基于石英晶体滤波器的低频微弱信号检测系统设计与实现

发布时间：2018-06-07 07:02

本文选题：微弱信号检测 + 石英晶体谐振器　；参考：《陕西师范大学》2014年硕士论文

【摘要】：在很多应用场合,需要对微弱信号进行检测,微弱信号检测对检测系统的设计有着特殊的要求。随着科技的进步,微弱信号检测系统也在不断的改进与发展,目前在检测系统中被广泛使用的设备为锁定放大器。在锁定放大器中,输入信号通过相敏检测器将其频谱迁移到直流,再经过低通滤波器滤除噪声后输出,输出信号是与输入信号的幅度成正比的直流信号。本文参照锁定放大器进行微弱信号检测的基本原理,提出了一种低成本,易于实现的微弱信号检测系统,该系统的实现方案是利用混频器将输入的微弱信号变频至某个固定频率,后级电路对此固定频率的信号进行选频放大,克服了放大倍数过高时,直流放大中失调电压造成输出漂移严重的缺点。在该设计方案中,需要一个窄带带通滤波器,普通的LC滤波器不能满足此要求,有源带通滤波器则因为稳定性的影响,也很难实现很高的频率选择性。石英晶体谐振器由于具有极高的Q值,能够达到窄带滤波的效果。用石英晶体谐振器构建晶体滤波器的方法常见于射频信号处理。本文提出的微弱信号检测方案与射频接收机中超外差接收的原理类似,不过本方案中的石英晶体滤波器由32.768KHz的低频石英晶体谐振器和运算放大器构成,在低频段实现了窄带滤波。该系统具有带宽窄、设计简单、成本低等优点。论文重点论述了如何利用石英晶体谐振器设计低频窄带滤波器,在此基础上设计了基于石英晶体滤波器的微弱信号检测系统,该系统通过引入混频器有效克服了石英晶体滤波器中心频率固定的缺陷,并采用多级滤波器以提高系统的频率选择性。文中详细分析了检测系统设计方案以及具体电路实现,并对设计的检测系统进行了全面测试。测试结果表明,系统具有极高的频率选择性,在10Hz～200KHz频率范围内,3dB绝对带宽小于2Hz,能够很好的检测出0.5uV峰峰值的微弱信号,同时在不同频率下具有较好的一致性,因此能够满足大多数微弱信号检测系统的应用要求。
[Abstract]:In many applications, weak signals need to be detected, and weak signal detection has special requirements for the design of detection system. With the development of science and technology, weak signal detection system has been continuously improved and developed. At present, lock amplifier is widely used in the detection system. In the locked amplifier, the input signal migrates the frequency spectrum to DC through the phase sensitive detector, and then filters the noise through the low-pass filter. The output signal is a DC signal proportional to the amplitude of the input signal. According to the basic principle of lock-in amplifier for weak signal detection, a low cost and easy to implement weak signal detection system is proposed in this paper. The scheme of the system is to use mixer to convert the weak input signal to a fixed frequency. The latter circuit selects the frequency to amplify the signal of the fixed frequency, which overcomes the high amplification ratio. The offset voltage in DC amplifier causes the serious drawback of output drift. In this design, a narrow band pass filter is needed, but the ordinary LC filter can not meet this requirement, and the active band pass filter is difficult to achieve high frequency selectivity because of the influence of stability. Because of its high Q value, quartz crystal resonator can achieve the effect of narrow band filter. The method of using quartz crystal resonator to construct crystal filter is commonly used in RF signal processing. The weak signal detection scheme proposed in this paper is similar to the principle of superheterodyne reception in radio frequency receiver, but the quartz crystal filter in this scheme is composed of 32.768KHz low frequency quartz crystal resonator and operational amplifier. Narrow band filtering is realized in low frequency band. The system has the advantages of narrow width, simple design and low cost. This paper mainly discusses how to use quartz crystal resonator to design low frequency narrow band filter, and then designs a weak signal detection system based on quartz crystal filter. The system overcomes the defect of fixed central frequency of quartz crystal filter by introducing mixer, and adopts multistage filter to improve the frequency selectivity of the system. In this paper, the design scheme and the circuit implementation of the detection system are analyzed in detail, and the overall test of the designed detection system is carried out. The test results show that the system has very high frequency selectivity, and the absolute bandwidth of 3 dB is less than 2 Hz in the 10Hz~200KHz frequency range, which can detect the weak signal of the peak value of 0.5uV well, and has good consistency at different frequencies. Therefore, it can meet the application requirements of most weak signal detection systems.
【学位授予单位】：陕西师范大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN713;TN911.23

【参考文献】