US2892968A

US2892968A - Voltage responsive screen control methods and systems

Info

Publication number: US2892968A
Application number: US617739A
Authority: US
Inventors: Hartmut P Kallmann; Rosenberg Barnett
Original assignee: Research Corp
Current assignee: Research Corp
Priority date: 1956-10-23
Filing date: 1956-10-23
Publication date: 1959-06-30
Anticipated expiration: 1976-06-30

Description

June 1959 H. P. KALLMANN ET AL 2,392,968

VOLTAGE RESPONSIVE SCREEN CONTROL METHODS AND SYSTEMS Filed Oct. 25, 1956 2 Sheets-Sheet 2 FIG. 2.

MODU- LA TOR F01? WA RD V01. 77165 500,965

Pill. 55 .7/

AMPL lF/El? 5 WE E F CONT REVERSE BLANK IN6 VOL 7' A65 BAH/g7 ROSENBERG @463; NW Till/M ATTORNEY5 United VOLTAGE RESPONSIVE SCREEN CONTROL METHODS AND SYSTEMS Hartmut P. Kallmann, Riverdale, and Barnett Rosenberg, New York, N.Y., assignors to Research Corporation, New York, N.Y., a corporation of New York Application October 23, 1956, Serial No. 617,739

7 Claims. (Cl. 315-169) This invention relates to voltage-responsive screen control methods and systems for energizing selected localized regions in a screen containing voltage-responsive material, while avoiding undesired energization of other regions in the screen. The methods and systems of the present invention are highly suitable for use in the electrical recording, storage and recalling of information and in displaying information such as wave forms, patterns, coordinate values, and other data, and are particularly well adapted and advantageous for fiat-screen television. The methods and apparatus of the present invention are very well adapted for use with screens utilizing voltage-responsive material and wherein during operation various localized regions of the screen are selected and energized by the application of voltage difierentials thereto. In the control methods and apparatus of the present invention selected localized regions or elemental volumes of voltageresponsive material are energized by voltages applied in the forward direction through unidirectional current conducting means.

Among the many advantages of the illustrative embodiments of the present invention described herein are those resulting from the fact that other elemental volumes of the voltage-responsive material are maintained in a substantially unenergized condition. That is, they remain blankedout. They are blanked out by voltage diiierentials acting in the reverse direction through the unidirectional current conduction means.

The methods and apparatus of the present invention are highly adapted for use with screens including pairs of control grids for energizing selected localized regions or elemental volumes of the screens and are particularly advantageous for display screens such as fiat television screens including material emitting visible light at selected energized areas as controlled by the control grids.

A number of important advantages result from the methods and apparatus of the present invention when applied to electroluminescent display screens for showing television pictures. The illustrative embodiments of the present invention utilize electroluminescent materials in flat television screens. The brilliance and distinctness of the illuminated spots in the display screen are greatly enhanced by the present invention.

In the illustrative method described as embodying the present invention, the excitation voltage is applied in the forward direction through unidirectional current conduction means to selected pairs of conductive elements of the two control grids and thus to the desired selected ele-- mental volumes of the electroluminescent material at juncture points so as to create visible light at these desired points. In the method described any undesired excitation of the electroluminescent material is prevented by the application of blanking voltages. These blanking voltages are applied in the reverse direction through unidirectional current conduction means to other respective conductive elements of the two grids, thus controlling the electric fields within the elemental volumes of the electroluminescent material at other respective junctures in the 2,892,968 Patented June 30, 1959 ice screen and suppressing any creation of visible light at these other points.

Electroluminescent materials have the property that the application of an electric field through an elemental volume of the material causes that volume to emit visible light. Electroluminescent materials generally exhibit the characteristic that the light output over a range of values rises very rapidly with the magnitude of the applied voltage.

