US3833833A - Drive circuitry for light emitting film displays - Google Patents

Drive circuitry for light emitting film displays Download PDF

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US3833833A
US3833833A US00390097A US39009773A US3833833A US 3833833 A US3833833 A US 3833833A US 00390097 A US00390097 A US 00390097A US 39009773 A US39009773 A US 39009773A US 3833833 A US3833833 A US 3833833A
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    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B44/00Circuit arrangements for operating electroluminescent light sources

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  • ABSTRACT Driving circuitry for multiplexed light emitting film displays is shown wherein the unselected segment electrodes of a segment matrix and/or the unselected digit electrodes are connected together to prevent establishment of floating complex series-parallel capacitance networks which could otherwise drive certain of the unselected electrodes to emit unwanted light.
  • the polarity of the voltage applied to inductors forming part of the electrode drive circuits is reversed during each segment drive cycle to eliminate decrease of light intensity of a respectively fired electrode due to energy losses incurred in the inductors and in the display.
  • Light emitting films are well known in the art for use as data displays or the like and are disclosed, for exari1 ple, in the U.S. Pat. to Gordon Steele et al, US. Pat. No. 3,560,784, issued on Feb. 2, 197 l
  • Such films comprise basically a polycry-stalline phosphor film or the like having electrode layers on opposite sides thereof, at least one of which is transparent. The assembly forms a capacitor and when a voltage of sufficient potential is applied across the electrode layers, the phosphor film will glow in the area between the opposite energized electrodes and will be visible through the transparent electrode.
  • Light emitting films of the above type when used for data displays, have certain characteristics which require special driving circuits for energizing the same. For example, it has been found that application of an appreciable DC voltage potential across the electrode layers tends to degrade the life of the film. Also, in digital displays of either the segment matrix or the dot matrix type, a relatively large number of segment electrodes (in the case of a segment matrix) or a large number of X-Y electrodes (in the case of a dot matrix) are required, particularly for a multi-digit display. Also, a large number of independent drive circuits are required to drive such electrodes. This number is reduced to some extent by driving the array of electrodes at a high rate in a multiplexed fashion wherein only one digit is formed at a time, with the persistence characteristic of the film and the persistence of vision of the eye eliminating flickering.
  • the various unselected electrodes are found to form a number of series and parallel capacitor combinations in circuit with a selected electrode pair and thus when the selected pair is driven to the proper voltage necessary to cause the same to emit a required amount of light, relatively high voltages are also supplied to the unselected pairs, causing unwanted light emission by at least some of those unselected pairs.
  • Another object is to reduce the complication, and consequently the cost, of drive circuitry for light emitting film displays of the above type.
  • Another object is to maintain full illumination of different energized electrodes of a light emitting film display of the above type regardless of the amount of repetitive usage of such electrodes.
  • Another object is to increase the operating life of light emitting films of the above type.
  • each electrode is connected in circuit with a respective inductor to form a resonant circuit, the inductors and corresponding electrodes being connected together through low impedance switching means so as to maintain all unselected electrodes at a fixed reference voltage at all times.
  • a switching device alternately connects the inductors of the segment electrodes to voltages of different potentials so that energy stored in the inductors of both selected and unselected segments is always decaying at the same rate during the time interval when a segment electrode may be energized.
  • each of the unselected electrodes is connected to a common reference voltage and only one digit array is selected at a time, the capacitances thereof cannot be combined in different complex series-parallel paths which could otherwise cause unwanted light emission of such unselected pairs. That is, the voltage applied to the unselected pairs will remain constant and well below that required to luminesce. Furthermore, only a negligible DC component will be applied across the electrode pairs.
  • the energy stored in such inductors is always decaying during the time interval when a segment electrode may be energized.
  • FIG. 1 illustrates diagramatically a multiplexing arrangement of data display light emitting films embodying a preferred form of the present invention.
  • FIG. 2 illustrates a display panel including a typical FIG. 5 is a diagram showing the waveforms at specific points in the circuit of FIG. 1.
  • FIG. 6 is a schematic diagram of a modified form of the invention.
  • FIGS. 2 and 3 a multidigit display panel, generally indicated at 11, is illustrated. Although only three digit arrays 12, 13, and 14 are shown, it should be understood that a greater number of such arrays may be incorporated in the panel, for example, twelve.
  • the display panel which per se forms no part of the present invention, may comprise a glass substrate 15 (FIG. 3) to which are bonded a series of separated transparent electrodes 16 in a common layer or plane.
  • the electrodes 16 are located side-by-side and form the digit electrodes.
  • a transparent polycrystalline phosphor film 17 is interposed between a dielectric film 18 and a second transparent dielectric film 19, the latter being bonded to the surfaces of the digit electrodes 16.
