Can you explain to me briefly why the Rfb resistor must be as close to the Z unknown as possible?
Rfb should not be as close as Z unknown as possible...
Rfb should be chosen in such a way to allow the ADC work in the optimal region, that is, not too small or too big input signal.
Remember that the ADC ideal input signal, before transimpedance amplifier, should be biased at Vdd/2.
Let me know if you have any question, please.
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