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外差干涉是实现纳米精度长度测量的重要手段。采用电子倍频、混频、高频计数的方法可处理外差信号实现亚纳米分辨率，具有电路简单、能计大数的优点，但会引入电子信号的相位畸变，引入测量的动态误差。本文通过理论和实验分析了这一误差，表明在电子倍频中锁相环引起的相位畸变仅在亚纳米量级，但在混频环节中带通滤波器引入的相位畸变则可达几纳米，引入较严重的误差。本文通过采用低频差横向塞曼激光器产生３２０ｋＨｚ的外差信号，并采用ＦＰＧＡ技术实现倍频后的高频率信号直接计数，省略混频环节，从而实现了高测量分辨率并避免了这一误差。
Heterodyne interference is an important means to measure the length of nanometer precision. The method of frequency doubling, mixing and high-frequency counting can process the heterodyne signal to realize the sub-nanometer resolution. The method has the advantages of simple circuit and counting of large numbers, but introduces the phase distortion of the electronic signal and introduces the dynamic error of the measurement. This paper analyzes the error theoretically and experimentally, and shows that the phase distortion caused by the PLL is only on the sub-nanometer scale, but the phase distortion introduced by the band-pass filter in the frequency mixing section can reach several nanometers , Introduce more serious error. In this paper, a low frequency difference transverse Zeeman laser to generate 320kHz heterodyne signal, and FPGA technology to multiply the high frequency signal directly counting, eliminating the mixing step, resulting in high measurement resolution and to avoid this error.