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Message ID: 2567     Entry time: Tue May 11 19:23:51 2021
Author: Radhika 
Type: DailyProgress 
Category: 2um Photodiodes 
Subject: ADC noise level spectrum 

It is important to characterize the noise levels of all instruments used in the current PD testing setup. We generally expect ~5uV/rHz of ADC input noise. Verifying/correcting this value will be key to ensuring that our overall gain is enough to amplify various signals above the ADC noise floor.

I terminated the input to ADC channel 31 with a 50-ohm BNC terminator. I used diaggui to generate the resulting amplitude spectra, with 0.03 BW (attached). To convert counts to volts, I took a range of 20V divided by 2^16 counts, resulting in a scaling of 3e-4 V/count. I plan to conduct another test to confirm this value (feeding a known voltage and comparing to the output). In the meanwhile, the resulting noise level consistent with our expectation of a few uV/rHz.

Attachment 1: adcnoise_210511.xml.gz  917 kB  Uploaded Tue May 11 20:25:52 2021
Attachment 2: adcnoise.png  24 kB  Uploaded Mon May 17 14:21:33 2021  | Hide | Hide all
adcnoise.png
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