Lowest drift, lowest noise voltage reference (ADR1000AHZ)

[MiDi]

Asking me, how did ADI get to their DS value of 0.5ppm/year, which is at least 10x less than what we see?
For me "typical" means at least 2/3 of significant samples from production line satisfy DS value.
ADI following VPG way with MBS or are all those we see engineering samples with worse specs?

You got the early samples.. Would be better to wait till they fine-tune their production process.. 

Guess or do you have secret information?

[iMo]

In Sept2021 within the Germany remote workshop ADI designers described the pretty recent history of ADR1000 R&D.
While doing such an exercise you certainly would produce XX thousands of chips (early ones). Some quantities get packaged, some stay as dies. There are many subcontractors/customers who evaluate(d) them, not only our voltnuts from eevblog are involved. Thus I can imagine myself there are thousands of ADR1000s floating around I would call "an early sample".. That is with all chips, imho, but for example nobody will spend a year with daily elaborating an LM358 (as you do with the ADR1xxx) whether it fits the strict DS values perfectly, or not..

[dietert1]

One plausible speculation is that early samples are missing some vendor side burn-in and selection. Later they will be able to offer parts including burn-in and selection. Probably the datasheet drift specs were assumptions based on the LTZ1000 datasheet

Regards, Dieter

[iMo]

ADI started to think about the LTZ1000 replacement in 2016. They started R&D in 2016 from scratch. First chips in packages are dated Q34 2018, afaik. As the experts here say you need years to evaluate the parameters of such fine technology all chips you got so far are those I would call "early samples".. 

[branadic]

As far as I've heard, early engineering samples such as date code 1727 haven't seen the bake and burn (168 h @ 150 °C), while all later date codes (1839, 2108) are production samples.

-branadic-

[iMo]

Make a small "heating hat" where you can regulate the temperature and put on it on its case, thus you can burn-in it while it is soldered already in your board..

[iMo]

Make a small "heating hat" where you can regulate the temperature and put on it on its case, thus you can burn-in it while it is soldered already in your board..

Like a micro oven inside another micro oven (414 resistor size for comparison)

I thought a small hat which fits just on the top of the ADR1k package - that is for burn-in only - such you can heat the body of the ADR1k up to those 120-150C, while the ADR1k is already soldered into your board (you do not want to cook your entire pcb with all other components on it in an oven, or do you?

[cellularmitosis]

Can you just use the built-in heater for burn-in?  Temporarily use a pull-down on the temp-control resistor divider?

[iMo]

Can you just use the built-in heater for burn-in?  Temporarily use a pull-down on the temp-control resistor divider?

You have to calculate the current needed. The thermal resistance of the package is 216 C/W (soldered in two layer pcb, DS), thus you would need aprox 49mA through the 240ohm ADR1k heater to get the chip at 150C with 25C ambient (double-check my math plz).
PS: the "annealing recipe" above expects stepping the temperature up and down at various temperatures, thus it seems to me to be easier to have the burn-in hat with easy temp reg put on your head. 

[Kleinstein]

One could use the internal heat for a burn in, at least for the lower temperatures. Depending on ther thermals around the chip the temperature is limited, especcily if there is only a 15 V or so supply.
There is howerver still the question on which temperature profile and maybe zener current would be correct for the burn in. There are different processes going on and hotter is not always better. The glass temperature of epoxies is just within the possible range. Another point is thermal stress that can build up when keeping the ref at a higher temperature for a long time.

[iMo]

You would need 11.8V on the internal 240ohm heater to get 580mW, that is aprox 150C on chip provided the case is 216C/W thermal resistance and ambient is 25C.
PS: the internal heater resistance is specified around 240ohm at 1mA heater current in the DS. It could be pretty different at 49mA (and such high temp), however..

[manganin]

Years ago I built an aging rig for the AD587 references. The total power comsumption of 100 chips was so high, that no separate heater was needed. The temperature control loop simply adjusted the supply voltage.

Thanks to the distributed heat source, the temperature gradients were minimal. So I could trust that all the chips got the same treatment.

Smaller number of chips (less power dissipated) requires of course better insulation to get the same temperature.

[Andreas]

Hello,

update on ageing drift of my ADR1000A#01 + #02 now at 5 kHrs
see also:
https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg4397278/#msg4397278

the 6.6V zener outputs still drift -0.3 ppm/khr while the 10V output is better (the voltage divider drifts the other direction most probably due to still high humidity).
The Jump on ADR#02 on day 180 by +0.7ppm was created by a flat battery for ~3 days (I had forgotten to attach the charger).
At the same time I had also a Jump of 0.4 ppm on the LTZ9 sanity check so not all of the 0.7 ppm are true.
But afterwards I have still a permanent hysteresis of ~0.4 ppm due to the power off phase.

So regarding hysteresis this observation confirms the measurements of Dr. Frank.
https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg4398226/#msg4398226

with best regards

Andreas

[branadic]

I guess we can call it "All Drift Reference 1000" 
My experiment is still running too, but it is not yet conclusive. At some point (after around 6000 - 7000 h) the drift changed sign and is now drifting upwards instead of downwards.

