Author Topic: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x  (Read 237975 times)

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Offline Dave

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #450 on: August 27, 2017, 08:45:35 pm »
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
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Offline floobydust

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #451 on: August 27, 2017, 10:03:38 pm »
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:
 
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Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #452 on: August 28, 2017, 04:19:21 pm »
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.
 

Offline ultrasmurf

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #453 on: September 09, 2017, 04:14:52 am »
Is there anyone building a PCB kit to build a voltage reference standard using this 2DW ?
 

Offline chuckb

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #454 on: September 12, 2017, 11:42:05 am »
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.
 

Offline Cerebus

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #455 on: September 12, 2017, 12:42:12 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.
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Offline chuckb

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #456 on: September 14, 2017, 09:57:45 pm »
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.
 
 

Offline floobydust

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #457 on: September 15, 2017, 12:05:06 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
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?
 

Offline floobydust

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #458 on: September 15, 2017, 12:34:25 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
Designing an oven: http://bbs.38hot.net/forum.php?mod=viewthread&tid=60144
Drift measurements: http://bbs.38hot.net/forum.php?mod=viewthread&tid=224449

You can run a URL through google translate.

« Last Edit: September 15, 2017, 12:37:28 am by floobydust »
 

Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #459 on: September 15, 2017, 08:13:10 am »
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
 

Offline julian1

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #460 on: October 01, 2017, 12:49:13 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.



A plot over time shows the reference voltage and board temperature. The sample interval is 10 minutes, 8333 obs, over 57 days.



A plot using reference V versus the board thermocouple temperature,



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.
 

Offline chuckb

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #461 on: November 27, 2017, 12:39:44 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.
 
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Offline cellularmitosis

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #462 on: April 27, 2018, 09:01:25 pm »
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?
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Offline Vgkid

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #463 on: April 27, 2018, 09:17:19 pm »
His last date online was Dec 07,2017...
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Offline branadic

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #464 on: May 27, 2018, 12:50:42 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.

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Offline branadic

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #465 on: May 27, 2018, 06:33:21 pm »
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.

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Offline branadic

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #466 on: May 30, 2018, 10:33:59 am »
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.

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Offline Gyro

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #467 on: May 30, 2018, 02:39:07 pm »
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.
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Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #468 on: May 30, 2018, 03:00:18 pm »
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.
 

Offline cellularmitosis

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #469 on: May 30, 2018, 03:12:13 pm »
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.
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Offline Cerebus

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #470 on: May 30, 2018, 03:14:10 pm »
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.
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Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #471 on: May 30, 2018, 03:48:10 pm »
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.
 
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Offline branadic

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #472 on: May 30, 2018, 07:40:01 pm »
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.

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« Last Edit: May 30, 2018, 07:46:16 pm by branadic »
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Offline branadic

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #473 on: May 30, 2018, 10:41:19 pm »
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.

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Offline AG7CK

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #474 on: May 31, 2018, 01:59:30 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:


 


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