Author Topic: DIY low frequency noise meter and some measurement result of voltage references  (Read 65608 times)

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Offline Echo88

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Maybe this doc is relevant in this case: http://www.sensorsportal.com/HTML/DIGEST/january_2011/P_745.pdf  :-//
 
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Offline antintedo

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Here's my take on the project. Grounded input (scope noise floor 0.8mV):
https://i.imgur.com/wPVcXfr.png

I chose to use 400u MKP cap as the input capacitor. Settling time is excellent, 10V step takes only around a minute to stabilize. Overall pretty satisfying results, but the voltnut within demands more performance :-DD

There seems to be a problem with ADA4528 input current noise or my design of the input stage. Initially two channels were paralleled, but the resulting noise floor was noticeably larger than using just a single channel (image). I wonder if I got ICs from an underperforming batch or SMD metal film resistors I chose affect the performance so much.
 

Offline Echo88

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Like described in the thread you may characterise your amplifier:
sweep across the frequency range of the LNA with a defined constant input amplitude to see the real amplification of the amp instead of assuming it,
make a high resolution FFT to see if 50Hz couples to strong in the LNA and that way artificially increases your noise when viewed with the oscilloscope,
test a few different noise sources to do a sanity-check: different voltage references like a LM399/REF102/ADR445/LTC6655, batteries, short

Only that way you will truly know your LNA and can actually reliably work with it. Otherwise you will doubt the results and it may have problems you dont know about.

Only a guess: did you use a dual channel ADA4528-2 or single channel ADA4528-1 and maybe now see intermodulation-related errors?  :-//
 
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