Apparatus for mutually synchronizing oscillators in switching centers of a telecommunication network

Claim 1

Apparatus for mutually synchronizing central office clock oscillators in each of a plurality of interconnected switching centers constituting a telecommunication network, the apparatus in each switching center comprising: adjustable clock oscillator means having an output frequency which is adjustable in value in dependence on the value of a synchronizing signal, first and second synchronizing circuits for producing synchronizing circuit output signals responsive to phase comparisons between said adjustable clock oscillator and the clock oscillator outputs of others of said switching centers connected to the defined switching center, each said synchronizing circuit comprising a plurality of line frequency dividers, each of which receives one of said clock oscillator outputs from said other switching centers and produces frequency-divided outputs therefrom, a central office frequency divider for producing a divided-output signal from said adjustable clock oscillator output, a plurality of phase comparators, each of which compares the output from one of said line frequency dividers with the output from said central office divider and produces an output signal of a value corresponding to the phase difference therebetween, adding means for producing an output signal of a value corresponding to the sum of said phase comparator output signals and means for producing the synchronizing circuit output signal from said adding means output signal, said first synchronizing circuit including means for producing an output signal having a control range corresponding to the phase difference between said adjustable clock oscillator and the clock oscillator in at least one of said other switching centers conditioned by the greatest possible no-load frequency difference between said adjustable clock oscillator and the clock oscillator in said at least one other switching center, the generation of a reference phase occurring upon the crossing of said control range by said first synchronizing circuit output signal, said second synchronizing circuit including means for producing an output signal having an operating range corresponding to the phase difference between said adjustable clock signal and the clock signal from said at least one other switching center and the greatest possible propagation time variation in a line connecting two of said switching centers and means for combining said first and second synchronizing circuit output signals for producing said synchronizing signal.