Microphone amplifier circuit

摘要

The invention provides a microphone amplifier circuit which enhances the SNR (signal noise ratio) and expands the dynamic range by reducing the noise level. A microphone amplifier circuit includes a preamplifier which amplifies an audio signal from a capacitor microphone, a level detection circuit which outputs a level detection signal when the level of the audio signal is in the vicinity of the noise level of the microphone amplifier circuit, and an attenuator which attenuates the level of the audio signal outputted from the preamplifier in response to the level detection signal. The preamplifier includes an operational amplifier, a feedback capacitor and a feedback resistor.

主权项

1. A microphone amplifier circuit comprising:
a preamplifier amplifying an audio signal from a capacitor microphone and having a predetermined gain, wherein the preamplifier comprises an operational amplifier having a first capacitor and a feedback resistor each coupled between an output terminal and an input terminal of the operational amplifier to set a gain thereof; a level detection circuit having an input coupled to one of the audio signal and an output of the preamplifier and outputting a level detection signal when a level of the audio signal is in a vicinity of a noise level of the microphone amplifier circuit; and an attenuator attenuating the level of the audio signal outputted from the preamplifier in amounts varying in response to a state of the level detection signal.