Flat Screen Television System

Abstract

An electroluminescent array and a method and circuit arrangement for energizing the discrete elemental points on the electroluminescent array a row at a time and in a manner to energize each discrete elemental point on the selected row for different periods of time to establish a plurality of different light intensities to obtain a gradient of gray scales across the selected row visually to display a single scan line portion of a video display pattern. The electroluminescent array may include a predetermined number of row circuit lines and a predetermined number of column circuit lines arranged in a cross grid X-Y pattern to form a circuit juncture at each crossing of the column and row circuit lines, and a threshold-operated electroluminescent circuit is connected at each of the junctures. Each threshold-operated electroluminescent circuit, most advantageously, comprises a bidirectional threshold-switching device having time delay characteristics, and electroluminescent element, and a resistor. Means are provided to apply operating potential sequentially to each of the row circuit lines one after the other and, while any given row circuit line is energized each of the electroluminescent circuits connected along that row will remain in a stable off condition until a given start signal is applied to each of the column circuit lines at which time the electroluminescent circuit connected to the junctures of the selected row and the column circuit lines will be energized to emit light. The light intensity from each of the electroluminescent circuits connected across the selected row will depend on the point in time the electroluminescent circuit is rendered operative to emit light from the electroluminescent element thereof. Most advantageously, all of the electroluminescent circuits along the selected row circuit line are simultaneously deenergized by the removal of the operating potential from the row circuit line, and the next row circuit line receives operating potential to receive a subsequent scan of video information.

Description

This invention relates generally to panel-type information display arrays, and more particularly to two-dimensional display devices for visual reproduction of electronic video signals, and to the method and apparatus for controlling such arrays. Specifically, this invention is directed to energizing and deenergizing a plurality of electroluminescent circuits along a given row circuit line at points in time corresponding to the amplitude of the video information to be applied at the particular discrete electroluminescent circuit along the row circuit line, and all of the electroluminescent circuits are extinguished simultaneously thus providing a gray scale for the electroluminescent array to display rapidly changing video signal information therefrom.

Heretofore, many problems had been encountered in the development of the electroluminescent matricies of the two-dimensional display type. Some of the problems encountered are the result of certain minimum requirements which must be met to provide reliable energization and deenergization of discrete electroluminescent points. Some of the requirements are: The electroluminescent element must be controlled in accordance with the stored video signal information; and the switching device used to control the electroluminescent element must exhibit a well-defined threshold voltage value. The tolerance to the threshold voltage value of a multitude of threshold-switching devices must be very close. In addition, the electroluminescent elements must exhibit low power consumption, and must be capable of batch fabrication in geometrics that can be assembled into display panels. A common type of construction for an electroluminescent display panel is the cross grid or X-Y type. The parallel placed electrodes of this type of construction are divided into strips and oriented at right angles to each other. Although such panels generally display a cartesian coordinate system, the may, if desired, display a polar coordinate system or any other system desired. In this type of display panel an alternating current voltage is applied between the selected X and Y cross grids to energize the electroluminescent element at the juncture thereof. In practice, X-Y display panels of this type possess many such junctures each of which constitutes a connection means for a picture element to form a point on the electroluminescent array. Energizing selected picture elements would make possible the display of television pictures, or other information patterns or numbers. However, many problems have been encountered in trying to achieve a faithfully produced or reproduced image on display screens of the X-Y display panel type. The requirement of sequentially applying operating potentials to successive rows or columns to successively to energize each electroluminescent element causes energization of undesired electroluminescent elements due to capacitive cross coupling in the array.

It is the object of this invention to provide the means whereby an electroluminescent array is controlled a line at a time, rather than an element at a time, to produce a gray scale gradient sufficient faithfully to reproduce or produce video display patterns thereon.

Briefly, this invention provides means to energize a complete row of electroluminescent elements by applying operating potential to the selected row circuit line while each column circuit line receives video signal information which will energize the electroluminescent circuits along the selected row circuit lines at different points in time to emit different amounts of light intensity from the discrete picture elements along the row circuit line, and the operating POTENTIAL applied to the selected row circuit line is removed therefrom simultaneously to deenergize all the picture elements therealong. The next row circuit line is then energized and video information applied thereto, and this process is repeated a line at a time ultimately completely to form a display pattern. When the speed of the sequential line-at-a-time scanning of the electroluminescent array is selected to correspond to the speed of conventional transmitted scanning signals from television stations, a conventional television picture can be reproduced from the electroluminescent array.

