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 SigmaDelta modulator, and a fourth-order, single-bit digital SigmaDelta modulator. The complete interface circuit features a current consumption of 574 muA 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 SigmaDelta modulator, to relax the requirements of the operational amplifiers. The proposed MEMS microphone interface circuit is designed in a 0.35-mum CMOS technology. Post-layout and Montecarlo simulation results of the overall circuit are reported to validate the performance.