GB1417231A - Colour television display apparatus - Google Patents

Abstract

1417231 Colour television PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 21 Feb 1973 [24 Feb 1972] 8436/73 Heading H4F The beam current levels of a three-gun cathode-ray tube are corrected during three successive line periods at the beginning of each field. During these three line periods a signal fed from a pulse generator 35 to a level insertion circuit 59 (also Fig. 5, not shown) receiving the separated luminance signal causes the circuit 59 to pass to a distributer circuit 75 a reference level, the signal passed to distributer 75 during the other line periods of each field being the received luminance signal. Level insertion circuit 59 also provides a second output to cut off a chrominance amplifier 69 during the specified three line periods at the start of each field, the output of amplifier 69 being fed to matrix circuit 115 to derive red, green and blue colour difference signals which are fed to respective blanking circuits 95, 93, 91 (also Fig. 4, not shown) in which the modified luminance signal from distributer 75 is added to the colour difference signals, a different signal being passed to each of blanking circuits 95, 93, 91 from pulse generator 35 so as to suppress the luminance reference level in two of the three line periods during which it is present in the output of distributer 75, the outputs of blanking circuits 95, 93, 91 being red, green and blue signals respectively, each of which has a reference level (from the luminance signal) in a different one of the specified three line periods. These signals are supplied to respective beam current level correction circuits 133, 135, 137 (also Fig. 4, not shown) which receive blanking signals from pulse generator 35 and respective correction signals from storage devices 163, 165, 167, each of which is connected by a respective switch 177, 178, 179 to a measuring circuit 187 (also Fig. 3, not shown) during that line period during which the input to the respective beam current correction circuit 133, 135, 137 has the reference level, the storage devices 163, 165, 167 retaining the stored values for the following field period. Brightness control may be effected by adjusting a potentiometer (509, Fig. 5, not shown) in the level insertion circuit 59. White-point correction is carried out using adjustable resistors (429, Fig. 4, not shown) in the beam current level correction circuits 133, 135, 137. Pulse generator 35 includes a shift register (603, Fig. 6, not shown) and a plurality of gate circuits. The beam current level correction may alternatively be applied to an assembly of several individual cathode-ray tubes.