US3601531A

US3601531A - Plasma display panel apparatus having multilevel stable states for variable intensity

Info

Publication number: US3601531A
Application number: US765939A
Authority: US
Inventors: Donald L Bitzer; Hiram Gene Slottow; William Petty
Original assignee: University of Illinois
Current assignee: University of Illinois; University of Illinois Foundation
Priority date: 1968-10-08
Filing date: 1968-10-08
Publication date: 1971-08-24
Anticipated expiration: 1988-08-24

Abstract

A plasma display panel apparatus having multilevel stable states for providing a display of variable intensity, the apparatus including means for initially setting in an amount of wall charge in each respective cell according to the intensity of the information to be displayed, and means for providing a sustaining signal for displaying the cells and maintaining the respective wall charges therein, the sustaining signal waveform having alternate stable and unstable regions. The means for setting in of the initial wall charge in respective cells is provided such that the cells having information which is to be displayed with a higher intensity are supplied with a higher initial wall charge than the cells having information which is to be displayed at a relatively lower intensity. The level of intensity depends on the slope of the exciting or sustaining signal at the time of discharge of the cell. The apparatus providing a rippled sustaining signal of alternate stable and unstable regions insures that the initial wall charge information set into the display panel will remain at the initial level, thereby providing a constantly recurring permanent display.

Description

United States Patent [72] Inventors Donald L. Bitzer Urbana; Hiram Gene Slottow, Urbana; William Petty, Champaign, all of, I11.

[211 App]. No. 765,939

[22] Filed Oct. 8, 1968 [45} Patented Aug. 24, 1971 [73] Assignee University of Illinois Foundation Urbana, Ill.

[54] PLASMA DISPLAY PANEL APPARATUS HAVING MULTILEVEL STABLE STATES FOR VARIABLE INTENSITY 8 Claims, 11 Drawing Figs.

[52] US. Cl l78/7.3 D,

[51] Int. Cl H04n 5/66 [50] Field ofSearch 315/167,

168,169, 169 TV; 178/67 A, 6.7, 7.3 D, 7.5 D, 6 A

[56] References Cited UNITED STATES PATENTS 2,595,617 5/1952 Toolon 178/6 A 2,994,011 7/1961 Belknap et a1. 315/169 7 SYNC.

34-susrlunsn WALL cgAges l l l INFO. g 1 TO BE DlSPLAYED 1 l l LL CHARGE 3,048,824 8/1967 Thompson 315/169 3,356,898 12/1967 Dano 315/169 3,379,831 4/1968 Hashimoto 178/73 D Primary ExaminerRichard Murray Assistant Examiner-Richard P. Lange Attorney-Merriam, Marshall, Shapiro & Klose ABSTRACT: A plasma display panel apparatus having multilevel stable states for providing a display of variable intensity, the apparatus including means for initially setting in an amount of wall charge in each respective cell according to the intensity of the information to be displayed, and means for providing a sustaining signal for displaying the cells and maintaining the respective wall charges therein, the sustaining signal waveform having alternate stable and unstable regions. The means for setting in of the initial wall charge in respective cells is provided such that the cells having information which is to be displayed with a higher intensity are supplied with a higher initial wall charge than the cells having information which is to be displayedat a relatively lower intensity. The level of intensity depends on the slope of the exciting or sustaining signal at the time of discharge of the cell. The apparatus providing a rippled sustaining signal of alternate stable and unstable regions insures that the initial wall charge information set into the display panel will remain at the initial level, thereby providing a constantly recurring permanent display.

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INVENTORS DONALD L. BITZER H. GENE SLOTTOW WILLIAM D. PETTY PLASMA DISPLAY PANEL APPARATUS HAVING MULTILEVEL STABLE STATES FOR VARIABLE INTENSITY This invention relates to gaseous discharge devices, and in particular to a gaseous discharge display panel having multilevel stable states for providing variable intensity.

The subject matter of the present invention is related to apparatus disclosed in a copending application of Donald L.

