Author Topic: Lowest drift, lowest noise voltage reference (ADR1000AHZ)  (Read 144987 times)

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Offline wutieru

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #125 on: October 12, 2021, 01:04:30 pm »
Niose with FFT
 

Offline Andreas

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #126 on: October 13, 2021, 05:31:16 am »
Helllo,

ok this is with bandwidth limiter.
So the fuzzyness of the signal is much better now.

FFT reveals that there is one frequency outside the passband of the LNA which is in amplitude similar than the passband signal.
I am not familiar with this scope. For me it looks like you did a linear frequency display with 157 Hz center frequency and 313 Hz span.
So roughly 31 Hz / div.
I guess that the (red marked) discrete frequency is the mains frequency with 50 Hz.

I usually use a metal cookies box to shield against fields from outside operating the DUT on batteries. But even with the shield I have to put all transformers away with a minimum distance of 1 m. Even my HP34401A internal transformer (shielding around transformer and the housing of the Instrument) has to be at a minimum distance of 0.5 m.

On a quiet place I have the 50 Hz hum  ~18 dB below the pass band for a ADR1000A.
See attachment with double logarithmic display.

with best regards

Andreas
 

Offline wutieru

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #127 on: October 13, 2021, 09:13:22 am »
Yes, there is 50Hz noise Exist, it comes from the test environment, I changed another oscilloscope, it disappeared, it seems that the shielding of KS oscilloscope is not very good.
 

Offline Andreas

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #128 on: October 17, 2021, 02:25:16 pm »

So you can see, it's a bake&burn process with the circuit powered, otherwise it would be a bake only. Hope that answers your question.


So according to that what is published the burn in cirquit would look something like this.
(the resitors of course cemented wire wound for the high temperature).
The unused heater is connected to substrate.

any comments?

with best regards

Andreas

 

Offline branadicTopic starter

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #129 on: October 17, 2021, 08:31:18 pm »
I can't really comment on that as I simply don't know. However, with respect to the question at MM2021 if the internal heater could be used for a bake&burn, Erics answer was related to the ADR1001, not to the ADR1000.
So one could propably set the oven temperature to a value of 150 °C, which would translate to a divider of 17.74k : 1k with the numbers given for the datasheet circuit and use the build in heater for the bake&burn of the ADR1000?

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Offline rigrunner

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #130 on: October 17, 2021, 10:12:52 pm »
I've been experimenting with heater temperature on the ADR1000.
Running the ADR heater at 85C for 48hrs, 110C for another 48hrs and then 150C for a further 48hrs briefly changed the drift direction on my sample of 1.
I'm still playing around with heating and will post should I discover anything useful.
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Offline wutieru

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #131 on: October 18, 2021, 01:20:58 am »
I think the burning@150° process is irreversible.  Test it several times and see how the curve changes?
 

Offline wutieru

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #132 on: October 18, 2021, 01:28:42 am »
Power off-on testing,first interval 3 hours,second interval 30 minutes.
It seems that the voltage has changed a little  after a long time of power off.

 

Offline Andreas

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #133 on: October 18, 2021, 05:13:28 am »
Running the ADR heater at 85C for 48hrs, 110C for another 48hrs and then 150C for a further 48hrs briefly changed the drift direction on my sample of 1.
The more interesting things would be:
- does the noise actually decrease.
- does the ageing drift (after a settling time) decrease.

Question: how did you check that the temperature was actually 150 deg C?

with best regards

Andreas
 

Offline Andreas

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #134 on: October 18, 2021, 05:26:46 am »
So one could propably set the oven temperature to a value of 150 °C, which would translate to a divider of 17.74k : 1k with the numbers given for the datasheet circuit and use the build in heater for the

Hello,

I fear this is not true with my sample.
when calculating from my measurements I get a slope of -2.24 mV/K for the sensing transistor with 70K and pin 6+8 connected. (offset 648.9 mV)
To get 150 deg C temperature I would have to set around 312 mV. which translates with a zener voltage of 6600 mV to a ratio 20.15K : 1K.

But will the Zener really still have 6600 mV at 150 deg C?

with best regards

Andreas
 

Offline branadicTopic starter

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #135 on: October 18, 2021, 06:57:51 am »
Quote
I fear this is not true with my sample.

