In practice there are three methods of accomplishing this phase difference. 在实践中有三种方法来获得相位差。
A frequency tracking method is proposed.The synchronism sampling is achieved to improve the measuring precision of frequency and phase difference. 本文提出一种频率跟踪方法，可以在不过零开始采样的情况下，实现整周期采样，保证频率和相位差测量的精度。
