Author Topic: Ultra Precision Reference LTZ1000  (Read 1333376 times)

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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1525 on: September 25, 2016, 05:18:36 am »
Hello Ken,

do you have a S&H cirquit which generates no charge injection (noise) above that level?

with best regards

Andreas
 

Offline Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #1526 on: September 25, 2016, 08:35:00 am »
For just a reference charge injection is not that critical, as this will be largely a constant offset. So the critical part would be only the drift in charge injection. The H11F1 is also relatively slow (and speed may show drift) - this could add quite some dead time and thus require a low frequency.

Even with pulsing the zener, one would not get away with all the 1/f noise of the reference. It still is the same chip and thus long lived metastable states can still survive the pulsing, and new ones can get populated.  I am not even sure that this would give a real advantage in 1/f noise.
 

Offline zlymex

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Re: Ultra Precision Reference LTZ1000
« Reply #1527 on: September 26, 2016, 03:22:02 am »
......
AFAIK, the 1/f noise of a Zener operated in avalanche mode [like the LTZ1K is], will be inversely proportional to the square root of the Zener current.  So, going from 5mA to 20mA would (theoretically) reduce the 1/f noise by 1/2.  I got that from my ancient Motorola Zener Diode Handbook.

That is true. However, there is one thing I don't understand, because I don't know the physics behind the zener LF noise.
I thought the LTZ1k is the best as far as the LF noise is concerned, specifying at 1.2uVpp typical at 5mA zener current.
But, there is this 2DW233(of a particular maker), showing much small LF noise than LTZ1k at 5mA, typically 0.4uVpp :scared:  This is equivalent to a LTZ1k operating at 45mA. Anyone can explain the possible reason?
( https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg938465/?topicseen#msg938465 )
 

Offline zlymex

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Re: Ultra Precision Reference LTZ1000
« Reply #1528 on: September 26, 2016, 06:28:33 am »
....... 
Is there any way to speak with a scientist or engineer at the factory where those Zeners were made to get some additional information on them?

I tried but no result. I cannot find anything of related publications neither. They didn't mention that 2DW233 in their website in particular(such as special process or ultra-low noise). Those low noise 2DW233 is selling at similar price(all very cheap) as other manufactures with severe noise. The low noise feature of this 2DW233 is only recognized by amateurs like me.
 

Offline JS

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Re: Ultra Precision Reference LTZ1000
« Reply #1529 on: September 26, 2016, 02:49:26 pm »
....... 
Is there any way to speak with a scientist or engineer at the factory where those Zeners were made to get some additional information on them?

I tried but no result. I cannot find anything of related publications neither. They didn't mention that 2DW233 in their website in particular(such as special process or ultra-low noise). Those low noise 2DW233 is selling at similar price(all very cheap) as other manufactures with severe noise. The low noise feature of this 2DW233 is only recognized by amateurs like me.

Maybe it's just a typo  :-\

JS
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Offline zlymex

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Re: Ultra Precision Reference LTZ1000
« Reply #1530 on: September 26, 2016, 03:12:14 pm »
....... 
Is there any way to speak with a scientist or engineer at the factory where those Zeners were made to get some additional information on them?

I tried but no result. I cannot find anything of related publications neither. They didn't mention that 2DW233 in their website in particular(such as special process or ultra-low noise). Those low noise 2DW233 is selling at similar price(all very cheap) as other manufactures with severe noise. The low noise feature of this 2DW233 is only recognized by amateurs like me.

Maybe it's just a typo  :-\

JS
If you meant the noise, no.
There is no specification for the noise in the datasheet. The ultra-low noise feature of 2DW233 was found out by actual measurement of many people at different places and on different times.
 

Offline JS

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Re: Ultra Precision Reference LTZ1000
« Reply #1531 on: September 26, 2016, 03:41:19 pm »
....... 
Is there any way to speak with a scientist or engineer at the factory where those Zeners were made to get some additional information on them?

I tried but no result. I cannot find anything of related publications neither. They didn't mention that 2DW233 in their website in particular(such as special process or ultra-low noise). Those low noise 2DW233 is selling at similar price(all very cheap) as other manufactures with severe noise. The low noise feature of this 2DW233 is only recognized by amateurs like me.

Maybe it's just a typo  :-\

JS
If you meant the noise, no.
There is no specification for the noise in the datasheet. The ultra-low noise feature of 2DW233 was found out by actual measurement of many people at different places and on different times.

Oh, that's nice then, thanks for the info!

JS
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Offline chickenHeadKnob

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Re: Ultra Precision Reference LTZ1000
« Reply #1532 on: September 26, 2016, 04:39:05 pm »

I tried but no result. I cannot find anything of related publications neither. They didn't mention that 2DW233 in their website in particular(such as special process or ultra-low noise). Those low noise 2DW233 is selling at similar price(all very cheap) as other manufactures with severe noise. The low noise feature of this 2DW233 is only recognized by amateurs like me.

