GB1342497A - Demodulating systems for colour television receivers - Google Patents

Abstract

1342497 Colour television SANYO ELECTRIC CO Ltd 19 April 1971 [15 March 1971] 9984/71 Heading H4F In a chrominance demodulation circuit a colour television signal is fed to a signal separator 3 and the PAL chrominance signal with swinging colour bursts is fed to parallel 0 and 180 degrees phase shifters 9, 8 which are alternately connected to a band-pass amplifier 4 via a switch 10 operated by pulses at line frequency. The bandpass amplifier 4 passes the PAL chrominance signal to the R-Y demodulator 5 and passes the colour bursts via a gate 6 to control the operation of an oscillator 16 via a phase detector 13. Regardless of the phase of operation of the switch 10 the R-Y component of the chrominance signal fed to the demodulator 5 is of the same polarity for every line and is the same polarity as the output of the oscillator 16. For the B-Y component of the chrominance signal there is provided a band pass amplifier 4<SP>1</SP>, gate 6<SP>1</SP>, oscillator 16<SP>1</SP> and demodulator 5<SP>1</SP>. In an alternative embodiment (Fig. 3, not shown) one band-pass amplifier and one gate are used instead of the two amplifiers 4, 4<SP>1</SP>, and two gates 6, 6<SP>1</SP>, the amplifier receiving the output from the signal separator, the separated colour bursts and chrominance signal being separately phase shifted by a respective pair of phase shifters and associated switch before being passed to the R-Y oscillator and R-Y demodulator respectively. In this case the two switches may be operated in antiphase, to give a -(R-Y) output from the R-Y demodulator. Alternatively (Fig. 4, not shown) the chrominance signal may be fed without phase-shift to both demodulators, the colour bursts being phaseshifted as before before being passed to the R-Y oscillator, the output from the R-Y oscillator also being phase shifted by a pair of phase shifters and a switch operated in phase or antiphase with the switch of the colour burst phase shifter, thus giving an output from the R-Y demodulator of + (R-Y) or -(R-Y) as desired.