It is needed to detect phase - difference accurately for measuring the resonant frequency of high - precision quartz crystal. Phase changes dramatically for weak signal. In order to improve the precision of phase-difference detection of weak signal, this paper propose adaptive notch algorithm for filtering out the desired signals, and then improving SNR by using bandwidth compression algorithm for the signal after notch filter. In order to verify the validity of this method, a hardware system based on DSP is developed. The resonant frequency of quartz crystal is detected by this system and the detectable error is beyond 2PPM when SNR below - 60dBm.%微弱激励下的石英晶体其输出信号的频率、幅度和相位输出变化都非常大.本文采用π网络零相位检测法测量石英晶体的串联谐振频率,针对微弱信号的相位检测采用自适应陷波滤出期单信号,然后对陷波后信号进行带宽压缩提高信噪比,从而检测出π网络零相位点,估计出石英晶体的谐振频率.文中研制了基于数字信号处理器的检测系统,实验表明系统在信号功率小于- 60dBm情况下,相位检测精度达到2PPM.
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