GB443896A - Improvements in or relating to television - Google Patents

Abstract

443,896. Television. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and JESTY, L. C., c/o General Electric Co., Ltd., Wembley, Middlesex. Oct. 6, 1934, Nos. 22870 /34 and 7031/35. [Classes 40 (iii) and 40 (v)] The usual deflection of a cathode-ray beam is corrected by an auxiliary deflection produced under the control of synchronizing signals. As applied to colour television, the screen of the cathode ray tube receiver is composed of strips 5, 6, 7, 5, 6, 7 ..., Fig. 1, of material which fluoresce with red, green, and blue light respectively and each of which is backed by an electrode 1, 2, 3, 1, 2, 3 ... connected in groups, as shown, to common leads 8, 9, 10. The synchronizing signals occurring between each line are used to give each lead 8, 9, 10 a positive potential in turn so that the cathode-ray beam is drawn to the correct strip in spite of any inaccuracies in the usual deflecting means. In a modification in which the screen is viewed from the other side to that on which it is scanned, the strips are arranged in the order 1, 1, 2, 3, 3, 2, 1 ... Fig. 2, and an electrode system 4, 5, is arranged behind the strips, as shown, and adapted to be energized over leads 6, 7. By giving the lead 6 a positive potential and the lead 7 a negative potential, the cathoderay beam is drawn to the strips 1; if the lead 7 is made positive and the lead 6 negative, the beam is drawn to the strips 3, 3 ; by making both leads negative, the beam is repelled to impinge on strips 2. The invention, may be applied to interlaced scanning and to a stereoscopic system of reproduction, in which one eye views one set of strips on the screen and the other eye views the interlacing strips. The electrostatic electrodes 1, 2, 3, Fig. 1, may be replaced by electromagnetic solenoids. A circuit for applying a positive potential to each of the leads 8, 9, 10, Fig. 1, in turn under the control of synchronizing impulses comprises three gas-filled valves 1 2, 3, Fig. 3, to the grids of which the picture signals and synchronizing impulses are applied from lead 11 over condensers C1, C2, C3. Each valve is adapted to become conducting in turn under the control of synchronizing impulses, thus energizing each of the terminals 8, 9, 10 in turn. When valve 1 is conducting, the grid bias on valve 3 is determined by the potential difference between the point 5 and the tapping 7 on the potentiometer 6 across the supply 4, 5. This is arranged to be such that valve 3 cannot be rendered conducting by a synchronizing impulse. The grid bias of valve 2 is similarly dependent on the potential difference between the points 5, 7, but is lowered by the current flowing in resistance R1 from which a tapping P1 is taken to the grid of valve 2. This bias is such that valve 2 will become conducting on the arrival of the synchronizing impulse, the bias of valve 3 then being lowered in preparation for the next synchronizing impulse and an impulse passing over condenser K12 to extinguish valve 1 whose bias will then be determined solely by the potential difference between the points 5, 7. The image signals flow in each of the resistances R1, R2, R3 in turn and tappings Q1, O1 Q2, 02, Q3, 03 are taken to common terminals 13, 14. Terminal 13 is connected to the Wehnelt cylinder so that tappings O1, 02, 03 determine the average intensity of the cathode-ray beam. Terminal 14 is connected to a variable mu valve in the cathode-ray modulating circuit, so that tappings Q1, Q2, Q3 determine the degree of modulation of the cathode-ray beam. The invention is also applicable to transmitters ; e.g. a cathode-ray tube provides a luminous scanning spot and a tri-colour filter having adjacent lines of different colour is placed between the object and the screen of the cathode-ray tube. Specification 425,267 is referred to.