Patent GB-1407855-A (GB)
Title: Vacuum tube
IPC: H01J31/40
Filed: 1972-11-21
Abstract: 1407855 Cathode-ray storage tubes INTERNATIONAL BUSINESS MACHINES CORP 21 Nov 1972 [28 Dec 1971] 53671/72 Heading H1D [Also in Division H4] A method of operating a vacuum tube comprising an electron gun 110, a photoconduotor layer 116 on a conductor layer 118 and a charge storage grid 126, includes differentially charging the grid and scanning the photoconductor layer with an electron beam, whereby the beam falling on the photoconductor layer is modulated by the charge on the grid. Many operative modes, not all as claimed, of reading, writing and storage for photoconductor and grid, including thransferring information within the tube are detailed, the storage in the latter case being maintained by electron beam sweeping. In Fig. 2, scan generator 124 is conventional except for a variable scan rate for converting data from a first to a second data rate as required for telephone-computer information transfers for example or two separate scan generators may be used. Deflection may be magnetic or otherwise. Grid 126 may be a dielectric coated aperture conductor plate or a self-supporting dielectric with a conductor on the side away from the gun or a planar mesh with dielectric coating. Potassium or calcium fluoride and MgO dielectrics exhibit γ > 1 for particular electron energies (Fig. 3, not shown). High resistance and thick dielectrics produce long RC times. Fig. 4 (not shown) is apparatus for writing information on grid 126 from an external data source through either input (111) or modulation input (142) including variable bias (140) with bias modulator (141) of a non- inverting transistor amplifier, and light source (150) for illumination while writing. Fig. 5 (not shown) for converting p./c. information to grid information includes videoamplifier (123), and driving conversion logic (144) controlling bias through input (142). Fig. 6 (not shown) is a transmission grid vidicon intrusion alarm, current through conductor (118) varying on scene change. Fig. 7 (not shown) enables information transfer from grid (126) to storage p./c. (116), the operation utilizing transient illumination source (150). Steps described in detail include for example writing data from an electrical source on to the grid, and on to a storage p./c. from an external electrical source or an external optical source; reading informaton from the grid, from a TV p./c. (i.e. rapid evanescent conductivity), or storage p./c.; transfer from grid to p./c. and vice versa; addition of information on grid and p./c.; information erasure; and use as an intrusion alarm, an inverse of the scene being stored on grid (126), the monitor detecting any positive or negative current w.r.t. a preset level, the scene being illuminated to produce no black spots lower than a constant current; alternatively several circuits may be used to give an alarm whenever the differing current does not correspond with the constant level or the black area; also the average current and occurrence of currents in excess of the established level may be measured, so detecting any large black area. Also described are scan conversion modes using a grid storage vidicon, a flood gun being used in some instances.