I tried to buy these from the ali-express seller you mentioned but after 75 days and no shipment I canceled the payment. At least Aliexpress claims they refunded me - I haven't checked my credit card bill yet. It was the first time I tried aliexpress  so I don't know what the transaction failure rate is. It is apparently less reliable than ebay. I have never had any problems with chinese ebay sellers. Its all for the good though, I changed my mind on what approach to take and testing these would just be a waste of time now. There is some value in the pursuit references that are temp compensated, non-ovenized,  cheap  and maybe a little drifty  but ultra low noise. Say for longscale ADCs that can be disciplined once a day (or more often) to a stable master lab reference.
 

Offline zlymex

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Re: Ultra Precision Reference LTZ1000
« Reply #1533 on: September 27, 2016, 09:47:54 am »

I tried to buy these from the ali-express seller you mentioned but after 75 days and no shipment I canceled the payment. .........

I'm sorry to hear that. I didn't know AliExpress before I came across some people at an electric unicycle forum who often buy electronic parts from AliExpress with free international shipping(which is slow). I buy most of my electronic parts at taobao.com that backstaged by the same Alibaba but has a dedicated on-line chat system allowing sellers and buyers to talk. One difference(of taobao and aliexpress with eBay) is that they don't charge/tax e-stores on per item base therefore the average unit price tends to be very low and the number of items in a e-store is huge so is the number of daily packages. These often result in poor management and poor service especially when they are short handed.

Any way, I've bought 500+ pieces of 2DW233 just in case they stop producing it using the same technique(and I may not find the ultra-low noise zener anywhere in the world in that case).
 

Offline chickenHeadKnob

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Re: Ultra Precision Reference LTZ1000
« Reply #1534 on: September 27, 2016, 01:43:03 pm »

I tried to buy these from the ali-express seller you mentioned but after 75 days and no shipment I canceled the payment. .........

I'm sorry to hear that. I didn't know AliExpress before I came across some people at an electric unicycle forum who often buy electronic parts from AliExpress with free international shipping(which is slow). I buy most of my electronic parts at taobao.com that backstaged by the same Alibaba but has a dedicated on-line chat system allowing sellers and buyers to talk. One difference(of taobao and aliexpress with eBay) is that they don't charge/tax e-stores on per item base therefore the average unit price tends to be very low and the number of items in a e-store is huge so is the number of daily packages. These often result in poor management and poor service especially when they are short handed.

Any way, I've bought 500+ pieces of 2DW233 just in case they stop producing it using the same technique(and I may not find the ultra-low noise zener anywhere in the world in that case).

No need to be sorry! If it wasn't for your interesting insight into the the Chinese semiconductor scene I wouldn't have known about these. My plan was to try with 80 parts, characterize them, and hope that was enough for a lifetime buy. Yes I realize it is too uncertain to source these parts for someone not in China, even the diamond brand factory may not exactly  know how to reproduce them from one batch to another. My plan now is to use LT1027 with a Walt Jung style noise reduction circuit.
best regards
 

Offline zlymex

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Re: Ultra Precision Reference LTZ1000
« Reply #1535 on: September 28, 2016, 12:39:26 am »
Using a copper block is a good idea. I've build a test circuit without one and the noise is not as low as expected.
2DW233 is a temperature compensated (two identical zeners back to back) on its own, and altering the applied current will find the zero-TC spot.
 

Offline acbern

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Re: Ultra Precision Reference LTZ1000
« Reply #1536 on: September 28, 2016, 05:58:29 am »
Does anybody have data re. the aging rate of the 2DW233? Is it comparable to the LTZ1000?
 

Offline Kjelt

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Re: Ultra Precision Reference LTZ1000
« Reply #1537 on: September 28, 2016, 07:22:07 am »
This is getting confusing, is it an idea to start a seperate topic on the 2DW233 ?
 

Offline zlymex

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Re: Ultra Precision Reference LTZ1000
« Reply #1538 on: September 28, 2016, 11:45:11 am »
 

Offline plesa

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Re: Ultra Precision Reference LTZ1000
« Reply #1539 on: October 05, 2016, 06:56:01 pm »
After difficulties with PWW resistors I finally finished all 4 LTZ1000 boards from TiN and started collecting data.
Almost all resistors are PWW made by Edwin except 4x 100k resistors which were out of tempco spec.
He has some manufacturing issues with potting.
Missing PWW were replaced by pre-selected Vishay UXB series resistors.
Initial measurement by 34411A/34410A is rock stable, so I used ratio measurement with 34401A and 34420A.
 

