Author Topic: Lowest drift, lowest noise voltage reference (ADR1000AHZ)  (Read 128793 times)

0 Members and 3 Guests are viewing this topic.

Online dietert1

  • Super Contributor
  • ***
  • Posts: 2007
  • Country: br
    • CADT Homepage
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #175 on: November 22, 2021, 09:13:01 pm »
If you run the reference with its own heater inside an oven made to keep the divider at constant temperature, you could use the reference heater signal for TC adjustment, as proposed in the LTZ1000 datasheet. Inside the oven the heater is well protected from ambient temperature changes and you have a fixed operation point, so higher order terms will be negligible. If you bring the heater signal out of the oven, you can fine tune the adjustment without opening the oven. In your case an extremely small contribution will be necessary (maybe 100 MOhm instead of 400 KOhm).

Why not use a TEC oven? You can keep temperatures lower and near usual ambient temperatures, so any kind of power failure or the like will cause less deviation. Our LTFLU ovens restart with less than 0.1 or 0.2 ppm deviation after 24 h without TEC control. I know because one of our Arroyos used to turn off every two or three months (for no good reason). Meanwhile i solved that problem: Send output on command once per minute.

Regards, Dieter
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 3207
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #176 on: November 26, 2021, 08:03:19 am »
Hello,

now I have built 2 burn in PCBs for the ADR1000A.
This one is intended for noise measurements before and after the burn in.

But I fear that T2 base emitter voltage is too low (0.41V) to give any useful noise measurements.

with best regards

Andreas
 
The following users thanked this post: quarks

Online Kleinstein

  • Super Contributor
  • ***
  • Posts: 14018
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #177 on: November 26, 2021, 08:29:38 am »
The circuit is a bit tricky, as the current is driven from the external 1.8 K resistor on top, and not controlled by the transistor inside the ADR1000. So the TC and noise would not be the same as in the normal circuit. If not carefull there may even be change to damage (at least stress) the transistor from too much base current (e.g. at higher temperarure when VBE goes down). So I don't think the board is really good for burn in.

Why not use the "normal" circuit with maybe lower grade resistors ?
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 3207
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #178 on: November 26, 2021, 07:20:45 pm »
Why not use the "normal" circuit with maybe lower grade resistors ?

Hello,

sorry I did not find a suitable Op-amp which is specced for up to 150 deg environment temperature.
And what do you mean with "lower grade" resistors. Can there be lower grade resistors than the 5% metal oxide resistors (with 235 deg C maximum temperature?)

In the mean time I measured the noise of the cirquit.

Unfortunately I have typical 7uVpp over a 100 sec time span with this cirquit.

with best regards

Andreas


 
The following users thanked this post: miro123

Online dietert1

  • Super Contributor
  • ***
  • Posts: 2007
  • Country: br
    • CADT Homepage
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #179 on: November 26, 2021, 08:39:08 pm »
If you have a small p-channel mosfet, it can prevent excessive base current while hot. You connect source to reference output Pin3, gate to the collector of Q2 Pin5 and drain to ground Pin7.

Regards, Dieter
 
The following users thanked this post: Andreas

Online Kleinstein

  • Super Contributor
  • ***
  • Posts: 14018
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #180 on: November 26, 2021, 08:55:23 pm »
For protection of the transisitor a resistor at pin 7 would be enough. The temperature / output measurement would than be not from ground, but pin 7 instead.

I did not consider that the whole circuit is planed to run so hot. In this case it would be a bit tricky to build a circuit to work with high temperature parts.
In principle one could consider a circuit with discrete transistors (e.g. 2N2222), maybe as a cascode and than a emitter-follower. 
 
The more logical way would be the OP and most of the resistors at a lower temperature and only the reference chip itself hot. This could possibly be some 60-80 C for most of the circuit and than the ref internal heater to reach the final temperature.
 

