Patent GB-768688-A (GB)
Title: Improvements in and relating to electric pulse selecting circuits
IPC: H04Q11/04
Filed: 1954-01-13
Abstract: 768,688. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., and STENNING, L. C. Feb. 9, 1955 [Jan. 13, 1954], No. 1021/54. Class 40 (4). A circuit for selecting a pulse train from a number of pulse trains of different phases comprises a coincidence gate, fed with clock pulses, and connected in a closed circulating circuit whose circulationtime is equal to the pulse repetition period, the circulating circuit being provided with means for modifying the circulation time until the pulse output from the gate has the desired phase. When the subsciber's loop closes relay A operates followed by relay C. Relay A opens gate 51. Relay C pulses the bi-stable trigger circuit 49 to set it in its "0" position, and also passes a pulse over condenser 39 to open gate 41 long enough to pass a datum pulse to gate 42 which thereupon passes a clock pulse in the datum position to trigger the blocking oscillator 44. The resulting pulse is fed to the input 60 of the magnetostrictive delay line 14. The blocking oscillator also changes the bi-stable trigger 48 into its " 1 " position, thereby opening gate 46. 100 Ás. later the delay line output 45 emits a pulse which passes through gates 46 and 42 to trip the blocking oscillator, whereupon the cycle recommences. When A releases at the beginning of the first dial impulse it opens gate 51 to pass a pulse from the 45Ás. coil 52 which changes the bistable trigger 53 to its "1 " position which in turn changes the bi-stable trigger 48 to its " 0 " position. Relay A also changes over to " 1 " position, the mono-stable " flip-flop " 55 which has a 250 ms. return time. This does not affect the trigger 49, so that with both 48 and 49 in the " 0 " position gate 54 is opened to pass a pulse from coil 56, after only 90 Ás. delay, to the blocking oscillator 44. The circulating pulse has thus been advanced in phase by 10 Ás. This pulse is also passed back to trigger to change it to the "1 " position, so that subsequent outputs from the delay line are taken from the 100 Ás. coil 45. When A reoperates at the end of the impulse, it restores trigger 53 to its " 0 position. Each subsequent dial impulse operates in a similar manner to advance the phase by 10 Ás. 250 ms. after the end of the first dial train the " flipflop " 55 restores to the " 0 " position, thereby moving trigger 49 to the " 1 " position. This provides an enabling potential for gate 59 instead of gate 54 so that on the next dial impulse an output is taken for recirculation from the 99 Ás. coil 58 of the delay line, thereby advancing the phase of the pulse by 1 Ás. and so on. Thus, a total phase advance is effected proportional to the number represented by the two dialled digits. The coils 56 and 58 may be arranged at positions corresponding to 110 Ás. and 101 Ás. respectively so that the phase of the pulse is retarded instead of advanced. In a modification asparate 1 Ás. and 10 Ás. delay lines are provided and switched in as required to provide the requisite retardation of phase. In a further embodiment the dial is replaced by a pulse generator enabled by a switch which is maintained operated until the requisite phaseshift is obtained. Specification 767,684 is referred to.