Electronics > Metrology

ADR1399 reference

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I know, but - see below (the same setup), I will run the pops free LM399H#2 (1500h BI) over night.. Both 1399 (0h BI) I have are half of the LM399H#2 noise..

Looking at the standard deviation of a 7 V ref reading is bit unusual. It still reflects the ref. noise, but only for a limited times scale of some 4 - 400 seconds. So more normal way would be to look at the alan deviation.
Anyway the difference is not that large. It is mainly having the jumps in the external LM399 ref and less or smaller jumps for the ADR. One would always see a combination of both references: The good lm399 in the 34401 and than either a more normal LM399 or the slightly lower noise ADR1399.  The fact that there is quite some difference shows that the reference in the meter is way better than normal. With a more normal ref. in the meter one would not see much difference (70% noise even with a noise free external ref., though the way the test is done may be more sensitive to peak then RMS noise).

Even for the relatively long time scale use in the test, the ADC noise is still a good part of the noise.

That is 10V external Vref. Both HP399 and LM399 are the 34401A's refs (inside the meter). The peaks in the STD show where a reference shifted its voltage abruptly (or it is EMI). Those pictures are not about any stability over time..

I have the data thus tomorrow, after the Starship's orbital flight, I will show you ADEV/MADEV as well :)

But sure, I do understand the replacement of the old HP399 with the fresh ADR1399 is tricky..  ::)

PS: CONT in the ADR1001 thread..


--- Quote from: Kleinstein on November 17, 2023, 03:46:45 pm ---The capacitor should not be hat critical. Even leakage is not a problem. When using MLCC I would plan for 2 x 1 µF to conpensate for the drop in capacitance under voltage and the 1 µF value is already on the low side to start with.

--- End quote ---
What about the capacitor itself in parallel (instead of the RC circuit) according to the datasheet:
"Another single element passive that works directly with the ADR1399 is a 10 μF tantalum capacitor, even though the series resistance can
measure less than 5 Ω on an impedance analyzer."
Has anyone checked this?

I did not try that as i think the better solution is a low leakage cap with a known resistor instead of unknown capacitor ESR. Trying to save a 1 cent part on a 15 $ reference?

Here i have a three month log of the ADR1399 SMD evaluation kit i got one year ago. It got an outer oven at 38.2 °C. These are 4 second measurements with residual TC corrected. The log shows a drift of about 1.4 ppm and the internal temperature of the P6048 in red. One can assume the drift of about 1.3 ppm is caused by the Vishay NOMC divider used for the 10 V gain stage. Maybe a confirmation of results Andreas showed above.

Regards, Dieter


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