A Multi-channel Time-frequency Comparison System Based On FPGA

Time is one of the most important physical quantities. The value comparison among various standard time signal in the same accuracy circumstances, which is also named the comparison of time-frequency, has also been the focus of scientific research. With the rapid development of electronic technology and the continuous innovation of high-precision time interval measurement method, as well as the importance of high-precision time standards has been constantly improved in the national life, scientific research activities and national defense engineering, the research about the comparison system of time-frequency has become a hot topic in the field of electronics and measurement at home and abroad.Time interval measurement is the core in the comparation system of time-frequency. This paper firstly introduced some kinds of time interval measurement methods, and classifily compared their merit, weaknesse and practicality. After ananlyzing the testing indicator of time performance in the BD/GPS dual-mode inter-station synchronization systems, there prensent a quantitative method of the delay time interval measurement based on DCM (Digital Clock Manager). At the same time, this paper designed the multi-channel time-frequency comparation system based on FPGA (Field Programmable Gate Array), making full use of the resources advantage of the large-scale programmable logic devices, such as in general hardware, in programming flexibility and IP core. It present the system-designed diagram, and used the EDA method to pragram and design the time interval measurement module, the analysis module, the multi-channel serial communication and the frequency calibration modules, verified and timly simulate those modules, as well as completed all the design and production of the hardware circuit modules, including power modules, RS232 interface circuit, RS485 interface circuit, frequency calibration circuit, JTAG debug interface circuit. Meanwhile, using the matured virtual instrument technology, it achieved many functions, such as synchronous communication, mass data storage, real-time dynamic data and image display, overrun alarm.Through the online debugging of the system and experimental data, the analysis showed that, the multi-channel comparation system of time-frequency designed in this paper, whose measurement accuracy reach 1.67ns in the high- stability conditions of 10M clock input, is almost 20 times than that of the accuracy of electronic counting, at the same time, its largest measurement error reduced to 8% of the original. In general, this design of the BD/GPS dual-mode inter-station synchronization systems can meet the requirements of the product-detection and the factory- testing.