Wide Range and High-Precision 1PPS Time Interval Measurement Method

High precision time interval measurement between two 1PPS signals is important in timekeeping. In time interval measurement between two 1PPS, the method of using the surface acoustic wave filter (SWAF) as the time-interpolator and calculating the time interval through the cross-correlation algorithm has high resolution and accuracy. However, the narrow pulses generated by the event start and end edges excite the SAWF. The response of SAWF has a duration of 200ns. Time intervals smaller than the response duration cannot be measured. The cross-correlation method also limits the measurement speed. In this paper, FPGA is used as the delay module to delay two 1PPS signals respectively. By measuring the time interval between each 1PPS signal and their delay signals respectively, the measurement dead zone is avoided. The calculation time is saved by gradually reducing the number of interpolation steps. Two 1PPS from the hydrogen maser were measured at room temperature and the results showed that the RMS error of this work is higher than 4.5ps and the resolution is higher than 2ps for the time interval of two 1PPS signals when the ADC is 14bit.