Online dietert1

  • Super Contributor
  • ***
  • Posts: 2007
  • Country: br
    • CADT Homepage
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #181 on: November 26, 2021, 09:04:58 pm »
The p-channel mosfet i proposed is a 150 °C capable substitute for an opamp. It brings the reference ciruit into an operational state very similar to the standard circuit and supports the intended noise measurements during burn-in.

Regards, Dieter
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 3207
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #182 on: November 27, 2021, 11:04:45 am »
Hello,

so your suggestion is this way - right?

This will shunt away current from the zener and base as soon as the base current increases.

I do not think that it helps for the noise but it should help against base current overload so I will implement it.
I still have some BSS84p or similar which are not ideal for the job but should work.

with best regards

Andreas
 

Offline miro123

  • Regular Contributor
  • *
  • Posts: 197
  • Country: nl
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #183 on: November 27, 2021, 12:51:09 pm »
In the mean time I measured the noise of the cirquit.
Unfortunately I have typical 7uVpp over a 100 sec time span with this cirquit.
Interesting graphs. The noise spectrum flatten around 100Hz.
Is this typical ADR1000 behavior or limitation of measurement setup?
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 3207
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #184 on: November 27, 2021, 01:55:39 pm »
Hello,

uVpp is always 1/f noise measured with a bandwidth limited amplifier (0.1-10 Hz)
Additionally I have a 1000 Hz math filter in the scope to reduce noise of the scope input.

The flattening should be around the quantisation noise of the scope (16 bit mode)

The reason why im showing above 10 Hz is just to see wether I have too much mains frequency (50 Hz) noise in the measurement.

with best regards

Andreas


« Last Edit: November 27, 2021, 02:10:19 pm by Andreas »
 

Offline mawyatt

  • Super Contributor
  • ***
  • Posts: 3180
  • Country: us
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #185 on: November 27, 2021, 02:28:17 pm »
Why not use the "normal" circuit with maybe lower grade resistors ?

Hello,

sorry I did not find a suitable Op-amp which is specced for up to 150 deg environment temperature.
And what do you mean with "lower grade" resistors. Can there be lower grade resistors than the 5% metal oxide resistors (with 235 deg C maximum temperature?)

In the mean time I measured the noise of the cirquit.

Unfortunately I have typical 7uVpp over a 100 sec time span with this cirquit.

with best regards

Andreas

Nice!! What scope and setup did you use for the spectrum plots, those are impressive indeed!!

Best,
Curiosity killed the cat, also depleted my wallet!
~Wyatt Labs by Mike~
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 3207
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #186 on: November 27, 2021, 03:43:51 pm »
Hello,

Setup is a low noise 10000 fold amplifier 0.1-10 Hz bandwidth (cirquit attached as Filt1105w.pdf) here:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg834013/#msg834013

together with the DUT (voltage reference) in a metal cookies box (all battery supplied).
Scope is a PicoScope 5444A. (the successor model sold today is a 5444D)

Settings:
20 MHz hardware bandwidth limiter.
10 mV/Div resulting in 1uV/Div with the low noise amplifier.
16 Bit hardware resolution.
Sample rate 20 kS/s 100 seconds (2 Million samples per scan, 19 scans as input for FFTs).
1 kHz digital filter. (far enough away from the 10 Hz hardware filter).
FFT with rectangular window 1 Million points (binning of 2 Million samples)
Averaging of 19 FFT outputs (not input samples) to reduce noise floor of the scope (not the DUT).

without 1kHz filter and without averaging the FFT looks like this:

with best regards

Andreas

 
The following users thanked this post: mawyatt

Online Kleinstein

  • Super Contributor
  • ***
  • Posts: 14018
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #187 on: November 27, 2021, 04:39:19 pm »
The simplified circuit can be sensitive to noise in the supply to provide the external current. If the P-MOSFET gets active some (on the order of 1/200) of the noise of the MOSFET can also enter the result. The TC would likely also be quite a bit higher than the normal reference circuit and there can thus be noise from temperature fluctuations.

