Patent GB-711552-A (GB)
Title: Improvements in frequency controllable oscillating circuit arrangements
Inventor: ADLER ROBERT
IPC: H04N5/12
Filed: 1952-07-30
Abstract: 711,552. Pulse and valve circuits frequency modulation. ZENITH RADIO CORPORATION. July 30, 1952, No. 19296/52. Classes 40 (5) and 40 (6). [Also in Group XXXV] In a synchronized oscillator circuit a sine wave from filter 1, Fig. 1, is squared in clipper circuit 2, differentiated by circuit 3 and the resulting positive or negative pulses are effective to cause device 4 to produce a periodic wave which is applied to the filter 1. A control signal is applied to circuit 2 to vary the phase of the output and thus the frequency of the oscillator. The control signal may be the synchronizing signal in a television receiver or the modulation in a frequency modulated carrier generator. The filter may be a piezo-electric crystal and the clipper a transformer core or half-wave rectifier. A sine wave from resonant circuit 7, 8, Fig. 2, is applied to the primary of transformer 10 having a saturable core to produce a square wave of flux, a differentiated pulse signal appearing across the secondary 11 and being applied to leaky-grid rectifier 12 so that only the positivegoing pulses are effective. The anode circuit of valve 12 feeds the resonant circuit 7, 8 and a control signal applied over secondary 15 applies a magnetic bias to the core to vary the phase of the differentiated pulses. In a modification, Fig. 3, a sine wave from crystal 16 is applied to hexode 18 which passes a rectangular wave of current through transformer primary 22 to develop differentiated pulses across secondary 23. The positive-going pulses are bye-passed by rectifier 25, the negative-going pulses maintaining the crystal 16 in oscillation. A control signal applied across resistor 19 causes the time of conduction of valve 18 to vary and thus the time of occurrence of the differentiated pulses. In a modification, Fig. 4, for synchronizing the line time base of a television receiver, the generator 40 feeds line coils 42 in series with a small resistor 83 across which is shunted an auxiliary coil 84 which resonates at line frequency with capacitor 85. The video signal with positivegoing synchronizing pulses is applied to the grid of valve 49 where slicing occurs due to gridcurrent and cut-off conditions. The electron beam, after passing focusing and acceleration electrodes falls on anodes 58, 66 during a synchronizing pulse to an equal extent if the generator 40 is in synchronism with the pulses. since the current through auxiliary deflection coil 84 is at zero. Otherwise there is an unequal flow of current in load resistors 61, 68 resulting in a deflection potential existing between electrodes 59, 67 to cause the beam in valve 60 to leave the edge of the intercepting anode 79 earlier or later, as appropriate. The flow of anode current through resistor 80 produces a negative-going pulse which after differentiation in circuit 81, 82 synchronizes or triggers generator 40. When the generator 40 is running in synchronism with the controlling pulses there will be a flow of current in the anode load resistor 76 to provide a frame synchronizing signal which is fed to generator 39, a capacitor 77 integrating the output. Since during the time that the beam in valve 49 is operative it falls on anode 58, or 66 the output from anode 73 is deficient during these periods. This deficiency is corrected by feeding signals from anodes 58, 66 to generator 39 over resistors 74, 75. A.C. components in the circuits of the anodes 58, 66 are bye-passed by capacitors 63, 70 while the effect of any noise pulses is minimized by the use of capacitor 64, 71. In a modification the anode 73 is dispensed with and the frame synchronizing signal obtained from the anodes 58, 66. In a further modification, Fig. 5, video signals from terminal 43 are fed to a separator circuit 87 supplying frame synchronizing signals to generator 39 and line synchronizing signals to the centre tap of coil 89. The line generator 40 feeds the parallel resonant circuit 108, 109 so that diodes 90, 91 act as a phase detector, the output from the anodes being fed over smoothing circuits to deflection electrodes 59, 67. The external coil 84 may be replaced by a sinusoidal oscillation from the line generator fed to the electrodes 59, 67.