A differential capacitive sensing circuit for micro-machined omnidirectional microphone

This paper presents a low-noise differential capacitive sensing circuit for omnidirectional microphone to detection accurate sound-source. The adaptive readout circuitry supports high-resolution signal acquisition from capacitive, resistive, voltage and current mode sensors. The chip was fabricated in TSMC 0.35um 2P4M CMOS process, its area is 2.31*2.39μm², dissipates 6mW at 3.3V in a typical sensors application utilizing periodic sleep mode, and can read out a wide range of sensors with high sensitivity. The circuit includes a non-overlap clock generator and highly sensitive readout amplifier. Fully differential structure provides good noise suppression ability. And the amplifier offset can be eliminated by the Correlated Double Sampling (CDS). It achieves low noise performance while capacitors variation from 100fF to 3pF. This paper presents a circuit of tiny capacitor sensor.