Offline plesa

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Re: Ultra Precision Reference LTZ1000
« Reply #1540 on: October 05, 2016, 09:24:54 pm »
After difficulties with PWW resistors I finally finished all 4 LTZ1000 boards from TiN and started collecting data.
Almost all resistors are PWW made by Edwin except 4x 100k resistors which were out of tempco spec.
He has some manufacturing issues with potting.
Missing PWW were replaced by pre-selected Vishay UXB series resistors.
Initial measurement by 34411A/34410A is rock stable, so I used ratio measurement with 34401A and 34420A.

Very cool!  I'm looking forward to your measurement results!  Is that your temperature chamber on the right side of the photo?

-Ken

Only usable for measurement seems to be 34420A, 34401A in ratio mode is much more fluctuating (2 last digits) on same references. It is not temperature chamber, only the polystyrene box from pharmacy without any heater. But it seems to be good enough.
 

Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #1541 on: October 06, 2016, 04:57:00 am »
Neat setup. I see my earpick trick works for you too  :-DMM. Will you have datalogging running as well?
Would like to see reference board pics in your setup, once you done with measurements.

And what would be the ultimate plan of using these modules? Long-term testing or some practical application, if that's ok to ask?
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Offline d-smes

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Re: Ultra Precision Reference LTZ1000
« Reply #1542 on: October 07, 2016, 09:22:15 pm »
Data sheet thermal resistance specification for the LTZ1000 (non-A version) doesn't seem right.  Looking at the "Die Temperature Rise vs Heater Power" graph in the data sheet, I see 85C rise with 0.5W of heater power which equates to 170 C/W or about twice the specified 80 C/W data sheet value.  The "A" version does looks about right: ~82C rise with 0.2W is close to the 400 C/W data sheet value.  Can anyone explain this discrepancy?   Am I supposed to add normal circuit configuration power dissipation of the transistors & zener to the heater power when doing this calculation?

I ask because I'm leaning towards a 4-layer board layout with considerable copper pours for the leads and inner layers to equalize lead temperature per data sheet recommendation.  I'm wondering what this will cost by way of heater power.  To answer this, I'm trying to determine how much heat escapes by way of the leads versus the case.  I thought comparing thermal resistances of the highly isolated "A" part versus non-A would yield insight.   Instead, I can't seem to make the numbers add up...
 

Offline Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #1543 on: October 07, 2016, 10:58:48 pm »
Usually the thermal resistance for a TO99 is about 160 K/W. Also the similar size TO39 is in that range. So I guess the 80 K/W number is wrong, or in forced air or with rather short leads.

The thermal resistance of the wire can be estimated form the dimensions and the known material. My calculation give something like 900 K/W for the 8 full 15 mm leads, and about 300 W/K for 5 mm leads. So there is quite some power going through the leads, especially if short. With extra thermal insulation around the case the heat flow through the pins can be the major part.

 

Offline JS

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Re: Ultra Precision Reference LTZ1000
« Reply #1544 on: October 08, 2016, 12:49:23 am »
Data sheet thermal resistance specification for the LTZ1000 (non-A version) doesn't seem right.  Looking at the "Die Temperature Rise vs Heater Power" graph in the data sheet, I see 85C rise with 0.5W of heater power which equates to 170 C/W or about twice the specified 80 C/W data sheet value.  The "A" version does looks about right: ~82C rise with 0.2W is close to the 400 C/W data sheet value.  Can anyone explain this discrepancy?   Am I supposed to add normal circuit configuration power dissipation of the transistors & zener to the heater power when doing this calculation?

I ask because I'm leaning towards a 4-layer board layout with considerable copper pours for the leads and inner layers to equalize lead temperature per data sheet recommendation.  I'm wondering what this will cost by way of heater power.  To answer this, I'm trying to determine how much heat escapes by way of the leads versus the case.  I thought comparing thermal resistances of the highly isolated "A" part versus non-A would yield insight.   Instead, I can't seem to make the numbers add up...

  Wouldn't that add to the mechanical stress on the board? As some are using thinner PCBs and/or cut outs to allow for less mechanical stress, I guess adding 2 extra layers would be against that effort. Some soft thermal potting or pad may help equalize the lead temperature without adding mechanical stress.

JS
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Offline plesa

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Re: Ultra Precision Reference LTZ1000
« Reply #1545 on: October 10, 2016, 09:29:31 am »
Neat setup. I see my earpick trick works for you too  :-DMM. Will you have datalogging running as well?
Would like to see reference board pics in your setup, once you done with measurements.

And what would be the ultimate plan of using these modules? Long-term testing or some practical application, if that's ok to ask?

Yep, they are amazing.Earpick is in lab easy available :)
Data logging is in progress. I upgraded RPi to latest Raspbian Jessie kernel and it stopped working.
I would like to use them for 10V reference including 10k reference in better case.
 

