ADR1001 - Ovenized Voltage Reference System

[iMo]

Below the last ADR1001#1 measurement after almost a year on.
The hw V7, with the aprox 2ppm increase due to the added 4n7 feedback capacitor at the OPA189.

I've switched off the reference, and I will continue after some time to see the hysteresis, if any.

Hopefully the ADR1001 will be released soon such we can see in the DS how to wire it.. 
PS: the latest message from ADI - around FEB2024

[iMo]

This is the noise coming off myADR1001#1 10V reference box in the 0.1 to 10Hz band as shown with my \$\textrm{Noise Indicator}\$.
Both Vreference as well as the \$\textrm{Noise Indicator}\$ have been powered from batteries (each its own battery), the o'scope via an isolation transformer.
The Vreference itself is not shielded (a plastic box).
The voltage fed via an aprox 35cm long twisted CAT pair directly into the LM399 socket (located in the shielded \$\textrm{Noise Indicator}\$), the zener's cathode resistor disconnected.
The background noise with this setup is 0.16-0.18uVpp, with the wires shorted at one external Vref's post.
The indicated noise levels around 2uVpp (at 10V OPA189 buffered output) look similar (or better?) to the better one ADR1399 sample I have got (and less a half noise level of my best LM399s).

PS: the ADI's info in the first post here says "0.7uVpp in 0.1-10Hz at [onchip] buffer's 5V output"..
PS1: there is the standard 1uF serial 4R7 at the Noise Indicator's input in this setup (coming from the 399 zener's RC compensation). That actually loads the output of myADR1k#1 reference as well.

[iMo]

Let me continue here with the ADR1001#1 vs HP399 (inside my 34401A) and vs LM399H#2 (inside my 34401A as the replacement of the HP399).

The old HP399 is pretty hairy - it pops and cracks couple of times every 12 seconds period on the o'scope screen when looking at it with my Noise Indicator (below see some shots). Its background noise is rather low, and perhaps once in many hours staring into the scope I saw a popfree clean 3.1uVpp which is at the best end of all my 399s.

When the HP399 was off the meter I replaced it with a LM399H#2 which showed me no pops in past (as seen with the noise indicator).

Below the results while measuring my ADR1001#1 based 10V reference (with also none pops while in Noise Indicator).

HP399 - it pops and cracks always, wildly, like radon gas in the cloud chamber, but it is "pre-selected by HP" and 25+ years in service, therefore its ADEV (pink) shows lower sigma with long taus. The amplitudes of its fluctuations are lower than those of the LM399H#2 it seems.

LM399H#2 - it "cracked" only 6 times over the night run  , amplitudes of the fluctuations are a bit higher.
Its ADEV (blue) is better at lower taus, worse at the longer taus compared to the HP399.

You may also see how a running STD can nicely detect the pops and cracks in the incoming data stream (like you staring into the smartphone at the incoming numbers and you see the STD is 1.5uV - it means something happened during last N samples)..

Conclusion - we need a Popcorn Indicator 

[iMo]

And the HP399 pops as seen on the scope.
10mV == 1uV

PS: Mind the pops here are derivatives of what happens - as the 0.1-10Hz filter is RC coupled (1000uF/1k5 high pass) thus a single short "pop" on the screen means usually a shift of the voltage up or down.

[iMo]

I put the HP399 back into the DMM.
I wired a 3u3/50V Wima foil parallel to the HP399's zener as well as a 0.47u/40V tantalum to its heater (both caps soldered directly at its socket from the bottom).
I put a foam cap on the HP399 from top and bottom (aprox 3x3cm foam blocks).

The overnight run shows the capacitor has indeed some effect - see below - the ADEV and running STD are slightly better.

Better improvement would be easily possible with an RC low pass filter, imho, like 10k/3u3, that would require a replacement of the 706 opamp with something with say 10-20pA input bias (706 got max 200pA, and max 1.5uV/C, that is nothing special).

[Kleinstein]

The input bias of the AD706 is not that bad. It would be the least problem. If needed one could use less than 10 K and more than 3.3 µF for the capacitor. AFAIR I have some 5 K and 6.8 µF at my ADC circuit.
A film capacitor directly at the LM399 may not be that ideal as it could be borderline instable. Better have some series R or use an electrolytic with significant ESR.

The reference filtering for the HP34401 does not have to be very low cross over. There are mainly 2 frequency ranges where it helps: one is at low frequencies, like 2.5 / 25 Hz for 10 / 1 PLC operation and the other is at some 10-375 kHz as the as the modulation frequencies. The 2.5 Hz band is nearly out of reach and the higher frequencies are relatively easy.

[iMo]

Hmm, doable..
Note: the pcb picture from xdevs.com

With say +-200pA max the Vref's voltage shift with a 10k resistor will be +-2uV which is rather negligible..

[iMo]

Here is the myADR1001#1 aging report.
The jump there has been caused by adding the 4n7 feedback capacitor to the OPA189.
The myADR1001#1 and 34401A have been off for a week, then 4 days warm up of both.
No "visible" hysteresis observed.
The 34401A needs 3-4days for the warm up. There are two phases visible - first it goes some 1-2ppm higher after first 6 hours on, the second it is slowly dropping down for 3-4 days by those 1-2ppm and stays "stable". Would be great to know how to track down where it happens inside the meter, it is pretty annoying.. 

[iMo]

This is how an overnight measurement looks like.
On top - raw data off the 34401A, then Median10 applied, then TEMA(0.005) applied.
Finally the raw data MADEV of the measurement.
The ADR1001#1 shows aprox 9.999878 Volt. I've been planning the LAB3 measurement around the new year, to get an idea where the reference fluctuated since April/July.

