US 3790849 A
A capacitive memory gas discharge display device having a pair of drive lines for each cell of the device located directly within the gaseous environment. The conductors are at least partially covered with a dielectric serving as a means of providing a uniform spacing between the wires, a means to keep the wires from shorting and a means for developing a capacitive charge from the firing of the cell, such charge providing a memory for the particular cell such that the voltage required for refiring the cell is less, by the amount of the charged voltage, than the voltage required for the initial firing.
Description (OCR text may contain errors)
United States Patent Mayer et a1.
CAPACITIVE MEMORY GAS DISCHARGE DISPLAY DEVICE HAVING INTERNAL CONDUCTORS Inventors: William N. Mayer, White Bear Lake; Richard A. Strorn, Minneapolis; Meredith S. Ulstad, Edina, all of Minn.
Control Data Corporation, Minneapolis, Minn.
Filed: Apr. 24, 1972 Appl. No.: 247,073
US. Cl. 315/169 TV, 313/188, 313/217 Int. Cl. H051: 37/00 Field of Search.. 315/169 R, 169 TV; 313/188,
References Cited UNITED STATES PATENTS Toombs 313/210 X Baker et a1. 315/169 TV X 3,617,796 1 [/1971 Caras 313/220 3,585,443 6/1971 Krembs 315/169 R 3,136,912 6/1964 Evans et a]. 315/169 TV UX 3,634,719 1/1972 Ernsthausen 315/169 TV X Primary Examiner-Herman Karl Saalbach Assistant Examiner.1ames B. Mullins Attorney, Agent, or Firm-William .l. McGinnis, Jr.
[ ABSTRACT A capacitive memory gas discharge display device having a pair of drive lines for each cell of the device located directly within the gaseous environment. The conductors are at least partially covered with a dielectric serving as a means of providing a unifonn spacing between the wires, a means to keep the wires from shorting and a means for developing a capacitive charge from the firing of the cell, such charge providing a memory for the particular cell such that the voltage required for retiring the cell is less, by the amount of the charged voltage, than the voltage required for the initial firing.
2 Claims, 10 Drawing Figures PATENTEU FEB 5 I974 SHEET 1 BF 3 SUSTAIN WRITE CLAMP Y AXIS DRIVE CIRCUITRY w I l I I ll in I A mm A R586 X NS 3 F l I I l I l I I l I l I I l l l I l I l I I I I l l I I IIL PAIENTED 3. 790.849
SHEET 2 0F 3 YIHEA v Q I Vmln -dl -dmin d2 Pd (Torrcm) PASCHEN CURVE PMENTEUFEB sum SIIEEIJUFZB 1 cAPActTi'vt; MEMORY cAs DISCHARGE DISPLAY DEVICE HAVING INTERNAL CONDUCTORS BACKGROUND OF THE INVENTION This invention relates to a capacitive memory gas discharge display device having internal dielectric coated conductors.
In recent years a technology has developed in display apparatus to provide an inexpensive replacement for the cathode ray tube in solhe of its application. One very promising technology is that involving a flat panel gaseous discharge dis lay which has the advantage of being cheaper, lighter in weight, less bulky, requiring less power, and being directly responsive to digital signals There are two distinct types of panels. A first type of panel depends on a di'rect current flow between conductors and is similar in operation to the neon bulb panel indicator or power indicator lights that have been used for some time. Sometimes low frequency alternating current is used in such devices to even out the sputter or emission type of wear that occurs with the electrodes in such devices. The panel still depends, however, on an ionized current path between conductors which are separated from one another. Recently some panels of this type have been devised using conductors coated with porous insulation to prevent the conductors from contacting one another. This first type of panel does not exhibit inherent or capacitive memory phenomena as does the second type of panel.
