An Unbiased MEMS Capacitance-Controlled Oscillator as a Microphone for HMI Applications

Abstract

MEMS microphones are usually DC biased with a voltage exceeding 10V and a large resistance, requiring a charge pump and a high-ohmic link between the ASIC and the MEMS. This DC biasing is needed to obtain enough sensitivity for medium to high quality microphones. This manuscript inves-tigates capacitance-controlled oscillators which allow to directly connect the MEMS sensor to the oscillator; this solution is prone to scaling. A new type of configuration (referred to as Cross-Connected Sensor) is presented and discussed. Its main advantage is the increase in the sensitivity and, when integrated in an ADC architecture, in the achievable SNR. The proposed solution is intended for Human-Machine Interface applications given their moderate SNR requirements.