GB1473126A - - Google Patents

Abstract

1473126 Colour television SONY CORP 8 Aug 1974 [10 Aug 1973] 35027/74 Heading H4F A known decoding system, Fig. 3, for a PAL chrominance signal is modified so that when a monochrome signal is received a PAL-switch 23 cannot be switched during active line periods in response to noise applied to a resonance circuit 34; such erroneous switching would produce noise on the reproduced monochrome picture. The PAL chrominance signal is supplied via band-pass amplifiers 12, 14 to a oneline delay circuit 17, an adder 15 and a subtractor 16. The output of adder 15 is supplied to a B-Y demodulator 21 and the output of subtractor 16 is supplied to an R-Y demodulator 26a via an inverter 24 and PAL-switch 23 operated, during reception of a colour signal, at the end of each line period. The output of band-pass amplifier 12 is fed to a burst gate 31 which supplies a colour killer circuit 39, a subcarrier oscillator 33 and a synchronous detector 32 which supplies a pulse signal to resonance circuit 34 the output of which is fed to a waveform shaping circuit 35 which controls the phase of a flip-flop 26 which also receives line synchronizing pulses at terminal 25 and controls PAL-switch 23. In one embodiment (Fig. 6, not shown) the line synchronizing pulses are supplied to the emitter of a transistor (44) included in shaping circuit 35, the base of the transistor receiving the output of the resonance circuit 34, so that this transistor is conductive, producing an output of circuit 35, only when a line synchronizing pulse coincides with the positive peak portion of the output of resonance circuit 34. In a second embodiment (Fig. 7, not shown) the colour killer signal from circuit 39 is also supplied to resonance circuit 34 to disable its operation during monochrome reception.