GB1211936A - Improvements in or relating to colour television signal decoders - Google Patents

Abstract

1,211,936. Colour television. RANK ORGANISATION Ltd. 28 Feb., 1969 [1 March, 1968], No. 10159/68. Heading H4F. Demodulating apparatus for PAL colour television signals comprises gates 20, 30 which sample the incoming chrominance signals on line 10 at chrominance carrier frequency and at the phase of the B-Y and R-Y colour difference signals respectively. The sampled signals are fed via a one line period delay line 25 (or 35) and an integrator 28 (or 38) and added to the undelayed but integrated 27 (or 37) sampled signals to produce the colour difference signal B-Y (or ŒR-Y). Gates 20 and 30 are opened by pulses derived by pulse generators 23 and 33 in response to locally generated chrominance carrier frequency signals that are 90 degrees out of phase on lines 42 and 43, a phase inverter being switched in and out of line 43 at line rate. Delay line 25, and similarly delay line 35, comprises a plurality of reactive elements, e.g. capacitors 1-284,, equal to the number of chrominance carrier periods in a line, each associated with a transfer means T1 to T284 comprising active solid state devices for passing a charge to its associated reactive elements when enabled. The transfer means are energized over leads E1 to E284 one during each chrominance carrier period by trigger pulses from switch 50 controlled by pulse generator 51. Thus a charge placed on the element 1 will reach output 26 of the delay line after exactly 284 chrominance carrier periods, i.e. one scanning line period.