GB562513A - Improvements in or relating to apparatus for controlling the frequency of oscillators - Google Patents

Abstract

562,513. Automatic control systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Dec. 31, 1942, No. 18570. Convention date, Dec. 31, 1941. [Class 38 (iv)] [Also in Group XL] A saw-tooth oscillator is controlled as to frequency or phase by combining the sawtooth wave with opposed phases of a synchronizing pulse, the resultant being rectified to provide a control voltage for regulating the oscillator. The system is particularly applicable for synchronizing the cathode-ray deflecting circuit in a television receiver. A relaxation oscillator comprises condensers 33, 34, charging resistance 36, and discharging valve 32, the latter being triggered by pulses supplied by a blocking oscillator 27. The saw-tooth voltage across the condensers 33, 34 is applied to the grid of an amplifier 37 which feeds saw-tooth current to the scanning coils 22 of a television reproducer 11. Incoming synchronizing signals are amplified at 10 and separated from the video signals and applied through transformer 43 to opposite ends CB of a resistance, the midpoint A of which receives the saw-tooth voltage from the condenser 34 of the relaxation oscillator. The resultant voltages at CB thus comprise a saw-tooth voltage with the synchronizing pulses superposed in opposite senses. These voltages are rectified in the opposed diodes 51, 53 and the mean of their rectified voltages is taken through resistances 58, 59 to the grid of a valve 61, the plate of which applies a control voltage in the grid circuit of the blocking- oscillator 27. Any change from the normal phase relation of the saw-tooth voltage and the pulses establishes a correcting voltage on the grid of the valve 61 and on the grid of the blocking oscillator, in such sense as to restore the phase relation to normal. A similar control circuit is employed for synchronizing the framefrequency current through the coils 23. Alternating components are removed from the output of the valve 61 by a condenser 63 and a resistance-condenser branch 64, 66. The outputs of the rectifiers 51, 53 may be combined by applying them to the grids of separate valves having a common resistance in their plate circuits, Fig. 2 (not shown). Specification 525,342 is referred to.