GB1173847A - A Method of Operating a Direct Viewing Bistable Storage Tube - Google Patents

Abstract

1,173,847. Cathode-ray storage and display tubes. TEKTRONIX Inc. 14 Oct., 1968 [16 Oct., 1967], No. 48585/68. Heading H1D. In a direct-viewing bi-stable storage tube in which a non-stored " write-through " charge image is displayed during bi-stable storage of another charge image on the same storage dielectric and the two images, for example, displayed side-by-side, the non-stored image is displayed with high brightness by interrupting bombardment by the writing beam of the storage dielectric portions corresponding to the non-stored charge image during writing. This is to reduce the bombardment time per unit area in order to prevent the potential of the non- stored charge image from exceeding the critical minimum voltage necessary for bi-stable storage. At the same time a high average beam current necessary for high brightness is maintained. Further, with use of a high beam current small changes in the grid bias voltage due to power supply ripple are of less significance. The beam bombardment is interrupted either by pulsing the writing beam on and off or by a " dither " movement of the beam in a closed, e.g. circular, path. The two methods may also be combined. Movement of the beam in a circular path produces an annular trace which may be used as a pointer or moved to outline the form of a character. The annular trace may be of sufficiently small diameter that the centre of the trace is not visible to the eye. The storage dielectric is flooded with electrons during the formation of the non-stored " write-through " charge image but the flood electrons may be cut off during the formation of the stored charge image. In the circuit arrangement shown comprising a directview storage tube with a storage dielectric layer 14 of phosphor material, a single writing gun 18, 20, 22, pairs of deflection plates 24, 26 and a pair of flood guns 28, 30, the control grid 20 of the writing gun and the horizontal and vertical deflection plates 24, 26 may be connected via three-position switches 54, 50, 38 in " Store," " Pulsed W.T. (write-through) " and " Dither W.T." modes of operation. The phosphor layer 14 may be in the form of separate dots, allowing the conductive film 16 to serve as a collector of the secondary electrons or the phosphor layer may be sufficiently porous to enable the transmission of secondary electrons through it. The invention may also be applied to a direct-view storage tube of the mesh storage target type.