US3922583A

US3922583A - Method and means for increasing the operating range of gas panel displays

Info

Publication number: US3922583A
Application number: US483759A
Authority: US
Inventors: Conrad Lanza
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1974-06-27
Filing date: 1974-06-27
Publication date: 1975-11-25
Anticipated expiration: 1992-11-25
Also published as: FR2276684A1; JPS513820A; GB1504365A; FR2276684B1

Abstract

An A. C. gas discharge display and memory device is driven with sustain pulses which operate at a frequency such that the sustain pulses terminate within the region of the gas discharge curve slightly after currents reach their maximum and flow begins to terminate. Frequencies are selected such that for the lower applied voltages, cells will not fire. To permit operation within this region of the discharge curve at frequencies which will allow deionization, relatively slow risetime sustain pulses are used. For Neon with traces of Argon at pressures between 400 to 800 Torr., alternating sustain pulses having a frequency range of from 40 to 80 K Hz and a risetime range of from 1.8 to 2.2 Mu sec. have been found to be optimum.

Description

United States Patent [1 1 3,922,583 Lanza 1 Nov. 25, l 975 [54] METHOD AND MEANS FOR INCREASING 3,801,861 4/1974 Petty et a1 1. 315/169 R X THE OPERATING RANGE OF GAS PANEL DISPLAYS Primary Examiner-Nathan Kaufman Attorney, Agent, or Firm-John A. Jordan [75] Inventor: Conrad Lanza, Putnam Valley, NY

[73] Assignee: International Business Machines [57] ABSTRACT Corporation An A. C. gas discharge display and memory device is [22] Filed; June 27 1974 driven with sustain pulses which operate at a frequency such that the sustain pulses terminate within [2]] p -I 483,759 the region of the gas discharge curve slightly after cur rents reach their maximum and flow begins to termi- (52] C| 315/169 TV; 315/169 R nate. Frequencies are selected such that for the lower 5 1 1 im. cl. nose 37/00 P voltagcs' Cells will not To Perm Opera- [58] Fidd of Search h 315H69 R 169 tion within this region of the discharge curve at fre- 340/324 C quencies which will allow deionization, relatively slow risetime sustain pulses are used. For Neon with traces [56] References Cited of Argon at pressures between 400 to 800 Torr. alternating sustain pulses having a frequency range of from 3 573 542 :A PATENTS 31 169 40 to 80 K Hz and a risetime range of from 148 to 212 ayer 62K a. i i t 4 i i i u 5/ R i h b f d b 3,673,460 6/1972 Johnson et al. 315/169 R p Sec ave een mm 0 6 Op mum 3,761,773 9/1973 Johnson et a1. 315/169 TV 4 Claims, 6 Drawing Figures "W175 ERASE 3 l PULSE GEN R1 we 15 i ERASF PiJtSE GEN 1 1 GAS PANEL 1 1 /5M 1 WRITE i ERASE 1 PULSE GEN RN 1 C2 0 /7 N 1 ROW DECUDE were U.S. Patent Nov. 25, 1975 Sheet 1 014 3,922,583

1 WRITE/ ERASE PULSE GEN. 11/ WHITE ERASE PULSE GEN.

: GAS PANEL 311 WRITE ERASE I PULSE GEN. RN

cf 11 i ROW DECODE I 10910 DATA INPUT DATA PROCESSOR /9 001111111 DECODE LOGIC 5 1 L WR|TE/ERASEP h PULSE GEN WRITE/ERASE WAVE PULSE c511 SHAPER I i I A 12 11111111 U 11111110 WE vA5 PULSES SHAPER n 1 FIG. 1

SQUARE WAVE PULSE osc. r- L r r1 US. Patent Nov. 25, 1975 Sheetf4 3,922,583

FIG. 4A 140 q V V 80 v V V r V 60 200V V TIME ()JS) GAS FIG. 4B

US. Patent Nov. 25, 1975 Sheet4 f4 3,922,583

Fl G

M2 'QJPEQ 120 M4 KHZ 0 2 l l 1 7- 200 OPERATING 7 MARGINS METHOD AND MEANS FOR INCREASING THE OPERATING RANGE OF GAS PANEL DISPLAYS RELATED APPLICATIONS The following US. applications, assigned to the assignee of the present invention, are cited as disclosing related inventions directed to gas panel display devices,

BACKGROUND OF THE INVENTION The present invention relates to gas discharge display and memory devices. More particularly, the present invention relates to a method and apparatus for applying sustain voltage pulses to gas discharge display and memory panels of the A. C. variety.

