Low-noise CMOS analog-to-digital interface for MEMS resistive microphone

The design and implementation of a CMOS integrated analog to digital interface dedicated to hybrid integration of MEMS resistive microphone is presented. Audio sensing is achieved with an innovative low-cost technology that uses single crystal piezoresistive silicon nanowires as transducer in a MEMS. The circuit composed of a low-noise instrumentation preamplifier followed by a single bit fourth order continuous-time sigma-delta modulator (CT-ΣΔM) includes bias circuit for sensor. To join low power applications where extensive digital processing is employed, 0.28 μm CMOS process with a 2.5 V supply has been adopted. The test chip occupies an area of 1 mm². Post-layout simulation exhibits promising performances where noise density is below 8 nV/VHz within the frequency range from 10 Hz to 10 kHz. Complete interface circuit features a current consumption of 2.4 mA.