The switching devices used in this invention are one layer type threshold semiconductor devices each having substantially identical conduction characteristics for positive and negative applied voltages but which may have slightly different threshold voltage values with respect to one another. The threshold-switching devices initially presents a very high resistance in response to an applied voltage of either polarity below and upper threshold level and in response to an applied voltage of either polarity above the upper threshold level, changes a high to a low resistance condition, such change occurring after an inherent time delay of the threshold switching devices, but once switching is established it is substantially instantaneous. The threshold semiconductor switching devices automatically reset themselves to their high resistance state when the current therethrough drops below a minimum holding current value which is near zero. The threshold-switching devices have a substantially reduced threshold voltage value immediately after they are rendered nonconductive, and after a relatively short recovery delay time, during which the threshold voltage value progressively increases, the normal initial threshold voltage value is again reached. Semiconductor materials used to form such threshold-switching devices most advantageously are of the type disclosed in U.S. Pat. No. 3,271,591 issued to Standford R. Ovshinsky and sometimes referred to therein as "mechanism devices without memory." By varying the semiconductor composition or the treatment of the material disclosed in the above-mentioned patent, the upper and lower threshold levels, the blocking or leakage resistance, and the inherent time delay characteristics thereof are readily varied to obtain the desired range of conditions necessary for proper operation of electroluminescent array systems constructed and operated in accordance with this invention. It has been discovered that the inherent characteristics of the above type of threshold switching device has unexpected advantage when used in certain methods of operation for displaying video signal information. An inherent characteristic of particular importance is that of a varying time delay between the time a threshold voltage is applied to the threshold-switching device and the time the threshold-switching device actually changes from its high resistance blocking condition to its low resistance conducting condition, but when switching occurred it is substantially instantaneous, as for example in the order of nanoseconds. However, the turn-on time delay of these devices will vary with changes in applied voltage in excess of the threshold voltage value of the particular devices involved, and increase in voltage from the threshold voltage value to a greater voltage causing a decrease in the inherent turn-on time delay. Therefore, if a voltage pulse having an amplitude equal to or greater than the threshold voltage value of the switching device involved is applied thereto but exists for a period of time less then the inherent time delay corresponding to that particular voltage amplitude, the threshold-switching device will not be rendered conductive. However, it is also true that if an amplitude-response signal is applied to the threshold-switching device, the inherent time delay of the switching device will cause it to be rendered conductive at a point in time determined by the amplitude of the applied signal. Therefore, if an operating potential of alternating current voltage is applied to the threshold-switching devices used in this invention, and which alternating current voltage is of a sufficiently high frequency so that periodic pulses of the applied frequency have a time duration less than the inherent time delay corresponding to the amplitude of the applied voltage, then a voltage value in excess of the threshold voltage value of the threshold-switching device may be applied thereto without rendering the switching device conductive.

Yet another inherent characteristic of the threshold-switching devices most advantageously used in this invention is that of the inherent recovery time delay of the threshold voltage value back to the original or normal threshold voltage value after the switching devices are turned off as a result of decreasing currents therethrough below the minimum holding current. That is, there will exist a substantially diminished threshold voltage value after the switching devices are turned off and which will increase with increasing time back to the original or normal threshold voltage value. Therefore, if a pulse or voltage is applied to any one of the threshold-switching devices within the recovery time delay period after it is rendered nonconductive, this pulse need only have an amplitude equal to the then existing threshold voltage value to again render the threshold-switching device conductive. If the operating potential applied to the threshold-switching devices is an alternating current voltage of sufficient frequency so that each successive periodic pulse of the applied potential will occur within the inherent time delay for full recovery of the switching device, these switching devices will be continuously rendered conductive on each half cycle of the applied voltage even if the applied voltage is substantially below the normal or initial threshold voltage value of the threshold-switching devices involved.

By utilizing the inherent turn-on time delay and recovery time delay characteristics of the threshold switching devices mentioned hereinabove, many novel and unobvious advantages are realized. The need for selecting a multitude of threshold-switching devices with substantially the same threshold voltage value is eliminated in that the efficient and reliable operating range of these switching devices, (the tolerance range) is substantially increased in proportion to increasing the frequency of the applied operating potential. All these switching devices are readily batch fabricated as thin films or layers in contact with flat deposited surfaces of electroluminescent material thus making it possible to form flat relatively thin display screens.

Many objects, features and advantages of this invention will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawings wherein like reference numerals throughout the various views of the drawings are intended to designate similar elements or components.

FIG. 1 is a simplified block diagram of an electroluminescent display system constructed and operated in accordance with this invention;

FIG. 2 is a schematic diagram illustrating the circuit components of an electroluminescent circuit which is used at each picture element of the electroluminescent array of this invention;

FIG. 3 is a voltage current characteristic of the threshold-switching device used in this invention;

FIG. 4 is a graphic representation of the inherent turn-on time delay of the threshold-switching device used in this invention;

FIG. 5 is a graphic representation of the inherent recovery time delay of the threshold-switching device used in this invention;

FIG. 5A is a graphic representation of the frequency versus threshold voltage value of its threshold-switching device used in this invention;

FIG. 6 is a series of waveforms illustrating the operation of a plurality of electroluminescent circuits along a given row circuit line of an X-Y electroluminescent array to establish the desired variations in light intensity from each electroluminescent circuit along the selected row to provide a gray scale for the display pattern formed by the apparatus of FIG. 1.

