基于FPGA的高分辨率电容检测系统设计

Design of high resolution capacitance detection system based on FPGA

针对环境湿度可以改变湿敏电容的容值这一特性,提出了一种基于现场可编程门阵列(FPGA)的高分辨率电容检测系统设计方法,对系统方案、数据采集、误差来源进行了全面的分析。文中使用电容-频率电路将电容的容值变化转化为脉冲信号的持续时间。利用FPGA设计时间间隔测量电路,使用系统时钟控制的同步计数器保证整个检测电路的量程大小,采用延迟单元设计延迟链以进一步提高测量分辨率。分析了测量误差来源并提出了相应解决办法。实验结果表明,该时间间隔测量电路达到了皮秒量级,可测量的脉冲信号持续时间的精度在2 s之内,可以测量皮法量级的电容变化。

Aiming at the characteristic that the ambient humidity can change the capacitance value of the humidity sensitive capacitor,a design method of high resolution capacitance detection system based on Field Programmable Gate Array(FPGA)is proposed.The system scheme,data acquisition and error sources are analyzed comprehensively.In this paper,a capacitor-to-frequency circuit is used to convert the capacitance change into the time interval of the pulse signal.The time interval measurement circuit is designed by FPGA,the synchronization counter controlled by the system clock is used to ensure the range of the whole detection circuit,and the delay chain is designed by the delay unit to further improve the measurement resolution.The sources of measurement errors are analyzed and the corresponding solutions are put forward.The experimental results show that the time interval measurement circuit reaches the picosecond level,the precision of the pulse duration is within 2 s,and the capacitance change of picomethod level can be measured.