Patent GB-1106843-A (GB)
Title: Apparatus for correcting timing errors in television signals
IPC: H04N5/95
Filed: 1965-03-24
Abstract: 1,106,843. Variable delay system; television; transistor gating circuits. FERNSEH G.m.b.H. 24 March, 1965 [24 March, 1964; 25 Sept., 1964; 30 Jan., 1965], No. 12438/65. Headings H3A, H3T, H4F and H4R. A television signal, e.g. from a magnetic recorder, is progressively delayed in a succession of delay line stages and that stage is determined at the output of which the synchronizing pulses in the television signal coincide with pulses from a reference source, and the television signals are applied from that stage to an output while outputs from the other stages are inhibited. Fig. 1 shows an embodiment in which television signals are applied to a tapped delay 50 while the synchronizing pulses from the signal are extracted by synch. separator 2 and shaped by pulse shaper 3 and applied to a second similar tapped delay line 10. Coincidence stages 21, 22, &c. are connected to the taps of the line 10 to determine coincidence between the synch. pulse at the tapping and a reference pulse applied on wire 4. Operation of a coincidence stage causes the closing of one of the switches 41, 42, &c. corresponding to the operated coincidence stage, to connect the television signal from the corresponding output of the delay line 50 to an output line 5. A store 31, 32, &c. is connected in each line between the coincidence stage and the switch 41, 42, &c. to maintain the switch closed in the interval between pulses. In order to prevent more than one coincidence stage being operated a gate 6 is provided in lead 4 so as to gate out the reference pulses from succeeding coincidence gates as soon as one coincidence gate is operated. In alternative forms of the invention only one line is used and coincidence established at the output tappings of that line. In Fig. 2 (not shown), a narrow synchronizing pulse is derived from the line synchronizing pulse of the television signal and this narrow pulse is added to the original signal which is then applied to a tapped line (60). Coincidence gates on the tappings determine coincidence between the narrow pulses and reference pulses and operate corresponding gates to gate the television signal from the appropriate tapping. A transistor circuit for the coincidence gate and store for use in this embodiment is shown in Fig. 3, in which transistor 72 in the bi-stable pair 72, 73 is normally non-conducting but may be switched on by the coincidence of a reinforced synch. pulse from the appropriate tapping on the line and a reference pulse applied to line 74. When 72 conducts the television signal may be taken from the emitter terminal, the transistor 72 acting as a linear device. The bi-stable circuit remains in the set condition until a reset pulse is applied over line 71. When the circuit is set an interconnection from the collector of the second transistor, e.g. 73 or 83, to the base of the corresponding transistor in the circuit connected to the succeeding tap prevents the succeeding circuit being energized if there is any overlap of the reference and the synchronizing pulses. Alternatively each tapping may be provided with a synch. separator and pulse shaper to derive a narrow pulse from the signal at the tap, which is applied to a coincidence gate to determine from which output the signal should be taken. The coincidence gates or stores are interconnected so that the operation of one gate disables the following gate to prevent the output being taken from more than one tap. Circuits comprising transistor synch. separators, diode coincidence (or " AND ") gates, bi-stable transistor circuits, and transistor, thyristor, or diode bridge, gating circuits, are described with reference to Figs. 5, 6, and 7 (not shown), for this alternative embodiment. Reference has been directed by the Comptroller to Specification 888,380.