Lowest drift, lowest noise voltage reference (ADR1000AHZ)

[Kleinstein]

In some cases one can indeed speed up things with just a higher temperature.  Many prodesses speed up by a factor or 2 every 5-10 K. So it would need some 50-100 K more to get a factor of 1000 speed up.
With some thermal activated processes the exponential law holds over a really large range. The limits may be more with the measurement (both at the fast and slow end).

The shape of the curve loops like 2 processes, a slighlty faster settling one going negative and a slower one going positive.
Given the same type of sample and no additional turn around visible it is even quite likely that this are the same 2 processes.

The rather high temperature however also comes with a downside: the residual aging processes also get faster and this result in more drift after the initial settling.

[branadic]

I disagree, you can't compare ADR1000 with a totally different schematic and components involved with ADR1001 and correlate aging curve shapes. You could though for same devices and designs, such as multiple ADR1001 running at different temperatures.

-branadic-

[Kleinstein]

I have not realized that imo' curve was for a different, though still similar chip.  So hard to tell if the same porcesses are involved.

The point of the parts around the actual reference is also a good one.  There is drift from the actual reference chip, but possibly also from the resistors around them.  The ADR1000 should have a realtively good attenuation of drift - from the DS a factor of ~ 200 for the set temperature and ~ 230 for the "60 K" resistor R2. It is a bit unclear, but I would not expect much effect from the resistors.  I tend to see R2 as the more critical. 1 ppm overall drif would need some 200 ppm of drift from the resistor. Over 14000 hours is not that likely to get for a good resistor.
So chances are most of the drift seen for the ADR1000 ciruit is actually from the reference chip and not from the resistors.
What resistor types are used for R2 in brandic's reference ? ( the info may be somewhere at the start of the thread, but hard to find - the picture shows 2 metal cans, some SMD and a DIP16 array (likely for the set temperature)).

[iMo]

The initial drift at the high temperature with my ADR1001 has been measured directly at the 10V output of the ADR1001. That involved basically the same "schematics" as the most 10V refs with ADR/LTZ1000 with 10V output. Sure - the resistors are different technology. My guess would be the initial drift comes from the ADR1000 structure we most probably have the same technology (as I doubt ADI has developed a new kind of reference for the ADR1001).

[branadic]

That is just speculation unless someone shows a bare die image of what's inside an ADR1001 package. Until then I wouldn't even think about similar behavior especially if some 13 hours on a single specimen were measured with a 6.5 digit meter.

-branadic-

[Noopy]

That is just speculation unless someone shows a bare die image of what's inside an ADR1001 package.

I would love to!!! :'(

[balun]

That is just speculation unless someone shows a bare die image of what's inside an ADR1001 package.

I would love to!!! :'(

I would donate one to you if you tell me where to get it.

[Noopy]

That is just speculation unless someone shows a bare die image of what's inside an ADR1001 package.

I would love to!!! :'(

I would donate one to you if you tell me where to get it.

That's very kind but the problem is you can't buy one and you (or at least I) can't sample one. 

[Andreas]

Hello,

update on ageing drift of my ADR1000A#01 + #02 now at 9 kHrs
see also:
https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg4709861/#msg4709861

Humidity is still low but the 10V output divider drift is still rising.
So now it is clear that the 6V6 to 10V divider has its own ageing drift.

If I take the X-Axis not in days but in sqrt(kHrs) getting 3 kHrs out of
the sqrt(9 kHrs) the ageing drift of both
6V6 outputs is nearly linear with -2 ppm/sqrt(kHrs).
Except for the last kHr where ageing drift seems to get slower.

with best regards

Andreas

[Dr. Frank]

Here's my ADR1000 #3 drift report, fresh from the 3458A as of today.
It's the buffered, raw V_Z of the ADR1000.
For the last 6 months, the voltage drift seems to have stabilized to reasonable -1ppm/a.



As a reference, here are the overall drifts of my Volt Group. One can see the improved Transfer Accuracy of about 0.1ppm.



Yesterday, TiN finally uncovered his revolutionary 10 Digit Cryogenic Standard HP3458A.
As a premiere, I'd like to present my mediocre 9 digit, 0.02ppm Standard Deviation, hand written protocol from today.
I can keep up with TiN a little bit, as my transcript was done with a PTB pencil, so it must be extremely precise.



Frank

[branadic]

So this is ADR1000#3, what about ADR1000#1 and #2?

-branadic-

[Dr. Frank]

I already had 10 references running continuosly,  2 further intermittently, so I assembled 1 PCB only. Sorry.

[branadic]

I meanwhile switched from hours to days on the horizontal axis, so here is an update after 634 days (15228 hours) of operation. In general the ADR1000 based reference seems to be stable, but shows some variation that I can't really correlate with temperature nor humidity. Due to missing access of the buffered raw zener voltage it is unknown whether this is a result of the resistor network of the boost stage or the reference and its associated components.

