Design And Realization Of High Precision Clock Synchronous Micro-step Phase-Shifter

Accurate positioning of land-based radio navigation system is attributed to the complete synchronization of signals from different transmitting stations under which condition the receiver could eliminate clock error between transmitters and receivers. However, a long-term drift rate occurs to atomic clock, so a long-period operation would reduce its precision, causing drifting of signal frequency and phase, thereby requiring correction. To overcome this defect, a device is in need to precisely correct the clock frequency to offset phase drifting and realize high-precision synchronization.Micro-step shifter, a device to precisely adjust the frequency and phase of signals, could fix the signal phase to the standard clock. Traditional digital shifter is mainly composed of PIN diode and ferrite devices. And the frequency and phase regulation is done utilizing phase-locked loop technology, with major defects such as low phase-shift precision, few phase-shift bit number(less than 7), inflexible regulating methods and high sensitivity to environment.After a study on the composition of navigation transmitting system and clock synchronization principal and an analysis of time-frequency characteristic of atomic clock, a scheme based on Direct Digital Synthesis and Complex Programmable Logic Device technologies is put forward to realize precise and speed-controllable phase-shifting of atomic clock's output signal.The clock synchronization principal of navigation transmitting system and atomic clock's time-frequency characteristic are analyzed firstly and the overall design scheme and target of micro-step phase shifter are introduced. Then the micro-step phase shifter is introduced in terms of electronic circuit design, software development and data processing methods. The electronic circuits mainly includes MCU control circuit, DDS phase-shift circuit, CPLD partial frequency division phase-measuring circuit, output circuit, power source circuit. Software development consists of DDS phase-shifting, pulse-per-second signal generation, phase-shifting signal generation, clock error measurement and lead-lag phase discrimination. Data procession includes filtering and noise-reduction of clock error data and the extraction of phase-shifting value. At last, corresponding tests are conducted to verify the functions of the device, the results of which demonstrate that the device could realize precise measurement of phase shift and phase error, meeting the design requirements.