All three capacitors are used to resist interference. Capacitors are characterized by passing high frequency and resisting low frequency to prevent high frequency interference signals from passing through the circuit. The first capacitor absorbs the interference signal at the input end, so that the interference basically does not enter the operational amplifier. The second AC negative feedback capacitor basically does not amplify the interference AC signal, and the third capacitor is used to absorb the interference signal and stabilize the voltage.

Because AC is a useless signal in this system, it is considered as an open circuit according to the calculation of DC amplifier, and the capacitance is not involved in the operation.