7mA and 8mA in open air.  Covered in tissues the zero T-C current is between 6mA and 7mA.

That's better!
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 12, 2016, 04:44:25 am
An 6-8 mA current for zero TC sounds very good. However the optimum current seems to be quite temperature dependent if it already changes so much from open to air and covered.

It is interesting to see an negative TC and thus falling voltage at high current. The normal zener refs like 1N829 are the other way around with a negative TC at low currents and a positive at high currents.

It might be interesting to do full characterization with 1 or 2 samples, as this units seem to be different from the more normal western zeners and the DS does not give much information. Is the diode in forward direction reasonably normal and working as a temperature sensor ?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 12, 2016, 05:06:48 am
I will mount a second device and take the same tests for currents causing rising and falling current. And I will have a try at measuring a single diode.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 12, 2016, 05:27:47 am
An 6-8 mA current for zero TC sounds very good. However the optimum current seems to be quite temperature dependent if it already changes so much from open to air and covered.

It is interesting to see an negative TC and thus falling voltage at high current. The normal zener refs like 1N829 are the other way around with a negative TC at low currents and a positive at high currents.

It might be interesting to do full characterization with 1 or 2 samples, as this units seem to be different from the more normal western zeners and the DS does not give much information. Is the diode in forward direction reasonably normal and working as a temperature sensor ?

A second mounted sample works exactly the same. High current causes voltage to fall. Low current causes voltage to rise.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 12, 2016, 10:47:11 am
I will mount a second device and take the same tests for currents causing rising and falling current. And I will have a try at measuring a single diode.

I mounted a device with the red dot at HI of the SMU. The device case is at LO of the SMU.

1mA of forced current creates 0.73 V. 1mA of reverse current creates -5V.

5mA creates  0.78V. -5mA creates -5.26V

I think that explains the device behavior.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Galaxyrise on November 12, 2016, 12:55:24 pm

1mA of forced current creates 0.73 V. 1mA of reverse current creates -5V.

5mA creates  0.78V. -5mA creates -5.26V

I think that explains the device behavior.

 Seems to me that you're measuring a combination of temperature coefficient and dynamic resistance there, and the two measurements are not even the same difference in temperature.  I don't know how to draw any conclusions from it.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 12, 2016, 01:18:34 pm

1mA of forced current creates 0.73 V. 1mA of reverse current creates -5V.

5mA creates  0.78V. -5mA creates -5.26V

I think that explains the device behavior.

 Seems to me that you're measuring a combination of temperature coefficient and dynamic resistance there, and the two measurements are not even the same difference in temperature.  I don't know how to draw any conclusions from it.

The observation is that there are two devices; a 5V zener in series with a 0.7v diode. Nothing more complicated than that.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SvanGool on November 12, 2016, 07:22:39 pm
The observation is that there are two devices; a 5V zener in series with a 0.7v diode. Nothing more complicated than that.

Just for clarity, are you concluding that using the circuit of Alex in https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/msg1068444/#msg1068444 (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/msg1068444/#msg1068444) or are you grounding the open midpoint and are you applying  a positive voltage > 7V, via a resistor, to the kathode of D2?

I would think that D2 is a diode, because it is as a reversed zener  in the first case. Or are we saying the same?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 12, 2016, 08:05:01 pm
So a low TC can be obtained with both diodes in series, as an 5.4 V zener with posistive TC  and one working as a normal diode with negative TC. At some current (about 5-10 mA) the TCs will compensate, since the TC depends on the current. For a normal diode the TC gets smaller (less negative) with more current. For this zener it seems the TC is also getting smaller (a little faster than that of the diode) at high current as the overall TC seems to turn negative on high currents.

Having the two diodes in series makes it possible to use the normal diode as a temperature sensor - for compensation of residual temperature dependence (not just linear) or a regulated temperature. With the diode as a sensor one might be able to get quantitative values for the TC at maybe 5 and 10 mA.

The rather good stability even at 10 mA for a device with compensating current near 7-8 mA suggests that even with not so perfect current the TC is quite low.

o far the reference looks very good - 2 more points to check:
1) One point is hysteresis: So is the voltage the same starting from cold or a higher temperature.
    For a test one could do a sequence like: off - 7.5 mA (optimum current) - 25 mA (to heat the device)  and than 7.5 mA again.

2) The last big question is long time stability. Here the SMU might not be good enough as a current source and this would be more like testing ready made reference units with case and possibly temperature control.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 13, 2016, 11:08:00 am
So a low TC can be obtained with both diodes in series, as an 5.4 V zener with posistive TC  and one working as a normal diode with negative TC. At some current (about 5-10 mA) the TCs will compensate, since the TC depends on the current. For a normal diode the TC gets smaller (less negative) with more current. For this zener it seems the TC is also getting smaller (a little faster than that of the diode) at high current as the overall TC seems to turn negative on high currents.

Having the two diodes in series makes it possible to use the normal diode as a temperature sensor - for compensation of residual temperature dependence (not just linear) or a regulated temperature. With the diode as a sensor one might be able to get quantitative values for the TC at maybe 5 and 10 mA.

The rather good stability even at 10 mA for a device with compensating current near 7-8 mA suggests that even with not so perfect current the TC is quite low.

o far the reference looks very good - 2 more points to check:
1) One point is hysteresis: So is the voltage the same starting from cold or a higher temperature.
    For a test one could do a sequence like: off - 7.5 mA (optimum current) - 25 mA (to heat the device)  and than 7.5 mA again.

2) The last big question is long time stability. Here the SMU might not be good enough as a current source and this would be more like testing ready made reference units with case and possibly temperature control.

Forcing current with a SMU, the voltage is never stable in the bottom 3 or 4 digits. There is no way to measure hysteresis unless a very stable circuit is built and placed in an enclosure.

My opinion is that a stable circuit will require the same heroic effort that is built into a Fluke 731B. Selected and matched tempco resistors. Lots of places for mistakes to show up.

Then the reference diodes have to be aged and characterized and only the best one is good enough.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on November 13, 2016, 11:38:36 am
I just had a "quick and dirty" thought about sending a fairly low noise / stable current through these somewhat easily.
If the SMUs and PSUs tend to be too noisy / erratic when sourcing current into them, maybe something simple like a "12V" vechicle battery through a series resistor would be more stable and low noise at least over time spans of minutes at a time at this low output current level.  I suppose a laptop battery pack or something like that might also work if the voltage is high enough to give some decent headroom.

Of course air current / thermal variations would have to be kept to a minimum with something like Bob Pease's "nested cardboard boxes" trick and tissue or something.
 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 13, 2016, 08:50:45 pm
This week's order from factory is about to close. If you want to buy one of those please PM me.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 13, 2016, 09:08:23 pm
The differential resistance on the zeners should be reasonable low. So changes in the resistors are attenuated by a factor of about current setting resistor to zener resistance. This could be something in the range of 50-100 if one assumes 6 V to set the current. So the demands on the resistors are not that extreme.

For the first tests I would not assume the zeners to be as good as high end parts like LTZ1000 or LTFLU. We would be very happy it could come close to the LM399 / LM129H. So it is about resolving changes in the 10 ppm range. Some thermal shielding and soldering to a board is likely needed - alone from thermal EMF.

The measurements from VintageNut suggest he got quite good stability with the SMU as a current source. But it can depend on the individual units and environment. A dedicated reference circuit could work as well - the demands for the current setting resistors are not that high (e.g. even 100 ppm/K thick film might be good enough), at least for the hysteresis test.

Attached is a suggested simple test circuit. Paralleling R3 to R2 could be used to temporarily increase the current. The lower diode of the ref can be used to get a rough idea of the reference temperature.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 14, 2016, 12:59:02 am
Hello Kleinstein

Can you please give some analysis of how your circuit is better or different from the circuit used by zlymex on the first page of this thread?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 14, 2016, 03:14:52 am
The circuit I showed uses only 2 (instead of 3) resistors that need to be stable. Just to get a stable current for one ref. chip, even the second resistor does not really need to be a good one either.

The difference is also not that big - just replace D1/D3 with a resistor and you are back at the circuit from the first page.

For doing a transient / current step test, it might be an advantage that the current does not depend on the voltage of the ref chip under test, but on the other one. One can look at D2/D4 (e.g. 6.2 V) or at the sum of both references (12.4 V). If you want scaling to 10 V, it works slightly better (less sensitive to resistor drift) if you start from 12 V than starting from 6.2 V.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: edavid on November 18, 2016, 10:06:24 am
Here is the translated datasheet.

Thank you for preparing this translation, but I think the listed pinout is incorrect.  For the devices I received from VintageNut, pins 1 and 2 are anodes, and pin 3 is the common cathode.

Also, I measure a resistance of ~800K between the 2 anodes.  Does anyone know why that is?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on November 18, 2016, 04:52:48 pm

Thank you for preparing this translation, but I think the listed pinout is incorrect.  For the devices I received from VintageNut, pins 1 and 2 are anodes, and pin 3 is the common cathode.

Hello,

The translation corresponds to the picture from the datasheet. (first page on the thread).
Do you really measure 5.6 instead of 0.7V on the ground referenced diode when using a pull-up resistor?

With best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: edavid on November 18, 2016, 04:57:26 pm
Thank you for preparing this translation, but I think the listed pinout is incorrect.  For the devices I received from VintageNut, pins 1 and 2 are anodes, and pin 3 is the common cathode.
The translation corresponds to the picture from the datasheet. (first page on the thread).
Yes, that is also incorrect (or doesn't match the parts I received).  Very odd.

Quote
Do you really measure 5.6 instead of 0.7V on the ground referenced diode when using a pull-up resistor?
Sorry, I don't understand this question.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on November 18, 2016, 05:27:25 pm
if you take the cirquit from Alex:

https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/msg1068444/#msg1068444 (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/msg1068444/#msg1068444)
e.g. with 15V supply and resistor = 1K

what voltage do you measure between Pin 3 (case of zener) and ground?

With best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 18, 2016, 07:51:06 pm
I've measured (by a multimeter diode test only so far) one of the devices I've received and it is indeed a common cathode configuration, as shown on the attached diagram.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on November 18, 2016, 09:35:23 pm
So its more difficult to measure the chip temperature since the forward diode is not referred to GND.

With best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 18, 2016, 09:52:06 pm
So its more difficult to measure the chip temperature since the forward diode is not referred to GND.

With best regards

Andreas

It will be easy in a negative reference configuration though ;) . In a positive reference the diode can still be used easily for a temperature stabilization with an external heater.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 19, 2016, 12:45:05 am
I'm running a measurement on the first sample right now. The circuit is attached. R1 is actually a resistor decade set at 515 Ohm, that is a reasonably stable point. The zener is connected through an IC socket, the 10V source is my JVR reference, so it is quite stable, C1 is a Mylar film capacitor. Right now I'm using the 34465A. I might leave it running over the weekend with 3558A though.

Cheers

Alex

P.S. - first impressions are ... interesting. Very little random noise but the device is (relatively) sensitive to temperature variations and air movements. I suspect that it can only be useful with a good temperature stabilizing loop. With ~7.5mA and 6 Volts the dissipation is quite high and so is self-heating. As a result, any air movements produce noticeable voltage shifts (few ppm even with a good foam envelope around the device). The dynamic resistance at 7.5mA is about 13-14 Ohm. We'll see how it performs over the weekend.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: edavid on November 19, 2016, 03:20:50 am
P.S. - first impressions are ... interesting. Very little random noise but the device is (relatively) sensitive to temperature variations and air movements. I suspect that it can only be useful with a good temperature stabilizing loop. With ~7.5mA and 6 Volts the dissipation is quite high and so is self-heating. As a result, any air movements produce noticeable voltage shifts (few ppm even with a good foam envelope around the device). The dynamic resistance at 7.5mA is about 13-14 Ohm. We'll see how it performs over the weekend.

Is your device a 2DW232 or 2DW233?  I know zlymex told us not to pay much attention to the nominal current, but...
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on November 19, 2016, 04:02:15 am
..... With ~7.5mA and 6 Volts the dissipation is quite high and so is self-heating. As a result, any air movements produce noticeable voltage shifts (few ppm even with a good foam envelope around the device). ......
The foam should be in touch with the case and legs, leaving as small gaps as possible. I just use tissues.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 19, 2016, 04:56:33 am
P.S. - first impressions are ... interesting. Very little random noise but the device is (relatively) sensitive to temperature variations and air movements. I suspect that it can only be useful with a good temperature stabilizing loop. With ~7.5mA and 6 Volts the dissipation is quite high and so is self-heating. As a result, any air movements produce noticeable voltage shifts (few ppm even with a good foam envelope around the device). The dynamic resistance at 7.5mA is about 13-14 Ohm. We'll see how it performs over the weekend.

Is your device a 2DW232 or 2DW233?  I know zlymex told us not to pay much attention to the nominal current, but...

2DW232

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 19, 2016, 06:43:29 am
Here is a one hour run result from this afternoon, the temperature probe is inside the foam enclosure but not touching the zener.

Cheers

Alex

(http://www.ant-audio.co.uk/Service/Ref/2DW232_01.gif)

(http://www.ant-audio.co.uk/Service/Ref/2DW232_setup.jpg)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 19, 2016, 06:59:38 am
This does not look good at all. I might need a better adjustment of the current to get a low TC and thus less sensitivity to temperature variations. Keep in mind that the optimum current depends on the temperature - so it could be a different value with the added foam.

To check if the variations are temperature related one cold also monitor the forward diode only. This might also help to find the right current.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 19, 2016, 09:13:10 am
Just a thought, is the Red dot on the package (if the same as zlymex's photo) added on test to indicate which diode has the most stable zener breakdown characteristics?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 19, 2016, 09:16:30 am
This does not look good at all.

I disagree. The temperature fluctuations are on the order of 50ppm/C or less. I didn't have time to find a better current as every time the current is changed the zener changes the temperature and it takes a while to get to the optimum point. But that is possible to resolve in various ways. Most important for me is how smooth the curve is. The LTZ1000 under similar conditions looks mush more "rugged" (though completely flat  ;) ).

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: edavid on November 19, 2016, 09:39:39 am
Just a thought, is the Red dot on the package (if the same as zlymex's photo) added on test to indicate which diode has the most stable zener breakdown characteristics?

All of mine have the dot on pin 1 (near the tab).

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 19, 2016, 04:41:26 pm
Just a thought, is the Red dot on the package (if the same as zlymex's photo) added on test to indicate which diode has the most stable zener breakdown characteristics?

All of mine have the dot on pin 1 (near the tab).
That dot is used to tell parts apart when you ordered it in unmarked form. 2DW233 got a yellow dot, 2DW234 red, 2DW236 grey.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 19, 2016, 10:07:12 pm
Thanks technix, that makes more sense, I haven't seen the package part number lettering yet (maybe today with luck)  It also clears a small nagging worry that the dot might mean 'reject' (in the same way that die testers do on a wafer) :D. It looks as if the target zero Tc current for these parts will be closer to 10mA (2DW234) rather than 7.5mA then, that should save some time.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Seekonk on November 20, 2016, 03:04:58 am

[/quote]
That dot is used to tell parts apart when you ordered it in unmarked form. 2DW233 got a yellow dot, 2DW234 red, 2DW236 grey.
[/quote]

So, they are all marked 2DW232 and the red dot makes them a 2DW234.

Now the work begins.

Many thanks to zlymex  and VintageNut.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: edavid on November 20, 2016, 03:13:44 am

Quote
That dot is used to tell parts apart when you ordered it in unmarked form. 2DW233 got a yellow dot, 2DW234 red, 2DW236 grey.

So, they are all marked 2DW232 and the red dot makes them a 2DW234.

Wait, he didn't say that!

zlymex or technix, what does it mean when the part is marked 2DW232 *and* it has a red dot?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 20, 2016, 04:29:51 am

Quote
That dot is used to tell parts apart when you ordered it in unmarked form. 2DW233 got a yellow dot, 2DW234 red, 2DW236 grey.

So, they are all marked 2DW232 and the red dot makes them a 2DW234.

Wait, he didn't say that!

zlymex or technix, what does it mean when the part is marked 2DW232 *and* it has a red dot?

I will confirm it with the factory next Monday. Stop using it for now though, they may be technically counterfeits.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on November 20, 2016, 04:23:19 pm
Just a thought, is the Red dot on the package (if the same as zlymex's photo) added on test to indicate which diode has the most stable zener breakdown characteristics?
Dotted pin is negative terminal, un-dotted pin(of 1 or 2) is positive terminal, pin 3 for reserve. This is from a datasheet.

Red dot is for 2DW232, yellow dot is for 2DW233, pink dot is for 2DW234, green dot is for 2DW235.
 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 20, 2016, 05:43:12 pm
Just a thought, is the Red dot on the package (if the same as zlymex's photo) added on test to indicate which diode has the most stable zener breakdown characteristics?
Dotted pin is negative terminal, un-dotted pin(of 1 or 2) is positive terminal, pin 3 for reserve. This is from a datasheet.

Red dot is for 2DW232, yellow dot is for 2DW233, pink dot is for 2DW234, green dot is for 2DW235.
Maybe we are referring to a different datasheet? I have obtained a full catalog from the factory and it have said none of that.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on November 20, 2016, 05:49:45 pm
Just a thought, is the Red dot on the package (if the same as zlymex's photo) added on test to indicate which diode has the most stable zener breakdown characteristics?
Dotted pin is negative terminal, un-dotted pin(of 1 or 2) is positive terminal, pin 3 for reserve. This is from a datasheet.

Red dot is for 2DW232, yellow dot is for 2DW233, pink dot is for 2DW234, green dot is for 2DW235.
Maybe we are referring to a different datasheet? I have obtained a full catalog from the factory and it have said none of that.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 20, 2016, 09:35:08 pm
Just a thought, is the Red dot on the package (if the same as zlymex's photo) added on test to indicate which diode has the most stable zener breakdown characteristics?
Dotted pin is negative terminal, un-dotted pin(of 1 or 2) is positive terminal, pin 3 for reserve. This is from a datasheet.

Red dot is for 2DW232, yellow dot is for 2DW233, pink dot is for 2DW234, green dot is for 2DW235.
Maybe we are referring to a different datasheet? I have obtained a full catalog from the factory and it have said none of that.

This is definitely a different datasheet I am referring to. I have posted a translated datasheet based on what I got.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: BravoV on November 20, 2016, 11:35:57 pm
So there are "multiple" different datasheets spreading in the wild ?  :palm:
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on November 21, 2016, 12:40:44 am
So there are "multiple" different datasheets spreading in the wild ?  :palm:
There are, but not contradictory, only one has slightly more information than the other.
The datasheet I was referred to(with pin dots explaination) is on the very first page of this thread.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 21, 2016, 02:40:34 am
Unfortunately (for most of us anyway) it's in Chinese. The only English language data we have is what technix kindly translated (and even that doesn't include information on the dot significance).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 21, 2016, 07:30:42 am
Unfortunately (for most of us anyway) it's in Chinese. The only English language data we have is what technix kindly translated (and even that doesn't include information on the dot significance).
I have contacted the factory about the dot last Friday, and at least for Shanghai No. 17 Radio Factory their dots don't signify anything regarding pins.

The one I translated is extracted from the catalog the factory provided me.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: edavid on November 21, 2016, 07:34:27 am
I have contacted the factory about the dot last Friday, and at least for Shanghai No. 17 Radio Factory their dots don't signify anything regarding pins.

The one I translated is extracted from the catalog the factory provided me.

Did you ask them about why the datasheet has the wrong pinout?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 21, 2016, 07:39:56 am
I have contacted the factory about the dot last Friday, and at least for Shanghai No. 17 Radio Factory their dots don't signify anything regarding pins.

The one I translated is extracted from the catalog the factory provided me.

Did you ask them about why the datasheet has the wrong pinout?
The one on the first page is not their datasheet.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: edavid on November 21, 2016, 10:21:55 am
I have contacted the factory about the dot last Friday, and at least for Shanghai No. 17 Radio Factory their dots don't signify anything regarding pins.

The one I translated is extracted from the catalog the factory provided me.

Did you ask them about why the datasheet has the wrong pinout?
The one on the first page is not their datasheet.
Your translation has the wrong pinout also - did that come from their datasheet?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 21, 2016, 05:51:27 pm
I have contacted the factory about the dot last Friday, and at least for Shanghai No. 17 Radio Factory their dots don't signify anything regarding pins.

The one I translated is extracted from the catalog the factory provided me.

Did you ask them about why the datasheet has the wrong pinout?
The one on the first page is not their datasheet.
Your translation has the wrong pinout also - did that come from their datasheet?
No that one is not. I measured it and put the words in a wrong way. I will fix it and reupload.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 21, 2016, 11:30:35 pm
Hmm, by far the most stable results I get are from a single zener (without the second diode in series), at about 1.4mA current and 5.246V zener voltage (the same setup as before, the resistor value is 3430 Ohm). Here is a 10min run, vertical scale 0.1ppm (0.5uV), HP3458A at NPLC100.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 22, 2016, 12:14:54 am
My opinion is that at room temperature, the shape of the TC curve is "peaky". There may be an optimal current at room temp, but if room temp wanders even a little bit, the voltage is much too sensitive.

If the shape of the datasheet TC curve can be believed, it appears that these 2DW23X parts behave much better at 50 deg C than at room temperature.

To prove this will require some gear that at present I do not possess.

Here is what I did to satisfy my curiosity, I ran one of the 2DW parts in a banana jack mounted to the front of a KE2461. I manually searched for a current that gave as stable of a voltage as possible. The I touched the metal can. Immediately the voltage started to climb.

Another thing that may help is to create a solid copper heatsink into which the 2Dw package can be inserted.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 22, 2016, 01:07:25 am
Here is what I did to satisfy my curiosity, I ran one of the 2DW parts in a banana jack mounted to the front of a KE2461. I manually searched for a current that gave as stable of a voltage as possible. The I touched the metal can. Immediately the voltage started to climb.

This way you are finding a thermal balance, not a zero tempco. Try the current value about 1.4mA I've found for a single zener (the second half is not connected).

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: TiN on November 22, 2016, 01:26:35 am
I can test up to 65-70C for theories above ;)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 22, 2016, 02:31:00 am
I can test up to 65-70C for theories above ;)

...and you write Ninja Python code. You can create an automatic characterization program and save a mountain of data.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 22, 2016, 02:58:38 am
You might want to try going to a much higher current in the series zener+diode mode. One of my samples is shifting by around 10uV when subjected to the cold finger test while running at 20mA.  That's very roughly the same order of shift as I see in my 1N829A at it's nominal zero Tc current (8mA).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 22, 2016, 03:13:26 am
I can test up to 65-70C for theories above ;)

...and you write Ninja Python code. You can create an automatic characterization program and save a mountain of data.
Maybe I will try the automated characterization process if I know hoe to get good measurement, and give you guys an updated translated datasheet with some measured data points.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 22, 2016, 03:22:03 am
You might want to try going to a much higher current in the series zener+diode mode. One of my samples is shifting by around 10uV when subjected to the cold finger test while running at 20mA.  That's very roughly the same order of shift as I see in my 1N829A at it's nominal zero Tc current (8mA).

Did you wrap the device to reduce air flow over the device?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 22, 2016, 03:32:24 am
Hmm, by far the most stable results I get are from a single zener (without the second diode in series), at about 1.4mA current and 5.246V zener voltage (the same setup as before, the resistor value is 3430 Ohm). Here is a 10min run, vertical scale 0.1ppm (0.5uV), HP3458A at NPLC100.

This is very interesting. So it looks like one can also use it as a 5.2-5.3 V reference at lower current. For some applications this can be the more interesting operating point, as it is lower power and a divider from 5.3 V to 5 V (or 10.5 V to 10 V) is less sensitive to resistor drift as one from 6 or 7 V. Reducing the sensitivity of the resistors by something like a factor of 5 can be a really big advantage.

Even with this lower power, it looks really low noise and stable. For most application this can be good enough - hard to find something with lower noise. You have to take into account that some of the noise in the curve could be still the LTZ1000 inside the 3458.

The curve shape with a maximum in voltage over temperature will likely exist at all currents. Changing the current will shift the maximum and thus the temperature with zero linear TC to different temperatures. So there is likely nothing special with the 50-60C temperature where the curve in the DS has its maximum. Finding the compensating current is finding the curve where the maximum (and thus zero slope) is at the working temperature.

Choosing a higher, regulated temperature (which might end up at 50 C because this a practical temperature) is attractive as in the horizontal region of the curve there is no need for a super stable temperature.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 22, 2016, 05:51:56 am
You might want to try going to a much higher current in the series zener+diode mode. One of my samples is shifting by around 10uV when subjected to the cold finger test while running at 20mA.  That's very roughly the same order of shift as I see in my 1N829A at it's nominal zero Tc current (8mA).

Did you wrap the device to reduce air flow over the device?

Sorry, got called away. That was free-air, I wasn't looking for precise results, just trying to find a turnover point. I was driving it in Zener+diode mode (dot pin -ve), via a 1k resistor. Applying a cold finger was causing an increase in voltage up to about 26V input, above 27V input it turned over and started dropping instead. At about 26.5V it seemed to reach equibrium (~10uV shift). At all times the device felt warm / hot so I was always applying a cooling effect.

Not a particularly scientific test I know, but I was getting fed up with seeing large (100uV or more) shifts when I touched the package and decided to just keep ramping up the current to see what happened. 20mA was way above the current I was expecting to apply. I haven't yet tried the same on other devices to see how repeatable this is - this current is uncomfortably close to the 30mA Iz Max.

Edit: Maybe this is the current level needed to hit 50'C package temperature in free-air, so you could maybe achieve the same result at lower current if package is thermally insulated.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: BravoV on November 22, 2016, 06:18:53 am
Maybe I will try the automated characterization process if I know hoe to get good measurement, and give you guys an updated translated datasheet with some measured data points.

Please delete the 1st translated datasheet, as it may mislead future readers.

And post the original datasheet here that you got from the manufacturer, even its in Chinese, at least Zlymex can verify your translation.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on November 22, 2016, 06:53:03 am
Maybe I will try the automated characterization process if I know hoe to get good measurement, and give you guys an updated translated datasheet with some measured data points.

Please delete the 1st translated datasheet, as it may mislead future readers.

And post the original datasheet here that you got from the manufacturer, even its in Chinese, at least Zlymex can verify your translation.
I will delete the original translation if you find it misleading. Keep in mind that this is the very first sentence an instructor will tell every Chinese EE student: do not trust in datasheets blindly, characterize everything yourself before using it.

Those parts made under Chinese traditional part numbering systems can (when talking parts made before the mid-80s the word would be "very likely will") vary from piece to piece as the standards is extremely lax. So if you are using parts in Chinese part numbering system, measure it before even thinking about using it, as you may be in for a surprise, especially when talking about older parts.

The discrepency between the datasheet Zlymex posted and the pinout the factory told me (not in the original datasheet - I had to phone in to confirm) is a clear indication of this problem.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 22, 2016, 07:14:37 am
Using the finger to test the sensitivity to temperature can be a little misleading: there are two point where the finger will not cause a change: one is when the TC of the device is zero and a second is when the device temperature is the same as the finger, so there will be no more change in temperature.
 
Increasing the current will also increase the temperature, so one is probing at different temperatures, not just different currents. It depends on the thermal design how those two parameters are combined.

From the turn on transients the VintageNut did, the TC seems to turn more negative at higher current. It is still the question if this due to the higher temperature or due to the higher current. The test is still useful to find the suitable current for the given thermal conditions. However one tends to look at the changes below (before) equilibrium temperature. So it is not the most accurate way.
Form the curved shape of the curve in the DS it is suggested that a higher temperature gives a more negative TC. If the DS curve can be believed this would be something like -0.2 ppm/K². So a self heating of 10 K would change the TC by about -2 ppm/K.

Without a good DS, the logical thing would be to measure the curves you would wish to have in a good DS.
To get data relative to the true chip temperature one could use the normal diode as an approximate temperature sensor. This would need 2 voltmeters and likely an external heater. The DMM for the normal diode voltage (-> temperature) does not need to be that accurate, but the one for the zener voltage should be. So it would be first to check the forward diode with current only through that diode (to reduce self heating), or maybe use the start of transient. Than with the same current one could test on increasing temperature. So raw data would be zener voltage versus diode voltage.

The measurements from Alex Nikitin suggest, the using only one diode (and lower current) might be the even more interesting operation point.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 22, 2016, 01:11:58 pm
I drilled a hole in a solid copper plate and placed a 2DW232 inside the hole and mounted that on the front of the KE2461. Using 3mA, after a long stabilization period, the short term standard deviation is 2uV. That looks promising.

I still think that running this device close to 50C will give the best long term stability.

I am looking forward to someone having a proposed method of ovenizing this device. 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Galaxyrise on November 22, 2016, 02:28:35 pm
Thank you Zlymex and VintageNut for letting me play in these reindeer games :)

I've been working on a little temperature controlled test environment and put it to work this weekend running tests on one of the ones
I got, hunting for an inflection point in the temperature response. I ran it at various currents from 3mA to 18mA, changing the temperature of the chamber from 23C to 40C.  Consistent with the findings of others in this thread, the TC did not change sign in this interval, with the smallest tempco being at 18mA.  (I observed roughly 25ppm/C at 18mA. Even though the test wasn't set up to accurately measure TC, it still seemed like a pretty linear temperature response from 23 to 35C at that current.) 

I don't know what the die temperatures were, since I haven't done a pulsed current test yet.  (I need a different setup to take measurements fast enough.)

I just got some enameled nichrome wire, so I'm going to try to turn one of things into a little oven and see if I can find the temperature response curve from the datasheet.  Then I can use the zener voltage at that zero point to stabilize it.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Galaxyrise on November 22, 2016, 06:30:04 pm
I got things set up and did a fairly extreme temperature excursion at 5mA (I raised the outside to about 113C, though the die temperature was certainly much lower.)  The zener voltage followed a curve not unlike the datasheet.  However, the zener's parabola was only just barely visible in the total voltage; the magnitudes of the temperature coefficients is that different at 5mA.