In electroluminescent display screens a pair of grids of conductive elements are arranged in spaced relationship so that the various conductive elements of the two grids pass near to each other at numerous spaced juncture points. Electroluminescent material is positioned between these grids at these junctures. When voltage differentials of the proper values are applied between selected conductive elements in the two grids, light is emitted from the volumes of the electroluminescent material located at the points where the energized conductors pass near each other. The electric fields created within the body of the electroluminescent material in the screen by the applied voltages are strongest at the points where these conductors pass most closely together. Thus, the emitted light is brightest at these points. But, in display screens as known prior to our invention, the applied voltages also created undesired strong fields at other regions within the body of the electroluminescent material in the screen.

One of the problems which has seriously interfered with the operation of prior electroluminescent screens is the fact that such undesired substantial voltage fields are created along the full lengths of the energized conductive elements in the grids. This causes undesired visible light to be emitted along the lengths of these conductive elements. This background of light is confused with the brighter point of light created at the juncture points of the energized elements. In operating prior electroluminescent display screens wherein the two grids are arranged at right angles to each other, the effect is to create crosses of light with brighter spots appearing at the juncture point. Thus, there is a lack of distinctness and clarity in the information displayed in prior screens. The brilliance and contrast which can be obtained from prior screens is very limited.

Moreover, in prior screens there is the added difi'iculty that the brightness which can be obtained for the viewer is drastically limited. This brightness is limited by the undesired creation of background illumination. Any attempt to increase the brightness at the desired points by increasing the applied voltage in prior screens also causes a large increase in the background illumination. The effective increase in background illumination as seen by the viewer, more than offsets the increase in brightness at the desired points.

Elforts have been made in the past without much success in trying to overcome this problem. These have involved the use of specialized electroluminescent materials and have attempted to utilize specialized phase relationships within the electroluminescent material in an effort to increase the desired brightness While suppressing the undesired excitation in neighboring areas.

Among the advantages of the present invention are those resulting from the fact that an increased voltage field is applied at the desired point or points within the various elemental volumes of the electroluminescent material while greatly minimizing any undesired fields at other points within the display screen. In this way the brilliance of the light from the desired points is greatly increased while at-the same time the undesired background light caused by undesired excitation of the electroluminescent material is markedly decreased.

Among the many further advantages of the present invention are those resulting from the fact that it improves the definition, clarity, and brightness characteristics of the display screen thus greatly enhancing the usefulness and intelligibility of the displayed information. The result is a big improvement in fiat-screen television display systems.

It is among the objects of this invention to provide an electroluminescent display screen control method and apparatus having improved definition and brightness characteristics.

Among the further important advantages of the present invention are those resulting from the fact that it enables an increased operating voltage differential to be applied at any desired point within the electroluminescentmaterial while decreasing the effective voltage diiferential applied to the other areas where no light output is desired. The resulting improvement in definition arid brilliance in many cases is of the order of hundreds of times that in prior screens. The present invention enables the rising light output characteristics of electroluminescent materials with respect to applied voltage to be utilized to great advantage. By virtue of the markedly increased voltage differentials obtainable in operation the light output from the desired points is increased by substan tial amounts, which in many cases are of the order of hundreds of times that avialable in the prior art, while the background illumination is actually decreased markedly below that obtainable in any prior art screens of which we are aware.

In this specification and in the accompanying draw ings are described and shown, electroluminescent display screen control methods and systems embodying our invention and various modifications thereof are suggested, but it is to be understood that these are not intended to be exhaustive nor limiting of the invention, but on the contrary are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the manner of applying the method and apparatus in practical use so that they may modify and adapt it in various forms, each as may be best suited to the conditions of a particular use.

The various aspects, objects and advantages of the present invention will be more fully understood from a consideration of the following specification in conjunction with the accompanying drawings, in which:

Figure 1 is a schematic circuit diagram with portions being shown in perspective and cut-away, illustrating a voltage-responsive screen control method and apparatus embodying the present invention; in this illustrative embodiment the screen is shown as being an electroluminescent display screen;

Figure 2 is a schematic circuit diagram of a modified method and apparatus similar with that illustrated in Figure 1;

Figure 3 is a schematic circuit diagram of a portion of the display screen of Figure 1 and of Figure 2 for purposes of explaining the improved operation;

Figures 4A and 4B are schematic circuit diagrams for purposes of explanation;

Figure 5 is a graphical type representation of the way in which the light output from electroluminescent materials generally rises much faster than the applied voltage over a range of values;

Figure 6 is an illustration used in connection with an explanation of the prior art and its limitations.

