The high stability of device resolution based precise phase difference measurement

In the precise phase difference measurement, we developed the dual phase coincidence detection method combined with a common oscillator. There is a certain frequency difference between the common oscillator and the two standard frequency signals which have the same nominal frequency. Utilizing the phase coincidence detection and a suitable processing, the time interval with the phase difference information can be obtained, and without one cycle count error. The key technique is the phase coincidence detection circuit, and the measurement resolution of the phase coincidence detection circuit is always finite. For example, the resolution of this kind of stable and reliable circuit can only be nanosecond level. It is hard to realize a high precision only based on this resolution. When the common oscillator signal is used to take the phase coincidence detection with the two comparison signals, there will be two detection fuzzy areas because of the finite detection resolution surrounding the strict phase coincidences. The actual measurement precision of the instrument depends on not the resolution of the coincidence detection circuit but the stability of resolution. The edge stability of the fuzzy area and the fluctuation difference of the two fuzzy areas is the key to determine the measurement resolution. It is also the principle for us to design the circuit. Compared with the dual mixer time difference measuring method (DMTD) this kind of the precise phase difference measurement system can show smaller drift — a few picoseconds per day. Its measurement resolution for the short-term stability is finer than 1 ps and it can be further improved. A novel coincidence detection circuit that is a little bit similar to the dual balanced mixer circuit is used in the measuring device. The difference is that the two input signals are both small-voltage narrow pulse signals. The time-domain characteristics of the circuit can be used to get the "phase coincidence" envelope formed by the monotonous phase change between the signals. By means of the stability of the envelope front edge, we can periodically obtain the measuring gate signals.