Referring now to FIG. 1 there is seen a simplified form of circuit arrangement which can be used to operate an electroluminescent array in accordance with the principles of this invention. A control circuit is designated generally by reference numeral 10 to operate a cross grid X-Y electroluminescent array 12 in response to a video signal information receiver 14. The video signal information receiver 14 may be a conventional television receiver to provide the appropriate video signal information and synchronizing pulse signal information to operate a plurality of electroluminescent circuits 16 along a given one of a plurality of row circuit lines 17, 18, 19, 20, and 21 one line at a time. The video signal information is applied to a plurality of column circuit lines 22, 23, 24, 25, 26, and 27 in parallel fashion, but means are provided to delay the energization of the discrete electroluminescent elements along the selected row in response to the amplitude of the applied video signal information so that each electroluminescent circuit will be energized to a period of time corresponding to the amplitude or relative brightness of the signal to be displayed.

To operate the electroluminescent array 12, in accordance with this invention, preferably there is provided a gated oscillator 28 which receives synchronizing signals from the video signal information receiver 14 via a line 29 to operate the gated oscillator 28 in such a manner as to sequentially energize the lines 17-21 at a speed corresponding to the vertical sweep speed, as for example, of a television set. A video signal information converter and parallel output circuit 30 receives video signal information from the video signal information receiver 14 via a video line 31 and converts the serial input of the video information to a parallel output, this being accomplished by any suitable well-known means for serial to parallel conversion. After all the video information is stored in the video signal information converter and parallel output 30 a synchronizing pulse via a line 32 will apply the stored video information simultaneously or substantially simultaneously to all of the electroluminescent circuits 16 along a given selected row, as for example the row circuit line 17. Each of the electroluminescent elements 16 along the row circuit line 17 is rendered operative at a different point in time during which the operating potential is applied to the row circuit line 17, the electroluminescent elements being energized for the longest period of time emitting the brightest light and the electroluminescent elements energized for the shortest period of time and emitting the least amount of light and a plurality of variation therebetween, thus forming a gray scale for a given picture line to be displayed. The line 17, when receiving operating potential or energized, is commutated off rapidly and an operating potential is applied to the next line 18 while video signal information is being stored and processed in the video signal information converter and parallel output 30, and thereafter the video signal information is applied to the plurality of column circuit lines 22-27 to energize all of the electroluminescent elements along the row circuit line 18, this action repeating rapidly until all the row circuit lines have been energized to form a complete frame of video signal information. After the last row circuit line is energized the scanning operation repeats itself to form another frame of video information and, as such, can produce rapidly changing display patterns on the electroluminescent array 12 substantially corresponding to video signal information on a television receiver.

Referring now to FIG. 2 there is seen the circuit components of an electroluminescent circuit used in accordance with this invention. The electroluminescent circuit 16 includes a resistor 35 connected to a voltage amplitude and time delay threshold-switching device 36, which, in turn, is connected to an electroluminescent element 37. Although the circuit arrangement shown in FIG. 2 is illustrated as a series connection, it should be understood that the broad concepts of this invention incorporate all circuit connections possible with these components to emit light therefrom in response to selectively applied video signal information. The electroluminescent element 37 acts as a capacitator in the circuit, and when the threshold-switching device 36 is rendered conductive charge is applied to the electrode 37a. When the current through the threshold-switching device 36 decreases below a minimum holding current, the charge on the electrode 37a remains until the next half cycle of applied voltage of opposite polarity is applied across the electroluminescent circuit to add with the charge on the electroluminescent element rendering the threshold-switching device 35 conductive to discharge the electroluminescent element and recharge it with a voltage of opposite polarity. Therefore, the electroluminescent circuit is a bistable circuit remaining in its table off condition until the threshold-switching device 36 is initially rendered conductive, for at least one pulse, and thereafter the electroluminescent circuit will remain in a stable on condiction as long as voltage is applied to the juncture of the electrodes 17 and 22. The inherent recovery time delay of the threshold-switching device 36 increases the bistable range of the electroluminescent circuit beyond that which is normally obtainable with capacitive reactive bistable circuits.

