GB701985A - Improvements in or relating to television receivers - Google Patents

Abstract

701,985. Pulse discriminating circuits. STANDARD TELEPHONES & CABLES, Ltd. Feb. 15, 1952 [Feb. 19, 1951], No. 3972/51. Class 40 (6) In a circuit for separating television line and frame synchronizing pulses the mixed pulses are applied to an input of a pentode valve to produce an output which is applied to a further valve feeding another input circuit of the pentode through an integrating circuit the arrangement being such that the combination of a frame pulse and an integrated frame pulse produces a second output from the pentode from which a frame synchronizing pulse is derived. Line synchronizing pulses are derived from the second valve. In the circuit shown the video signal is applied to grid of a pentode V1 biased so that only the synchronizing pulses (which are positive going) cause the valve to conduct. The output from the screen grid is applied to the grid of valve V2 which feeds its output through an integrating network R3, C3 to the suppressor grid of valve V1. This grid is normally biased to cut-off but the integrated frame pulses permit anode current to pass. The end of the first frame pulse at the control grid causes the anode current to be rapidly cut-off producing a sharp positive frame synchronizing pulse at the output capacitor C4. Line synchronizing pulses may be derived from the screen or anode of the second valve. According to the Provisional Specification the integrating circuit could be replaced by a delay line and the circuit arranged such that frame pulses on the control and suppressor grids but not line pulses overlap so that frame output pulses are produced.