In the ciruit with the extra feedback (P MOSFET or 2 x NPN) one may also want some capacitance (e.g. at pin 3) to slow down the loop at 1 defined point to make sure it gets stable and is not oscillating.
 

Online dietert1

  • Super Contributor
  • ***
  • Posts: 2007
  • Country: br
    • CADT Homepage
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #188 on: November 27, 2021, 05:58:42 pm »
Andreas, yes that's what i thought. According to datasheet the BSS84p operates up to 150 °C.

Without regulation the power supply noise gets divided by 1K/100R=10. With regulation it will be much less. And i think you get regulation already at room temperature, as (13.9 - 6.43V) / 1K gives about 7.5 mA, not 4.3 mA. So there should be base current at room temperature.

Yes, there is a chance for oscillation, as the two transistors have enough gain to make a nice oscillator. If it happens, it can be solved by removing C4. The mod poses no risk to the rare/expensive reference. But of course one can make a ADR1000 dummy from discrete parts to check a circuit for "fatal threats".

Regards, Dieter
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 3207
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #189 on: November 27, 2021, 06:30:41 pm »
Hello,

its not 1K for the upper resistor but 1K8. (I wanted to stay below 5 mA)

with best regards

Andreas
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 3207
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #190 on: December 02, 2021, 08:00:26 am »
Hello,

pre-test for burn in cirquit with a temperature sweep from 60 to 130 deg C.
Above ~80 deg C the base emitter voltage of T2 decreases by the shunted current of the FET.
So the cirquit works.

But obviously the zener current decreases from initially 4.1 mA (410mV) to around 3 mA (300 mV) at 130 deg C.
So the cirquit is not ideal but should be ok for burn in.

Another effect is due to the massive heat sink capacity of the aluminium bar where the ADR is connected to.
The self heating seems to be only around 2-3 deg C.
(but this is measured with around 8 NPLC of my ADC#25 since my DMMs are occupied by ADR#1)

with best regards

Andreas

 

Online dietert1

  • Super Contributor
  • ***
  • Posts: 2007
  • Country: br
    • CADT Homepage
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #191 on: December 02, 2021, 09:55:38 am »
While the p-channel mosfet works similar to the usual opamp, there is another variant with a p-channel depletion JFET shunt parallel to R1, i.e. S = U1pin4, G= U1pin5 and D=Gnd. That variant does not shunt zener current at high temperatures. The J175 datasheet says it can be used up to 150 °C.

Regards, DIeter
 

Online Kleinstein

  • Super Contributor
  • ***
  • Posts: 14018
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #192 on: December 02, 2021, 11:00:03 am »
In the normal operation with the closed loop the zener current is not constant, but going down. So the change in current is normal. The unusual part is more the constant current at lower temperature.

A problem with the circuit is that the noise and drift may well be more effected by the FET and not so much the reference itself. So one would not get a good real time measurement of the aging / burn in.
 

Online dietert1

  • Super Contributor
  • ***
  • Posts: 2007
  • Country: br
    • CADT Homepage
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #193 on: December 02, 2021, 11:12:48 am »
From previous discussion it was clear that the loop amplifier in this application isn't critical. If one uses the output of the on-chip transistor, it becomes the input stage and determines noise and temperature dependent offset.

Regards, Dieter
 

Offline MaxTesla

  • Contributor
  • Posts: 19
  • Country: ch
Re: First Tests ADR1000AHZ
« Reply #194 on: December 06, 2021, 01:57:09 pm »
Hello,
Thanks to ScoobyDoo and branadic, I got 5 samples and some PCBs.
Here's the mockup board, where I made the first tests.

The lower zener voltage compared to the LTZ1000 now allows this Reference Amplifier to be trimmed to zero T.C. for a given oven temperature, by individual selection of the collector resistor R2. Compare this to the +50ppm/K for the unregulated LTZ1000.

That trimming process is the same procedure as for the SZA263 and LTFLU in the different FLUKE instruments.

