ADR1399 reference

[iMo]

For you the most important params are the long term stability of ratio matching and ratio matching tempco. It looks like the Vishay array is much more worse than the ADI in those parameters. As the price both are comparable. There is a difference in the technology afaik, the Vishay is NiCr, the ADI is BiCMOS.

[Kleinstein]

There is a difference in the technology: the LT5400 is NiCr on silicon.  AFAIK the TDP1603 is NiCr on ceramics and in a larger size case.  The case effects on how much mechanical stress from the PCB transfers to the actual resistor.

The specs for those higher end resistor arrays are tricky, as some just represent the test-limits and not the actual performance.  Things like the long term drift are very hard to test - at least not fast, so they can include them in the data-sheet when the part comes out.
The TC specs are also hard to compare, as they are for different temperature ranges. The actual relevant range is likely much smaller again.
For a single unit build one may not care that much about the spec limits, more about the typical performace. One would do some tests anyway and find out if one gets a poor sample.

The big plus for the TDP1603 is that it has 8 resistors and not just 4. This allow to get a nomianl 7 to 10 ratio and thus no extra -5% step. With more resistors one also gets additional statistic averaging which can help quite a bit with the TCR matching.

Despite the not that great spec limits ( < 5 ppm/K rel. TC for -55 to +125 C), I would consider the TDP1603 a reasonable choice. I would expect the TC matching more in the < 1 ppm/K range for the near room temperature range and thus good enough for the ADR1399.

[branadic]

It looks like the Vishay array is much more worse than the ADI in those parameters.

Don't be fooled by the datasheet specifications, measure yourself. They behave way better than what the datasheet suggests. We already learned that for the noise figure and same is true for the matching. It only reflects that measurement limits of Vishay.
If they were as bad as per datasheet, references such as W/F7000 wouldn't work as good as they do.

-branadic-

[iMo]

FYI - I've found this PhD paper on the ADI's SiCr resistors in their 0.35um CMOS process, with an interesting measurement setup (most of you do at home, afaik)..
Here is the paper..

PS: it could easily be ADI will use them in the upcoming ADR1001 - that will solve all our problems, hopefully 

[cellularmitosis]

200k start-up resistor is used since it is in original LM399 datasheet.

Just a note: I don't believe the LT1001 inputs nor output extend to the negative rail (0V), so the startup resistor probably isn't needed.  However, not a bad idea to include the footprint on the PCB anyway, in case you want to try other op amps.

[DavidKo]

I have updated the schematic and added the power supply. I have prepared it as symmetrical, but with half wave rectifier to be able to run from single output transformer.

[Andreas]

Hmm,

do you really think 10uF with one way rectification are sufficient for up to 200mA current on heat up?

with best regards

Andreas

[DavidKo]

It is only placeholder. I have not calculated/simulated the correct value. The values can be different. Now I'm trying to fit 2 references + PS + amplifier to one PCB and be able to split it to 2 separate refences (without amplifier) if needed - I do not want to de-solder the refence from PCB.

I'm still not sure if it make sense to use such a simple split power supply or to create one power supply with full rectifier and power both heating and reference from it. Reference part have this possibility, but the power part on PCB was intended for mainly for burn in. I have thought to use LM317+LM336 for reduced temperature coefficient as one supply for both parts.

[Andreas]

Hello,

first ADR1399 populated on my ageing board.
So after some initial checks/measurements the automated ageing measurement can start soon.

with best regards

Andreas

[Andreas]

Hello,

first 1/f noise measurement with the LS8-package here:

its ~2.1uVpp in average with up to ~1uV popcorn noise on sample #01.
So much more than the 1.4 uVpp from the datasheet.

So following questions arise:

- simply a bad sample?

- is the 1.4 uVpp in the data sheet only for the metal can package. (branadic showed a measurement at beginning of this thread)
  https://www.eevblog.com/forum/metrology/adr1399-reference/msg4213732/#msg4213732

- has the heater voltage a influence (data sheet condition 30V heater voltage against my 15V)?

someone else with 1/f noise measurement for different packages/heater voltages?

with best regards

Andreas

[Andreas]

Hello shodan,

guessing that your 2 devices are both with the LS8-package.

I now have measured my #01 LS8-Sample with 15V and 30 V heater supply from a linear power supply.
(Zener supplied with 2K4 from 15V regulated battery voltage).

Result with this setup is in both cases 2.0 uVpp average 1/f noise. -> not heater supply voltage correlated.

with best regards

Andreas

[Kleinstein]

I don't see the RC damping element for the ADR1399 on Andrea's PCB (it could still be on the back side). This may in theory add some noise from added rinding.
The 0.1-10 Hz noise usually means a 10 second window for the observation - a longer window will add some noise from lower frequencies, from an amplifier. Over 10 s windows the noise looks a little smaller.

Some of the rather low frequency part could be from mechanical stress / acoustic coupling. Without a cover there could also be thermal effects, even though there are no covar leads and thus hopefully less thermal EMF. 

[Andreas]

Hello,

after populating the other ADR1399 in LS8-package I checked the Zener voltage with heater against the voltage with Heater off.

on the x-Axis the zener voltage (in mV) with heater active.
On the y-Axis the temperature drift (Heater active - Heater inactive) / Temperature difference.

