GB1337655A - Decoding system for a television receiver - Google Patents

Abstract

1337655 Colour television SONY CORP 22 June 1971 [17 Oct 1970 17 Nov 1970] 29312/71 Heading H4F A decoder for PAL colour television signals utilizes only every second line of chrominance information by use of a one line delay line 2 and switch 4 operated at the end of each line period. As a result all the signals fed to the demodulators 7 and 8 have the same modulation axes, demodulator 8 being fed with a sub-carrier frequency reference signal of B-Y phase, and demodulator 7 being fed with a reference signal coinciding in phase with the burst signals from switch 6 gated out by gate 10. The resulting demodulated signals are matrixed at 18 with the luminance component applied at 19 to produce red, green and blue component signals. The B-Y reference signal is produced by averaging the burst phases in the incoming signal to give a signal of -(B-Y) phase which is inverted at 17. In an alternative embodiment the delay 2 is provided after the switch 4, the switch passing every second line and burst gate 10 and each demodulator being connected to the switch output directly and via the delay line. Alternatively, switch 4 may be replaced by a diode witch (22, Fig. 7, not shown) which has two outputs one producing chrominance signals with positive B-Y and R-Y modulation axes and the other signals having positive B-Y and negative R-Y modulation axes. Burst gate 10 and demodulator 7 are then fed from one of these outputs and demodulator 8 from the other output. In a further embodiment the chrominance signals are demodulated along the R-Y and B-Y axes by adding the outputs from continuous wave generators 11 and 15 in the correct proportions to give a signal along the R-Y axis, which is then used to control the oscillator 12. Delay line 2 may have a delay of an odd multiple of one line period.