-branadic-

[Dr. Frank]

Here are the stability data for the ADR #3 as of today.
The reference now seems to have stabilized, as its drift was < 0.5ppm over the last seven months.
In comparison there are my two LTZ1000A, which had been thermally pre conditioned, with -1.0 and -1.5 ppm/ 2 years.
My Fluke 7000, which is the worst drifter from the batch, still has a higher drift of about -1.5ppm/year, but that's still inside its specification.
I assume, that its 7V => 10V stage is the culprit.

I never want to suggest anything by such comparisons, but maybe the single ratio divider IC is also the root cause for branadics ADR1000's big 10V drift.
It wouldn't cost you anything but an additional jack at the lower point of this divider, to measure the direct reference voltage.

Frank

[branadic]

@ Frank
From what I see the initial drift is not that much different to your buffered zener voltage. However, on my reference at some point a drift with reverse direction is taking over, which could potentially be the resistor network, I fully agree. Nevertheless, this drift meanwhile seems to have stabilized too and I only see some variations, that can't directly be correlated with temperature or humidity, which is a bit odd.

Connecting an additional jack to the inverting input of the gain stage is a little tricky. I had quite some bad experience with that in the past, since this node is of high impedance, prone to introduce all sorts of noise/hum/disturbance.

On the other hand my reference board was designed to connect both Z- and Z+ points to add a second and different gain stage as a piggyback solution, hence why the regulated voltage is accessable on the board. I had hoped that a different and working solution (PWM-based gain stage or PWM-supoorted resistor divider gain stage) would show up here on the forum, but unfortunately that hasn't happened.
Custom made precision resistor networks at least where not in my scope, but could still be an option, including waiting forever for them to arrive.

-branadic-

[DH7DN]

@Dr. Frank

I don't know what "baseline 3458A" means and at this point I'm afraid to ask.    Could you explain it briefly, please? 

[Dr. Frank]

@Dr. Frank

I don't know what "baseline 3458A" means and at this point I'm afraid to ask.    Could you explain it briefly, please? 

That's my expression for a new calibration point, derived from a voltage reference with low uncertainty.

Over the past 10 years, or so, me and other volt-nuts exchanged voltage references, either on Metrology Meetings @ branadic, from the calibrated Fluke 7000 ensemble, which was calibrated by TiN to <0.5ppm uncertainty, by sending a known voltage reference from one participant to another, by personal meetings, or by sending one of my own DIY references to 'ap' for calibration.

This way, I was able to determine the drift rate of my ensemble of 8 references, and the averaged "Volt" of this whole ensemble. This predicted mean value fitted within 0.5ppm to the latest traveling standard which branadic had sent around last year. I meanwhile monitor the drift of 4 additional references, and the LTZ1000A inside my HP3458A.

So it's time now to get a new baseline point.

Frank

PS: I got my first baseline point in December 2009, when I acquired my Fluke 5442A (with unknown uncertainty) and compared it to my first two LTZ1000 prototype references, built in around 2004 and running since then.

[DH7DN]

Doing "inter-voltnut" comparisons is a good (and also very important/necessary) metrological practice. Thank you very much for your explanation, Dr. Frank. 

[chris_11]

So long story short, within 40 years there is only a very small improvement on heated buried zener references. Todays much cleaner and more precise processes make popcorn noise less likely, but in essence the ADR1000 winds up with comparable drift to the LTZ1000A.
Or did I miss something?

[Andreas]

Hello,

update on ageing drift of my ADR1000A#01 + #02 now at 10 kHrs
see also:
https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg4789418/#msg4789418

At the moment the zener drift is around -0.3 ppm for the last kHr on the 6.6V outputs.

Humidity is still low but the 10V output divider drift is still rising.
It does not fully compensate the falling drift of the zener so the resulting drift is ~-0.1 ppm for the 10V output.

with best regards

Andreas

[branadic]

I passed 16550 hours, so here is an update.

-branadic-

[Andreas]

Hello,

I now passed 11 kHrs:

the 10V output on ADR#01 seems to stabilize.
the 6V6 output ageing rates are slowing down.
And this even with SQRT on the X-Axis.

Divider drift is still rising.
Since spring has passed the humidity rH% is now rising.

with best regards

Andreas

[branadic]

Divider drift is still rising.

Could you perform a fit to tell what formular it follows? Looks like a ld(x) function.

-branadic-

[Andreas]

Hello branadic,

Good  idea!
if I use the time axis as sqrt(kHr) I get a near linear behaviour above 1kHr

with best regards

Andreas

[branadic]

Two years of data, time for an update of my graph.

-branadic-