A second type of panel, the type under consideration in this application, depends on a capacitive memory effect, sometimes called inherent memory, to fire the cells in the device and maintain the display. The first type of panel must have the display message as a continuous input whereas the second type of panel only requires signals for new elements of the display and a sustain signal to use the memory. The successful operation of such a device depends on the conductors being direct current insulated from one another so that no direct-current ionized conductive discharge path forms. This type of panel has been found to be more reliable, less critical as to voltages, and more easily controlled than the conductive path or direct current device. Heretofore, such capacitive discharge panels have had the conducting elements on the outside of the panel, with the gas medium inside, so that the panel itself would provide the required dielectric element. This invention therefore relates to the provision of an improved capacitive discharge panel having an internal dielectric element cooperating with internal conductors.
In the prior art capacitive type gaseous discharge dis play panels, it has been found that precision manufac turing of the parts is essential to proper performance of the panel as is a reasonably high degree of accuracy of the mixture of the gas supplied, the pressure at which the gas is maintained, and the operational voltages. U. S. Pat. No. 3,559,190 granted on Jan. 26, l97l to D. L. Bitzer et al, illustrates some of the earlier work in the capacitive memory gas discharge display art. Separate and discrete cells are shown in that patent and drive lines outside the gaseous atmosphere are shown. The drive lines are capacitively coupled through a dielectric, such as glass, to the individual cells.
U. S. Pat. No. 3,499,167 granted on Mar. 3, 1970 to Baker et al is also of interest in that it teaches the confining of a discharge at the intersection of a pair of drive lines, the confinement being quite dependent upon the pressure of the gas. The drive lines are on opposite sides of a pair of dielectric surfaces between which the gas is confined and through which capacitive coupling of the drive lines to the cell is achieved.
In these and all other known prior art gas discharge displays and/or memories, the amount of capacitance between the cell and the drive lines is critical and is governed by the dimension of the dielectric material. Also critical is the dimension between the surfaces of the dielectric materials which define the thickness of the cell. Another critical parameter is the amount of gas pressure, especially in those panels that depend on containing the individual discharge by gas pressure. The operational voltages must also be held within relatively close limits so that the ignition of a cell as well as its being sustained and selectively extinguished can be accomplished. Thus, a change in environmental pressure or temperature has a great deal of significance in the prior art. Such changes may well produce a warping of the prior art panel or other changing of dimension that causes a malfunction. The present invention is not particularly susceptable to such environmental changes.
SUMMARY OF THE INVENTION A capacitive memory discharge device is provided with conductors placed directly in the gaseous atmosphere which are at least partially coated with dielectric material so that no direct conductive path will form. The thickness of the dielectric material is established at a predetermined tolerance so that the individual cells of the display will have uniform characteristics.
One embodiment of the invention uses anodized conductors since the anodized metal surface is a suitable dielectric and the anodizing process may be controlled to produce a surface of the required uniformity. Aluminum wire, for example, provides a suitable conductor for this purpose which may be suitably anodized.
The anodizing process has one particularly desirable characteristic in that it insures that there are no holes in the dielectric which would allow an ionized gas conductive path to form between conductors. Such a con-v ductive path would make a cell inoperative in the desired capacitive memory mode of operation.
As a result of the initial firing of any selected cell, charges are impressed on the dielectric covering the conductor thus providing a memory for that cell. In the prior art, these charges were impressed on the dielectric plates between which the gas is confined, the dimension between the plates (d) being quite critical. In the prior art, d was not only critical, but also difficult to consistently maintain or uniformly produce in large displays because maintaining equal spacing between two panels is quite difficult when the panels must also be thin enough to capacitively couple the exterior drive lines to the cells. In the present invention, the dimension between the panels confining the gas is not at all critical, thus removing a substantial obstacle to the manufacture of a reliable display panel assembly.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a typical configuration for the gas discharge display and/or memory.
FIG. 2 is an exploded perspective view of a section of a typical panel assembly of this invention.
FIG. 3 is a cross-section of a gas discharge display panel of prior art.
FIG. 3A is a cross-section of one cell of an embodiment of the present invention.
FIG. 4 is a Paschen curve, showing the firing voltage at various points for the pressure and distance product.
FIG. 5 is a perspective of a pair of conductors forming one cell of another configuration of the present invention.
FIG. 6 is a perspective view of a pair of conductors within the gas discharge display panel representing still another embodiment.
