A 4.7μW switched-bias MEMS microphone preamplifier for ultra-low-power voice interfaces

This paper presents a switched-bias MEMS microphone preamplifier for an ultra-low-power voice interface. A switched-MOSFET periodically changes the MOSFET between strong inversion and accumulation to inherently reduce 1/f noise. In addition, a proposed coupling capacitor allows the microphone to benefit from a high bias voltage while the preamp can use a low VDD. The preamp achieves 7.3μVrms input referred noise (A-weighted) with 3.4μA, improving NEF by 4.5×. Acoustic testing with the preamp and MEMS microphone shows 61.3dBA SNR at 94dB SPL.