Patent GB-931947-A (GB)
Title: Improvements in or relating to circuit arrangements for synchronizing time-base oscillators
IPC: H04N5/12
Filed: 1961-10-13
Abstract: 931,947. Automatic phase-control systems; valve saw-tooth generators. PHILIPS ELECTRICAL INDUSTRIES Ltd. Oct. 13, 1961 [Oct. 17, 1960], No. 36831/61. Classes 40 (5) and 40 (6). A timebase generator is synchronized by " flywheel sync. " or directly applied synchronizing pulses and during loss of synchronism larger amplitude sync. pulses are applied through a normally non-conductive member to rapidly and directly synchronize the generator. In Fig. 1, a Miller transitron saw-tooth generator 38 is phase controlled by a phase discriminator tube 1 to whose anode, normally at earth potential, differentiated flyback pulses 27 from a vertical or line scan output stage 30 are applied and, to its second control grid, slightly delayed vertical or line sync. pulses 2, so that A.F.C. voltage is produced across integrating circuit 35, 36 and applied to the saw-tooth generator suppressor grid. Incoming sync. pulses 2 also produce on the screen grid 12 negative pulses 13, 16 applied to the cathode of a diode 18 and passing through the latter to the screen grid of saw-tooth generator 38 to synchronize it, except when, during synchronism, flyback pulses from it are coincidently applied to the anode of the diode. In that case attenuated pulses 16<SP>1</SP> pass over resistor 39 shunting the diode 18 to finely synchronize the generator 38. In a modification, the diode 18 is replaced by a triode with anode of low operating D.C. voltage and capacitively coupled to the screen grid of generator 38, vertical or horizontal sync. pulses being applied to the triode grid, and being effective on the generator 38 only during loss of synchronism. Fine control is then effected by attenuated pulses continuously applied to the screen grid from the phase discriminator tube. In a further modification, sync. pulses and flyback pulses are both in series applied to the triode grid which becomes self-biased by a C.R. network so that interference between sine. pulses ia biased off during synchronism, the C.R. time constant being so short that, during loss of synchronism, a smaller bias is rapidly produced and sync. pulses from the triode anode pass to the saw-tooth generator. In Fig. 8, horizontal sync. pulse and flyback pulse amplitudes are added across a triode grid leak C.R. network 57, 58 and inverted flyback pulses 61<SP>1</SP> differentiated by a capacitor 73, applied to the anode. A beat frequency output arises only during loss of synchronism and is added to the beat frequency A.F.G. voltage from a phase discriminator before application to a reactance circuit 79 controlling the frequency and phase of a sinusoidal oscillator 65 generating across output capacitor 67 the horizontal time base sawtooth. The network 83 by-passes to earth the flyback pulse frequency, but not the beat frequency. In Fig. 7 (not shown), the sum of the horizontal sync. and flyback pulse amplitudes during synchronism are applied to a selfbiasing pentode with screen grid receiving a negative flyback pulse. Only during loss of synchronism does a sync. pulse pass from the pentode anode to a control grid of a sinusoidal oscillator generating the timebase (also controlled by a phase discriminator and reactance circuit as in Fig. 8). The timebase generator may alternatively be a multivibrator. Specification 927,602 and German Specification 965,500 are referred to.