Last thing I did before bed was to bump the current up to 10mA.  I did not have the time to do this one properly, but I did not see an inflection point in the zener voltage any more (dV stayed positive for the entire test), and the overall TC looked much less.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 22, 2016, 10:47:01 pm
Here are the overnight results with a single zener and 1.38mA current. The tempco is about -6ppm/C, the noise is low and the stability looks good. 2ppm/div vertical scale on Volts.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 22, 2016, 11:06:50 pm
This is good information. Here is what I see. For most of this time span, the voltage is rising despite what is happening with temperature. At around 08:00, the voltage is stable. After stability is reached, the zener voltage responds to temperature change in the opposite direction of the temperature change.

This long time to warm up is what I have seen operating the device in its intended configuration. If the device is operated at a temperature much higher than ambient, then the warmup time should be eliminated.



Here are the overnight results with a single zener and 1.38mA current. The tempco is about -6ppm/C, the noise is low and the stability looks good. 2ppm/div vertical scale on Volts.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 22, 2016, 11:20:32 pm
This is good information. Here is what I see. For most of this time span, the voltage is rising despite what is happening with temperature. At around 08:00, the voltage is stable. After stability is reached, the zener voltage responds to temperature change in the opposite direction of the temperature change.

This long time to warm up is what I have seen operating the device in its intended configuration. If the device is operated at a temperature much higher than ambient, then the warmup time should be eliminated.

At 1.4mA the dissipation is only 7mW, so not much to warm up with. The temperature readings are not for the zener itself, but for the enclosure, that might explain the discrepancies. I will try next time to log the voltage on the second zener in a diode connection, that would give a very good tracking of the actual zener temperature.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 23, 2016, 12:01:15 am
This is good information. Here is what I see. For most of this time span, the voltage is rising despite what is happening with temperature. At around 08:00, the voltage is stable. After stability is reached, the zener voltage responds to temperature change in the opposite direction of the temperature change.

This long time to warm up is what I have seen operating the device in its intended configuration. If the device is operated at a temperature much higher than ambient, then the warmup time should be eliminated.

At 1.4mA the dissipation is only 7mW, so not much to warm up with. The temperature readings are not for the zener itself, but for the enclosure, that might explain the discrepancies. I will try next time to log the voltage on the second zener in a diode connection, that would give a very good tracking of the actual zener temperature.

Cheers

Alex

I do not see any discrepancies. I see the zener voltage rising to some asymptotic voltage despite any ups and downs of temperature. If this is not "warm up" then it is some other march toward some sort of equilibrium that appears to be achieved at 08:00 where temperature is flat and voltage is flat. During that flat time, zener voltage and temperature appear to be at equilibrium.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 23, 2016, 12:10:10 am
I do not see any discrepancies. I see the zener voltage rising to some asymptotic voltage despite any ups and downs of temperature. If this is not "warm up" then it is some other march toward some sort of equilibrium that appears to be achieved at 08:00 where temperature is flat and voltage is flat. During that flat time, zener voltage and temperature appear to be at equilibrium.

Hmm, what I see is that the temperature is steadily falling (with some variations on the temperature sensor which may not necessarily affect the zener - as I've said, the temperature sensor is not in a direct contact with the zener). More important for me is the fact that the voltage comes back to exactly the same value at the end of the run at 25C as it was at the very beginning (less than 1ppm difference).

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on November 23, 2016, 01:28:03 am
Hmm, what I see is that the temperature is steadily falling (with some variations on the temperature sensor which may not necessarily affect the zener - as I've said, the temperature sensor is not in a direct contact with the zener). More important for me is the fact that the voltage comes back to exactly the same value at the end of the run at 25C as it was at the very beginning (less than 1ppm difference).

Cheers

Alex

Alex,
Could you post the raw figures for that run please? I'd like to run some statistics on them.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 23, 2016, 01:49:41 am
Hmm, what I see is that the temperature is steadily falling (with some variations on the temperature sensor which may not necessarily affect the zener - as I've said, the temperature sensor is not in a direct contact with the zener). More important for me is the fact that the voltage comes back to exactly the same value at the end of the run at 25C as it was at the very beginning (less than 1ppm difference).

Cheers

Alex

Alex,

Could you post the raw figures for that run please? I'd like to run some statistics on them.


Here. It includes several step changes in the current at the very beginning which I've cut off of the uploaded graph. Steps in the resistor value are 3.449K, 3.448K, 3.446K and 3.447K (at that value the main overnight test was run).

Cheers

Alex

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Seekonk on November 23, 2016, 02:20:18 am
For thermal mass, this defective press in triac jumped out of the junkbox.  Dug out the old part and potted it in this 3/4 inch slug.
Large nut would also work.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 23, 2016, 03:06:48 am
Using the same sample as I was using yesterday (the 20mA run), I am seeing the same stable point as Alex for the Zener alone... 1.4mA, 5.251V. This appears to be another turnover point: Negative TC below, Positive TC above. My sample seems to hold within about 20uV over a range between 20-24'C.

I guess the two turnover points make some kind of sense, the higher the current the more positive the TC of the zener becomes until it matches the negative TC of the diode, but not until about 20mA. Much higher than the expected 5 - 7.5mA. Below 20mA it seems that the positive TC slope of the zener is too low. [Edit:] I'm assuming that the TC of the diode will remain pretty much -0.6mV/'C regardless of current.

A solution (if achieving lower noise than at 1.4mA operation is a priority) may be to add a divided down portion of the diode forward drop to the zener voltage. Maybe this could be done by biasing the diode separately and using passive divider?

One other thing. Has anyone else noticed that the leads seem to be made of rather stiff grade magnetic steel? I've avoided risking my good cutters on them but even my carbide ones take a bit of force. There also seems to be a bit of crazing on the glass to metal seals of most samples, possibly due to the lead length and stiffness. I think they will need mounting with care to avoid stresses.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 23, 2016, 03:28:20 am
[Edit:] I'm assuming that the TC of the diode will remain pretty much -0.6mV/'C regardless of current.

Isn't it -2.2 ... -2.5mV/C ?

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 23, 2016, 03:46:51 am
Oops!  :-[

Can't think now why that figure is sticking in my (somewhat defective) head!
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 23, 2016, 04:10:23 am
For most cases I would prefer the 1.4 mA operation point. The noise already seems to be low (e.g. much better than an LM329 or LM399), possibly at the level an LTZ1000 would get at 5 mA. If you really care, just use 2 in parallel or series - not that expensive and still low power.

Also the 5.25 V level could be a big plus if one wants to scale to 5 V (or 10 V starting from 2 diodes in series).

Adding only a part of the diode drop should work to get a different operating point (higher current) for compensation. I don't even think one would need separate biasing - just a divider to get something like half the diode voltage.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 23, 2016, 04:47:47 am
True, if it performs so well at low current there really isn't any need to go higher.

Quote
Adding only a part of the diode drop should work to get a different operating point (higher current) for compensation. I don't even think one would need separate biasing - just a divider to get something like half the diode voltage.

Actually, yes, it is that simple isn't it, I was over-thinking it.  Correcting by balancing a Positive TC with an adjustable negative TC (assuming relatively flat profiles) just feels a little more comfortable than relying on the TC turnover point of the zener alone, at least both slopes are going in predictable directions. Maybe this has the possibility of yielding a lower overall TC over a wider temperature range, it might on the other hand be needless (drift introducing) added complexity. It seems worth a try though.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on November 23, 2016, 05:56:11 am
For some reason I'm having problems with file uploads to the forum today; so you're not going to get any charts.

I've taken a look at the figures Alex kindly uploaded. Doing a linear regression of voltage against temperature gives a tempco of -24.3 ppm/C with a correlation coefficient (R2) of 0.76 which is a fairly strong correlation. On a scatter plot there are 3 islands of outliers, all well away from the main line. The scatter plot suggests that relatively there's a lot of noise in the temperature readings.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SvanGool on November 23, 2016, 08:28:59 am
@Cerebus
If I look at the graph from previous page I would say that an app. 5.25V reference level and app. -60uV (min/max) in 2.5C (min/max) would make app -5 to -6 ppm/C (as Alex already said).
Why don't your numbers come close to that?

If this is quite good lineair, as you also say, then the TC could be indeed nicely compensated, like Giro proposes by a divider like this one (with different numbers) of Zlymex:
https://www.eevblog.com/forum/metrology/spread-sheet-aided-design-of-compensation-for-7v-to-10v-step-up-resistor-set/ (https://www.eevblog.com/forum/metrology/spread-sheet-aided-design-of-compensation-for-7v-to-10v-step-up-resistor-set/)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on November 23, 2016, 02:04:20 pm
@Cerebus
If I look at the graph from previous page I would say that an app. 5.25V reference level and app. -60uV (min/max) in 2.5C (min/max) would make app -5 to -6 ppm/C (as Alex already said).
Why don't your numbers come close to that?

If this is quite good lineair, as you also say, then the TC could be indeed nicely compensated, like Giro proposes by a divider like this one (with different numbers) of Zlymex:
https://www.eevblog.com/forum/metrology/spread-sheet-aided-design-of-compensation-for-7v-to-10v-step-up-resistor-set/ (https://www.eevblog.com/forum/metrology/spread-sheet-aided-design-of-compensation-for-7v-to-10v-step-up-resistor-set/)

I didn't imply anything about the linearity. Are you perhaps confused by the mention of a linear regression? I'm not saying that the tempco is X, just that X is what pops out of a linear regression of this narrow temperature range. A linear regression seems reasonable (as opposed to other curve fits) as, for the small temperature span in Alex's figures, the curve is quite linear - over a wider temperature I'd expect it to be more polynomial in nature. The disparity from more empirically arrived at figures is in part the small range and in part the sheer amount of noise in the temperature data - the latter makes it difficult to really see what's going on, precisely why I wanted to try some numerical methods. I wish I could fix my uploading problem as the scatter diagram is quite informative, there's a lot of smearing across temperature but there's also a very clear central trend. It might be beginning to flatten out at lower temperatures but, again, the noise in the temperature data makes that unclear.

I actually spent the evening hacking about some foam, a peltier device, a couple of heatsinks, a thermocouple, a breadboard and a ZIF socket, to see if I could come up with a fixture that makes for a more controlled testing environment - I'm perhaps 20% of the way there.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 24, 2016, 12:33:23 am
Here is a graph of many hours overnight at 6mA mounted to a copper bar on the front of a KE2461. The graph starts during the day when the sun is shining into my office/lab. This device appears to be a candidate as a temperature sensor.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 24, 2016, 01:14:34 am
For some reason I'm having problems with file uploads to the forum today; so you're not going to get any charts.

I've taken a look at the figures Alex kindly uploaded. Doing a linear regression of voltage against temperature gives a tempco of -24.3 ppm/C with a correlation coefficient (R2) of 0.76 which is a fairly strong correlation. On a scatter plot there are 3 islands of outliers, all well away from the main line. The scatter plot suggests that relatively there's a lot of noise in the temperature readings.

Is it -24.3 ppm/C or -24.3 uV/C (which is about -5ppm/C)?

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on November 24, 2016, 01:37:01 am
For some reason I'm having problems with file uploads to the forum today; so you're not going to get any charts.

I've taken a look at the figures Alex kindly uploaded. Doing a linear regression of voltage against temperature gives a tempco of -24.3 ppm/C with a correlation coefficient (R2) of 0.76 which is a fairly strong correlation. On a scatter plot there are 3 islands of outliers, all well away from the main line. The scatter plot suggests that relatively there's a lot of noise in the temperature readings.

Is it -24.3 ppm/C or -24.3 uV/C (which is about -5ppm/C)?

Cheers

Alex

It's just the m in y = mx + c, where y is volts and x is Celsius so, yes, it's effectively uV/C. Sorry, I should have been clearer but it was getting late here.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 24, 2016, 03:26:45 am
Here is a graph of many hours overnight at 6mA mounted to a copper bar on the front of a KE2461. The graph starts during the day when the sun is shining into my office/lab. This device appears to be a candidate as a temperature sensor.

At 6 mA the TC of the zener is supposed to about compensate with the TC of the normal diode. So no wonder you get a lot of sensitivity to temperature variations with just the zener, should be somewhere in the +1-2mV/K range. So the 160 µV of voltage change would correspond to something like 0.1-0.2 K.

There should be no need for an external compensation of the linear TC. It should be possible to to find an operating current where the linear TC tends towards zero for a given temperature. There even seem to be two such current settings. One low (e.g. 1mA range) for just the zener and one rather high (e.g. 10 mA, but could be 5-20 mA depending on sample) for the series configuration. It just seems to be a little tricky to find one of those points, especially the one at higher current.

The 5 ppm/K (at 1.4 mA) is already a useful value / not that bad. To get a rough idea one would need TC data for a few different currents - to get an idea on how accurate one should find that ideal current. The curves with an external temperature sensor are not that accurate - so it would be really preferred to use the internal diode as a temperature sensor - at least for relative changes.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 24, 2016, 03:51:03 am
It is being operated with both diodes in series. Looking for the current that produces the least swings in voltage for ambient temperature in my office/lab.


Here is a graph of many hours overnight at 6mA mounted to a copper bar on the front of a KE2461. The graph starts during the day when the sun is shining into my office/lab. This device appears to be a candidate as a temperature sensor.

At 6 mA the TC of the zener is supposed to about compensate with the TC of the normal diode. So no wonder you get a lot of sensitivity to temperature variations with just the zener, should be somewhere in the +1-2mV/K range. So the 160 µV of voltage change would correspond to something like 0.1-0.2 K.

There should be no need for an external compensation of the linear TC. It should be possible to to find an operating current where the linear TC tends towards zero for a given temperature. There even seem to be two such current settings. One low (e.g. 1mA range) for just the zener and one rather high (e.g. 10 mA, but could be 5-20 mA depending on sample) for the series configuration. It just seems to be a little tricky to find one of those points, especially the one at higher current.

The 5 ppm/K (at 1.4 mA) is already a useful value / not that bad. To get a rough idea one would need TC data for a few different currents - to get an idea on how accurate one should find that ideal current. The curves with an external temperature sensor are not that accurate - so it would be really preferred to use the internal diode as a temperature sensor - at least for relative changes.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 24, 2016, 03:55:17 am
It is being operated with both diodes in series. Looking for the current that produces the least swings in voltage for ambient temperature in my office/lab.

For both diodes in series and 6mA current the voltage is very low!

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 24, 2016, 03:57:01 am
I've been playing around with the divider approach today and it looks as if it is possible to achieve very low TC values over a limited temperature range even with a simple hook up. I've attached the schematic for clarity but it's basically just taking the output voltage from a divider tap across the forward biased diode. I simply used a 2k cermet preset, it took a little tweaking but it looks as if the flat portion of the TC curve can be adjusted to any temperature and operating current, in this case about 23'C and is very flat over a few degrees. TC is sensitive to both divider ratio and supply current as you would expect.

Operating the device at 5.010mA with the divider (pot) measuring 765R / 1k3 the output of my sample is 5.878V  Temperature profile came out as follows (values relative to 23'C case temperature):

20'C     -12uV
20.5'C  -4uV
21'C     -3uV
21.5'C  -2uV
22'C     -1uV
22.5'C   0
23'C      0
23.5'C   -1uV
24'C      -5uV
24.5'C   -7uV
25'C      -14uV

Temperatures were measured during device warm-up (it finally settled at about 25.3'C) using a thermocouple taped to the side of the can. I was using a Geller SVR-T and Muirhead decade divider with Datron 1041M, null meter style. I repeated 3 times, each warm-up taking less than 5 mins, with consistent results (obviously the readings were a bit noisy at this level).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 24, 2016, 03:59:49 am
It is being operated with both diodes in series. Looking for the current that produces the least swings in voltage for ambient temperature in my office/lab.

For both diodes in series and 6mA current the voltage is very low!

Cheers

Alex


Pilot error. I grabbed the wrong one. i have 4 of these mounted to banana plugs. One is wired for just the one diode. Arrrggghhh
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 24, 2016, 08:43:43 am
I've been playing around with the divider approach today and it looks as if it is possible to achieve very low TC values over a limited temperature range even with a simple hook up. I've attached the schematic for clarity but it's basically just taking the output voltage from a divider tap across the forward biased diode. I simply used a 2k cermet preset, it took a little tweaking but it looks as if the flat portion of the TC curve can be adjusted to any temperature and operating current, in this case about 23'C and is very flat over a few degrees. TC is sensitive to both divider ratio and supply current as you would expect.

Operating the device at 5.010mA with the divider (pot) measuring 765R / 1k3 the output of my sample is 5.878V  Temperature profile came out as follows (values relative to 23'C case temperature):

20'C     -12uV
20.5'C  -4uV
21'C     -3uV
21.5'C  -2uV
22'C     -1uV
22.5'C   0
23'C      0
23.5'C   -1uV
24'C      -5uV
24.5'C   -7uV
25'C      -14uV

Temperatures were measured during device warm-up (it finally settled at about 25.3'C) using a thermocouple taped to the side of the can. I was using a Geller SVR-T and Muirhead decade divider with Datron 1041M, null meter style. I repeated 3 times, each warm-up taking less than 5 mins, with consistent results (obviously the readings were a bit noisy at this level).

It's now 5 hours later... The room has cooled a couple of degrees so the package temperature has dropped to 23.7'C. The voltage is now +3uV from the previous 23.5'C value (+7uV from the previous 24'C value). Operating current is still sitting at 5.010mA and there has been plenty of time for any thermocouple effects to stabilise.

It probably says as much about the SVR-T's TC and the Muirhead's ratio stability as it does about the sample but that's pleasingly close. Either that or everything is drifting rather conveniently in the same direction. Surprising though. :D


EDIT: Probably happy chance above. One hour later, case temperature is now 22.9'C and voltage -6uV vs previous 23'C reading. Room temperature has dropped quite fast now the heating has gone off though, so the higher thermal mass items probably aren't keeping pace. I'm off the edge of my measurement capability here.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: TiN on November 25, 2016, 12:19:54 am
First candy test. Nothing fancy, just K2400 run with help of little snake (https://xdevs.com/doc/xDevs.com/IV-tracer/testiv.py).

(https://xdevs.com/doc/xDevs.com/IV-tracer/2dw232_test3.png)

Blue line - pin2-pin3 junction
Orange line - pin1-pin2 junction

Voltage sourced -10 to +10V, current compliance 20mADC

DATA 1 (XLS) (https://xdevs.com/doc/xDevs.com/IV-tracer/2dw232-hi_pin2_lo-pin1.xlsx)
DATA 2 (XLS) (https://xdevs.com/doc/xDevs.com/IV-tracer/2dw232-hi_pin3_lo-pin2.xlsx)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: evb149 on November 25, 2016, 01:10:55 am
Thank you.
That's interesting so if I'm understanding this right:
pin 1-pin2 is something like a *back to back" zener with a roughly symmetric +/-6.2VDC breakdown in each applied polarity

pin2-pin3 is something that basically looks like a VBE junction of a small signal BJT with forward conduction of roughly 1 VBE and a reverse zener breakdown of 5.2V.

I had no idea from my understanding of the diagram in the datasheet that the device behaved like this.  I was expecting symmetrical back to back zeners of identical characteristics with a common center point, similar to what you show between pin1-pin2 if you neglect the middle common lead entirely.

Is this your interpretation of your test results or am I misunderstanding your setup? 

EDIT: I guess pin2-pin3 behaves like a normal 5.4VDC zener which is a single device with the usual non-symmetric VF/VR (which is like a BJT VBE but no need to otherwise liken it to a BJT)

So really this thing is behaving like
PIN1---[K-D1-A][A-D2-K]--PIN2--[D3]---PIN3
...with D1,D2 = (6.2-VF) volt zeners back to back, D3=5.4V single zener with perhaps my being incorrect in stating the A, K designations.
 
So you could either operate it as
A: a single (ZENER+DIODE series ) PIN1-[D1+D2]-PIN2: 6.2V overall
B: a single ZENER (5.4V reverse polarity) PIN2-PIN3 of a certain polarity.
C: a single DIODE (VF forward polarity) PIN2-PIN3 of the other polarity.

And if you measure from PIN1---PIN3 I guess you get VZ(D1)+VF(D2)+VF(D3) or something like that depending on your applied polarity?  In which case you'd expect the double VF tempco of D2+D3 is designed to balance the D1 VZ tempco, or maybe PIN2-PIN3 is meant to be independently used only for temperature monitoring/control and the reference taken only from PIN1-PIN2.



First candy test. Nothing fancy, just K2400 run with help of little snake (https://xdevs.com/doc/xDevs.com/IV-tracer/testiv.py).

(https://xdevs.com/doc/xDevs.com/IV-tracer/2dw232_test1.png)

Blue line - pin2-pin3 junction
Orange line - pin1-pin2 junction

Voltage sourced -10 to +10V, current compliance 20mADC

DATA 1 (XLS) (https://xdevs.com/doc/xDevs.com/IV-tracer/2dw232-hi_pin2_lo-pin1.xlsx)
DATA 2 (XLS) (https://xdevs.com/doc/xDevs.com/IV-tracer/2dw232-hi_pin3_lo-pin2.xlsx)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: TiN on November 25, 2016, 01:13:10 am
Yea, correct.
I'll have to try pin 1-3 too :)

Zoom in region +/-1nA :

(http://xdevs.com/doc/xDevs.com/IV-tracer/2dw232_test2.png)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: 2N3055 on November 25, 2016, 02:32:40 am
Yea, correct.
I'll have to try pin 1-3 too :)

It should be the same...
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 25, 2016, 03:55:27 am
First candy test. Nothing fancy, just K2400 run with help of little snake (https://xdevs.com/doc/xDevs.com/IV-tracer/testiv.py).

(https://xdevs.com/doc/xDevs.com/IV-tracer/2dw232_test1.png)

Blue line - pin2-pin3 junction
Orange line - pin1-pin2 junction

Voltage sourced -10 to +10V, current compliance 20mADC

DATA 1 (XLS) (https://xdevs.com/doc/xDevs.com/IV-tracer/2dw232-hi_pin2_lo-pin1.xlsx)
DATA 2 (XLS) (https://xdevs.com/doc/xDevs.com/IV-tracer/2dw232-hi_pin3_lo-pin2.xlsx)

How long did this trace take and in what order did you measure the parameters (back to back zeners vs the single zener trace)? Unfortunately device (junction) temperature is the important factor rather than ambient temperature. If the device temperature changed at all during the sweep then the characteristics will have been changing too. There is little data in the critical conduction areas, where Temperature coefficients of the forward and reverse biased zeners are so critical. If you read back through the posts you will see that Alex found a TC turnover point at 1.4mA for the Zener alone and I found another at 20mA for series Zener and forward biased Zener (diode) at 20mA. I can't see either showing up on the sweep (although at -20mA it may just be visible at the botton left of the trace), also the slopes on the left and right of the trace are different too (right hand one is shallower with no hint of turnover visible), when I would have expected them to be near identical this makes me think that device temperature was changing,

EDIT: Sorry, I think I'm getting tangled up between I/V curves with TC.  :palm: Something still doesn't look right in comparison between the bottom left and top right slopes though (back to back Zeners).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SvanGool on November 25, 2016, 04:00:59 am
@TiN
Could it be that either 1-3 or 2-3 is inverted (otherwise you have two zeners in the same direction, which is not the case according 1-2)?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 25, 2016, 05:43:58 am
Be aware that when you sweep across a sign change, the instrument is on two completely different ranges.

If you want to rule out different range offsets and/or different range linearities, only sweep from 0V to 10V then reverse the banana plugs at the SMU and then run the 0 to 10V sweep again. Now you have the full characterization and only use one range of the SMU.

Also, when you sweep from -10V to +10V continuously, the device is decreasing voltage (and heat) in the first half of the sweep and increasing voltage (and heat) in the second half of the sweep.

Sweeping from 0V to 10V for both halves of the curve may reduce the difference in heating as well.

These devices are very sensitive to change in temperature.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on November 25, 2016, 07:28:54 am
Be aware that when you sweep across a sign change, the instrument is on two completely different ranges.

Why do you think that?

Unlike some of the other 2xxx range of instruments, I don't have schematics for the Keithley 2400 but I'd be surprised if it doesn't use the same current balancing integrating ADC that the other 2xxx series instruments do and the 'source' side of things is explicitly called out as 4 quadrant in the specifications.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 25, 2016, 08:23:16 am
Be aware that when you sweep across a sign change, the instrument is on two completely different ranges.

Why do you think that?

Unlike some of the other 2xxx range of instruments, I don't have schematics for the Keithley 2400 but I'd be surprised if it doesn't use the same current balancing integrating ADC that the other 2xxx series instruments do and the 'source' side of things is explicitly called out as 4 quadrant in the specifications.

The calibration report with data would be the definitive document.

TiN, did you have your K2400 calibrated? Do you have the data report?

Attached is the pertinent info from a 2450 that I used. Source +10V actual is 10.00022. Source -10V actual is -9.99997

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on November 25, 2016, 09:08:52 am
Be aware that when you sweep across a sign change, the instrument is on two completely different ranges.

Why do you think that?

Unlike some of the other 2xxx range of instruments, I don't have schematics for the Keithley 2400 but I'd be surprised if it doesn't use the same current balancing integrating ADC that the other 2xxx series instruments do and the 'source' side of things is explicitly called out as 4 quadrant in the specifications.

The calibration report with data would be the definitive document.

TiN, did you have your K2400 calibrated? Do you have the data report?

Attached is the pertinent info from a 2450 that I used. Source +10V actual is 10.00022. Source -10V actual is -9.99997

You said "two completely different ranges" and I want to understand why you think that and if indeed that is the case. The calibration points aren't evidence of that, just of one range with 30uV offset and 19 ppm gain errors (and doubtless some linearity error too) unless there's something about the way the K2400 works that you know and that I don't.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: TiN on November 25, 2016, 09:25:40 am
I'll calibrate and generate report for you once get back, no problem. I calibrated it some year ago, and two years before it was calibrated by Tek Taiwan. Here's that old report (https://dev.xdevs.com/attachments/download/816/2400-0788393%20as%20returned.pdf).

I'm out from lab next 5 days. I don't think this basic test suffer much from SMU specs. Sweep was rather fast,  ~2minutes total, with 5mV increments. I can run sweeps with 3458 as sampler, that shall fix linearity issue? :)

My plan for next step is to mount diode to copper slug, put YSI 44008 thermistor on it and attach to TEC for controlling temperature. Then I can run much slower sweeps with focus just in zener regions with temperature points from +15 to +65 in 1C step. Pretty sure can do 0.005C stability with the setup.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 25, 2016, 09:50:41 am
Has anyone tried duplicating the voltage divider TC compensation adjustment that I posted?

Given that the connection between the zener and the forward biased diode/zener is brought out (unlike a 1N82x for instance) then I can only assume that this is how TC adjustment would normally be implemented (unless every application runs it at 50'C). Whilst running with an individual zener biased at 1.4mA appears workable, this doesn't tie up with any of the listed datasheet parameters.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 25, 2016, 10:06:28 am
Be aware that when you sweep across a sign change, the instrument is on two completely different ranges.

Why do you think that?

Unlike some of the other 2xxx range of instruments, I don't have schematics for the Keithley 2400 but I'd be surprised if it doesn't use the same current balancing integrating ADC that the other 2xxx series instruments do and the 'source' side of things is explicitly called out as 4 quadrant in the specifications.

The calibration report with data would be the definitive document.

TiN, did you have your K2400 calibrated? Do you have the data report?

Attached is the pertinent info from a 2450 that I used. Source +10V actual is 10.00022. Source -10V actual is -9.99997

You said "two completely different ranges" and I want to understand why you think that and if indeed that is the case. The calibration points aren't evidence of that, just of one range with 30uV offset and 19 ppm gain errors (and doubtless some linearity error too) unless there's something about the way the K2400 works that you know and that I don't.

No, I don't have special knowledge. I look at the calibration report and see that the + and - source have a different measured value absolute value. So, even if a device being measured were perfectly symmetric in its behavior for + and - voltage, the 2400 would not necessarily plot a symmetric curve.

The best thing to do would be to plot curves that are the measured values with the uncertainties added and subtracted. You have three curves. The measured curve and the curves that represent the most negative uncertainty and the most positive uncertainty. You cannot know symmetry any better than the min and max uncertainty curves.

In practice, most of the keithley gear is far better than the worst-case specifications. To know if and how much better, you have to perform some tests to quantify the offset and noise of the range being used.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: TiN on November 25, 2016, 10:12:09 am
I'd expect changes from selfheating in diodes would be magnitude more than this error from SMUs ADC (which is almost a clone of K2000). Anyway, running same sweep with 3458 in parallel is no difficulty.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 25, 2016, 10:15:28 am
I'd expect changes from selfheating in diodes would be magnitude more than this error from SMUs ADC (which is almost a clone of K2000). Anyway, running same sweep with 3458 in parallel is no difficulty.

Excellent. For symmetry of self heating I suggest starting at 0V and sweeping to 10V, maybe pause for some recovery and then sweep from 0 to -10V.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: plesa on November 25, 2016, 10:24:28 am
I'd expect changes from selfheating in diodes would be magnitude more than this error from SMUs ADC (which is almost a clone of K2000). Anyway, running same sweep with 3458 in parallel is no difficulty.

Excellent. For symmetry of self heating I suggest starting at 0V and sweeping to 10V, maybe pause for some recovery and then sweep from 0 to -10V.

Keithley 2400 has pulse option, which will eliminate self heating. Similar way I measured parameters of LTZ1000 on 2636B.
If we agree in meantime what and how measure, I can program it and measure all zeners which I will be distributing in EU next week when I will be back home :)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: TiN on November 25, 2016, 10:29:33 am
I was thinking of pulsed sweeps too. I believe 4142B SMU has pulsed modes natively.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 25, 2016, 01:16:46 pm
I was thinking of pulsed sweeps too. I believe 4142B SMU has pulsed modes natively.

Pulse mode measurement usually is much smaller than 1 NPLC giving lower resolution. No free lunch. It will be instructive to see the results.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Galaxyrise on November 25, 2016, 02:33:23 pm
I took my "heated" 2dw232 and breadboarded it into the following circuit, just using cheap resistors.  The objective was to see if it would start, and to tweak the heater parameters. the 4.4mA zener current put the 0TC point of the zener is at a good place to heat the zener to.

It does start. The integrator gain was reduced 100x from the LTZ1000 circuit to get it to oscillate less. The result was much worse than I expected; almost 100ppm/C. 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 25, 2016, 09:37:33 pm
At 4 mA the TC of the zener section alone should be rather high (and the zener + diode) is likely not yet really low.

