A Low-Noise, High-Input-Impedance Pre-Amplifier for Piezoelectric MEMS Microphone

This paper proposes a low-noise, high-input-impedance pre-amplifier for piezoelectric MEMS microphones. It connects directly to the piezoelectric audio sensor without the need for auxiliary biases and operates under a low supply voltage, with a low power consumption, and a small silicon footprint. To recognize a wide range of sound pressure levels with low THD, the pre-amplifier can switch between two modes, i.e., a 20dB high-gain mode and a 10dB low-gain mode. It also incorporates an impedance-enhanced ESD design for the IO pads and a source follower for impedance conversion and input noise suppression. The design is implemented in 0.18-µm CMOS process, and the performance estimation is based on post-layout simulation. The input referred noise of the proposed pre-amplifier is 8.77µVrms in low-gain mode and 3.65µVrms in high-gain mode. it also features a DC input impedance of 190 GΩ, 74.56 dB PSRR, 10.4/20.9 dB system gain, 0.136%/0.044% THD with 94 dBSPL input. It consumes 86.5 µA of current under a 1.6-3.6 V power supply and occupies an active silicon area of 0.23 mm².