FIG. 7 is a cross-section of an embodiment of this invention illustrating grooved construction of the enclosing panels.
FIG. 8 is a perspective view of a pair of conductors partially coated with dielectric material, forming another configuration of this invention.
FIG. 9 is a perspective view of a three-dimensional embodiment of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS In FIG. I, a gaseous discharge display panel 10 is shown with 64 individual cells 102 arranged in an 8 X 8 array. A set of eight Y-drive lines enter the display from the Y-axis drive circuitry 126. A set of eight X- drive lines 13 enter the display from the X-axis drive circuitry and intersect with the Y-drive lines 15 to form cells 102. The X-axis drive circuitry 108 comprises a normal and special sustain block 110, two write and erase blocks 112 and 114, and 4 clamp blocks 116, I18, 120 and 122. Write and erase block 112 applies voltage to a group of drive lines formed by the top four X drive lines 13, and write and erase block 114 applies voltage to a group of drive lines formed by the lower four-X-drive lines 13. Clamp 116 is connected to the first line of the top group and the first line of the bottom group, clamp 118 is connected to the second line of the top group and the second line of the bottom group, clamp 120 is connected to the third line of the top group and the third line of the bottom group, and clamp 122 is connected to the fourth line of the top group and the fourth line of the bottom group.
This matrix interconnection of the write and erase blocks and the clamp blocks shown in FIG. 1 allows individual line selection while eliminating the need for a write and erase block for each line. An individual line is selected by energizing either block 112 or block 114 and also energizing one individual clamp block. For ex ample, in order to apply a write signal to the top X-line 13, write block 112 and clamp 116 are energized. Selecting clamp 116 has the effect of disabling it and allowing the write current of block 112 to flow through the top X-line 13 to display 10. The remaining three lines in the top group are clamped to ground by clamps 118, 120 and 122. The top line of the second group energized by write block 114 is also free to conduct current to display 10 because clamp 116 is disabled, however, write block 114 has not been energized, so no current is applied. Each of the drive lines may be individually selected by the proper selection of one write and erase block and one clamp block.
After the desired lines have been written, voltage from sustain block of FIG. 1 is applied to all X- lines 13 through 8 individual capacitors 124 to sustain the display. When it is desired to erase the display, the line selection used is identical to that used in the write procedure.
The configuration of the Y-axis drive circuitry 126 is identical to that of the X-axis drive circuitry 108. A particular cell 102 then receives one-half of the voltage applied to it from the X-axis drive circuit 108 and onehalf from the Y-axis drive circuits 126.
The detailed circuitry of the various blocks of FIG. 1 are shown in detail in the U. S. Pat. No. 3,573,542, granted Apr. 6, 1971, to Mayer et al. The instant invention, is, of course, not limited to the particular method of cell selection shown in FIG. 1, nor to the particular circuitry of U. S. Pat. No. 3,573,542, this being one illustrative way of driving the display.
FIG. 2 illustrates an exploded perspective view of the panel assembly 10. Sandwiched between panel side 11 and panel side 12 are X-drive lines 13 and Y-drive lines 15, the intersecting region defining individual cells'102. X-drive lines 13 are formed with a dielectric coating 14 which also serves as a direct current insulation and Y drive lines 15 are similarly formed with a dielectric coating 16 which also serves to insulate the conductors from one another so that no direct current ionized conductive path forms therebetween. Side panels 11 and I2 are sealed together by any one of a number of wellknown sealing means, with the drive lines sandwiched between. The volume between side panels 11 and 12 is evacuated and an appropriate ionizable'gas such as a neon gas mixture is introduced. For each individual cell voltage is applied to an X-drive line and to a Y-drive line 15 providing a total voltage at a selected cell. The voltages must total to the firing voltage required as shown in the Paschen curve 20 of FIG. 4.