Even with external temperature control one should start with an current that produces a rather low TC. The main thing the temperature control is effective with is avoiding the second order TC - here even a rough regulation helps a lot. So a reasonable aim would be more like a current set to have a linear TC somewhere in the < 10 ppm/C range and than have temperature control down to the 0.1 K range. It might be possible to use the oven (e.g. use modulated temperature for adjustment) also to do in circuit adjustment of the current to get the TC really down (e.g. < 1 ppm/K).

There is nothing special with the 50 C setting : the curve from the DS is just a typical one, with a lot of possible variations between samples (e.g. current to get a similar curve might be anywhere from about 3 mA to 20 mA, or at a 5 mA current the maximum in voltage could be at a totally different temperature. So even with temperature control one should have an individually set current.

If one only has cheap resistors available one should use the unscaled output from the reference, the scaled up version can be still Ok to set the current.

For temperature control the internal sensor is rather slow - thus not that much gain possible in a simple configuration. To get a really good regulation one might need a second, faster sensor. One could still use the ref. internal sensor for the integral part. So the internal sensor still sets the final temperature, but the external sensor allows faster settling and reaction.

Using a resistor as a heat has the difficulty that this is square law heater - this would need a rather conservative / slow loop tuning. It might be better to use a transistor as a heater as this allows an nearly linear heater response.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 26, 2016, 02:48:09 am
I have been setting up tests and allowing the device to tell me what it wants to do.

The device is mounted to a banana plug and to a solid copper bar and wrapped in tissues. It is at ambient but is shielded from direct drafts.

Here is 6mA of current over a long time. You can see the HVAC system of my house trying to control temperature.

The thing to note here is that when first turned on, throwing away the first 50 to 100 samples, the 2DW232 voltage rises. So, the 6mA current is below zero TC for ambient temperature in my office/lab.

 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: VintageNut on November 26, 2016, 03:00:29 am
Next, I  forced 30mA, the max datasheet current, and watched. The voltage decreases indicating that 30mA is above zero TC for my office/lab.

Next, I performed a manual decade current search and determined that zero TC is between 10mA and 20mA ambient operation. Then I performed a binary search between 10mA and 20mA. The first good current is 16.25mA. The sequence was 10mA -> 20mA -> 15mA -> 17.5mA -> 16.25mA. 16.25mA is probably not optimal but it is very good for short term.

For 200 or so samples the standard deviation is less than 3uV. 



Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Galaxyrise on November 26, 2016, 07:03:31 am
At 4 mA the TC of the zener section alone should be rather high (and the zener + diode) is likely not yet really low.
I don't think one can ever say the TC of the zener section alone is high without stating the temperature.  I went with 4mA to have a zero TC temperature that was sufficiently elevated from room temperature. I had started by heating the unit while measuring the zener and zener+diode voltages.  I chose the point where the zener voltage had zero slope as the heater set-point.  However, it certainly didn't work out this way, so something is wrong with my understanding or my technique.

Quote
If one only has cheap resistors available one should use the unscaled output from the reference, the scaled up version can be still Ok to set the current.
The 100ppm/C number was just the zener voltage; I wasn't expecting the scaled up number to be stable at all in this prototype. So as a result, the diode current was also fairly unstable, but I expected this to have a very attenuated result on th zener voltage.

Quote
For temperature control the internal sensor is rather slow
So perhaps my zero TC discovery was done too quickly.  I will try the temperature ramp again but much slower and see if the zero TC values move.

Quote
Using a resistor as a heat has the difficulty that this is square law heater... It might be better to use a transistor as a heater as this allows an nearly linear heater response.
I think the resistor's response is linear enough in the 20mA region that it should be stabilizing at.  I could mount the transistor on the case as well.  Hmm... I wonder if I could mount a SOT23 transistor to the bottom of the case...
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 26, 2016, 08:51:08 am
I don't think a sot23 transistor would give enough heater power without getting rather hot locally and thus causing steep temperature gradients and thus possible thermal EMF problems.  AFAIK the LTZ1000 uses something like 100-200 mW, with the heater directly on the chip. So I would plan with a similar power rating, maybe even a little bit more. I would more think about gluing an TO126 to the top of the case. Heating only the ref chip may not be that good, as the pins seem to be some kind of steel and thus could show thermal EMF. 

From the voltage versus temperature curve (for one "typical" sample) form the DS the second order TC is about -0.25 ppm/K², the data from Gyro give something like -0.33ppm/K².  An 50 K higher temperature would give an additional TC of some -30 ppm/K. So adjusting the temperature is not an alternative to finding the right current. To get an Idea one how to use the chips it would be good if we had data for the TC of one diode for a few different currents.

The data from Gyro also suggest that his zener + diode at 5 mA would have and TC of about 1/3 of the normal diode which would be -600 µV/K or -100 ppm/K. So if at all zero TC would be at low temperature and 5 mA or more practical a much higher current (e.g. 15-20 mA). Getting zero TC for the zener alone somewhere at 1-1.5 mA suggest a TC of about -2 mV/K or -300 ppm/K for the series configuration at this current.

Unless the current gets too low, I would prefer the lower current operating point with only the zener anyway. For a heated version this would alow for more insulation and thus also less heating power.
Needing something like 16 mA to get zero TC is quite a lot - so this ref. might be more practical to use as zener only and than lower current. An important factor could also be how fast the TC changes with the current, so how accurate the current adjustment needs to be - chances are this is easier at high current.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 28, 2016, 09:56:14 pm
Here is the data I've collected over the weekend. The lab temperature varied from 24C to 20C. I've measure the zener only voltage with 1.397mA current through it (10V source with 3.401K resistor) using HP3458A and the diode only voltage with 0.65mA current through the diode using 34465A. The temperature of the case was measure with a thermocouple couple of times, so the diode voltage of 715mV corresponds to 22C. The resulting graph is attached. It looks like for this current the zener goes through a tempco sign change somewhere between 20C and 21C. The vertical scale for the zener voltage is 10uV or about 2ppm/div, for the diode voltage 2mV/div or ~1C/div. The zener noise is very low and there is no "pop-corn" noise visible so far.

Cheers

Alex

P.S. - added a zoomed-in graph for the "flat" part from 6am till 10pm on Saturday. The vertical scale for the zener voltage is 0.1ppm, for the diode voltage - 0.2mV or ~0.1C/div
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 29, 2016, 03:19:52 am
The stability / noise looks good. For the noise it is hard to tell how much comes from the meter and how much from the reference. So even the low current is sufficient for a low noise reference.

From the long run, it looks like much of the variations is still due to temperature variations. As the current is already adjusted for a small TC, one might need temperature stabilization to get a considerably more stable ref.. Current adjustment can only compensate the linear TC, but the second order effect still remains. Here temperature stabilization is likely more promising than even more adjustment / compensation.

Looking at the two points, where the diode shows 717 mV, there is a small but visible difference (about 2 ppm). This is more than the expected uncertainty of the meter. So this would be a first indication for aging or maybe hysteresis, the two still unknown parameters.

A phase of stable temperature gives a nice looking curve, but not much to learn from this. A similar measurement with more temperature variations would be more interesting.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 29, 2016, 03:52:43 am

Looking at the two points, where the diode shows 717 mV, there is a small but visible difference (about 2 ppm). This is more than the expected uncertainty of the meter. So this would be a first indication for aging or maybe hysteresis, the two still unknown parameters.

Looking at these two points, the voltage difference is about 3uV or ~0.6ppm . As one of these points sits on a relatively fast temperature gradient it could be a number of variations, including thermal effects with connections. Right now the whole thing is rather messy built (literally in last few minutes before i've left the office on Friday  :) ), with some of the connections made with standard banana connectors and crocodile clips. I was not expecting to catch sub-ppm changes  ::) .

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Squantor on November 29, 2016, 06:17:12 am
Well, I bought some 2DW232's from aliexpress. This was before the group buy action. After almost two months they have arrived. Just wanted to do a quick lashup.

Whats this? Seems like a bit of a crack in between the bottom and lid of the TO-5 package? Pop, Oh  :palm: ... Well, lets wait until the real devices arrive ;).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 29, 2016, 07:43:30 am
Classic, I wonder how they perform!  :-DD  How desperate do you need to be to do that, given the factory price?

It looks as if gold plated leads might be a givaway, the 17th Radio Factory ones have stiff tinned silver ones.

Edit: Given the taller than normal TO5 package, I wonder if this is standard practice for the other (noisier) manufacturers, or just fakes? I can't see any purpose in putting standard DO?? glass packages inside a can aside from maybe either thermal matching or keeping the light out???
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on November 29, 2016, 07:52:49 am
Whats this? Seems like a bit of a crack in between the bottom and lid of the TO-5 package?

OMG: they are shurely more than double the price of the standard thing:
Triple hermetically sealing !!!
So nearly infinite long term stability.

With best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 29, 2016, 08:02:39 am
This might not such a bad construction if you want two thermally coupled diodes. Could be one of the less good versions from an other manufacturer. Could be still good enough to test something like an oven for temperature stabilization
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on November 29, 2016, 08:12:16 am
At least they have the "right" polarity for a ground sensed temperature junction.
But I fear the chip is too small to have a good noise figure.

With best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 29, 2016, 08:25:34 am
I've done a bit more work on my voltage divider TC compensation from last week. This time setting for 2mA. Compensation performance seems similar to before. There are clearly fixed end-stops to the compensation range (see attached diagram):

Alex's Zener-only @ Iz=1.45mA:        R1=[edit]0R,  R2=0R             (Zener only TC turnover point)
Last week, Zener+Diode @ Iz=5mA  R1=765R,       R2=1k3
Today, Zener+Diode @ Iz=2mA          R1=1k6,        R2=460R
Zener+Diode @ Iz=20mA approx.      R1=0R,          R2=infinite      (Zener+Diode TC turnover point)

These set the bounds of passive voltage divider compensation, with a (possibly linear) ratio range for different operating currents. One thing that isn't clear to me... Can some (small) amount of divider compensation improve on the TC of Zener alone?

EDIT: The Diode isn't Present in Alex's Zener only configuration. In the voltage divider configurations, regardless of the divider ratio, the entire Diode forward voltage is in series with the Zener supply. This will change the Zener current with temperature and is another factor that the divider needs to compensate (so maybe not linear).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 29, 2016, 08:57:33 am
Using the divider is just a way to adjust the TC part from the "normal" diode. This allows to operate the zener diode at a different current - not just the about 1.4 mA with zero TC or the about 20 mA (could be less with other samples) point where the TC of the zener and diode compensate.

The normal diode has a pretty linear dependence on temperature. The curvature for the 1.4 mA and 5 mA current looks comparable so not much change there too. I don't think there is a really magic point, that would give a significant better performance than using the "right" current for either only the zener or the series connection. There is only the disadvantage, that one needs two more stable resistors. Also the output impedance is a little higher.

For many applications I would prefer the zener only operation: the noise already seems to be very low (e.g. comparable to LTZ1000 or OP07).  Also 5.3 V is rather attractive to divide down to 5 V (or 10 V from two of the refs in series).

One disadvantage I suspect is, that at low currents the TC could be quite sensitive to the exact current. So choosing the right current could be more important. Towards higher currents it looks like the TC is less dependent on the current - so less critical choice of current. Here some more data are still missing. It is not clear that the zero TC will be near 1.4 mA for all samples, though it looks like the two from Alex and Gyro could be similar.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 29, 2016, 09:08:58 am
I agree, Zener-only operation looks preferable if noise is low enough at that current (which it seems to be). Adding divider resistors does introduce more complexity and opportunities for drift (or best case, opportunity for fine trim  :-\).

The only reason I can see for persuing Zener+Diode voltage divider configuration now is if it can be shown to widen (or re-position maybe) the flat TC area, which I am not convinced about having seen Alex's plots.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 30, 2016, 12:44:23 am
The results from VintageNut around post#180 suggest that using the series configuration a current slightly higher than for zero TC still gives good stability. He got zero TC around 8 mA and still low drift and thus low TC at 10 mA. So the TC seems to be not that sensitive to the current at higher currents.

There is a second order temperature effect, and thus the TC changes with current and temperature. Through the current one can choose the temperature, where voltage versus temperature has it's flat part. The curvature might be a little larger at low current - but this is comparing data from a limited range and the data-sheet.

To get a very stable voltage one would likely need temperature regulation - and this is very effective to compensate for 2nd order effects. Compensation of the second order effect is likely more complicated. One may not even have to use the internal diode as a sensor, though one has the option. The LTFLU circuits also work with an external temperature sensor.

For using the zener only, it might be still Ok or even good to let the current also flow through the other diode. This eliminates the one pin resistance and also slightly works against the curvature. My first estimate would be a about a 10% reduction, if current comes from a 10 V source. So likely not practical to get second order compensation, as this would need a rather low resistance and low voltage. It should also shift the current to even lower currents, as it would add a little positive TC.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: TiN on November 30, 2016, 01:20:50 am
I'm backski, so ideas of what to measure next are welcome.
Will have 2002s and 3458 measuring tempco's with TEC box , but after few days should have time for 2DW love.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on November 30, 2016, 01:24:31 am
I did run another logging session overnight with a slightly more current, to see what changes. Below are the results from both runs, in a form of V(t) curves. 10uV (~2ppm) /div for the Volts scale, and the temperature derived from the internal diode voltage, taking 0.715 V = 22C and -2mV/C tempco (not very accurate, but gives an idea of what is happening) . Visible "hysteresis" effects are most likely due to an imperfect wiring and temperature gradients.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on November 30, 2016, 02:33:58 am
The curvature looks quite strong: -5E-6 V/K² is considerably more than the DS gave for 5 mA (about -1.5 E-6V/K²). This could be a drawback for the low current operating point, if used without temperature regulation.

The difference in current is quite small, so it's a little hard to tell how much the TC changes with current. Adding 4µA shifts the flat portion of the curve by about 0.7 K. So if one wants this point to match a given temperature by something like +-1 K the current would need to be adjusted down to the 0.5% range. So current adjustment might need to quite accurate, even with temperature regulation.

Edit: The relatively large sensitivity of the TC to the current might be useful to do 2 nd order compensation: If the current increases with temperature this would counteract the curvature. With a relatively small resistance (e.g. 500 Ohms range) and thus not so high voltage to drive the current through both diodes in series this might work. However this comes at the price of being more more sensitive to resistor drift. The optimum current will also shift to slightly smaller values in this case.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on November 30, 2016, 07:24:19 am
This looks as if it could be a helpful paper:

Quote
Developing for 2DW_(232-236)~(14-18) Type Silicon Reference Voltage Diode
SONG Chuan-li, WEI Dong, MA Rui-fen 
This article introduces the development process and result of 2DW_(232-236)~(14-18) type silicon reference voltage diode.

Unfortunately the download site seems to need some sort of login, and I don't have the language capabilies. Anyone able to access it? Maybe zlymex, blueskull or technix?

http://en.cnki.com.cn/Article_en/CJFDTOTAL-SDDZ200003019.htm (http://en.cnki.com.cn/Article_en/CJFDTOTAL-SDDZ200003019.htm)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on December 01, 2016, 05:45:38 am
This looks as if it could be a helpful paper:

Quote
Developing for 2DW_(232-236)~(14-18) Type Silicon Reference Voltage Diode
SONG Chuan-li, WEI Dong, MA Rui-fen 
This article introduces the development process and result of 2DW_(232-236)~(14-18) type silicon reference voltage diode.

Unfortunately the download site seems to need some sort of login, and I don't have the language capabilies. Anyone able to access it? Maybe zlymex, blueskull or technix?

http://en.cnki.com.cn/Article_en/CJFDTOTAL-SDDZ200003019.htm (http://en.cnki.com.cn/Article_en/CJFDTOTAL-SDDZ200003019.htm)
You need to either buy access to the article, or if you have connections to Chinese academia and the school have bought access for students and faculty. If this thread came up a few months earlier I would use my Donghua University student identity to grab that document for you.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on December 03, 2016, 02:33:08 am
This looks as if it could be a helpful paper:

Quote
Developing for 2DW_(232-236)~(14-18) Type Silicon Reference Voltage Diode
SONG Chuan-li, WEI Dong, MA Rui-fen 
This article introduces the development process and result of 2DW_(232-236)~(14-18) type silicon reference voltage diode.

Unfortunately the download site seems to need some sort of login, and I don't have the language capabilies. Anyone able to access it? Maybe zlymex, blueskull or technix?

http://en.cnki.com.cn/Article_en/CJFDTOTAL-SDDZ200003019.htm (http://en.cnki.com.cn/Article_en/CJFDTOTAL-SDDZ200003019.htm)
I have the account for the site, and I had downloaded that article before, but it is in Chinese. Attached it anyway.
The article was published in 2000 by three authors apparently from Shandong province(not from Shanghai). They claimed that the zener was sub-surface, and use surface passivation process to achieve high stability, low dynamic impedance, low TC and high reliability(no mentioning of the low noise). They describe the manufacture process such as lithography, dispersing and evaporation of aluminum etc to which I'm not familiar.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on December 03, 2016, 05:15:29 am
Thanks zlymex,

I guess it was too good to be true that the abstract was in English. Thanks for the brief summary though, interesting that they may be 'single component' (as opposed to IC) burried zeners, the only ones in captivity maybe? I guess there's nothing that can easilly tie this in with the 17th Radio Factory apart from maybe the low noise, which would hopefully result.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on December 03, 2016, 09:05:44 am
... They describe the manufacture process such as lithography, dispersing and evaporation of aluminum etc to which I'm not familiar.

I spot a likely mistranslation. Was "dispersing" perhaps "diffusion"?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on December 03, 2016, 02:49:07 pm
Maybe someone of us that have a microscope can saw one can open and post some die shots?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: plesa on December 05, 2016, 10:55:12 am
All EU members should receive agreed quantities (12/8/4) next week.
People in distribution chain make it without any profit. In case someone want to compensate I asked to send donation to UNICEF.
Thanks zlymex and VintageNut!
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on December 05, 2016, 11:55:56 am
... They describe the manufacture process such as lithography, dispersing and evaporation of aluminum etc to which I'm not familiar.

I spot a likely mistranslation. Was "dispersing" perhaps "diffusion"?
That is correct.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: eliocor on December 05, 2016, 12:00:49 pm
I want to thank Zlymex, VintageNut and Plesa (and all of the others) for the efforts they have spent for all of us.
As politely and rightly suggested, I provided to make a donation to Unicef.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: CalMachine on December 05, 2016, 03:42:39 pm
Any more of these legit "diamond" 2DW232s around I can purchase to play with? :D
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on December 05, 2016, 04:07:29 pm
Any more of these legit "diamond" 2DW232s around I can purchase to play with? :D
I have struck an agreement with the factory. 75 US cents each, plus $5 shipping to most parts of the world.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on December 05, 2016, 09:43:02 pm
@technix:

Have you had any opportunity to study the temperature coefficients of the factory ones yet? I'm just wondering if they show the same TC turnover characteristics as the ones that we have.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on December 06, 2016, 12:39:00 am
Another run, this time 96 hours, at 1.406mA. If the zener temperature can be stabilized +/-0.1C near the "zero tempco" point, than stability and noise could be quite good, from that data. According to the measurements of 0.1-10Hz peak-to-peak noise zlymex has posted at the beginning of this thread, even at 1.4mA the noise should be lower than that of the LTZ1000 at 4mA.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Theboel on December 06, 2016, 01:51:37 am
Hi Alex,
from yours first graph I see two dip in zener voltage and its related to increase in temp but then when temp get down also the zener also lowering. did I missing something ?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on December 06, 2016, 01:59:17 am
Hi Alex,
from yours first graph I see two dip in zener voltage and its related to increase in temp but then when temp get down also the zener also lowering. did I missing something ?

Look at the second graph - the zener voltage crosses a "zero tempco" point about 21.6C and on both sides from that point the voltage will go down as the tempco changes sign.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on December 06, 2016, 02:52:03 am
Quote
Look at the second graph - the zener voltage crosses a "zero tempco" point about 21.6C and on both sides from that point the voltage will go down as the tempco changes sign.

That first plot is a really neat graphical demonstration of the TC turnover characteristic, I bet you couldn't have come up with a better temperature profile if you'd tried.  :)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on December 06, 2016, 03:42:02 am
The data at 1.4 mA look quite good, but to get really good stability, temperature stabilization would be needed. The curvature is quite large and thus a low TC is only there in a rather limited range (e.g. +-5 C). As the ref. is low power one could go for something like 50 C. I am not so sure the internal sensor alone is really useful for regulation, due to a relatively slow response.

The second point that might be worth a test is to see if there is hysteresis after larger temperature excursion (e.g. heating to something like 60 C).

A third point would be to check how much the compensating point varies from sample to sample - worst case other samples might have compensation at to low a current.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zlymex on December 06, 2016, 03:51:47 am
I suggest to perform an accelerate aging before actual test, which can be done in three ways as described by a manufacturer:
1. high temperature storage, 150 degree C for 120 hours
2. room temperature storage, for a month
3. power aging: run a 40mA to 50mA current through the device for 24 hours

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on December 06, 2016, 05:25:53 am
To get an estimate how much aging is expected, it would be a good idea to have a measurement before accelerated aging too.

The three steps might not be alternatives, but separate steps to do the aging. I don't think just a month a room temperature should do much alone.

For the 150 C step is might be important how fast or slow the units are cooled down. To get a stable state is might be better to do slow cooling in the 120 - 80 C range. In this range there is the glass transition of epoxy glues, and fast cooling can leave it in a less stable state.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: pmcouto on December 11, 2016, 02:06:25 am
I received my 2DW232 yesterday.

Thanks to Zlymex for providing the parts and to VintageNut and Plesa for handling the distribution.  :-+
As Plesa suggested, a donation to Unicef has been made.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on December 11, 2016, 04:27:32 am
Thanks from my side too. Have received the parts yesterday.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SvanGool on December 11, 2016, 06:29:36 am
Me too.

Thanks Zlymex, VintageNut and Plesa !  :-+
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on December 11, 2016, 07:21:12 am
Yes, me too got a few. Thanks so much!

Now I am preparing some temperature scanning, after noting down initial "not yet aged" voltages at fixed temp and current.

Now the question: are the two diodes back to back meant to be equivalent?  The voltages do differ open swapping pins. If not, which diode is the "right" one to choose?

Somehow the physicist inside me would conjecture, based on symmetry,  that stability is max when the two voltages are identical.....

Thanks,
BK
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on December 11, 2016, 07:57:09 am
I would expect the diodes to be nominally the same. Just like there is scattering between chips, there can be some between the two on one chip. Though I would expect not that much difference for the two on one chip.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on December 11, 2016, 08:09:51 am
As we have two zeners in one package, it would be good to use both and to use the case as a screen, I plan to do a proper layout for the circuit attached below. R6-R9 are from a single  LT5400-B1 array, providing a good tracking and long term stability, R1 and R2 are selected to pull apart the "zero tempco" points, providing a lower combined tempco, and the voltages from both zeners are added together, further lowering the noise. R5 is selected/adjusted to get exactly 10V output and the tempco/stability contribution of R3-R5 network is about 1/20 of individual resistors, so a quality metal film type should be OK.

Cheers

Alex

(http://www.ant-audio.co.uk/Service/Ref/2DW232_reference_01.gif)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on December 11, 2016, 08:31:57 am
I don't think it will help much for the TC to have two diodes combined with slightly different compensating temperature. They will both have a second order component of similar size and just slightly different linear TC. So the sum will be essentially the same as the curve at intermediate current. If at all the diodes would need more coupling to get any nonlinear effect - but than a difference in absolute value would be important.

Due to the relatively large curvature, the best option for a really stable output is in using temperature stabilization. So the second diode would be valuable as a temperature sensor. Even without temperature regulation, just a temperature reading would make current adjustment much easier and allow for later compensation. For use without temperature stabilization, the series version with higher current might be more useful.

Judging from the DS curve, the second order TC seems to be smaller there. Also adjusting the current could be less critical.

For the circuit around it, I do not really like the idea of starting with negative reference and than add an inverter. It needs even more stable resistors. I could be Ok if you want a +-10 V reference of cause.

The more natural way would be to use two of the 5.25 V refs in series to get a 10.5 V output.  A possible higher output would be only for biasing. The alternative bridge version does not even need the higher voltage. The appealing point is that a divider 10.5 to 10 V is not that sensitive to resistor drift or TC - so even with 20 ppm/K resistors the output would only chance by 1 ppm/K.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on December 11, 2016, 09:03:01 am
I would rather get a lower noise. The tempco is not very high around the "zero point" anyway, so the temperature stabilisation does not require to be very accurate and can be done with an external sensor. The dissipation is low (total ~15mW) and a temperature around 50C with 0.1C stability should be fine. Two zeners in series is a good idea (using both zeners in each package you would get a half of a single zener noise), but it would require isolation between two cases and a good thermal contact at the same time. It is much simpler if the case is "grounded", and I could use my favourite LM35D in a metal can as a temperature sensor sitting in the same copper bar, providing a very quick and stable regulation.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Fixup on December 11, 2016, 09:08:42 pm
Hi,

I also received the references on friday :)
Thank you Zlymex, VintageNut and Plesa.
Also nice of you to suggest the compensation to Unicef!

Now I need to start aging the references while I'm waiting for my "new" meter to arrive (Solartron 7075)  :D   
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: edavid on December 12, 2016, 03:12:09 am
I would expect the diodes to be nominally the same. Just like there is scattering between chips, there can be some between the two on one chip. Though I would expect not that much difference for the two on one chip.

Do we know that both diodes are on one chip?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on December 12, 2016, 03:20:46 am
The very first post in the thread has a picture from the inside. So at least the units on the picture look like 2 more or less identical parts on one die. However other manufacturers might have two dies of even two separate capsuled diodes.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: plesa on December 12, 2016, 03:54:06 am
I'm going to make die photo of 2DW233, so we will see. It seems to be covered by some epoxy, which require some nasty etching process by hot nitric acid or sulfuric acid.
Thanks to all of you for donation to UNICEF :clap:
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: klaus11 on December 12, 2016, 11:55:34 pm
Hi,

I also received the references and donate Unicef.
Thank you Zlymex, VintageNut and Plesa.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bingo600 on December 13, 2016, 12:36:03 am
I also received mine , and donated to Unicef.

Thanx goes to all that made this happen, Zylmex Vintagenut Plesa et all.  :-+ :-+

/Bingo

 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Squantor on December 13, 2016, 01:24:55 am
Also adding my thanks here :)

Zylmex, Vintagenut and Plesa, Thanks for all your hard work and effort on making this possible. Had a nice weekend with playing with these devices :).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Fixup on December 13, 2016, 09:07:48 am
Hi,

Today I received a book (Calibration philosophy in practice second edition).
In that they had described little about zener references that confirms that the other diode needs to be in series with the other zener diode.
There is also some info about the 732B.

Pics attached :)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: 2N3055 on December 13, 2016, 10:23:00 am
I received diodes today too...
I wasn't home so I had my wife open it..
She goes .." wow, this is something packed like some kind of sweets, a desert... Did somebody send you holiday sweets ? ...".
I was chuckling.. " ... better than that honey, better than that..."

Thank you Zlymex, VintageNut and Plesa.

I also donated to Unicef..
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on December 13, 2016, 08:45:52 pm
Hi,

Today I received a book (Calibration philosophy in practice second edition).
In that they had described little about zener references that confirms that the other diode needs to be in series with the other zener diode.
There is also some info about the 732B.

Pics attached :)

I have this book too - it is a great read. I should however note that the book describes zeners with 6.2-6.3V voltage with a diode in series. The 2DW232 has a zener voltage about 6V with a diode in series (5.25V without a diode) , much lower, and so the tempco of a zener only is closer to zero unless you put a lot of current in and elevate the temperature.

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Seekonk on December 13, 2016, 11:29:07 pm
In looking at that 7-8 picture I thought about some old General Electric RA1 that I have.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on December 14, 2016, 11:53:10 pm
I've connected the second zener in the package, and it has a slightly higher current for the zero tempco point - about 1.7mA . Here are two short term (15 min each) measurement runs with HP3458A at NPLC1 and NPLC10. Vertical scale is 1uV (~0.2ppm) /div. Lab temperature was reasonably stable at about 24C. The trendline on the second graph is 10 per Mov Av, so should be equivalent to NPLC100, same as the trendline on the first graph. Looks different though... .

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on December 15, 2016, 03:26:50 am
At that noise level, some of the noise could be due to temperature fluctuations and thermal EMF, e.g. at the pins. Quite some of the noise could come from the DMM (internal ref) as well.
I don't see a big difference, except from the difference integration time. There might be minor differences from AZ switching - but this would be more a question of the DMM.

To really judge the quality one would likely need something like a small board and enclosure and possibly even temperature regulation (at least measurement). Only than one can really see the drift over time and hysteresis after temperature excursions. This are likely the main uncertainties, that could still become a problem for some applications.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: guenthert on December 15, 2016, 04:19:55 am
Hi,

Today I received a book (Calibration philosophy in practice second edition).
In that they had described little about zener references that confirms that the other diode needs to be in series with the other zener diode.
There is also some info about the 732B.

Pics attached :)
Thanks for the excerpt.  Not meaning to distract from the topic of the thread, but I couldn't help noticing, that the book states that for a reference amplifier the "reference voltage Vref is the sum of the zener voltage and the voltage across the base-emitter junction of the transistor" [see Figure 7-7] .  However they then show the simplified diagram (Figure 7-9) of a Fluke 732B where the reference voltage input to the op-amp is taken from the collector of the transistor in the reference amplifier.  Is the diagram correct?  Is the difference negligible?   
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Alex Nikitin on December 15, 2016, 10:26:31 am
Thanks for the excerpt.  Not meaning to distract from the topic of the thread, but I couldn't help noticing, that the book states that for a reference amplifier the "reference voltage Vref is the sum of the zener voltage and the voltage across the base-emitter junction of the transistor" [see Figure 7-7] .  However they then show the simplified diagram (Figure 7-9) of a Fluke 732B where the reference voltage input to the op-amp is taken from the collector of the transistor in the reference amplifier.  Is the diagram correct?  Is the difference negligible?

