Electronics > Metrology
LM399 based 10 V reference
Birb:
Other thing I noticed: While the LT5400 is not capable of producing the 1:2.333 resistor ratios, it can produce 1:2.5 and 1:2.25, the former creating around 9.8V and the latter 10.111V.
Therefore, if three voltage references are averaged with two in the 1:2.25 configuration and one in the 1:2.5 configuration, then the LT5400 is also capable of producing 10V with a small remainder. (At the expense of cost!)
(Though one question is if averaging is fine if the voltage references are just connected directly?)
In addition, while 1:14 is not available, the LT5400 can also produce 1:16 which could be used to step up 7V to 7.5V, which can then be divided by an LTC1043, to produce 2.5ish volts, for ADCs
(I might try this in the future, though that depends on time)
Kleinstein:
Averaging a 1:2.25 and 1:2.5 from different references does not work that simple. It would add quite some importantance to the resistors, about as much as doing the 9.8 to 10 V or 10.11 to 10 V step. It could be still simple averaging with 3 equal resistors and thus easy matching.
It depends one the actual voltage of the LM399 (or ADR1399) how much step there would actually be left from 10.11 V nominal. It would make sense to first check a few references. If they are on the high side the 9.8 V to 10 V step could be smaller than the 10.11 to 10 V step. With only some 2 or 1.1 % nominal (and possibly better) one should get an attenuation for some 50 or 90 (or better) for resistor drift. That could be good enough for a LM399 / ADR1399. AFAIR the LM399 has a tolerance of 2% - so look at the actual voltage first.
The going down version could be a little simper, using only 1 amplifier, with 1 divider at the 7 V and than the gain.
Birb:
Something minor I note is that the LT5400 in the 1:2.5 ratio configuration uses the 1:10 variant, which means the 1:2.5 ratio has a generally higher resistance than the 1:2.25 (Variant 8 or 1:9), so the Johnson noise would be higher
(Though I'd assume this is very negliglible)
Anyways, I think this config might be better suited to use ADR1399 due to lower drift and tempcos.
Here's a schematic showing the conceptual 1x NOMCA resistor network LM399 voltage reference.
dietert1:
There was a thread about statistical arrays, where the conclusion was to better use NOMCT instead of NOMCA. They have an improved passivation and generate less excess noise. They can be used for < 1 ppm applications, see e.g. ADR1001 long term study by Andreas.
Regards, Dieter
Edit: Sorry i meant ADR1000. Andreas' most recent post:
https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg5662371/#msg5662371.
The resistor array part used is TDP16031002AUF, see:
https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg4547699/#msg4547699.
Echo88:
https://cds.cern.ch/record/2814429/files/2109.02448.pdf
https://www.researchgate.net/publication/367220764_Review_on_Excess_Noise_Measurements_of_Resistors
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