CMOS Interface for Capacitive Sensors with Custom Fully-Differential Amplifiers

In many applications it is crucial to design reliable and efficient analog readout circuits for micro-electromechanical (MEMS) capacitive sensors. In this paper, we describe the switched-capacitor, open-loop, capacitive-sensing readout circuit, which was designed and manufactured in 0.18 μm technology. Non-standard application of a fully differential amplifier structure is also presented. The post-layout simulation results are described to show the proper operation of the circuit. They show that with the proper symmetrical design of the differential signal path the output offset voltage can be kept at acceptable level.