A 430- μ A 68.2-dB-SNR 133-dBSPL-AOP CMOS-MEMS Digital Microphone Based on Electrostatic Force Feedback Control

Abstract

This article introduces a high-acoustic-dynamic-range and low-power digital microphone based on the electrostatic force feedback control (EFFC). The proposed design adjusts the sensitivity of the micro-electro-mechanical system (MEMS) by adaptively biasing it at different input amplitudes, thereby extending the dynamic range (DR). The proposed adaptive biasing technique allows the induced electrostatic force to function as a mechanical gain prior to the analog front end (AFE), consequently relaxing the noise performance requirements of the readout electronics. A capacitive feedback (CFB) instrumentation amplifier (IA) with an adjustable gain is employed to effectively reduce the thermal noise introduced by the feedback resistor in conventional resistive feedback (RFB) IAs. A sub-sampling amplitude detector (SSAD) composed of cascaded low-order decimation filters is proposed to achieve efficient acoustic volume detection. The detection results are used to control a fast-settling predictive reference charge pump (PRCP). The PRCP adopts a closed-loop architecture to achieve accurate adjustable bias voltage, with the proposed prediction logic to significantly reduce the settling time. The proposed system achieves a signal-to-noise ratio (SNR) of 68.2 dB at 94 dBSPL and an acoustic overload point (AOP) of 133 dBSPL, with a current consumption of $430~{\mu }$ A at a clock frequency of 3.072 MHz. The measured acoustic DR is 107.2 dB.