Patent GB-823219-A (GB)
Title: Improvements in or relating to position-selecting, scanning and like systems
Inventor: ARCHER JOHN
IPC: H01J31/12
Filed: 1954-12-23
Abstract: 823,219. Cathode-ray tubes. PHILIPS ELECTRICAL INDUSTRIES Ltd. Dec. 6, 1955 [Dec. 23, 1954], No. 34965/55. Divided out of 823,201. Class 39(1). [Also in Group XL(b)] A luminous display of use more particularly for television comprises an electric discharge tube incorporating a single luminescent screen together with a plurality of electron beam sources disposed in rows and columns and each arranged to scan only a local section of the screen, interconnections being provided to permit the sources to be selected and scanned in a sequence such as to produce systematic scanning of the whole screen. Fig. 5 illustrates the general arrangement, but shows only two electron sources. A particular construction designed for 405 line television standards may comprise 720 such sources arranged in 36 vertical columns and 20 horizontal rows. A transparent plate 1 carries the luminescent screen 2 and the electron beams are derived from a common filamentary cathode structure in the form of an assembly of parallel-connected filament wires, one for each column. Each source includes an electron gun comprising a grid 6 and first, second and third anodes 10, 5 and 4, and is associated with vertical and horizontal electrostatic scanning plates 7 and 8. The grids in each row are commoned by conductive connection and may comprise simply a strip with a row of suitably spaced apertures. Similarly, the first and second anodes are connected together in columns. The third anodes are all conductively connected and may comprise a single plate pierced with holes. The horizontal deflection plates are connected together in rows and comprise strips extending for the full vertical dimension of the display. Likewise, the vertical deflection plates comprise strips extending for the full horizontal dimension. Fig. 6, shows the arrangement of deflection plates for a small section 4 x 4 of the display, the dotted rectangles indicating the area scanned by each electron beam. In operation, the grids and first anodes are normally maintained at potentials chosen to suppress the electron beams. Any one beam may then be released by raising the potential of the row of grids and column of first anodes which intersect at the position of the selected beam. To effect scanning in accordance with normal television practice, the potentials are controlled so as to release the beams one by one along a row whilst successively advancing the rows. Synchronously with this, the horizontal and vertical deflection plates are controlled by sweep signals in such manner that left-toright line-by-line scanning down the display area proceeds, the horizontal scanning due to any one electron beam commencing at the lefthand edge of its allotted section as the immediately preceding one terminates at the righthand edge of its section. In one way of doing this, as shown in Fig. 6, successive columns and rows are controlled by 90 degree phase-advanced sine-waves, the arrangement relying on the substantial linearity of the sine waves between 45 degrees. The phasing of operations is such that each beam is released only during the 45 degree period of its controlling sine wave cycle, so that the scanning produced by the remainder of the cycle is ineffective, but to allow for lack of precision in timing, each beam is restricted to its allotted region by means of a mask 9 which obscures overswept portions of the beam. An alternative obscuring arrangement may comprise thin conductive partitions normal to and near or at the luminescent screen. Reference is made to the use of triangular and sawtooth deflection voltages. The potentials for controlling the grids and first anodes to release the beams may be derived from distributers, and the specification describes a number of arrangements based on delay lines and discharge tube circuits. In order to reduce the number of connections which must be brought out of the tube, an arrangement is described, Fig. 8 (not shown), in which both the first and second anodes are employed. This reduces the connection required for the horizontal control from 36 to 12 but involves interconnections of the anodes within the tube. Modulation of the cathode-ray beams by a picture signal is effected by applying the signal to the cathode. Preferably the filaments have numerous parallel connections to reduce heating potential differences along the filaments and prevent modulation by the heating voltage. The production of a pattern on the luminous screen corresponding to the boundaries of individual sections of the screen may be prevented by the use of negative feedback between the screen and modulation circuit, a transparent conductive layer over the screen or means responsive to secondary emission from the screen being provided to generate a signal from current reaching the screen. The invention may be adapted for colour television by constructing the luminous screen of a pattern of vertical bars of coloured phosphor.