Research On Time Interval Measurement Of 1PPS Based On SAW Technology

Time interval measurement technology is widely used in communication,navigation,medical,defense and military,astronomical observation.The development of these fields puts forward higher requirements for time interval measurement.Therefore,the research on time interval measurement technology is of great significance.Traditional time interval measurement methods are difficult to be further improved due to the limitations of electronic devices.This paper studies the time interpolation method based on SAW filter to realize the high-precision measurement of two 1PPS time intervals.The paper studies the frequency characteristics of SAW devices.It is found that the SAW band pass filter has the characteristics of narrow passband,high stopband inhibition ratio,small ripple in passband and good consistency.This time interval measurement method uses SAW filter as a time interpolator,samples the impulse response signal of SAW filter,and carries out data processing such as cubic spline interpolation and cross-correlation operation,so as to realize high-precision time interval measurement.The time interval measurement system designed in this paper constructs a two-channel measurement structure,and uses FPGA to build a logic circuit to delay the 1PPS signal and avoid the dead time.The measurement system uses cubic spline interpolation to reconstruct the impulse response signal of SAW filter,which can improve the measurement resolution of time interval by increasing the number of interpolation points.The system performs cubic spline interpolation on the sampling points of the impulse response signal twice.The first time,the interpolation is performed with the interpolation node spacing of 8ps.Secondly,the peak value of the cross-correlation function is interpolated with the interpolation node spacing of0.8ps.This algorithm ensures the accuracy of time interval calculation and reduces the complexity of data processing.In addition,in order to reduce the measurement error,this paper analyzes the mathematical relationship between random noise and time interval measurement error in the measurement system,as well as the mathematical relationship between spectrum aliasing and high-order harmonics and time interval measurement error in the measurement system.The ADC sampling frequency is set to 120 MHz,and the power fallback method is proposed to reduce the nonlinear measurement error caused by amplifier.In this paper,the test platform of 1PPS time interval measurement system based on SAW filter is built.The calibration experiment is carried out for the time interval measurement system designed in this paper,and then the measurement resolution,accuracy,measurement stability and nonlinearity are tested.The test data show that the resolution of the time interval measurement system designed in this paper can reach 5ps,the single measurement accuracy can reach 5.75 ps rms,and the measurement stability can reach 0.55ps@200s.