This paper presents a low distortion analog front-end (AFE) circuit to process electret microphone output signal. A source follower is employed for the input buffer to interface electret microphone directly to the IC with level shifting. A single-ended to differential converter with output common-mode control is presented to compensate the common-mode variation resulted from gate to source voltage variation in the source follower. A replica stage is adopted to control the output bias voltage of the single-ended to differential converter. The prototype AFE circuit fabricated in a 0.35μm CMOS technology achieves 68.2dB peak SNDR and 79.9dB SFDR over an audio signal bandwidth of 20kHz with 2.5V supply while consuming 1.05mW.