  • a series of separated segment electrodes 20 in a common layer which may be opaque, are bonded to the dielectric layer 18 and are arranged in groups of eight, overlaying respective digit electrodes 16. Seven of such segment electrodes 20 form the figure 8 as seen in FIG. 2, and the eighth which may or may not be used forms a decimal point 21.
  • the total capacitance per segment is approximately 48 pf. (pico farads) for horizontal segments and 60 pf. for vertical segments.
  • an inductor 22 of approximately 50 mh. (millihenries) is connected between each digit electrode 16 and a common line 29.
  • the corresponding segment electrodes 20 of the different digit arrays 12, 13, 14, etc. are connected together through respective lines 23 and each such line is connected through an inductor 24 of approximately 50 mh. to a switching device shown generally at 39, capable of alternately connecting all of the inductors 24 to the positive side of a DC power source 39b of one potential (V,) and to the negative side of a DC power source 39a and 3912 are connected to the common line 29.
  • PNP transistors 26, forming digit switching devices, are connected between respective digit electrodes 16 and a third DC power supply source 27.
  • a diode 28 is connected in series with the collector of each transistor 26 for a purpose to be described later.
  • an NPN transistor 30 is connected between each segment line 23 and the common line 29.
  • a diode 32 is connected in series with the collector of each of the transistors 30.
  • NPN transistors for digit drivers and NPN transistors for segment drivers are arbitrary. NPN digit drivers and PNP segment drivers would function as well.
  • the optimum potentials of the power supplies 27, 39a and 39b depend on the resistances of the inductors 22 and 24 and the voltage drop across the transistors 26 and 30 and diodes 28 and 32.
  • the voltage drop across the transistors 22 and 24 plus diodes 28 and 32 is approximately 0.9 volts and the voltage drop across each inductor is not more than 0.5 volts or a total of approximately 1.5 volts.
  • the diode 28 becomes reverse-biased to prevent clipping of the positive half of the cycle.
  • the respective diode 32 prevents clipping of the negative half of the cycle.
  • the peak voltage across each of the transistors is approximately one half the voltage across the selected electrode pair or pairs.
  • the peak voltage across the transistors 26 and 30 is approximately I75 volts each and thus the peak voltage across each selected electrode pair is 350 volts, making 700 volts peak-to-peak.
  • the transistors 26 and 30 are preferably turned on during the half cycle in which the diodes 28 and 32 are back-biased.
  • the transistors 26 and 30 are preferably turned off for approximately 30 MS.
  • the different transistors 26 are in conducting condition and are turned off sequentially in a re-occurring manner to sequentially bias the different electrodes 16 to energized condition. Circuitry for performing this function may be conventional and is therefore not disclosed herein.
  • each numeral display requires from two to seven segment electrodes to be energized at a time. Therefore, if C equals the capacitance of a single electrode pair, and N equals the number of digits in the display, then the total capacitance seen by any transistor 30 is 2C for a selected digit and (N-l )C for all unselected digits or a total of (N+l )C. Since all segment electrodes are connected to the common line 29, the capacitance seen at the juncture of the inductor 22 and electrode 16 is 2C for each driven segment electrode plus C for each undriven segment electrode or 2PC (7-P)C 7+P)C where P equals the number of selected segment electrodes.
  • the total range of equivalent digit electrode capacitance is 9C to 14C, not including that of the decimal point electrode 21. If the decimal point electrode capacitance is 0.2C, the total range of digit capacitance is 9.2C to 14.4C or an average of l 1.8C i 22 percent. Since a 22 percent variation in capacitance results in approximately a l 1 percent variation in voltage, (V I V (L/C) and since the voltage applied to the selected digit electrode 16 is one half of the total voltage across a selected electrode pair, the voltage uncertainty due to variations in the number of segment electrodes which are driven at any one time is approximately 5 percent, which results in a negligible change in light intensity.
  • the rate of change of current through inductors 24 during the period T (FIG. 5) of a display cycle can be changed by changing the potential V of the power supply 39a so that the energy lost per display cycle is independent of whether a segment electrode is driven or not. That is, the potential V of power supply 39a is dictated by the losses or Q of the L-C combination (inductor 24-segment electrode 20) while the potential V, of the power supply 39b may be of any convenient voltage.
  • T /T -l-T For a given V and V the duty cycle or T /T -l-T may be computed from the expression: Inductor current I V T V T /(T,+T )RVsw/R Where Vsw the voltage across the series combination of transistors 30 an diodes 32 and R the resistance of inductors 24
  • FIG. 4 illustrates one example of a device suitable for this purpose.
  • FIG. 6 illustrates a modified form of the invention wherein the drive circuitry, including inductors 24, for the segment electrodes 20, are similar to those shown in FIG. 1. However, the inductors 22 for the digit electrodes 16 are omitted and in lieu thereof, the unselected digit electrodes 16 are each connected through a normally on transistor 50 and resistor 51 to ground potential.
  • a second transistor 52 and resistor 53 are connected between the electrode 16 and a DC source 54 of minus volts.
  • the latter transistor 52 is normally biased to of condition and the base thereof is connected to a signal input 55 through a capacitor 56.