The diagram is correct. Look carefully where the output is. The reference voltage is at the base of the transistor and it is compared with the output by the divider R1/R2. The transistor works both as a part of the reference and as a part of the error amplifier, hence the name "reference amplifier" for the device used (Fig 7-7).

Cheers

Alex
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: CalMachine on December 17, 2016, 02:18:25 pm
Would anyone happen to have access to a model/library file of one of these references?  :-DMM
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on December 17, 2016, 07:52:23 pm
Would anyone happen to have access to a model/library file of one of these references?  :-DMM
I don't think there is any... If someone knows how to fully characterize it maybe we can create one ourselves.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: CalMachine on December 18, 2016, 01:05:25 am
Would anyone happen to have access to a model/library file of one of these references?  :-DMM
I don't think there is any... If someone knows how to fully characterize it maybe we can create one ourselves.

I think you're right.  After an hour or so of searching around for one, I decided one didn't exist and wanted to try to make one myself with LTSpice...  Using LTSpice is quite a bit different than the Multisim I used while in school, so it's like starting from scratch.  Once I get my hands on some of these, I can begin to try to help characterize them so maybe we can all accumulate data and get a good avg characterization put into a model.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Pipelie on December 18, 2016, 08:05:13 pm
I did a quick tested months ago, here is the result.  hope you guys like it.
Test gear:
1.DMM: Agilent 3458A
2. Constant current generate by  Xitron2000 
3.Kaye LTR 140,  use to maintain 2dw232's temperature .

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on December 18, 2016, 08:58:52 pm
Really nice data:
Especially the temperature runs could be a good basis for a model.

That sample seems to be dead on with the 5 mA compensating current for a reasonable temperature. Not sure how much that varies with samples. Classification (to DW232 / 233...) is likely only for one of the zeners - so the polarity could matter, and the 2 nd zener might be different (e.g. other current). Having the colored dots suggest that there was some testing done.

The curvature is similar to that shown from the DS: about -2 µV/K² , could be even less at higher current. So the series configuration as an clear advantage here.

Changing the current from 4 to 6 mA changes the linear TC (0C) from 70µV/K to 210 µV/K or about 10 ppm/K to 30 ppm/K  (for 45 C this would be about -10ppm/K to +10 ppm/K).  So a 0.1 mA change in current would give about 1 ppm/K in change of TC.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on December 18, 2016, 10:35:29 pm
I can't claim that I was particularly successful in this. I got four diodes, ran each of the 8 Zeners, with and without in series with its partner, and nowhere I could find a maximum Zener voltage over temperature. Range about 10-50 degs C, for currents from 1mA to 7.5mA and 10mA. Currents not very systematic, though. I wonder whether I make a stupid error?

This runs in a Peltier-controlled environment that works perfectly for scanning laser diodes. See the pics! One is a wide scan, the other is more focused, no trace of an extremum is seen in either, rather it is monotonic. This pattern is the same for all diodes in all tests....

Right now I am about leaving for holidays but I wanted to share this.
Happy holidays!

Edit: And yes, I switched DW232 for WD232, I know that already ;-))
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on December 18, 2016, 11:09:34 pm
Quote
. Range about 10-50 degs C, for currents from 1mA to 7.5mA and 10mA

With both diodes in series you need to go higher current. I had to go up to  around 20mA before mine was temperature stable.  From memory about 6.25V drop, and at 20mA it runs > 40deg C. Doing the finger test by touching the case, will actually cool the unit.  This is the reverse of the situation when run at lower current.

With a simple op-amp feedback circuit I was able to peg the last digit of my 6.5 digit 34401a when left overnight with room temperature varying over a few degrees.

 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on December 18, 2016, 11:14:40 pm
The diodes seem to be rather different. So not all will work well at 5 mA. Some might need considerably more than that to get zero TC in series configuration.

For the two curves you show, the TC is about -600µV/K at 7.5 mA and -2500µV/K at 1.5mA.
With a higher current the TC should change to more positive. So the 7.5 mA are still quite a bit low to get compensation. Well possible that even 15 mA might not be enough for this diode/direction.

The 1.5 mA point is closer to get a small TC with just the zener alone. Without the forward diode the TC would be somewhere is -500 µV/K range. So one should find a small TC for just the zener and a current slightly higher than 1.5 mA, maybe about 2 mA. With 1 or 2 more short tests one should be able to find that current.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on December 18, 2016, 11:50:15 pm
Thanks for the useful remarks!  I will test and report when back.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Pipelie on December 20, 2016, 09:05:34 pm
I translated the Chinese character to English. 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: BFX on December 22, 2016, 06:24:14 am
Christmas gift arrived today  8)  :-+
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on January 05, 2017, 03:38:48 am
So - right back from vacations, I ran initial tests on the diodes of the group buy. What had puzzled me was that according to what was said, the 2DW232 would have a stable point for 5mA, when both diodes run in anti-series. Actually I now looked much higher and got the correct current at 26-28mA or so. Well, the question arises why making the effort of using different labels for the various diodes when the true values are far away anyway. For a single diode the optimal current was about 2.0-2.4mA.   

Now here a thorough characterization of one such 2DW232. It is all quite as expected, but reassuring at least for me.

Scans for the two single diodes, each for 3 different currents around 2.2mA:

(http://hololaser.kwaoo.me/electronics/pics/DWplot3single.png)

Scans for the diodes in anti-series, in both directions, need about 27mA:

(http://hololaser.kwaoo.me/electronics/pics/DWplot3series.png)

Here a comparison of a single diode with both diodes in anti-series, the broadening clearly shows
that the 2-diode configuration has a better temperature stability due to partial cancellation of TCs:

(http://hololaser.kwaoo.me/electronics/pics/DWplot3singleNseries.png)

In practice I modified a setup I normally use for scanning laser diodes, incl some LabVEW program and a new digital PWM TEC controller. This allows to scan over temperature quite straightforwardly:

(http://hololaser.kwaoo.me/electronics/pics/2DW232XY-30pm-27mAs.png)

Just the other day I received a bunch of 2DW233 from technicx, and will do some comparisons over time. Plus noise measurements, which is interesting for me for laser diode drivers.

Thanks to all providing the group buys!
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 05, 2017, 05:23:16 am
Thanks for the nice data.

From the reports so far, there seems to be a lot scattering between diode samples. So the best working current is really different between samples and could be much higher than 5 mA for some. I would consider more than 20 mA not very practical any more, as this already quite a lot of heat.
Interesting to see that the two diodes in one case seem to be very similar.

What is the absolute voltage of those diodes. There might be a correlation of voltage to the compensating current. If that relation is known selecting could be easier and faster.

The second order TC of the single diode is considerable higher - clearly visible here.
With good adjustment of the current and temperature regulation this might not be such a big problem, but for an unregulated reference this could be a problem.

So there are several possible uses:
1) both diodes in series, with well tuned current, but not (or less accurate) temperature control, for low noise.
2) both diodes in series,  with good temperature control, for a stable and low noise reference at 6-7 V.
3) Single diode with accurate set current and good temperature control for a low noise ref in the 5.x range (good for divider towards 5 V and maybe 10 V with two in series).

The first two cases would like a diode with low compensating current (e.g. < 8 mA). The last case might prefer one with higher (e.g. > 1.5 mA for the single diode) current for lower noise.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on January 07, 2017, 11:31:43 pm
..
What is the absolute voltage of those diodes. There might be a correlation of voltage to the compensating current. If that relation is known selecting could be easier and faster.
..

I am not 100% sure what you mean. Probably the voltage for some given fixed nominal current and temperature? Or the voltage at the TC minimum current for a given temperature? I guess, the former - the second wouldnt help speeding up the process since one would need to find the TC point first, also the current varies a lot which means the voltage varies as well.
 

What I found so far by checking a few samples (3 each) that the diodes from the group buy (2DW232) and the ones from technix (2DW233) differ substantially. For the 2-diode config, the 2DW232's need arond 30mA (even up to 40!), while the 2DW233 need around 4-8mA, which seems more reasonable. Quite counterintuitive for the markings... 
The zero TC region was prescribed at about 30 degrees. For the 2DW232 it is hard to get it lower, probably the self-heating interferes.

So, should we fix some nominal conditions for facilitate comparisons, so see whether a pattern emerges (if that makes any sense at all?)
If so, which comparison point for the Zener voltages should we choose ? What about 10mA at say, 30 degrees?

I'd like to correlate this to noise measurements too. Somewhere in the literature mentioned here it was said that less stable diodes correlate with larger noise (which makes of course perfect sense).

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 08, 2017, 12:07:10 am
A current of 10 mA could be a good point to compare. This should give a relatively low TC across all diodes (both in series). I don't think one even needs to have a well specified temperature to compare, though is would help.

The Idea is just that there usually is a correlation from the TC of a zener and it voltage. Zeners with low voltage (e.g. 4 V) usually have a negative TC and those with higher voltage have a more positive and above 6 V usually a positive TC. So chances are the 2DW232 with high compensating current have the lower voltage.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on January 08, 2017, 08:13:43 pm
Following the excellent advice in the comments here, I have tried implementing a test circuit,
 

The test prototype has the following features,

  - incorporates current adjustment so that the tempco (temperature coefficient) of the two zeners may be balanced against each other

  - uses the voltage drop of both the reverse biased and forward biased zeners to create the reference. This results in a higher current configuration (~20mA) which produces a lower noise output.

  - uses a subtracting op-amp to extract the voltage drop across the forward-biased zener from the reference-output for use as an on-die temperature sensor (2mV ~= 1C)

  - implements a propotional-integral control loop in response to the on-die temperature sense with an  adjustable operational temperature setpoint (trimpot) and a 200ohm resistor bonded to the case of zener for heater stabilization.


The current adjustment to trim tempco balance is done by manual binary search. The procedure involves letting the unit cool, applying power and noting the direction of the output voltage as it heats. With some experimentation it is possible to dial in the reference voltage so that voltage initially increases and then dips slightly as temperature converges on the regulation setpoint.


Test data -

Two plots (others and more details at http://blog.julian1.io/index.html (http://blog.julian1.io/index.html))

The lhs represents area of higher temperature, and the rhs lower temperature. At startup, the temperature rises and the voltage increases. At a certain temperature the tempco (mV/C) of the forward biased zener is balanced by the tempco of the reversed biased zener, and a local vertex is reached. After a small retracement, there appears to be another unknown secondary affect and curve. The trace eventually converges on the regulation temperature/voltage.

(http://blog.julian1.io/public/images/dw232/run-03/plot-04.png)

Skipping the first startup observations, provides a higher resolution view on the y axis. The plot shows output voltage varying by 8uV over the course of approximately 15 minutes.

Conditions involve an open room, exposed breadboard, high-ambient temperatures over 30C, circulating air currents, and 7 digit values from the 6.5digit rated data-acquisition unit. Additionally the circuit uses only two precision resistors - the resistors for the op-amps are inexpensive 1/4watt and not tempco rated.

(http://blog.julian1.io//public/images/dw232/run-03/plot-05.png)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 08, 2017, 10:50:20 pm
This an interesting way of plotting the data, but quite nice.

There seems to be more than just temperature that is influencing the temperature. I think this could be some delayed effects like creep in epoxy or thermal gradients and thermal EMF at the contacts. During turn on also the current source could contribute.

For the curve shown, the temperature (or current) chosen seems to be a little higher than the optimum. There is still quite some TC (e.g. 5 ppm/K range) in the last phase. A more accurate adjustment of the current or temperature to find the point where TC crosses zero might need a slower, more regulated temperature change (e.g. modulation of the set point of the temperature stabilization).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on January 09, 2017, 05:57:17 pm
... influencing the temperature. I think this could be some delayed effects like creep in epoxy or thermal gradients and thermal EMF at the contacts. During turn on also the current source could contribute.

Yes, I suspect some latent thermal effects. In the plots, the dw232 and board starts from ambient which is about 33C. It then climbs almost 30C to running temp. So there are heat gradients on the pcb and components. It would be better to get everything up to running temperature for 10 minutes, and then change the temperature setpoint -2, -1, 0 +1, +2 C and take the measurements.

Quote
For the curve shown, the temperature (or current) chosen seems to be a little higher than the optimum.

Yes, it's definitely slightly off. As good as I could get from stuffing about for 10 minutes.

Quote
e.g. modulation of the set point of the temperature stabilization.

Good point, the slope is near 0 around the vertex of the parabola which means that voltage is not as useful as the adjustment parameter. Dialing in operating temperature should provide more control.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on January 10, 2017, 07:13:45 pm
I changed the board around for a two op-amp design - after realizing that the reversed-bias zener would do equally well for on-die temperature regulation compared with the forward-biased one.
 
(http://blog.julian1.io/public/images/dw232/DSC02615.JPG)


Some more test data,

Plot of a cold start. The operating temperature setpoint has been more finely adjusted to be closer to the balanced tempco vertex.

(http://blog.julian1.io/public/images/dw232/run-08/output/plot-04.png)

A plot of a longer run over the course of about 18 hours, shows that output is stronly correlated with ambient temperature. Since the on-die temperature is now regulated to a high degree - suspicion must be on other board components.

(http://blog.julian1.io/public/images/dw232/run-07/output/plot-01.png)

The linear relationship is clear when voltage change is plotted directly against ambient temperature. The output variation is around 40uV over 4 degrees.

(http://blog.julian1.io/public/images/dw232/run-07/output/plot-03.png)

40uV / 4C = 10uV/C, 10uV / 6.26V = 1.6ppm/C

The op-27 op-amps are rated at 0.2uV/C and probably do not contribute a lot to the variation.

However the Vishay trimpots are rated to +-10ppm/C.

Since these are needed for setting current and temperature, it is not clear how much further improvement is possible without entirely ovenizing the board.

I also wonder if the lm399 in the DAQ may have some contribution.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 10, 2017, 11:21:48 pm
The set point for the reference now looks much better: the slow final part looks more horizontal.

It somewhat depends on the surrounding circuit how much these parts influence the current. In the usual circuit 3 resistors that have an influence. But normally the influence should not be that large, as the zener resistance should be relatively large compared to the current setting resistor. To reduce the importance of the trimmer one usually combines it with fixed resistors to set the approximate value and thus have the trimmer only for a small adjustment.
The rather high current might be a problem here, as the zener resistance could include quite some substrate part and also the resistance of the pins and copper traces can get important.

There are also things like thermal stress to the resistors and the pins that might have an influence - so for a really high stability reference the cheap paper based boards are not ideal.

For a very stable system it might be worth to stabilize the temperature of a few more resistors as well, especially if you also need scaling to let's say 10 V. It might not be so much more effort to stabilize much of the circuit compared to only the chip itself.

The DAQ system could also contribute, though it might not be the LM399 ref used there, but other parts. The LM399 would definitely be a major part when is comes to noise. I would expect the noise level of the 2DW232 at something like 1/20 of the LM399.  So meaningful noise measurement would need something like a low frequency AC coupling and low noise amplification.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on January 11, 2017, 09:29:20 am
Hello,

in the datasheets of other temperature compensated zeners (1N829A) the T.C. over current is given as "typical" curve (Figure 1):

http://www.microsemi.com/document-portal/doc_download/10940-sa6-3-pdf (http://www.microsemi.com/document-portal/doc_download/10940-sa6-3-pdf)

my idea to measure was to measure those zeners pair-wise,
and keep the sum current constant.
So within a 1N829 pair I would set a temperature and then measure the one zener at 2mA .. 13mA and the other at 13 mA .. 2 mA (sum = 2 * 7.5 mA).
The idea is to keep the self heating constant.

with best regards

Andreas
 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 12, 2017, 03:54:59 am
The 2DW232 has two zener diodes of about 5.3 V. So to use them as a compensated zener reference one uses one of the two in forward direction an the other as a zener diode.

From what a saw here so far, the TC seems to depend more on the current than with the 1N821 type diodes. A something like 1-2 mA the single diode is near zero TC and thus about -2 mV/k for the series connection, and at something like 15-30 mA the series connection has zero TC.

So keeping the sum of currents constant only works for just the zeners (e.g. 1-2 mA range).
For the series mode, it is the voltage of the single diode, that could be used to look at relative temperatures.
So it is plots like the ones from julian1 that give ref. voltage vs diode voltage.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Edwin G. Pettis on January 12, 2017, 04:39:55 am
Julian1, if you check the data sheet of the 1240W trimmer, you will find that in addition to the end-to-end TCR of ±10 PPM/°C, there is an additional term of ±25 PPM/°C through the wiper, this term will cause a larger TCR to be seen from the wiper.  An additional problem for these trimmers is a requirement for a minimum amount of current through the wiper to maintain a good 'connection' between the wiper and resistive element, too little current can cause instability in the wiper's output.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on January 12, 2017, 05:18:12 am
Julian1, if you check the data sheet of the 1240W trimmer, you will find that in addition to the end-to-end TCR of ±10 PPM/°C, there is an additional term of ±25 PPM/°C through the wiper, this term will cause a larger TCR to be seen from the wiper.  An additional problem for these trimmers is a requirement for a minimum amount of current through the wiper to maintain a good 'connection' between the wiper and resistive element, too little current can cause instability in the wiper's output.

Thanks Edwin. I confirmed that it's problematic, by shielding nearby components with Kapton tape then pointing a heatgun at the trimmer for 10C rise, and then logging the result. It is is as you say.

The other issue is the precision fixed 120 ohm in series with the zener. This is fine in the ltz-1000 type circuits when the zener is running at a few mA. But at 120 ohm it is dropping 2.9V with the current of 24mA through the dw232! Calculating out its tempco contribution, gives 6uV/C.

After discovering this, I've changed the circuit to use a 10ohm series resistor + 10ohm current adjust trimmer both on the high side of the zener.

This reduces the voltage-drop 10x on the resistor and by the same amount its contribution to tempco. The divider for the other op-amp input which was the vishay trimpot can then be exchanged for a fixed resistor divider with values chosen to center the needed 24mA current.

The details are here, http://blog.julian1.io/2017/01/11/dw232-circuit-4.html (http://blog.julian1.io/2017/01/11/dw232-circuit-4.html) 

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 12, 2017, 05:59:26 am
From the parts used I would guess something like scale up by a factor set with the trimmer and than use the 120 Ohms to set the current. What is the circuit used ?

AFAIK about the only advantage of a smaller resistor is less self heating. 25 mA and 3 V is already 75 mW - so a low TC and high power rating could be important. Lowering the voltage and resistor on the down side increases sensitivity to the OPs offset.  So there is a limit on how low the voltage drop should go. Also wire resistance gets more important with resistors in the 10 Ohms range. A 10 Ohm trimmer is also rather low and could have more trouble with the wiper contact. So I would prefer something like 20 Ohms and 100 Ohms +100 Ohms trimmer in series in parallel.

The high current shows it's downside.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on January 12, 2017, 06:09:26 am
Quote
It might not be so much more effort to stabilize much of the circuit compared to only the chip itself.

This is a really interesting point. At first I was a bit disappointed by how slow the stabilization loop was compared with using an on-die heater such as in the ltz-1000 circuits. But the the tradeoff is that a lot more can be done for the divider resistors.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 12, 2017, 07:00:30 am
The loop with sensor on the chip and an external heater can be quite slow. But this should be still fast compared to the time it needs for the rest of the circuit to stabilize. Many instruments need something like 15 minutes minimum and maybe 1 hour to get really stable.

The main disadvantage is that the capacitors for the analog temperature circuit might get quite large. Warmup time should be still rather fast. For final stability the limiting part is more like humidity in the board and this needs quite long, even if the thermal system is fast.

For stabilizing more of the circuit, a few more resistors are not a problem, as long as the thermal power is constant and low. I would expect the power for the stabilization to be about proportional to the power of the part that is stabilized - something like 1-3 times the power. Variable and higher power parts like OPs might be better outside. A constant temperature box was quite common in old the days instruments.

Using a resistor as a heater could be a problem, as the heat follows a square law. So it might be better to to use a transistor and control it's current at a more or less constant voltage. This way also no power is lost to an extra control element. As a first step one could still have the resistor (or maybe a diode) at the reference and use the heat from the controlling transistor to heat a metal case around the critical part of the circuit.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on January 15, 2017, 04:09:48 pm
Quote
What is the circuit used ?

Basic circuit (ignoring stabilizing caps, emitter-follower current buffer, decoupling etc), has been this one,

(http://localhost:4000/public/images/dw232/DSC02648.JPG)

After playing with the 10ohm fixed + 10ohm trimmer in-series on the high-side of the zener, I had issues getting repeatable runs with the regulation. So I've followed your advice - and the circuit is now a 120 fixed resistor + 100 trimmer (set at ~= 10ohm) in series with the zener and a fixed-resistor divider.

The fixed-divider pair are what I had available - super-cheap 1/4 watt resistors from Ebay.


(http://localhost:4000/public/images/dw232/DSC02649.JPG)

Despite this, the results look a lot better,

The stabilization locks in quicker, with no excursions,

(http://localhost:4000/public/images/dw232/run-16/output/plot-01.png)
 
And there is no weird secondary spiral around the tempco apex!

(http://localhost:4000/public/images/dw232/run-16/output/plot-04.png)

After getting to operating temperature, a 10 minute run has only one observation point not within a 10uV range using 6.5 digit daq.

(http://localhost:4000/public/images/dw232/run-16/output/plot-05.png)

Some more plots are here, http://blog.julian1.io/2017/01/15/dw232-circuit-5.html (http://blog.julian1.io/2017/01/15/dw232-circuit-5.html)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on January 15, 2017, 06:06:41 pm
There is a emitter-follower 2n3904 immediately on the output of op27 to provide the necessary 24mA current drive for the zener.

I am wondering how bad this is in terms of PSRR?. According to the op27 datasheet schemtic, the op27 output stage is simply a class AB amplifier powered directly by the rails - so is hanging another npn emitter-follower after it really a problem?

The alternative would be to swap the op27 over to the opa277 (better op-amp anyway at lower bandwidth) which has a max current output of 35mA which is enough to drive the zener directly. Although that seems like a lot of current for a soic package, and perhaps any gains made for noise, and PSRR/isolation would be cancelled by thermal effects in the op-amp.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 15, 2017, 08:56:00 pm
The output stage of the OP is not a problem for the PSRR and drift. Having an extra external emitter follower is more or less needed at this current level to keep the heat dissipation low for the OP and this way prevent thermal effects. If at all the input stage can be slightly influenced by the supply voltage. However with modern OPs and the usual 78xx regulators for the supply PSRR is usually not a big problem.

The fixed divider is relatively high impedance for the OP27.  For this reason the OP277 or similar would be a better choice. If the OP is just there to provide the current to the zener reference even the cheaper OP07 could be good enough. With the 120+x Ohms to set the current, variations at the OPs output voltage should be reduced by the a factor of about 20 - 100, as the zener resistance is much lower than 120 Ohms.

I am not sure the 100 Ohms port in series to the 120 Ohms is such a good idea. I just don't trust the wiper contact so much - but this a pure feeling. I would prefer adjustments to the 51 K resistor (e.g. a 330-470 K resistor in series with a 50-100 K pot that comes in parallel to that resistor).

I think the next step for better stability would be a case, to get air current out and make the temperature more uniform - this is especially important as the heater is not directly at the chip and there is quite a heat source.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on January 15, 2017, 10:07:18 pm
Hello,

here a status report, I was investigating about a dozen diodes.

In brief, there is quite some tension to obtain a reasonably low TC0 point and low noise at the same time.

There are two sets of diodes which differ a lot, but are fairly consistent within each set:

Set 1: 2DW232 from Group Buy
Set 2: 2DW233 from technix
Set 3: fake 2DW232 with internal DO-style diodes


Here a list of typical values I measured.

"nominal" means fixed standard I and T values for comparison,
"TC0" means current for a desired TC0 point around 30+/-10C

Tempco mV/C was measured between 22 and 28C, and current for mV/mA between 9 and 11mA,
both were extremely linear in this range.

                                    mA      T     Vz      Noise uV_pp     tempco mV/C     mV/mA       

Single diode Set1
nominal current and T     10      25    5.4        0.5                  +1                    +7
TC0 point                       2.5     35    5.2        4


Series diodes Set1 
nominal current and T     10      25    6.2        0.5                 -0.5                 +9.5
TC0 point                       26      25    6.2        0.3


Single diode Set2
nominal current and T     10      25    5.3        0.7               +1.5                   +2
TC0 point                       0.5     40    5.2        15


Series diodes Set2
nominal current and T     10      25    6.1        4                 +0.04                  +5
TC0 point                       7.5     40    6.2        5


Single diode Set3
nominal current and T     10      25    5.6        1         
TC0 point                       none found


Series diodes Set3
nominal current and T     10      25    6.4        5           
TC0 point                       none found


Comments:

1) Surprising is the high noise for series configuration of Set 2. Also the low noise for the single diode configuration of the fake diodes.

2) The only combination with low noise and TC0 near room temp is series configuration of Set 1, however at around 30mA. Which is a bit high for practical purposes.

3) This means that for a more reasonable current of 10mA and low noise, temperature stabilization appears necessary.

4) The tempco of the forward diode with -1.5mV/C was lower than what is usually assumed

5) I was trying to see whether one can cancel the tempco at 10mA/25C by an extra LM234 current regulator, along the lines of page 8/fig 15 in http://www.ti.com/lit/ds/symlink/lm334.pdf (http://www.ti.com/lit/ds/symlink/lm334.pdf)   by using the forward diode of the 2DW23x.

However it turns out that given the measured values of tempco mV/C and mV/mA, this is physically not possible (it would require negative resistances of R1 or R2).

6) It would be interesting to compare more diodes from different batches.


Edit:
7) BTW for the fake diodes the polarity was reversed, that may explain the discrepancy of data sheets.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 15, 2017, 11:15:31 pm
A way to get a zero TC at a lower current (e.g. for set 1) would be using only half (or more 2/3) the forward diode. This could be a resistive divider over the diode. So kind of averaging between single diode and series connection. I think this is easier than a modified current source.
A slight shift to lower currents could be possible if only the voltage of the zener is used to derive the current. But this would be only something like a + 0.02%/K for the current instead of something like a +0.5%/K to shift it all the way to 10 mA.
The other way around (using the voltage over the forward diode to set the current would shift the compensation point for the single diode slight up (and thus towards lower noise), to maybe 3 mA for set 1.

The lower than normal -1.5 mV/K for the forward diode fits the relatively high voltage of the diode.

For the diodes from set 2 it is strange so see so much higher noise in the series configuration. Is this real ? Normally there is not that much noise for a forward diode.
The lower differential resistance for set 2 would also be an advantage.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on January 15, 2017, 11:32:45 pm
Quote
A way to get a zero TC at a lower current (e.g. for set 1) would be using only half (or more 2/3) the forward diode. This could be a resistive divider over the diode. So kind of averaging between single diode and series connection. I think this is easier than a modified current source.
A slight shift to lower currents could be possible if only the voltage of the zener is used to derive the current. But this would be only something like a + 0.02%/K for the current instead of something like a +0.5%/K to shift it all the way to 10 mA.

Just a reminder that I tried that approach on set 1 with reasonable results at lower currents...

https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/301/ (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/301/)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on January 16, 2017, 12:41:59 am
For the diodes from set 2 it is strange so see so much higher noise in the series configuration. Is this real ? Normally there is not that much noise for a forward diode.


Yes it is, I tested a couple (4 and 6) of each of Set1 and Set2 and within each set variations are minor.
Strangely also Set3 shows this behaviour but I tested only 2 of those.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on January 16, 2017, 12:46:59 am
Just a reminder that I tried that approach on set 1 with reasonable results at lower currents...

https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/301/ (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/301/)

Oh indeed yes, thanks for reminding - the earlier parts of the thread went out of my brain buffer.... I will try that!
Perhaps even one resistor works by stealing some current from the forward diode, depending on the sign of the needed correction. A quick calculation will show whether this would be feasible.

Incidentally I really aim for like 10mA since below the noise increases substantially, at least for the diodes I got.

Thanks for your answers!
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 17, 2017, 04:53:04 am
The idea of splitting the diode to adjust the TC for currents in a rather large current range has one weakness: it needs 2 extra stable resistors, especially if you are in the middle range. In principle it should work.

For the idea of modifying the current source to shift the TC a little, I found a relatively simple circuit for use with just the zener reference. As far as this is possible for the different part is resembles how the LTZ1000 works: the voltage over the forward diode is used to set the current for the zener part.
The positive features are that one only needs one really stable resistor with already low sensitivity of about 1/100. The other two resistors are less critical by a about a factor of 10-20. The current for zero TC will be slightly higher than for a constant current, but not by much (could be 10% as a rough estimate). With the 2DW232 output voltage would be near 5.4 V and thus relatively well suited to divide down to a stable 5 V, e.g. with divider directly at the reference.

The capacitor included helps startup - one might need some small additions here too. By pure luck the shown circuit with standard parts shows zero TC in the temperature range.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on January 17, 2017, 07:16:26 am
Quote
I am not sure the 100 Ohms port in series to the 120 Ohms is such a good idea. I just don't trust the wiper contact so much - but this a pure feeling. I would prefer adjustments to the 51 K resistor (e.g. a 330-470 K resistor in series with a 50-100 K pot that comes in parallel to that resistor).

Is the circuit more tempco sensitive to the 100ohm trimmer wiper, than a pot+fixed across the 51k? Perhaps because of the low resistance of the zener. I will definitely swap it around if that's the case.

I put the 100 trimmer in series with the 120, because that's how the ltz1000 circuit did it for the tunable tempco circuit in the ltz1000 datasheet (there it is a 120 + 200 trimmer). But maybe that's not a good example, because they use the on-die transistor collectors for the inverting op-amp inputs and didn't have the choice.

I am looking at buying 10ppm/C thin-film SMT 1206 resistors, in which case it might be possible to position all the tempco sensitive stuff on a carrier with the dw232 embedded in some thermal epoxy  .
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 17, 2017, 08:48:07 am
I would be somewhat careful with precision SMT resistors. Especially the larger SMT form factors tend to be sensitive to board bending and expansion of the board. Still you need the large Form factor to get rid of the heat. I would prefer the old style THT form factor for precision parts.

For a constant temperature, I would prefer a metal enclosure around the critical part (e.g. part of PCB): reference and the 3 critical resistors. The OPs might already be better outside. Only an extra divider to get scaling (e.g. to get 10 V) and maybe some resistors to set the temperature are possibly also better inside.
Potting with epoxy could cause more trouble than good - it can swell with humidity and have delayed relaxations.

