GB1492567A - Processing circuit for television chromatic signals - Google Patents

Abstract

1492567 Colour television INDESIT INDUSTRIA ELETTRODOMESTICA ITALIANA SpA 4 Dec 1974 [7 Dec 1973] 52396/74 Heading H4F The phase of operation of a switching voltage generator 23 controlling a PAL switch 24 and a further switch 14 is determined by the output of a phase comparator 16 having one input connected to the output of a subcarrier regenerator 18 and a second input connected to switch 14 and a 90 degree phase shifter 12. The apparatus may receive a PAL signal having either "swinging" bursts or a burst (of phase 135 degrees relative to the B-Y modulation axis) only in every second line period. The bursts are separated by a burst gate 10 and the subcarrier regenerator 18 receives, via switch 14, the output of phase shifter 12 during every second line period and generates a subcarrier in phase with the thus received bursts. For a received signal having "swinging" bursts the bursts passed to subcarrier regenerator 18 when the phase of switching voltage generator 23 is "correct" are of phase 225 degrees relative to the B-Y modulation axis, the burst input to phase comparator 16 from switch 14 in alternate line periods and phase shifter 12 in the intervening line periods is of phase 225 degrees in every line period, and phase comparator 16 provides, via a low-pass filter, a positive output which prevents a gate 21 passing a signal and leaves the operation of switching voltage generator 23 undisturbed. If, however, the phase of switching voltage generator 23 is "wrong", the subcarrier regenerator 18 receives bursts of phase 315 degrees and the burst input to phase comparator 16 alternates in phase between 135 and 315 degrees and the phase comparator provides, via the lowpass filter, a zero output to enable gate 21 to pass a pulse from a generator 22 to switching voltage generator 23 to reset it. For a received signal having a burst only in every second line period no bursts are passed to subcarrier regenerator 18 if the phase of the switching voltage generator is "wrong" and again the output of phase comparator 16 is zero. The output of subcarrier regenerator 18 is passed via 45 degree phase shifter 20 and 90 degree phase shifter 26 to B-Y demodulator 6, and also via a detector 19 to control a colour killer circuit 4 and an amplifier 2. In an alternative embodiment the output of phase comparator 16 controls switching voltage generator 23 directly.