基于交流电桥的动态微弱电容检测电路

基于MEMS技术研制的微电容超声传感器,在超声波作用下其有效电容的变化量仅为飞法级,且变化速度非常快,检测很困难.本文提出的半桥式交流电容检测电路能把快速变化的电容信号转换为电压信号,并加载到高频正弦激励信号中,再通过放大、解调、滤波得出电容变化量.该电路能很好地抑制寄生电容的影响,有良好的线性和稳定性,在200kHz的超声波作用下灵敏度可以达到2.8mV/fF,基本满足对超声传感器电容变化量的检测.

Micro Capacitance Measuring Circuit Based on AC Bridge

The Capacitive Micromachined Ultrasonic Transducers based on MEMS technology has developed.Under the action of ultrasound,the change of its effective capacitance is only fF-level and changes very fast,so measuring is very difficult.The half AC bridge capacitance detection circuit presented in this paper can convert the rapidly changing capacitance signal into voltage signal,and load the voltage signal into high-frequency sinusoidal excitation signal,then obtain capacitance variation through amplification,demodulation and filtering.The circuit effectively inhibits the influence of stray capacitance,and the linearity and stability of the circuit are good.The sensitivity can achieve 2.8mV/fF with 200kHz ultrasonic wave,and basically meet the needs of the micro capacitance change detection of the Capacitive Micromachined Ultrasonic Transducers.