With the wiper of the pot, I would expect some uncertainty in the contact resistance. Even if this is only in the 10 mOhms range, this would be 0.1% of a 100 Ohms resistor. I would really prefer trimming with the 51 K resistor (we have the choice here), with something like fixed + trimmer in parallel. Or with the pot + coupling resistor version.
One might use a trimmer to do the adjustment and than replace it with fixed resistors for the final version.
AFAIK the TC is not changing that fast with the current. So the current setting does not need to be so super exact at zero TC. From the curves Bertik showed something like 5 % might be good enough if the temperature is stable. Though a better tuned TC could reduce the sensitivity to changes in the set temperature and may allow for just regulating an outer shell for the whole circuit (except power regulation).

For the circuit, the 3 resistors have a sensitivity of about 1 ppm change of output voltage for an 100 ppm change in resistance. The reason the low ohms resistor is more important is, because it gets quite some current and thus has more self heating.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: CalMachine on January 18, 2017, 12:22:26 pm
Got some goodies today!  :-+   I'm excited to start testing and prototyping
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on January 18, 2017, 01:51:01 pm

For the circuit, the 3 resistors have a sensitivity of about 1 ppm change of output voltage for an 100 ppm change in resistance. 

I had a play with removing the current adjustment trimmer completely - in favor of using fixed resistors. The result has been quite positive.

It is possible to use a fixed resistor divider anywhere in the range of 4.7/10k to 5.1/10k on the inverting op-amp input. This gives a change of up to 9mV on the reference output and corresponding change in zener current.

The important part - is that within this range - it is possible to adjust the set-point temperature to align with whatever the new TC0 is as it changes with the zener current.

This reduces the circuit to needing just a single trimmer (for set-point temperature). It is also more practical - and there is no complicated binary search for TC0.  Instead we can do a single datalogging cold-start to get a plot of the TC0 point, and then dial in the regulation set-point in one step according to the value read.

On this basis, I think I'll abandon the carrier idea - and instead get some precision low tempco Vishay resistors for the divider.

The only unknown - is that all tests used the same dw232 component, so I don't have much sense of how sample variation in the dw232 may change things.

More details and plots,
http://blog.julian1.io/2017/01/18/dw232-circuit-6.html (http://blog.julian1.io/2017/01/18/dw232-circuit-6.html)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 19, 2017, 02:47:43 am
It is possible to do the fine adjustment with the temperature instead of the current. Form the older data, a 10% change in the current gives something like a 15 K shift in the temperature for zero TC. So the temperature might be used to do the last 5-10% adjustment (if needed). The data from the other users here suggest that there is a spread of more than 10% in the optimum current. So one will likely still need an individually matched resistor or something like a parallel (or series) combination of 2 or 3 resistors to get close enough. The resistors for finer steps do not need to be so accurate.

Even with larger THT parts it is still possible to have the resistors in the temperature regulated part too. Even with the heater directly at the chip, this heater can also partially stabilize the rest of the circuit. It depends on where the thermal insulation is. Even with 3 critical resistors this is no that large. One can combine a heater at the reference with one at a metal enclosure (e.g. use a diode (e.g. 2,x V zener) to heat the reference directly and the transistor to heat the case.

A final circuit / board needed to judge about long time stability would need good resistors - temperature regulation can compensate for a high TC, but not for aging of the resistors.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on January 19, 2017, 07:02:21 am
The idea of splitting the diode to adjust the TC for currents in a rather large current range has one weakness: it needs 2 extra stable resistors, especially if you are in the middle range. In principle it should work.

For the idea of modifying the current source to shift the TC a little, I found a relatively simple circuit for use with just the zener reference. As far as this is possible for the different part is resembles how the LTZ1000 works: the voltage over the forward diode is used to set the current for the zener part.
...

Now I was looking into both proposals: splitting the voltage 1:2 over the forward diode, as described above, does indeed work moderately well: it moves the TC0 current to 10mA while the temperature is about 26C degrees. And the noise stayed below a uV_pp, so this looks OK. However for one thing: the stability is reduced, it yields about 3ppm/C which is in between the curves shown previously (see yellow curve in attachemt).  This was for two SMD mini melf 25ppm resistors 910 and 1800 Ohms soldered across the pins, perhaps this can be improved.

But I also found this more recent proposal interesting, and analysed the circuit numerically. As far as I can see, barring a mistake, for the measured (linearized) tempo values of the two diodes, it turns out that this circuit implies a Zener current of about 70mA!  (Assuming current through forward diode is 10mA at 25C). There does not seem to be enough degrees of freedom for the resistors to get around it (R2 and R6 come out as proportional).

Incidentally my diodes are far different as compared to the first noise measurements in the thread: no way sub-uV noise for 1-2mA!  It is more than 10 or 15uV there. I get low noise only in the order of 10mA and above.



Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on January 20, 2017, 04:16:49 am
The proposed circuit with a different current through the forward diode and zener is not for a current much different from the TC=0 point of just the zener diode. Getting the current from the diode voltage shifts the zero TC point only a little higher (maybe 10%). The main advantage of that circuit would be that only R1 needs to be really stable, the other resistors are less critical by about a factor of 10. Accordingly these resistors only allow a minute adjustment for the zener current.
With a ref chip from set 1 (high current ones) the operating point would be more like 2,x mA (thus R1 should be about 300-400 Ohms) and 5,3 V from only the zener diode. The current for the forward diode should be keep smaller so the other resistors stay less critical. So this might not be good for super low noise, more like a simple, hopefully stable reference, that might be good for dividing down to 5 V.

In principle this circuit might work with a reference from the 2 nd set and there shift the zero TC current for the series reference from 7.5 mA towards maybe 10 mA / 2 mA.
However the lower current through the forward diode is not that good, and the stability advantage is essentially gone.

With temperature stabilization of the whole circuit, it might be possible to use 2 ref chips as 2 zeners and one forward diode in series. This should give an intermediate operation current maybe in the 5 mA range and thus low noise.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: rsjsouza on January 24, 2017, 06:13:10 am
Thanks to technix I got my bag of 20 units yesterday. In the search of suitable documents I couldn't download the SJ document linked in the first thread (it asked for a login). I then found this page (http://www.worldstdindex.com/soft4/3211639.htm) which links to three versions (1974, 1992, 2002). 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: gamalot on February 10, 2017, 03:34:55 pm
Hello VoltNuts,
                      I am interested in sourcing 2DW232/2DW233 from 17th Radio factory in Shanghai ...

Can anyone pint me to their website and/or provide contacts details ?

Thank you very much !
Best regards

Flinstone

I don't think they have any website or other contacts details except a phone number, do you speak chinese?  :-//
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: chickenHeadKnob on February 10, 2017, 06:13:37 pm
Zlymex has been offline since Jan 4 on this forum. It is the new year holiday period for China but I am starting to worry.. hope it is going good with you.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on February 11, 2017, 05:44:19 am
technix is Chinese, he's the one who's been talking to them in person, he lives near the factory.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: gamalot on February 11, 2017, 05:54:51 am
I don't think they have any website or other contacts details except a phone number, do you speak chinese?  :-//

I have colleagues that speak chinese - a phone number or email address could be a good start ...
Thanks

Flinstone

+86 21 6377 2411

Good luck  :)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: CalMachine on February 11, 2017, 05:56:49 am
technix is Chinese, he's the one who's been talking to them in person, he lives near the factory.

I got mine from Technix.  I have not had a chance to characterize any of them yet, however :(  They do seem like the legit low noise ones!
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: gamalot on February 12, 2017, 12:06:36 am
Hello VoltNuts - has anyone got a street address of 17th radio of factory, mail address - as one of colleagues - who speaks chinese - will try to contact them locally ?

I also wonder in which IC process these are made to manufacture those so low noisy ... - some competitors manufacture them in silicon epitaxial planar process but those will not be low noisy.

Can anyone forward the datasheet from 17th radio factory about those 2DW232 ... 2DW235 series of zener diodes ?

Thank you very much !
Best regards

Flinstone

Address : No.175, Dongjiadu Road, Huangpu District, Shanghai, China

No email address published.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on February 13, 2017, 01:06:17 pm
Hello VoltNuts - has anyone got a street address of 17th radio of factory, mail address - as one of colleagues - who speaks chinese - will try to contact them locally ?

I also wonder in which IC process these are made to manufacture those so low noisy ... - some competitors manufacture them in silicon epitaxial planar process but those will not be low noisy.

Can anyone forward the datasheet from 17th radio factory about those 2DW232 ... 2DW235 series of zener diodes ?

Thank you very much !
Best regards

Flinstone

Address : No.175, Dongjiadu Road, Huangpu District, Shanghai, China

No email address published.
That address is on their officially registry but the office have moved to Pudong. I live in Shanghai though, and their office is within public transit range for me.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on February 16, 2017, 06:15:42 pm
I am going to try and create a better board for my 2DW23x - to get some long-term drift data - which at the moment is missing information.
 

In the meantime, I found a source for some minature peltier coolers. This would open the possiblity of replacing the heating loop used for thermal stabilisation with a Peltier cooler to do the same thing. The regulation temperature could be set to co-incide with expected room temperature - say 23C.

Advantages,

  - less thermal stress on the 2DW23x when cycling between use and non-use. Reduced hysteresis issues. Also between the time that the part is manufactured and the time that it is deployed/used.

  - It feels elegant to balance the heating effect from the 20-30mA zener current with a cooling loop. At the moment there needs to be enough headroom above the ordinary heated temperature for the temperature regulation loop to have room to work in various ambient settings.

  - The poor power efficiency of Peltier devices is discouraging. But if we accept that the reference is already high-current then it seems less of an issue.

  - lower thermal gradients over the device - because the regulation setpoint is closer to ambient temperature.
 
  - More amenable to the carrier board solution - to keep the precision resistors at the same temperature as the 2DW23x. This is because of the lower second-order TCR affects of the Z201 around 25C .

Disadvantages,

 - Is it just really over-complexifying the design, and assembly?

Some more details, http://blog.julian1.io/2017/02/16/2dw232-circuit-7.html (http://blog.julian1.io/2017/02/16/2dw232-circuit-7.html)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on February 17, 2017, 02:12:41 am
  - The poor power efficiency of Peltier devices is discouraging. But if we accept that the reference is already high-current then it seems less of an issue.

People always seem to get this one wrong. If you use a Peltier device at the right point on its characteristic curve(s) the efficiency is quite good. It's easy to get a  decent CoP (Coefficient of Performance, the ratio of heat moved to energy supplied) if you pick the right point on the curve. The higher the deltaT across the device, the lower the efficiency, the higher the heat flow as a proportion of the rated maximum the lower the efficiency.

If you use small deltaTs (say 10 degrees) and under-rate the device (say ~20%) you can get a CoP of 3.5 without trying too hard. So, a 60W peltier will maintain a temperature difference of 10 degrees, removing 12W of heat for a 3.4W supply of power - change that to 20 degrees and the CoP falls to 1.5, 30 degrees and the CoP falls below unity.

So, for a 300mW semiconductor device to be cooled, pick a 3W Peltier device, a 33 C/W heatsink for the hot side of the Peltier device and you'll get your device to 10 degrees below ambient for a power budget of 100 mW.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on February 17, 2017, 03:38:18 am
For testing stability, I would take the raw (e.g. 5.3 V for just the zener or 6.2 V for zener+diode) voltage as the critical part. I don't think one would need super stable resistors for the first test, as the temperature of the resistor(s) could be stable as well. Before doing a long time test, it might be a good idea to look for thermal hysteresis.

There is an advantage in using a temperature above room temperature: this also makes that circuit part low relative humidity. Cooling below room temperature can be critical as this could even lead to condensation. So even with a peltier element a temperature around 30 C (for the resistors) is likely more suitable. So more like no active cooling if the room temperature is low.
For good efficiency, a peltier element should be operated at reduced current, if the temperature difference is small. AFAIK the current for best efficiency goes down proportional to temperature difference. So 20% of the nominal current at 10 C difference is about right. Still a good heat sink for the hot outer side is needed.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: z01z on February 17, 2017, 09:23:27 pm
Some more details, http://blog.julian1.io/2017/02/16/2dw232-circuit-7.html (http://blog.julian1.io/2017/02/16/2dw232-circuit-7.html)
A cautionary note about the foil resistors you've mentioned in your blog: you might get lucky and get one with the TCR as good as the typical range mentioned in the datasheet but only the worst case range is guaranteed. You might want to check out the TC measurement topic (https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on February 17, 2017, 10:26:52 pm

A cautionary note about the foil resistors you've mentioned in your blog: you might get lucky and get one with the TCR as good as the typical range mentioned in the datasheet but only the worst case range is guaranteed. You might want to check out the TC measurement topic (https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/).

Thanks for the heads up on expectations for the z201. I haven't put a lot of thought into it and was even kind of buying on price. My initial intention was to use s102 which are 2ppm/C. Then I saw the z201 range with apparent 10x better TCR with only a modest difference in price.

I think I am probably juggling a couple of different goals. The important thing is to create a reference suitable to be left powered on for six months in order to obtain some longer-term drift data. For this task - perhaps inexpensive resistors would be fine as Kleinstein notes. So long as data was sampled (perhaps once per week) under identical room temperature conditions.

For price/performance, Vishay ptf56 look impressive with 5-10ppm/C. The 10k ptf56 are less than $1. In a divider ratio they're probably about 2ppm. I tested voltage sensitivity of the 2DW232 in series configuration to current and it's about 1/80x.

I am not sure how to account for resistor hysteresis except perhaps to sample and record their resistance - or by buying more expensive ones...
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on February 17, 2017, 10:59:54 pm
I am following this with interest, by having similar plans. Ultimatively it will be about a low noise, constant current laser diode driver but the basic reference stage should be similar. So far I was using Peltier control of the Zener temperature, but that in a test setup and not for real use, where it would be overkill and anyway a PWM control should better not be used anywhere near a low-noise reference.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: MrBungle on February 18, 2017, 04:21:45 pm
I am following this with interest, by having similar plans. Ultimatively it will be about a low noise, constant current laser diode driver...
Trying hard not to go off topic, but have to say I like the cut of your jib!  :-+
I'm following for the exact same reason  ;D
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on February 18, 2017, 08:17:09 pm
How good the resistors for a long time drift test need to be is a difficult question. If the refs are really good, it is well possible that the resistor(s) set the final drift performance of the full reference circuit. If the references show a lot of drift, it would be a kind of wast using very good resistors, bit we don't know up front. How good reference drift can be resolved also depends on the equipment available. So with an equipment that might be good to a few ppm/a one should use resistors that do add much more error. To get a 1 ppm stability for the voltage would need something like 50-100 ppm for the resistor.
At least the two resistors for setting the gain should be measurable (e.g. check the voltage ratio with an DMM). So at least for those resistors the PTF56 should be good enough, especially as the power is rather low for those. For the final current setting resistor the PTF56 could be about the lower limit on how good the resistors should be for a long time stable reference.

Ideally one would do a long term drift test with more than one unit - they may not behave all the same.
With similar diodes one might be able to do this with several zeners in series  - thus only one precision current source and switchable test points to measure the voltage.

How much resistor drift cause voltage drift depends on the zener resistance. There are a few crude data on this, but it might be worth checking the actual used refs at a current closer to the one used. This could be an important property for an reference and with lower voltage zener diodes this figure is expected to be not as good as the classical 6.2 V + forward compensated zeners.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Conrad Hoffman on February 22, 2017, 08:21:54 am
Just a comment on resistors- trust no one! Measure the actual resistors you're going to use, immersing them in warm/hot mineral oil and cold. Solder some and recheck the values. The resistor you know is far better than the promise of a data sheet.  8)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on February 25, 2017, 10:32:58 pm
PCB boards look quite nice,

(http://blog.julian1.io/public/images/dw232/pcb/DSC03021.JPG)

The circuit works, even if there's a bunch of goofy things that could have done differently.

(http://blog.julian1.io/public/images/dw232/pcb/out.jpg)

I'll make one last stab at adjustable current and set-point trim with Bourns 3250 trimmers - since trimmers are just so convenient. I believe I can get a reasonable current range for the 2DW232 TC0 with only around 5% of the total divider resistance on the trimmer - with it's poor TCR.

If overall circuit tempco is still poor then everything will be fixed resistors.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: BFX on February 26, 2017, 05:51:56 am
PCB boards look quite nice,

(http://blog.julian1.io/public/images/dw232/pcb/DSC03021.JPG)

The circuit works, even if there's a bunch of goofy things that could have done differently.

(http://blog.julian1.io/public/images/dw232/pcb/out.jpg)

I'll make one last stab at adjustable current and set-point trim with Bourns 3250 trimmers - since trimmers are just so convenient. I believe I can get a reasonable current range for the 2DW232 TC0 with only around 5% of the total divider resistance on the trimmer - with it's poor TCR.

If overall circuit tempco is still poor then everything will be fixed resistors.

It's so nice could you please provide schematics , gerber and so?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on February 26, 2017, 08:28:23 am
Quote
It's so nice could you please provide schematics , gerber and so?

I've made a bunch of mistakes with the prototype. The main one being not to pull the temp-sense and temp-set signals out to the pin-headers to make it easy to monitor and dial in settings.  :palm: Instead, II need to probe at the op-amp input pads to get these readings. It would also be good to have easy test-points for data-logging resistor drift/hysteresis. I'll put up the source files when I'm confident that some of these useability issues are fixed.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: BFX on February 26, 2017, 10:38:33 am
Quote
It's so nice could you please provide schematics , gerber and so?

I've made a bunch of mistakes with the prototype. The main one being not to pull the temp-sense and temp-set signals out to the pin-headers to make it easy to monitor and dial in settings.  :palm: Instead, II need to probe at the op-amp input pads to get these readings. It would also be good to have easy test-points for data-logging resistor drift/hysteresis. I'll put up the source files when I'm confident that some of these useability issues are fixed.
Discussing mistakes might be also helpful 8)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: CalMachine on March 20, 2017, 11:40:04 am
Finally got a quick and dirty prototype made just so I can get my RPi logging set the way I want it before the big boys are made!  Here is what I have so far...  I pretty much just copied the circuit provided by Zylmex.

Preliminary logging results to come!

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Pipelie on March 20, 2017, 12:31:29 pm
 :-+
looking forward to see  the test result.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on March 24, 2017, 08:43:22 pm
(http://blog.julian1.io/public/images/dw232/DSC06317.JPG)

I've put another board together. The resistors used are,

    Vishay ptf56-Z (5ppm/C) for OP feedback divider and temp-set divider.
    Vishay z201 (0.2ppm/C) for 200ohm current limit resistor.
    Bourns 3250w for t-set fine adjustment.

Unfortunately, the non temp stabalized components are pretty temperature senstive.

(http://blog.julian1.io/public/images/dw232/run-45/output/plot-03.png)

I discovered it is possible to test resistor contribution to circuit tempco by spraying them with isopropyl and observing the effect of evaporative cooling on the ref output. The z201 shows no obvious change, while the ptf56 produce a 100uV-200uV change.

The goal was to gather some longer term drift data - but I suspect the ptf56 will need to be exchanged for z201 for that.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SvanGool on March 24, 2017, 09:06:08 pm
@julian1

Your graph is showing app. 3.2PPM/°C and the extreme 200uV change is still less than 33PPM over the whole temperature delta.
Maybe I have my goals lower set than yours, but for a 6.5 digit DVM this is good enough and I wouldn't use this reference for anything better than that, or am I underrating the device?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on March 25, 2017, 06:49:22 am
Even with some sensitivity to room temperature, one can still look for long term drift. If in doubt, just make sure the temperature is approximately the same. So if the temperature is within 2 K, the error would be only 6 ppm. Closer temperature mating is possible.

There just is a limit on how much drift is detectable. Higher quality resistor could permit a lower detection limit, but I don't expect the reference to be that good. One parameters that determines how good this reference is for a long term stable ref. is the zener resistance in relation the the current. The number of R_zener * I_zener / U_zener is the relevant figure of merit. To a first approximation this gives how much drift of the current setting resistors transfers to the output voltage. Due to the lower zener voltage the R_zener is expected to be higher compared to the more normal 6.8-7 V compensated zeners.


At least the effect of the resistors would the amplifier and the set temperature can be checked for additional aging drift, by direct measurement of the voltages. So one would know if there is a lot of drift and could in principle correct (add resistors or numerically).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on March 25, 2017, 08:12:21 am
@julian1

Your graph is showing app. 3.2PPM/°C and the extreme 200uV change is still less than 33PPM over the whole temperature delta.
Maybe I have my goals lower set than yours, but for a 6.5 digit DVM this is good enough and I wouldn't use this reference for anything better than that, or am I underrating the device?

Well I feel encouraged by your positive view. The circuit is rather more fiddly to set up than I want - in terms of setting the 2DW232 current to fixTC0, and then dialing in the heater stabilizer to cancel second-order temperature effects.

But having done that work - it's frustrating that everything ultimately comes down to (expensive) resistor choices rather than the $1 cost of the semiconductor. This seems to be universally true of voltage references regardless of device - microsemi zener, lm399, ltz1000,
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on March 25, 2017, 08:39:28 am

There just is a limit on how much drift is detectable. Higher quality resistor could permit a lower detection limit, but I don't expect the reference to be that good. One parameters that determines how good this reference is for a long term stable ref. is the zener resistance in relation the the current. The number of R_zener * I_zener / U_zener is the relevant figure of merit. To a first approximation this gives how much drift of the current setting resistors transfers to the output voltage. Due to the lower zener voltage the R_zener is expected to be higher compared to the more normal 6.8-7 V compensated zeners.


Good information. The high current - over 20mA would also tend to dominate. And that might also be another argument to use better resistors for the main divider.

I can certainly extract drift characteristics over and above tempco effects - either by controlling conditions at the time of measurement, or statistically - by multivariate regression. But I am wondering if there is an issue that I would be measuring ptf56 drift rather than 2dw232 drift.

The current pcb board didn't pull the main feedback divider out to the pin-headers. I assumed that with the op-amp output and z-ref available then that value could be derived  - albeit with a small difference due to the op-amp input offset voltage. But that may have been an oversight.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SvanGool on March 25, 2017, 11:14:47 am
It's frustrating that everything ultimately comes down to (expensive) resistor choices rather than the $1 cost of the semiconductor. This seems to be universally true of voltage references regardless of device - microsemi zener, lm399, ltz1000.

That is funny, there is another thread going on which is tending in the opposite direction: https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg1168867/#msg1168867 (https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg1168867/#msg1168867) and later. I think that you have to make the best out of the components you selected to use and Kleinstein gave some good advises on that path. Maybe you haven't squeezed your design yet to the limit, don't give up yet, I'm indeed already positive on your current results.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: amspire on March 25, 2017, 11:27:48 am
I had got some 2DW232's from here:

https://www.aliexpress.com/item/10PCS-2DW232-quality-assurance/32589219690.html (https://www.aliexpress.com/item/10PCS-2DW232-quality-assurance/32589219690.html)

Wasn't sure if they were the genuine "diamond" references, so I decided to see what was inside anyway.
(https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=302435)

Similar to the 2DW234 photo (taken in 2013) posted in the first page of this thread, but it has an opaque white enamel/epoxy/gunk instead of the brown gunk in the older photo. The chip layouts are similar, but it looks like my chip is about 12% longer then the 2013 chip.
(https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/?action=dlattach;attach=226642;image)

Seems to work with the zero TC point at about the correct current and voltage, but I haven't done any serious testing.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: amspire on March 25, 2017, 11:50:09 am
This is the best image I can get of my zener chip
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on March 25, 2017, 01:40:45 pm
Nice pictures at @amspire!. How did you remove the case jacket - with an angle grinder or hacksaw?. I would like to open one of mine, but lack the tooling.


I have populated another board - with the best parts I have on hand.  The divider is now 5k (z201) + 2k (s102) + 1k (z201) / 10k (z201) giving a current around 25mA and t-set of 47C.

The majority of the divider voltage drop and therefore tempco sensitivity will be across the z201 (0.2ppm) resistors instead of the 102 (2ppm).

It is curious that noise appears lower (even despite my terrible cabling) - with obs varying around 5uV over quite a few minutes. At the 7th digit - that must be near the limit of my lm399 based daq to measure. I'm not sure if that could be attributable to the resistors, or lower operating temp, different 2dw232 part or just a rearrangement of my cables.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: BravoV on March 25, 2017, 01:47:04 pm
Similar to the 2DW234 photo (taken in 2013) posted in the first page of this thread, but it has an opaque white enamel/epoxy/gunk instead of the brown gunk in the older photo.

Richard, have you try to clean the epoxy to reveal the die using strong solvent like acetone or MEK ?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: amspire on March 25, 2017, 01:58:41 pm
Nice pictures at @amspire!. How did you remove the case jacket - with an angle grinder or hacksaw?. I would like to open one of mine, but lack the tooling.
My Lindstrom wirecutters. The metal is fairly soft. Just did a cut on part of the top corner to make a hole, and then worked my way down.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: CalMachine on March 25, 2017, 02:09:51 pm
Well it seems as if my very first prototype is more of a thermometer!   :-DD

Each X axis hash is ~6 hours.

Time to make adjustments to the zener current to find the TC
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: amspire on March 25, 2017, 02:48:10 pm
Richard, have you try to clean the epoxy to reveal the die using strong solvent like acetone or MEK ?
Done my best to clean my "2DW232". This is taken on a stereo microscope (45x magnification) with my camera plugged straight into one of the lens sockets with a $5 adapter.

(https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=302543)

Here is another 2013 photo from the first page of this thread:
(https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=258920)
This is a precision 0.2mm grid over the chip, if anyone wants the size.
(https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=302545)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: amspire on March 25, 2017, 03:02:37 pm
Well it seems as if my very first prototype is more of a thermometer!   :-DD
One of the ways I was thinking of doing a temp controlled reference is to run the second diode at a current perhaps half the first diode zero TC current along with a resistor in series to bring the voltage drop up to the first diode. Then you just have a op-amp based temp controller that just keeps the two voltages identical.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on March 25, 2017, 04:14:22 pm
Nice pictures at @amspire!. How did you remove the case jacket - with an angle grinder or hacksaw?. I would like to open one of mine, but lack the tooling.
My Lindstrom wirecutters. The metal is fairly soft. Just did a cut on part of the top corner to make a hole, and then worked my way down.

Good thanks. wirecutters and tin-snips are pretty effective. For reference, here's one of my 2dw232 sourced by zlymex.

(http://blog.julian1.io/public/images/dw232/die.jpg)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: amspire on March 25, 2017, 04:21:37 pm
For reference, here's one of my 2dw232 sourced by zlymex.
That looks like exactly the same white stuff that I have. It is looking like I did get genuine Diamond zeners.

It is good to know.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on March 25, 2017, 07:52:02 pm
The overall drift of the reference circuit is set be the zener itself and that of the resistor(s) scaled with a certain factor.
That factor depends on the zener resistance: with the LTZ1000 (and good quality 6.6-7 V compensated zeners) it is about 0.01. So for ultimate stability good resistor(s) are important, but still in many cases the zener itself is the larger contribution.

It might be interesting to see on how sensitive the 2DW232 reference is to resistor change. I would expect is to be more sensitive, as usually the zener resistance is high for a 5.7 V zener compared to a 6.2 V zener. I would expect the experts constructing the zeners refs know that and choose the 6.2 V for lowest R_Zener despite of higher noise. I could be that by some means the 2DW232 also got low R_Zener, despite of using the low voltage. Lower noise at the lower voltage is not such a surprise. A suitable test could be intentionally increasing the current by something like 1 % (e.g. add 20 K in parallel to the 200 Ohms) and observe the increase in voltage.

How much the temperature setting resistors contribute depends on the TC compensation - with adjustment this should be better than the more of less fixed TC of the unheated LTZ1000. So with reasonable adjustment of the current, the temperature setting resistors (and the temperature regulation itself) should not be that critical. This is the advantage one gains from individual adjustment of the TC. Of cause one has to pay the extra effort for the adjustment.

So with the 2DW232 it should be only drift in the current setting that really matters.  The resistor ratio used for amplification can be measured. I don't think the OPs offset should be so important - so reading the OPs output and the zener output should be good enough for this. To resolve an 1 ppm change for the reference would only need to resolve something like a 20-100 ppm change in the voltage ratio.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on March 26, 2017, 12:53:04 am
I wonder if I should saw one of mine own open and take a picture? Mine came directly from the factory and should be the same as the one sent to folks that bought through me.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on March 27, 2017, 04:45:31 am
It seems that there are at least two different batches of the original diamond brand, the one that has a fatter font and a date code below the 2DWxxx (like pictured here in this thread), and one with thinner font and no date code (and white epoxy).  It seems that they differ quite a bit at least as far as the noise is concerned. I am collecting statistics while waiting for more samples to arrive from various sources.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: amspire on March 27, 2017, 07:25:01 am
My 2WD232s have a 16-4 date code and white gunk that is like a thin silicone sealant. Also although the chip looks identical to the ones sealed with the brown gunk, it seems to be slightly larger.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: janode on May 11, 2017, 12:51:59 am
My 2WD232s have a 16-4 date code and white gunk that is like a thin silicone sealant. Also although the chip looks identical to the ones sealed with the brown gunk, it seems to be slightly larger.

I got some from the same source. Are you sure those are 16-4? Printing quality isn't great on all of them. I got 15-4. I cut one open and it looks exactly the same on the inside. They also look identical to what I got from zlymex.. Even the date code is the same!
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on May 14, 2017, 10:38:28 pm
Here a summary of some findings:   http://hololaser.kwaoo.me/electronics/2DW23x.html (http://hololaser.kwaoo.me/electronics/2DW23x.html)

Relatedly: http://hololaser.kwaoo.me/electronics/LowNoise.html (http://hololaser.kwaoo.me/electronics/LowNoise.html)

Cheers,
BK
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zhtoor on May 20, 2017, 08:12:05 pm
Hello gazelle,

could you tell me how and where did you order these?

thanks and regards.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Muxr on May 23, 2017, 04:51:43 pm
These look like they have the "Diamond" logo and the date code: https://www.aliexpress.com/item/10PCS-2DW232-quality-assurance/32589219690.html?spm=2114.13010608.0.0.RXTW5A (https://www.aliexpress.com/item/10PCS-2DW232-quality-assurance/32589219690.html?spm=2114.13010608.0.0.RXTW5A)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SvanGool on May 25, 2017, 06:42:33 am
Well, at least that shows that Technix got them from the same factory with QA label, as you did.
This is the QA label I got with my purchase from Technix:
(http://homit.nl/EEVblog/Diamond.jpg)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: chuckb on June 03, 2017, 02:44:37 pm
2DW234 and 2DW236

I got a few 2DW236 zeners from China but the noise performance was obviously worse than the 2DW234. I notice the metal can had a different finish (matt vs bright), the part number lettering was a different font, there was no date code and on closer inspection the zener die was 0.5mm square verses rectangular with a 0.72mm length.