Referring now to FIG. 3, a prior art display panel 30 is shown. X-drive lines 13 are shown attached to dielectric 14a and Y-drive lines 15 are shown attached to dielectric 160. The ionizable gas 17 occupies the area between dielectric 14a and dielectric 16a. The distance between dielectric 14a and dielectric 16a is shown as d min which represents the shortest or minimum distance of discharge when the firing voltage has been reached. FIG. 3A illustrates the present invention with an X-drive line 13 touching a Y-drive line 15 to form a cell 102. Ionizable gas 17 fills the space between side panel 11 and side panel 12. The shortest physical distance between X-drive line 13 and Y-drive line 15 is shown as d l" a possible maximum discharge path is shown as d 2" with d min shown as greater than d l" but less than d 2. The distance d min" is dependent upon the constraints of the Paschen curve of FIG. 4.
Referring now to the Paschen curve of FIG. 4, it is obvious that the firing voltage is dependent upon the pressure of the gas 17 and on the distance d of ionization. The prior art example of FIG. 3 in association with the Paschen curve of FIG. 4 illustrates the strict requirement for maintaining d min" uniform for each of the spaced intersections of conductor X-drive line 13 and Y-drive lines 15. Since the pressure of the gas 17 is constant between dielectric of 14a and 16a, d min must be maintained constant in order to have identical firing voltages for each of the intersections. Thus, not only must the dimension between dielectric 14a and di electric 16a be carefully maintained, but also the dimensions of the dielectric 14a and 16a themselves must be kept very uniform in the prior art.
In FIG. 3A, the pressure of gas 17 is constant but the conductor spacing need not be rigidly controlled in the sense of having to maintain an absolute physical spacing. If the X-drive line 13 together with dielectric 14 is, for example, moved further away from Y-drive line and its dielectric 16, then d min" will be different than illustrated in FIG. 3A and will simply be a dimension which is one of an infinite number between the minimum d 1" and a maximum dimension shown here as d 2." Therefore, the dimension between the side panels 11 and 12 is not critical nor is the thickness of side panels 11 and 12 critical. The most critical dimensions are the wall thickness of dielectric l4 and dielectric 16. As mentioned earlier, these dimensions are subject to control.
Preferably the dielectric coatings of conductors 13 and 15 will be in contact for the sake of increased uniforrnity of individual cells but this is not a limitation of the invention to this requirement as the dielectric surfaces associated with the conductors may be spaced apart. If the thickness of the dielectric coatings is maintained with a reasonable degree of uniformity, then the cells will be reasonably uniform when the dielectric surfaces are touching. However, if the surfaces are separated, then an additional standard must be applied to the separating distance to maintain cell uniformity.
Referring again to FIG. 4 the Paschen curve illustrates a firing voltage curve 21 (V) which is dependent on the-product of the pressure of gas 17 (P) and the discharge distance (d). Point 23 on the curve illustrates the firing voltage required at d I", point 24 illustrates the firing voltage at d 2" and point 22 illustrates the firing voltage at d min, all at the same pressure with only the distance term in the product (Pd) being varied.
FIG. 5 illustrates another embodiment of this invention with a cell 102 with X-line 13b of rectangular cross section having dielectric 14b and Y-drive line 15b of rectangular cross section having dielectric 16b.
FIG. 6 illustrates yet another embodiment of this invention with cell 102 having an X-drive line 13b of rectangular cross section and a generally circular Y- drive line 15.
FIG. 7 illustrates a variation in configuration of the side panels which enclose X-drive lines 13 and Y-drive lines 15. Side panel 12a is shown with channels 18 to receive X-drive lines 13. Side panel 11a is shown with channels 19 to receive Y-drive lines 15.
FIG. 8 illustrates still another configuration of this invention. Dielectric 14c on X-drive line 13 is shown partially surrounding X-drive line 13. Similarly, dielectric 160 is shown partially surrounding Y-drive line 15. The open section of X-drive line 13 and the open section of Y-drive line 15 face outwardly from each other so that dielectric 14c and dielectric 15c touch (or almost touch) at intersection 102. The dielectric also insulates the conductors from one another but need not entirely encompass each conductor. Insulation is needed only to insure that the breakdown voltage for any possible direct conduction path is greater than the voltage used for capacitive memory operation.