Offline d-smes

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Re: Ultra Precision Reference LTZ1000
« Reply #1546 on: October 10, 2016, 01:29:15 pm »
Usually the thermal resistance for a TO99 is about 160 K/W. Also the similar size TO39 is in that range. So I guess the 80 K/W number is wrong, or in forced air or with rather short leads.

The thermal resistance of the wire can be estimated form the dimensions and the known material. My calculation give something like 900 K/W for the 8 full 15 mm leads, and about 300 W/K for 5 mm leads. So there is quite some power going through the leads, especially if short. With extra thermal insulation around the case the heat flow through the pins can be the major part.
Thanks for the confirmation data sheet figure of 80 K/W is wrong.  I just looked at LT1012 data sheet where TO-5 has Rth-JA = 150 K/W and Rth-JC = 45 K/W which further attests to the error.

Once a plastic cap is placed over the part and insulation placed about leads to kill air currents, it looks like overall thermal resistance will be just as high as the "A" part and the majority of heat flow will be through the leads.   It makes sense now why the data sheet recommends equal size PC traces to equalize heat loss and maintain them at similar temperatures.

@JS  The wire leads will offer plenty of mechanical compliance in the x-y axis.  If z-axis (direction of leads) mechanical compliance is necessary, I could add a "S" bend to each lead before soldering into board.   But I doubt mechanical stress is even an issue for a TO-5 part.  I realize someone flexed their reference board and saw several uV of change, but it wasn't clear how much of that came from stress on resistors and op-amps versus the LTZ1000.
 

Offline Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #1547 on: October 10, 2016, 06:45:29 pm »
Due to the extra about 300 K/W extra internal thermal resistance the A version can operate with a lower heating power if the temperature is choose for the same maximum ambient 
temperature. However the difference is not that big - comparing long an short leads can be a similar difference.
 

Offline d-smes

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Re: Ultra Precision Reference LTZ1000
« Reply #1548 on: October 10, 2016, 11:22:49 pm »
Due to the extra about 300 K/W extra internal thermal resistance the A version can operate with a lower heating power if the temperature is choose for the same maximum ambient 
temperature. However the difference is not that big - comparing long an short leads can be a similar difference.
I totally agree.   But now that we know it's 150 K/W (instead of 80) for non-A and 400 K/W for A part, the difference is smaller.  Couple that with everyone putting insulation around the parts, and long leads (best for equal lead temperature at the board per this thread) and now majority of heat flow is out the leads to the PCB.  So, not much difference between A and non-A parts.  Makes me wonder if non-A designs run short of thermal margin of heater setting...

I forgot to mention, I looked at the "Die Temperature Rise vs Heater Power" graph from the data sheet again, and it does extrapolate to zero temperature rise at zero heater power.  So the rest of the die elements are assumed de-energized for this graph.  But I agree with what DiligentMinds is saying- when doing design, die (zener et.el.) dissipation will subtract from heater power necessary to reach target temperature.  If that quantity goes zero/negative, you've lost thermal regulation and your reference turns to crap.
 

Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #1549 on: October 12, 2016, 04:16:56 pm »
Well, hope nobody mind if I jump in with few practical items into this nice talk.
I was talking to one of volt-nuts (not known member here), and we decided to build and test another KX LTZ-reference for him.
Complete assembly will be tested for tempco and aged for 168 hours and later shipped cold to the final destination via regular mail.

To keep things bit more exiting for me, I decided to try few new things this time.

A. Use VPG VHD200 divider, 1K/13K hermetic oil-filled resistor. My previous LTZ references were using separate resistors.
In theory this should provide better thermal stability, as temperature setpoint divider is now tightly coupled thermally in same oil-filled package.

Rest of resistors are custom 2 x VPG 75K 1%, VPG 120R 0.01%. These have custom PO VFR part-numbers, but I'd expect they are VHP101-based.
Whole lot was bought for 190$USD from eBay, including unrelated resistors on photo.

Chip will be LTZ1000ACH.



B. I want to try ADA4522-1ARZ opamp instead of my usual LTC2057's to see if any difference would be visible on output noise/short-term stability (I expect none, but who knows).



And initial check, using 3458A.



Usual datalog:



Not a bad start, eh? -1ppm from 120 Ω. :)
Ignore first hour when ACAL was ran. 8:15 to 10:30 is measurement with DELAY 5 on 100ohm range. Few samples were overflow, as 3458A's max overrange is just 120 ohms, so data from 11:15 is with 1KΩ range and DELAY 1. All samples NPLC100, AZER ON, with resistor right at therminals as on photo.

P.S. Bonus quiz, what are rest resistors are for?  ;D
« Last Edit: October 12, 2016, 04:43:38 pm by TiN »
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