I am designing the below circuit for measuring the difference between two voltages after amplifying. I have 1KHz filter at inverting input and relay RG for setting gain 1 to calibrate the offset of the opamp. Would the filter at one of the terminals cause any issue? What is the max possible Coff that RG relay can have to minimize the parasitic mismatch between RG terminals?
The layout guidelines of the INA821 mentions this:
Take care to make sure that both input paths are well-matched for source impedance and capacitance to avoid converting common-mode signals into differential signals. Even slight mismatch in parasitic capacitance at the gain setting pins can degrade CMRR over frequency. For example, in applications that implement gain switching using switches or PhotoMOS® relays to change the value of RG, select the component so that the switch capacitance is as small as possible and most importantly so that capacitance mismatch between the RG pins is minimized.
