Are there any standard techniques/practices when a...
# analog-designl
Luke Harold Miles
03/31/2024, 6:26 PMAre there any standard techniques/practices when amplifying many signals against a common line like this?
I've been treating all the amps as independent, but maybe that's silly and they should share their auto-zero circuits or something¿
I am lacking relevant keywords.
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Boris Murmann
03/31/2024, 7:25 PMIn your diagram, does +10mV mean 210mV relative to ground?
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Luke Harold Miles
03/31/2024, 7:50 PMYes
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Boris Murmann
03/31/2024, 8:05 PMLooks to me like you'll need as many differential pairs as inputs in your design. What are your specs? It's hard to suggest circuits without any. For example, does your voltage gain need to be accurate & linear. Do you need low offset, etc.
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Luke Harold Miles
03/31/2024, 9:07 PMMainly I need low input offset, like 0.1mV. I guess it's just like 100 independent diffamps then like you said.
Luke Harold Miles
03/31/2024, 9:16 PMCloser to 10uv would be ideal. I am struggling to achieve that. I was thinking maybe I should use an instrumentation amp. Although I'm guessing it would be rather large. Looks like someone made one for chipalooza.
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Robin Tsang
04/01/2024, 1:01 PMLook up chopper-stabilized amplifiers for low-offset
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Luke Harold Miles
04/01/2024, 5:33 PM@Robin Tsang Thanks for tip -- I couldn't find any very complete circuits online -- do you know a good paper or repo?
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Robin Tsang
04/01/2024, 6:15 PMFrom my textbook back in the day:
Philip E. Allen and Douglas R. Holbert, CMOS Analog Circuit Design 2nd Edition, "Chopper-Stabilized Op Amps", pp. 410-414, New York: Oxford University Press Inc., 2002
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Robin Tsang
04/01/2024, 6:29 PMYou can think of chopping, in the time-domain, as flipping the offset back and forth (positive and negative), resulting in an average of zero offset at the output. In the frequency domain, you can think of it as modulating the input signal up to a fixed chop frequency, add the offset of the opamp at DC, and then demodulating the opamp output back down to DC while the DC offset is modulated up to the chop frequency, resulting in no offset at the output. You can get artifacts from doing this, which may or may not work for your application.
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