Bitzer, H. Gene Slottow and R. H. Willson, U.S. Ser. No. 1

plasma display panel." Reference may also be had to the following publications disclosing the type of plasma panel related to the present invention, such publications being incorporated herein in their entirety;

l. Bitzer, D. L. and Slottow, H. G. The Plasma Display PanelA Digitally Addressable Display with Inherent Memory, Proceedings of the Full Joint Computer Conference, San Francisco, California, Nov. 1966.

v 2. Arora, B. M., Bitzer, D. L., Slottow, H. G., and Willson, R. H., The Plasma Display Panel-A New Device for Information Display and Storage, Proceedings of the Eighth National Symposium of the Society for Information Display, May 1967 3. Bitzer, D. L. and Slottow, H. G. The Plasma Display Panel-A New Device for Direct View of Graphics, Conference on Emerging Concepts in Computer Graphics, University of Illinois Nov. 1967, to be published by Benjamin Publishing Company, New York.

4. Bitzer, D. L. and Slottow, H. 6., Principles and Applications of the Plasma Display Panel, Proceedings of the OAR Research Applications Conference, Office of Aerospace Research, Arlington, Va., Mar. 1968. (Also published in the Proceedings of the 1968 Microelectronics Symposium, I.E.E.E., June 1968.

It is to be understood that the terms plasma panel or plasma display panel" is defined by and is characterized by the gaseous discharge panel as described in the previously mentioned copending application and above listed publications.

This application is concerned with apparatus and a method for providing a new variable intensity technique for the plasma display panel. This technique is based on a stability theory for the plasma display panel which is discussed in the following sections.

The effective extension of the plasma display technique to provide variable intensity, or grey scale implies the existence of two properties. First a means must exist by which the intensity of a cell can be varied. Second it must be possible to sustain different cells in an array at different intensities. The first property, by itself, would make possible only a way of controlling the overall brightness of an image on the plasma display panel. The second property, however, makes possible the shading that id characteristic of images produced by half tone printing or displayed on television.

Several techniques for obtaining grey scale have already been described in the above-mentioned copending application. One of these replaces each cell by a group of cells from which the light is selectively filtered. With n cells in each group it is possible to obtain 2" brightnesslevels. A second technique allows control of the number of discharges that occur in a basic time interval-TN. field time for example. Unlike the cell group technique, the present invention does not increase the number of required cells. It is, however, most applicable to'applications where the image is changed, or in renewed, after each basic interval.

In accordance with the present invention there is provided apparatus and a method wherein the intensity of each cell can be set independently and can be' sustained indefinitely just as the single intensity is now sustained. This approach depends on two properties of the plasma display cell. First, the intensity of a discharge is related to the form of the exciting waveform at the time of firing and to the time during which charged particles are collected. For some cells this relation can be ex- 0 pressed as a function of the slope of the exciting signal.

Second, with a properly shaped waveform the plasma display cell can exhibit a number of discrete stable states, each corresponding to a different slope of the exciting voltage, and therefore to a different intensity. To understand this invention, we first review some principles of the plasma display cell itself.

The cell, in the on state, fires once each half cycle, when the exciting voltage and the wall voltage equal the firing voltage. In equilibrium the charge transferred during each discharge is the same, and the exciting voltage at the times of successive discharges are equal in magnitude, but opposite in polarity. This voltage is called the recurrent voltage. Any small change in wall charge causes a corresponding change in recurrent voltage, which because of the relation between voltage slope and total charge transferred to the walls, reduces the original perturbation. This restoring effect is generally precise and rapid. However, as will be hereinafter described in more detail, reduction of the perturbation can be made arbitrarily slow, it can also be made to grow exponentially, and at the limit of stability, it can persist indefinitely. The deliberate introduction of a perturbation in this case will thus change the stateand the intensity.

Although a quasi-stable state would be useful in a televisionlike display in which a new picture was generated in each basic interval, only stable states are acceptable in the kind of information display described herein. As will be noted, however, regions of instability can alternate with regions of stability. Small perturbations from any stable state will then damp out Small and any state once reached will persist indefinitely until it is changed by new information.

