微小差分电容检测电路设计
摘 要
电容式传感器广泛应用于位移、振动、角度、加速度等物理量的精密测量中。由于受结构限制，其输出电容信号很小，一般为几pF至几十pF，精密测量其值更小，因此其后续测量电路的选择与设计非常关键。本文简要介绍了传统及现有小电容测量方法，重点设计了一种用于微小差分电容检测的交流放大电路，阐述了此方法的基本原理及参数的选取原则。实验结果和理论分析具有良好的一致性，并仿真出了实验结果，该电路具有抗寄生电容能力强、容易实现、成本低等优点。
关键词：差分电容，高频信号，电容传感器，抗寄生电容
Design of measured circuit about micro differential capacitive
Abstract
The capacitive sensor widely used in precision measuring physical quantity such as displacement, vibration, angle and acceleration. For the structure limit, the output of capacitance sensor is very small, about several pF to several dozens pF, and smaller in the precision measurement, so it is important to select and design the capacitance measurement circuit. Several techniques for measuring of small capacitance including methods with tradition are briefly overviewed. A kind of AC amplifier circuit for micro differential capacitance sense is introduced in the text. The experiment results show a good correspondence with the theoretical analysis. The basic principle of the method and the principle of choose the parameters in the circuit are provided and test conclusion is given. The measurement is free of stray immune capacity, low-cost and easy for realization.
Key word: differential capacitance, high frequency signal, capacitive sensor, stray-immune capacitance
目 录
1 绪论 1
1.1 电子测量技术的发展 .............................................. 1 1.1.1 电子测量的特点 ................................................ 1 1.1.2 常用的几种电容测量方法 ........................................ 2 1.2 课题研究的目的和意义 ............................................ 3 1.3 本课题的任务和内容 .............................................. 4
2 电容式传感器 5
2.1 电容传感器的分类 ................................................ 5 2.1.1 变极距型电容传感器 ............................................ 6 2.1.2 变面积型电容传感器 ............................................ 8 2.1.3 变介电常数型电容传感器 ........................................ 9 2.2 电容传感器的特点 ............................................... 10 2.2.1 优点 ......................................................... 10 2.2.2 缺点 ......................................................... 10 2.3 应用中存在的问题 ............................................... 11 2.3.1 附加损耗 ..................................................... 11 2.3.2 边缘效应 ..................................................... 12
3 电容电压转换电路 13
3.1 变压器电桥 ..................................................... 13 3.2 二极管T型网络 ................................................. 13 3.3 谐振法 ......................................................... 14 3.4 差动脉冲调宽电路 ............................................... 14 3.5 运算放大器电路 ................................................. 16
4 两种微小电容检测的方法
17
4.1 直流充放电法 ................................................... 17 4.2 高压双边交流激励法 ............................................. 18
5 消除寄生电容的屏蔽技术
20
5.1 增加传感器原始电容值 ........................................... 20 5.2 传感器的接地和屏蔽 ............................................. 20
微小差分电容检测电路设计
