Patent GB-1160118-A (GB)
Title: Synchronising Device of a Receiver in a Pulse Code Modulation Communication System
Inventor: JOUSSET ANTOINE
IPC: H04J3/06
Filed: 1966-09-19
Abstract: 1,160,118. Multiplex pulse code signalling. A. JOUSSET and C. JACQUART. 19 Sept., 1966 [17 Sept., 1965], No. 41728/66. Heading H4L. A device for synchronizing a receiver in a time division multiplex pulse code system, wherein the synchronization signal consists of a particular arrangement of a group of pulses in a frame, comprises a synchronization error detector producing an error pulse for each error detected, and means controlled by the error pulses for displacing the receiver distributer and is characterized in that the distributer displacement means is only actuated when the error pulses are produced at an average frequency greater than a predetermined value 1/T 1  during a time period greater than a predetermined value T 2 , the times T 1  and T 2  being integral multiples of the duration of a frame and T 2  being greater than T 1 . A sixteen channel system is described, each channel comprising eight digits and the sixteenth channel carrying signalling information by means of seven digits, the remaining digit providing a synchronizing signal consisting of alternate positive and negative code elements in each frame. The sampling period for each channel is 128 micro seconds. The incoming signal is limited at 1 and supplied via a pulse regenerator 3 to a decoder 7 controlled by a code element distributer 5. The output of limiter 1 also controls a clock pulse generator 2 supplying timing pulses for distributer 5 and also controlling the channel distributer 6. A trigger 111 co-operating with AND gates 112, 113 under the control of distributers 5 and 6 produces two trains of pulses, each train comprising pulses separated by 256 microseconds and the pulses in one train being displaced in relation to the pulse in the other train by 128 microseconds. An AND gate 121 receives the output of limiter 1 together with the output of gate 112 and an AND gate 122 receives the output of limiter 1 after inversion at 124 together with the output of gate 113. As a result of the operation of trigger 111 the sync. signal of the previous frame is applied at the same time as the sine. signal of the present frame to the AND gate 121 so that when the system is synchronized no output is passed to OR gate 123. Similarly, as a result of trigger 111, the sync. signal of the present frame inverted at 124 is applied to AND gate 122 together with a signal from gate 113 representing the sync. signal of the present frame so that again no output is passed to OR gate 123 when the system is synchronized. In a prior arrangement, any output of gate 123 is supplied direct to a synchronism restoring device 130 comprising a trigger 131 actuated by the clock pulses from 2 and an AND gate 132 receiving the clock pulses and the output of trigger 131. When the trigger receives only clock pulses an output is provided via AND gate 132 to operate the distributers 5, 6 normally, but when both inputs to trigger 131 are energized it provides no output and the distributers are not operated for the duration of a clock pulse, this process being repeated until synchronization is restored. In order to ensure that this hunting process is not started for random errors in the reception of the sync. signal which do not necessarily indicate loss of synchronism, a delay circuit 140 is included in the present arrangement which comprises two seriesconnected flip-flop delay devices 141, 142 and an AND gate 143 receiving the output of delay 142 and the output of gate 123. On the occurrence of each error pulse from gate 123 the circuit 141 is operated for a time T 1  so that a series of error pulses maintain this circuit operated. The delay circuit 142 is operated when the output from 141 reaches a duration of T 2  and reverts when the output from 141 ceases.