基于相敏解调的微弱电容测量电路设计

基于相敏解调的微弱电容测量电路设计(任务书,开题报告,论文15000字)
摘  要
本文使用交流激励式方法测量微弱电容，采用以小电阻替代大电阻的T形网络结构来减小交流激励式电容-电压转换电路中由较大反馈电阻产生的热噪声而产成的温度漂移的影响，通过将驱动电缆技术运用在交流激励式电容-电压转化电路中，来消除寄生电容造成的影响，确保电容信号能以较高的精度转换为交流电压信号。由相敏解调原理，采用模拟乘法器和滤波器实现参考信号和调制信号之间互相关运算，起到抑制噪声的作用，将信号解调单元的信噪比提升。由直接数字合成原理及特点，以集成芯片为核心，设计出双路相位可调的信号发生单元，为电容-电压转换和信号解调提供稳定的载波和参考信号，解决了以往方法中不足，提高了微弱电容检测系统的精度。
关键词：相敏解调  微弱电容检测  交流激励  电容传感器

Design of weak capacitance measurement circuit based on phase sensitive demodulation
Abstract
    The excitation type measuring small capacitance, and using a T shaped network structure with small resistance value to substitute for the large value resistance decrease AC incentive capacitance voltage conversion circuit in the high value feedback resistor thermal noise caused by the temperature drift impact; will drive cable technology and AC excitation capacitance - voltage conversion circuit combination, eliminate the influence of the parasitic capacitance of the surrounding environment and the attached cable capacitance, control of high precision capacitance signals into AC voltage conversion. According to the phase sensitive demodulation principle, through the analog multiplier and 8 order Butterworth filter to achieve the cross-correlation operation reference signal and modulation signal and to suppress noise, improve signal to noise ratio of the signal demodulation unit. According to the principle and the characteristics of direct digital synthesis, with special integrated DDS chip as the core, complete with adjustable dual phase signal generating unit design, capacitance voltage conversion unit and a signal demodulation unit provides the frequency and amplitude stability of the carrier signal and the reference signal, overcome the traditional method in signal amplitude, frequency stability, low, rely on analog phase-shift circuit to realize the modulation channel and the reference channel the in-phase relationship between the phase shift and so on, to improve the accuracy of the weak capacitance measurement system.
Keywords: Phase sensitive demodulation;Small capacitance detection;AC drive;   Capacitance sensor

目  录
摘  要    I
Abstract    II
第一章 引言    1
1.1 课题背景及研究的目的和意义    1
第二章 微弱电容检测系统总体方案设计    6
2.1 交流激励式电容转换电路    6
    2.1.1 反馈电阻热噪声的影响及消除    6
    2.2.2 电缆电容的影响及消除    7
   2.2 信号解调电路的研究    9
    2.2.1相敏解调原理    9
    2.2.2 相敏解调方案比较    10
2.3 信号发生电路的研究    12
    2.3.1信号实现方式对比    12
    2.3.2 直接数字合成的工作原理及结构    12
2.4 微弱电容检测系统总体方案    15
第三章 微弱电容检测系统的硬件设计    16
    3.1 交流激励式电容转换单元实现    16
3.1.1 交流激励式电容转换电路    16
3.1.2 交流放大电路    17
3.2 乘法相敏解调单元实现    18
3.2.1 乘法器电路    18
3.2.2 低通滤波电路设计    20
3.3 基于AD9953的双路信号发生电路    22
3.3.1 高精度DDS信号发生电路设计    23
3.3.2 I/V转换电路设计    24
第四章 实验及分析    26
4.1 引言    26
4.1 信号发生单元测试    26
结束语    28
参考文献    29
致谢    32