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this post was submitted on 26 Jun 2023
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Thanks for posting this! I’m particularly excited about the use of the opamp as a transimpedance amplifier, converting a current from a photodiode to a voltage, then being able to feed that signal straight into the ADC. Depending on the performance, this could simplify my design work significantly.
I found some basic documentation on that here - https://www.ti.com/lit/an/slaae81/slaae81.pdf?ts=1689294975621
IIRC, a low side (relative to ground) is straightforward. But high side current sensing (measuring and amplifying the current measurement where one resistor side is NOT tied to ground/zero volts) has some subtle accuracy issues.
Note that worst case CMRR is 44db, so 1mA at 0V and 1mA at 3V will have a ~0.03V difference. CMRR is that non-ideal property where the change of Voltage that the OpAmp operates at will kinda sorta leak out to the output / results.
Operating at near 0V will minimize this error. Or the Chopper-mode will cut down on that if you must do high side current sense.
There are lots of different opamps for a reason, they all have tradeoffs. This TI one is chopper mode which should have better CMRR than a lot of others IIRC.