  • a diode 57 is connected between the electrode 16 and ground to provide a low impedance path to ground during the positive half cycle of the segment drive. Resistors 53 and 51 limit current through the electrode pairs to a level below that which may cause damage to the display.
  • a positive pulse 60 to a selected signal input 55 Upon application of a positive pulse 60 to a selected signal input 55 the respective transistor 50 is turned off and transistor 52 turned on to apply minus 175 volts to the corresponding electrode 16.
  • the minus 175 volt potential, applied to thedigit electrode 16 will occur during a positive half of the voltage waveform 49 (FIG. 5) applied to the segment electrodes, resulting in a total peak voltage across the digit and segment electrodes of 350 volts to cause emission.
  • the circuitry of FIG. 6 may apply a DC component across the electrode pairs, the duty cycle for the digit electrode drive circuitry is typically no more than 1% and therefore the DC component is negligible.
  • a drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a series of main electrodes on one side and a series of groups of secondary electrodes on the other side, each of said groups being associated with a respective one of said main electrodes, comprising inductors connected in circuit with respective ones of the electrodes of one of said series, power supply means for applying an electrical potential for different ones of said main electrodes,
  • said power supply means including a group of main switching devices connected in circuit with respective ones of said main electrodes;
  • said last mentioned power supply means including a group of secondary switching devices connected in circuit with respective ones of said secondary electrodes whereby, when any of said main switching devices and any of said secondary switching devices associated with a last mentioned main switching device are simultaneously turned off, energy stored in respective ones of said electrodes to cause light emission;
  • a drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a main electrode on one side and a plurality of secondary electrodes on the other side, comprising inductors connected in circuit with respective ones of said secondary electrodes,
  • said power supply means including a main switching device connected in circuit with said main electrode;
  • said last mentioned power supply means including secondary switching devices connected in circuit with respective ones of said inductors whereby, when said main switching device and any of said secondary switching devices are simultaneously turned off, energy stored in respective ones of said inductors will be transferred to respective ones of said secondary electrodes to cause light emission;
  • switching devices having a common electrical connection.
  • a drive circuit according to claim 4 comprising means for alternately applying different voltage potentials to said common electrical connection.
  • a drive circuit according to claim 4 comprising means for alternately applying voltage potentials of different polarities to said common electrical connection.
  • a drive circuit according to claim 5 comprising means for concurrently operating said last mentioned means and for turning off said switching devices.
  • a drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a main electrode on one side and a plurality of secondary electrodes on the other side, comprising a main inductor connected in circuit with said main electrode,
  • said power supply means for applying an electrical potential to said main inductor, said power means including a main switching device connected in circuit with said main inductor,
  • said last mentioned power supply means including secondary switching devices connected in circuit with respective ones of said secondary inductors whereby, when said main switching device and any of said secondary switching devices are simultaneously turned off, energy stored in respective ones of said inductors will be transferred to respective ones of said electrodes to cause light emission,
  • main and secondary switching means having a common electrical connection.
  • a drive circuit according to claim 7 wherein said main inductor is connected in series with said main electrode and said secondary inductors are connected in series with respective ones of said secondary electrodes.
  • a drive circuit according to claim 8 wherein said main switching device comprises a switching transistor connected to a point intermediate said main inductor and said main electrode, and
  • said secondary switching device comprises switching transistors connected to points intermediate said secondary inductors and respective ones of said secondary electrodes.
  • a drive circuit according to claim 10 comprising means for back-biasing said transistors.
  • a drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a plurality of main electrodes on one side and a plural ity of groups of secondary electrodes on the other side, each of said groups being associated with a respective one of said main electrodes, comprising main inductors connected in circuit with respective ones of said main electrodes,
  • said power supply means including main switching devices connected in circuit with respective ones of said main electrodes;
  • said last mentioned power supply means including secondary switching devices connected in circuit with respective ones of said secondary electrodes whereby, when any of said main switching devices and any of said secondary switching devices associated with a said last mentioned main switching device are simultaneously turned off, energy stored in respective ones of said inductors will be transferred to respective ones of said electrodes to cause light emission;
  • said inductors having a common electrical connection.
  • a device according to claim 14 comprising means for alternately applying different voltag'e potentials to said secondary inductors.
  • a device according to claim 14 comprising means for changing said voltage potential applied to said secondary inductors when said switching devices are turned off.