In the future if I have a concern about a batch of chips I will use diagonal cutters, remove the case and just look at the die. Based on my samples and other comments on this thread, the low noise chips are 0.72mm long and rectangular.

The 2DW236 sample I received were connected common anode. In a series configuration that means you will measure 0.7v on the case, pin3. The 2DW234 rectangular chips seem to be common cathode with 5-6 volts on the case, pin 3.

The 2DW236 zeners came with Factory QC paperwork also. But keep in mind they meet all the data sheet specs. It would be great if these special low noise zeners had a unique part number so they did not get mixed up with the normal 2DW23X zeners.

I'm evaluating the 2DW234 and they are very low noise. It's a challenge to measure it. I don't do the 0.1Hz to 10Hz measurements I build two identical systems and measure the difference with a nanovoltmeter. This gives a better picture of the overall worst case performance. I need to temperature regulate the parts before I will be able to get good stability numbers. Maybe I'll have that running in the next month.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: bertik on June 03, 2017, 05:09:56 pm
This is entirely consistent with my findings: the ones without date code typically have a lot more noise - irrespective of 2DW234 or 2DW236. Actually I couldn't find any consistent electrical difference between the various 2DW23x if from the same source. See http://hololaser.kwaoo.me/electronics/2DW23x.html#noise (http://hololaser.kwaoo.me/electronics/2DW23x.html#noise) for a plot.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: chuckb on June 05, 2017, 12:59:14 pm
There is an easy test to determine if you have the special die inside your zener package. The special die is configured as common cathode. The cathode is connected to the case.

Therefore I set up a test with my Fluke 289, or K2000 on the diode scale with the black lead on the case. When I connect the red lead to pin 1 or 2 the meter displays about 0.7v for the good rectangular die. A normal zener will read open in this test.

The test does not guarantee a low noise device, however it is an easy first test if you have concerns about a group of parts you have purchased.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: uwezi on June 14, 2017, 08:53:34 am
As a latecomer to this discussion: is there still a possibility to join in for ~20 pcs to Sweden?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on June 15, 2017, 09:32:23 am
As a latecomer to this discussion: is there still a possibility to join in for ~20 pcs to Sweden?
There is an aggregate thread. I just placed an order for a batch of diodes so you may need to wait a while for the aggregate to build up again.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Muxr on June 15, 2017, 09:55:23 am
This is the agregation thread: https://www.eevblog.com/forum/metrology/factory-2dw23x-order-aggregation-thread/ (https://www.eevblog.com/forum/metrology/factory-2dw23x-order-aggregation-thread/)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: chuckb on July 27, 2017, 12:51:04 pm
Many of my older 2DW23X diodes with 2014-2016 date codes had 0.72v diode drop with a 1ma test current. The latest batch from Technix are measuring 0.66V. They were tested at the same temperature. If your circuits are sensitive to that voltage you may want to evaluate the new chips. I have not had time to fully test them out yet. I'm off on a 1 week vacation now.

One very good change is the older chips seemed to have plain steel leads that would not solder well. The leads on the latest chips take solder very well.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: GigaJoe on August 06, 2017, 02:22:17 am
Interesting , got a package, ...233 model:

diode has very high internal impedance, this lead it to very sensitive  to a current flow.  I'm still puzzle about why 2 diodes in a package, noy a single, or let say 4, or 6 .... and common cathode, seems, due-to manufact. process. Anyway:

2 internal diodes in parallel, just to decrease the diode internal resistance, hook to a precision voltage source, + 2 variable multi-turn resistors, 10K + 100, 100 ohm - give an option to dial up a fraction of microamp. So heating, cooling, adjusting current, I received 2-3 ppm/C  in a range 20-30C.   Thinking , of 6-8 in parallel, with 50 ohm multi-turn trimpot to adjust current for optimal temp stability, and possible to dial each to diff rising or falling temp. trend, it may allow me to compensate temp. further

With total 3.7 ma current, it observe a self heating.   

while I waiting trimpots ( takes weeks, i think) will do an aging\torching  process  ... will see ...


Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on August 06, 2017, 02:34:17 am
The zener impedance also depends on the current. Especially at low current the impedance can be relatively high. An important figure of merit is the number  R_zener * I_zener / U_zener. This gives approximately how much drift / TC of the current setting series resistor will be attenuated. To get a good long time stable reference it is important to get a low value here otherwise one would need more and more expensive resistors.

With just the zener diode, the current where the TC crosses zero is relatively low - like in the 0.5 - 2 mA range. So a high R_Z is kind of normal. Also zener diode at around 5.2 V usually have a higher differential resistance, compared to the 6.2 V ones. So it would be a surprise if one could get good values at the low current and around 5.2 V voltage.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: GigaJoe on August 06, 2017, 09:33:39 am
2 hours: 50 ma, + 140 C , ( 2 diodes in parallel ) - increase output +2 mV , comparing before torture, wonder , is it a good exercise ? 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: 2N3055 on August 06, 2017, 09:43:59 am
2 hours: 50 ma, + 140 C , ( 2 diodes in parallel ) - increase output +2 ma , comparing before torture, wonder , is it a good exercise ?

140°C is way too high... die seems to be attached to case with epoxy .. 140°C will damage die attach... 65-85°C is probably better choice.. And best would be to let it age on working temp. for 500 hours...
It will take a long time to settle back to working temp after excessive heating.. 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: GigaJoe on August 06, 2017, 10:46:17 am
nothing shaking inside   ::) ,   maybe it survive. One more thing, usually after thermal shock all references a bit shifted, and this one, not an exception, a few thermal shocks, had eliminated this shift, heat to + 100 it back precisely to the same point.

BTW, found,  this forum:
REDUCING OF THE TIME DRIFT OF ZENER STABILIZATION VOLTAGES, famous DATRON, Thanks zlymex !
https://www.eevblog.com/forum/metrology/t-c-hysteresis-measurements-on-brand-new-lt1027dcls8-5-voltage-reference/?action=dlattach;attach=239750 (https://www.eevblog.com/forum/metrology/t-c-hysteresis-measurements-on-brand-new-lt1027dcls8-5-voltage-reference/?action=dlattach;attach=239750)
need to heat it up at 100 C for 4 hours, then cool slowly, and ,they heating it in an active state,  so i running to solder 10 on board , run max Amps, and heat it a few hours ....
upd, didn't read with attention ( as usual)  its a single cycle , around 70 - 100 cycles need to complete aging process .... ops ...


Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: 2N3055 on August 06, 2017, 08:16:34 pm
I didn't say it's gonna fall of..  :-DD

I know about that document.. It is good read, but not so much relevant here in terms of temperatures and such, completely different diode and technology.. Principle is true, of course..
Read first 10 posts in this thread.. Zylmex boiled them to be sure they won't go over 100°C.

Such high and short thermal shocks are just shocks that will damage it.. You need to make temperature high enough to soften epoxy and than keep it there long enough that it creeps and plastically deforms to release all tensions on die..  If you do it on a temp that's too high, it will relax for that temp, and when it cools it will again be in tension.. Trick is to do it somewhere closer to work temp so residual tension is not too much and that will fall in place during later work at nominal temp.

Accelerated aging only helps with first few hundreds hours, where changes are huge.. Last few ppms will take years and you can't rush it.
It is more helpful with less soft die attach materials (metals). Epoxy is softer and flows more easily on room temp..
If you overdo heating, chances are you will put so much tension in die attach that it will take additional years to relieve.. Or you can fracture the die or put tears in die attach. That will act as nonlinearities that will manifest itself in all kinds of stochastic behaviour..
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Spikee on August 09, 2017, 04:05:18 am
I'm thinking about using this reference in one of my designs. Zero tempco is not a must, low noise has the higher priority.
Altrough a low-ish tempco is preferred. At this moment The LTC6655 is planning to be used.

I have a few questions. What is the recommended mode for this zener to be run at ? I see al kind of numbers flying by.
I would assume that his reference is made to be run / connected in a certain way in which it would perform best.
The vref voltage that is needed would be about 0.5V. So it will need to be divided (exact value does not matter that much).

I also saw talk about regulating the temperature of the vref accurately by measuring the internal temp using the second diode. Have other people tried this ?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on August 09, 2017, 05:18:55 am
There are essentially two possible modes of operation: one using only the zener diode at a relatively low current (e.g. 0.5-2 mA range). This operating point shows more curvature in the U vs T curve and also needs a rather well adjusted current to get a small TC. Due to the low current, the noise is not that extremely low, but usually still good, compared to something like an LM329 / LM399. In some cases the voltage in the 5.2 V range can be an advantage, as this can make dividing towards 5 V relatively stable.

The other operating point is using diode and zener in series. Here the current adjustment is less critical, but as a downside the current for a low TC can vary quite a lot between units, somewhere in the 7 mA - 40 mA range. So some units might not be practical to run in this mode. With the rather high current, self heating (and thus a critical thermal design) can be a problem. Usually the noise is very low and chances are that this circuit is also less sensitive to resistor drift.

Depending on how the current is set (e.g. using a current that changes with temperature), one can slight shift the zero TC temperature to slight low / higher currents. However this only a small change. It can be interesting for the zener only version to slightly increase the current at very little effort.

The diodes also seem to be different. The zero TC current can vary quite a lot - so some (lower current ones) are more suitable for the series mode and other (higher current ones) may not be practical in series mode but the better ones for the zener only mode. My guess is the diodes are made for the series mode - however many of the diodes measured so far seem to need a rather high current to achieve zero TC. At the nominal 5-7.5 mA current the TC is still relatively high with most units.

With an adjusted linear TC, there is no need for a super stable temperature regulation, however some regulation can be a real advantage, as the second order TC is relatively high, especially in the zener only mode. A sensor directly at the chip is a slight advantage, however for a fast regulation one would need sensor and heater close together. So using only the internal sensor can be tricky. Temperature regulation tends to about double to quadruple the power requirement. The rather high power in the series connected mode makes the version with temperature regulation really high power.

For 0.5 V reference one would need a divider in essentially any case. The divider could also very well limit the stability. The following amplifier might already be limiting and thus super low noise might not be such a big advantage.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: GigaJoe on August 09, 2017, 01:54:15 pm
had a prototype, use just a 2 zeners in parallel (a single package),   then 2 zeners as 2-nd packages with averaging, adjust current for first to positive curve, second as negative, need a few hours and patient, for narrow temp range, result less then 1 ppm, main trouble a current can drift , disturbing the result
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: vindoline on August 13, 2017, 03:33:35 am
OK, so I've got 30 of these fancy new 2DW232 & 233 Zeners on my bench and I'm anxious to build something. What's the consensus on how to "age" them? Should I actually drop them in boiling water? For how long? How many times? Should I set up a board to burn them in? What current, etc? Should I just build up a 10V circuit and run it at some arbitrary current until it begins to settle down, and then try and find the zero tempco current?

Any advice is welcome!
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on August 13, 2017, 04:37:41 am
I won't expect a gross effect of aging. So one could likely just build a reference circuit and adjust the current for a low TC. I would start without extra aging before building the circuit - alone to get an idea of the order of magnitude for the drift.

A first thing might be looking for the zero TC point for just the zener diode (around 1-2 mA). This would give an indication if the diodes are more suitable for series configuration of just using the zener diode(s). To a certain degree the diodes determine which circuit is possible. There seem to be some diodes that do not reach TC compensation for the series configuration at a feasible current.

The first circuit would likely not be a 10 V reference but just the unscaled reference: so either around 5.2 V or 6.5 V, maybe double if 2 chips are used. The second step would than be likely some temperature stabilization (especially the zener only version likely needs it) and only after some drift tests one could decide if it is worth to build a stable scaling to 10 V. For a 10 V scaling the zener only configuration with 2 in series has some benefits. For a really stable reference the resistor(s) needed around the zener are very likely more expensive than the diode. This is especially true for a 10 V scaling even if one could start at 10.5 V.

I would prefer accelerated aging in circuit, so one could see how much the diode changes. Part of the aging would be the likely epoxy glue. These glues usually have a glass transition in the 100-140 C range. So the logical stabilization of the glue would be by heating so something like 80-100 C, holding it there for something like 1-3 hours and than slowly (could be days: e.g. 0.5-1 hour for the first 10 K and than doubling the time for the next 10 K and so on) cool it down.

To get a curve on aging one could do repeated equal cycles to maybe 80 C or so. It depends on the part how many cycles are needed. An upfront estimate is rather difficult. How practical such a stabilization curve is, depends on the instrumentation.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: chuckb on August 13, 2017, 06:20:57 am
I'm monitoring a setup with the diode in series mode with 20ma of bias current. I have temporarily added insulation around the case so the case is operating at 100 deg C, the die will be warmer. I have measured -120uV / day (at 6V) for the last three days. I hope it slows down soon!
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on August 13, 2017, 07:52:39 pm
100 C is already quite high in temperature. So more interesting for testing, maybe accelerated aging (if it slows down).

Is the -120 µV/day measured at constant temperature ? Without an individually adjusted current the TC of the diodes can be relatively high (e.g. 200 µV / K would not be such a surprise to me).
It might help to get separate measurements for the voltage of both diodes (forward and zener mode).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: vindoline on August 13, 2017, 11:00:39 pm
I'm monitoring a setup with the diode in series mode with 20ma of bias current. I have temporarily added insulation around the case so the case is operating at 100 deg C, the die will be warmer. I have measured -120uV / day (at 6V) for the last three days. I hope it slows down soon!

Wow, your Zener is really toasty at 20 mA! Are you sure it's not 100 F? I just ran one of my 2DW232 overnight at 15 mA. It's insulated in foam inside a box and the thermocouple is physically on the metal can. It has stabilized at 31.9 C (89.4 F)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: chuckb on August 14, 2017, 01:18:16 am
The zener and electronics are in a small thermal chamber with no forced air movement. The case is operating at 100 deg C. I have seen TO-39 junction to case thermal resistances ranging from 15-45 deg C / watt in the literature. That would indicate a chip temperature of up to 105 deg C.

Yes, this is an accelerated aging test. The Zero TC point for this diode is around 78 deg C. I run the diode for a day at 100 deg C then lower it to 78 deg C and record the voltage. I also check that the turnover temperature has not changed. It has not.

I am in the middle of automating the process of finding the zero TC point. To do it correctly takes HOURS of recording voltages by hand. Good thing I'm retired now! The spreadsheet of data for this setup has 500 rows of data. I will add a scanner to check several more voltages during the next group of tests. The bias voltage could be moving. The bias resistor could be drifting. Or one of the diodes inside the 2DW234 could be changing voltage.


BTW I use a - SciGene Hybex Microsample Incubation System for a small thermal chamber (heat only). You can get them surplus for less than $100 and it contains a 200 watt heater and a Watlow SD31 Digital temperature controller. The heater is very large for the chamber size so I have some metal plates on the bottom of the chamber to add thermal mass and slow down the peak rate of temperature change. It also minimizes temperature overshoot.
I typically change the chamber from 1-10 deg C, wait 30 minutes for everything to stabilized and record the voltages. You start a temperature sweep in 10 deg C steps till you find the turn over temperature then go back and do 1 deg C steps (or smaller) to find the exact temperature.

This whole process really makes me appreciate the LM399 and the LTZ1000 with heated chips!

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on August 14, 2017, 01:21:02 am
Hello,

Lymex suggested soft thermal shocks:

https://www.eevblog.com/forum/metrology/t-c-hysteresis-measurements-on-brand-new-lt1027dcls8-5-voltage-reference/msg981794/#msg981794 (https://www.eevblog.com/forum/metrology/t-c-hysteresis-measurements-on-brand-new-lt1027dcls8-5-voltage-reference/msg981794/#msg981794)

other hints for reference zeners (selecting for low noise) can be found here:
http://volt-nuts.febo.narkive.com/9QIiUfpN/some-questions-to-zeners-1n823-1n829 (http://volt-nuts.febo.narkive.com/9QIiUfpN/some-questions-to-zeners-1n823-1n829)

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Dave on August 27, 2017, 10:30:09 am
I am now in queue for the aggregated order, but I'd like to do something ahead of time while I'm waiting for these to arrive.
I don't want to reveal my plans before I have something to show, but I would need measurements of the device cans to be able to pull it off. The two datasheets that I found in this thread both show slightly different dimensions, so I don't know which to trust.

Would someone that has already received the genuine diamond brand diodes be so kind and grab some measurements for me?

I need the diameter of the lip, the diameter of the can (the wider part just above the lip), the height of the package, the thickness of the lip and the size of the little tab (width, length).
These measurements must be from the biggest one you can find in your bin.

If anyone would be so kind to take the time to do it, I would really appreciate it. :-+

I will, of course, share my whole project once I manage to bring it to life. ^-^
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: cellularmitosis on August 27, 2017, 11:44:57 am

Caveats: I just measured one (didn't look for the largest one), and I used a cheap Harbor Freight set of calipers.

Curious to see what you come up with :)

Edit: oops, wrong units.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Dave on August 27, 2017, 12:30:13 pm
Thank you, cellularmitosis!  :-+ :-+ :-+
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Dave on August 27, 2017, 01:21:50 pm
There is one more measurement that I still need to get this done: the thickness of the lip. Thanks! :)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: cellularmitosis on August 27, 2017, 01:50:20 pm
This one is a bit more difficult to get an exact measurement, because the lip has a bit of a chamfer, but I'll call it 0.030"
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: floobydust on August 28, 2017, 01:49:25 am
I found another datasheet for the part; posting because it was hard to find: "Guiyang 873 plant (Guiyang Zhongguang), 873 factory is 2002 version of 2DW23X military standard drafting unit"
It's very close to TO-39 package.

I also see this part in gold lead/brass base, and black paint-dipped offerings.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Dave on August 28, 2017, 03:36:14 am
Thanks for the input. I suppose I can give you a little teaser, but I won't say much. ^-^
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: zhtoor on August 28, 2017, 03:39:36 am
Thanks for the input. I suppose I can give you a little teaser, but I won't say much. ^-^

hello,

an isothermal block with temperature control maybe and then averaging for still lower noise reference?

regards.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Dave on August 28, 2017, 06:45:35 am
I'm aware of the zero-TC bias point and I was planning on measuring batches of diodes to cherrypick the very best ones out of the batch. As for the noise figures, I suppose I'm gonna have to build zlymex' LF amplifier to characterize that.

an isothermal block with temperature control maybe and then averaging for still lower noise reference?
That obvious, eh? ;D
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: floobydust on August 28, 2017, 08:03:38 am
Ranking parts, I use an audio amp to listen to the noise quality, find microphonics, hum, AM radio etc.
Worth trying. It's pretty easy to find the popcorn with headphones on  :popcorn:
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on August 29, 2017, 02:19:21 am
According to the measurements from Bertik, there seems to be quite a scattering among the 2DW23x. So it might be effective to select a good one than using many for simple averaging. With the sum of several refs a single poor one can ruin the noise / drift performance. So it is not always getting better with averaging. To check for poor samples some check on the noise is definitely a good idea. Not all of them seem to be low noise.

In the zener + diode mode the current and thus power is already quite high (more like 10-20 mA) and the noise of a good one is already very low.  The tendency would be more like looking for a way to reduce the power, than going for even lower noise at the cost of even more power.  The oven for temperature control can  about double (at normal room temperature) the power requirements - so power consumption and thus heat can get a problem.

With very good thermal coupling one might consider a mode with 2 zeners and 1 diode - to get an intermediate operating current. Though with 2 refs in series the power reduction might not be that much.

In the zener only mode, the power is rather low (e.g. 1 mA) thus using more than one reference might be of some interest, though mainly the 2 zeners in series to make is a 11 V reference that is good for scaling down to 10 V.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: ultrasmurf on September 09, 2017, 02:14:52 pm
Is there anyone building a PCB kit to build a voltage reference standard using this 2DW ?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: chuckb on September 12, 2017, 09:42:05 pm
ultrasmurf - I have not seen any mention of a kit for these devices.

general question - Is the chip to package attachment epoxy or solder? Because the back side of the chip is electrically conductive to the case, doesn't that indicate that solder is the chip attachment method? Or is there a conductive epoxy with <<1 ohm of resistance used inside chips?

I would have the option to burn-in the 2DW23X at a higher temperature if the attachment is solder.

BTW my -120uV / day drift stopped after two weeks of intermittent operation. I am now trying to isolate a 4uV / deg C thermal EMF but I'm not detecting any daily drift more than say 2uV / day. I don't try to measure absolute values to this precision, I measure the difference between two identical systems with an HP34420A Nanovoltmeter.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on September 12, 2017, 10:42:12 pm
general question - Is the chip to package attachment epoxy or solder? Because the back side of the chip is electrically conductive to the case, doesn't that indicate that solder is the chip attachment method? Or is there a conductive epoxy with <<1 ohm of resistance used inside chips?

There have been a few photos of decapsulated packages that have been added to this thread (a google image search is probably more helpful than the forum search facility). I suggest that you judge for yourself  but I would say that it looks like epoxy.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: chuckb on September 15, 2017, 07:57:45 am
general question - Is the chip to package attachment epoxy or solder?

I sacrificed another good 2DW234 for our general knowledge. This unit was produced in the last few months. I removed the case and saw the familiar white RTV covering the chip. My friend Jim, the one with the microscopes, used a very sharp scalpel and pried the chip off of the header. The chip cracked in the process. It may not be clear in the pictures but there is solder on the bottom of the chip. The grain pattern on the solder matched the grain on the metal of the header.

The LTZ1000 uses epoxy for the die attachment. But this "normal chip" uses the normal process of solder for die attachment.
 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: floobydust on September 15, 2017, 10:05:06 am
There's some die pics (OP's links) of older and relatively recent parts here: http://bbs.38hot.net/forum.php?mod=viewthread&tid=120731 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=120731)
With the lid off, one pic of the 2DW energized and the die edges emitting light, like an LED   :-//  I have no idea if photons are expected.

If that is white RTV, I'd wonder if the off-gassing reacts with the die, seems like the wrong material to use?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: floobydust on September 15, 2017, 10:34:25 am
Found 2017/7 posts from bbs.38hot.net, I thought worth reposting a few pics here:

2DW232 reference http://bbs.38hot.net/forum.php?mod=viewthread&tid=228933 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=228933)
Designing an oven: http://bbs.38hot.net/forum.php?mod=viewthread&tid=60144 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=60144)
Drift measurements: http://bbs.38hot.net/forum.php?mod=viewthread&tid=224449 (http://hhttp://bbs.38hot.net/forum.php?mod=viewthread&tid=224449)

You can run a URL through google translate.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on September 15, 2017, 06:13:10 pm
The reference circuit from 38hot looks odd: It uses 4 ref chip for averaging (in series mode), but still has the chips in parallel and uses an amplifier to make a 6.3 to 10 V step. The more logical way would be having 2 chips in series (and still maybe 2 in parallel if really needed) and than use a divider for 12.6 V to 10 V. This would result in less sensitivity to the resistors.

The filtering used is also odd, as most of the filtering only effects the amplified part. It also uses 2 OPs - one should be sufficient.

The heater circuit looks like mainly a proportional control, in a way they can't decide between using an heater resistor and the MOSFET as a heater. The way the mosfet is controlled (with no source resistor) is also somewhat odd - the TC of the MOSFET can have quite an negative influence. The mechanical setup looks somewhat interesting, but could be a problem with stress to the board.

The white mas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: julian1 on October 01, 2017, 11:49:13 am
This is a bit frustrating. I had a 34970a logging my 2dw232 reference since late March to try and extract drift information. Unfortunately the data-logger has limited on-device storage, and truncated the observations to only the last two months of data. I should have verified everything was working and/or periodically offloaded the data, but failed to properly track the project.

The main resistor dividers and current limiting resistor are vishay z201. The reference was placed in a slightly opened carboard box to reduce air circulation, but is not otherwise temperature stabilized. The 2dw232 itself is temp stabilized, with a heater resistor and makes use of the temp-sense feedback voltage from one of the zeners. There are two thermocouples - one loose in the box, and another epoxied to the pcb board.

(http://blog.julian1.io/public/images/2dw232-long/DSC03376.JPG)

A plot over time shows the reference voltage and board temperature. The sample interval is 10 minutes, 8333 obs, over 57 days.

(http://blog.julian1.io/public/images/2dw232-long/output/plot-01.png)

A plot using reference V versus the board thermocouple temperature,

(http://blog.julian1.io/public/images/2dw232-long/output/plot-03.png)

Temperature effects dominate and I can't really identify long term directional change - maybe it's increasing.

One point, is that I am not really sure how much of the obvious temperature sensitivity to attribute to the reference and how much to the data-logger which is exposed to fairly wild room temperatures - from around 0C to 20C. Theoretically at least, with the expensive Vishay resistors the 2dw232 ought to be better than the lm399 of the data-logger.

The original intention was to run three different references, so that any variance would be revealed over and above temperature effects.

I will try to post the schematic when I get kicad installed again.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: chuckb on November 27, 2017, 11:39:44 am
After testing some factory fresh 2DW234 parts from Technix I notice the voltage grouping was surprisingly tight. This was at 50 deg C and 10ma. Also when the voltage was a little high it had a positive temp co. When the voltage was low it had a negative temp co. See attached.

Andreas saw a similar result when he plotted LM399 unheated temp co vs voltage. I stole his graphic because I liked it and I attached it here.

The parts I got from different suppliers on TAOBAO were low noise but many of them would not reach a minimum temp co unless I ran them at 80 deg C and 20 ma.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: cellularmitosis on April 28, 2018, 07:01:25 am
This is a bit frustrating. I had a 34970a logging my 2dw232 reference since late March to try and extract drift information. Unfortunately the data-logger has limited on-device storage, and truncated the observations to only the last two months of data. I should have verified everything was working and/or periodically offloaded the data, but failed to properly track the project.

The main resistor dividers and current limiting resistor are vishay z201. The reference was placed in a slightly opened carboard box to reduce air circulation, but is not otherwise temperature stabilized. The 2dw232 itself is temp stabilized, with a heater resistor and makes use of the temp-sense feedback voltage from one of the zeners. There are two thermocouples - one loose in the box, and another epoxied to the pcb board.


Hi julian1, any update over the past 6 months?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Vgkid on April 28, 2018, 07:17:19 am
His last date online was Dec 07,2017...
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on May 27, 2018, 10:50:42 pm
I wonder if someone managed to finalize a low noise, temperature stablized and temperatur regulated voltage reference with the devices? All work shown here is still more or less under construction.
I started a few measurements on a sample too, but planing is still in progress.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on May 28, 2018, 04:33:21 am
Sad to read about that and sad that we lost the connection to the chineese volt nuts, seems like they want to be on their own.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on May 30, 2018, 08:33:59 pm
After some experiments with a first 2DW232 specimen and a single diode I had the feeling that, even though everything was thermally shielded and put inside a cookie box, the reference was still very sensitive to humans presence. I than paralled both zeners and everything improved significantly. I'm not sure why, but maybe the open anode of the second diode leads to some rectification?

I use a 1k pww resistor supplied by 12V from a LT3042 demoboard and a lab power supply. Furthermore I machined some aluminium rod with a 8.2mm hole for the zener drilled into it and a flat on the side with a crystal heater (40.8 ± 1.5 °C and a stability of <0.1K) glued to it that I still had laying around from fromer experiements. The stability is currently beyond my measurement capabilities and limited by my meter (Prema5017 SC). So I think I need to board everything together with a boost stage or at least a buffer and start measurements on our 3458A at work.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on May 31, 2018, 12:39:07 am
I'm probably wrong, but I don't remember anyone posting the results of paralleling the two Zeners before. We've certainly got data for with and without the forward biased diode junction but I don't remember parallel.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on May 31, 2018, 01:00:18 am
The TC of the zener depends on the current. A 12 V supply and a 1 K resistor means about 5-7 mA. This is one the high side to get a low TC from just a Zener and likely and the low side for having both diodes in series. So both zeners in parallel likely reduced the TC a lot as the current per diode got lower. It might need even lower current to get zero TC (more like 1-2 mA per diode).

I also have not seen both diodes in parallel, but this is an option if the noise from a single diode is too high.

The general idea to get a very stable voltage with the 2DW23x is to choose a current for low TC and than add some temperature stabilization. A low TC reduces the requirements for the regulation and the even a crude regulation makes the TC adjustment less critical and takes care of the temperature dependence of the TC.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: cellularmitosis on May 31, 2018, 01:12:13 am
Has any tried adding a resistor from the mid-point to either ground or VCC, to inject or steal some current, so that a different amount of current is flowing through the zener vs the diode?

I had this idea after reading about how the zero-TC point can be impractical on some units (~40mA).  I'm guessing that getting independent current control through each component would allow for a much lower current zero-TC point.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on May 31, 2018, 01:14:10 am
The TC of the zener depends on the current. A 12 V supply and a 1 K resistor means about 5-7 mA. This is one the high side to get a low TC from just a Zener and likely and the low side for having both diodes in series. So both zeners in parallel likely reduced the TC a lot as the current per diode got lower. It might need even lower current to get zero TC (more like 1-2 mA per diode).

Not necessarily so. The 1N829 temperature compensated zeners (conventional and zener in series in one device) are specified at 7.5mA for a 5ppm tempco. As always, the exact diode characteristics are going to determine the outcome but 5-7mA isn't out of the plausible range for a low tempco.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on May 31, 2018, 01:48:10 am
The 1N82x diodes and AFAIR also the 2DW23x are specified for 7.5 mA. However most of the reports so far show that for series connection the zero TC current is more like 10- 30 mA or even too high.