As shown in Figure 1, the electroluminescent display screen, generally indicated at 10, includes a suitable rigid planar support member or backing 12 of inert electrically insulating material. For example, this support may be a plate of glass, or a plate of Lucite or Plexiglas (methylmethacrylate). A grid of inert condu'ctiveele ments or strips 14 extends across the front face of the support 12 and ar'eshown in spaced parallel relationship insulated from each other. When a glass backing .12 is used, these conductive elements 14 are strips of conductive glass material, such as tin oxide glass, extending across the face of the backing. Also, it is satisfactory to use chemically deposited or evaporated metal conductors 14, of materials such as copper, aluminum, gold, and silver, suitably spaced as by etching or by scribing.

For purposes of clarity in illustration, these conductive elements 14 are shown as being spaced a considerable distance apart. But in the typical screen 10, these conductors are often quite closely spaced, for example, as many as 50 or conductors per lineal inch may be used, depending upon the total area of the screen and upon the distance from which it is to be used. For cinema type electroluminescent display screens the total area is much greater and only a few conductive elements 14 per inch are used.

Overlying the grid of conductors 14 is a layer or slab of electroluminescent material 16. A layer of zinc sulfide copper-activated material has proven very satisfactory. Other electroluminescent materials such as zinc selenide or cadmium sulfide activated with copper may also be used.

This electroluminescent layer may satisfactorily be prepared by dispersing the powdered electroluminescent phosphor material in melted castor wax. This melted electroluminescent matrix is then spread in a layer having a thickness in the range from one to ten mils over the conductors 14-. We have found that an electroluminescent layer 5 mils thick is preferable for most applications as giving good definition plus brilliance. Next, a transparent covering plate 18 is placed over the matrix layer 16. This transparent covering plate has a grid of conductive elements 20 extending across its lower face in spaced parallel relationship insulated from each other. This cover plate is pressed down upon the molten matrix of castor wax and phosphor material so as to exclude the air, and the castor wax is allowed to harden.

The conductors 20 are transparent. They may satisfactorily be prepared by evaporating thin plating of conductive metal such as gold, silver, copper, or aluminum upon the undersurface of the cover plate 18. When a glass covering plate is used, they may satisfactorily be formed by strips of conductive tin oxide glass. The conductive plating ma be etched or scribed to produce the individual conductive elements 20 insulated from each other.

In the foregoing description we have set forth certain desirable materials which may be used to advantage in constructing the electroluminescent display screen 10. However, it is to be understood that it is an advantage of the present invention that any voltage-responsive ma terial may be used which has the characteristic that one of its characteristics at least over a suitable operating range changes with increased voltage differential applied thereto. In the illustrative display screen shown any electroluminescent material may be used which has the characteristic that its light output at least over a suitable operating range increases with increased voltage differential applied thereto. Any inert insulating material having good insulation strength may be used to provide the backing 12. Similarly, any suitable material rn'ay be used to provide the transparent cover 18 and the transparent conductors 20.

Regardless of the particular materials which are used, it is important that the screen 10 be constructed such that the total resistance as measured along the length of each of the conductive elements 14 and along the? length of each of the conductive elements 20 should be markedly less than the total resistance at each juncture point from a conductor 14 to a conductor 20 through the electroluminescent materialle. For example, we find that it is desirable to have the resistance measured through the layer 16 ateach juncture at least 100 times as large as the resistance measured along the lengths of the individual conductors 1'4 and 2t),

In order to control the electroluminescent screen, each of the conductive elements is connected by a lead 22 to unidirectional current conduction means 24, shown as pairs of rectifiers in series. These rectifiers all have the same conductive relationship with the respective conductive elements to which they are coupled. They are shown as having their favored (i.e. low resistance) direction of conduction facing forward toward these conductive elements. These conductive elements are controlled by conductive means including a first source of control voltage 26, called the forward voltage source and including a second source of control voltage 28 called the reverse blanking voltage source.