As temperature difference I assumed 60 K (95 degC - 35 deg C assumed temperature for self heating of the 3 mA zener current).
Result is ppm/K between heater on and heater off.

For me it looks like the the lower zener voltage has a lower unheated tempco.
Maybe there is some zero T.C. near a zener voltage of ~ 7010 mV.

with best regards

Andreas

[Kleinstein]

It is normal to have a correlation between the zener TC and voltage. Normally a higher voltage means a more positive TC.

The temperature range from some 90 C heated to some 30 C unheated is quite large and the 2nd order TC part can be relevant. So the parts with the least change from cold to hot would not have the lowest TC around 90 C.

To get an idea on the TC at different temperatures one may have to look on the zener voltage chamge just after turning the heater off. I would not be surprized to see something like like voltage first going up and than down again.

[Andreas]

Hello,

overview over ADR1399#01-#04 with noise and (unheated/heated) T.C.
All measured 1/f noise (0.1-10Hz) is above 1.9 uVpp/100 sec as average over 19 measurements.
I found more or less popcorn noise on every sample with #4 being the worst with 1.6 uV.

I want to operate the devices for at least 1-2 weeks before doing next measurements after initial ageing.

with best regards

Andreas

[Kleinstein]

The cut-out around the references are nice for the thermals, but it would be better to have them in slightly different way.  One could have them more in the 90 deg. angle scheme, so that if the center part expands from heat the center part could rotate a little in one direction to relief the stress.

[Kleinstein]

The center island with the reference is still quite large. I think one could reduce it a bit by removing parts from the edges and corners. Less area mean less heat loss.

The outside part with the OP-amps is quite dense packed and may get a bit warm.  Some of the OP amps should get away with just a +15 V and GND for the supply to save on the power consumption and reduce the heat.

[Andreas]

Hmm,

what is 0 deg and 90 deg (with regard to the pin position in room)

the largest difference should be when the heater area is below the temperature sensor versus above the themperature sensor.
https://www.richis-lab.de/images/REF01/21x06.jpg

So best guess: Pin 4 on top side versus Pin 8 on top side (with the LS8-package) would give maximum difference.

Additional thermal isolation around the PCB should reduce the effect.

with best regards

Andreas

[Kleinstein]

The orientation effect can have two components: a chance in the thermals and a change in mechanical stress. Both would likely depend a lot on the PCB design and case. So interesting to note an order of magnitude, but a different design may behave quite different.

With the TO46 metal case part of the effect can be local from the plastic cover that comes with it. Even there the air flow can be different.

[opa627bm]

Stupid question here, any obvious improvement if I replace my LM399 in my Power Design 2010 to this ADR1399?

[MegaVolt]

Stupid question here, any obvious improvement if I replace my LM399 in my Power Design 2010 to this ADR1399?

It is possible to reduce the output noise. This will work if the output noise is dominated by the noise of the reference source.

[xerbo]

Mouser have recently got some evaluation boards in stock: https://www.mouser.co.uk/ProductDetail/?qs=4ASt3YYao0UVSWYehgmbvQ%3D%3D, users guide: https://wiki.analog.com/resources/eval/adr1399e-ebz.

Bought one to test, for the price (£54 including VAT) it seems like a pretty good deal for a fully tested and assembled board.

[Andreas]

Hello,

some days ago I started with initial drift measurements on ADR1399#1 - #4.
Initially I had placed the board above my LM399 ageing box.
To see better the self heating of the ADR reference board I put it on a cooler place (a unused analog power supply).
This gave up to 3 ppm jumps for 2-3 deg C lower board temperature.

To exclude a rather large T.C. or a influence of the on board multiplexers (MAX4052A) I made T.C. measurements.
So except for ADR1399#4 the box tempco near room temperature is below 0.1 ppm/K.
All 4 samples had a negative T.C. near 25 deg C. (whereas on my LM399 I have more or less only a open hysteresis depending on rising/falling temperature).
On ADR#1 I checked direct measurement of ADR output versus multiplexer output which gave no significant difference.

So I have to look for different influence on "position dependant drift".

with best regards

Andreas

[dietert1]

Mouser have recently got some evaluation boards in stock: https://www.mouser.co.uk/ProductDetail/?qs=4ASt3YYao0UVSWYehgmbvQ%3D%3D, users guide: https://wiki.analog.com/resources/eval/adr1399e-ebz.

Bought one to test, for the price (£54 including VAT) it seems like a pretty good deal for a fully tested and assembled board.

One of those arrived here yesterday. It works, yet i don't know whether those AD people understand what they are doing. Not only the switchmode converter and the missing low thermal EMF output.
In their wiki they explain they wanted to make something "portable calibrator style". But where is the calibration value? I got "7.05 V" that's it. Probably they can do a precision measurement, but they didn't do so?
Guess their 573 € LTZ1000 kit is similar and the chinese offering an LTZ1000 board on ebay for a fraction of the price understands better what a reference is good for.
Sorry for the rant.

Regards, Dieter

[xerbo]

The utilised switchmode converter is isolated and has a built in low noise linear regulator so should be fine. As for the terminals I think they are going for the "give it as much thermal mass as possible to minimise thermal gradients" approach, weather or not that is effective I don't know (probably not very).

But as a portable calibrator it is totally and utterly useless, the fact you already need a already calibrated voltmeter is probably a killer for most people.