For a better understanding of the threshold-switching device used in this invention reference is now made to FIGS. 3, 4, 5 and 5a which illustrate the various electrical characteristics of the threshold-switching device 36. The threshold-switching device 36 is symmetrical in its operation, blocking current substantially equally in each direction and conducting current substantially equally in each direction, and the switching between the blocking and conducting condition being extremely rapid after the inherent time delay. FIG. 3 is an I-V curve illustrating the AC operation of the threshold-switching device 36, it being understood that either the first or third quadrant alone will represent the application of a direct current voltage (DC). Considering a DC voltage applied across the threshold-switching device 36, represented by the first quadrant of FIG. 3, the threshold-switching device 36 is normally in its high resistance blocking condition, and, as the DC voltage is increased, the voltage current characteristics of the device are illustrated by the curve 40, the electrical resistance of the device being high and substantially blocking current flow therethrough. When the voltage is increased to a threshold voltage value, the high electrical resistance of the semiconductor materials substantially instantaneously decreases in at least one path through the semiconductor material forming the threshold-switching device 36 to a low electrical resistance, the substantially instantaneous switching occurring after the inherent time delay as indicated by the curve 41. This provides a low electrical resistance conducting condition for conducting current therethrough. The low electrical resistance is many orders of magnitude less than the high electrical resistance. The conducting condition is illustrated by the curve 42 and it is noted that there is a substantially linear current characteristic and a substantially constant voltage characteristic which is the same for increases and decreases in current. In other words, current is conducted at a substantially constant voltage. The low resistance condition of the semiconductor material forming the threshold-switching device 36 has a voltage drop which is a minor fraction of the voltage drop in the high resistance blocking condition.

As the voltage is decreased, the current decreases along the curve 42 and when the current decreases below the minimum current-holding value the electrical resistance of the conductive path or paths through the semiconductor material quickly return to the high electrical resistance, as illustrated by the curve 43, to reestablish the high resistance blocking condition. In other words, a minimum holding current is required to maintain the threshold-switching device 36 in its conductive condition and when the current falls below the minimum holding current value the low electrical resistance condition of the threshold-switching device 36 immediately returns to the high electrical resistance condition. However, the threshold voltage value of the threshold-switching device is substantially reduced immediately after the threshold-switching device is rendered nonconductive and the threshold voltage value increases to the normal initial threshold voltage value after a predetermined recovery time delay.

When AC is applied to the threshold-switching device 36, the I-V curve is illustrated by quadrants 1 and 3 of the FIG. 3. Here the threshold-switching device 36 is in its blocking condition when the peak value of the applied alternating current voltage is below the threshold voltage value of the device. The blocking condition being illustrated by the curves 40--40 in both quadrants 1 and 3. When, however, the peak valve of the applied alternating current voltage increases above the threshold voltage value of the device, the device is substantially instantaneously switched along the curves 41--41 to the conducting condition illustrated by the curves 42--42, the device switching during each half cycle of the applied alternating current voltage. As the applied alternating current voltage nears zero so that the current through the threshold-switching device 36 falls below the minimum holding current value, the device switches along the curves 43--43 from the low electrical resistance condition to the high electrical resistance condition to the high electrical resistance condition illustrated by the curves 40--40, this switching occurring near the end of each half of the cycle.

Referring now to FIG. 4 there is illustrated the inherent turn-on time delay characteristic of the threshold switching device 36 where the normal threshold voltage value is indicated at V.sub.T and the inherent time delay at the threshold voltage value is indicated at T.sub.d and the variation in time delay is illustrated by the curve 45. The threshold-switching device 36 has an inherent time delay between the time the threshold voltage is applied thereto and the time the switching device is actually rendered conductive, and this time is inversely proportional to the amount of overvoltage applied to the threshold-switching device, as illustrated by the curve 45. The values of the inherent time delay and the threshold voltage may be altered by, among other things, changing the composition of the semiconductor material used in forming the threshold-switching device 36 or by varying the thickness of the layer or film forming the threshold-switching device. However, it will be noted that the time delay T.sub.d will decrease with increases of applied voltage between the V.sub.T and V.sub.P1. Therefore, the time duration of the applied voltage on the threshold-switching device 36 need only be as long as the time delay corresponding to the time delay of the voltage value in excess of V.sub.T. FIG. 5 illustrates the inherent recovery time delay T.sub.d of the threshold-switching device 36 to recover to its normal threshold voltage value after the threshold-switching device is rendered nonconductive, this being indicated by the curve 46. Here it can be seen that immediately after the threshold-switching device 36 is rendered nonconductive it will have a substantially reduced threshold voltage value which increases with time until the normal threshold value V.sub.T is again reached, the time delays being readily selected by, among other things, varying the composition of the material used to form the threshold-switching device 36. If the threshold-switching device 36 is operated by a series of voltage pulses, as, for example, alternating current voltage or pulsating direct current voltage, only an initial voltage pulse need have a voltage amplitude and time duration corresponding to the initial threshold voltage value and time delay as illustrated in FIG. 4, or a lesser time delay corresponding to the the overvoltage of the applied pulse. However, if a subsequent pulse of voltage is applied to the threshold-switching device 36 before the threshold-switching device is fully recovered to its normal or initial threshold voltage value, as indicated at V.sub.T in FIG. 4, this subsequent pulse voltage need only have an amplitude equal to the then existing threshold voltage value, which may be, for example, any where between 0.01V.sub. T to V.sub.T depending upon the point in time the next pulse of voltage is applied. The turn-on time delay illustrated in FIG. 4 may persist regardless of the time at which the subsequent pulse of voltage is applied to the threshold-switching device 36 the only difference being a decrease or shifting of the entire curve 45 as indicated by the family of curves shown in broken lines at 45a. Therefore, in accordance with this invention, once the threshold-switching device is rendered conductive, it can be successively rendered conductive by closely spaced pulses which have voltage amplitudes less than the initial normal threshold voltage value of the switching device. However, if the applied voltage, whether direct current or alternating current pulses, is extinguished for the time interval td corresponding to the inherent recovery time delay of FIG. 5, the threshold-switching device 36 will fully recover to its initial normal threshold voltage value and no longer will be rendered conductive as a result of a continuously applied voltage having an amplitude below the threshold voltage value of the threshold-switching device.