The bad (and more common) case it with a zero TC current too high and thus a negative TC - the case of less than 7.5 mA is not that bad as there is more room to reduce the current than to go up.

Having a different current for the zener and forward diode gives a few more options for adjustment, but not really significant.
For both the zener and the forward diode is takes more current to get a more positive TC. So if at all it might help to reduce the forward diode current if the compensating current is on the low side - though this is the easier and rare case anyway. A much higher current for the forward diode would cause quite some extra heat at the resistor.

There is in theory the option to use the forward diode voltage to set the current through the zener. I have shown such a circuit earlier in the thread. This would give a more negative TC and thus shift the zero TC current up. Thus is might be an option if only one diode in forward direction is used - still both diodes in parallel are likely higher current and lower noise.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on May 31, 2018, 05:40:01 am
No problem with the noise of a single zener. A first quick & dirty measurement showed 498.86nVpp with 122.53nV standard deviation of a single device (see attachement). As I said, I'm currently limited with my meter I have at hand in my privat lab (integration time 40s).
I have a few LT1001 laying around and will need to setup a board with boost to 10V circuit to get depper into it. With the current setup (zener + heater) as described above and imperfect thermal isolation the circuit draws 12mA @ 13V.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on May 31, 2018, 08:41:19 am
Quote
It may not be clear in the pictures but there is solder on the bottom of the chip. The grain pattern on the solder matched the grain on the metal of the header.

I don't think the die is soldered, but may glued with conductive glue. Soldering is not common, would show in a different surface and would not peel of of the case the way your pictures suggest.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: AG7CK on May 31, 2018, 11:59:30 am
The TC of the zener depends on the current. A 12 V supply and a 1 K resistor means about 5-7 mA. This is one the high side to get a low TC from just a Zener and likely and the low side for having both diodes in series. So both zeners in parallel likely reduced the TC a lot as the current per diode got lower. It might need even lower current to get zero TC (more like 1-2 mA per diode).

Not necessarily so. The 1N829 temperature compensated zeners (conventional and zener in series in one device) are specified at 7.5mA for a 5ppm tempco. As always, the exact diode characteristics are going to determine the outcome but 5-7mA isn't out of the plausible range for a low tempco.

Your 5-7 mA is imo reasonable and reminds me of an handwritten label I saw in a video years ago.

---

Easy find: Ca. 14:00 minutes & 6.5 mA for 1N829A:

https://www.youtube.com/watch?v=onqsjDJq4I0 (https://www.youtube.com/watch?v=onqsjDJq4I0)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: pigrew on June 05, 2018, 03:25:14 pm
I ordered a set of 2DW232 from AliExpress, and they were delivered last week (no time for measurements, yet).

They ended up being "15-4" date code with a painted red dot on each. Inside, they have the smaller die (barely larger than two bond pads), covered in the white RTV-silicone-like substance.

The wire-bonds are not gold. I left a 2DW232 in salt water for the day, and the wirebond is still intact. I'll assume they are silver (which has a reasonably low thermal voltage with respect to copper and gold).

Why is the silicone used? One total guess is that it is to block the emitted light (mentioned earlier in this thread, I've not looked for it) in order to reduce the coupling between diodes?

Also, an interposer layer would be a good idea in order to reduce mechanical stress, though this would likely require a third bond pad and a more complicated silicon process to maybe do an extra implant for a top-side contact.

The leads are magnetic, and don't seem to easily rust, so I'll assume they are kovar.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Cerebus on June 06, 2018, 12:13:22 am
The wire-bonds are not gold. I left a 2DW232 in salt water for the day, and the wirebond is still intact. I'll assume they are silver (which has a reasonably low thermal voltage with respect to copper and gold).

An odd assumption when aluminium bond wires are common and aluminium doesn't corrode in the presence of chloride ions (or all my aluminium cooking pans would have some big holes in the bottom).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on June 13, 2018, 06:19:17 am
I managed to put some parts together (2DW232 with both diodes paralleled, PTF56 resistors and LT1001) on a protoboard and to mount a selfmade aluminum heat sink (a rod with a flat and a crystal heater glued to the flat) to the zener diode. I didn't meet the 10V yet and the circuit needs some trimming, but it's ready to go for first measurements on the 3458A.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on June 13, 2018, 06:38:09 am
The noise could very well be mainly the noise of the meter (e.g. LM399 reference). If the reference is as good as hoped for (the best reports so far)  the noise level of just the reference should be much lower.  To really get an idea of the noise it would take something like the difference of 2 zener diodes.

If you want to make a stable 10 V reference from 2DW232 is would be a good idea to start with 2 of the zeners in series (could also be the old style bridge circuit) to give some 10.6 V. The divider down to 10 V is than less sensitive to resistor drift than an amplifier starting from 5.3 V or 7 V.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on June 13, 2018, 06:42:36 am
Quote
The noise could very well be mainly the noise of the meter (e.g. LM399 reference).

That is exactly the case, that's why I measured with two different integration times to see this effect. I currently build a second board with exactly the same parts, still on protoboard level.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on June 18, 2018, 08:07:12 pm
During the last days I measured the "10V"-output of the 2DW232 reference with our 3458A. Seems like I do have a negative T.C. problem. However, the measurement represents the extrem small noise of the reference. Hence, there is a lot of potential inside this small little puppy, so time to dig further into making everything a bit more stable.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on June 19, 2018, 01:08:02 am
The TC of the reference depends on the zener current, with a more positive TC for a higher current. For the 10 V reference there is also the TC of the resistors to set the gain (or divider if 2 refs in series are used).  For those temperature compensated zeners (e.g. old time standard 1N829) it was common practice to adjust the TC close to zero by choosing the individually suitable current.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Magnificent Bastard on June 19, 2018, 01:32:32 am
During the last days I measured the "10V"-ouput of the 2DW232 reference with our 3458A. Seems like I do have a negative T.C. problem. However, the measurement represents the extrem small noise of the reference. Hence, there is a lot of potential inside this small little puppy, so time to dig further into making everything a bit more stable.

-branadic-

Can you say what the horizontal units are?  (hours, or minutes, or..?)  It looks like that there is nearly one-division of time lag between a temperature change and the resulting voltage change...
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on June 19, 2018, 03:07:48 am
The horizontal time scale is 342.290 * 4s / 3600 / 24 = 15,85 days.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on June 30, 2018, 08:39:13 am
After some analysis of the data I found a lag between voltage and temperature f ~570 * 4s = 38min. How? I used cross-correlation (Ocatve function xcov) and searched for the minimum. I than adjusted data by the found time lag and calculated correlation coefficient and the result is almost -1.
This is a good way to also evaluate humidtiy time constant.

However, circuit now needs some modification to get rid of it.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on June 30, 2018, 01:46:23 pm
Hello branadic,

38 minutes is quite large.
So either a large thermal mass is involved (3458A?) or the temperature sensor is not at the place of interest. (zener / DMM).
Perhaps you need more than one temperature sensor to decide between DMM or zener.

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on June 30, 2018, 07:35:26 pm
Hi Andreas,

38min is the change of voltage of the reference (inside a package of cotton covered by a small cookie box) by ambient temperature. So yes you are right, I need to dig into that and put a temperature sensor inside the cookie box, close to the reference.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 22, 2018, 06:09:52 am
To understand a device you need to understand the datasheet, here is part 1.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 22, 2018, 06:35:28 am
And the second part.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 22, 2018, 06:55:46 am
Looking at the given datasheet values results in an individual resistor between 800R (6V) to 700R (6.5V) for the circuit zlymex showed. So the parallel connection of the diodes I tryed is not the intended use. Need to solder a lil' bit and change my configuration.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 22, 2018, 07:42:14 am
What is interesting between two datasheets is the pin assignment:

Yongguang Elektronik Co., Ltd. states:
Output 1 indicates the negative terminal with color point, 2 is positive terminal, and 3 is empty.

While Shenzhen Shenxin Electronics Co., Ltd. states:
The color point of the pin "1". "2" is the negative end and the other end is the positive pole. At the end, the pin "3" is the spare pin.

So what is now correct for the Shanghai 17th Radio Factory diamond zeners that have been spread here?

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: technix on August 22, 2018, 07:53:32 am
What is interesting between two datasheets is the pin assignment:

Yongguang Elektronik Co., Ltd. states:
Output 1 indicates the negative terminal with color point, 2 is positive terminal, and 3 is empty.

While Shenzhen Shenxin Electronics Co., Ltd. states:
The color point of the pin "1". "2" is the negative end and the other end is the positive pole. At the end, the pin "3" is the spare pin.

So what is now correct for the Shanghai 17th Radio Factory diamond zeners that have been spread here?

-branadic-
For the 17th Radio Factory, they make dual Zeners. One of the pin is shorted to the case, that pin is the common pin. It can be either common anode or common cathode, depending on what you ordered.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: GigaJoe on August 23, 2018, 03:29:24 am
was there any data about long term stability? or I missed it?
or it just something for a short term stability with very low noise ?
Does it make sense  to spare an effort for building something for a long them,  or rather move to LT1021,1027, ad587 ( I'm starting to hate all this low tempco precision resistors game)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Magnificent Bastard on August 23, 2018, 04:23:07 am
was there any data about long term stability? or I missed it?
or it just something for a short term stability with very low noise ?
Does it make sense  to spare an effort for building something for a long them,  or rather move to LT1021,1027, ad587 ( I'm starting to hate all this low tempco precision resistors game)

These are buried (subsurface) Zener diodes, and so their LF noise time-drift should be inline with anything else you can buy with one of these type of diodes.  The operating current multiplied by the die temperature is what drives time drift rate with these.  The LF noise is related to 1/sqrt(Iz), so the operating current is a trade-off between time drift and LF noise.  At 5mA Iz, and a 45oC die temperature, I would expect less than 1ppm/a time drift, and less than 1uVpp of LF noise.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 23, 2018, 04:43:12 am
The only data published can be found here (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=258883)

Partial translated:
"...Most devices have a 100-hour stability within 20 ppm. If the voltage change caused by the temperature is subtracted, then the true time drift may be smaller. Therefore, it can be said that there is no tendency to have any divergent drift. However, in view of the fact that there is still a lack of longer and more reliable data to prove, it is not yet possible to draw conclusions..."

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on August 23, 2018, 06:23:13 am
One problem with the 2DW232 refs seems to be rather wide scattering in properties, not just between sources, but also between the ones form a single batch. So the data-sheets are of a limited value - quite a few data shown in this thread show performance outside the specs. There is a tendency to need more current to get zero TC.

The reference itself is supposed to be a burried zener. However besides the intrinsic drift of the silicon, there is also a possible stress effect, e.g. from glue / solder to fix the chip to the case and a possible cover / case. So not all buried zeners are the same with drift. The quoted 20 ppm for 100 hours seem to be for a higher temperature (e.g. 100 C) - so this might be reasonable good, if used at a more moderate temperature. Given the large deviations from the DS so far, the drift data may not be that reliable. It takes years and a large number of refs tested to really know.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 23, 2018, 06:35:21 am
Don't call it problem, call it a challenge  :-+

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: GigaJoe on August 23, 2018, 11:03:42 am
buried (subsurface) Zener diodes, and so their LF noise time-drift should be inline with anything else you can buy with one of these type of diodes. 

I have a doubt about it, if the process would be so simple, then anyone can reproduce it.  But problems to grow a prefect semiconductor lay in  millions layers. starting with a regular process parameters, and quality of raw materials, and finish with fancy problems like unwanted injection of atoms that disrupting a structure, or metal atoms diffusion from conductor  that connecting atoms to output legs .... So it not soo simple ....

The variation of crystals may indirectly indicate an overall quality - that means a significant effort for selection, and even this doesn't guarantee a long term stability for a simply reason, during manufacturer process crystal was contaminated, and defects slowly spreading ....

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on August 23, 2018, 03:04:51 pm
These are buried (subsurface) Zener diodes,

Hello,

I cannot find this term in the translated data sheet.
So my guess: they are (low noise) temperature compensated zeners like 1N821-1N829a

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: GigaJoe on August 23, 2018, 03:20:22 pm
it seems all long term  stable zeners in use technique called buried zener ... it a common name may not reflected in a documentation, if marketing dept. will not insist on ...
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on August 23, 2018, 03:53:00 pm
it seems all long term  stable zeners in use technique called buried zener ...

no,

buried zener is generated by a special ion implant method
(which is more costly than a planar zener).

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 30, 2018, 02:16:14 am
Corrected the table in the translated datasheet in post #507 (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/msg1763462/#msg1763462)

Currently I do some zero t.c. current measurement in the intended configuration on one device, while I'm still not sure if the zener is connected correctly or if I really understood the datasheet. Pin 1 (red dot) is used as the output, while pin 2 is connected to ground and pin 3 is left open.
I use a QH40A crystal heater mounted on a flat of an aluminium rod. The rod has a through hole of 8.2mm in which the diode fits in. Further I use a SMT172 sensor in TO18 package, that is thermally connected  to the reference diode. Attached are the first results of my measurements.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 30, 2018, 09:25:25 pm
For me it looks like the datasheets available on the web have nothing to do with the 2DW232 devices on my desk. I can't find a resistor value that leads in a t.c. as low as 5ppm/K.
It's the first device I'm analyzing, but it leaves a bad tasting. As far as I can see Wolfgang investigated on 2DW233 and 2DW234 (http://hololaser.kwaoo.me/electronics/2DW23x.html) and found also values, that have nothing to do with the datasheets.
Maybe I get the datasheet wrong? Any comments on that?

Added first results of different specimen @ approx. 5mA.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on August 31, 2018, 01:23:05 am
One problem with the data sheets is that there seem to be several manufacturers (and additional fakes) for the nominal same part. However the parts seem to be quite different, with higher and lower noise parts.

Other here in the thread have have also observed that it would need quite a bit more than the nominal 5-10 mA to get a zero TC. So the shown curve are kind of typical for the part seen so far, though there where a few to reach zero TC below 20 mA.

At least with some other parts that had such a high current in series mode, there is a second option to use the reference. When using the zener diode alone, chances are the TC can cross zero at some 1-3 mA. So those diodes that would need to much current in series mode might still be useful in single diode mode.

Even with getting zero linear TC by choosing the right current, there is quite some second order part. So for a really constant voltage it would likely need temperature stabilization anyway. Still a low linear TC reduces the requirements.

The single diode more would give some 5.3 V and this can also be an advantage: with 2 such diodes in series (or as a bridge) one would get some 10.5 V and thus a less sensitive divider down to 10 V.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 31, 2018, 01:43:56 am
Well, I will try the rest of my devices, there is still a bunch of diodes left. But I will also try to parallel the zeners and to connect a silicon diode to form a temperature compensated zener. Don't know about what this results in, but it's worth a try to see what happens. Therefore I cut the common lead and solder a smd silicon diode to the case.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on August 31, 2018, 02:08:21 am
Using a normal diode together with the zener will likely not work very well: The forward voltage in the 2DW232 is rather high and thus the TC of the diode is low. So if at all it would need a similar high forward voltage diode (e.g. BAV199, maybe a zener) to get a comparable result. To get a lower current for zero TC it would need an even higher forward voltage and thus less TC for the diode.

The second problem it thermal coupling that is not that good and could lead to extra thermal induced noise.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on August 31, 2018, 04:40:15 am
Maybe I get the datasheet wrong? Any comments on that?

Hello,

there are only 2 test-temperatures specified in the data sheet. 25 deg C and 75 deg C
the slope through these 2 temperatures should be less than 5 ppm/K
(nothing specified in between).

so between the 25 deg C and 75 deg C point the difference should be below 50K * 5ppm/K * 6.2V = 1.6 mV at 5 mA test current.
provided that you use pin 1 (with dot) as negative pin and both diodes in series.

with best regards

Andreas

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 31, 2018, 04:45:56 am
Andreas, two different datasheet give two different connection schemes:

1. "Polarity arrangement: output 1 indicates the negative terminal with color point, 2 is positive terminal, and 3 is empty. "
2. "The color point of the pin "1". "2" is the negative side and the other side is the positive side. At the end, the pin "3" is the spare pin."

One the other hand there is a diagram in one of the datasheet showing the output voltage over the whole temperature range (-55 ... + 125°C). Since now I used pin 1 as the output pin. I will change the connection to see if there is any difference.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on August 31, 2018, 04:56:25 am
Andreas, two different datasheet give two different connection schemes:


overlooked that: so which of the 2 data sheet corresponds to your devices?

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 31, 2018, 05:11:35 am
By now? None of them.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 31, 2018, 07:06:51 am
Meanwhile I measured three devices and the third device also in reverse connection. 750R (General Radio Type 1434-G) resistor on 9.984V from a LT3042 board that is powered by a lab supply, so almost 5mA.
I also plotted voltage vs. current for this measurement. Interesting to note, the values fit to a straight line.
Next step is to measure the individual zener on the third device.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SZA263 on August 31, 2018, 07:38:07 am
My devices (Technix) differs from the datasheet. The divice is composed by two 5,36V@5mA zeners connected in Common Kathode.
So with the connection suggested in DS, color dot (pin1: Yel in my 232's Red in my 233's) on the negaive side and pin 2 on the positive side, one diode is used as a true zener and the other as a temperature compensating diode.
My device (random pick from a batch of 20) is mounted alone in a small cardbox and is connected to a quite stable power supply (Tek PS501-1) via a 770 ohm 50 ppM resistor.
The voltage of the compensated zener (two diodes in series) @5mA is 6.06236V (Datron 1062) and the Tc (with the normal room temperature variation) il less than 5 ppm/°C.
(DUT or measuring instrument drift?) :-//
Heating it with a finger, shows a little positive Tc, but it fully agrees with the DS data: the zero Tc point is obtained at about 60°C @5mA, with a positive Tc under this temp and a negative Tc over.
I am running the device at 25..28°C so it is operating on the positive Tc side of the curve. A brief test a 3.3mA shows a better behaviour in this range of temperature.
I need to do a more extensive and accurate test on the device, but at first sight it seems to me very good.
No test on noise and long term drift (WIP).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 31, 2018, 07:49:37 am
I got my devices from VintageNut, not from Technix. They are common cathode too. Currently I'm running measurements on the single diodes.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SZA263 on August 31, 2018, 08:22:17 am
If you want to use a single diode, you should run it with a much lower current (say few hundreds of uA), but this will increase the noise and the differential resistance of the zener.
But why? The device is intended to run with both of the diodes in series, like any other Tc compensated device. LTZ1000, LM399, SZA263, LTFLU and the 1N821..9 devices are based on a diode-zener series.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 31, 2018, 08:43:12 am
Just for investigation to understand, what is wrong with the devices I have.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on August 31, 2018, 04:37:01 pm
If you want to use a single diode, you should run it with a much lower current (say few hundreds of uA), but this will increase the noise and the differential resistance of the zener.
But why? The device is intended to run with both of the diodes in series, like any other Tc compensated device. LTZ1000, LM399, SZA263, LTFLU and the 1N821..9 devices are based on a diode-zener series.

The zeners inside seem to be quite different. For a device close to the DS performance the series mode with a current in the 5-10 mA range is good, if this gives a low TC.
However the ones Brandic has would need too much current (e.g. > 50 mA) to reach the zero TC point. So the series mode is not a real option. Chances are they might be useful with just the zener. Because of the different zener the zero TC current in just Zener mode is expected to be also higher, so more like 2-5 mA.  There seem to be a larger 2nd order effect though - so the series mode has some advantage, but needs diodes to get low TC at a reasonable current.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SZA263 on August 31, 2018, 06:22:34 pm
Please don't forget the self-heathing effect due to the power dissipation of the device.
The thermal resistance Junction to ambient (Rth-ja) of 2DW23x is not defined in DS, but i think it is about 400K/W. A DO35 case (1N4148) has 300K/W but the chip is bonded to two huge (referred to chip dimension) terminals, while  2DW has only one side bonded to case.
One of the Branadic's plots shows a working point at about 6.2V 30mA., very close to the power dissipation limit of the device (200 mW), and in this case the junction is at a temperature about 80 °C higher of the ambient. So the temperature plot (Branadic's 26-38 °C) is seen by the point of view of the junction as a 106-118 °C span, rather lower if seen in K or %.
If the device could survive with a power dissipation of 2.5 W, the junction will be at 1000 °C, and the 12 °C ambient variation will cause a very,very low drift...
My 2DW232 DUT used as datasheet @5mA without any exotic medium has a Tc less than the declared 5 ppM/K.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on August 31, 2018, 11:00:26 pm
Again, picked up a random device. It's again common cathode with:
pin 3-1: 5.27175V @ 5mA (942.5R on 9.984V)
pin 3-2: 5.2688V @ 5mA  (943R on 9.984V)

Did the same measurement as before, thus 790R (GenRad) on 9.984V and changing temperature, with the reference connected as follows: pin 1 to ground and pin 2 to the resistor. I don't see any difference to the results before.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 01, 2018, 04:50:54 am
So I have characterized the single diodes of reference #4 in forward and backward direction @5mA. I found the t.c. as follows:

Pin 3-2: 464.37µV/K
Pin 3-1: 476.5µV/K
Pin 2-3: -1.5925mV/K
Pin 1-3: -1.589mV/K

So maybe the package with the additional pin3 for the common connection is not by accident but for an extra resistor to control the current through the compensation diode?

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on September 01, 2018, 04:58:01 am
So I have characterized the single diodes of reference #4 in forward and backward direction @5mA. I found the t.c. as follows:

Pin 3-2: 464.37µV/K
Pin 3-1: 476.5µV/K


Hello,

so the zener voltage is too low.
(zener tempco usually increases with zener voltage).

did you test the dynamic resistance of the zener too?

with best regards

Andreas

edit:
mhm from this diagram:
https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=510608 (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=510608)
you have more than 10 ohms dynamic resistance (more than 10mV/mA near 5 mA).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 01, 2018, 05:10:50 am
Quote
did you test the dynamic resistance of the zener too?

No. How would you measure it? Typically to measure it, a small AC signal is superposed on a Zener current and measured as the differential impedance. But how should I do that?

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on September 01, 2018, 05:12:05 am
see edit above
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 01, 2018, 05:35:07 am
So if I get you correct you come to the same conclusion, 5mA is to small for that parts and I need to get to much higher currents?

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on September 01, 2018, 05:42:17 am
I would not expect the thermal resistance to be that high. The normal TO5 is around 200 K/W. Self heating can be a problem, but it still makes sense to use the external temperature to define a TC. Self heating would be mainly a constant shift in temperature.
A rather high current and thus high power can be still a problem as trying to stabilize the temperature would about double the power consumption. So a current much above 10 mA is likely not practical.

Reducing the current through the forward diode would make the TC even worse.  Though not very attractive because of 2 extra resistors involved it would be possible to use only about 1/4 to 1/3 of the forward diode voltage. This way one could adjust the linear TC at a given current.

As the operating current does not match the DS, it might be worth checking if the diodes are at least very low noise. If the noise is not really low, it might not be worth looking for a way to compensate the TC.

My best guess would be using these "high current" diodes in a zener only mode, at a current lower than 5 mA. Maybe 1-2 mA could lead to a low TC and the noise might still be acceptable. With a slightly temperature dependent current (use the other diode), the zero TC point could be shifted to a little higher current.

The Zener impedance would be from a superimposed AC current and measuring the AC voltage. With typical a few 10 Ohms the 1 K resistor to provide the DC current could be ignored. Its not about precision but order of magnitude. A good zener would be < 10 Ohms, > 50 Ohms could be a problem.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SZA263 on September 01, 2018, 06:14:37 am
Quote
No. How would you measure it?
If you want calculate the dynamic resistance of a zener @ 5mA simply take the zener voltage at a little lower current Imin (say 4.9 mA): call it Vmin; then take the voltage at a little higher current Imax (say 5.1 mA): call it Vmax. The dynamic resistance , linearized around 5 mA is  Rd = (Vmax - Vmin)/(Imax - Imin)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 01, 2018, 06:31:33 am
Cracked diode #3 open and found the same white stuff covering the silicon as shown here before in post #420 (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/msg1169715/#msg1169715). So this devices I received from VintageNut are not the ones zlymex presented here.  :--

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on September 01, 2018, 06:34:58 am
So if I get you correct you come to the same conclusion, 5mA is to small for that parts and I need to get to much higher currents?

the 6.05 V at 5mA are obviously too low to get a good compensation.
So you might have more luck if you select for devices with 6.2 ... 6.4 V @ 5 mA. (both diodes).

with best regards

Andreas


Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 01, 2018, 08:46:44 am
Quote
the 6.05 V at 5mA are obviously too low to get a good compensation.
So you might have more luck if you select for devices with 6.2 ... 6.4 V @ 5 mA. (both diodes).

Well, then none out of 12 devices do match this criteria, as 11 out of 12 devices are below 6.1V. I currently test the one with the highest voltage of around 6.12V @ 5mA over temperature, but as I alway say: Hope dies last, but it dies.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 02, 2018, 12:03:50 am
As stated before, the diodes I have are far away from what is presented in the datasheets. Zero t.c. current for diode #7 is in the order of 23 - 24mA, still searching for the exact point. However, far far away from 5mA. An the rest of the diodes will need even higher currents to get to zero t.c. point.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Magnificent Bastard on September 02, 2018, 01:15:11 am
As stated before, the diodes I have are far away from what is presented in the datasheets. Zero t.c. current for diode #7 is in the order of 23 - 24mA, still searching for the exact point. However, far far away from 5mA. An the rest of the diodes will need even higher currents to get to zero t.c. point.

-branadic-

In engineering, "Just because you CAN, does not always mean that you SHOULD".  Yes, you can get compensation by operating these diode pairs in series, but you would be far better off running only ONE diode-- and then finding the current that gets you zero-TC at lab temperature.  This will produce an upside-down parabolic voltage curve with temperature.  By adding a thermistor (e. g. silicon type PTC) with a shunt resistor and with that in series with a larger resistance to equal the value you have found-- you can flatten-out that parabolic voltage curve almost exactly.  This "hybrid" resistance would be a current source for the Zener, the other end of which is connected to your 10V output.  Then, follow that by a zero-drift amp (e.g. opa189), and voilà, now you have a 10V reference.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Magnificent Bastard on September 02, 2018, 01:25:19 am
buried (subsurface) Zener diodes, and so their LF noise time-drift should be inline with anything else you can buy with one of these type of diodes. 

I have a doubt about it, if the process would be so simple, then anyone can reproduce it.  But problems to grow a prefect semiconductor lay in  millions layers. starting with a regular process parameters, and quality of raw materials, and finish with fancy problems like unwanted injection of atoms that disrupting a structure, or metal atoms diffusion from conductor  that connecting atoms to output legs .... So it not soo simple ....

The variation of crystals may indirectly indicate an overall quality - that means a significant effort for selection, and even this doesn't guarantee a long term stability for a simply reason, during manufacturer process crystal was contaminated, and defects slowly spreading ....

Go to http://translate.google.com (http://translate.google.com) (or use the chrome or chromium browser), and then type in this URL: http://bbs.38hot.net/thread-120731-1-1.html (http://bbs.38hot.net/thread-120731-1-1.html)
( >>>HERE<<< (https://translate.google.com/translate?sl=auto&tl=en&js=y&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fbbs.38hot.net%2Fthread-120731-1-1.html&edit-text=) is an "all in one" link if you are lazy ).


About 3/4 the way down in the page, we have a post by user Archwang:

"The discussion Ni originally "high power stability," page 68, PN zener diode emitting end portion work described herein to a breakdown occurs; surface Breakdown causes the device to be noisy. This is the case with the first two samples.  The new 2DW234 does not emit light when it is working, suggesting that the device is likely to have a buried structure. Moreover, according to the longshort altar friend's previous reminder, the two PN junction directions in this device are exactly opposite to other products, indicating that the production process has undergone major changes. The buried Zener in the literature report is also the formation of P-type impurity diffusion, which may be related to this change."
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 02, 2018, 02:23:04 am
Quote
In engineering, "Just because you CAN, does not always mean that you SHOULD".  Yes, you can get compensation by operating these diode pairs in series, but you would be far better off running only ONE diode-- and then finding the current that gets you zero-TC at lab temperature.  This will produce an upside-down parabolic voltage curve with temperature.  By adding a thermistor (e. g. silicon type PTC) with a shunt resistor and with that in series with a larger resistance to equal the value you have found-- you can flatten-out that parabolic voltage curve almost exactly.  This "hybrid" resistance would be a current source for the Zener, the other end of which is connected to your 10V output.  Then, follow that by a zero-drift amp (e.g. opa189), and voilà, now you have a 10V reference.

At a certain point, when playing with LMx99 and LTZ1000 there is a moment when you want to do it the way old engineers did, because you can learn a lot and develope a gut feeling for the things that you do. On the other hand, there are a lot of volt nuts out there, that started with 1N829 and the sort of references. I started with the game when such references became unobtanium or expensive. So going along this way is not a waste of time.
Specimen #7 won't be a travel reference, but a sample to learn from. So after I found the working point I will now go on. Thus I need to measure noise and that sort of stuff.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on September 02, 2018, 03:09:35 am
Measuring noise can be an important point. While some of the 2DW232 can be very good with noise, not all of them are. So there is little use in finding the exact zero TC point if turns out too noisy.

Sorting out the noisy ones could be faster than checking for low TC.

For those that don't work well (no low TC) in series mode, there is still the option of using only the zener (at much lower current) or using something like 1/3 of the forward diode.  It's not as good in many aspects, but still a possibility.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on September 02, 2018, 03:15:55 am
As stated before, the diodes I have are far away from what is presented in the datasheets. Zero t.c. current for diode #7 is in the order of 23 - 24mA, still searching for the exact point. However, far far away from 5mA. An the rest of the diodes will need even higher currents to get to zero t.c. point.

-branadic-

@branadic,

You're beginning to replicate some for the findings from the earlier days (wow 2016  :o) of this thread, you might want to go back and do some digging from about page 10. I also found the Zero TC turnover point (zener+diode in series) in the 20mA region, again well off 'published' spec. Alex found a Zero TC turnover point (zener alone) at about 1.4mA.

I also found that a potential divider across the zener, in the series zener + diode configuration yielded some promising results (Reply #264) when running at lower currents (~5mA) that you may want to try replicating with your better test gear. Diagram attached for reference.

Chris.


