GB706173A - Television pick-up devices - Google Patents

Abstract

706,173. Television pick-up tubes. CATHODEON, Ltd. April 24, 1951 [March 2, 1950], No. 5378/50. Class 39(1) [Also in Groups XXXVI and XL(b)] A television signal-generating device comprises a first photo con ductive layer 3 of selenium or cad mium sulphide upon which the image is projected to cause the conductivity to vary from point-to point over the surface, a seconc photo conductive layer 5 which is rendered conducting point-by-point by means of a source of radiatior scanning the surface, and a pair of transparent aluminium electrodes 2, 4 connected to a circuit 12, 13 so that the process of scanning sets up a current in the circuit modulated in accordance with the point-by-point variation in the light intensity of the image. In the embodiment shown, the scanning is effected by means of an electron beam which impinges on a fluorescent screen 15 to produce a light spot which renders the photo conductive layer 5 conducting. An opaque layer 4 having high conductivity at right angles to the major surfaces but low conductivity parallel to the major surfaces, and made for example of soda-lime glass incorporating a suitable pigment, separates the two photo-conductive layers to prevent interference between the light of the image and scanning spot. By arranging the photo conductive layers to have different spectral response curves, the layer 4 may be omitted. In a further embodiment, Fig. 5 (not shown), the photo conductive layer 5 is replaced by a layer of material such as silica or magnesium fluoride which is rendered conducting by electron bombardment. The opaque layer is not necessary in this modification and may be omitted or replaced by a mosaic of mutually insulated conducting particles, e.g. silver globules.