In FIG. 5A the threshold voltage value versus frequency characteristic of the threshold-switching device 36 is illustrated by a curve 47. Because of the inherent recovery time delay of the threshold-switching device 36, the threshold-switching device will operate within a bistable operating range, regardless of the type of load or circuit arrangement to which it is connected. Therefore, when the threshold-switching device 36 is used in conjunction with a capacitive reactive circuit which also has a bistable operating range, the combined bistable characteristics of the capacitive reactive device, here being an electroluminescent element, and the bistable operating range of the threshold-switching device combine to form a substantially increased bistable operating range with an increase in frequency. That is, the amount of increase of the bistable range of an electroluminescent circuit of this invention increases in accordance with an increase in the differential between the initial normal threshold voltage value and the then existing threshold voltage value. This is indicated by the increase in vertical spacing between the extended broken line at the value V.sub.T and the curve 47, of FIG. 5A.

Therefore, by forming an electroluminescent circuit using the threshold-switching device disclosed hereinabove, the electroluminescent array 12, of FIG. 1, can be operated in a novel and unique manner. In accordance with this invention, a continuously applied operating potential, which may be considered a packet, either of AC or DC voltage, is sequentially applied to the row circuit lines 17-21. For example, during one instance the row circuit line 17 has applied thereto the alternating current voltage 50, of FIG. 6, and none of the electroluminescent circuits 16 along the row circuit line 17 will be energized. However, when a video signal pulse is applied to each of the column circuit lines 22-27 the electroluminescent circuit across the junctures will be rendered operative response to a time delay corresponding to the amount of video information to be displayed. That is, if the relative brightness of each of the electroluminescent circuits 16 can be divided into 10 equal brightness intervals or levels, indicated by B.sub.1 -B.sub.10, Fig. 6, the application of a video pulse at any one of these intervals will determine the amount of brightness obtained by the electroluminescent circuit, at the juncture of the row circuit line 17 and any given one of the plurality of column circuit lines 22-27. Therefore, when a video pulse 52 is applied to a selected one of the column circuit lines 22-27, for example, during the interval B.sub.7, the brightness of the selected electroluminescent circuit 16 will be seven-tenths of the total brightness obtainable by the application of all the pulses within the wave packet containing the sine wave pulses 50. While the electroluminescent circuit 16 is energized, the voltage variation across the electroluminescent element is substantially an AC voltage varying about a zero reference line 54. However, the voltage variation is across the entire electroluminescent circuit may be a varying direct current voltage because of a combination of the applied alternating current voltage to the line 17 and the video pulse applied to any one of the lines 22-27, as illustrated by the varying direct current voltage 50a. When a video signal is applied to a selected one of the column circuit lines 22-27 to render the selected electroluminescent circuit conductive for a shorter period of time, as for example, at the time interval represented by B.sub.5, the light emitted from the electroluminescent circuit 16 is reduced so as to emit five-tenths of the total light output of the electroluminescent element during the interval when both an operating potential and a video signal are applied to the selected circuit lines. The minimum amount of light obtainable from any given electroluminescent circuit 16 will be that represented by the brightness level B.sub.1 which allows only a single pulse of alternating current voltage to be applied to the electroluminescent element 37. On the other hand, the maximum amount of brightness obtainable from a selected electroluminescent element 37 is achieved by applying a video pulse to a selected one of the column circuit lines 22-27 at the same time the applied operating potential is applied to the selected row circuit line so that the entire time interval, or all the pulses within the wave packet, is used to energize the electroluminescent element 37. Therefore, by operating the electroluminescent array 12 in accordance with the method disclosed herein and illustrated in FIG. 6, a plurality of different light intensities is obtainable from each of the electroluminescent circuits 16 depending on the point in time the video signal information is applied to the vertical column circuit lines 22-27 while a selected one of the row circuit lines 17-21 has operating potential applied thereto. The row circuit lines 17-21 are sequentially scanned one after the other either from top to bottom or from bottom to top to provide the line-at-a-time scanning of the entire electroluminescent array 12, thereby allowing an entire frame of video display pattern to be formed.

