| 摘要 |
1,154,474. Automatic phase control systems. FERNSEH G.m.b.H. 12 Sept., 1966 [11 Sept., 1965], No. 40648/66. Headings H3A and H4R. Timing errors in a television signal, e.g. from a magnetic recorder, are compensated by adding a high frequency signal, locked in phase with the line synchronizing signal, to the signal during line blanking intervals and comparing the phase of this high frequency signal with that of a second high frequency signal which is locked in phase with line synchronizing pulses from a reference source. An error signal derived from the phase comparison controls a delay device through which the television signal is passed to compensate the timing errors. The system is preferably used after an initial stage of compensation for timing errors has reduced them to less than about 30nS. The high frequency signal to be added to the television signal during, e.g. the back porch interval may be derived from an oscillator switched on by the output of a monostable multivibrator which is triggered by the line synch. pulses of the signal, or it may be derived from a ringing resonant circuit which is excited by the differentiated leading or trailing edge of the line synch. pulse and whose damping is such that the oscillations decay substantially to zero in the period between synch. pulses. In a recording installation for colour television signals which may have a timing error compensator for limiting the phase deviations of the chrominance sub-carrier this same compensator may be utilized for timing error compensation, in which case a switch may be provided so that the compensator may be controlled by the chrominance sub-carrier during colour reproduction and by the high frequency signal phase comparator during monochrome reproduction. In such a case three comparatively simple compensators may be connected in series, Fig. 5 (not shown). |