Quote
... which would translate to a divider of 17.74k : 1k with the numbers given for the datasheet circuit

Using the temperature sensor as a diode requires for sure a different divider setpoint.

-branadic-
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Offline Vtile

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #136 on: October 18, 2021, 04:34:08 pm »
If there is any analogy to metallurgy, glass working and mineral manipulation by annealing one should not only apply heat, but also control the cooldown. Rule of thumb on those mentioned before is that slower is better.
 

Offline rigrunner

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #137 on: October 18, 2021, 05:08:55 pm »
The more interesting things would be:
- does the noise actually decrease.
No noise reduction yet.

- does the ageing drift (after a settling time) decrease.
It is still drifting at about the same rate.

Question: how did you check that the temperature was actually 150 deg C?

Measuring the diode voltage across Q2 using -2mV/C 

If there is any analogy to metallurgy, glass working and mineral manipulation by annealing one should not only apply heat, but also control the cooldown. Rule of thumb on those mentioned before is that slower is better.

Stepped temperature tests are something I had considered on a fresh ADR. I may try that when I have finished poking ADR#1.
« Last Edit: October 18, 2021, 05:28:27 pm by rigrunner »
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Offline rigrunner

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #138 on: October 18, 2021, 05:24:46 pm »
when calculating from my measurements I get a slope of -2.24 mV/K for the sensing transistor with 70K and pin 6+8 connected. (offset 648.9 mV)
To get 150 deg C temperature I would have to set around 312 mV. which translates with a zener voltage of 6600 mV to a ratio 20.15K : 1K.

But will the Zener really still have 6600 mV at 150 deg C?

With Q2 configured as a diode I measure around 574mV @ 25.2C for a 71K5 R3. ADR#1 and a random used LTZ are in the same ball park.


« Last Edit: October 18, 2021, 05:26:52 pm by rigrunner »
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Offline Andreas

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #139 on: October 18, 2021, 07:09:00 pm »
With Q2 configured as a diode I measure around 574mV @ 25.2C for a 71K5 R3. ADR#1 and a random used LTZ are in the same ball park.

The question is: how this is measured.
I need sampling with 1 NPLC (faster would be better) and measuring the very first sample (with heater off)
after power on to get 592.3 mV @ 25.3 deg C and 69.8K.
Due to self heating the voltage changes quickly during the first seconds
and finally stabilizes at around -20 mV lower level (+10 deg C).

... which would translate to a divider of 17.74k : 1k with the numbers given for the datasheet circuit
Ok, in datasheet the pull up resistor is only 62K so we have a slightly higher collector current.
But which datasheet numbers do you refer to? For Q2 I see only the table 7 with some values.

Measuring the diode voltage across Q2 using -2mV/C 

With my cirquit this would be roughly 10% too low. So only around 135 deg C.

This is one reason why I want to use 2*25W-aluminium wirewound resistors as heater
and sensing the case/environment temperature of the ADR with a PT1000 sensor.
The whole in a termo-isolated coffee mug or something like that.

with best regards

Andreas
 

Offline rigrunner

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #140 on: October 18, 2021, 08:12:28 pm »
With Q2 configured as a diode I measure around 574mV @ 25.2C for a 71K5 R3. ADR#1 and a random used LTZ are in the same ball park.

The question is: how this is measured.
I need sampling with 1 NPLC (faster would be better) and measuring the very first sample (with heater off)
after power on to get 592.3 mV @ 25.3 deg C and 69.8K.
Due to self heating the voltage changes quickly during the first seconds
and finally stabilizes at around -20 mV lower level (+10 deg C).


I can measure Q2 voltage with the opamp from the heater side of things removed.
I'll need to play around with my logging setup. I currently trigger a sample every minute.

    Measuring the diode voltage across Q2 using -2mV/C
With my cirquit this would be roughly 10% too low. So only around 135 deg C.

Best I can do at the moment for checking ADR can temperature is take a thermal image.

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Offline Kleinstein

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #141 on: October 18, 2021, 08:14:41 pm »
I think the burning@150° process is irreversible.  Test it several times and see how the curve changes?

I would expect some reversible effect of the heating to 150 C.
The 150 C are likely above, or at least close to the glass temperature of the die attach glue.
So this would kind of reset the glassy structure to a relatively open (high free volume) state. How much of this is retained depends on the speed of cool down and later aging at lower temperature like 60 C during operation.

