Research Of GPS Disciplined Digital Timekeeping Clock

Characteristics of GPS are world-wide, all-weather coverage, continuity, real-time and high-precision. High-precision time can be obtained by using GPS signal to calibrate local clock. A military project needs my lab to make a hand-held, low power, with a high precision timekeeping clock. At present, the existing timekeeping clock at home and abroad can not meet the needs, so this thesis do the research.Aging of crystal oscillator is a main factor influencing the accuracy of clock. Compensation can be achieved by varying the frequency dividing radio or fine-turning the oscillation frequency. At present, most of the time-holder adopt voltage-controlled oscillator phase-locked loop program, which not only correcting time but also locking frequency, but the circuit is hard to be designed, it needs a high precision DAC, multi-channel power and carefully designed analog circuits. An adder-based clock circuit, with its frequency dividing ratio being able to adjusted fine and smoothly, is introduced in this thesis. The OCXO or TCXO is used for timekeeping, the frequency lose of crystal oscillator is measured by the standard time signals from GPS, the frequency lose can be compensated by varying the frequency dividing radio based on ABC clock circuit. The circuit scheme, correcting only time but not locking frequency, has the advantages of being high precision, fully digital and easy to be designed. For the scheme, general design of the system and chip selection is completed, a test platform is also built in this thesis. The logic design of ABC clock circuit adopt CPLD. The high accuracy time interval is measured by TDC-GP2. The design of Kalman Filter is used MATLAB software. As the GPS pps has jitter, two filter algorithm are analysised, designed and experimented in this thesis.The timekeeping clock uses the stability of frequency is±2×10 E? 9and the nominal frequency is 20MHz OCXO, the practical test result has the precision of 1ms/day. The timekeeping clock selects the stability of frequency is±1×10 E? 8 and the rated frequency is 20MHz wide temperature type crystal digital Warming (DTCXO) with its power dissipation is 0.54W.