GB1225862A - - Google Patents

Abstract

1,225,862. Colour television. BRITISH RADIO CORP. Ltd. 3 July, 1969 [4 July, 1968], No. 32048/68. Heading H4F. Brightness-control circuit for a colour television receiver comprises a pulse generator coupled to the luminance channel which generates a recurring pulse of which the amplitude and sign are manually-variable, the pulse having a leading edge at the end of each line-blanking interval and a trailing edge at the beginning of the next succeeding line-blanking interval, whereby the level of the video portion of the luminance signal can be adjusted in dependence upon the amplitude and sign of the added pulse without an accompanying adjustment in the level of the front and back porches of the linesynchronizing pulses. Thus the front and back porches of the line-synchronizing pulses are always at black level despite adjustment of the brightness control. The recurring pulses are also added throughout the frame synchronizing intervals, the tips of the synchronizing pulses being first D.C. restored. The combined luminance signal and recurring pulse are applied to an amplifier or to three amplifiers for controlling the three guns of the receiver CRT, and the or each amplifier includes a loop circuit embodying a back-porch clamp. The chrominance signals may be combined with the luminance signals in the three amplifiers.