GB743156A - Improvements relating to colour television apparatus - Google Patents

Abstract

743,156. Colour television tubes. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Sept. 10, 1954 [Sept. 19, 1953], No. 25907/53. Addition to 714,154, [Group XL (b)]. Class 39 (1). [Also in Group XL (b)] The target electrode of a pick-up tube employed in a colour television system (see Group XL (b)) is constructed as shown in Fig. 1 of a dielectric sheet 1 on one face 2 of which is deposited the normal mosaic of photosensitive elements and on the other face 3 of which are deposited two mutually insulated transparent signal output electrodes 4 and 5 arranged in the form of intermeshing vertical strips 6 and 8 connected together by transverse end strips 7 and 9. The strips 6 and 8 extend at right angles to the direction of line scan. An image is projected on to the target through a filter comprised of a repeating series of red, green and blue strip filter elements arranged parallel to strips 6 and 8 and of such a width that one group of three filter elements corresponds to each strip 6 and 8 as indicated by dotted lines 10. Preferably the filter elements are in the form of thin metallic films deposited over strips 6 and 8 and producing the desired colour selection by interference effects. In addition to the image, the target is continuously illuminated through the filter by a white biasing light. The signal trains derived from the two output electrodes then take the form shown in Fig. 3, wherein the signal groups 27 and 29 representing red, green and blue components of the image occur alternately in the two outputs and are each followed by a pulse 28, 30 extending below the level set by the biasing light. The pulses 28 and 30 serve to control the gating of the colour components into separate channels. As an alternative to the use of a biasing light, sheet 1 may be made slightly conductive and a positive bias potential (relative to cathode potential in a low velocity tube) applied to the two output electrodes so that the mosaic elements normally charge to the bias level by leakage through the sheet.