GB1361578A - Colour television - Google Patents

Abstract

1361578 Colour television SHARP KK 16 Nov 1972 [16 Nov 1971 21 Feb 1972] 52978/72 Heading H4F A PAL colour television receiver includes a first burst gate, 2, passing all the received "swinging" bursts, and a second burst gate 6 passing the bursts of alternate lines, the output from gate 2 controlling an oscillator 5, the output of which is either phase compared with the output of gate 6 or is vectorially added to the output of an oscillator controlled by the output of gate 6, to produce a reference sub-carrier which is phase-inverted in alternate lines at 11 by a signal which also controls gate 6, to provide a reference sub-carrier of correct phase for demodulating the R - Y chrominance component irrespective of the phase of the bursts passed by gate 6. In the embodiment of Fig. 1, oscillator 5 produces a reference sub-carrier of phase f50, Fig. 2, which is fed to B - Y demodulator 13 and a reference sub-carrier of phase f<SP>1</SP>50 which is added at 10 to the output of oscillator 9 which is of phase f<SP>1</SP>B1 or f<SP>1</SP>B2 (this phase being 90 degrees phase retarded relative to the bursts passed by gate 6) to produce a sub-carrier of phase f<SP>1</SP>51 or f<SP>1</SP>52 respectively, which is fed to switch 11 where it is phase-inverted on those lines when gate 6 is closed, and then via 90 degrees phase-advancer 12 to R - Y demodulator 14. In the alternative embodiment (Fig. 4, not shown) the output of oscillator 5 is of + (R - Y) phase and is fed via a 90 degrees phase retarder to demodulator 13 and directly to a phase discriminator receiving the output of gate 6, to produce a control voltage which is fed to a selective phase shifter to provide a signal which is in phase with or antiphase with the output of oscillator 5, and this signal is then phase inverted for alternate lines and fed to demodulator 14. Instead of the reference sub-carrier fed to demodulator 14 being phase-inverted on alternate lines, the chrominance signal may be so inverted, the reference input being of constant. phase.