Patent ID: 8600079
Filing Date: 2013-12-03
Classification: H04B

Abstract:
1. An amplifier circuit of a capacitor microphone, comprising: a capacitor microphone generating a signal corresponding to a sound received by the capacitor microphone; an operational amplifier comprising a first input terminal, a second input terminal and an output terminal; an input capacitor connected to the second input terminal; a first wiring connecting the first input terminal and the capacitor microphone; a second wiring connecting the second input terminal and the input capacitor; a feedback capacitor connected between the output terminal and the first input terminal; a third wiring supplying a supply voltage; and a coupling capacitor connected between the second wiring and the third wiring so as to be connected to the second input terminal, wherein the operational amplifier is configured to amplify the signal generated by the capacitor microphone, a noise in the power supply voltage is induced in the first wiring through parasitic capacitance coupling between the first wiring and the third wiring and enters the first input terminal, the coupling capacitor is configured to cancel out the noise entering the first input terminal and the noise entering the second input terminal, the third wiring is connected to the operational amplifier so that neither the first input terminal nor the second input terminal is connected to the third wiring.