Patent ID: 9710000
Date: 2017-07-18
CPC Classifications: G05F,H03F,H04R

Claim:
1. A bias circuit structured to supply a bias voltage to a microphone, the bias circuit comprising: a variable gain amplifier structured to amplify a reference voltage; a low-pass filter structured to remove a high-frequency component of an output of the variable gain amplifier; and a voltage follower amplifier structured to receive an output voltage of the low-pass filter, and structured to supply the output voltage to the microphone, wherein the bias circuit further comprises: a first line; a second line having a potential lower than that of the first line; and a voltage source that is coupled between the first line and the second line and structured to generate the reference voltage, and wherein the variable gain amplifier comprises; and wherein the voltage follower amplifier comprises: a second operational amplifier coupled between the first line and the second line, and having its non-inverting input terminal receiving the output voltage of the low-pass filter and its inverting terminal directly coupled to its output terminal.