Patent GB-1025143-A (GB)
Title: Improvements relating to circuit arrangements for synchronising an oscillator
IPC: H04N5/12
Filed: 1962-10-22
Abstract: 1,025,143. Automatic phase control systems; sawtooth circuits. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. Oct. 22, 1962 [Oct. 20, 1961; April 14, 1962; July 13, 1962; Aug. 28, 1962], No. 39809/62. Headings H3A and H3P. A television receiver field timebase generator 21 is synchronized directly by integrated field sync. pulses producing a direct synchronizing signal 35. Moreover, further signals are derived from the generator as by integration at 30, 31, Fig. 7, to produce sawtooth signals 36 of parabolic flank and added to the direct sync. signals 35 to produce on the grid of rectifier valve 26 a resultant rectified negative signal which also controls, through varying positively the D.C. voltage on capacitor 22, the timebase natural frequency, the arrangement being such that after direct synchronization takes place the middle region of the leading edge of pulse 35 triggers instead the timebase generator. The concave parabolic curve ensures that the triggering takes place only immediately before direct synchronizing, so that undesired interference pulses are ineffective. The positive D.C. on the anode of rectifier 26 is effective over the range of the natural period of the timebase generator as that the catching range is increased. A negative bias applied through resistor 38 reduces to near zero the control voltage from rectifier 26 to compensate timebase natural frequency changes when the height control 24 is adjusted. This effect may also be compensated (Fig. 11) by connecting the anode of rectifier 26 to H.T. through the resistor 24, and changes due to variable current through the rectifier 26 may be compensated by a resistor shunting this rectifier. The frequency adjust resistor 23 is then put in series with the capacitor 22. The bias through resistor 38 may be omitted by connecting the cathode of blocking oscillator 21 to a positive voltage tapped from the cathode circuit of a timebase sweep amplifier. In a Figure 12 a multivibrator is controlled, and a diode rectifies the sum of waves 35, 36, and replaces the tube 26. In a Figure 13 the grid of the blocking oscillator 21 rectifies the sum of waves 35 and a sawtooth wave across capacitor 22 and the resultant negative D.C. voltage across capacitor 22, suitably increased by a positive voltage, and smoothed, applied to a D.C. amplifier valve 53 whose anode voltage controls the charging of capacitor 22. A parabolic voltage 36 may be obtained in this case by connecting the earthed terminal of capacitor 22 to the cathode of a timebase output valve. In a Figure 14 the integrated field synchronizing pulses 35 are rectified and applied to the grid of valve 26, so that if the amplitude of the sync. pulses diminishes, causing a tendency for the controlled frequency to decrease, the anode output of valve 26 is positively increased and compensates for this. In a modification (Figs. 1-6) field synchronizing pulses are integrated and on the integrated waveform are superimposed, with opposite polarity, differentiated flyback pulses from a field scanning timebase generator (blocking oscillator or multivibrator). This composite waveform is then rectified to produce a D.C. control voltage which, through a cathode follower, controls the timebase generator so that its natural frequency is reduced. If, however, the natural frequency is less than that of the field sync. pulses then since the latter are also applied to the grid of the generator, they establish control and the D.C. voltage is inoperative. This created a two-sided catching range of say Œ 5 c/s. for a television receiver field scan.