Apparatus for synchronizing pulse trains in a digital telephone system

Claim 1

A method for synchronizing pulse trains in a digital telephone system including an exchange (EX) and a plurality of telephone sets (TA) connected to the exchange via lines, the exchange including a central processor (EXCP) and a plurality of line circuits (DEC), each of the telephone sets including a separate line circuit (DIC), each of said line circuits (DEC) and (DIC) having reception and transmission directions and including a primary counter, a time position counter, and a synchronizing detector (SD) which detects, in the reception direction of the line circuits, the reception of a synchronizing window containing at least two consecutive synchronizing bits of opposing polarity preceded by a plurality of logical Zeros, said method comprising generating and transmitting to the synchronizing detector a synchronizing signal consisting of said consecutive synchronizing bits of opposite polarity preceded by said plurality of logical Zeros, transmitting during the duration of the first of the synchronizing bits a zero resetting signal to said primary counter (CTR), feeding a high frequency signal to the primary counter and in the primary counter dividing the high frequency signal down and sending a resulting control signal of lower frequency to the time position counter (CTP), sending the zero resetting signal also to said counter (CTP), and utilizing the change between said first and said second synchronizing bits to cause the zero resetting of the counters (CTR) and (CTP) to take place rapidly due to the steep derivative of the transition between the synchronizing bits, whereupon the counters resume counting in a precisely defined manner enhancing synchronization.

Claim 2

A method for synchronizing pulse trains in a digital telephone system including an exchange (EX) and a plurality of telephone sets (TA) connected to the exchange via lines, the exchange including a central processor (EXCP) and a plurality of line circuits (DEC), each of the telephone sets including a separate line circuit (DIC), each of said line circuits (DEC) and (DIC) having reception and transmission directions and including a primary counter, a time position counter, and a synchronizing detector (SD) which detects, in the reception direction of the line circuits, the reception of a synchronizing window containing at least two consecutive synchronizing bits of opposing polarity preceded by a plurality of logical Zeros, said method comprising generating and transmitting to the synchronizing detector a synchronizing signal consisting of said consecutive synchronizing bits of opposite polarity preceded by said plurality of logical Zeros, transmitting during the duration of the first of the synchronizing bits a zero resetting signal to said primary counter (CTR), feeding a high frequency signal to the primary counter and in the primary counter dividing the high frequency signal down and sending a resulting control signal of lower frequency to the time position counter (CTP), sending the zero resetting signal also to said counter (CTP), and utilizing the change between said first and said second synchronizing bits to cause the zero resetting of the counters (CTR) and (CTP) to take place rapidly due to the steep derivative of the transition between the synchronizing bits, whereupon the counters resume counting in a precisely defined manner enhancing synchronization.