Method and apparatus for synchronizing master and local time base systems

Claim 1

A time base synchronization system for synchronizing a local time base consisting of a cyclically recurring series of sequential time slots generated by a voltage controlled local oscillator and local digital main counter with a master time base consisting of a cyclically recurring series of sequential time slots generated by a master oscillator and master main digital counter comprising coarse sycnhronizing means for bringing said time bases into coarse synchronization, said coarse synchronizing means comprising means coupled to the master main counter for generating a coarse synchronization signal at the beginning of the first time slot in said series of time slots in the master time base, and means coupled to the local main counter and responsive to said coarse synchronization signal for adjusting the local main counter to begin generating the said first time slot in the series of slots in the local time base upon receipt of said coarse signal; and fine synchronizing means for bringing said time bases into fine synchronization, said fine synchronizing means comprising means coupled to the local main counter for generating a fine synchronization request signal at the start of a predetermined one of the remaining time slots in the local time base, means including a master secondary counter coupled to the master main counter for measuring the elapsed time between the receipt of said fine synchronization request signal by the master main counter and the beginning of said predetermined one time slot in the master time base and for generating a fine synchronization reply signal at the beginning of a time period before the end of said predetermined one slot in the master time base which is equal to said elaspsed time, means including a local secondary counter coupled to the local main counter for measuring the elapsed time between the receipt of said fine synchronization reply signal by the local and the end of said predetermined one time slot in the local time base to produce a digital synchronization error signal, means for computing from said digital synchronization error signal a frequency error, time error and phase error, means for coupling said frequency and phase errors as corrections to said local oscillator and said time error as a correction to said local main counter, synchronization state logic means obtaining as inputs said coarse synchronization signal and fine synchronization reply signal for generating a time varying gain output in dependence on the number of cycles of said time slots between error corrections, said gain outputs coupled respectively to said local oscillator and said local main counter to control the gain at which said correction signals are entered thereto, error limit logic means coupled to said synchronization error measuring means for producing error limit signals when said error exceeds a predetermined range of values, and sequencing logic means having as inputs said fine synchronization reply signal and the error limit signal output of said error limit logic means and having outputs coupled to to said synchronization state logic means and said means for computing and responsive to said fine synchronization and error limit signals for producing said sequencing signals to cause said synchronization system to follow a programmed control state sequence in which transfer between control states for large initial errors is made automatically for a predetermined number of sequentially occurring corrections and is dependent upon the magnitude of the synchronization error for subsequent corrections.