An accurate CMOS interface small capacitance variation sensing circuit for capacitive MEMS sensor applications

Abstract

ABSTRACTAn accurate front-end CMOS interface circuit for sensing very small capacitance changes in capacitive sensors is presented in this paper. The proposed structure scales capacitance variation to the sensible impedance changing. The scaling factor of the circuit can be easily tuned by adjusting bias points of the transistors. In order to cancel or decrease the parasitic components, the RC feedback and input transistor cascading techniques are used in the design. To simulate the circuit, HSPICE simulator is utilized to verify the validity of the theoretical formulations in 0.18 µm technology. According to schematic and post layout simulation results input impedance changes linearly versus capacitance variations up to 0.7 GHz while the sensor capacitance changing is varied between 0~200fF. Total dc power consumption is obtained as low as 1.2 mW with 1.8 V power supply.