基于CPLD和TDC的微电容传感器信号检测电路设计

摘要

针对电容传感器的工作原理,以复杂可编程逻辑器件(CPLD)为核心,采用基于时间数字转换器(TDC)技术的芯片PS021,设计了一种高精度的微小电容测量电路.给出了PS021的测量原理和电路的软、硬件设计.采用PS021结合CPLD采集处理电容信号,外围电路简洁,应用方便,软件设计通过对PS021内部可编程寄存器的合理设置实现高精度的测量.实验结果表明:电路在10 Hz刷新频率时能够达到8 aF的有效精度,最高刷新频率可达50 kHz;电路实现了1fF～0.01 aF的分辨率,有效精度位(ENOB)可达22位；高精度高刷新率可缓和测量速度和分辨率的矛盾,提高了微小电容的测量精度.%Aiming at the work principle of capacitive sensor, a high-precision detecting circuit for micro-capacitance measurement using complex programmable logic device( CPLD) is as core,PS021 is used, based on time to digital converter(TDC) technology. The measurement principle of PS021 ,the design of circuit hardware and software are presented. PS021 and CPLD are used to process the capacitance signal. It makes the circuit simple and easy to application. By setting the internal registers of PS021 through software, high precision measurement is achieved. The experimental results show that the circuit has a good performance with resolution of 8 aF in 10 Hz update rate, the highest update rate can be up to 50 kHz, the resolution ranges 1 fF~0. 01 aF,and the effective number of precision bits ( ENOB) is up to 22 bits. The high precision and high update rate can ease the contradiction between measurement speed and resolution. And the design improves the measurement precision of micro capacitance.