I want to use a digital potentiometer as the gain resistor on the AD620. I need to modify gain from about 80 to about 500 depending on the input conditions. What problems, if any, should I expect.
The main concern would be that the gain resistor pins of instrumentation amplifiers are sensitive to capacitances. It would be good to pick a digital potentiometer that has small output capacitances at its wipers in order to minimize errors. What inputs are you expecting into the instrumentation amplifier? DC? AC? May I ask what your application is?
There is a reference circuit at this link which implements the same circuit you are creating with the use of AD5292, but with AD8221 as its instrumentation amplifier. It might be of help to you.
FYI. Application is an intermediate amplifier for different types of load cells and the final instrument.
Gain variations of 500 to 80 is less than 3 bits in your final conversion (assuming this goes to an ADC).
The resistor inside the digital pot won't be very accurate or have a great tempco, so you might be better off just fixing the gain and rely on a high resolution delta sigma converter to cover the range.
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