| 摘要 |
1,251,185. Colour television. RANK ORGANISATION Ltd. 18 Nov., 1968 [5 Dec., 1967], No. 55245/67. Heading H4F. Relates to a means for controlling a reference oscillator 20 operating at the subcarrier frequency in a PAL colour television receiver by means of the two colour component signals E u and E v which have been separated from the composite colour video signal; alternatively the phase alternation may be effected at field frequency. The colour components, when separated in the PAL receivers as shown in Fig. 1, contain no phase errors since the errors in successive lines are cancelled out. Thus the phase of one, or a combination of both, of the components may be compared in a phase detector 22 with the phase of the reference oscillator in order to ensure that the oscillator locks to the subcarrier frequency and to obviate the possibility of it locking to one of the adjacent frequency components in the frequency spectrum of the output of the oscillator. The error signal from phase detector 22 is used to effect coarse control of the oscillator 20, fine control of the oscillator 20 being effected by the burst gating pulse derived from the chrominance signal by means of a burst keyer 18, the phases of the outputs from the keyer and oscillator 20 being compared at 19 to give the fine control signal. |