In the control system shown, the forward voltage source supplies direct voltage at three

terminals

30, 31, and 32. The center terminal 31 is neutral and is connected to the common return circuit of the system, as in-, dicated by the ground connection symbol. The positive terminal is connected by a lead 34 to selective energizing means, generally indicated at 36, and including a first wiper switch 38 and a second wiper switch 40 which are ganged together and driven in synchronism by a synchronous type motor 42.

In order to feed voltage in the forward direction selectively through the unidirectional current conduction means 24, the lead 34 is connected by means of a slipring and wiper arm 44 of the switch 38 to the various switch contacts 46. From each of these contacts 46 the control circuit passes by way of individual leads 48 through the respective rectifiers 24 to the conductive elements 20.

In this control system the negative terminal 32 of the forward voltage source is connected by a lead 50 through a modulator 52 and by a lead 54 to second selective energizing means, generally indicated at 56. This second selective energizing means includes a first wiper switch 58 and a second wiper switch 60, which are ganged together and driven in synchronism by a synchronous type motor 62.

In this control system the first and second selective energizing

means

36 and 56, respectively, are identical in construction, except that the driving motor 62 is energized to rotate the switches 58 and at a slower rate than the corresponding switches 38 and 40. This difference in switching speeds produces the desired different horizontal and vertical rates of sweep of the illuminated spot across the screen 10, in accordance with the type of information being displayed. For a television type of display, the picture is produced by rapidly sweeping the illuminated spot horizontally to paint the horizontal line segments of the picture and by progressing vertically at a correspondingly slower rate from one line segment to the next. For such a display, the

switches

38 and 40 are driven at a rapid rate to create the line segments of the picture in the screen 10 while the switches 58 and 60 move correspondingly slower.

The various conductive elements 14 in the other control grid are individually connected by leads 64 to second unidirectional current conduction means 66 shown as pairs of series connected rectifiers. These rectifiers are all arranged in the same conductive relationship with respect to the associated conductive elements 14. Their favored direction of conduction, that is, the direction of low resistance, is facing away from the conductive elements 14. These pairs of rectifiers 66 are connected by leads 68 to the respective contacts 70 of the wiper switch 58. The return circuit from the contact 70- is completed through a rotating wiper contact and slip-ring 72 to the lead 54. r

In operation, as the contact arms 44 and 72 rotate, they selectively apply a voltage field across elemental volumes of the electroluminescent material at the various juncture points in the screen 10, causing these various points to emit visible light. The forward control circuit for energizing the desired points can be traced from the positive terminal 30 through the lead 34, the slip-ring and arm .44, any one of the contacts 46, a corresponding lead 48 and through the corresponding pair of rectifiers 24 and by a lead 22 to the corresponding one of the conductors 28. The return circuit passes from any one of the conductive elements 14 through the corresponding lead 64 and a corresponding pair of rectifiers 66 and a lead 68 to one of the contacts 70 and thence through the arm and slip-ring 72 to the lead 54 and back through the modulator 52 and through the lead 50 to the negative terminal 32.

For interlaced scanning as now used in commercial television, alternate ones of the leads 68 are connected in succession to adjacent contacts 70 over one-half of the switch 58, and the respective intermediate leads 68 are connected in succession to adjacent contacts 70 over the other one-half of the switch 78.

The modulator 52 controls the strength of the voltage field applied through the electroluminescent material at the respective juncture points of the screen 10 and thus controls the relative intensity of the light emitted-at the various points of the screen 10 in accordance with the information being displayed. The modulator 52 may be any electrical valve whose effective conductivity is controllable in response to a control signal fed in through the control line 74. For example, a triode may be used with the anode circuit connected to the lead 54, and the cathode circuit connected to the lead 50; the grid is controlled by line 74.

