GB955831A - Improvements in or relating to image converter tubes - Google Patents

Abstract

955,831. Cathode-ray tubes. PHILIPS ELECTRICAL INDUSTRIES Ltd. Sept. 14, 1960 [Sept. 17, 1950], No. 31672/60. Heading H1D. In an image converter tube comprising an electron gun, a target, and an electron-collecting anode therebetween, the target comprises a first grid electrode 25 on the gun side thereof, a plurality of combinations each arranged over an aperture in grid 25 and together forming a continuous layer, and a second electrode 26 arranged on the far side of the target. Each combination comprises a photo-conductive, or bombardment-induced-conductive, part, whose conductivity is controlled by the image to be converted, and a resistive part whose conductivity is not so controlled, the two parts of each combination forming an electrical series-connected circuit between the first and second electrodes. In operation, one of the electrodes 25, 26 is maintained at a low positive potential, relative to the gun cathode, and the other at a negative potential, and a potential image is formed on the gun side of the target in the apertures of grid 25 by electromagnetic radiation, or by particle bombardment from a photocathode, or a modulated electron beam, and scanned, signals being derived either from beam electrons collected by first electrode 25 or from electrons returned to the anode. As shown in Fig. 2, the target comprises a conductive glass foil 20, of 10<SP>9</SP> to 10<SP>12</SP> ohm cm. resistivity, supporting, but insulated from, the first grid electrode 25, and photo-conductive elements 23 contacting, and in the apertures of, the grid 25, the second electrode 26 comprising a transparent conductive coating. Alternatively, the target may comprise a conductive glass foil and a continuous photo-conductive layer between two electrodes each comprising spaced parallel conductors, the conductors of one electrode lying between those of the other. In Fig. 4, two grid electrodes 45, 46 are disposed on opposite sides of a photo-conductive layer 42, parts of which are shielded from incident radiation by opaque insulating strips 47, so that the conductivity of these parts is not controlled by the image to be converted, whereas the remaining parts are irradiated through transparent electrode 46. Owing to the high capacity between the first and second target electrodes, it is preferred to derive output signals from the anode, and for these signals to have a low signal-to-noise ratio, either the photo-conductive material should be adjacent the second electrode, or a third electrode 50, Fig. 5, is supported on, but insulated from, electrode 15, electrodes 50, 16 being at a low positive potential and electrode 15 at a negative potential. Lead monoxide, cadmium sulphide or antimony trisulphide may be used as photoconductive materials, and zinc sulphide, magnesium oxide or silicon carbide as B.I.C. materials. On the gun side the target combinations may be coated with a protective magnesium oxide layer.