-branadic-

[branadic]

Let me share an update of my measurement results (10V output, so we don't look at the raw zener voltage).
Any shift of the signals can be explained by either turning on/off instruments, removing equipment from the setup, changing batteries and the like, so what really counts is the overall behavior of the references, not the details.
What can be observed is a downward drift first, a change in sign second, followed by a steady state at the moment, while we have to be patient how that evolves next.

My current suggestion for a future experiment is to have three ADR references running at different oven temperatures:

1. running ADR oven at its zero t.c. temperature (~50 °C, that is a resistor ratio of about 11.5:1 for the datasheet circuit or about 0.52 V for the circuit using the temperature sensing transistor as a diode)
2. running ADR at 75 °C oven temperature (that is a resistor ratio of about 13:1 for the datasheet circuit or about 0.465 V for the circuit using the temperature sensing transistor as a diode)
3. running ADR at 100 °C oven temperature (that is a resistor ratio of about 14.6:1 for the datasheet circuit or about 0.41 V for the circuit using the temperature sensing transistor as a diode)

The comparison of the drift between these three references should indicate what time it takes for the references to stabilize at which temperature, though it's not an abolute measure. Once stabilized the oven of the latter two references can be set to the zero t.c. temperature of their zener. For this experiment I would use the raw zener voltage buffered and preferable nanovoltmeters to measure the differences.

-branadic-

[KT88]

My current suggestion for a future experiment is to have three ADR references running at different oven temperatures:

1. running ADR oven at its zero t.c. temperature (~50 °C, that is a resistor ratio of about 11.5:1 for the datasheet circuit or about 0.52 V for the circuit using the temperature sensing transistor as a diode)
2. running ADR at 75 °C oven temperature (that is a resistor ratio of about 13:1 for the datasheet circuit or about 0.465 V for the circuit using the temperature sensing transistor as a diode)
3. running ADR at 100 °C oven temperature (that is a resistor ratio of about 14.6:1 for the datasheet circuit or about 0.41 V for the circuit using the temperature sensing transistor as a diode)

-branadic-

Ideally a couple of specimens from at least three production lots should be taken to get a more meaningfull result. Of course that would be quite a challenge when it comes to different production lots...

Cheers
Andreas

[Andreas]

Hello,

I also think that you need at least 3 samples per group.
With my LTZ-References one of 9 samples (LTZ#8) showed more than 1 year until it stabilized below the typical 1-2 ppm/year.
During first year I had a -3.4 ppm drift.

For the rising drift: I think it is partly related to the humidity of the output voltage divider.
So I guess it will fall again during upcoming months (winter) when humidity is falling.

with best regards

Andreas

[branadic]

From an academical point of view I agree to the sample size, but it's a question of cost and samples at hand and at least I have 5 ADR samples including the required resistors left with which I can do further investigation. I'm not claiming statistical relevance, but indication only.

Edit: While humidity influence is a valid assumption for possible drift, I don't see any real correleation and hence no causality yet.

-branadic-

[iMo]

Guys, while observing your efforts and cost of material and electricity you spend a single well working 10V reference is worth of a Bugatti Chiron.. 

[openloop]

The ADA4084 suggested in the ADR1000 datasheet may be a bit questionable.

Just realized: Configuration, where grounds for force and signal are separate (as in a diagram in ADR1000 datasheet), appears to be problematic indeed for ADA4084.

Look at the Fig.48 (p18) from ADA4084 datasheet. The left side (right where we are) is not a good place to be. Some minor action of the heater (lifting the "force" ground a bit) might cause offset to go off by up to 0.5mV!
That will translate into, like, 2uV of additional swing of reference, on top of everything else...

I do not like ADA4084 here at all.

[Andreas]

Hello,

update on ageing drift of my ADR1000A#01 + #02 now at 6 kHrs
see also:
https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg4464853/#msg4464853

the 6.6V zener outputs are now at -0.5 ppm/khr while the 10V output is still better at ~ -0.3 pm/kHr.
As it is getting more and more cold outside and now after a rainy phase starting with less air humidity:
I am very curious wether the different 10V output of the statistical divider is correlated with humidity or simple ageing drift.

with best regards

Andreas

[dietert1]

As far as i understand the diagram, the division ratio of the statistical divider drifted about 1 ppm in 250 days. That's an interesting result by itself. Which part are you using for the divider?

Regards, Dieter

[branadic]

Thanks for your update Andreas, 0.5 ppm/khr still isn't the typical 0.5 ppm/a as per datasheet
Also interesting to see the difference between buffered and scaled output.
I'm heading towards 12.000 h with the sample I'm running.

-branadic-

[Andreas]

Hello Dieter,

I am using a TDP16031002AUF.
Effectively 6 out of the 8 resistors in the DIP16 package are used for a *1.5 configuration.

with best regards

Andreas

[ap]

Although this formally seems not to be a NOMC network, it seems to use the same materials (NiCr). So the 1ppm in 250 days seem way more than one would expect.