GB1448979A - Circuit arrangements for colour television receivers - Google Patents

Abstract

1448979 Colour television EMI Ltd 14 Dec 1973 [4 Jan 1973] 547/73 Heading H4F A received PAL colour television signal is split into its U and V components by a one-line delay line (not shown) an adder (not shown) to derive the U component, a 180 degree phaseshifter 1 and an adder 2 to derive the V component, the V component being passed to a demodulator 9 via a switch 3 operated at the end of each line period, a direct path 6 and a 180 degree phase shifter 5 to derive a constantphase V<SP>1</SP> component; a reference oscillator 11 connected to demodulator 9 is synchronized by bursts derived either from a burst gate (12<SP>1</SP>, Fig. 2, not shown) connected to receive the V<SP>1</SP> component fed to demodulator 9, or from a burst gate 12, the bursts being passed via a switch 13 ganged with switch 3, direct path 15 and 180 degrees phase shifter 16, oscillator 11 operating at the mean phase of the received bursts, which is the phase of the V<SP>1</SP> component fed to demodulator 9. The U component is demodulated by a second demodulator (18, Fig. 2, not shown), the reference signal for which is derived either from a second oscillator (21) synchronized by the U components of the bursts, or from oscillator 11 if the phase of switch 3 relative to the received signal is monitored to generate a control signal which operates a phase shifting device inserted between the oscillator 11 and the U-demodulator.