I measured Uref vs. temperature, which always gives a negative, flat parable. The zero T.C. point varies from 45 to 60°C for a fixed value of R2, and the T.C. varies from about +5 .. -5ppm/K over 24 ... 80°C only.

At a fixed divider ratio R4:R5 for around 52°C oven temperature for all five samples, the individual T.C.s are well below +/- 2ppm/K.
It follows that the attenuation factors for R3 and the most critical R4, R5 are at least 10 times greater than in the datasheet. These resistors now can have much relaxed stability specifications, only R1 and R2 should be PWW or BMF types.

I also measured the low frequency noise 0.1 .. 10Hz, like branadic and Castorp.
I use an LNA from Andreas, and always made "typical" measurements of 10sec long samples, so to have a direct comparison to my LTZ1000s, but also to the measurements done by Andreas.
100s measurement time or averaging give no essentially different results.
Other LNAs will give different absolute noise figures, so these results are not directly comparable .
 
The noise of the ADRs RefAmp evidently is about 50% of the LTZ1000, which several others also have confirmed.

ADR #1 would be the most quiet sample, but it suffers from  :popcorn: noise, or frequent dips, but with a very moderate amplitude of maybe 400nVpp.
The ADA4522 buffer contributes a lot to the overall noise, so I have to investigate if it's only this specific unit, or what can be done to improve this.

I will add the noise figures of these samples, when measured with my 3458A, maybe now I can see a pronounced difference.

As my 34465A showed much higher stability / lower noise when I replaced its LM399 reference by a LTZ1000 clone PCB, my idea is to replace the LTZ1000 in my 3458A with an ADR1000 (*).
Maybe its noise figures will also go down, best by a factor of 2.
Castorp found that in his DVM other components overwhelmed the noise budget, so let's see what happens.

I would like to remind that TiN some time ago made a similar experiment on one of his 3458A, by implementing 4 parallel LTZ references, which would also yield 50% noise of a single LTZ.
I'm not aware what his final result was.

Anyhow, I think this new device will require quite a big time slot during the Metrology Meeting 2021, and I'm excited to meet the volt-nuts community personally and we'll have some fruitful discussions and comparisons   ;)

Frank

(*) my 3458A already has a modified FW, with CAL? 2,5 = 6.50000V (7V reference lower limit).
Thanks to Poul-Henning Kamp for your advice how to correct the checksum.


Hello Frank,

in your post you mentioned that you modified your 3458a's firmware to accept the lower voltage value of the ADR.
Would you mind sharing the process? I like to try it as well...

BR,

Max
 

Offline Dr. Frank

  • Super Contributor
  • ***
  • Posts: 2377
  • Country: de
Re: First Tests ADR1000AHZ
« Reply #195 on: December 06, 2021, 05:05:26 pm »
...
 
The noise of the ADRs RefAmp evidently is about 50% of the LTZ1000, which several others also have confirmed.

...

As my 34465A showed much higher stability / lower noise when I replaced its LM399 reference by a LTZ1000 clone PCB, my idea is to replace the LTZ1000 in my 3458A with an ADR1000 (*).
Maybe its noise figures will also go down, best by a factor of 2.
....

I would like to remind that TiN some time ago made a similar experiment on one of his 3458A, by implementing 4 parallel LTZ references, which would also yield 50% noise of a single LTZ.
I'm not aware what his final result was.


Frank

(*) my 3458A already has a modified FW, with CAL? 2,5 = 6.50000V (7V reference lower limit).
Thanks to Poul-Henning Kamp for your advice how to correct the checksum.


Hello Frank,

in your post you mentioned that you modified your 3458a's firmware to accept the lower voltage value of the ADR.
Would you mind sharing the process? I like to try it as well...

BR,

Max

Hello Max,

It was not sufficient to only change the minimum limit for the CAL? 2,5 parameter, i.e. the minimum internal voltage reference, to 6.5000V, but it was also necessary to modify all those lower ACAL limits, which the lower reference voltage also affects.
This can be identified by comparing the auto-calibration constants of a 3458A with two different reference voltages, like a regular LTZ1000, and one with a different LTZ chip, or with an ADR1000 on board, and slightly faked calibration reference values.
TiN kindly helped me by testing my first version on one of his 3458As, and sending me dumps of all his calibration constants. With the ADR1000, he found out, that the ACAL procedure gave system errors, due to several  lower limit violations.

