Patent GB-1471911-A (GB)
Title: Visual display devices
IPC: H01J17/49
Filed: 1975-02-07
Abstract: 1471911 Gas discharge display panel FERRANTI Ltd 7 Feb 1975 [8 Feb 1974] 05956/74 Heading H1D In a D.C. cathode gas discharge display panel with an array of cells 15<SP>1</SP>, in individual apertures or with insulated inter-cell connections in one large aperture, with electrodes CI1 &c., IR1 &c., on two faceplates in contact with the gas and parallel to respective co-ordinate axes, economy in drive circuitry is gained by introducing one (Fig. 2, not shown) or two auxiliary electrodes (grids) 1GC1 &c., 1GR1 &c. into each cell, connected in a set parallel to one axis or in two sets parallel respectively to the two axes. One set of electrodes, 1C1 &c., communicates directly with the cells, the other 1R1 &c. via individual current limiting resistors. The cells are divided into blocks, typically 5 + 7 for alphanumeric display, shown separated by chained lines. Hose electrodes if any without grids running parallel (IR1, &c. Fig. 1, not shown) have separate drive circuits for every electrode: those with parallel grids, i.e. both rows and columns in Fig. 3, connect all the first electrodes of one type in each block. 1C1, 2C1, 3C1 or 1R1, 2R1, 3R1 in common, all the second electrodes in common, &c. to respective drive units 14<SP>1</SP>, 11<SP>1</SP>. The grids to all cells of each block are connected in common for each direction provided 1CG &c., 1RG &c.: the voltage between the main electrodes is maintained between "sustain" and "triggering" levels and the grid(s) in each cell is/are set to intermediate levels which inhibit triggering for all blocks except those to be accessed. Pulses are applied to the main electrodes of the first column of each block and to all the required rows, or vice versa, to trigger the cells required in the accessed block; successive columns are then pulsed in turn together with appropriate row pulses; the cells remain lit as the column is stepped on. To erase, opposite pulses are applied to the main electrodes. The device is made from five layers assembled face to face, edge sealed and gas filled (Fig. 5, not shown), the first layer being transparent and carrying transparent (SnO) electrodes, the second and fourth being opaque perforated blanks, the third being opaque and perforated and carrying the crossed grid electrodes coated on opposite faces, with the inner edges of annular regions entering the apertures, and the fifth carrying electrodes transverse to those of the first, offset to one side of the apertures to allow for film resistors in series. Alternatively, the third plate may be a blank, with the second and fourth carrying respective grid electrodes. The single grid arrangement can then be adopted by omitting one of the grid plates. The blocks may be separated by lines of inactive cells used to supply starting ions to the neighbouring active cells. The grids may alternatively be made of wire. The device may be operated on either polarity. With two grids per cell characters are written separately to all blocks, but with only one grid and individual row drive circuits, all rows can be written simultaneously as the column is stepped forward, the economy in drive circuits being then limited to the columns only.