US3793628A

US3793628A - Electroluminescent display device

Info

Publication number: US3793628A
Application number: US00285734A
Authority: US
Inventors: J Gaur
Original assignee: Ncr
Current assignee: NCR Voyix Corp
Priority date: 1972-09-01
Filing date: 1972-09-01
Publication date: 1974-02-19
Anticipated expiration: 1991-02-19
Also published as: AU5936673A; DE2342792C2; CA1005551A; FR2198251A1; DE2342792A1; GB1423873A; ZA735523B; BE804266A; JPS4968691A; NL7311646A; FR2198251B1; CH578222A5; JPS5918713B2; IT993129B; AU473280B2

Abstract

An electroluminescent display device wherein a matrix of column and row conductors is formed with electroluminescent cells interconnecting the juncture of rows and columns. Means are provided for connecting selected rows and columns to a source of voltage in a particular sequence whereby the cell positioned at the juncture of a selected column and row is caused to luminesce during each selected period while all non-selected cells are inhibited to fire except only once during the entire period of operation of displaying a pattern on the device.

Description

Unite States Patent [1 1 Gaul Feb. 19, 1974 [5 ELECTROLUMINESCENT DISPLAY 3,668,688 6/1972 Schmersal 340/324 M DEVICE 3,673,460 6 1972 Johnson et al. 315/169 R [75] Inventor: Jai P. Gaur, Dayton, Ohio Primary Examiner David L Trafton [73] Assignee: The National Cash Register Attorney, Agent, or FirmJ. T. Cavender; Albert L.

Company, Dayton, Ohio Sessler, Jr.; Edward Dugas [22] Filed: Sept. 1, 1972 [57] ABSTRACT [21] APPL 285,734 An electroluminescent display device wherein a matrix of column and row conductors is formed with 52 Cl 340/324 M, 315/169 R electroluminescent cells interconnecting the juncture 51 Int. Cl. G08b 5/36 of rows and columns- Means are Provided for connect- [58] Field of Search 340/324 M, 343, 344; ing Selected rows and columns to a Source Of voltage 315/169 R, 169 TV in a particular sequence whereby the cell positioned at the juncture of a selected column and row is caused to 56 References Cited luminesce during each selected period while all non- UNITED STATES PATENTS selected cells are inhibited to fire except only once 3 6 296 10,197 J h 340/166 during the entire period of operation of displaying a 0 nson 3,334,269 8/1967 Heureux 340 324 M x pattern on the devlce 3,614,739 l0/l971 Johnson 340/166 R 20 Claims, 17 Drawing Figures r {l VOLTAGE 30V 23 i 22 270 SOURCE a $2 A J COLUMN B .44 f a" 02 SELECTOR Q12 .Q L 2 f 29 E D l k 27b J25d J if 01 TWO f PHASE IL GEI I SA T EDR Yea I 24 o-l 1 E --1 W i ROW T7 27d SELECTOR 25b t CELL 2 MATRIX H 28 I 25o l 2o 4 PAIIEIIIEIIFEBI Y 3.793.628

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ELECTROLUMINESCENT DISPLAY DEVICE BACKGROUND OF THE INVENTION The present invention relates generally to display or data storage systems which are comprised of a matrix of electroluminescent cells. More particularly, the invention relates to a novel system for selectively lighting a particular cell in the matrix while minimizing the lighting of all non-selected cells. A particular phenomenon is encountered when gas cells are used as the electroluminescent source. When an electric field of sufficient magnitude is applied to an electroluminescent cell of the gas type, ionization of the gas (gaseous discharge) occurs within the cell, which causes positive charges to be deposited on the dielectric material covering the cathode, and electrons to be deposited on the dielectric material covering the anode. The charges deposited on the walls are trapped because of the capacitive coupling effect exerted by the cell walls and electrodes. Since positive ions are attached to the cathode wall and electrons are attached to the anode wall, the wall charge will be of a polarity opposite to that of the electric field which instigated the gas discharge. Therefore, after a discharge the total voltage impressed on the cell will be the algebraic sums of the voltage applied to the cell plus the voltage contributed by the wall charge. The gas discharge which occurs in the cell continues until the wall voltage builds to a value point where the applied voltage can no longer sustain ionization, and the cell turns off. In order to ignite the cell again using the same magnitude of applied voltage, it is necessary to reverse the polarity of the applied voltage. Because the wall charge is trapped within the cell, the wall voltage will always oppose the voltage which initiated the gas discharge. The major problem associated with the use of gas cells in a display matrix is the firing of the unselected cells due to the fact that a voltage is supplied to one side of the unselected cell.

