Patent ID: 9270238
Filing Date: 2016-02-23
CPC Classification: H03F,H04R

Claim Text:
1. A preamplifier for a digital condenser microphone, comprising: a bias terminal for applying a bias voltage to an input signal when the input signal is output from a microphone condenser; an impedance unit connected to the bias terminal and to which the bias voltage is applied via the bias terminal; and an operational amplifier for receiving the input signal, converting the input signal into an output signal, and outputting the output signal; wherein the impedance unit comprises a plurality of transistors and a plurality of switches corresponding to the transistors and the total impedance of the impedance unit is adjusted by controlling ON/OFF operations of the plurality of switches based on a result of whether the detected directed current (DC) voltage level of the output signal from the operational amplifier has reached a reference value.