基于峰值检测的MEMS器件微弱电容检测电路

针对MEMS器件研制中微弱信号的检测问题,提出了一种适用于电容式MEMS器件的微弱电容检测电路.此电路采用峰值检测技术,原理及结构简单;只检测待测电容的变化量,既可用于差分式检测,也可应用于单一待测电容的情况.首先利用正弦载波信号和微分电路对电容量进行载波调制,再通过减法电路得到幅值与电容变化量成比例的正弦信号,最后采用峰值检测方法解调信号,得到直流量输出.利用微小可调电容进行标定,结果表明检测电路的线性度良好,灵敏度约为3.631V/pF,精度达到0.2%.利用该检测电路检测MEMS陀螺上振动频率为2.85kHz的梳齿驱动器的电容量变化,输出信号频率为（2.85±0.02）kHz,误差低于0.7%,说明该电路能够应用于MEMS器件的微弱电容检测.

Micro Capacitance Measuring Circuit Based on Peak Detection for MEMS Device

For the measurement of weak signal in MEMS device, a micro capacitance measuring circuit was proposed. The circuit has simple principle and structure, which is based on peak detection method and only measures capacitance variation. Moreover, it can be used not only for differential detection, but also when there is only one sensing capacitor. First, capacitances were modulated by sine carrier wave and differential circuits. Then, sine signal with amplitude proportional to capacitance variation was got by subtraction circuit. Last, modulated signal was demodulated to DC output with peak detection method. Calibration was done with micro adjustable capacitors and a high precision LCR tester. Results indicate that the linearity of the circuit is good, the sensitivity is 3.631 V/pF, and the accuracy reaches 0.2%. Experiment was carried out with the comb actuator with vibration frequency of 2.85 kHz on a MEMS gyroscope. The frequency of output signal is (2.85±0.02) kHZ with relative error no more than 0.7%, which indicates that the micro capacitance measuring circuit is applicable for capacitive MEMS device.