GB602053A - Improvements relating to colour television reception - Google Patents

Abstract

602,053. Colour television ; cathode-ray tubes. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 13, 1945, No. 26814. Convention date, Oct. 13, 1944. [Class 40 (iii)] [Also in Group XL (a)] In a colour television receiving system in which the image is produced on a target composed of a repeating series of strips which produce light of different colours under electron bombardment, light-sensitive means are provided which generate a control signal when the scanning beam scans a strip and produces a colour other than that intended, said control signals operating means to return the beam to the strip intended to be scanned. A cathoderay tube 15 (Fig. 1) having a target 11 formed as a repeating series of strips of luminescent material, such as the strips 21, 22, 23 (Fig. 2) adapted to produce, upon activation by an electron beam, light of three component colours, e.g. red, green and blue, is provided with three windows in the form of lenses 47 spaced equidistantly about the tube periphery and serving to direct light from the target 11 to three photo cells 49, 51, 53 which are arranged to respond respectively to the red, green and blue light, produced at the target, by means of suitable filter elements. The signals developed by the photo cells are fed to the control grids of valves 65, 67, 69, the operative periods of each being determined by the polarity of a voltage applied to the screens 71, 73, 75 from sources L, N, M. When operative, the outputs of the valves 65, 67, 69 feed pairs of amplifiers 77, 79 ; 85, 87 ; and 93, 95 ; each pair comprising an amplifier having, an odd and even number of stages respectively and connected to additionally control the vertical deflection source 43. The operative periods of these latter pairs of amplifiers are controlled by signals from sources H, G, K, which bear -a phase relationship to the signals L, N, M,. as shown in Fig. 4. The arrangement is such that when the scanning beam departs from the colour line intended to be scanned (e.g. due to supply voltage variations), one of the photo cells, depending on the colour line to which the beam strays, generates a signal which, after amplification in the appropriate amplifiers, supplies an additional controlling signal to the vertical deflection' source 43 to return the scanning beam to the desired colour line. The polarity of this controlling signal which determines the direction (up or down) in which the beam is to be returned, is determined by which one of the amplifiers is conditioned to operate, this being determined by the phase relationship of the voltages L, N, M, G, H, K. These latter voltages are derived from, and synchronously controlled by, the line synchronizing pulses A (Fig. 4) in the circuit of Fig. 3 (not shown). In a modification, Fig. 5, a combination of electro-mechanical optical means are employed to accomplish the objects obtained with the electronic arrangement of Fig. 2. In this arrangement the control signals supplied to the vertical deflection source 43 are generated by photo cells 249, 251, each of which is positioned to receive light from the screen 11 through rotating colour filters 261. The target screen 11 used in both embodiments of the invention may be formed as described in U.S.A. Specification 2,310,863.