A 15-bit 140- W Scalable-Bandwidth Inverter-Based Modulator for a MEMS Microphone With

Abstract

A discrete-time audio modulator for a MEMS microphone with digital output is presented that features a scalable signal bandwidth to also support ultrasonic frequencies for prox- imity sensing applications such as gesture recognition. The modu- lator achieves low power consumption and a small die area by using simple digital inverter instead of OTAs. To increase the robustness of the inverter approach, an LDO is used to provide an internally generated supply which regulates the inverter bias point. The LDO also improves the power supply rejection of the pseudo-differential architecture to above 78 dB. The presented modulator sup- ports a scalable signal bandwidth up to 100 kHz, by dynamically adjusting the internal supply vol tage depending on the sampling frequency. In the nominal 20-kHz audio band, it dissipates 140 W from a minimum 1.5-V supply and achieves a DR of 92.6 dB, a SNDR of 87.9 dB, and a THD of dB, respectively.