I've been playing around with the divider approach today and it looks as if it is possible to achieve very low TC values over a limited temperature range even with a simple hook up. I've attached the schematic for clarity but it's basically just taking the output voltage from a divider tap across the forward biased diode. I simply used a 2k cermet preset, it took a little tweaking but it looks as if the flat portion of the TC curve can be adjusted to any temperature and operating current, in this case about 23'C and is very flat over a few degrees. TC is sensitive to both divider ratio and supply current as you would expect.

Operating the device at 5.010mA with the divider (pot) measuring 765R / 1k3 the output of my sample is 5.878V  Temperature profile came out as follows (values relative to 23'C case temperature):

20'C     -12uV
20.5'C  -4uV
21'C     -3uV
21.5'C  -2uV
22'C     -1uV
22.5'C   0
23'C      0
23.5'C   -1uV
24'C      -5uV
24.5'C   -7uV
25'C      -14uV

Temperatures were measured during device warm-up (it finally settled at about 25.3'C) using a thermocouple taped to the side of the can. I was using a Geller SVR-T and Muirhead decade divider with Datron 1041M, null meter style. I repeated 3 times, each warm-up taking less than 5 mins, with consistent results (obviously the readings were a bit noisy at this level).

(https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=272784;image)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 02, 2018, 03:41:00 am
Quote
You're beginning to replicate some for the findings from the earlier days (wow 2016  :o) of this thread, you might want to go back and do some digging from about page 10. I also found the Zero TC turnover point (zener+diode in series) in the 20mA region, again well off 'published' spec. Alex found a Zero TC turnover point (zener alone) at about 1.4mA.

I also found that a potential divider across the zener, in the series zener + diode configuration yielded some promising results (Reply #264) when running at lower currents (~5mA) that you may want to try replicating with your better test gear. Diagram attached for reference.

Thanks for those comments. I currently found the time for playing with the diodes, so I'm a bit late. I already read through the complete thread and also found your approach, but denied it because of to many resistors being involved. I currently go on with #7 and if I stuck I maybe take a look at the option using one zener only.

Found the zero t.c. current at 23.2mA. I keep the reference mounted to the crystal heater. I received some small dewar type 00 C but found they are still quite big. So I will put everything inside a small flask together with some foam and cotton as thermal isolation.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on September 02, 2018, 03:50:31 am
That's good - I just didn't want you 'running out of steam' on them before being able to get some decent low TC measurments. I wouldn't be too concerned about the resistors - those were just roughly measured values from the 2k pot that I had strapped to it. Obviously they would become more critical for a stable reference but not particularly for TC evaluation.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on September 02, 2018, 05:42:08 am
The resistor part over the forward diode would be responsible for something in the 500 mV range and thus around 10% of the total voltage. So these resistors would be still less critical than scaling the voltage from 6 V to 5 V or 10 V.

Due to the relatively high power at a little over 20 mA of current, the thermal insulation should not be too good, other wise the temperature would be to high, from self heating alone.

If thermal regulation is used, the larger second order TC for the zener only version would not be such a problem.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 02, 2018, 08:07:20 pm
No problem Kleinstein, the thermal loss seems big enough so that the crystal heater is sourcing ~30 - 40mW.
If you like I can send you one sample so you can experiment by yourself and post and share your results over here. You are then able to show how you would operate this device.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on September 03, 2018, 04:22:45 am
Nice build  :-+

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 04, 2018, 05:09:37 am
Thanks Andreas.
I started a first 24h measurement the day before but had an issue with my wiring that was a little bit odd. So I rewired everything, connected the crystal heater from a seperate lab power supply to the 10V output of the LT3042 board and started the measurement again yesterday to see if everything is stable. But due to an error of the temperature system (SMTAS04usbmini) the record stopped after 2.3h. Damn  :--
However, the reference looks stable within that time at around 6.25025V and is still sitting there from what I can read on the front panel of the meter. The measurement seems to be dominated by the noise of my meter, so time to do the next step, noise measurement.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 06, 2018, 04:47:12 am
Repeated "longterm" measurement, this time I recorded about 18h but also measured low frequency noise (0.1 - 10Hz, replace micro by nano in the plots). Looks promissing, even though the current through the zener is high.

Furthermore I received some 2DW232 and 2DW233 from the netherlands today. Thank you very much. They differ by the fact, that they don't have a date code printed on top. So I will measure them within the next days to see how they perform.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: imo on September 06, 2018, 05:34:15 am
Why do you consider those diodes ultra low noise when they do ~400uVpp?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Echo88 on September 06, 2018, 05:35:42 am
"replace micro by nano in the plots"
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 06, 2018, 05:38:09 am
Quote
Why do you consider those diodes ultra low noise when they do ~400uVpp?

The scope can't be configured for a gain of 80dB of the low noise amplifier, so I configured it as x0.1 and the remaining 60dB is just a replacement of micro by nano ;)

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on September 06, 2018, 05:48:43 am
The noise data look really good. One has to consider that this should include the amplifier's noise as well. So only part of the noise if from the reference. So one should check the amplifiers own noise, with a short, or maybe a 7.2 V battery so that the input cap does get discharged)

I would suspect the temperature effect is more from the meter than from the reference.

The remaining unknown is the longer time drift. However this needs time and maybe a better meter.
 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 06, 2018, 06:02:54 am
Quote
The noise data look really good. One has to consider that this should include the amplifier's noise as well. So only part of the noise if from the reference. So one should check the amplifiers own noise, with a short, or maybe a 7.2 V battery so that the input cap does get discharged)

Did that already, but can repeat that and add it. It's the low noise amp from pipelie with 100nVpp noise floor.

Quote
I would suspect the temperature effect is more from the meter than from the reference.

Correct.

Quote
The remaining unknown is the longer time drift. However this needs time and maybe a better meter.

Not necessarily, the multimeter is okay for that, you just have to measure long enough.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 06, 2018, 09:37:56 pm
The references I received from the netherlands draw a different picture. I now get a positive t.c. at 5mA (6.37V reference voltage) so need to decrease the current through the diodes. Nice to have some different parts on the desk.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on September 07, 2018, 05:11:24 am
Hello,

which approximate T.C. at 5 mA?

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 08, 2018, 06:40:19 am
Added the results in the post above. The t.c. of this 2DW232 is to high even though the reference is running at 5mA. So maybe this is an outlier? I need to measure the rest of the references so we will see how they compare soon.

Another 2DW232 received today, this time from Italy and it was already characterized. Thank you very much.
To confirm the results I measured this reference with 770R. The current of 5.1mA in this configuration is a little bit to high, so the t.c. doesn't perfectly match but it's close to what is given in the datasheet. Next measurement is already running.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: imo on September 08, 2018, 08:06:43 pm
OT: what would happen if you feed the diode with a simple 2xPNP 5mA current mirror?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 08, 2018, 08:35:14 pm
Found almost zero t.c. current for that specimen at about 3.29mA which equals a 1.2k resistor on 10V.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 09, 2018, 08:54:33 am
Quote
OT: what would happen if you feed the diode with a simple 2xPNP 5mA current mirror?

Why should you? My goal is to use a circuit as shown in the first post of this thread, thus the boosted zener ouput voltage (10V on the opamp output) is feeding the zener itself through the current setting resistor. This is why I try to find to optimal current setting resistor while powering everything from a low noise 10V source for now. Next step is to calculate the optimal resistor values of the boost stage to get 10V.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 12, 2018, 02:28:36 am
Measured a little bit more at the italian sample and found, that this device shows excess popcorn noise. Attached are measurements of multiple temperature runs with 1k2 (3.29mA) and 1k247 (~3.16mA) as well as a 10h measurement at 3.29mA.
Need to investigate that a little deeper.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on September 12, 2018, 02:51:42 am
The popcorn noise looks really nasty / high amplitude. Give that these references are not that expensive, I would consider this one defective.
If at all it might be a candidate to investigate / demonstrate popcorn noise.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SZA263 on September 12, 2018, 03:35:54 am
The noise seems too high in amplitude and too regular in frequency. The jumps seems to appear every '500' of your time scale, and seems to not appear during cooling phase.
IMHO is a residual switching noise from the heater. Try to rerun a cycle with heater switched off, disregarding the absolute voltage variation, only to see if the noise is still present.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 12, 2018, 03:57:19 am
No, you can see the jumps in the temperature cycling measurements during cooling phase, which takes much longer then heating phase and includes a temperature lag between case temperature of the reference diode and the actual die temperature. The heater is simply turned on and heats up to ~38°C. I then wait a while for everything to temperature stabilize and I then turn of the heater. Because of the thermal mass and thermal capacity (aluminium rod) the setup slowly cools down. It's not a controlled cooling, but a cooling due to convection into free air. So there is no switching noise of the heater.

In the 10h measurement (last picture) the temperature was almost stable at about 38°C (heater was turned on for the whole time). So I don't think it is a heater switching, since the heater is not switching but regulating.

EDIT: I currently have a measurement at higher current (~5mA) with heater on (~38°C) running and up to now can't see any jumps, which also seems to prove that it is popcorn noise. The disadvantage is, that a better temperature stability is necessay, as this operating point is on the positive side of the t.c. curve with ~7ppm/K.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 12, 2018, 07:52:28 pm
Measuring long enough at 5.1mA (770R) proves there is (almost?) no popcorn noise visible and disproves the theory that the noise is due to the heater.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SvanGool on September 12, 2018, 08:42:40 pm
If I look at the discussion here and further: https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/msg1054431/#msg1054431 (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/msg1054431/#msg1054431), you are unfortunate because you are not measuring a device which has the zero TC and low noise point close to each other. I would quickly test some other devices that you have (hint  ;) ).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 13, 2018, 03:30:09 am
No, I'm not unfortunate, it's simply scientifics everyday, sometimes you loose and sometimes others are winning :)
I repeated the 10h measurement at 3.29mA and again can see excess popcorn noise so it's neither the heater influence nor a measuring artefact, but fact.

So the only option is to use this device at 5mA and because of positive t.c. with a more stable oven (https://www.eevblog.com/forum/projects/small-oven-for-2x-lt1236-(python-reference)-no1/msg608110/#msg608110). Work in progress...

Meanwhile I can again take a look at the samples I received from the netherlands ;)

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on September 13, 2018, 06:35:21 am
Hello branadic,

according to data sheet the zero T.C. point is more at 65 deg C than at room temperature.
Perhaps worth a try.

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 13, 2018, 06:57:33 am
Well, with respect to blackdog even shorting the resistor on the crystal heater would only give 50°C (https://translate.google.de/translate?sl=nl&tl=en&js=y&prev=_t&hl=de&ie=UTF-8&u=https%3A%2F%2Fwww.circuitsonline.net%2Fforum%2Fview%2F114717%23highlight%3Dqh40a&edit-text=).

Quote
The oven
The first problem is the temperature of the QH40A, which is about 41C and too low for my application.
The components that I mount on it also generate heat and then it goes roughly at 35 to 36 degrees, I estimate.
That means that kidney can be arranged more properly.
So ... that is "Reverse Engeneration" and that is successful, the circuit is very simple.
An opamp and a bridge circuit with a PTC of 2K in one leg.
The manufacturer has probably already taken into account a different temperature.
After I had drawn the diagram and what had counted on it turned out pretty simpe.
There is a 560 Ohm resistor in a part of the bridge, if you short-circuit it he will cut to about 52C.
Exactly what I needed to have him arrange reasonably on a summer day.

(http://www.bramcam.nl/NA/NA-01-Oven-Ref/QH40A-01.jpg)

So for 65°C it needs a different oven design. Where did you find 65°C? I had in mind that a t.c. value of 5ppm/k between 25°C and 75°C is given in the datasheet.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on September 13, 2018, 03:58:02 pm
Hello branadic,

according to data sheet the zero T.C. point is more at 65 deg C than at room temperature.
Perhaps worth a try.

with best regards

Andreas

The TC depends on temperature and current.  A relatively small change in current is sufficient to shift the temperature for zero first order TC. The curve in the DS is just an example curve.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on September 13, 2018, 04:12:36 pm

So for 65°C it needs a different oven design. Where did you find 65°C? I had in mind that a t.c. value of 5ppm/k between 25°C and 75°C is given in the datasheet.


https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=509624 (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/?action=dlattach;attach=509624)

See figure 1 (Typical curve)

ok its more 55 - 60 deg C for the flat top.

But it is a typical curve (so some reserve in temperature range cannot be bad).

with best regards

Andreas
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on September 14, 2018, 01:20:09 am
With changing the current one can adjust the linear TC and thus the Temperature where the zero crossing will occur.  With a just slightly different current one can usually (if the unit is OK)  get it at any point in the usual temperature range (e.g. -50 V to +150 C). There is nothing special about 55-60 C

So it is OK to first design the oven part for a suitable temperature and than adjust the TC via the current.  The oven temperature has to take into account the self heating that can be quite a bit if 20 mA are needed. 50-60 C could be a suitable temperature if high ambient is allowed for. With a moderate ambient it could be 45 C.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 14, 2018, 04:16:36 am
Even though it's not directly related to the topic I use this place to correct for the circuit of the QH40A heater here, as I've already linked to the circuit.

Quote
So it is OK to first design the oven part for a suitable temperature and than adjust the TC via the current.  The oven temperature has to take into account the self heating that can be quite a bit if 20 mA are needed. 50-60 C could be a suitable temperature if high ambient is allowed for. With a moderate ambient it could be 45 C.

Well, that's only half of the truth... for a portable reference you want low current, but also zero t.c. so you need to find a sample with zero t.c. at idealy room temperature on lowest current. Furthermore you have to watch for popcorn noise at this low current and prove that it's low noise. At the end it's a trade-off between temperature, current and noise.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on September 17, 2018, 05:53:16 pm
Did some measurements on the 5x 2DW232 samples from the netherland this weekend...

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: imo on September 17, 2018, 11:33:21 pm
Above diodes: that means 50-60ppm/C in an average?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on September 18, 2018, 02:20:53 am
The later diodes (no 2-5) seem to need a considerably lower current for low TC.
So these samples seem to be very much on the low current side opposed to the samples from the other source.

It is quite annoying having so much scattering. I thing they should do a little more binning / sorting in china, so one would know wether one gets a diode good for operation a 1 mA in series mode for a low power reference or one good for 5 mA in series mode if power is not an issue or one good for 1-2 mA in Zener only mode for a 5.2 V reference (to divide down to 5 V with little errors from the resistors). All 3 cases can be interesting, but different applications and normally different part numbers.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: GigaJoe on October 06, 2018, 08:05:11 am
this one , made in the 17th century, I think,   covered with patina.
for over 100 years,  it should be pretty stable
(https://image.ibb.co/mc8dte/0001.jpg)
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on October 07, 2018, 03:09:28 am
Measured a lil' bit on a first sample 2DW233 from the netherlands. With 10ppm/K @ 7.5mA it's still not meating my understanding of t.c. given in the datasheet. So maybe Andreas is right and the spec means, if you draw a line between 25°C point and 75°C point this line has a slope of 5ppm/K. Such a value would be useless as it ignores everything in between, so I take it as a marketing gag.
However, I can find an operating point at a current of 4.3mA so I can operate it heated with my crystal heater. Need to look for noise.

Still have another 4 samples for testing.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on October 07, 2018, 03:26:53 am
The scattering in parameters seem to be rather large. So compare the 2DW232 more too an 1N821 than 1N829.  If the current for zero TC is still in a good range (like 3-10 mA) this is not such a big problem. To get a low TC one would need an individually matched current anyway. A small search range helps a little, but not that much.

The bad ones are those that need more than 10 mA in series mode, which would be quite a lot of self heating. These might still be of some use in a different mode (e.g. zener only or 2 zeners + 1 diode).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: GigaJoe on October 07, 2018, 03:08:04 pm
Well, i have 233
and connecting in parallel 2 internal diode, simply. TC is "U" shape ; if temp UP  and low current  V down,  high current V up.  to  find a neutral spot is a time and patience,  my record approx. +0.15ppm/C. 

so from that above, that has a month in 120-150C and current 25ma im building 6 in parallel,  in assumption that some has negative and some positive TC,  due to current , and able to self compensate.

btw feeding by precise 10V a low TC spot offer 1023 Ohm resistor. after month it 880 ohm,  so parameters  i assumed drifted significantly.
233 2 diodes in parallel approx 4ma. for low TC, to adjust low TC spot i use 20ohm multi-turn trimmer.   using an owen even more fun as possible to compensate even  current resistors drift, due to positive or negative diode TC.  just adjust the current
 
"after month" - I mean 30 days, under 140C and 25ma.

they oxidize significantly,  even legs lost some coating and to tinned it back i have to use some crazy flux.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: IconicPCB on October 07, 2018, 03:49:09 pm
Giga Joe,

What is the spread of currents ( resistors at nominally 10V )?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: GigaJoe on October 07, 2018, 04:16:32 pm
Uh ... I'm actually just started building the  board,  so all this measurements and so ..  And tell precisely later what happens ... But as I can recall spread from 4.1ma to 4.6 ma per diode in parallel I think i played with 4-5 of them. The biggest trouble to use it , was an internal resistance,  60-80 ohm,  means even slightest current change and everything changed. Like in comparison LM399 0.1 ohm but yes it not  a pure zener. 


Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on October 07, 2018, 06:28:37 pm
The higher differential resistance is a downside of using it at a lower current.  60-80 Ohms is really quite high for a current around 4 mA.
The LM399 is not a fair comparison here, as it includes an internal amplifier and current source. One should more compare it to zener references like the 1N825 which gives <10-15 Ohms  at 7.5 mA.  So yes it needs a reasonable stable resistor.

Operating in the 4-5 mA range is nice, as it limits self heating to a reasonable level. I don't think one would use several in parallel of these, as the noise level should already be low enough for most practical applications. More like using 2 in series (or a bridge circuit) to get a reference of around 10.5 V and than divide down to 10.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on October 08, 2018, 05:08:12 am
I completed my design for a 10V reference with the first 2DW233 sample. As the crystal heater is mounted to an aluminium rod with a diameter of 16mm and the reference diode with a diameter of 8.2mm is stuck into it, there is still enough material around the diode to insert all resistors necessary into it as well. I will use PTF56 for that purpose. So I need a single sided board on each side to connect everything. A LT1001 in smd package will thus be temperature stabilized too. This is some sort of 3D mounting concept and thus a pretty compact design.

-branadic-

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: GigaJoe on October 09, 2018, 05:14:54 am
some diodes drifting up to 20mV / day.   so I hook all diodes with 1K resistor  (approx 2ma per single internal diode) I put everything in a box tossed it under bed.  will wait a month till it settle ...  then measure\see\figureout ... guess, diodes recovering after harsh forces ... 

( i notices with LM399 , same picture , after 6 month under high temp, they drifted a lot ... then stopped and became rock solid ... will see )
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on November 27, 2018, 08:15:15 am
As announced I've build the ovenized 2DW233 reference. It took a while for the boards to arrive at my place. However, here is how the ovenized reference looks like now. I first powered it up and it shows a 9.97V output by now, which is almost what I expected and planed to use a precision multiturn pot to set it exactly to 10V anyway. The ovenized reference is still small enough to fit into the flask shown a few posts before together with some foam. So it's now time to perform some more measurements on this particular device.

-branadic-

EDIT: The complete ovenized reference inside the flask with some additional thermal insulation draws about 19mA @ 12V. A LT1763 based voltage regulator is sitting inside the flask too.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Andreas on February 18, 2019, 09:09:03 am
Hmm,

still no real "zero T.C." results? or did I overlook something?

I went a different way:
I bought cheap SMD (SOT-23) double zeners (ESD-protection diodes AZ23C5V6)
https://de.rs-online.com/web/p/zener-dioden/7081857/?sra=pstk

Ok they are not really low noise (around 2uVpp at 7.5 mA) but two T.C. measurements with my standard voltage regulators of 9.35V and 14.0V and a simple 1K 1% series resistor with both diodes in series look promising that the zero T.C. will be somewhere between 3 and 7.5 mA.

At 9.35V I got: -20.2 ppm/K in average
At 14.0V I got: +20.1 ppm/K average T.C.

Of course that does not tell anything about long term stability etc.
But +/- 20 ppm/K on first try is rather good compared to some other cheap references.

with best regards

Andreas

Update: The best result I got:
at 10.6V: +0.23 ppm/K average T.C. (green curve)
but the diagram shows that the temperature range for "zero T.C." is very limited
some degress left or right from the optimum it rises quickly above 1 deg/K

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on February 27, 2019, 03:37:37 am
Quote
still no real "zero T.C." results? or did I overlook something?

Nope, I couldn't perform this measurements yet as I was of the bench because of illness. But it's on my to do list. Back on the bench since monday I finallized my 9x LTZ1000 references and performed first measurements.

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: janaf on March 13, 2019, 09:36:21 pm
Thanks for sharing. Even if these are not time/temperature reference stable, they could be used in very low noise power supplies...
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on March 13, 2019, 09:49:21 pm
Quote
Even if these are not time/temperature reference stable

Well, I'm not sure about that. I currently have one 2DW233 with an oven running and it looks like it starts to settle down, but to be sure about that it needs a bit of time to get a statement on that.

Re: vintage ltz1000 from 1986 NIB !. (https://www.eevblog.com/forum/metrology/vintage-ltz1000-from-1986-nib-!/msg2251494/#msg2251494)

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: janaf on April 05, 2019, 11:32:16 pm
A batch of 2DW233 from taobao just arrived.

https://item.taobao.com/item.htm?spm=a1z09.2.0.0.gpf2Zk&id=35815633601

They have the 'right' symbol, the factory symbol is also on the bags.
Mine have house marks/bin color dots? on them, ie may have been subject to selection.

Some stats on 25pcs at 7.5mA (per diode) fresh out of the bags:

- Average voltage 5.65V, +/-0.05V
- The pairs all matched within +/-12mV with a standard deviation 8.3mV.
- For roughly one in 5 device pairs, the two diodes where within 2mV from each other.

EDIT: Updated stats for 'back-to-back' zener+diode:
- Average voltage 6.414, 15 devices within +/-60mV

 

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on April 05, 2019, 11:44:51 pm
25 Ohms is quite a high resistance.
The real test would be if the noise is low - the "wrong" diodes tend to have a much higher noise.
If low noise the other question is if a low TC can be obtained at a reasonable current. There seem to be some batches with low noise, but too high a current for low TC. 
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: janaf on April 06, 2019, 12:02:55 am
The 25 ohm was a single quick and dirty measurement... will do some better ones.

Will do noise measurements soon.
The noise presented by the OP, was that per single diode or a pair?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: janaf on April 06, 2019, 01:19:24 am
Did some slightly better measurements of the impedance. It's a bit hard as there's a lot of temperature drift  :-//.....

In the end, I let each point stabilize for a couple of minutes. Then, the impedance was around 6.5-ish ohms at 7- mA.


Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on April 06, 2019, 01:44:08 am
The relevant noise if for a series connection of the diodes, so one as a zener and the other as a forward diode. Ideally this would be at a current where the TC is low.  AFAIR the current for a low TC can vary quite a lot - the 7.5 mA are more like an ideal value, but others have found some 5 mA to > 30 mA (thus no practical zero TC).
To get a really good noise test it would need a suitable current for low TC first so that temperature fluctuations would not give so much contribution.

The difference between a good low noise zener and a different more normal zener is huge - like a factor of 10 or 100. So a first test could use a fixed e.g. 7.5 mA current.

For the differential resistance one could use an AC current super imposed, so that the temperature would not change that fast.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: janaf on April 06, 2019, 02:23:23 am
Here's the local impedance for a fast sweep, marginal self heating, 1mS per data point.

EDIT New graph with back-to-back diode-zener connection.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: janaf on April 06, 2019, 02:44:47 am
Ah, yes of course, back to back would give temp compensation. I wasn't thinking much of that as I'll use mine for quiet power supplies, not primarily as a reference.  :-+
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: IconicPCB on April 06, 2019, 07:52:03 am
Consider using one an d a half diodes i series.

By that i mean two zeners plus a normal diode.
The net effect isdoubling of reference voltage with lower temperature zero tc point.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on April 06, 2019, 06:02:58 pm
Consider using one an d a half diodes i series.

By that i mean two zeners plus a normal diode.
The net effect isdoubling of reference voltage with lower temperature zero tc point.

2 Zener +  1 Diode in forward direction is an option, if one can ensure good thermal contact.  The temperature where you get zero TC depends on the current, and it does not need much change in current to shift the temperature. So it's more about lowering the current, than getting a lower temperature. It could be especially an option for those diodes that would need more than 25 mA to get zero TC, when used as 1 zener +  1 forward diode.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: IconicPCB on April 06, 2019, 09:37:16 pm
Yes.. depends on Your perspective.

I was looking to get  the zero temp coefficient point at room temperature and could not reach it within reasonable ( op amp output ) current level.

It struck me that I could achieve zero tempco setting by combining the diodes in above fashion .
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: branadic on April 15, 2019, 12:28:03 am
So I have my ovenized 2DW233 running for a while now, with the resistors being inside the oven (see posts before). The reference is still decreasing in output voltage but shows indication of getting stable in average output voltage soon.
However, the short term readings themself are quite unstable. I found, that low frequency noise (0.1 - 10Hz) has increased to about 10µVpp. I'm not sure if this is due to the reference itself or the fact that the resistors (PTF56) are ovensized at a temperature of about 40°C producing excessive noise.
Anyone out there with experience in PTF56 resistor noise at higher temperature or long term noise behavior of 2DW233?

-branadic-
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Edwin G. Pettis on April 15, 2019, 04:03:55 am
As far as the resistors go, any significant increase in noise over and above the normal thermal noise would be caused by faulty weld joints.  In the case of the diodes, most likely source of increasing noise above the expected thermal limit would be caused by additional contamination of the semiconductor, another quality control issue.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on April 15, 2019, 04:48:04 am
The DW232 circuit may be more sensitive to resistor effects than the LTZ1000 circuit. However the resistors should not contribute much to the noise, at least not the direct way.  I see more a chance that the resistors may be part of the voltage drift, though it would need quite some change to explain the observed effect.

There may be an indirect effect on noise: the circuit should ideally be initially adjusted to get a low TC of the reference at the operating point and set temperature. This would keep the effect of temperature variations low. However if things drift chances are the TC could also change and the reference can become more sensitive to temperature variations.

Of cause one can never exclude a possibly really bad resistor, e.g. with a poor contact of the end cap.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Edwin G. Pettis on April 15, 2019, 05:34:08 am
To be clear, a poor weld joint particularly with the sandwich type of joint can indeed produce microvolts of noise and offset, PTF resistors utilize sandwich welds.  Further more, there are no end caps on precision resistors they cause way too high TCR, those are almost always relegated to power resistors.  With a sandwich weld, it can initially appear good but deteriorate with time and heat, while 40°C isn't particularly hot it is certainly hotter than room temperature.  I have seem many a sandwich weld joint pass all kinds of testing including high temperature stress and still fail later on, on the other hand there are sandwich joints which can pass all testing and remain good for the rest of the component's life.

It was said earlier that the circuitry was in an 40°C oven so unless his oven is fluctuating, temperature is not the primary suspect, although he did not mention how long he had been running the circuit in the oven.  As I mentioned the diode's quality could also be suspect for unexpected noise.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on April 15, 2019, 07:44:23 pm
I still can't work out why they use such thick and incredibly stiff steel wires on these devices... both from the perspective of thermal emfs and cracking of the glass seals, visible in janaf's second photo (#602).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SilverSolder on April 15, 2019, 10:06:01 pm

The steel isn't plain soft iron or anything, it is selected to match the thermal coefficient of glass (to prevent it cracking due to temperature swings).
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: babysitter on April 15, 2019, 10:11:26 pm

The steel isn't plain soft iron or anything, it is selected to match the thermal coefficient of glass (to prevent it cracking due to temperature swings).

Its possibly an alloy named KOVAR or a cousin of it, whose temperature coefficient of expansion matches that of (borosilicate) glass. Also there is invar, which has close to zero tce.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on April 16, 2019, 06:50:53 am
Hmmm, maybe it is Kovar, it is highly magnetic / ferrous. The trouble is that it is so thick and stiff compared to the seals that, at best, you get surface chipping of the glass, as seen in the photo. The leads are certainly much thicker / stiffer than anything I've ever come across on a TO-5 can. I can see no reason for it.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: ramon on April 17, 2019, 11:41:27 pm
I still can't work out why they use such thick and incredibly stiff steel wires on these devices... both from the perspective of thermal emfs and cracking of the glass seals, visible in janaf's second photo (#602).

Can you provide a source of information regarding thermal emf of steel? I have tried many times to find such data without success.
Steel has a relatively low thermal conductivity.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Gyro on April 18, 2019, 02:26:50 am
Copper-steel (or ever copper-pure iron) thermal emf is hard to find (steel would depend on composition too). If the leads are indeed some Kovar alloy, as seems likely, then the thermal emf is around 40uV/'C.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: SilverSolder on April 18, 2019, 02:55:34 am
The thermal EMFs should cancel out, as long as everything is at a stable temperature?
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on April 18, 2019, 03:23:48 am
At least most of the thermal EMF should cancel. It would be mainly the temperature difference between the solder junctions of the 2 relevant pins. In addition the temperature difference tends to be rather stable and the stable part would be seen as part of the reference.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: sorin on June 02, 2019, 12:28:45 am
Recently i bought 10 pcs 2DW232 from aliexpress.
Can anyone suggest me a simple method to test if them are originals or fake?
I have only 2 Multimeter (UT61E + AN850B), 1 Power Suply KA3005D and a Rigol DS2072A.

Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: 42Khz on June 02, 2019, 12:42:18 am
Recently i bought 10 pcs 2DW232 from aliexpress.
Can anyone suggest me a simple method to test if them are originals or fake?
I have only 2 Multimeter (UT61E + AN850B), 1 Power Suply KA3005D and a Rigol DS2072A.

The easiest way is to crack one open.
If it's a single die inside covered in some gunk it's probably real (I'm not aware of any fakes like that) and if it's two discrete zeners it's a fake.
Title: Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
Post by: Kleinstein on June 02, 2019, 01:59:02 am
Looking inside is probably the easiest way.
A non destructive way would be to build a simple reference circuit and measure the noise. Chances are high the fake ones would be much higher noise. I would not mind "fakes" that are very low noise.