Design And Implementation Of Seamless Switching System With Dual Frequency Sources

With the development of science and technology,electronic systems have higher requirements on the stability and reliability of the reference frequency signal.In order to ensure the stability and reliability of the reference frequency signal of the electronic system,two or more frequency sources with redundant configuration are used to provide the reference frequency signal.In the system,one frequency source is used as the master frequency and the others as the backup frequency.When the output signal of master frequency source is abnormal,using the backup frequency source to provide frequency signal to ensure the normal operation of the electronic system.In order to avoid the losing of output signal and hopping of time difference data caused by switching signals,it is necessary to research on multiple frequency sources seamless switching method.At present,the common method to switch for multiple frequency sources is steering master-backup signals respectively to keep the signals synchronous in time and connecting the electronic switch after the signals.There are some disadvantages such as signal losing in the common method.To overcome the disadvantages,a new seamless switching method of dual-frequency sources is proposed in this paper.This method uses digital phase-locking to lock the output signal to the master frequency signal.When the abnormal state of master frequency signal is detected,the phase of the output signal is slowly shifted and gradually locked on the back-up frequency signal through finetuning phase to achieve the output signal's continuity and stability after switching.In order to verify the seamless switching method proposed in this paper,the dualfrequency source seamless switching verification system is designed and implemented by using a field programmable gate array.Meanwhile,a test platform is built to test the system performance and verify the feasibility of the method.The main research contents of the paper are as follows:1.The research significance and development status of the seamless switching of master and backup frequency sources are analyzed and described.Aiming at the disadvantage of seamless switching method of multi-frequency sources based on switch,a new method by phase fine-tuning is proposed and compared with the common method.2.The key technologies of the seamless switching method of dual-frequency sources are studied,including the principle of digital phase-locked loop and digital phase discrimination method,abnormal detection of phase difference and attribution judgment method of abnormal frequency signal,and seamless switching method of multi-frequency sources.3.A verification system for seamless switching of dual-frequency sources is designed and implemented based on FPGA.The system is designed and divided into modules of FPGA.Each module is programed and simulated.At the same time,a test platform is built to test the verification system.When the system is locked normally,the output signal's locking accuracy to the input signal is 10 ns,and the system output signal's frequency stability is 1.565×10-11 when Tau = 1s,and the frequency stability is 4.4×10-13 when Tau = 10000 s.When the frequency source is switched,the frequency stability is 1.87×10-11,and the phase change value per second is below 0.5ns after the frequency source switching.Test results show that the method proposed in this paper can achieve seamless and smooth switching of frequency sources.