Therefore, video signal information received by the video signal information receiver 14, which may be a conventional portion of a television receiver, is processed in the usual manner therein and a vertical sweep synchronizing pulse is applied to the gated oscillator 28. The gated oscillator then operates to apply an operating potential to a selected row circuit line, for example, row circuit line 17, for a time duration corresponding to the sweep time duration of a conventional television receiver. When the operating potential applied to selected ones of the row circuit lines is an AC voltage, as illustrated herein, the time duration between pulses may be selected to be within the inherent recovery time delay of the threshold-switching device 36. In this mode of operation the threshold-switching device 36 acts basically as an isolation device to isolate all picture elements from being energized until the appropriate video pulse is applied thereto after which time all the pulses remaining within the packet of operating potential will be applied to the electroluminescent element 37 without further consideration of the initial normal threshold voltage value of the threshold-switching device 36.

By selecting the points in time at which each of the electroluminescent circuits along a selected row circuit line is energized, and by terminating energization of all the electroluminescent circuits simultaneously when shifting the operating potential from one line to the next, each of the electroluminescent element will emit different amounts of light thus forming the gray scale necessary to display television pictures on a flat screen electroluminescent array. The simultaneous termination of energization of all the electroluminescent circuits on a given row circuit line, in accordance with this invention, is a straightforward method of compensating for the inherent recovery delay of the threshold-switching devices since a given row circuit line is energized with operating potential only once during each frame of video information displayed.

Accordingly, by utilizing threshold switching devices, having the electrical characteristics disclosed herein, in combination with an electroluminescent circuit arrangement wherein the electroluminescent element thereof acts as a capacitor, and by operating a plurality of such electroluminescent circuits in accordance with this invention, a plurality of different light intensities are obtainable to establish a gray scale substantially corresponding to the gray scale of the video information to be displayed. From the foregoing description it will be understood that variations and modifications may be effected without departing from the spirit and scope of the novel concepts of this invention.

Claims

We claim:

1. A method for controlling energization of discrete points on a display array of the type having row and column circuit lines respectively having pairs of circuit junctures therealong, a light control and emitting circuit across each pair of circuit junctures, and each of said light control and emitting circuits including a light-emitting element connected in circuit with a switching means having display-producing and display-cancelling conditions of operation where an operating potential applied to the associated circuit junctures are respectively effectual and ineffectual upon the associated light-emitting element, said method comprising the steps of: applying sequentially an operating potential to selected ones of the said row circuit lines for a given line scan period to energize the same, and applying to the column circuit lines signals controlled by the relative brightness of selected portions of video signal information to be displayed along a selected line of the display array which signals operate the switching means to their display-producing condition for intervals during said scan period which terminate at the end of said scan period and being at points in time which are a function of the relative brightness of the associated video signal information, the degree of brightness of the display produced by said light-emitting elements being a function of the length of said intervals.

2. The method of controlling energization of discrete points of a display array according to claim 1 wherein the said applied operating potential is an alternating current voltage providing a predetermined number of cycles during the time the selected row of circuit lines is energized thereby, and the number of cycles used to render effectual selected ones of the light-emitting elements along said selected energized row circuit line determining the relative brightness of the display produced by said light-emitting elements.

3. The method of controlling energization of discrete points on a display array according to claim 1 further including the step of converting said video signal information from amplitude signal information to pulse width signal information applied to said column circuit lines and corresponding in time duration to the amplitude of the video signal information, thus energizing selected ones of said light-emitting elements for periods of time corresponding to the relative brightness of the video signal information involved.

4. The method for controlling energization of discrete points on a display array according to claim 1 wherein each light control and emitting circuit connected across each pair of junctures of said row and column circuit lines has at least one circuit component which has inherent time delay characteristics to provide a time delay which is a function of the amplitude of the video signal information involved.

5. The method for controlling energization of discrete points on display array according to claim 1 wherein each of said switch means of each light control and emitting circuit is a voltage amplitude threshold switching means having a threshold voltage value which when exceeded by an applied voltage drives the same into a conductive state until current is interrupted therethrough, each of said threshold-switching means connected in series with a different one of the said light-emitting elements of said array, said threshold-switching means have an inherent turn-on time delay between the time a voltage in excess of the threshold voltage value of said threshold-switching means is applied thereto and the time said threshold-switching means is rendered conductive and an inherent recovery time delay between the time said threshold-switching means is rendered nonconductive and the time that said threshold-switching means recovers to its initial normal threshold voltage value, the threshold voltage value thereof immediately after said threshold-switching means is rendered nonconductive being substantially less than the said initial normal threshold voltage value and progressively increasing to said initial normal threshold voltage value, said operating potential applied to said selected row circuit line being below said initial normal threshold voltage value but greater than the then existing threshold voltage value after said threshold-switching device is rendered conductive, said threshold-switching means being rendered conductive by said operating potential during the time interval of said inherent recovery time delay.