Gas panels of the type to which the present invention is directed are well known in the art. As briefly described in the above cited related applications, the gas panels of the type to which the present invention is directed typically have two glass plates maintained in spaced-apart relationship, and are arranged to have sealed between the spaced-apart plates, an ionizable medium. To provide matrix addressability whereby selected local regions within the ionizable medium may be selectively ionized, sets of horizontal and vertical conductors are employed. Typically, the set of horizontal conductors comprises an array of parallel insulated conductors arranged on the inner surface of one plate and horizontally extending thereacross. Likewise, the set of vertical conductors comprise an array of parallel insulated conductors arranged on the inner surface of the other plate vertically extending thereacross, generally orthogonal to the parallel horizontal conductors. When an appropriate voltage is applied between a selected one of the horizontal conductors and a selected one of the vertical conductors, ionization occurs at the crossover point of the two conductors whereby light is emitted. Generally, the crossover points are referred to as cells and a display pattern or image is formed by ionizing selected cells.

Operation of the gas panel of the variety above described typically involves continuous application of periodic alternating sustain signals to the sets of horizon tal and vertical conductors. Thus, during one half of a sustain cycle, one set of conductors is driven positive while the other set of conductors is driven negative. During the other half portion of the sustain cycle, the voltage signals are reversed. The sustaining signals, however, are not sufficient to ionize the ionizable gaseous medium. To start ionization in a selected cell, a write voltage is typically superimposed upon the sustain voltage at the appropriate horizontal and vertical conductors. To deionize a previously ionized, i.e. written 2 cell, an erase voltage of appropriate waveform is superimposed upon the sustain voltage.

One of the major advantages to gas panels of the above described variety resides in the fact that their cells exhibit an inherent memory. The inherent memory comes about by virtue of charges that accumulate on the insulated conductors during ionization of a selective cell. Thus, when a write voltage is applied to a selected cell, the ionization that occurs during this writing produces positive and negative charges on the opposing insulating walls of the cell, i.e. upon the opposing insulating surfaces of intersecting conductors. The voltage of this charge opposes the voltage applied between the vertical and horizontal conductor so that the sum of these voltages quickly falls below the voltage required for ionization, and light is emitted from these cells for only a brief instant (about 15 p. Sec. The current which flows during this short time deposits a substantial charge on the cell walls. Since the first arriving sustain voltage pulse following the write operation is opposite in polarity to the write pulse, and thus is of the same polarity as the charge stored on the cell walls during the write operation, the cell again ionizes since the sum of the applied sustain voltage and the voltage of the stored charge is sufficient in magnitude to effect such ionization. Since the sustain pulse during this second ionization is opposite in polarity to the sustain pulse applied during the initial write operation ionization, the charge accumulated upon the cell walls reverses during the second ionization. Accordingly, the second arriving sustain pulse following the initial write operation will have the same polarity as that of the charge accumulated during the second ionization such that the sum of the voltages across the cell is sufficient to again effect ionization, and the process continues on in alternating fashion until an erase pulse is applied.

Thus, it can be seen that during the application of a write pulse, initial charge is accumulated upon the walls of the cell which charge is sufficient when combined with the alternating sustain voltage to cause the cell to be ionized each half cycle whereby light is emitted. Although the sustain voltage is applied simultaneously to all cells, only previously written cells ionize and accumulate charge so as to permit the sustain voltage to maintain their written condition.

A possible explanation for ionization in gas panel display devices may be helpful, by way of background, in facilitating an understanding of the context out of which the present invention arises. Independently of any voltage on the conductors of a cell, the cell ionizable gaseous medium ordinarily contains some free electrons and positive ions, and pilot lights may be deployed around the edge of the panel to establish a suitable background level of ionization. When a voltage is applied across the conductors ofa cell, an electric field is formed in which the electrons are accelerated so that electrons collide frequently with neutral atoms and thereby produce additional electron-ion pairs. At relatively low voltages an equilibrium condition may be reached where there is a moderate level of ionization but ions are lost by recombination as fast as they are created by collision between atoms and electrons. However, at some higher voltage level, electron-ion pairs are created faster than their loss, and these electrons in turn produce additional ionization so that an avalanche of free charges occurs. It is evident, then. that both the height and the width of the voltage waveform applied to the cell are involved in creating the avalanche ionization condition.

For additional background on the operation of gas discharge display and memory panels of the type described herein, reference is made to the early publication of D. L. Bitzer et al entitled, The Plasma Display Panel-A Digitally Addressable Display With Inherent memory, Proceedings of the Fall Joint Computer Conference, IEEE, San Francisco, California, November, 1966, pages 54l-547. Exemplary of the prior art patents existing in this area are US. Pat. No. 3,499,167 to Baker et al, US. Pat. No. 3,618,017 to Murayama et al and US Pat. No. 3,673,460 to Johnson et al.

One of the difficulties encountered in A. C. gas dis charge display and memory panels resides in the fact that the operating margin or window is poor, i.e. narrow. The operating margin may be defined as the difference between the minimum sustain voltage required to be applied to sustain ionization of previously written cells and the maximum sustain voltage which may be applied before unwritten cells begin to turn on. The normal end-of-life of a gas discharge display panel occurs when the operating margin of the panel, as a whole, is reduced below a tolerable magnitude. Thus, where the operating margin is narrow to begin with, the life of the panel is unacceptably short. Although the life of a gas discharge display panel having a narrow operating margin may be extended. to some degree, by fabricating same within close physical tolerances, such constraints act to make manufacturing costs prohibitive. One particular approach to obviating the problem of narrow operating margins is described in US. Pat. No. 3,573,542 to Mayer et al. The difficulty with the Mayer et al and like prior art approaches to obviating the problem ofa narrow operating margin resides in the fact that they rely upon somewhat specialized and costly driving circuitry.

SUMMARY It is, therefore, an object of the present invention to provide an improved gas discharge display and memory panel.

It is further object of the present invention to provide a gas discharge display and memory panel which is low in cost and exhibits long life.

It is yet a further object of the present invention to provide a gas discharge display and memory panel which exhibits an improved operating margin.

It is yet still a further object of the present invention to provide a gas discharge display and memory panel which is driven by simple driving circuitry, and yet ex hibits a superior operating margin.

It is yet still another object of the present invention to provide novel method and apparatus for applying particular sustain pulses to a gas discharge display and memory panel such that the operating margin of the panel is greatly improved.

It has been found, in accordance with the principles of the present invention, that by driving A. C. gas discharge display and memory devices with alternating sustain pulses at frequencies such that the sustain pulses terminates just after the region of the gas discharge curve characteristics where the family of currents for variously applied voltages reach their maximum and flow begins to terminate, the operating margin of such panels is greatly improved. Frequencies are selected such that for the lower applied voltages, cells will not fire. To permit operation within this region of the discharge curve characteristics at frequencies which will allow deionization between pulses, relatively slow risetime sustain pulses are used. It has been found, that for neon with traces of argon at between 400 and 800 Torr., alternating sustain pulses having a frequency range of from 40 to K Hz and a risetime range of from 1.8 to 2.2 t See. will act to increase the operating margin by at least percent, while other perameters such as the controllability, addressability, etc., remain the same.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiment of the invention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a total display system using the sustain drive circuitry method and apparatus, in accordance with the principles of the present invention.

FIG. 2 shows a plot of experimental data verifying the trend of operating margin increase with increasing frequency, using 2.0 p, Sec. risetime pulses.

FIG. 3 shows a plot of the gas discharge breakdown characteristics, as a function of time, for four different amplitudes of the applied voltage V with each of the applied voltages having negligible risetimes.

FIG. 4a shows a plot of the gas discharge breakdown characteristics, as a function of time, for various amplitudes of the applied voltage, V,,, with each of the ap plied voltages having a 2 u Sec. risetime.

FIG. 4b shows a schematic representation of how the applied voltage V, appears across the ionizable gas and dielectric medium in a gas discharge display and memory cell, according to the present invention.

FIG. 5 shows a plot of the charge transfer characteristics for a 33 K Hz sustain pulse with 2 pi Sec. rise-time as compared to a 50 K Hz sustain pulse with a 2 t See. risetime, each applied to neon with traces of argon at approximately 600 Torr.

DETAILED DESCRIPTION OF THE DRAWINGS In the typical display system configuration shown in FIG. 1, AC. gas discharge and memory panel I is shown having its horizontal and vertical conductor arrays respectively coupled to row drive lines R R and column drive lines C,C-. Typical gas panels structural configurations, in accordance with the hereinabove described principles, are shown in US. Pat. No. 3,808,497 to Greeson, Jr. et al and copending US. application No. 353,026 to Berkenblit et al. Likewise, the above cited Baker et al patent and Bitzer et al article describe typical structural configurations for gas discharge display and memory panels.

It is clear, that the number of column and row drive lines correspond, respectively, to the number of horizontal and vertical insulated conductors in gas panel 1 whereby, an MxN matrix array of display cells may be selectively addressed by appropriate application of write-erase select pulses to appropriate ones of the row and column drive lines. Although the selection scheme is a matter of design choice, typically half-select write and erase pulses are employed. Accordingly, as shown in FIG. 1, if it was desired to turn on, i.e. write the display cell at the intersection of drive lines R, and C write pulses would be superimposed via

pulse generators

3 and 5, upon the out of phase sustain pulses applied to the R and C, drive lines to thereby increase the effective amplitude of the sustain pulses for the duration of these write pulses. For half-select operation, the out of phase write pulses are of equal amplitude. Likewise, as is well known to those skilled in the art, half-select erase pulses may be superimposed upon the 180 out of phase sustain pulses to provide selective erase operations.

As shown in FIG. I, the sets of row and column writeerase pulse generators 33N and 5-5N act 0t superimpose write-erase pulses upon out of phase sustain pulses in response to write and erase signal indications from row and column decode logic circuitry 7 and 9, respectively. It is clear, that in the accordance with the arrangement shown in FIG. 1, any of a variety of data may be digitally displayed upon gas panel 1. Typically, the gas panel is employed to display alpha-numeric information in cooperation with a digital processor. Thus, digital processor 11 may readily act to control row and column decode logic circuitry 7 and 9 so as to display selected information therefrom. The manner by which wave shaper circuits l3 and 15 and pulse oscilator 17 act to produce sustain pulses, in accordance with the principles of the present invention, will be more fully understood with reference to a description FIGS. 2-5.

FIG. 2 shows a plot of the maximum sustain voltage V Max. and minimum sustain voltage V Min. as a function of frequency. As hereinabove mentioned, the difference between V Max. and V Min. is the operating margin. V Max. may be defined as that voltage above which previously unwritten cells begin to turn on while V Min. may be defined as that voltage below which ionization will not be sustained upon the application of a write pulse. The plot of FIG. 2 experimentally verifies that the operating range increases with increasing frequency, the increasing margin being achieved mainly by an increasing of V Max. with only a slight increase in V Min. The measured voltage points of FIG, 2 were obtained using neon gas with 0.001 argon at a pressure of 600 Torr. The dielectric covering the horizontal and vertical lines of the panel was coated with MgO, as described in the above mentioned copending application. The gap of the panel was 6.6 mils. A single cell was employed to make the measurements, with the plus signs in the plot indicating measurements, made with the adjacent cells ignited, and the circled dots indicating measurements made with the adjacent cells turned off. Although this plot reflects the results of measurements made upon a particular panel atrangement, it should be recognized that the main purpose of this plot is to verify the expansion trend of the operating margin with increasing frequency, and that similar trends could likewise be realized using panel arrangements with different perameters.

FIG. 3 shows a plot of typical gas breakdown charac teristics for a typical A.C. gas panel arrangement wherein the panel is driven with voltage pulses having substantially no, or very little, risetime. It is to be understood, that the plot of FIG. 3 is not necessarily to scale, but is merely depicted to show the general manner in wich the ionizable gas behaves with increasing applied voltages. As can be seen, the general relationship is such that ionization of the gas and voltage breakdown thereacross occurs more quickly with increasing magnitudes of the applied voltage V,,. Thus, for the lowest of the applied voltages it can be seen that the voltage drop across the gas V, does not break down until the voltage has been applied for around 3.0 1.1. See.

6 On the other hand, with application of the highest of the applied voltages shown in FIGv 3, the voltage drop across the gas V, breaks down significantly more quickly, i.e. after approximately 2.0 t Sec. of applied voltage.

It is to be noted that the discovered trend plotted in FIG. 2 is representative of what occurs with applied voltages having risetimes within the range of 1.8 to 2.2 p. Sec., while the breakdown characteristics shown in FIG. 3 are representative of what occurs with applied voltage pulses having negligible risetimes. The purpose of introducing risetimes of from 1.8 to 2.2 a See. will be more fully explained hereinafter. Suffice it to say at this point that the trend shown in FIG. 2 would also hold true with applied voltage pulses having a negligible risetime, but the expanded operating margin would occur at frequencies around 200 K Hz, i.e. ISO to 220 K Hz. In this regard, FIG. 4a shows the voltage breakdown characteristics as a function of time, for a mixture of neon and argon gas, for various amplitudes of the applied voltage pulses V As depicted in FIG. 4b, the voltage pulses V,, have a risetime of approximately 2 t See.

With reference to FIG. 4a, it can be seen that for voltages close to the threshold of the gas, a long buildup time is required, and any charge transfer which occurs takes place about 15 p Sec. after the application of the voltage. In particular, it can be seen that with I I0 V of applied voltage V,,, no breakdown is seen to occur. With US V of applied voltage current begins to flow and the charge transfer takes place at around 13 1. Sec., with a final steady state value for V, reached at approximately 15 p. See. It is evident, that as the drive voltage V, is increased, the charged build-up time becomes shorter and a final steady state value for V, is reached much sooner.

In accordance with the results depicted in FIG. 2, it can be seen that with the application of approximately 2 p. Sec. risetime pulses the operating margin begins to improve at around 35 K Hz and continues on up pass K Hz. Alternating voltage pulses within this frequency range exhibit half cycle time durations within the time range shown in FIG. 4a. Thus, FIG. 2 indicates that an improved operating margin may be achieved by utilizing alternating voltage pulses which have time durations between approximately I5 and 6 ,1 Sec.

It is the purpose of the present invention, then, to drive gas discharge display and memory devices with alternating sustain voltage pulses within a frequency range of between approximately 40 K Hz and 80 K Hz. As can be seen with reference to FIG. 4a, alternating sustain voltage pulses within such a frequency range will cause the gas discharge display and memory device to operate within the range of breakdown points of the family breakdown points, for typically applied break down voltages. Stated in another way, it is the purpose of the present invention to operate a gas discharge display and memory device such that the alternating sustain voltage pulses terminate as close as possible to the points of maximum current incident gas ionization. By operating the panel with alternating sustain pulses whose duration, and therefore frequency, is such as to terminate before the point of breakdown for the lower applied voltages, i.e. the lower sustain voltages, there is a virtual raising of the breakdown threshold, ie the maximum sustain voltage, V Max. Thus, with reference to FIG. 4a, a 50 K Hz alternating sustain pulse will terminate at around 10 ;1. Sec. As can be seen, this is 7 the region where current flow terminates for the higher of the applied sustain voltage pulses and where no current as yet had an opportunity to flow for the lower of the applied sustain voltages. Thus, in effect, the lower of the applied sustain voltage pulses can not sustain ionization.

The manner in which the operating margin is in creased by utilizing frequencies that effect a termination of the alternating sustain voltage pulses within the region of breakdown can be seen more clearly with reference to the charge transfer curve shown in FIG. 5. Using the voltage values in FIG. 4a at 15 p. Sec., the curve labeled 33 K Hz results. As can be seen, at 15 u Sec. charge transfer occurs as soon as the threshold is exceeded. However, if a transfer curve is derived from the results of FIG. 4a at u Sec, little charge transfer occurs until the voltage has been increased to about 120 volts, as can be seen by the curve labeled 50 K Hz. In this regard, it should be noted that the operating margin for the p, Sec. (33 K Hz) curve is defined by the intercepts of slope lines M and M Likewise, the operating margin for the l0 1. Sec. (50 K Hz) curve is defined by the intercepts of slope lines M and M 4. Each of these lines is taken at a point where the tangent to the curve has a slope of 2, a slope of 2 defining the steady state points of operation where equal charge transfer exists over every cycle of operation. As can be seen in FIG. 5, by using the 10 p. Sec. alternating sustain pulses, i.e. a 50 K Hz alternating signal, the point where charge transfer commences (at the intercept of M which corresponds to V Max.) is considerably raised, while the point where charge transfer terminates (at the intersect of M. which corresponds to V Min.) is only incrementally raised. Accordingly, the operating margin in this example is increased by approximately 100 percent.

In the plot of FIG. 3, the region of breakdown typically extends between approximately 2 p. Sec. and 3 p. Sec. On the other hand, typical alternating sustain pulse operation in the prior art utilizes sustain pulse frequencies anywhere from to K Hz which correspond to pulse durations of between 20 Sec. and 14.3 p. See. For the exemplary characteristics shown in FIG. 3 wherein negligible risetime is present, effective operation, in accordance with the principles of the present invention, would be achieved by utilizing sustain pulses which terminate at around 2.5 ;.t See. As can be seen, in a manner similarly described with reference to FIG. 4a, at this point the lower magnitude sustain pulses will not act to breakdown the ionizable gas since they will terminate before such occurs, and thus V Max. is increased. However, it should be appreciated that a 2.5 p. Sec. pulse corresponds to a 200 K Hz alternating sustain signal, and alternating sustain signals at this frequency level act to maintain ionization of the gas con tinuously, i.e. do not permit deionization between firings. It is evident that alternating sustain pulses which do not permit deionization cannot be employed, since under such conditions an ionized cell cannot be erased. Accordingly, operating gas discharged display and memory devices with sustain pulses which terminate within the region of gas breakdown and maximum current, in accordance with the principles of the present invention, cannot be realized utilizing sustain pulses with little or no risetime since such operation would require sustain pulse frequencies too high to permit deionization.

The above mentioned difficulty is overcome, in accordance with the principles of the present invention, by the technique of obviating the need for such high frequencies by utilizing pulses with a relatively slow risetime. The effect of using a relatively slow risetime pulse is to reduce the ionization rate, and therefore delay ionization. By delaying ionization, the general region of ionization and gas breakdown is sufficiently shifted, time-wise, to a point on the frequency scale which permits deionization between pulses and, accordingly, optimum operation.

It has been found, in accordance with the teachings and principles of the present invention, that sustain pulse risetimes of between [.8 and 2.2 p. Sec. effectively achieve the desired results whereby the alternating sustain pulses effectively terminate within the region of ionization, at frequencies which permit deionization. In this regard, it should be noted that at sustain pulse risetime greater than 2.2 p. Sec., ionization is suf ficiently weak such that visibility of discharge is inadequate. At risetimes below 1.8 t See, gas breakdown occurs after such a short time interval, as hereinabove indicated, that the frequency required to terminate pulses within the range of this interval is too high to permit deionization.

Although, in accordance with principles of the present invention, alternating sustain pulses having a frequency between 40 K Hz and 80 K Hz may be used, it is clear that the better results are achieved at the upper end of the frequency range, i.e. at the higher frequencies. This is brought out by the plot of FIG. 2 wherein it can be seen that the best operating margin is up around 80 K Hz. Depending upon the particular perameters employed in a given device, such as gas mixture and pressure, the higher frequencies are selected so long as the condition of non-deionization is not encountered. For the particular neon'argon gas panel arrangement hereinabove describe, alternating sustain pulse signals having a frequency of approximately 80 K Hz have been found to provide the best operating margin, while at the same time sufficiently avoiding the condition of non-deionization. However, as can be seen from FIG. 2, alternating sustain pulse signals of 60 and K Hz also provide nearly as good an operating margin. In this regard, it should be noted that the 50 K Hz charge transfer characteristic shown in FIG. 5 was depicted merely to show the manner by which the operating margin is improved, as compared to, for example, the 33 K Hz charge transfer characteristic. It is evident, that the charge transfer characteristics for signals higher than 50 K Hz would generally follow the 50 K Hz characteristic, somewhat to the right thereof. However, the percentage improvement in operating margin between the 33 K Hz charge transfer characteristic and the 50 K Hz charge transfer characteristic is the most significant in this example, and the same percentage improvement in operating margin would not necessarily be obtained by increasing the frequency the same number of K Hz upwardly from the 50 K Hz transfer characteristic.

In accordance with the principles of the present invention, then, alternating sustain signals having a frequency between 40 K Hz and K Hz and a risetime between 1.8 p. Sec. and 2.2 p. See, are employed to drive an AC. gas discharge display and memory panel. Typically, the gas discharge display and memory panel may comprise a neon-argon mixture of, for example, neon plus 0.001 argon, at a pressure of, for example,

9 600 Torr. The manner of driving an AC. gas discharge display and memory device with sustain pulses, in accordance with the principles of the present invention, may be implemented in the manner shown in FIG. I. As depicted there, a complementary output square-wave pulse oscilator 17 is employed to generate equal duration, out-of-phase, square waves pulses, as shown. The positive output pulse signal shown between T, and T is referenced to ground. Likewise, the negative output pulse produced simultaneously with this positive output pulse is referenced to ground. Square-wave oscilator 17 produces pulses with negligible risetime. It is evident, that each of the output pulses has the same pulse duration, with this duration being selected anywhere from approximately 6 to 12 p. Sec.

Wave shapers l3 and 15 respectively act upon the complementray square-wave outputs from oscilator 17 to introduce equal risetimes therein. As hereinabove mentioned, the risetimes introduced by wave shapers l3 and 15, although equal, may be anywhere between L8 and 2.2 u Sec. Although for convenience of explanation the arrangement of FIG. 1 shows introducing the risetimes in a separate operation, it is clear that a single generator may be employed to produce the alternating sustain signal of both selected frequency and selected risetime. It is also evident that other write-erase schemes may readily be employed, as is familiar to those skill in the art, rather than the arrangement shown in FIG. 1. In this regard it should be noted that the exact manner by which the write-erase pulses are superimposed upon the sustain pulses is not a part of the present invention, the present invention being primarily directed to the manner and means by which sustain-type pulses are generated and applied to the gas discharge display and memory device.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

I claim:

1. A method of operating the sustain function of a gas discharge display and memory panel to increase the operating margin thereof, said panel having substantially orthogonal sets of insulated X and Y conductors arranged so that the respective crossover points thereof form an array of memory cells selectively addressable by application of read and write pulses to appropriate 10 X and Y conductors, the improvement comprising the steps of;

applying alternating polarity sustain pulses between said sets of X and Y conductors at a frequency be tween 40 and K Hz; and

causing the said alternating polarity sustain pulses applied between said sets of X and Y conductors to be applied between said sets of X and Y conductors with a risetime between 1.8 and 2.2 u Sec.

2. The method as set forth in claim 1 wherein said frequency is approximately 80 K Hz and said risetime is approximately 2 u Sec.

3. In a system for driving a gas discharge display and memory panel having rows and columns of insulated conductors which cross one another to form a matrix of memory cells, said system for driving including sustain circuit means for applying alternating sustain voltage pulses between selected ones of said rows and columns of said insulated conductors with said pulses being applied at one phase to selected rows of said conductors and at opposite phase to selected columns of said conductors, the improvement comprising;

circuit means included in said sustain circuit means for providing said alternating sustain voltage pulses with a frequency between 40 K Hz and 80 K Hz; and

means included in said circuit means for providing said alternating sustain voltage pulses with a risetime between L8 and 2.2 t See.

4. in a gas discharge display and memory panel system having driving circuitry for applying opposite phase alternating sustain pulses to row and column arrays of insulated conductors with said row and clumn arrays of insulated conductors being in spaced-apart relationship and crossing in an ionizable gas to form a matrix array of memory cells, the improvement comprising,

means for producing said alternating sustain pulses at an operating frequency between 40 and 80 K Hz so that said pulses terminate at the approximate time the ionization current flow of said ionizable gas in said panel terminates and means for causing said alternating sustain pulses to have a risetime between l.8 and 2.2 ,4 Sec. so as to delay ionization buildup and said ionization current flow therein such that the said operating frequency of said sustain pulses is low enough to permit deionization of said ionizable gas, whereby the operating margin of said panel is improved without loss of addressability.

I. 4 1.! l 1b

Claims

1. A method of operating the sustain function of a gas discharge display and memory panel to increase the operating margin thereof, said panel having substantially orthogonal sets of insulated X and Y conductors arranged so that the respective crossover points thereof form an array of memory cells selectively addressable by application of read and write pulses to appropriate X and Y conductors, the improvement comprising the steps of; applying alternating polarity sustain pulses between said sets of X and Y conductors at a frequency between 40 and 80 K Hz; and causing the said alternating polarity sustain pulses applied between said sets of X and Y conductors to be applied between said sets of X and Y conductors with a risetime between 1.8 and 2.2 Mu Sec.

2. The method as set forth in claim 1 wherein said frequency is approximately 80 K Hz and said risetime is approximately 2 Mu Sec.

3. In a system for driving a gas discharge display and memory panel having rows and columns of insulated conductors which cross one another to form a matrix of memory cells, said system for driving including sustain circuit means for applying alternating sustain voltage pulses between selected ones of said rows and columns of said insulated conductors with said pulses being applied at one phase to selected rows of said conductors and at opposite phase to selected columns of said conductors, the improvement comprising; circuit means included in said sustain circuit means for providing said alternating sustain voltage pulses with a frequency between 40 K Hz and 80 K Hz; and means included in said circuit means for providing said alternating sustain voltage pulses with a risetime between 1.8 and 2.2 Mu Sec.

4. In a gas discharge display and memory panel system having driving circuitry for applying opposite phase alternating sustain pulses to row and column arrays of insulated conductors with said row and clumn arrays of insulated conductors being in spaced-apart relationship and crossing in an ionizable gas to form a matrix array of memory cells, the improvement comprising, means for producing said alternating sustain pulses at an operating frequency between 40 and 80 K Hz so that said pulses terminate at the approximate time the ionization current flow of said ionizable gas in said panel terminates and means for causing said alternating sustain pulses to have a risetime between 1.8 and 2.2 Mu Sec. so as to delay ionization buildup and said ionization current flow therein such that the said operating frequency of said sustain pulses is low enough to permit deionization of said ionizable gas, whereby the operating margin of said panel is improved without loss of addressability.