Improvements in mosaic targets for cathode-ray tubes particularly for television transmission

摘要

558,465. Cathode-ray tubes. WESTERN ELECTRIC CO., Inc. June 10, 1942, No. 7932. Convention date, May 1, 1941. [Classes 39 (i) and 40 (iii)] In a mosaic target for a television transmitting tube a conductive plate or mesh 40 carries a layer of photo-emissive material 60 which may be either continuous or discontinuous but remains solidly at the same potential as base 40. A number of particles of insulation 61, or a mesh of insulating material, are superimposed on, or embedded in, or between the particles of, the material 60. In operation, a picture is thrown on the layer 60 and the emitted photoelectrons are collected each by its nearest insulation 61 which is kept, by secondary emission, at a positive datum potential which ensures saturation of the photo-emission. When struck by a scanning beam, each particle of insulation, which has fallen below datum potential by an amount proportional to the picture element intensity, is restored to datum potential. The picture signal is supplied either by the induced pulse in conductor 40, or by the collected secondary current. The insulation 61 may comprise embedded glass beads, or woven glass fabric, or sputtered or sprayed quartz, alumina or magnesia particles. It may be treated with metallic oxide to increase its secondary-emission ratio. The mosaic yields a constant component of current proportional to the momentary total illumination and this information may be transmitted by the circuit of Fig. 5. The picture signals pass through the main amplifying chain 47, 48, 49 while the constant component is isolated and amplified by cathode follower valve 54, and is applied to vary the grid bias of the next valve 50 of the main chain. To this valve is also applied pulses from pulse generator 60. Consequently, during each flyback period a series of pulses is transmitted the amplitude of which is proportional to the total momentary intensity of the picture. Specifications 472,861, 472,862 and 517,756 are referred to.