6. A method for controlling energization of discrete points on a display array of the type having row and column circuit lines respectively having pairs of circuit junctures therealong, a light control and emitting circuit across each pair of said junctures, and each of said light control and emitting circuits including a light-emitting element connected in circuit with a voltage amplitude responsive threshold-switching means which is initially rendered operative at a predetermined threshold voltage value, comprising the steps of: applying an operating potential for energizing said light-emitting element simultaneously to all the light control and emitting circuits along a selected row circuit line, said operating potential being below at least an initial threshold voltage value of said threshold-switching means; applying to said column circuit lines video signal controlled information having a voltage amplitude which when combined with the continuously applied operating potential is sufficient to energize the light control and emitting circuits at the junctures along the said selected row circuit line for a period of time corresponding to the light intensity of the video signal information to be displayed; and removing said operation potential from the previously selected row circuit line and applying operating potential to the next successive row circuit line to be energized with video signal controlled information.

7. A circuit arrangement for controlling energization of a display array, comprising: a first group of circuit lines and a second group of circuit lines, each of said first and second group of circuit lines arranged with respect to one another to form respective pairs of circuit junctures corresponding in number to the number of discrete points on a display array; a light control and emitting circuit connected between each of said pair of junctures formed by said first and second group of circuit lines, each of said light control and emitting circuits including a light-emitting element and threshold-switching means connected in a circuit with said light-emitting element, said threshold-switching means being rendered conductive a predetermined threshold voltage value after an inherent turn-on time delay to operatively energize the light-emitting element associated therewith; means for applying to selective ones of said first group of the circuit lines an operating potential below the threshold voltage value of said threshold-switching means of each of said light control and emitting circuits; means for applying video signal controlled voltages to each of the circuit lines in said the second group of circuit lines to raise the voltage across the threshold-switching means connected thereto to or above said threshold voltage value to energize the light-emitting elements of the light control and emitting circuits at the junctures of the selected one of said first group of circuit lines and each of the second circuit lines for a period of time corresponding to the brightness of the video information to be displayed thereby; the degree of brightness of the display produced by said light-emitting elements being a function of the length of time the light-emitting elements involved are energized; and means for selectively terminating the conduction of the threshold-switching means of all of the light control and emitting circuits along a selected one of said first group of circuit lines.

8. The circuit arrangement for controlling energization of a display array according to claim 7 further including means for delaying of said video signal controlled voltages for a period which is a function of the amplitude of the video signal information.

9. The circuit arrangement for controlling energization of a display array according to claim 7 wherein the inherent turn-on time delay of the threshold-switching means of each light control and emitting circuit determines the point in time when the light-emitting element emits light therefrom in accordance with the amplitude of video signal information.

10. A method for controlling the energization of discrete points on a display array of the type having a plurality of row circuit lines and a plurality of column circuit lines having pairs of circuit junctures associated with the crossing points thereof, a light control and emitting circuit across each of said pair of junctures, each light control and emitting circuit including a light-emitting element connected in series with a voltage amplitude threshold-switching device which is rendered conductive at a predetermined threshold voltage value, said method comprising the steps of: applying an operating potential to selected ones of the said row circuit lines to energize the same, said operating potential at least initially having a maximum voltage amplitude below the threshold voltage value of said threshold-switching devices; applying to said column circuit lines signal information dependent upon the relative brightness of selected portions of video signal information to be displayed along a selected line of the display array which signal information effects the delayed application to the various threshold-switching devices connected to the selected energized row circuit line of a resultant applied voltage exceeding the threshold voltage value thereof to render the same conducting, the delay thereof being for a period of time corresponding to the relative brightness of the associated video signal information, a maximum delay time corresponding to a minimum brightness and a minimum delay time corresponding to a maximum brightness; and simultaneously rendering nonconductive threshold-switching devices connected to said selected energized row circuit line simultaneously to deenergize any energized light-emitting element therealong.

11. The method of controlling the energization of discrete points of a display array according to claim 10 wherein the said applied operating potential is an alternating current voltage providing a predetermined number of cycles during the time the selected row of circuit lines is energized thereby, and the number of cycles thereof passing through a conductive threshold switching device to the associated light-emitting element determining the relative brightness of said light-emitting element.

