| With the advancement of technology and the development of society,people's demand for time synchronization accuracy is constantly increasing.At present,the demand for time synchronization in 5G,digital TV and other fields has increased to tens of nanoseconds.As a high-precision clock synchronization technology,White Rabbit can achieve 2000 nodes,over 10 km distance,and sub-nanosecond time synchronization,which has attracted more and more attention.White Rabbit mainly uses the following key technologies: synchronous Ethernet technology,precision time synchronization protocol,and digital phase detection technology.Synchronous Ethernet technology is responsible for completing the frequency synchronization in the entire network.The precision time synchronization protocol completes the rough synchronization of time information,and White Rabbit's high-precision time synchronization performance is mainly accomplished by digital phase detection technology.This paper mainly studies the Digital Dual Mixer Time Difference technology used in White Rabbit,and the main work involved includes:1.Aiming at the basic principle and implementation of the Digital Dual Mixer Time Difference technology in White Rabbit,it is analyzed and studied.In the general Digital Dual Mixer Time Difference technical solution,a first-stage D flip-flop is usually used for sampling and amplification in the signal sampling and amplifying module.It does not consider that the output signal will have serious metastability when the input signal and the reference signal frequency are close problems directly affect the accuracy of the phase detection results.To solve this problem,the original scheme was improved,and the method of edge extraction after two-stage D flip-flop cascade was adopted to improve the accuracy of phase detection in metastable state,and the feasibility of the method was verified through experiments;2.The signal shaping and edge extraction algorithms were simulated and analyzed using MATLAB.The simulation experiment was designed using the control variable method.The performance of the algorithm under different glitch widths and sampling clock frequencies was compared and studied.It is concluded that the lower the glitch width and the higher the sampling clock frequency,the better the phase detection performance;3.Based on the aforementioned research,the White Rabbit time transfer test was carried out,and 3m,23 m,1km,and 10 km fiber lengths were tested and verified in the laboratory environment.The test results show that after the improved scheme,the synchronization deviation distribution drops from 204.7ps to 160 ps under the condition of 3m fiber length,which proves that the improved scheme is helpful to improve the time synchronization performance. |
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