A prior art system for utilizing electroluminescent cells in an X-Y display matrix is disclosed in U. S. Pat. No. 3,343,128, entitled Electroluminescent Panel Driver Circuit" by Raymond 1. Rogers.

The above prior art system uses a means for applying suppression pulses to the unselected rows of the matrix. This results in a potential difference at the cross-over point of the unselected row and selected column, which is insufficient to ignite the cell interposed at the particular cross-over point. That approach requires complex circuitry.

Another form of control is the half-select mode, in which one half of the necessary voltage is applied to one side of the gas cell and the other half is applied to the other side thereby effectively applying a full voltage across the selected cell.

Again this scheme requires complex circuitry because each side of the cell has to float to half of the total voltage required to fire the cell.

. Another prior art patent of interest is U. S. Pat. No. 3,636,405, entitled Split Electrode Gas Cell by, William L. Cotter, wherein each cell of the matrix is provided with a split anode. A sustaining voltage is applied across a cathode and one of the anodes. Selective application of a positive pulse to one anode and a negative pulse to the other anode causes the cell to fire.

Th extra construction required in the cell increases the cost of each cell, thereby offsetting the advantages to be gained by that approach.

Another prior art device of interest is disclosed in U. S. Pat. No. 3,614,769 entitled Full Select-Half Select Plasma Display Driver Control by, William E. Coleman et al., wherein the problem of non-selected cell ignition is partially solved. The device of that patent operates by alternately connecting a selected row to a firing voltage and to a reference voltage such as ground. while alternately connecting a selected column to the referenced voltage and to a firing voltage. The referenced driving technique limits the firing of nonselected cells to ignite only twice during each cycle of scanning all the columns. Even though this ignition occurs only twice during a cycle of scanning all the columns, it can still be observed in a darkened room so as to detract from the purity of the selected cells. The present invention completely solves this problem of visual detection of non-selected cells.

SUMMARY OF THE lNVENTlON ln one embodiment of the present invention there is provided a display device wherein a matrix is formed using crossed rows and columns'of conductors and a plurality of electroluminescent cells connecting the rows and columns at their crossover points.

A voltage source is provided for igniting the cells. A first means is provided for cyclically connecting a selected column in circuit with the voltage source at a fixed frequency.

An additional means is provided for cyclically connecting a selected row and all non-selected columns in circuit with the voltage source at the fixed frequency, shifted in phase so as to minimize the luminescence of the non-selected cells to a level below human detection.

In a second embodiment of the invention, the first means for cycling connects a selected column in circuit with the voltage source at the fixed frequency while connecting all the non-selected columns to a reference potential, such as ground. The additional means for cycling connects a selected row in circuit with the voltage source at the fixed frequency, shifted in phase while connecting all non-selected rows to the voltage source. The above sequence of connection of the voltage source to the selected, and non-selected rows and columns insures that the selected cell will ignite while the non-selected cells are not ignited.

From the foregoing it can be seen that a principal object of the present invention is to provide an improved display matrix wherein only the electroluminescent cell chosen by row and column selection is visibly lit.

Another object of the present invention is to provide a device for selecting individual cells of a display matrix for illumination without visually illuminating any of the non-selected cells.

It is a further object of the present invention to provide an improved display device.

These and additional objects of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein form a part of the present invention.

BRIEF DESCRIPTION OF THEDRAWINGS FIG. I is a sectional view of a plasma cell that can be utilized with the present invention;

FIG. 2 is a schematic representation of a plurality of cells connected to a common column;

FIGS. 3a and 3b are clocked signals which are selectively applied to the plurality of cells shown in FIG. 2;

FIGS. 40 to 4e illustrate the proper application of the clock signals as per a first method of operation;

FIGS. 5a to 5e illustrate the proper application of the clock signals as per a second method of operation;

FIG. 6 illustrates in block diagram form one embodiment of the invention;

FIG. 7 illustrates a sub-block which may be substituted for a sub-block in the block diagram of FIG. 6; and

FIG. 8 illustrates in block diagram form another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 represents an electroluminescent cell, of the gas discharge type, which may be used with the present invention.

The cell 10 is comprised of two glass members 11 and 12 which are bonded together to form a chamber 13. A gas 14 such as neon, is inserted into the chamber under pressure. Electrodes l5 and 16 are positioned on either side of the chamber 14. Terminals A and B are connected to the electrodes for applying a potential to the gas. When a potential of sufficient magnitude is applied across terminals A and B a discharge occurs in the gas 14. The electrons and ions created by the discharge will attach to the anode and cathode sides of the glass members respectively, so as to produce a wall charge. The voltage attributed to the wall charge has a polarity opposite to that of the applied voltage which caused the discharge. When the wall charge builds to a certain level the cell can no longer sustain the discharge and the cell turns off. Upon reversal of the applied voltage another discharge occurs. This discharge occurs because the wall charge adds directly to the reverse applied voltage. For efficiency the voltage level of the alternating applied signal can be decreased to a lower value, which value when added to the wall charge will cause a discharge. By continually reversing the applied voltage the cell can be continuously lit (ignited). By maintaining the frequency of alternations high enough, the cell, to the human eye, will appear to be lit continuously. In general, the frequency of alternation is maintained substantially above 60 cycles/sec. In an operable embodiment of the system the voltage applied across the cell was approximately 250 volts and the gas mixture of neon, nitrogen, and argon at a pressure of 200 millimeters of mercury.

For ease of manufacture and utility, the cell of FIG. I is modified to contain a plurality of electrodes, with the group of electrodes positioned on one side of the cell being designated row electrodes and the group positioned on the opposite side being called the column electrodes.

FIG. 2 schematically represents a cross section of a cell wherein one column is shown as being common to four rows. The use of four rows is by way of example only, and either more or less rows or columns may be used as desired.

FIGS. 3a and 3b illustrate a continuous two phase clock signal which can be used with the present embodiments. The signal shown corresponds to only one time slot T, and is identical for all remaining time slots. The +V potential is of sufficient magnitude to cause the cell to fire if the wall charge is not opposed. One phase of the clock signal is designated (1),, with the out of phase signal having the designation Analog quadrative phased signals could also be used effectively in place of the digital clocks.

To explain the first scheme of preventing visible firing of unselected cells if FIG. 2 is now examined in combination with the wave forms of FIGS. 40 to 4e, the first scheme will be easier to understand. In FIG. 40 there is shown the voltages which are applied to column 1 for one scan cycle. The cycle is comprised of eight time slots, labeled T, to T inclusive. Each time slot is normally assigned to a particular column, therefore the arrangement of FIG. 4 would be used with a total of eight columns, even though only one is shown for simplicity. The technique is applicable to any number of columns or rows. T, would therefore be assigned to column 1, T to column 2, etc.... When column I is selected in its corresponding time slot T, the clocked signal (I), is applied to the column conductor. At all other non-select times the voltage on the column conductor is 45,. Whenever any row is selected, the clocked signal (1:, is applied to the row conductor; otherwise its voltage is maintained at +V.

There are four possible conditions of row selection and non-selection. Each condition is set forth in the following cases:

Case I Row 1 is never selected.

Since the row 1 is never selected, the applied voltage to it is +V. The very first pulse 4), or (b, on the column side fires the virgin cell once and deposits a positive charge on the column side and a negative charge on the row 1 side. The polarity of this charge is such as to oppose the applied field during the time when 4), and 11 are applied to the column side and, therefore, this cell never fires again.

Case II Row 2 is not selected during the selection time of this column (T,), but it is selected some other time (T, and T In this case the cell fires once with the very first pulse or 4: on the column side and when the row 2 is at +V. The wall charge deposited by this firing always opposes the applied field, except when row 2 is selected. It should be noted that when row 2 is selected in some other columns, the applied voltages on the two sides of this cell are in phase so the wall charge is not destroyed. Therefore this cell remains always charged and inhibits any more firing during the rest of the time.

Case III Row 3 is full selected in this column (T,), never selected in other columns. In this case the selected cell fires back and forth starting with the first pulse, 42, or that occurs during the selection time.

After the completion of the selection time the cell is left with positive charge on the row side and negative charge on the column side. The very first pulse dz, on the column side after the selection time fires the cell once and this reverses the polarity of the charge, which prohibits further firing of the cell in the unselected time. However, because of the polarity of this charge,

the cell does skip a firing with the first 4), pulse in the next selected time. Therefore the total number of times the selected cell fires remains unchanged.

Case Iv Row 4 is full selected in this column (T and is also selected in some or all other columns (T T and T As in Case III, during the selected time the cell fires back and forth. The last pulse in the selected time leaves the row side with a positive charge. If this row is selected by all other columns, then this charge polarity is not destroyed and the cell fires back with the first 4), pulse in the selected time. However, if this row is not selected in any one of the columns, the cell will fire once in that time duration, but skip one firing in its next selected time. Therefore the total number of times the selected cell fires remains unaltered.

From these four cases it is clearthat irrespective of the type of data i.e., mode of selection of rows, the unselected cells fire only once during the entire time of displaying the data, whereas the number of times the selected cells fire remains the same.

In some applications of the first scheme utilizing MOS devices there are substantial delays introduced into signals which have traversed different MOS paths. When these signals are later used to control a switch or switches they may cause undesirable overlapping in the off-on times of the switches. This undesirable overlapping could, when using the first system, cause the unselected cells to visibly fire; therefore a second scheme which eliminates all possibility of having a visible firing of the unselected cells is set forth with the wave forms of FIGS. 5a to 52. The only change in this second scheme as compared to the first scheme is to the column voltage. During the selection time the voltage is still dz but at all other times the voltage is placed at 0 or ground. Again setting out the four cases corresponding to row signal condition:

Case 1 Row 1 is never selected.

When a row is not selected or there is no data on the row line, its voltage is +V. The very first pulse 4), on the column side fires the virgin (uncharged) cell and deposits a positive charge on the column side and a negative charge on the row side. The field produced by this charge is opposite to the applied field at other times and therefore this cell never fires again.

Case I] Row 2 is not selected during the selection time (T of Column 1, but it is selected in other columns (T and T In this case the cell fires once when (1;, is applied to Column 1. The field produced by this wall charge op poses the applied field except when 4: is applied to the row side. It should be noted that when o is applied to the row side, either there is no applied field or the applied field is opposite to that of the wall charge. So long as the equivalent voltage of the wall charge does not exceed the firing voltage, the cell cannot fire back when there is no applied field. Hence this cell remains charged and inhibits any more firing during the rest of the time.

Case Ill Row 3 is full selected in Column 1 and is never selected in other columns.

During the selection time the cell fires back and forth and after the selection time the cell fires once again when the. column is grounded. This leaves the cell charged such as to oppose the applied field during the rest of the cycle and thus prohibits further firing of the cell. However, due to the polarity of the wall charge, the cell skips one firing with the first (1), pulse on the column side at the beginning of the next cycle and then fires back and forth. Therefore, the total number of times the cell fires remains unchanged.

Case IV Row 4 is full selected in Column 1 as well as in some other columns.

As in the previous case, the first grounding pulse after the selected time leaves the row side negatively charged and the column side positively charged. When this row is also selected in some other columns, the field due to the wall charge never adds to the applied field and the cell never fires back during the rest of the scan cycle. As in the previous case, the cell skips one firing in the selected time and the number of times the selected cell fires remains unaltered.

Again from the above it is clear that irrespective of the type of data on the row side or the mode of selecting rows, the unselected cells fire only once during the entire time of displaying the data, whereas all the selected cells fire an equal number of times. Therefore the brightness of all the selected cells is uniform over the entire matrix.

Referring now to FIG. 6 wherein a first embodiment of the switching technique of the first scheme as set forth in FIGS. 4a to 4e is shown; a matrix 20 is comprised of a plurality of row conductors 22, crossing a plurality of column conductors 21, with electroluminescent cells 10 connecting each of the crossing rows and columns at their juncture points.

A first bank of switches 26 operates to alternately connect each of the rows between a common point (ground) and the positive terminal of voltage supply 24. The other terminal of voltage supply 24 is connected to the common point. A two phase signal generator 29 provides two signals, (11, and (1, which are separated in phase by Other phase relationships may be used as long as an overlapping condition is avoided. A row select or 28 passes the signal (1) to a corresponding row select switch in bank 26. The selected switch is then alternated at the frequency of signal 41 thereby alternately connecting the selected row to the +V source and to the common point. The non-selected switches remain in the +V position.

A second bank of switches 23 operates to alternately connect each of the columns to the common point and the +V source.

The column select or 30 receives as inputs the 4:, and signals from the two phase clock generator 29. When a column is selected the 4), signal is fed to the switch connected to the selected column while all nonselected columns are fed the i12 signal. The selected columns (in this case the one served by switch 25d) will have the waveform shown in FIG. 4a applied to it while the selected row will have the waveform shown in FIG. 4d applied to it.

In FIG. 7 a first embodiment of the second scheme is shown, wherein, the column select or 31 can be substituted for the column select-or 30 in FIG. 6 by attaching its output leads to the corresponding switchlines labeled A, B, C or D. Column select or 31 receives the signal and feeds this signal to any selected column. All non-selected columns are maintained in thecommen or ground position.

The switches shown in the first and second bank are shown with mechanical arms. It would be obvious to a person skilled in the art that electronic switches could be used to achieve greater speed.

Referring now to FIG. 8 wherein a second embodiment of the first scheme is shown, the matrix is shown comprised of seven row conductors 22 and eight column conductors 21. One end of each column and row conductor is connected by an impedance means 32 to the positive terminal +V ofa two terminal supply 24..

Electroluminescent cells 10 interconnect column and row conductor at each crossover point.

A first bank 40 of driver switches 43 operates to connect selected rows to the negative terminal of supply 24. Each switch 43 in bank 40 is an NPN transistor, the collector of which is connected to the end of the row conductor opposite the end connected to the impedance means, with the emitter being connected to the negative terminal of supply 24, and the base being connected to one of the outputs of a binary to seven row decoder 44. In operation a positive signal on the base of transistor 43 will turn it on, connecting the selected row in circuit with the supply 24.

An identical bank 41 of driver switches is provided for column selection.

For row selection, input data is fed to a data timing control block 45 by means of a buffer circuit 46. The input data can for example come from a card reader or manual key selector. The data timing control circuit 45 and column selector 49 are provided with the same control signal from the binary counter 50 so as to load the desired data in the selected column. The binary counter 50 receives as its input the signal 4), from the two phase generator 29. The counters output is a repeating signal that is synchronized to the signal 4),. The repeating signal causes the column selector to sequentially scan all of the columns periodically at a frequency less than the frequency of the two phase signals, but greater than a frequency that is visible to the human eye. When a particular column is selected the ANDing circuit 48 feeds the signal dz, to the selected column driver, and the signal 4, to all the non-selected column drivers. In a similar manner the binary to seven row decoder feeds the signal 95 to the selected row driver while maintaining all other driver switches in the off position.

The second embodiment of FIG. 8 can be modified for the second scheme by not feeding the 4),; signal to the ANDing circuit 48 so that the non-selected column drivers are maintained in an on condition, with the selected column driver receiving the second phase signal While there has been shown what are considered to be preferred embodiments of the invention the same has been by way of example only and not by way of limitation, with the scope of the invention being limited only by the scope of the claims.

What is claimed is: I. A display device comprising in combination: a plurality of row conductors; a plurality of column conductors forming a matrix with said plurality of row conductors; a plurality of electroluminescent cells connecting rows to columns at their crossover points; a voltage source, the voltage level of which is sufficient to initially cause luminescence in a cell;

means for cyclically connecting a selected column in circuit with said voltage source at a fixed frequency; and

means for cyclically connecting a selected row and all non-selected columns in circuit with said voltage source at said fixed frequency shifted in phase so as to minimize luminescence of non-selected cells.

2. The display device according to claim I wherein said voltage source is a two terminal source, one terminal of which is connected to one end of said column and row conductors, and the other terminal of which is connected to each of said means for cyclically connecting.

3.'The display matrix according to claim 1 wherein said electroluminescent cells are comprised of an insulating envelope containing an ionizable medium, and at least one pair of insulated electrodes positioned for ionizing the medium when a voltage level commensurate with the ionization voltage of said medium is applied across a pair of electrodes, such that the ionization of said medium causes a wall charge to be attached to the interior wall surfaces of said insulating envelope.

4. The display device according to claim 1 wherein said means for cyclically connecting are operated at a fixed frequency which is sufficiently high so as to prevent visual detection of flicker in the selected electroluminescent cell.

5. An electroluminescent display matrix comprising in combination:

a plurality of row conductors;

a plurality of column conductors forming a matrix with said plurality of row conductors;

a plurality of electroluminescent cells connected between the crossings of row and column conductors;

a two terminal voltage source, one terminal of which is connected to a common point;

a first bank of switches for individually connecting each row conductor alternately between the common point and the other terminal of said voltage source;

a second bank of switches for individually connecting each column conductor alternately between the common point and the other terminal of said voltage source;

means for providing two phase clock signals;

means for alternating a selected switch in said second bank in response to said clock signal of one phase, while alternating all non-selected switches in said second bank in response to said clock signal of a second phase;

means for alternating a selected switch in said first bank in response to said clock signal of second phase, while'maintaining all non-selected switches in said first bank connected to the other terminal of said voltage source, so as to cause the electroluminescent cell connected between the selected row and column to luminesce as alternate potentials are applied across said cell, while minimizing the luminescence of non-selected cells.

6. The display matrix according to claim 5 wherein said electroluminescent cells are comprised of an insulating envelope containing an ionizable medium, at least one pair of insulated electrodes positioned for ionizing the medium when a voltage level commensurate with the ionization voltage of said medium is applied across a pair of electrodes, such that the ionization of said medium causes a wall charge to be attached to the interior wall surfaces of said insulating envelope.

7. The display device according to claim wherein the frequency of the two phase clock signal is sufficiently high so as to prevent visual detection of flicker in the selected electroluminescent cell.

8. An electroluminescent display matrix comprising in combination:

a plurality of row conductors;

a voltage source for providing a voltage level commensurate with the ignition voltage of said cells;

impedance means connecting said voltage source to one end of each of said row and column conductors;

a first bank of switches for individually connecting each of said row conductors in circuit with said voltage source;

a second bank of switches for individually connecting each of said column conductors in circuit with said voltage source;

a two phase signal source;

means for applying one phase of said two phase signal to each switch in said second bank, to alternately close and open each switch at the signal frequency;

means for applying the one phase of said two phase signal to the selected switch of said first bank of switches; and means for disconnecting the one phase signal from the selected switch in said second bank of switches, and for connecting the other phase signal to the selected switch so as to cause said electroluminescent cell connected between the selected row and column to be alternately connected in circuit with said voltage source causing said electroluminescent cell to alternately ignite for every alternation of the selected switches.

9. The electroluminescent display matrix according to claim 8 wherein said electroluminescent cells are comprised of an insulating envelope containing an ionizable medium, and at least one pair of insulated electrodes positioned for ionizing the medium when a voltage level commensurate with the ionization voltage of said medium is applied across a pair of electrodes, such that the ionization of said medium causes a wall charge to be attached to the interior wall surfaces of said insulating envelope.

10. The display matrix according to claim 8 wherein the frequency of the two phase signal is selected such that alternate ignitions of the electroluminescent cells appear continuous to the human eye.

11. A display device comprising in combination:

a plurality of row conductors;

a plurality of electroluminescent cells connecting rows to columns at their crossover points;

a voltage source, the voltage level of which is sufficient to initially cause luminescence in a cell;

means for cyclically connecting a selected column in circuit with said voltage source at a fixed frequency while connecting all non-selected columns to a reference potential; and

means for cyclically connecting a selected row in circuit with said voltage source at said fixed frequency shifted in phase while connecting all non-selected rows to said voltage source, so as to minimize luminescence of non-selected cells.

12. The display matrix according to claim 11 wherein said electroluminescent cells are comprised of an insulating envelope containing an ionizable medium, and at least one pair of insulated electrodes positioned for ionizing the medium when a voltage level commensurate with the ionization voltage of said medium is applied across a pair of electrodes, such that the ionization of said medium causes a wall charge to be attached to the interior wall surfaces of said insulating envelope.

13. The display device according to claim 11 wherein said means for cyclically connecting are operated at a fixed frequency which is sufficiently high so as to prevent visual detection of flicker in the selected electroluminescent cell.

14. An electroluminescent display matrix comprising in combination:

a plurality of row conductors;

means for providing two phase clock signals;

means for alternating a selected switch in said second bank in response to said clock signal of one phase while maintaining all non-selected switches in said second bank connected to said common point; and

means for alternating a selected switch in said first bank in response to said clock signal of second phase while maintaining all non-selected switches in said first bank connected to the other terminal of said voltage source so as to cause the electroluminescent cell connected between the selected row and column to luminesce as alternate potentials are applied across said cell, while minimizing the luminescence of non-selected cells.

15. The electroluminescent display matrix according to claim 14 wherein said electroluminescent cells are comprised of an insulating envelope containing an ionizable medium, and at least one pair of insulated electrodes positioned for ionizing the medium when a voltage level commensurate with the ionization voltage of said medium is applied across a pair of electrodes such that the ionization of said medium causes a wall charge to be attached to the interior wall surfaces of said insulating envelope.

16. The electroluminescent display matrix according to claim 14 wherein the frequency of said two phase clock signals is sufficiently high so as to prevent visual detection of flicker in the selected electroluminescent cell.

17. An electroluminescent display matrix comprising in combination:

a plurality of row conductors;

impedance means connecting the other terminal of said voltage source to one end of each of said row and column conductors;

a first bank of switches for individually connecting the opposite end of each of said row conductors to the common point;

a second bank of switches for individually connecting the opposite end of said column conductors to the common point;

means for providing two phase clock signals;

means for alternately closing a selected switch in said second bank in response to said clock signal of one phase while maintaining all non-selected switches in said second bank in the closed position; and

means for alternately closing a selected switch in said first bank in response to said clock signal of other phase while maintaining all non-selected switches in said first bank in the opened positions.

18. The electroluminescent display matrix according to claim 17 wherein said electroluminescent cells are comprised of an insulating envelope containing an ionizable medium, and at least one pair of insulated electrodes positioned for ionizing the medium when a voltage level commensurate with the ionization voltage of said medium is applied across a pair of electrodes, such that the ionization of said medium causes a wall charge to be attached to the interior wall surfaces of said insulating envelope.

19. The display matrix according to claim 17 wherein the frequency of the two phase signal is selected such that alternate ignitions of the electroluminescent cells appear continuous to the human eye.

20. A display device comprising in combination:

a plurality of row conductors;

a plurality of bistable display elements connecting rows to columns at their crossover points;

a first pulsating voltage source the voltage level of which is sufficient to cause said bistable display element to change state;

a second pulsating voltage source of the voltage level of which is sufficient to cause said bistable display elements to change state,said second source being out of phase with said first source;

means for connecting a selected column to said first pulsating voltage source; and

means for connecting a selected row and all nonselected columns to said second pulsating voltage SOUI'CC.

Claims

1. A display device comprising in combination: a plurality of row conductors; a plurality of column conductors forming a matrix with said plurality of row conductors; a plurality of electroluminescent cells connecting rows to columns at their crossover points; a voltage source, the voltage level of which is sufficient to initially cause luminescence in a cell; means for cyclically connecting a selected column in circuit with said voltage source at a fixed frequency; and means for cyclically connecting a selected row and all nonselected columns in circuit with said voltage source at said fixed frequency shifted in phase so as to minimize luminescence of non-selected cells.

2. The display device according to claim 1 wherein said voltage source is a two terminal source, one terminal of which is connected to one end of said column and row conductors, and the other terminal of which is connected to each of said means for cyclically connecting.

3. The display matrix according to claim 1 wherein said electroluminescent cells are comprised of an insulating envelope containing an ionizable medium, and at least one pair of insulated electrodes positioned for ionizing the medium when a voltage level commensurate with the ionization voltage of said medium is applied across a pair of electrodes, such that the ionization of said medium causes a wall charge to be attached to the interior wall surfaces of said insulating envelope.

5. An electroluminescent display matrix comprising in combination: a plurality of row conductors; a plurality of column conductors forming a matrix with said plurality of row conductors; a plurality of electroluminescent cells connected between the crossings of row and column conductors; a two terminal voltage source, one terminal of which is connected to a common point; a first bank of switches for individually connecting each row conductor alternately between the common point and the other terminal of said voltage source; a second bank of switches for individually connecting each column conductor alternately between the common point and the other terminal of said voltage source; means for providing two phase clock signals; means for alternating a selected switch in said second bank in response to said clock signal of one phase, while alternating all non-selected switches in said second bank in response to said clock signal of a second phase; means for alternating a selected switch in said first bank in response to said clock signal of second phase, while maintaining all non-selected switches in said first bank connected to the other terminal of said voltage source, so as to cause the electroluminescent cell connected between the selected row and column to luminesce as alternate potentials are applied across said cell, while minimizing the luminescence of non-selected cells.

7. The display device according to claim 5 wherein the frequency of the two phase clock signal is sufficiently high so as to prevent visual detection of flicker in the selected electroluminescent cell.

8. An electroluminescent display matrix comprising in combination: a plurality of row conductors; a plurality of column conductors forming a matrix with said plurality of row conductors; a plurality of electroluminescent cells connected between the crossings of row and column conductors; a voltage source for providing a voltage level commensurate with the ignition voltage of said cells; impedance means connecting said voltage source to one end of each of said row and column conductors; a first bank of switches for individually connecting each of said row conductors in circuit with said voltage source; a second bank of switches for individually connecting each of said column conductors in circuit with said voltage source; a two phase signal source; means for applying one phase of said two phase signal to each switch in said second bank, to alternately close and open each switch at the signal frequency; means for applying the one phase of said two phase signal to the selected switch of said first bank of switches; and means for disconnecting the one phase signal from the selected switch in said second bank of switches, and for connecting the other phase signal to the selected switch so as to cause said electroluminescent cell connected between the selected row and column to be alternately connected in circuit with said voltage source causing said electroluminescent cell to alternately ignite for every alternation of the selected switches.

11. A display device comprising in combination: a plurality of row conductors; a plurality of column conductors forming a matrix with said plurality of row conductors; a plurality of electroluminescent cells connecting rows to columns at their crossover points; a voltage source, the voltage level of which is sufficient to initially cause luminescence in a cell; means for cyclically connecting a selected column in circuit with said voltage source at a fixed frequency while connecting all non-selected columns to a reference potential; and means for cyclically connecting a selected row in circuit with said voltage source at said fixed frequency shifted in phase while connecting all non-selected rows to said voltage source, so as to minimize luminescence of non-selected cells.

14. An electroluminescent display matrix comprising in combination: a plurality of row conductors; a plurality of column conductors forming a matrix with said plurality of row conductors; a plurality of electroluminescent cells connected between the crossings of row and column conductors; a two terminal voltage source, one terminal of which is connected to a common point; a first bank of switches for individually connecting each row conductor alternately between the common point and the other terminal of said voltage source; a second bank of switches for individually connecting each column conductor alternately between the common point and the other terminal of said voltage source; means for providing two phase clock signals; means for alternating a selected switch in said second bank in response to said clock signal of one phase while maintaining all non-selected switches in said second bank connected to said common point; and means for alternating a selected switch in said first bank in response to said clock signal of second phase while maintaining all non-selected switches in said first bank connected to the other terminal of said voltage source so as to cause the electroluminescent cell connected between the selected row and column to luminesce as alternate potentials are applied across said cell, while minimizing the luminescence of non-selected cells.

17. An electroluminescent display matrix comprising in combination: a plurality of row conductors; a plurality of column conductors forming a matrix with said plurality of row conductors; a plurality of electroluminescent cells connected between the crossings of row and column conductors; a two terminal voltage source, one terminal of which is connected to a common point; impedance means connecting the other terminal of said voltage source to one end of each of said row and column conductors; a first bank of switches for individually connecting the opposite end of each of said row conductors to the common point; a second bank of switches for individually connecting the opposite end of said column conductors to the common point; means for providing two phase clock signals; means for alternately closing a selected switch in said second bank in response to said clock signal of one phase while maintaining all non-selected switches in said second bank in the closed position; and means for alternately closing a selected switch in said first bank in response to said clock signal of other phase while maintaining all non-selected switches in said first bank in the opened positions.

20. A display device comprising in combination: a plurality of row conductors; a plurality of column conductors forming a matrix with said plurality of row conductors; a plurality of bistable display elements connecting rows to columns at their crossover points; a first pulsating voltage source the voltage level of which is sufficient to cause said bistable display element to change state; a second pulsating voltage source of the voltage level of which is sufficient to cause said bistable display elements to change state,said second source being out of phase with said first source; means for connecting a selected column to said first pulsating voltage source; and means for connecting a selected row and all non-selected columns to said second pulsating voltage source.