APPARATUS FOR SYCHRONIZING PULSE TRAINS IN A DIGITAL TELEPHONE SYSTEM

摘要

The system includes, an exchange (EX) to which are connected a plurality of telephone sets (TA). The exchange contains a central processor (EXCP), a plurality of line boards, each of which containing a plurality of line circuits (DEC) for interfacing between the exchange and the connected telephone sets. Each telephone set contains a line circuit (DIC) in which there are included, a coder and decoder for PCM-coded information words. The system is completely digitized and transfers digital information in time-divided form between the telephone sets. For achieving accurate sychronization of the pulse trains between the different units while simultaneously reducing the jitter, the unit (DIC) is equipped with a counter (CTPT) which under control of a signal from a comparison circuit (CO) is reset to zero at given times, thereafter starting counting once again whereby synchronizing signals synchronizing window being sent via a line to a receiving unit (DIC) in a telephone set. The synchronizing window consists of a positive logical One signal and a negative logical One signal preceded by a given number of logical Zeros. The counters are reset to zero during the -1 pulse and the rapid derivative in the junction between positive and negative pulse in the synchronizing signal at the change is utilized to once again start the count (the zero-resetting ceases).