A Fourth-Order, Audio-Bandwidth, 87.5-dB SNDR ΣΔ Modulator for MEMS Microphones

This paper presents a complete interface circuit for capacitive MEMS microphones, consisting of the cascade of a preamplifier, a second-order, multi-bit analog Sigma Delta modulator, and a fourth-order, single-bit digital Sigma Delta modulator. The complete interface circuit features a current consumption of 574 mu A from a 3.3-V power supply, achieving a signal-to-noise and distortion ratio (SNDR) of 87.5 dB. The feed-forward technique has been used in the analog Sigma Delta modulator, to relax the requirements of the operational amplifiers. The proposed MEMS microphone interface circuit is designed in a 0.35-mu m CMOS technology. Post-layout and Montecarlo simulation results of the overall circuit are reported to validate the performance.