Patent GB-1126446-A (GB)
Title: Apparatus for the compensation of timing errors in a television signal
IPC: H04N5/95
Filed: 1966-09-16
Abstract: 1,126,446. Synchronizing television signals. FERNSEH G.m.b.H. 16 Sept., 1966 [16 Sept., 1965], No. 41482/66. Heading H3A. In an apparatus for correcting errors in timing of a television signal in which the signal is passed through a tapped line 10, Fig. 1, and the synchronizing pulses in the signal are compared, in units 11, with reference impulses on line 2 so that the signal is switched to the output on line 3 through the respective unit 11 in which the signal synchronizing pulses coincide with the reference impulses, a device 5 detects a faulty switching condition and operates switch 6 to cause the switching conditon of the units 11 to be restored to the condition obtaining before the fault condition was detected. Interconnections 7 between succeeding comparisonswitching stages 11 ensure that if one switching stage is operated the succeeding one is inhibited to prevent two adjacent stages being operated when the delay required is that intermediate a pair of adjacent taps. The faulty switching condition may be detected by monitoring the output level and operating the switch 6 when the level deviates in either direction from normal, or the signals on the interconnection 7 may be monitored via a diode network connected between the interconnections and the detector 5, Fig. 2 (not shown). Timing comparator and switch unit, Fig. 3, comprises an emitter follower 21 which feeds the television signal to the switch, comprising transistor 51, and the comparator circuit in which the signal is differentiated in the circuit consisting of transistors 22, 23, and inductor 24, to derive a narrow pulse coincident with the leading edge of the line synchronizing pulse, which is applied to one input of the " AND " circuit formed by diodes 31, 32. The other input of the " AND " circuit is fed with the reference impulses and when the two impulses coincide an output is produced which operates the bistable trigger formed by transistors 35, 45, and the signal at the emitter of transistor 35 cuts off switching transistor 51 to allow the television signal from emitter follower 21 to pass via resistors 52 and 53 to the output on line 54. In the event of a faulty switching condition being detected, the supply voltage on line 60 is momentarily interrupted immediately after a reference impulse has been applied to line 57. The interruption causes transistors 35 and 45 to stop conducting but capacitors 38 and 48 will still maintain some charge in accordance with the condition of the bi-stable during the period before the immediately preceding impulse, there having been insufficient time for a substantial change since that impulse, and therefore when the supply is restored to line 60 the bi-stable will resume the condition it had in the previous period, irrespective of the condition immediately preceding the supply interruption. Faulty switching condition detector, Fig. 4.- The output from the switching stages 11, Fig. 1, is applied over lead 13, Fig. 2, to transistor 61 and then via a gate, formed by transistors 62 and 63 to a phase-splitting amplifier 65. Gating pulses are applied via transformer 64 to sample the signal immediately after the reference impulse. If the signal deviates from normal either up, due to two gate circuits being opened simultaneously, or down, due to no gate circuit being opened, emitter follower 75 will be turned on harder and the output, applied to switching circuit 6, Fig. 1, will cause a momentary interruption of the supply to the bi-stable circuit in the time comparator and switching unit of Fig. 3.