The invention will be better understood from the following detailed description thereof taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a driving or exciting voltage waveform illustrating the alternation of stable and unstable sections or regions in the waveform in accordance with the principles of the present invention.;

FIG. 2 is a schematic diagram illustrating one embodiment of apparatus which can be utilized to provide the ripped waveform of FIG. 1;

FIGS. 3, 4 and 5 are various waveforms useful in explaining the principles of the present invention;

FIG. 6 is a schematic diagram illustrating a plasma display panel driven by suitable apparatus for providing the multilevel stable states in accordance with one aspect of this invention;

FIGS. 7 and 8, illustrate a sustaining signal for the plasma display panel of FIG. 6, with the indicated change in wall voltage-in FIG. 7 the change in wall voltage occurring at a point of high slope corresponding to a relatively bright or a high intensity cell, and in FIG. 8 the change in wall voltage occurring at a point of relatively lower slope on the sustaining signal waveform, corresponding to a relatively dimmer or less intense cell;

FIG. 9 illustrates apparatus for setting the wall charges in respective cells corresponding to the intensity of the information to be displayed; and

FlGs. 10 and II are schematic diagrams illustrating respective outputs of the apparatus shown in FIG. 9 for providing corresponding waveforms reflecting the difference in intensity between a respective bright cell of high intensity (corresponding to FIG. 7) and a relatively dimmer cell of less intensity (corresponding to FIG. 8).

FIG. 1 shows the alternation of stable and unstable sections in the exciting voltage wave. This shape follows from what we have determined, wherein sections of the waveform of FIG. 1 with a positive second derivative are unstable while sections with a negative sound derivative, if it is not too large, will be stable. Such sections are illustrated in FIG. 1. This network can be generated by driving an appropriate wave shaping network with a square wave. This technique together with a representative wave shaping circuit is shown in FIG. 2. As illustrated, the input to circuit 10 is a square wave of suitable amplitude and frequency, and the output is a rippled wave of the form shown in FIG. 1 with the alternating sections previously described.

The following is a detailed description of the stability considerations concerned in the concepts and teachings of this invention. The fundamental relation in a discussion of the stability of firing times in the plasma display cell is l', =V;V,, (1) where V and V, are the magnitudes of the wall voltage and the recurrent voltage (the exciting voltage V at the beginning of the i discharge), and V, is the firing voltage. The flow of charges to'the walls during the I discharge changes the wall voltage by an amount 2V, to V and the next discharge in the sequence is ignited when the exciting voltage reaches the next appropriate recurrent voltage.

ii-l (2) l r ll}- i-i-l FIG. 3 shows the relations among these voltages for an arbitrary exciting signal. We note, in particular, that since we are concerned with the magnitudes of these voltages, Vi, and w,

are always positive, and we, therefore, do not distinguish between the positive and negative half cycles.

Two successive values of wall voltage are related by the expression v..,,,= -v..,T- 3) and substituting from equation (1), we obtain the relation between two successive values of recurrent voltage V =2V; V, -2V (4) In terms of the difference 8, between V and the equilibrium value V and the difference 8 between V, and V this relation becomes The question of stability rests on the relation between the form of the exciting signal, V, and the change in wall voltage, ZV This change, in turn, depends on the intensity of the discharge. In general the intensity increases with over voltage. Therefore, since the discharge requires time to develop, the more intense discharge occurs when the slope of the exciting waveform at the time offiring is larger.

We assume now that the change in wall voltage can be expressed as a function of slope. lf at equilibrium a perturbation from equilibrium decreases to zero in time. For y beyond this range, the perturbation 8 grows and the system is unstable.

To separate the influence of the charge-slope relation from that of the waveform itself we replace the term df/dV by its equivalent dV dV dl dt (16) The first factor is a parameter of the cell that can be measured. The second term is the ratio of the time derivative of the slope to the slope itself.

It is instructive to consider the two cases at the limit of stability. When -y=0, a,- =a,. A perturbation 8 then alternates on successive half cycles and persists indefinitely. This condition could arise if the charge transferred were independent of the slope (df/dV=0), or if the slope did not change in the range that includes both the initial equilibrium voltages and the perturbed firing voltages. This second case is illustrated in FIG. 4.

When y=-2, a a and a perturbation 8 once introduced, persists indefinitely. The new firing times represent an equilibrium state just as the original firing times do. This case is illustrated in FIG. 5. To obtain an acceptable form for this voltage wave we must find a solution to the equation dV dt E If the charge transferred in a discharge were strictly proportional to the slope (df/dV=k), then a solution would be V=C( l-C(Ie""/k) (18) If, as is more typical, afldV is not constant, but varies smoothly with V, equation 18) is still an approximate solution to equation 17) over small ranges of V, provided that k is replaced by the local value of df ldVfor each range.

A third special case occurs when y=l. A perturbation for this case will be cancelled in the next discharge in the sequence. For values of -y=l, therefore, the approach to equilibrium of a cell after change of state will be rapid, a fact frequently observed in work with the plasma display cell.

A practical implication of the above concepts and teachings is that through control of the exciting voltage waveform, regions of stability could be alternated with regions of instability. This would lead to a multiplicity of stable states and a corresponding number of intensities.

Referring to FIGS. 6 through 11 there is illustrated a specific embodiment of the present invention utilizing the teachings thereof to provide a plasma display panel having multilevel stable states to obtain a display with variable intensity. As will be described in more detail in the following description, in general, the apparatus and methods herein illustrated are provided for initially setting in an amount of wall charge in each respective cell according to the intensity of the information to be displayed, and thereafter suitably discharging the cells having the respective wall charged by utilizing a sustaining signal having a wave shape, in accordance with the principles previously discussed so as to obtain the various intensity levels in the plasma display with various respective stable states.

In particular in FIG. 6, there is illustrated the plasma display panel 20 incorporating a gaseous medium, a first set of rows of electrodes 22 on one side thereof, and a second set of columns of electrodes 24 on the other side thereof and disposed orthogonal to the electrodes 22 of the type and as is described more completely in the previously mentioned copending application and publications. Alternatively, since the principle of the plasma panel, as explained in the previously mentioned copending application is the manipulation of the wall charges to impart information, the panel can be formed with one or both electrodes associated with a cell electrically insulated from the gaseous medium. To each of the electrodes 22 there is connected a corresponding wall charge setting means 26, which is its input receives the information to be displayed in the form of an electrical signal having an amplitude or voltage level corresponding to the respective intensity. For convenience only the first wall charge setting means 26 connected to the first row electrode 220 and the last wall charge setting means 28 connected to the last row electrode 22e is shown in FIG. 6, however it is to be understood that the remaining electrodes in between electrode 22a and 22s are connected to similar apparatus. Also, it is to be understood that the diagram illustrating the plasma display panel 22 in FIG. 6 is shown in a greatly enlarged view, since in most cases the illustrated cells are much closer together, typically being separated by about 25 thousandths of an inch from cell center to cell center. The panel can of course be of any suitable size, the illustration of five columns and rows being merely for convenience here. While it may not be particularly evident from FIG. 6, it is to be understood that the cells vary in intensity from the dimmest cells at the top left-hand corner of the plasma panel 20, namely cell 30, diagonally to the brightest cell 32 at the bottom right-hand corner of the panel.

The sustainer 34 illustrated in block diagram form in FIG. 6 can be obtained from the apparatus shown in FIG. 2, wherein a square wave is transformed by the wave shaping network into the rippled wave of FIG. 1 so as to obtain the multiple stable states. Thus, the sustaining signal shown in FIG. 7 and 8 is actually set in on all of the cells, that is, this signal represents the voltage difference between each of the respective column and row electrodes associated with the particular cells. It is to be understood that the principle underlying the obtaining of a variable intensity display is related to the fact that the level of intensity depends on the slope of the exciting signal at the time of discharge, and that this in turn depends on the initial wall charge. For example, referring to FIG. 7 there is represented the changes in wall voltage of a bright cell such as the cell 32 in FIG. 6 superimposed on a schematic representation of the rippled sustaining signal voltage supplied by sustainer 34 to row electrode 22e andcolumn electrode 24s. The vertical or ordinate axis of FIG. 7 has indicated thereon an index mark above and below the zero abscissa axis to indicate the voltage level of the initial wall charge, C which has been set into cell 32 by means of wall charge setting means 28 and the addresser 36, as will be described later in more detail. Also, the ordinate axis contains index marks, V, indicating the required voltage difference across the respective cell electrodes in order to bring about a discharge of the gaseous medium within the cell. As the sustaining signal is applied to cell 32, at a point indicated by reference number 38, on the sustaining signal waveform, the potential difference between the respective electrodes 22e,24e represented by the sum of the sustaining voltage and the voltage due to the initial wall charge equals the firing or discharge potential, V; so that the cell 32 discharges in what has been described as a pulsing discharge manner in the prior mentioned copending application-that is, the discharge is quickly extinguished by the formation of wall charges equal in amplitude to the initial wall charges C,, but opposite in polarity thereto forming on the cell walls. In FIG. 7, such a condition is represented by the wall voltage charging by an amount 2C or as indicated in the diagram to a level C above the reference zero abscissa.

It is to be particularly noted that the cell has discharged at the point in time indicated by the reference numeral 38 which is a point of relatively high slope on the sustaining signal waveform, which we have found to produce a relatively brighter display than when the cell is discharged at a point on the sustaining signal having a relatively lower slope which, for the sustaining signal example shown shown in FIG. 7, would occur towards the top of the first symmetrical half of the sustaining figure waveform of FIG. 7. It must be understood that the above description indicating what has been determined to be the attaining of a variable intensity as a function of the slope of the sustaining signal at the time of cell firing, relates to the overall average slope of the signal, and not to the very rapid and constantly changing rippled condition of the slope, which of course, as previously described has been provided so as to insure the maintaining of stable states in the plasma display. So as to completely understand the situation, what might be described as the average slope of the sustaining signal for the first symmetric half of the waveform has been indicated in dashed lines in FIGS. 7 and 8. Thus, it is clear that when considering the dashed line representation of the average slope condition of the sustaining signal at any particular time, the reference numeral 38 on the sustaining signal waveform occurs at a point of relatively higher slope than that further along to the right and top of the first symmetric half of this waveform.

If the firing of the cell such as at reference point 38 occurs at an unstable region of the sustaining signal, the cell voltage adjusts either up or down the slope until the next stable region is encountered, and the cell wall voltage is thus locked in at that particular stable state as described in the previous discussion above. In FIG. 8 there is illustrated a representation of a cell which is firing so as to display a relatively dim or low level intensity as compared to the higher intensity representation of FIG. 7. For example, we may assume that the cell 30 associated with row electrode 22a and column electrode 240 has been set with an initial wall charge corresponding to C by the wall charge setting means 26 and addresser 36 in accordance with the information to be displayed at this particular point on the display panel 20. Thus, as shown in FIG. 8, as the sustaining signal applied to the respective electrodes from sustainer 34 rises in voltage level, the wall voltage continues at the level corresponding to the initial wall charge, C until a respective point in time indicated by the reference numeral 40 on the sustaining signal where the sum of the wall voltage due to the initial charge, C and the voltage due to the sustaining signal equals in sum the firing voltage, V,. At this point, the pulsing discharge situation occurs with a resulting buildup of wall charges of opposite polarity in the cell 30 until a change in wall voltage corresponding to 20,. occurs, or as indicated as in FIG. 8, until the wall voltage level corresponding to C has been reached above the reference zero abscissa. The discharge is then extinguished and the wall voltage continues to the next firing point occurring on the next symmetric half cycle of the sustaining signal. It is to be noted here that the firing point 40 occurs at a point of relatively lower slope on the sustaining signal than the reference firing point 38 shown in FIG. 7, thus the cell 30 fires with a lower intensity than the cell 32. The wall voltage of cell 30 also adjust itself so as to stabilize at the closest stable region on the sustaining signal.

Thus, a complete variation in intensity between a low and high level can be provided by insuring that the cell will fire at a respective point on the sustaining signal waveform, or in other words at a particular time corresponding thereto. That is, if a bright high level intensity is desired, the discharge should occur at a point of relatively higher slope, such as illustrated in FIG. 7, as compared to if a relatively dimmer display of lower intensity is desired which occurs at a point of lower slope on the sustaining signal. In other words, the desired value or level of intensity for the displayed information can be provided by insuring that the initial wall charge of the cell is such that the firing of the cell will occur at the desired point along the sustaining signal waveform. For example, notice that in the case of a bright cell, the initial wall charge should be large (corresponding to C, in FIG. 7), whereas for a relatively dim cell, the relative value of the wall charge should be less (C in FIG. 8).

Referring now to FIGS. 9, 10 and 12 there is illustrated one embodiment of the desired means for setting in of the wall charges" in the respective cells according to the level of intensity desired. In FIG. 9, there is illustrated what might be termed an integrator 42 which receives an input signal represented by the signal source 44 having an amplitude which represents the intensity of the signal desired to be displayed. This signal source 44 is coupled between the base and emitter of transistor 46 with suitable circuit components being provided so as to insure that the output of the transistor between the collector and emitter will be a waveform having a slope proportional to the amplitude level of the signal source 44. For example, if the input waveform V(t,) is supplied to the integrator 42, representing as an illustration the bright information which is to be displayed at cell 32, the resulting output of the integrator 42 is a triangular waveform S (see FIG. 10) whose slope is proportional to the amplitude or intensity of the input signal V(t Similarly, for an initial input signal of V(t representing a low level or dim signal which is to be displayed at cell 30 on panel 20, the resulting output of integrator 42 consists of a triangular waveform S (see FIG. 11) whose slope is proportional to the amplitude or intensity of the initial information which is to be displayed. Thus, the integrator 42 is one illustration of a type of wall charge setting means which can be used to set the wall charges of respective cells of the plasma panel 20.

The actual setting of the wall charges is obtained by synchronizing the voltages placed on respective row electrodes 22 from the wall charge setting means such as the integrator 42 and the voltages placed on the column electrodes 24 by the'addresser 36. The addresser 36 provides a square wave shaped selection or addressing signal having a period corresponding to the lowest intensity level to be displayed. Well-known sync means 48 synchronize the placing of the respective voltages on the row and column electrodes. Thus, when the output signal S, is present from wall charge setting means 28 on row electrode 22e, the addresser 36 is synchronized so that at that time the proper selection signal is coupled to the column electrode 24s to discharge cell 32 and set the wall voltage of cell 32 at a voltage level corresponding to a charge of C representing the amplitude of the input signal V(t,). In a similar manner, the wall voltage corresponding to a charge C is set in on cell 30 by providing a suitable addressing or selection signal to the column electrode 24a, which together with the voltage corresponding to waveform 5 on row electrode 22a fires the cell 30 and sets in the desired initial wall voltage.

It is to be understood, of course, that in accordance with the principles of the present invention, the multiple intensity and permanent memory attained with this display apparatus can be provided by alternative embodiments. For instance, in connection with the means for setting in the initial wall charges in the respective cells, it may be more advantageous to employ other means than the integrator circuit 42 described herein. An alternative technique for setting the wall charge, and therefore, the wall voltage to a desired value is to apply a suitable signal to the cell so that the voltage across the cell is raised above the firing voltage, but while many charged particles remain in the volume, the voltage is reduced to the desired wall voltage level. The charged particles, attracted to the walls by the electric field, reduce the magnitude of the electric field, and, thereby, charge the wall voltage. Ideally, with a sufficiently large number of charged particles, the magnitude of the electric field will go to zero, and the wall voltage will become equal to the setting voltage.

Similarly, in connection with the rippled sustaining signal of the form shown in FIGS. 7 and 8, another alternative might be advantageous in certain situations. For example, note from the above discussion, and in particular, equation 15, that the boundaries between a stable and unstable state can be defined in two ways. In one, the second derivative of the cell voltage with respect to time actually changes sign. This change of sign is evident in the drawings of FIG. 1, FIG. 7, and FIG. 8. The value of the second derivative, however, need only change in a way that allows the quantity to alternate between a value that is greater than 2 and a value that is less than -2. For a cell in which the charge transferred were strictly proportional to the slope the waveforms would resemble those in FIGS. 1, 7, and 8, except that the perturbation from the smooth curve would be very small, and the second derivative would not change sign. The circuit and technique illustrated in FIG. 2 would again be appropriate, the components being chosen to provide a smaller amplitude for the ripple.

Whereas, in the above description of the present invention, there has been illustrated the application of the multiple stable state technique for providing variable intensity in a display panel, it is to be understood that the principles of the invention can also be applied to other nondisplay situations. For example, the application of multiple stable regions can be utilized in transferring information identified in multiple stable states.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom as modifications will be obvious to those skilled in the art.

What is claimed is:

1. In gaseous pulsing discharge display panel apparatus, including a gaseous medium in said panel, and display points defined by associated paired electrodes, said display points including gaseous discharge cells having cell walls for forming wall charges thereon, wherein information is transferred into and out of said panel by manipulating wall charges associated with the selective pulsing discharge of the gaseous medium at the display points by coupling suitable exciting signals to the associated paired electrodes, the improvement comprising means for displaying said information at variable intensity levels, including a multiple stable state sustaining signal generator coupled to said electrodes, said sustaining signal, having multiple stable regions associated therewith for discharging said gaseous medium in cooperation with said wall charges so as to maintain said information related to said wall charges in said panel at said selected display points.

2. Display panel apparatus as claimed in claim 1, including wall charge setting means for entering wall charges at respective display points proportional to the corresponding intensity level of said information, each of said stable regions related to a particular intensity level.

3. Display panel apparatus as claimed in claim 1, wherein said sustaining signal generator comprises means for generating a rippled sustaining signal waveform having alternating portions with a negative second derivative and a positive second derivative, said negative second derivative signal portions corresponding to said multiple stable regions.

4. Display panel apparatus as claimed in claim 3, wherein said means for generating a rippled sustaining signal waveform comprises a square wave generator and a wave-shaping network.

5. Display panel apparatus as claimed in claim 2, including addressing means for selecting and entering a value of wall charge at selected display points proportional to the level of intensity to be displayed at said display point, a bright display point having a higher wall charge and being sustained at one stable region, and a relatively dim display point having a lower wall charge and being sustained at another stable region.

6. In gaseous pulsing discharge display panel apparatus, including a gaseous medium in said panel, and display points defined by associated paired electrodes, said display points including gaseous discharge cells having cell walls for forming wall charges thereon, wherein information is transferred into and out of said panel by manipulating wall charges associated with the selective pulsing discharge of the gaseous medium at the display points by coupling suitable exciting signals to the associated paired electrodes, the improvement comprising means for maintaining said information at various discrete levels, including a multiple stable state sustaining signal generator coupled to said electrodes, said sustaining signal having multiple stable regions associated therewith for discharging said gaseous medium in cooperation with said wall charges so as to maintain said information related to said wall charges in said panel at said selected display points.

7. In the method of displaying video information in a gaseous pulsing discharge display panel having a gaseous medium in said panel, and display points defined by associated paired having multiple stable regions to said respective electrodes.

8. The method of displaying information as claimed in claim 7, for displaying video information of varying intensity levels, including addressing and simultaneously entering said wall charges at respective display points proportional to the cor-- responding intensity level of said video information, said wall charges being maintained at said display points and being sustained in association with a respective stable region.

@53 3 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 D601 531 Dated August 24, 1971 Inventorzs) Donald L. Bitzer et al.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2 line 39 delete "Small" and insert -e ponentia1ly- 1 Column 3, line- 3, "sound" should be "second".

Column 4,- line 33, "V=C(1- C(1-e /k) should be V=C(l-e /k) Column 6 line 32 after "initial" insert wall Column 6, line 65 "12" should be -11.

Signed and sealed this 7th day or March 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK At testing Officer Commissioner oi Patents

Claims

7. In the method of displaying video information in a gaseous pulsing discharge display panel having a gaseous medium in said panel, and display points defined by associated paired electrodes, said display points including gaseous discharge cells having cell walls for forming wall charges thereon, wherein said information is entered into the panel at selected display points by coupling addressing signals sufficient to discharge the gaseous medium to respective electrodes and form associated wall charges, said wall charges entered in said panel related to said information, the improved step of sustaining said information in said panel at various information levels by applying a multiple stable state sustaining signal having multiple stable regions to said respective electrodes.

8. The method of displaying information as claimed in claim 7, for displaying video information of varying intensity levels, including addressing and simultaneously entering said wall charges at respective display points proportional to the corresponding intensity level of said video information, said wall charges being maintained at said display points and being sustained in association with a respective stable region.