The 150 C would be enough for stress from thermal mismatch between the silicon and case to relax. So this would start again from the same level.

The curing of the glues part would be irreversible and probably well fisched after 1 week at 150 C.
 

Offline rigrunner

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #142 on: October 19, 2021, 02:10:16 am »
The question is: how this is measured.
I need sampling with 1 NPLC (faster would be better) and measuring the very first sample (with heater off)

3457a setup with NDIG=4, NPLC=.1, AZERO=1,TARM=AUTO,TRIG=SGL, NRDGS=1.
Readings were taken as fast as the pi could manage in a python loop with query(3457,'?')

594.98mV start and drops 13.62mV in 190 seconds to 581.36mV with self heating.


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Offline branadicTopic starter

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #143 on: October 19, 2021, 10:28:32 am »
Quote
But which datasheet numbers do you refer to? For Q2 I see only the table 7 with some values.

I'm refering exactly to that table, from which you can extrapolate the resistor values for a 150 °C oven temperature for the datasheet circuit.
However, things are different when using Q1 as a diode only. By the way, from what I measured on my first unit I get a -2.166 mV/K for Q1 used as a diode.

Running my reference for about 1850 h by now I don't observe any real settling, though not a steady drift either.
The linear drift rate is about -360 nV/day (~13 ppm/a), allthough a square fit matches much better, while a square-root fit shows large deviations and doesn't match well, at least by now.

-branadic-
« Last Edit: October 19, 2021, 04:55:50 pm by branadic »
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Offline harerod

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #144 on: October 19, 2021, 07:02:04 pm »
I have been asking myself how a gang-burn-in of several ADR1000 might be set up. I have some Vishay RSSD resistors in the lab, which usually serve as loads during EMI tests of power supplies. Those resistors feature a cylindrical ceramic body, which can accommodate several TO-99.

Today's test was about general feasibility. I usually wouldn't touch a breadboard with a ten feet pole, but in these trying times of component shortages, I decided to go retro. It turned out that the only THT OPAMP, which I had at hand, was a veteran that has been with me for a very long time. No component on that breadboard is younger than thirty years.

Since I didn't want to risk an ADR1000 for tests, I decided to use an 1N4148 as target and a KTY81-122 as sensor for a temperature regulator.

I was a bit concerned about flammability, so I took care with the setup:
The two devices go into the RSSD 25x168 100R.
Eager to start the experiment I didn't even bother cleaning out the cookie jar.
The RSSD is suspended by some highly flame resistant steel mounts from the mill router. Some electrical insulation goes under the mounts, not shown in the picture.
The cookie jar is wrapped in cotton cloth. The cotton cloth rests on a thick towel and is covered by another towel.
The whole heap is placed on a metal step ladder next to my desk. 

It turns out that in steady state the setup burns 13W in the RSSD. It is autumn here and I need central heating to keep the lab warm, so I am not bothered by the power dissipation.
 

Now that everybody had a good laugh - could anybody tell how critical that 150°C burn-in temperature is, please?

In which temperature band should the die be kept?
What is the lowest temperature that makes sense?
At which temperature can we expect damage to the ADR1000?
After all, according to the datasheet, 150°C is the junction temperature limit for storage and operation.
 

Offline Kleinstein

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #145 on: October 19, 2021, 07:22:55 pm »
The main part to worry about, when going high in temperature is the die attach glue.  Epoxy may not like a temperature much above 170 C. With a little patience I would consider some 140 C and maybe even 130 C sufficient. This should still be at least close to the usual epoxy galss temperarure. It just takes longer at a lower temperaure.  If the target is an open structure and thus fast cool down, I would like to start at the glass temperature or above, but not much below.

I may make absolutely sense to later use a step at a lower temperature, maybe some 20 C above the later oven temperature.
 
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Offline branadicTopic starter

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #146 on: October 19, 2021, 09:03:39 pm »
Quote
What is the lowest temperature that makes sense?

It depends on what the mechanism for the initial drift actually is.

