GB1377543A - Decoding systems for colour television receivers - Google Patents

Abstract

1377543 Colour television SONY CORP 8 Feb 1972 [12 Feb 1971] 5863/72 Heading H4F A PAL swinging burst chrominance signal decoding system comprises a pair of demodulators 12, 13 respectively demodulating the R-Y chrominance signal and the B-Y chrominance signal. The B-Y demodulator 13 is fed with a reference subcarrier signal derived from an oscillator 22, 23 phase locked in antiphase to the average phase of the swinging burst. The R-Y demodulator 12 receives its reference subcarrier signal from an oscillator circuit comprising a first switching circuit 15 deriving the burst signal in its original phase and in the inverted phase thereof on alternate lines and an oscillator 18, 19 phase locked to the average phase of the output of the first switching circuit 15. The output of the oscillator 18, 19 is fed directly to one input of a second switching circuit 20 and via a phase inverter 21 to a second input of said second switching circuit. The two switching circuits 15 and 20 are operated in synchronism by a flip-flop 17 such that the phase of the sub- carrier signal fed to demodulator 12 is always correct irrespective of the switching phase of flipflop 17 as caused by the indeterminate time of switching on of the television set.