Author Topic: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x  (Read 128466 times)

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Offline janaf

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #600 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...
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Offline branadic

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #601 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 !.

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« Last Edit: March 13, 2019, 09:51:50 pm by branadic »
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Offline janaf

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #602 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

 

« Last Edit: April 06, 2019, 07:31:48 pm by janaf »
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Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #603 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. 
 

Offline janaf

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #604 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?
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Offline janaf

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #605 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.


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Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #606 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.
 

Offline janaf

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #607 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.

« Last Edit: April 06, 2019, 07:26:43 pm by janaf »
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Offline janaf

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #608 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.  :-+
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Offline IconicPCB

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #609 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.
 

Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #610 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.
 

Offline IconicPCB

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #611 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 .
 

Offline branadic

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #612 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?

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Offline Edwin G. Pettis

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #613 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.
 

Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #614 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.
 

Offline Edwin G. Pettis

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #615 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.
 

Offline Gyro

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #616 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).
Chris

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Offline SilverSolder

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #617 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).
 

Offline babysitter

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #618 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.
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Offline Gyro

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #619 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.
« Last Edit: April 16, 2019, 06:56:19 am by Gyro »
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Offline ramon

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #620 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.
 

Offline Gyro

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #621 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.
Chris

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Offline SilverSolder

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #622 on: April 18, 2019, 02:55:34 am »
The thermal EMFs should cancel out, as long as everything is at a stable temperature?
 

Offline Kleinstein

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Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #623 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.
 


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