[ramon]

That is wonderfully flat. Can you plot two weeks?

[iMo]

I do 1-2 days only so far. Running it for 2 weeks at 100NPLC would require logging directly from the MCU onto an SDcard I do not have wired in yet. The logging via bluetooth into the smartphone (I've been doing now) is not reliable enough for such long term exercises. But what I can see so far the voltage sits on that value for several days and does a random walk within say +/-0.5ppm (raw not filtered) around the value based on the pops inside the references and EMI around.

[iMo]

That is wonderfully flat. Can you plot two weeks?

This is a week of data, 100NPLC HP34401A.

[branadic]

So Oct. 2023 passed and ADR1001 still isn't available at ADI website. But it seems like ADI sent 10 sample in November to someone in Shanghai, China (Leo Guo?).



Yet no sample order possible for me 

-branadic-

[floobydust]

I think those came through a back channel?  In the video they were packaged as loose pieces in the ESD bag, no label just felt pen writing on the ESD bag. A bit suspect.
That was in a blank U-Line (Canada) bubble mailer envelope, inside a DHL bag, inside a DHL box. A bit suspect.

Has anyone tried getting a quote on them from mainstream distributors?
edit: Could request an update either on the ADI voltage reference forum or contacting the team.
I suspect this part has LT roots, could go after the LT engineers for answers, the few that survived.

[iMo]

Based on my info from ADI the planned release is FEB 2024.

[Andreas]

Hello,

did anyone already do some (thermal) hysteresis measurements.
For me the temperature range 25 -> 10 -> 25 -> 40 -> 25 deg C environment would be interesting.

Is the ADR1001 sensitive to tilting?

with best regards

Andreas

[iMo]

Below today's startup measurement of myADR1001#1 box. Raw data after DMM TC correction. Vref box powered by the internal transformer as the power supply.

It made aprox -2ppm during the first 1.5h after the powering on.
The ref was powered off for 12hours (the longest power off since Dec2022), the final temperature inside the sandwich below was 35.5C. That indicates TC of myADR box aprox -0.14ppm/C (fyi the very first TC measurement in this thread - Reply #89 - was -0.144ppm/C).
Mind that it is the TC of entire Vref box, incl. the powering by the transformer ac power supply inside.

It settled down within the previous measurements levels, so the hysteresis is somewhere within the measurement noise.

34401A's 10V range was adjusted 3weeks back against the reference (after I replaced all 4 large elyts in the DMM), thus today I do TC correction only.

PS: the 34401A's adjustment step off the front panel is 10uV only at the 10V range.. 
PS1: to be less optimistic I would rather draw the green box 1ppm wide

[Kleinstein]

If the Temperature variations are from changes in the room temperature, chances are the meter to read the votlage would also see the changes. So the measurement includes the TC of the meter too.

[iMo]

I deleted the graph as I have to rethink the approach. The TC of the meter is always compensated in the postprocessing..
But I think the approach was wrong as the ppm vs Tamb included the aging drop..
So - you made 32 measurements (say during 1 year time frame), each made at certain Tamb, the TC of the meter is compensated against Tamb, and the Vref was dropping (because of the aging) during that time frame till say -2ppm at the end. How to get the TC of the Vref? Not an easy exercise, imho..

[Andreas]

How to get the TC of the Vref? Not an easy exercise, imho..

Why not temperature cycle the Vref over a larger temperature in a "environmental chamber" while keeping the DMM at constant temperature?

The other way would be to do 2-dimensional correlation (assuming that the ageing drift is linear over time or SQRT over time).
This is how I determined ageing + humidity coefficient of the AD586MNZ references

with best regards

Andreas

[iMo]

That was just an idea of myself to look at the measurements I did last year and try to derive the TC of the Vref out of it as well. I have to have a look at the aging drift fit and perhaps try the correlation..

[miro123]

And now the ADR1001 part has appeared on the ADI website

https://www.analog.com/en/products/adr1001.html#product-overview

Along with the user guide for the pocket calibrator part

https://www.analog.com/media/en/technical-documentation/user-guides/eval-adr1001-ug-2194.pdf

Now i need to try and get some......

The datasheet is still preliminary . I have no idea what AD gives for long term drift in datasheet page 3
Long Term Drift  6V6
 200h -3ppm
 1000h -5ppm
 2000h -5ppm
Then at page 5 the 5V Vref
 200h -2ppm
 1000h -4ppm
 2000h -5ppm

[iMo]

Well, what I've been missing in myADR1001#1 reference box:
1. Rlimit in the heater (4.7-10ohm)
2. 100nF capacitor in the output buffer feedback (Fig. 48, between BUF_S and BUF_F, 10V output)
Otherwise the DS fits well my previous measurements and the LTSpice model (ie the temperature settings).. 
What needs to be checked with production chips is the output resistance of the buffer (10V output)..

[ArdWar]

Uh huh? The 6V6 and 5V long term drift specs and charts don't quite make much sense unless they're somehow implying that the divider is actually part of the TC compensation and 5V is more stable than 6V6 itself.

[Andreas]

And now the ADR1001 part has appeared on the ADI website

https://www.analog.com/en/products/adr1001.html#product-overview

Hmm,
the T.C. curves are rather "discrete" (10 degree steps)
What I am fully missing is any specification for temperature hysteresis. (only switch off hysteresis which is rather large).

And the T.C. sweep of Imo is also only over a 10 deg span.

with best regards

Andreas