12. The method for controlling energization of discrete points on a display array according to claim 10 wherein said threshold-switching device of each light control and emitting circuits connected across each pair of junctures of said row and column circuit lines has an inherent time delay characteristic in its operation thereof to provide a time delay inversely proportionate to the amplitude to the video signal information applied thereto causing the light control and emitting circuit to be energized for a period of time corresponding to the amplitude of the video signal information.

13. A method of controlling a display array from stored groups of video signals each group of which represents the desired variation in intensity of light along a given line on a display face of the array at a given time, the array including contiguous rows of light-emitting elements positioned along said display face, each row of light-emitting elements to display a pattern corresponding to one of said groups of video signals, each light-emitting element presenting an indication upon application of an energizing pulse thereto, the method comprising cyclically feeding to each of said light-emitting elements an energizing pulse-producing voltage and during each feeding cycle effecting through said voltage and video signals the feeding to said light-emitting element of a number of energizing pulses which is a function of the amplitude of the corresponding stored video signal so the average intensity of the light produced by the light-emitting element varies with the amplitude of such signal.

14. The method of controlling a display array as recited in claim 13 wherein the energizing pulse-producing voltage is simultaneously applied to each row of light-emitting elements during each feeding cycle, the initiation of the application of said energizing pulse-producing voltage to said light-emitting elements occurring at a point in time spaced from the beginning of each feeding cycle an amount depending upon the amplitude of the corresponding stored video signal, and such application of the energizing pulse-producing voltage terminating simultaneously adjacent the end of each feeding cycle following which another row of light-emitting elements receive said energizing pulse-producing voltage.

15. A method for controlling the energization of a light control and emitting circuit including a light-emitting element which is connected in series with a voltage amplitude responsive threshold-switching means initially rendered operative at a predetermined threshold voltage value, comprising the steps of: cyclically applying to said light control and emitting circuit a pulsating voltage waveform of a predetermined number of pulses unrelated to the particular desired intensity of the light to be emitted by the light-emitting element and having amplitudes below at least an initial threshold voltage value of the associated threshold-switching means; and superimposing on said pulsating operating potential a light intensity controlling voltage having a characteristic which varies with the desired intensity of the light to be emitted by said light-emitting element and which, when combined with a pulse of said pulsating voltage waveform, is sufficient to produce across the associated threshold-switching means a resultant voltage exceeding said initial threshold voltage value, the superpositioning on said pulsating voltage waveform on said light intensity controlling voltage producing through the threshold-switching means during each repeated cycle of said pulsating voltage waveform a number of energizing pulses which is a function of said variable characteristic of the light intensity controlling voltage which indicates the desired light intensity, the intensity of the light produced by said light-emitting element varying with the number of energizing pulses fed to the same during each cycle of application of said pulsating voltage waveform.

16. A light control and emitting circuit comprising: a light-emitting element; voltage-responsive, threshold-switching means which is normally in a nonconductive state and switches to a conductive state when a voltage of at least a given threshold voltage value is applied thereacross and reverts to a nonconductive state when the current therethrough drops below a given minimum holding current value; a source of energizing voltage which cyclically provides during various given periods a pulsating voltage waveform of a predetermined number of pulses unrelated to the particular desired intensity of the light to be emitted by the light-emitting element and having amplitudes below at least an initial threshold voltage value of the associated threshold-switching means; a source of a light intensity controlling voltage having a characteristic which varies with the desired intensity of the light to be emitted by said light-emitting element and which, when combined with a pulse of said pulsating voltage waveform, is sufficient to produce across the associated threshold-switching means a resultant voltage exceeding said initial threshold voltage value; and circuit-forming means interconnecting said source of energizing voltage, said source of said light intensity controlling voltage, said threshold-switching means, and said light-emitting element for applying said pulsating voltage waveform and said light intensity controlling voltage in additive relation across said threshold-switching means to repeatedly switch the same into conduction during each of said given periods a number of times which is a function of said variable characteristic of the light intensity controlling voltage to effect the feeding to said light-emitting element of a corresponding number of energizing pulses, the intensity of the light produces by said light-emitting element varying with the number of energizing pulses fed to the same during each of said given periods.

17. A light control and emitting circuit comprising: a light-emitting element; a source of energizing voltage which repeatedly produces over various given periods a pulsating voltage waveform of a predetermined number of pulses unrelated to the particular desired intensity of the light to be emitted by the light-emitting element; a source of light intensity controlling voltage having a characteristic which varies with the desired intensity of the light to be emitted by said light-emitting element; and circuit-forming means interconnecting said source of energizing voltage, said source of said light intensity controlling voltage and said light-emitting element for feeding to said light-emitting element during each of said periods a number of energizing pulses which is a function of said variable characteristic of the light intensity controlling voltage, the intensity of the light produced by said light-emitting element varying with the number of energizing pulses fed to the same during each of said given periods.