A 1.0 mW, 71 dB SNDR, −1.8 dBFS input swing, fourth-order ΣΔ interface circuit for MEMS microphones

Abstract

In this paper a large input swing integrated interface circuit for MEMS microphones is presented. It consists of an high impedance input buffer followed by a multi-bit (12-levels) analog second order ΣΔ modulator and a fully-digital single-bit fourth-order ΣΔ modulator. The circuit, supplied with 3.3V, exhibits a current consumption of 215 µA for the analog part and 95 µA for the digital part. The measured signal-to-noise and distortion ratio (SNDR) is 71 dB, with an input signal amplitude as large as −1.8 dB with respect to full-scale, obtained thanks to the use of a feed-forward technique, which relaxes the voltage swing requirements of the operational amplifiers. The test chip fabricated in a 0.35 µm CMOS occupies an area of 3 mm2 including pads.