So the procedure is to search for the location of these additional, crucial constants CAL? XXX,5 inside the firmware (=> 13 EA), and then lower them by the approximate difference by the ADR1000 voltage, about 6.667V, and the lower limit of the LTZ1000, i.e. CAL? 2,5 = 7.000V, i.e. each new minimum value has be calculated to about -6% each.
The displayed minimum values CAL? XXX,5 are not represented directly in the firmware, instead they are a calculated product of several internal cal parameters, so that's a bit tricky to find them in the hex file.

For that you need an appropriate hex editor, which is also capable of calculating the DOUBLE numbers back and forth, by taking care for the correct endianess and correct byte-order inside the single or 6 fold EPROMs, so that you can now determine the new lower limits.
I've done that successfully on my 2nd firmware version, which I also run in my own 3458A.

TiN was again so kind to test it and he confirmed that now the basic calibration processes, CAL 0, CAL 10 and CAL 10000 are successful, as well as the ACAL ALL procedure.
Next step would be to optimize the ADR1000 reference board for lowest noise performance, maybe also using less noisy OpAmps inside the 3458A, and then check against another external ADR1000 reference, or another 4x averaged zener reference, if the 3458A then shows a lower noise performance as well.

I don't know, how much further hints or spoilers you want to receive, just let me know.

Frank   
 

Offline MaxTesla

  • Contributor
  • Posts: 19
  • Country: ch
Re: First Tests ADR1000AHZ
« Reply #196 on: December 06, 2021, 05:29:20 pm »
...
 
The noise of the ADRs RefAmp evidently is about 50% of the LTZ1000, which several others also have confirmed.

...

As my 34465A showed much higher stability / lower noise when I replaced its LM399 reference by a LTZ1000 clone PCB, my idea is to replace the LTZ1000 in my 3458A with an ADR1000 (*).
Maybe its noise figures will also go down, best by a factor of 2.
....

I would like to remind that TiN some time ago made a similar experiment on one of his 3458A, by implementing 4 parallel LTZ references, which would also yield 50% noise of a single LTZ.
I'm not aware what his final result was.


Frank

(*) my 3458A already has a modified FW, with CAL? 2,5 = 6.50000V (7V reference lower limit).
Thanks to Poul-Henning Kamp for your advice how to correct the checksum.


Hello Frank,

in your post you mentioned that you modified your 3458a's firmware to accept the lower voltage value of the ADR.
Would you mind sharing the process? I like to try it as well...

BR,

Max

Hello Max,

It was not sufficient to only change the minimum limit for the CAL? 2,5 parameter, i.e. the minimum internal voltage reference, to 6.5000V, but it was also necessary to modify all those lower ACAL limits, which the lower reference voltage also affects.
This can be identified by comparing the auto-calibration constants of a 3458A with two different reference voltages, like a regular LTZ1000, and one with a different LTZ chip, or with an ADR1000 on board, and slightly faked calibration reference values.
TiN kindly helped me by testing my first version on one of his 3458As, and sending me dumps of all his calibration constants. With the ADR1000, he found out, that the ACAL procedure gave system errors, due to several  lower limit violations.

So the procedure is to search for the location of these additional, crucial constants CAL? XXX,5 inside the firmware (=> 13 EA), and then lower them by the approximate difference by the ADR1000 voltage, about 6.667V, and the lower limit of the LTZ1000, i.e. CAL? 2,5 = 7.000V, i.e. each new minimum value has be calculated to about -6% each.
The displayed minimum values CAL? XXX,5 are not represented directly in the firmware, instead they are a calculated product of several internal cal parameters, so that's a bit tricky to find them in the hex file.