FIG. 9 illustrates an embodiment of the present invention in which a plurality of independent display grids each having X and Y drive lines are layered or sandwiched together in a single display panel 50. Panel sides 11 and 12 are provided in similar fashion to that shown in FIGS. 2 and 3A. Three display grids 52, 54, and 56 are shown in FIG. 9. Each grid is composed of X and Y drive lines and each grid may be driven independently from one another.
The panel is built up in layers with each grid supported in an appropriate sealing compound between supporting surfaces. Bottom grid 52 is sandwiched in sealent 58 between panel side 12 and member 60 which is rigid and open in the central panel sight area. Central grid 54 is supported in sealant 62 between member 60 and a similar member 64. Top grid 56 is sandwiched in sealant 66 betweenmember 64 and panel side 11. Members 60 and 64 may be complete transparent sheets if it is desired to maintain different gaseous atmospheres for the different grids.
As shown in the figure, the external leads for the X and Y drive lines for grid 54 extend towards the top of the figure and the external leads for the X and Y drive lines for grids 52 and 56 extend toward the bottom of the figure.
Of course, a three dimensional panel may be constructed of only two independent grids or more than the three grids shown in FIG. 9. The grids may be driven by sources at varying frequency to control the intensity or brightness of the discharge. It would be possible in a two grid panel, for example, to use the top grid for display purposes and the lower grid at a reduced frequency to serve as a pilot source for the top grid. Such a pilot grid would insure uniformity of the display grid by providing a source of photons to insure ignition of the display grid cells when desired.
Also, different colors may be produced by the different grids either by use of a different gaseous environment or association with various colored phosphors which glow in response to cell discharge. The depth effect may be altered by changing grid spacing depending upon whether the effect is desired for a certain application or is to be minimized.
The above description is not intended to limit this invention to the visible glow resulting from discharge. For example, the side panels 11 and 12 as shown in FIG. 2 could have multi-colored phosphorus applied in spots. A discharge in a particular cell 102 would then cause the particular phosphor adjacent that cell to glow.
The discharge does not have to be visible light but could be detected by means of photosensitive devices.
Furthermore, the panel sides 11 and 12 could be opaque and the fact that a cell has fired could be detected by suitable electrical means.
As a further illustration of the form of the invention disclosed in FIG. 3A without limiting the scope of the invention an example is now given. The wires forming the X and Y drive lines may be woven, much as oridinary window screen is woven, or trained and stretched on a jig having appropriately spaced pins about which the wire may be looped. In the latter case the X and Y drive lines are prepared identically but separately and sealed in the panel in the required perpendicular orientation, one set of drive lines over the other. The plates 11 and 12 may be separated from the drive lines or in contact therewith.
Aluminum wire in a size range from .005 in. diameter to .020 in. diameter is suitable for a cell density of up to about 50 cells per inch. Dielectric thickness can range from about .00025 in. to about .003 in. with .001 in. appearing to be optimum with anodized aluminum. Gas pressures have a useful range from about 300 torr to about 1,000 torr, with atmospheric pressure appearing to be near optimum and which also provides a low stress factor for the glass or other enclosing material. The gas mixture is primarily neon with a certain small fraction of additives known in the art such as argon or nitrogen. If the wires are to be spaced from one another, at their intersections, it would appear that the spacing should be no greater than .01 in.
MODE OF OPERATION A relatively high frequency voltage, having a peak value equal t one-half of the required firing voltage is applied to one of the X-drive lines 13 of FIG. 1 and a similar voltage of one-half the firing voltage is applied to one of the Y-drive lines 15 of FIG. 1 to ignite a selected cell 102. The alternating current supply is of a frequency suitable to exploit the dielectric properties of the conductor coatings in developing a capacitive discharge effect. Very generally, this implies frequencies in excess of kilohertz. The selection is done through the selection circuitry of FIG. 1. The one-half firing voltages add together at the selected cell 102 causing ionization and ignition. This ignition results in oppositely charged particles being attracted to the outer surface of dielectric insulation 14 and the outer surface of dielectric insulation 16. The voltage resulting from this charge condition is in such a direction as to oppose the applied firing voltage.
This charge is built up rapidly and helps to rapidly extinguish the ignition. The charges thus placed on the respective dielectric insulations l4 and 16 provide a "memory" so that another applied voltage, half on X- drive line 13 and half on Y-drive line 15 is substantially lower in magnitude than the original firing voltage. As explained in the aforementioned U. S. Pat. No. 3,573,542, this voltage is referred to as a sustain voltage. Therefore, by continually applying sustain voltages, a selected cell 102 will continue to glow and in the case of one or both of side panels 11 and 12 being transparent or translucent, can be observed.
To extinguish the selected cell 102, it is necessary to recuce the memory" charge so that another sustain pulse will not cause ignition. In this embodiment, a long risetime unidirectional voltage step is applied in a direction which will initiate the discharge of cell 102. The maturation of the cell discharge is highly dependent on the slope of the driving waveform and the applied step therefore, does not allow the discharge to fully mature. This procedure leaves the cell without a significant memory" charge so that the next sustain pulse is unable to cause ignition.
Each cell 102 is capable of being selectively ignited, sustained, and extinguished as described above. The flattened drive lines of FIG. 5 produce identical results as mentioned above. It is also true of the configuration shown in FIG. 6 and FIG. 8 respectively.
The apparatus of FIG. 7 operates in exactly the same way but the manufacture of the panels 110 and 12a to provide channels 18 and 19 respectively to contain the X-drive lines 13 and Y-drive lines 15 is unique. The glass is rolled in a pliable form in the usual manner, but the roller is provided with collars that form the channels as the glass is rolled out. It is cut to size and the drive lines are laid into the channels and finally the glass panels are scintered together forming a seal around the X-drive lines 13 and the Y-drive lines 15. After that has been accomplished, the volume between side panels 11a and including that of the channels is evacuated and ionizable gas is introduced.
Our invention is not limited to ionizable gas, but could be applied to an ionizable solid. Also, the dielectric on the drive lines need not be the result of anodization, but could be a deposited dielectric such as glass. It is intended that any appropriate dielectric coating on a conductor be considered as being disclosed herein. Such an appropriate dielectric is one which is free from holes or electrical leaks which would allow a direct current ionizable path to form and destroy the inherent or capacitive memory.
What is claimed is:
l. [n a capacitive memory type gas discharge display device, requiring insulation between electrical conductors and an ionizable gas atmosphere, of the type that is enclosed to retain the ionizable gas atmosphere, and which is provided with an external power means for generating and contracting a state of ignition, sustentation and extinguishment in individual display cells, the improvement comprising:
a. at least a pair of generally orthogonal electrical conductors within the device, one of said conductors being generally circular in cross section and the other of which being generally rectangular in cross section,
b. a solid dielectric means located within the device and affixed to the conductors therewithin and in which the dielectric means associated with the respective conductors forming individual display cells is in contact in the vicinity of the display cell,
0. means for connecting the electrical conductors to the external power means.
2. In a capacitive memory type gas discharge display device, requiring insulation between electrical conductors and an ionizable gas atmosphere, comprising a plurality of gas discharge cells formed within a pair of side panels sealed to retain the ionizable gas atmosphere, at least one of the side panels being capable of transmitting visible light, associated with external power means to ignite selected cells to sustain the ignition of the selected cells and to extinguish the selected cells, the improvement comprising:
a. solid dielectric means, consisting of an anodized surface, positioned within the ionizable gas atmosphere between the side panels;
b. a set of aluminum X-drive lines having the surface thereof anodized to constitute said solid dielectric means, being generally circular in cross section, positioned within the ionizable gas atmosphere;
0. a set of aluminum Y-drive lines having the surface thereof anodized to constitute said solid dielectric means, being generally rectangular in cross section, positioned within the ionizable gas atmosphere orthogonal to, and separated from the set of X-drive lines by the solid dielectric means, the dielectric means being in contact with the X and Y drive lines at discharge display points; and,
d. means for connecting the set of X-drive lines and the set of Y-drive lines to the power means.
l t It I!