In prior art electroluminescent screens, as schematically indicated in Figure 6, the operation of the screen produces a band of illumination at all points along the length of the grid conductor 20a which is energized. This background illumination results from the electric field which is created along the length of the conductor 20a. For example, assume that a positive voltage of say 50 volts is applied to the conductor 20a. That is, the voltage being applied to the conductor 20a is assumed to be 50 volts more positive than that of the electroluminescent layer. At all points along the length of this conductor 20a a voltage difference of 50 volts now exists between the conductor 20a and the body of the electroluminescent material, and this voltage difference causes the electroluminescent material to emit the band of light 80.

Similarly, assume that a negative voltage of 50 volts is applied to the grid conductor 14a. A band 82 of background illumination is created at all points along the length of the conductor 14a as a result of the voltage differential between the conductor 14a and the body of the electroluminescent material. At the juncture point where the conductive elements 14a and 20a approach each other most closely, a total voltage difference of volts is applied across an elemental volume of the electroluminescent material causing a brighter spot as indicated at 84.

Efforts have been made prior to the present invention to overcome this problem by operating the conductors of one of the grids at the same voltage as the body of the electroluminescent material, by grounding. This does not solve the problem because the conductors of the other grid must then be operated at twice the voltage differential with respect to the body of the electroluminescent material to obtain the same brilliance at the spot 84. As a result, a much brighter band of background illumination is created along the energized conductor.

In order to prevent any background illumination, a blanking voltage is applied in the reverse direction through the unidirectional current conduction means 24 and 66 to all of the

conductors

14 and 20 which are not being used to energize the desired spot in the screen 10.

Consideration is now directed to Figures 3, 4A and 4B in conjunction with Figure 1. For purposes of explanation, assume that a positive voltage as indicated by (Figure 3) of, say, 50 volts is applied in the forward direction through a pair of the rectifiers 24' to energize aselected one'of the conductors 2 A return circuit is completed from a selected conductor 14' in the other grid by appl-ying a negative voltage as indicated by (Figure 3) of, say, 50 volts through a pair of the rectifiers 66 in the forward direction. As a result, an elemental volume of electroluminescent material 86 at their juncture point is brightly illuminated, as desired.

This energizing voltage is applied in the forward'directron through the

rectifiers

24' and 66 so that, as indicated in Figure 4B, they offer a relatively small resistance 'to the applied voltage. These rectifiers. 24' and '66 are effectively in series with the elemental volume '86, and because of their low forward resistance, only asm'all voltage drop s appears across them. Most of the applied voltage appears across the'elemental volume 86 as indicated at V creating an intense electric field and brilliantly lighting this spot 86.

At the same time, positive blanking voltages of, say, 50 volts are applied in the reverse direction through the other pairs of rectifiers 66 to the other conductors 14 whilea return circuit is completed in the reversedirection through the other rectifiers 24 by applying negative voltages of, say, 50 volts, as indicated in Figure 3.

Advantageously, all of the other elemental volumes 88 of electroluminescent material along the positively ener- I the negatively energized conductive element 14' are now at juncture points with the other conductive elements 20 which are also being subjected to negative voltages applied in the reverse direction through the rectifiers 66. Thus, these elemental volumes are desirably held blanked out regardless of the magnitudes of the forward voltages on-the elements 14 and 20'.

With regard to the other elemental vohunes 92 at other points (i.e. not along the forwardly energized conductive elements 14 and 20'), it is seen that the blanking voltages are applied effectively in a series circuit through the

rectifiers

24 and 66 in the reverse high resistance direction. Thus, as indicated in Figure 4A, the great major portions m of the reverse blanking voltage appears across the

rectifiers

24 and 66. Only a very tiny fraction V of this voltage appears across each of the volumes 92. Thus, the volumes 92 are also maintained substantially completely blanked out while the volume 86 is brilliantly illuminated.

As a result of this advantageous operation, the forward voltages can be increased to much larger values than possible heretofore with comparable electroluminescent materials. The result is a many-fold increase in brilliance, definition and clarity. As diagrammatically illustrated in Figure the light output from electroluminescent materials over a range of values generally increases rapidly and at an increasing rate with applied voltage. Thus, the increases in applied voltage obtainable with the present invention often provide an increase in light output of 100 times or more for the same background illumination.

The baclrresistance, or reverse resistance of the unidirectional current conduction means 24 and 66 is preferably substantially greater than the resistance through the layer of electroluminescent material. With electroluminescent materials of the type giving a resistance through the layer 16 of a relatively low value, say less than a million ohms, then germanium type rectifiers may be used arranged to provide a reverse resistance of at least two million ohms or more.

With higher resistance layers 16, vacuum tube recti- 8 fiers maybe used. We have foundthat even with phosphor materials having a specific resistivity as high as 10 ohm-centimeters, highly satisfactory results are obtained by using tube rectifiers such as 6H6s.

To apply the reverse blanking voltage, the negative terminal 94 -of the source 28 -is connected through a lead 98 to -a conductive commutator disk 100 of the switch 40. This disk 1'00 has an insulating notch in its perimeter and thus engages all of the contacts 102 except the contact corresponding in position with the contact 46 being energized by the wiper arm 44.

Corresponding contacts

46 and 102 of the

switches

38 and 40 are connected together by jumper leads 104 as shown.

The neutral terminal 95 of the source 28 is grounded, and the positive terminal 96 is connected through a lead 106 to a commutator disk 108 of the switch 60 engaging all of the contacts 110 except that corresponding with the position of the arm 72 in the companion switch 58. Jumper leads 112

connect corresponding contacts

70 and 110.

In order to modulate the brilliance of the various bright spots so as to display the desired intelligence, for example to display a television program, an antenna 114 picks up the desired signal. This is amplified by the video amplifier and sweep control 116, the amplified signal being applied to the control line 74.

As indicated schematically by the

lines

118 and 120, the control 116 provides signals for synchronizing the sweeping speeds of the

motors

42 and 62.

The control system of Figure 2 is generally similar to that of Figure 1 and corresponding reference numerals are used in these two figures for parts performing corresponding functions.

The selective energizing means 36 for applying energizing voltage to selected conductive elements 20 includes a pulse generator 121 coupled through an isolating capacitor 122 to a lead 124 connected to an electrical delay-line network 126. This delay line includes a plurality of identical inductors 128 connected in series with a plurality of capacitors 130 connected in shunt across the line at the junctions of the respective inductors. The terminals of this delay line are indicated at 129 and 131.

A terminating impedance 132 having a value of Z corresponding with the characteristic impedance of the line is connected across the end-opposite to the input end which is fed by the lead 124. A positive voltage is fed via the lead 34 into the pulse generator, which supplies sharp square-wave pulses of positive voltage to the delay line. As these positive voltage pulses travel down the delay line from the

input terminals

129 and 131 toward the terminating impedance 132, successive leads 48 have brief positive voltage pulses applied thereto to produce the desired sweep. The termination 132 prevents reflections back down the line. The other input terminal 131 is connected to the other output terminal of the pulse generator by a lead 133 which is. grounded.

The pulse generator 121 may be a multivibrator circuit or a Schmidt trigger circuit controlled by the video amplifier and control 116 as diagrammatically indicated by the connection 134.

In order to blank out the other spots in the screen 10, a negative reverse blanking voltage is applied from a negative terminal 94 of the source 28 through the lead 98 and an isolating resistor 136 and through a lead 138 to the lead 124 feeding into the delay-line terminal 129. This negative voltage holds all the inductors 128 negative except at the place along the delay-line being traversed by the positive voltage pulse from the generator 121.

For purposes of emphasizing the desirability of utilizing unidirectional current conduction means having a high resistance in the reverse direction, pairs of seriesconnected rectifiers are shown in Figures 1, 2, and 3. When the back resistance of the rectifiers being used is lower than the desired relationship to the resistance ofthe electroluminescent layer 16 than that expressed above, then two or more rectifiers may desirably be connected in series as shown. Where each rectifier has a relatively high back resistance, then a single rectifier may be used.

As will be understood from the above specification the unidirectional current conduction means 24 and 66 are intended to operate to minimize resistance in the energizing circuit while maximizing the resistance in the blanking circuits. The concept of our invention includes means other than rectifiers for providing low forward resistance and high back resistance. The claimed method includes the steps of applying an energizing voltage in the forward direction through a low resistance path to selected elemental volumes of the" electroluminescent material, and simultaneously applying a blanking voltage of opposite polarity through high resistance paths to elemental volumes other than said selected ones.

The return circuit for the forward energizing voltage is traced through the switch 58 corresponding to that in the system of Figure 1.

The reverse blanking circuit is completed to the positive terminal 96 through the lead 106 from the switch 56 as in the system of Figure 1.

From the foregoing it will be understood that the electroluminescent display screen control methods and systems of the present invention described above are well suited to provide the advantages set forth, and since many possible embodiments may be made of the various features of this invention and as the method and apparatus herein described may be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense and that in certain instances, some of the features of the invention may be used without a corresponding use of other features, all without departing from the scope of the invention.

We claim:

1. An electroluminescent display screen control system comprising a first grid of spaced parallel conductors, a second grid of spaced parallel conductors in spaced electrically insulated relationship with said first grid, the conductors of said second grid being axially aligned at a substantial angle with respect to the axes of the conductors of said second grid, a layer of electroluminescent material positioned between said grids, first unidirectional current conduction means readily conducting current in a favored direction and resisting flow of current in the reverse direction and being connected to the respective conductors of said first grid in relationship to favor the conduction of current to said conductors, second unidirectional current conduction means readily conducting current in a favored direction and resisting the flow of current in the reverse direction and being connected to the respective conductors of said second grid in relationship to favor the conduction of current away therefrom, a control voltage source, circuit means selectively applying said control voltage through said first unidirectional current conduction means in the favored direction to a respective one of the conductors of said first grid and selectively returning said control voltage through said second unidirectional current conduction means in the favored direction from a respective one of the conductors of said second grid, and including means selectively applying a blanking voltage in the reverse direction through said first unidirectional current conduction means to other respective conductors of said first grid and selectively returning said blanking voltage in the reversed direction through the second unidirectional current conduction means from other respective conductors of said second grid.

2. In the art of operating electroluminescent display screens of the type including first and second grids of conductive elements arranged selectively to energize elemental volumes of electroluminescent material, the improved method for increasing the brilliance while preventing undesired background illumination comprising the steps of applying a blanking voltage in the reverse direction through unidirectional current conduction means to all of the conductive elements of said first grid except at least one while providing a return circuit for said blanking voltage through all of the conductive elements of the second grid except at least one, and simultaneously applying a voltage in the forward direction through unidirectional current conduction means to one of the other conductive elements of the first grid and providing a return circuit for said voltage through one of the other conductive elements of the second grid.

3. An improved electroluminescent display screen control system providing increased brilliance at the desired juncture points while blanking out the remainder of said screen and comprising a first grid of conductive elements in insulated relationship, a second grid of conductive elements in insulated relationship and spaced from said first conductive elements forming spaced junctures therewith, electroluminescent material between said grids, unidirectional current conduction means connected to the respective conductive elements of one of said grids and all having the same direction of conduction, first selective energizing means arranged to complete an energizing circuit through the unidirectional current conduction means and through selected conductive elements of said one grid and through said electroluminescent material and through selected conductive elements of the other grid, said energizing circuit including energizing voltage applied in the forward direction through the unidirectional current conduction means, thereby to energize the electroluminescent material at the junctures of the selected conductive elements of said grids, second selective blanking means arranged to complete a blanking circuit through the unidirectional current conduction means and through other selected conductive elements of said one grid and through said electroluminescent material and through other selected conductive elements of the other grid, said blanking circuit including blanking voltage applied in the reverse direction through the unidirectional current conduction means in the reverse direction, thereby to prevent any substantial illumination of the electroluminescent material at other junctures.

4. An electroluminescent display screen control system including a layer of electroluminescent material which admits light when an electric field is applied thereacross, a first grid including a plurality of non-intersecting conductors arranged along one surface of said electroluminescent layer, a second grid including a plurality of non-intersecting conductors arranged along the opposite surface of said electroluminescent layer, said grids being so oriented that projections of both grid structures form an intersecting pattern, a plurality of unidirectional current conduction elements connected to the respective conductors of said first grid in a first conductive relationship with respect thereto, a second plurality of unidirectional current conducting elements connected to the conductors of said second grid in a reverse current conducting relationship therewith, first switching means arranged to apply voltage in a forward direction through one of said unidirectional current conducting elements of the first plurality to one of the conductors of said first grid and arranged to complete a circuit through one of said unidirectional current conducting elements of the second plurality to one of the conductors of said second grid, and second switching means arranged to apply voltage in a reverse direction through said unidirectional current conducting elements of the first plurality to the other conductors of said first grid and completing a circuit through the unidirectional current conducting elements of the second plurality to the other conductors of said second grid.

5. A flat screen television control system comprising 11' first and second grid structures of spaced parallel conductive elements in spaced insulated relationship with oneanother so positioned that projections of both grid structures form an intersecting pattern, voltage-responsive light-emitting material at the points where thecon-r ductive elements of the first grid structure approach closest to the conductive elements of the second gridv structure, a plurality of rectifier means all connected in the same relationship to the conductive elements of the first grid, first switching means arranged to apply a control voltage in circuit from a selected one of the conductive elements of the first grid structure through an elemental volume of said light-emitting material to a selected conductive element of said second grid structure and in the forward direction through one of said rectifier means, and second switching means arranged to apply a blanking voltage in circuit through the other conductive elements of the first grid structure and through the other elemental volumes and the other conductive elements of the second grid and through said rectifiers in the reverse direction, an electrical delay line having spaced points therealong coupled to the conductive elements of one of said grid structures, a pulse generator coupled to one end of said delay line, an intensity modulator connected to said first switching means, and sweep control means connected, to said first and second switching means for operating themin synchronism.

6. An improved electroluminescent delay screen control system providing increased brilliance at the desired points while selectively blanking out other areas of the screen comprising a first grid of conductive elements in insulated relationship with one another, a second grid of conductive elements in insulated relationship with one another and spaced from the elements of the first grid and at an angle therewith forming spaced junctures between the respective elements of the grids, a plurality of unidirectional current conduction means connected to the re spective elements of one of said grids and all having the same relative favored direction of conduction with respect to the elements of said one grid, first and second synchronized switch means, a plurality of, conductive means connecting said first and second switch means to the elements of the first grid, a forward voltage source connected in circuit with said first switch means and the elements of the second grid, a reverse blanking voltage source of opposite polarity from said forward source connected in circuit with said second switch means and the elements of the second grid, said first switch means selectively applying said forward voltage source to at least one of the conductive means, said second switch means selectively applying said reverse blanking voltage source to other conductive means, a modulator for controlling the intensity of said forward voltage source, and control means for operating said synchronized switch means.

7. An improved electroluminescent display screen as claimed in claim 6 and including third and fourth switch means, a plurality of conductive means connecting said third and fourth switch means to the elements of the second grid, said third switch means being in circuit with said forward voltage source, and said fourth switch means being in circuit with said reverse blanking voltage source, said third switch means selectively applying said forward voltage source to at least one of the second plurality of conductive means, and said fourth switch means selectively applying said reverse blanking voltage source to others of the conductive means of the second plurality.

References Cited in the file of this patent UNITED STATES PATENTS 2,313,286 Okolicsanyi Mar. 9, 1943 2,698,915 Piper Jan. 4, 1955 2,749,480 Ruderfer June 5, 1956 2,774,813 Livingston Dec. 18, 1956 2,818,531 Peek Dec. 31, 1957