For that you need an appropriate hex editor, which is also capable of calculating the DOUBLE numbers back and forth, by taking care for the correct endianess and correct byte-order inside the single or 6 fold EPROMs, so that you can now determine the new lower limits.
I've done that successfully on my 2nd firmware version, which I also run in my own 3458A.

TiN was again so kind to test it and he confirmed that now the basic calibration processes, CAL 0, CAL 10 and CAL 10000 are successful, as well as the ACAL ALL procedure.
Next step would be to optimize the ADR1000 reference board for lowest noise performance, maybe also using less noisy OpAmps inside the 3458A, and then check against another external ADR1000 reference, or another 4x averaged zener reference, if the 3458A then shows a lower noise performance as well.

I don't know, how much further hints or spoilers you want to receive, just let me know.

Frank   

Hey Frank,

thanks for your detailed answer. This sounds like a lot of changes to the firmware (especially for my limit skillset regarding this kind of stuff). I will definitly have a look into it.
THB I was more on the look for a higher stability spec then lower noise, but for that I first need to finish some boards to test and select some ADRs.

For me it would seem a lot simpler to redesign the A9 board with a small (stable) amp which boosts the ADR output just enough to get in the range of working (i.e. 7 Volts if i remember it correctly).
Obviously noise is concerne in this regard, but this should be manageable (at least from my perspective today) with the right selcetion of ADR/Circuit and would be a "upgrade" path for others without touching any firmware.
To compare agiant I would use another ADR reference, as I am currently designing my take on a 10V reference.

Opions on this "plan" are obviously welcome :)

BR,

Max




 

Online Kleinstein

  • Super Contributor
  • ***
  • Posts: 14018
  • Country: de
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #197 on: December 06, 2021, 06:19:08 pm »
Adding some 6% of gain the reference circuit would still require very stable resistors, not to increase the drift. Added noise would be the least problem.
It it is just about getting a long term stable reference the old type LTZ1000 reference may be the better choice, maybe with a reduced temperature.

So far the limited reports on the ADR1000 are showing very low noise, but also still some drift. There is still some hope to improve on the drift with burn in or annealing, but I would not absolutely count on this. The advantage of the ADR1000 is more that it can get away with lesser grade resistors and still get good stability. With really good resistors the LTZ1000 may still be more stable.
 

Offline branadicTopic starter

  • Super Contributor
  • ***
  • Posts: 2377
  • Country: de
  • Sounds like noise
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #198 on: December 06, 2021, 07:40:45 pm »
Speaking of drift, I reached 3000 h but I'm not happy with the result. Nevertheless, I guess it is good advice to share such results anyway.

-branadic-
Computers exist to solve problems that we wouldn't have without them. AI exists to answer questions, we wouldn't ask without it.
 
The following users thanked this post: chickenHeadKnob, Andreas, doktor pyta

Offline MaxTesla

  • Contributor
  • Posts: 19
  • Country: ch
Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #199 on: December 06, 2021, 08:04:20 pm »
Adding some 6% of gain the reference circuit would still require very stable resistors, not to increase the drift. Added noise would be the least problem.
It it is just about getting a long term stable reference the old type LTZ1000 reference may be the better choice, maybe with a reduced temperature.

So far the limited reports on the ADR1000 are showing very low noise, but also still some drift. There is still some hope to improve on the drift with burn in or annealing, but I would not absolutely count on this. The advantage of the ADR1000 is more that it can get away with lesser grade resistors and still get good stability. With really good resistors the LTZ1000 may still be more stable.

Yes you might be right. But with the limited dataset I still plane on experimenting. I have treated myself with a set of VHP101 for a LTZ (70k,120,13k/1k) and the ADR (acc to the Datasheet). Plane is to put the LTZ in the mix with the ADR in with the same layout and test them side by side. This will take some time though as my ADR resistors are scheduled for march…goal is to compare drift and tempco. This will be done against my well aged 732a so may in a year from now I will have somewhat meaningful results, after that I will have a look at the A9 board project again I think.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf