US 3719940 A
A plasma display panel has horizontal and vertical orthogonal drive lines disposed on opposite sides of a gas filled envelope. To achieve higher resolution in the plasma display panel and prevent cell to cell interaction during operation in the sustain or addressing mode, the horizontal and vertical drive signals applied to adjacent cells are phase separated such that adjacent cells are energized at different time intervals to isolate cell to cell interaction and thus provide a honeycomb effect.
Description (OCR text may contain errors)
United States Patent [191 Lay et al.
[451 March 6, 1973  GAS DISPLAY PANEL DYNAMIC 3,432,724 3/1969 Frost ..3l5/l69 R HONEYCQMB 2,881,360 4/1959 Livingston ..315/l69 TV  Inventors: Frank M. Lay, Woodstock; Allen Primary Examiner john w. Caldwell W. McDowell, Kingston, both of NX Assistant Exammer--Marshall M. Curtis Attorney-Hanifin and .lancin and Joseph J. Conner-  Assignee: International Business Machines t n Corporation, Armonk, N.Y.
22 Filed: Dec. 31, 1970 [571 ABSTRACT ] Appl N05 103,238 A plasma displav panel has horizontal and vertical orthogonal drive lmes disposed on opposite sides of a gas filled envelope. To achieve higher resolution in the  U.S. Cl. ..340/324 R, 340/173 PL plasma display panel and prevent cell to cell interac  II."- Cl. tion i g Operation i the Sustain or addressing  held of Search""3l5/166' 169 169 mode, the horizontal and vertical drive signals applied 340/324 173 PL to adjacent cells are phase separated such that adjacent cells are energized at different time intervals to  References cued isolate cell to cell interaction and thus provide a UNITED STATES PATENTS honeycomb effect- 3,513,327 5/1970 Johnson ..340/324 R 7 Claims, 9 Drawing Figures 15 21 I l I E LINE 7 DRIVER 26, 2 LINE HORIZONTAL I6 SELECTION JDRIVFR cmcun 22 LINE I DRIVER s: :5 2 LINE omvra X WW SUSTAIN rZl IVIV'II 33 DRIVER 46 41 48 A9 2? WI s0 s1 7 J s.v+ 5 t. ERiSE Y1 W 144 S IN SUSWN LINE LINE LINE LINE um WRITE DRIVER iomvrn omvrnl DRIVER DRIVER 55 CONTROL cmcun f I I I 54 I'm DVSGZ 451 I 52 -53 3'):
VERTICAL 45 SELECTION CIRCUIT PATENTEUHAR ems 719,940
sum 1 OF 2 FIG. 1 v1 V2 v3 W F F a 19 L j 15, 25x. 5 M H1 LINE W DRIVER 26, 2 2 HORIZONTAL 1 "fi SELECTION 5? cmcun "3 LINE w DRIVER L 1 4-0 l -v $3 rfi LINE iEIIiII IZ. '.3HN DRIVERA M J X2 sH+ sH K SUSWN X SUSTAIN r27 K K 1L" if DRIVER DRIVER Y1 Y2 Y1 Y2 4 4 ERASE Y1 V V l 2 44 Y2.
SUSTAIN LINE LINE LINE LINE SUSTAIN I DRIVER DRIVER DRIVER DRIVER DRIVER 1 cmcun I Q L! av J51 e2 52 65 1 INVENTORS FRANK M. LAY
ALLEN w. w DOWELL ATTORNEY v PATENTEBHAR 61973 3'719'940 sum 2 or 2 l GAS DISPLAY PANEL DYNAMIC HONEYCOMB CROSS REFERENCE TO RELATED APPLICATIONS:
Application Ser. No. 886,100 for Improved Gas Cell Memory" filed by Frank M. Lay Dec. 18, 1969, now U.S. Pat. No. 3,666,981.
Application Ser. No. 885,086 for Improved Method and Apparatus For a Gas Display Panel filed by Tony N. Criscimagna et a1. Dec. 15,1969.
BACKGROUND OF THE INVENTION The present invention relates generally to a method of operating gaseous or plasma display panels and more particularly to a method of preventing firing or sustaining of unselected cells during adjacent cell addressing resulting from electrical or physical nonuniformities in the individual cells of a high resolution display.
Recent display developments include the so-called gaseous or plasma display panel, one example of which is shown in Electronics, Volume 41, Number 15, dated July 22, 1968, pages 39 et seq. This arrangement included a three-layer glass configuration in which the center layer included rows and columns of individual cells filled with ionizable gas, the outer glass layers having transparent conductors arrayed in orthogonal relationship in overlapping registry at each of the cells. A second arrangement consisted of open panel variation which eliminated the center layer of glass and its associated cells, the individual cells of this open panel configuration were selected by energizing selected orthogonal drive lines causing the gas in the cell or site between the selected conductors to ionize. However, to achieve reliable operation and compensate for nonuniformities in cells, the drive signals for the horizontal and vertical coordinate drive lines must be maintained uniform within a relatively high degree of precision. As the density of cells per unit area on the panel increases, the potential for erratic operation requires still greater precision of drive signals because of the presence of half select write or sustain signals on nonselected cells and the effect of cell firing on adjacent cells. The number of selected cells adjacent to unselected cells and their relative proximity represents a combination of variables including individual cell histories and character fonts. This makes the turn-on characteristic of any given cell unpredictably variable, since the plasma discharge activity in selected gas cells produces a cloud of charge particles which tends to spill over to adjacent cells tending to affect the state of the adjacent cells. One solution to this problem is to physically isolate cells as in the aforenoted three-layer panel honeycomb construction of the Electronics article so that plasma discharge activity in one cell does not spill over to adjacentcells. This poses many technical and economic problems since the honeycomb" con struction tends to limit the number of gas cells per unit area which can be provided on the display and the resolution of the display panel, i.e., the number of cells per unit area, consequently is diminished. Another solution to this problem is an electrostatic honeycomb which provides an isolation grid network which electrostatically shields each gas cell from all remaining gas cells defined by the coordinate intersections of the vertical and horizontal coordinate drive lines. This system operates by utilizing conductors connected to a ground plane interspersed between drive conductors. Such a solution is shown in the aforenoted U.S. Pat. No. 3,666,981. However, the art work required for a grid isolation network on a high density high resolution panel (60 to drive lines per inch) renders this type of construction complex and expensive.
SUMMARY OF THE INVENTION Accordingly, it is a primary feature of this invention to limit cell to cell interaction in a plasma display panel by utilizing a phase displacement of sustain signals applied to adjacent cells. When potentials of a given amplitude and polarity are applied to the opposite sides or walls of a gas cell and exceed the ignition potential of the gas, the cell walls become charged to opposite polarities and the cell is selectively ignited. When a plasma discharge takes place, a charge cloud of positive and negative particles forms in the cell area and the wall charge on opposite walls of the cell causes the negative electrons to migrate toward the position wall and the positive ions to migrate toward the negative wall. If adjacent cells have similar wall potentials, as occurs in conventional plasma displays in which all cells receive a sustain signal simultaneously, some of the charge particles may drift to adjacent cells thereby changing the characteristics of the adjacent cells, particularly in a high density or high resolution display.
The subject disclosure solves this problem by dividing the cells into two groups designated A and B groups in which adjacent cells in the horizontal and/or vertical direction are always in different groups. Where the subject invention is applied to both axes, two X drive signals for the horizontal drive and two Y drive signals for the vertical drive are employed, the two X and Y drive signals being phase displaced, but the X and Y conductors being separated by 90". Since the A cells are addressed or sustained at a different phase than the B cells, whenever cells of type A are addressed or sustained, cells of type B will act partially as an electrostatic honeycomb and vice-versa. By ensuring that adjacent cells are always energized by different drive signals and thus fired at different times, the wall potential and polarity of adjacent cells is always dissimilar such that cell to cell interaction is reduced to a nominal level and a high resolution display is possible. By applying the sustain signals in a two cycle sequence to the individual drive lines rather than to all drive lines simultaneously and controlling the polarity of the nonselected cells while addressing selected cells, both walls of all nonselected cells are maintained at the same relative potential and polarity such that only one of the charge particles resulting from discharge of a selected cell will be attracted by the wall charge of adjacent cells.
Accordingly, it is an object of the present invention to provide an improved method of operating a gas panel display which provides high resolution display characteristics combined with reliable read, write and sustain operations.
Another object of the present invention is to provide an improved method of plasma display panel operation which limits cell to cell interaction without a physical or electrostatic honeycomb.
A further feature of the present invention is to provide an improved plasma display panel operation by electrically isolating each gas cell from all adjacent gas cells to limit cell to cell interaction.
In one arrangement according to this invention, a gas display panel comprises a container filled with a gas having orthogonal drive conductors disposed on opposite sides of the container in which selected areas or cells of the panel are ignited by coincident selection of a pair of associated orthogonal conductors. A plurality of horizontal coordinate drive lines are disposed on one side of the gas panel and a plurality of vertical coordinate drive lines are disposed on the opposite side of the panel. The crossover regions of the horizontal and vertical coordinate drive lines define coordinate intersections, and the area between the coordinate lines at such intersections constitute gas cells which may be ignited by electrical firing potentials supplied to the associated vertical and horizontal coordinate drive lines. The various gas cells are selectively ignited or selectively not ignited to represent binary information.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a gas panel system operated in accordance with the principles of the present invention.
FIGS. 2A2H illustrate a family of waveforms to clarify the panel operation illustrated in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and more particularly to FIG. 1 thereof, there is illustrated a gas panel comprising 16 individual gas cells located at the respective intersections of vertical lines V, through V and horizontal lines H, through H In the illustrated embodiment of FIG. 1, the vertical drive lines are shown as conductors disposed on the upper surface of the panel, while the horizontal drive conductors, are disposed on the lower surface. The gas panel 10 ineludes an illuminable gas within a sealed envelope, and those regions within the vicinity of coordinate intersections of the vertical and horizontal drive lines are designated gas cells. A number of these cells are designated A and B to clarify the cell configuration wherein adjacent cells are in different groups. In one arrangement according to the'invention, a gas mixture of 99.9% neon and 0.1% argon was employed. For a more complete description of gas panel apparatus, reference is made to copending Application Ser. No. 785,210 filed Dec. 19, 1968 for Gas Panel Apparatus and Method" by George M. Krembs, now US. Pat. No. 3,611,019. The gas cells are selectively ignited or fired during a write operation by applying a first potential to its associated horizontal drive line and a second potential to its associated vertical'drive line of a magnitude such that the potentialdifference across the selected cell exceeds the ignition potential of the illuminable gas. Once ignited, each gas cell is maintained in the ignited state by a periodic sustain signal on the vertical and horizontal lines of sufficient amplitude to equal or exceed the sustain level, but lower in amplitude than the ignition potential. Typical operating potentials for a gas mixture of the type described are 190 volts for write, 150 volts for sustain. Any one of the ignited cells may be extinguished, termed an erase operation, by first reducing the potential difference across the cell to zero, then applying a pulse of erase amplitude and polarity opposite that of the last sustain alteration and maintaining the zero potential for a fixed period after the erase pulse. By selective write operations, information may be generated and displayed as a sequence of lighted cells in the form of alphanumeric or graphic data, and such information may be regenerated as long as desired by sustain operations. While the present invention will obviously utilize write, erase and sustain capability, for the purpose of clarity the invention will be described by way of illustration in terms of the sustain operation. For a more complete description of the operation of gas panel displays including write and erase operations, reference is made to the aforenoted copending Application Ser. No. 885,086
While not illustrated in the drawing in the interest of clarity, the gas panel 10 will include a plurality of pilot light gas cells selectively positioned on the panel which ionize the illuminable gas and thus serve to provide a more uniform operation of the ignition of the remaining gas cells. For a more complete description of pilot light gas cell operation, reference is made to copending Application Ser. No. 829,692 for Pilot Light Gas Cells For Gas Panels filed by P. Soltan on June 2, 1969, now US. Pat. No. 3, 609, 658. Such pilot cells when initially ignited are maintained by sustain signals applied to their respective coordinate intersections.
With respect to the general operation of the instant invention, the horizontal selection circuit 13 provides a signal of a given polarity on selected ones of lines 15 through 18 thereby to select a given one of associated line drivers 21 through 24 for a write or erase operation. Since the operation of the invention requires different horizontal and vertical sustain signals be applied to adjacent cells, two sustain drivers are required. X,
horizontal sustain driver 27 provides high voltage operating signals on a bus 31 and a bus 32 for con trolling the operation of X, line drivers 21 and 23,
while the identical X sustain driver 27' will control operation, of X line drivers 22 and 24. Input control signals on lines 33' are employed to control the X, and X sustain drivers 27". Vertical line drivers 41,,43 supply Y, operating potentials to respective vertical lines 46, 48, while line drivers 42, 44 supply Y operating potentials to respective vertical lines 47, 49. A vertical selection circuit 45 provides a signal of a given polarity on a selected one of the lines 51 through 54 thereby to select a given one of line drivers 41 through 44 for a write or erase operation. Y, sustain driver 55 supplies high voltage operating signals on buses 61 and 62 to the Y, line drivers 41, 43 in response to control signals applied to sustain driver 55 from line 63, while the identical Y sustain driver 55' supplies Y high voltage operating signals to line drivers 42, 44. All X and Y sustain drivers receive control signals from an erase and write control circuit whenever an erase or write operation takes place. At all other times the sustain drivers perform sustain operations in response to the control signals on respective input lines 33, 33' and 63, 63 respectively. Erase and write control circuit 60 receives control signals for performing write and erase operations, but such control is considered beyond the scope of the instant invention and has been omitted in the interest of clarity. For a more detailed description of such controls as well as details of the circuitry shown in block form in FIG. 1, reference is made to the aforenoted copending Application Ser. No. 885,086.
As previously described, the subject invention operates on the principle that the sustain signals in both the X and Y direction are applied to all cells simultaneously, but the signals applied to any row or column are 90 out of phase with the signals applied to the adjacent rows and columns. The potential on each of the horizontal lines H, through H and each of the vertical lines Y, through Y of the panel are square wave trains as illustrated in FIGS. 2A, 2B, 2C and 2D respectively. The resulting potential difference across each cell is a composite signal obtained by algebraically combining the respective coordinate potentials as shown in FIGS. 2E and 26.
Referring now to FIG. 2, the operation of the panel illustrated in FIG. 1 will be described in detail with reference to the waveforms shown in FIGS. 2A-2H. The timing cycle at which the respective X and Y drive signals are applied to the panel is a repetitive T,-T,, sequence, and the waveforms are shown with reference to this timing cycle. The horizontal sustain signals X,,
. X shown in FIGS. 2A and 2B which are applied to alternate rows of the gas panel matrix from sustain drivers 27, 27" are rectangular waveforms 180 out of phase with respect to each other. Likewise, the signals labelled Y,, Y, shown in FIGS. 2C and 2D which are applied to alternate vertical drive lines in the gas panel from sustain drivers 55, 55 are 180 out of phase with respect to each other, and also 90 out of phase with respect to the corresponding horizontal drive signals X, and X,. In the waveforms selected for illustration, the Y, and Y drive signals in FIGS. 2C and 2D precede their counterpart X, and X, signals in FIGS. 2A and 23 by 90. The waveform shown in FIG. 2E is a composite signal obtained by algebraically subtracting the X, waveform shown in FIG. 2A from the Y, waveform shown in FIG. 2C and represents the signal which will appear across the cells in alternate rows and columns. The waveform shown in FIG. 26 is obtained by algebraically subtracting the signal shown in FIG. 28 from the waveform shown in FIG. 2C and represents the composite signal applied across the cells of the remaining rows and columns. The composite waveforms shown in FIGS. 2E and 2G respectively exceed in amplitude the indicated minimum sustain level of the panel, and both the positive and negative excursions of the composite signals in FIGS. 2E and 2G are sufficient to maintain all previously ignited cells in the illuminated state. The signal waveforms in FIGs. 2F and 2H identify the firing times of the respective A and B cells.
With respect to the individual cells 65 and 67 shown in FIG. 1 and selected as representative of the A and B cells, the sustain operation of the instant invention will be described relative thereto, since they constitute a set of two adjacent cells (A and B) which are energized by X,, X, horizontal drive signals and the same vertical drive signal Y,. Alternatively, adjacent cells in the horizontal direction would be energized by Y,Y drive signals with a common X drive signal. Assuming that both cells 65 and 67 have been previously fired by a write operation and that it is now desired to sustain these ignited cells, the sustain signals X, and X shown in FIGS. 2A and 2B are applied from line drivers 21 and 22 to the respective X, and X drive lines 25 and 26. The Y, sustain signal identified by FIG. 2C is applied via line driver 41 to Y, line 46 and thus to cells 65 and 67. Starting at time T,, the composite potential shown in FIG. 2G (Y,-X,) exceeds the sustain potential level, and cell 67 is fired. This produces a wall charge phenomenon in which the cell walls are charged to opposite polarities, and the resulting charge cloud created by the discharge of cell 67 causes the ions and electrons to migrate to the negative and positive walls respectively. In conventional gas panel operation, when all gas cells are sustained simultaneously, the charge cloud elements tend to migrate to the walls of adjacent cells. However, in the instant invention, when B cells fire at time T,, both the X and Y conductors or walls of the adjacent A cells are at a positive potential, as shown in FIGS. 2A and 2C, but the resulting potential across these cells shown in FIG. 2E is zero. However, by virtue of the positive potential applied to both walls of the A cells at time T,, only the negative electrons will be attracted to the A cells, and as they tend to migrate to the A cells, the resulting unbalance of ions in the B cells will cause some electrons to return to the B cells. At time T the potential applied to the A cells shown in FIG. 2E rises to the sustain potential and cell 65 is reignited or sustained. However, the potential applied to both conductors of the B cell 67 is negative, and the net potential across the cell as indicated in FIG. 20 is zero. Under this condition only the ions from the A cell firing will be attracted to the negatively charged walls of the B cells. Accordingly, only half the charge particles will be attracted to the B cells when the adjacent A cells are fired and vice versa.'This action as shown in the two complete time cycles is repeated such that when either the A or B cell is fired, the opposite cell has the same polarity potential applied to both walls and the potential influence of adjacent wall charges is reduced by a minimum of 50 percent. The signals shown in FIGS. 2F and 2H identify the times at which the A and B pulses are fired, the B cells at times T, and T the A cells at T and T,. This operation is completely different from conventional sustain operation in which all cells are required to tire at the same quadrant and the charge cloud created when one cell is fired may drift to the adjacent cell and cancel both positive and negative wall charges thus causing the adjacent cell to fire or extinguish. Since this migration is one of the design limitations of conventional plasma display panels, the manner in which the density and thus resolution may be increased is obvious.
While the invention has been shown and described with reference to a sixteen cell panel to simplify the description thereof, it will be appreciated that in practice a high resolution gas panel is contemplated having between 50 and lines per inch or 2,500 to 10,000 cells per square inch. Whenever cells of type A are addressed or sustained, the cells of type B will act as an electrostatic honeycomb and vice versa and the conventional gas panel apparatus can be utilized. Variations in the shape of the applied horizontal and vertical sustain drive signals may be made without departing from the spirit of the invention. The essential difference between the instant invention and known prior art is the two cycle sequence for cell address or sustain to control the potential of adjacent cells whenever a cell is fired. While the invention has been shown in the preferred embodiment as a two-cycle sequence for both horizontal and vertical drivers, it is apparent that it may be applied to either the horizontal or vertical drive lines. In a specific display the resolution of one conductor configuration may be substantially higher than that of the associated conductor configuration and the invention applied only to the high intensity or high resolution axis of the panel.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.
What is claimed is:
1. A method for increasing the resolution of a gaseous discharge display panel having a gas filled envelope including first and second types of charge particles, said envelope having a first plurality of conductors disposed on one side and a second plurality of nonparallel conductors disposed on the opposite side thereof, the coordinate intersections of said first and second conductors defining a matrix of gaseous discharge cells, said cells being operated as two groups wherein each group comprises alternate cells, the steps of performing sustain operations on said cells by applying across the first of said groups a first sustain signalwaveform which exceeds the sustain level of said cells,
said first group comprising alternate cells along one axis of a matrix, simultaneously applying across said second group comprising the remaining cells a second sustain waveform having a phase different from said first sustain waveform whereby the wall charge of alternate cell walls is of a phase which retards migration of said charge particles during the gaseous discharge when said adjacent cells are sustained,
said second group of cells comprising alternate cells along said one axis, said cells being positioned adjacent said cells of said first group,
and means for reversing the above sequence by applying said first sustain signal waveform to said second group of cells and said second sustain signalwaveform to said first group of cells whereby all of said cells are sustained in a twocycle sequence while adjacent cells are maintained at a phase to limit migration of said wall charge particles to adjacent cells during each cycle of a complete sustain sequence.
2. The method of claim 1 including the further step of maintaining the sustain signals applied to said first group of cells out-of-phase with the sustain signal applied to said second group of adjacent cells.
3. A gaseous discharge panel comprising a plurality of gaseous discharge cells wherein said cells are initially discharged by addressing signals and maintained in a discharge condition by periodic sustain signals, said panel being adapted to increase the resolution of said display by limiting the interaction between adjacent cells comprising in combination,
container means filled with an ionizable gas including first and second types of charge particles,
a set of first conductors disposed on one side of said container means and a set of second conductors disposed on the opposite side of said container means,
said first and second sets of conductors being angularly related, the coordinate intersections of said first and second sets of conductors defining the location of said gaseous discharge cells, and
means for applying sustain signal waveforms to all cells simultaneously including means for displacing the phase of said sustain signal waveforms applied to adjacent ones of said first and second conductors, the sustain signal waveforms applied to alternate conductors being in phase whereby the wall charge produced in alternate cells retards migration of one of said types of charge particles from acell in which a discharge is initiated or sustained to an adjacent cell.
4. The apparatus of claim 3 wherein said means for applying sustain signal waveforms to all cells simultaneously comprises means for applying said phase displaced signals to adjacent cells during said complete sustain sequence in at least one of said sets of conductors such that adjacent cells are fired in a prescribed sequence to minimize interaction of said charge particles between adjacent cells.
5. Apparatus of the type claimed in claim 4 wherein said sustain signal waveforms applied to adjacent cells are 180 phase displaced with respect to each other.
6. Apparatus of the type claimed in claim 5 wherein corresponding sustain signal waveforms applied to opposite walls of said cells are phase displaced, each of said phase displaced signals addressing alternate cells in said gaseous panel display device.
7. A method for increasing the resolution in a gaseous discharge device by limiting interaction between adjacent cells in said gaseous discharge device during operation thereof, said gaseous discharge device, including a gas filled container with horizontal and vertical conductors disposed on opposite sides of said container, the coordinate intersections of said horizontal and vertical conductors defining the location of said gaseous discharge cells, the steps of generating a first square wave sustain signal,
applying said first sustain signal to alternate horizontal conductors,
generating a second square wave sustain signal displaced from said first square wave sustain signal,
applying said second sustain signal to a second group of horizontal conductors, the conductors in said second group being adjacent to the conductors in said first group in a vertical direction,
generating a third square wave sustain signal displaced 90 from said first sustain signal,
applying said third sustain signal to a third group of alternate vertical conductors,
generating a fourth square wave sustain signal displaced 90 from said second sustain signal,
applying said fourth sustain signal to a fourth group of vertical conductors, the conductors in said fourth group being adjacent the conductors in said adjacent said alternate cells in a horizontal and third group in a horizontal direction whereby, vertical direction is maintained below the sustain said square wave sustain signals at individual cell 10- level during this interval and at a phase to limit incations are algebraically combined such that the @factiOn of C g parti r sulting from the potential magnitude across alternate cells in both a 5 discharge of those hav mg pofentlal horizontal and vertical direction exceeds the "nude great" than Said Sustam PotemlaL sustain potential, while the potential across cells