GB994065A - Improvements in or relating to circuit arrangaments employing charge storage tubes - Google Patents

Abstract

994,065. Cathode-ray storage tubes. MULLARD Ltd. June 28, 1962 [Sept. 7, 1961], No. 32247/61. Heading H1D. In a cathode-ray tube storage arrangement, an electron beam is caused to effect a writing scan over a first path to produce a charge pattern on a target having an uninterrupted, secondary, emissive, storage surface on a conductive backing. A constant-current focused, electron beam is then caused to effect a non- destructive reading scan over a second path spaced from but adjacent to the first path and with an energy sufficient to produce a secondary emission ratio greater than one, so as to produce an output signal from the target backing or from a collector of secondary electrons emitted by the target. As shown, the target T, Fig. 6, is initially stabilized at -10V with switches Sa, Sb in position 1, and with a beam energy below the first cross-over potential, to erase any preceding charge pattern. Writing is then effected with switches Sa, Sb in position 2 and with a beam energy between the 1st and 2nd cross-over potentials, by scanning over a first raster W, Fig. 5A. Reading is then effected over a second raster R interlaced with the written raster, with switches Sa, Sb in position 3. Target elements in the path of the reading beam are charged positive by an amount dependent on the potentials of adjacent target elements and give rise to an output signal. It is found that a maximum of say 10V potential difference between adjacent target elements is possible. To obtain repeated readouts, a defocussed beam is scanned over the reading raster but with energy below the first cross-over potential, and with switches Sa, Sb in position 4, or the whole target is flooded with electrons, to stabilize the target elements in the path of the reading beam at 0V. In an alternative method of operation suitable for binary information, the stabilizing scan or flood between read-outs is omitted, and written patterns are erased and the target initially stabilized at 0V with switches Sa, Sb in position 4. After writing, and one or more initial reading scans, the target elements may be charged as shown in Fig. 7A, but due to redistribution of secondary electrons during the remainder of each read-out, and before the next, the most positive elements at +20V drift negatively to say + 19V and so give rise to an output signal for repeated read-outs. Instead of writing a charge pattern by secondary electron emission from a mica layer, the target T may be of B.I.C. material, e.g. ZnS or magnesium fluoride.