Patent ID: 8170238

Claim:
An integrated circuit attached to a microphone, comprising: a buffer, buffering a first signal generated by the microphone, and outputting the first signal as a second signal; a gain stage, amplifying the second signal according to an adjustable gain to obtain a third signal; an analog-to-digital converter (ADC), converting the third signal from analog to digital to obtain a fourth signal as an output of the integrated circuit; and a memory module, storing the adjustable gain, and outputting the adjustable gain to the gain stage for controlling amplification of the gain stage; wherein the gain stage comprises: a second operational amplifier, having a positive input terminal coupled to a voltage source and an output terminal generating the third signal; a first adjustable resistor, coupled between an output terminal of the buffer and a negative input terminal of the second operational amplifier, wherein the output terminal of the buffer generates the second signal; a second adjustable resistor, coupled between the negative input terminal and the output terminal of the second operational amplifier; and a gain control circuit, adjusting resistance of the first adjustable resistor and the second adjustable resistor according to the adjustable gain.