Electronics > Metrology

Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x

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serg-el:
If you looked closely at the figures, you might have noticed that the last measurements were taken with the ADVANTEST R6581.
From R6871E at 50 samples, the standard deviation is 0.51 μV.

Kleinstein:
From the early parts of this thread, there are reports the a good sample of the 2DW233 can be even lower noise than the LTZ1000. In addition the direct measurement also adds some noise from the ADC. Even at 100 PLC the noise may be relevant here.  The R6581 does not seem to be so very low noise . It is still not bad and the ADC also has some good aspects when it comes to noise. However there is also 1 weak point.

With 30 Zener diodes to start with it should be possible to possible to build 2 references to compare.

dietert1:
Thanks, now i can see the 100 nV steps. Don't know the Advantest instruments well, but the DVM seems to be very stable over several hours. In the case of our two LTFLUs i am logging the difference voltage with a HP 3456A in the 100 mV range, at the same resolution of 100 nV. Recently i cleaned the fan of that DVM and it shifted it's zero adjustment by 0.7 uV (in Autozero mode).

Regards, Dieter

GigaJoe:
I have approx 20 diodes , running at 10-15 mA ; all of them was thermally isolated and selfheated to approx 80-90C . Run it for 2 years. I finally disassemble setup, and set 1 can ( 2 diodes in parallel ) with current  adjustment to minimal temp-co (approx 0.3-0.5 ppm\C )  It runs a week as prototype without any PPM changes.

pico61:
Hello everybody,
after reading all the posts I wanted to try to experiment with 2DW23X zener references too.
I found a seller on AliExpress who offered them at a low price, around 18 € for 20 items, including shipping.
I had bought 20 2DW232s but, after the purchase, he informed me that he only had 2DW235s available.
The latter, according to the datasheet, should work with a nominal current of 15mA, in my opinion too high due to self-heating but then reading what zlymex wrote, I bought them anyway.
After about a month, they were delivered to me.
The first thing I checked was the presence of the diamond symbol on the case.
I started testing using a Keithley 220 current source and a Fluke 8846A multimeter.
I state that at least in this phase I am only interested in verifying stability rather than low noise, not having suitable instrumentation to evaluate it.
At first I set the generator to 15mA.
I tried to heat the zener to a temperature of about 50 ° C. I detected a large variation in the voltage, then I tried to increase the current in steps of 1 mA up to 30mA but without significant changes in the Tc. So I tried with lower currents, always with steps of 1 mA, up to 5mA.
I found two things: the first is that around 7mA the TC decreased (but I have not been able to investigate further) and the second that over 10mA the zener tended to self-heat.
Then, I wanted to try lowering the current to just 2mA. Amazed I discovered that the Tc was almost zero! I tried to heat it up to 80 ° C (from 23 °) and I got a variation of less than 100uV. I tried again to reduce the current down to less than 1.5mA and I discovered a feature: the Tc is reduced to zero with a positive value (+ temperature, + voltage) up to a current of 1.56mA. With lower values ​​it becomes negative (+ temperature, - voltage). For this it was easy to discover the point at zero TC.
The detected voltage, at a current of 1.56 mA, was 5.24792V.
I tried to leave the 2DW235 plugged in for twenty four hours and the variation was 20uV (5.24794V - less than 4ppm) with a room temperature going from 23 to 25 ° C. However I can't be sure if the variation is due to the zener reference or the F8846A or due to current variations of the K220.
I tried to switch it off and then back on several times, even several hours later, and the maximum variation was only +/- 10uV (+/- 2ppm).
I have some questions:
- has anyone already detected this behavior of the 2DW23X?
- could they be used with out-of-specification currents? And the behavior regarding noise at such low currents?

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