Eric Modica argued at MM2021: "... Another important aspect that carries over to the ADR1000 is the benefit of bake and burn process. So when I have first started working with buried zeners and Vrefs in general the conventional wisdom was that bake and burn speed up the aging of the part and that one could accelerate the early life drift to finish up sooner. That’s this area here, that’s the majority of your drift on parts like this, your uncertainty. So I’ve learned enough in my years working in analog design not to make broad generalisations, but what I’ve observed is that bake and burn is helpful primarily for low frequency noise reduction in this context. We have had tier 1 manufacturers tell us the same thing when we send them ADR1000s. Prior to instituting a bake and burn most of the parts look okay from a low frequency noise perspective, but if you look at it enough you find one that is extremly noisy and actually remedies with the bake and burn. So only being a process hobbiest myself, the only explaination I can give there is that you have these dangling hydrongene bonds at the surface of the SI and sometimes that amounts to surface charge and if that ends up in the vacinity of the zener, if you are unlucky enough, then this is the kind of thing that you get. And it’s really the only thing that would move at such low temperatures where you are running a bake and burn, say like a 150 °C...."

I don't know if this is the real deal and wouldn't argue against it, cause I can't prove him neither right nor wrong. However, I believe from what I've learned over the years on packaging of integrated circuits that two mechanisms are involved. One being the heavily doping in the silcon latice and the second coming from the assembly of the die within the package using die attach. All sorts of plastics, thermoplastic and thermoset, do suffer from stress after being (injection) molded or applied and cured. A thermal treatment afterwards can to some extend remove this stress in those and there are many examples where such thermal treatment process is being applied.
I don't know if there were ever studies to rule out what is actually the reason for the initial drift of voltage references in hermetically sealed packages and if they can be seperated from another and what is just stupid hypthesis, rumor or wisdom.
Nevertheless, the 150 °C treatment for 168 h Eric mentioned as well as the cycling that Cern performs on the LTZ1000 gives evidence that at least the stress due to the die attach is a major contributor. I do have build at least one LTZ reference, that was heat-treated using the cycling methode and what I observed on it was, that it settled within about two weeks. I know other forum members, not to mention any names here, that observed similar effects. However, I couldn't get enough people together to perform a double-blind experiment on that to give it more evidence.
So the answer to that die attach contribution would be: storing the Vref above or cycling around the glass transition temperature, whatever that is for the die attach used in the ADR. Chances are, it's in the range of 110 to 120 °C as for many epoxy materials in that field, but we simply don't know and Eric couldn't answer that either.

-branadic-
« Last Edit: October 19, 2021, 09:17:40 pm by branadic »
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Offline Andreas

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #147 on: October 19, 2021, 09:44:17 pm »
In which temperature band should the die be kept?
What is the lowest temperature that makes sense?
At which temperature can we expect damage to the ADR1000?
After all, according to the datasheet, 150°C is the junction temperature limit for storage and operation.

Hello,

so what I have heard now 150 deg C is the oven temperature to go? (or is it more the 125 deg C of other processes?)
In a bake & burn configuration we will also have some self heating by the biased zener.
(at room temperature this is ~10-11 deg C).

As already mentioned I have 2 x 25W heater resistors which I will put into a thermally isolated coffee mug or thermo-jar. So I think I will get away with 10-30 W power (or less). A PT1000 temperature sensor just arrived today. I will use one of my ADCs with 4 channel MUX to evaluate temperature. (2 channels for 0 deg C and 150 deg C reference resistors).

The PC software will allow ramping the temperature (e.g. from 145-155 deg C with 0.1K/min slope).

with best regards

Andreas
 

Offline Dr. Frank

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #148 on: October 19, 2021, 10:41:00 pm »
Hello colleagues,
I recommend not to go near or even above 150°C, as this is the absolute max. rating for storage and chip temperature, and 125°C is the maximum operating temperature, surely for some reason.

I would also chose around 120°C, what branadic has suggested, being a typical glass temperature for die attach.

You might use external heating and additional internal heating.

Such burn-in circuits are often designed with a passive substitution circuit around, i.e. w/o using any OpAmps or other semiconductor components, but appropriate HT resistors instead, due to these high environmental temperatures which are involved.

Frank
 
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Offline dietert1

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Re: Lowest drift, lowest noise voltage reference (ADR1000AHZ)
« Reply #149 on: October 19, 2021, 10:58:16 pm »
Which means the reference will be soldered after burn-in. No good, better try to run it in its circuit, maybe using an external oven at 85 °C and the internal heater to get the additional 35 °C.

Regards, Dieter
 


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