Study of CMOS integrated signal processing circuit in capacitive sensors

摘要

A CMOS integrated signal processing circuit based on capacitance resonance principle whose structure is simple in capacitive sensors is designed. The waveform of output voltage is improved by choosing bootstrap reference current mirror with initiate circuit, CMOS analogy switch and positive feedback of double-stage inverter in the circuit. Output voltage of this circuit is a symmetric square wave signal. The variation of sensitive capacitance, which is part of the capacitive sensors, can be denoted by the change of output voltage's frequency. The whole circuit is designed with 1. 5 μm P-well CMOS process and simulated by PSpice software. Output frequency varies from 261. 05 kHz to 47. 93 kHz if capacitance varies in the range of IFF ～15PF. And the variation of frequency can be easily detected using counter or SCU.