Patent ID: 6160450
Filing Date: 2000-12-12
Classification: H03F

Abstract:
An apparatus including a self-biased, phantom-powered and feedback-stabilized amplifier for an electret microphone, comprising:a power and signal terminal configured to couple to a dc power source via a load impedance and to an output signal circuit, convey dc power at a dc power voltage from said dc power source and convey an amplified signal to said output signal circuit;a reference terminal configured to couple and provide a return dc path at a dc reference voltage to said dc power source and to couple to a first electrode of an electret microphone;a current source circuit coupled to said power and signal terminal and configured to receive a portion of said dc power and provide a tail current;a differential FET amplifier circuit which includesa first input terminal configured to couple to a second electrode of said electret microphone and receive a microphone signal therefrom,a second input terminal configured to receive a feedback signal at a quiescent feedback voltage between said dc power voltage and said dc reference voltage,a tail circuit portion coupled to said current source circuit and configured to receive said tail current,an output circuit portion coupled to said reference terminal and configured to provide a differential signal corresponding to a difference between said microphone signal and said feedback signal;a diode coupled between said first input terminal and said reference terminal; anda feedback amplifier circuit coupled between said output circuit portion, said power and signal terminal and said reference terminal and configured to receive said differential signal and another portion of said dc power and in accordance therewith provide said amplified signal and said feedback signal at said quiescent feedback voltage, wherein said amplified signal corresponds to said microphone signal.