GB643911A - Improvements relating to the synchronisation of saw-tooth wave generators - Google Patents

Abstract

643,911. Automatic frequency control systems. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Feb. 18, 1948, No. 4769. Convention date, Nov. 29, 1946. [Class 38 (iv)] [Also in Group XL (b)] A sawtooth generator is synchronized by periodic pulses such as are received from a television transmitter by applying the pulses directly to a free-running multivibrator, and by also applying them indirectly through a phase-sensitive system, the multi-vibrator being used' to trigger the sawtooth generator. As shown, the line synchronizing pulses derived from the pulse separator 6 of a television receiver are fed directly by a condenser 9 to the pulse-generating multi-vibrator 10 which is thereby rapidly brought into loose synchronism during the starting period. The pulse generator 10 controls the line frequency sweep generator 7 for the C.R. tube 4, and also controls an auxiliary sawtooth generator 33. The incoming pulses from 6 are fed through a cathode-follower valve 51 and transformer 42 across one diagonal of a diode bridge detector 35 in series with a biassing condenser-shunted resistor 40. Across the other diagonal of the bridge the output from the sawtooth source 33 is applied in series with an output resistanceshunted condenser 39. The voltage across the condenser 39 varies according to the phase difference between the incoming pulses and the sawtooth voltage, and is applied to a valve 26 functioning as a variable resistance in the grid-earth connections of the multi-vibrator 10, and adjusting its frequency so as to set up and maintain phase agreement with the incoming pulses. In a modified circuit (Fig. 3, not shown), the multi-vibrator 10 operates at a multiple of the incoming pulse frequency. It feeds a second multi-vibrator which operates at the pulse frequency and controls the sawtooth generator 33.