Abstract

Driving circuitry for multiplexed light emitting film displays is shown wherein the unselected segment electrodes of a segment matrix and/or the unselected digit electrodes are connected together to prevent establishment of floating complex seriesparallel capacitance networks which could otherwise drive certain of the unselected electrodes to emit unwanted light. Also, the polarity of the voltage applied to inductors forming part of the electrode drive circuits is reversed during each segment drive cycle to eliminate decrease of light intensity of a respectively fired electrode due to energy losses incurred in the inductors and in the display.

Description

United States Patent Nelson Sept. 3, 1974 DRIVE CIRCUITRY FOR LIGHT EMITTING FILM DISPLAYS Alan H. Nelson, 4232 La Concetta Dr., Yorba Linda, Calif. 92686 Filed: Aug. 20, 1973 Appl. No.: 390,097
Inventor:
US. Cl 315/169 TV, 340/324 R, 340/336 Int. Cl. H05b 33/00 Field of Search 3l5/l69 TV, 169 R, 284;
340/324 R, 336, I66 EL References Cited UNITED STATES PATENTS Morgan 3l5/l69 R I-libi 3l5/l69 R Nishizawa 3l5/l69 TV 3,786,307 l/l974 Robinson 3l5/l69 TV Primary ExaminerJohn S. Heyman [57] ABSTRACT Driving circuitry for multiplexed light emitting film displays is shown wherein the unselected segment electrodes of a segment matrix and/or the unselected digit electrodes are connected together to prevent establishment of floating complex series-parallel capacitance networks which could otherwise drive certain of the unselected electrodes to emit unwanted light.
Also, the polarity of the voltage applied to inductors forming part of the electrode drive circuits is reversed during each segment drive cycle to eliminate decrease of light intensity of a respectively fired electrode due to energy losses incurred in the inductors and in the display.
16 Claims, 6 Drawing Figures PATENTEB SHEEI 1 OF 3 llalllllll'lllll DRIVE CIRCUITRY FOR LIGHT EMITTING FILM DISPLAYS BACKGROUND OF THE INVENTION This invention relates to electroluminescent displays and has particular reference to drive circuitry for light emitting film displays.
Light emitting films are well known in the art for use as data displays or the like and are disclosed, for exari1 ple, in the U.S. Pat. to Gordon Steele et al, US. Pat. No. 3,560,784, issued on Feb. 2, 197 l Such films comprise basically a polycry-stalline phosphor film or the like having electrode layers on opposite sides thereof, at least one of which is transparent. The assembly forms a capacitor and when a voltage of sufficient potential is applied across the electrode layers, the phosphor film will glow in the area between the opposite energized electrodes and will be visible through the transparent electrode.
Light emitting films of the above type, when used for data displays, have certain characteristics which require special driving circuits for energizing the same. For example, it has been found that application of an appreciable DC voltage potential across the electrode layers tends to degrade the life of the film. Also, in digital displays of either the segment matrix or the dot matrix type, a relatively large number of segment electrodes (in the case of a segment matrix) or a large number of X-Y electrodes (in the case of a dot matrix) are required, particularly for a multi-digit display. Also, a large number of independent drive circuits are required to drive such electrodes. This number is reduced to some extent by driving the array of electrodes at a high rate in a multiplexed fashion wherein only one digit is formed at a time, with the persistence characteristic of the film and the persistence of vision of the eye eliminating flickering.
In prior art driving circuits of the above type, the various unselected electrodes are found to form a number of series and parallel capacitor combinations in circuit with a selected electrode pair and thus when the selected pair is driven to the proper voltage necessary to cause the same to emit a required amount of light, relatively high voltages are also supplied to the unselected pairs, causing unwanted light emission by at least some of those unselected pairs. Thus, in order to prevent a voltage build-up in unselected electrode pairs sufficient to cause unwanted light emission, it has been necessary heretofore to limit the number of electrodes which may be connected in parallel.
Also, because of the large number of drive circuits required (even in a multiplex system) for driving the different electrodes of a data display unit, economy of circuitry is of paramount importance. Heretofore, although relatively simple drive circuits have been proposed, those of which applicant is aware result in a considerable amount of DC voltage being applied to the electrodes which tends to damage the film and/or electrodes and thus reduce its effective life. Efforts to eliminate this tendency have resulted heretofore in complex and expensive circuitry.
SUMMARY OF THE INVENTION It therefore becomes a principal object of the present invention to provide a drive circuitry for a multi-digit light emitting film display in which capacitive networks tending to drive unselected electrodes to illumination are essentially eliminated.
Another object is to reduce the complication, and consequently the cost, of drive circuitry for light emitting film displays of the above type.
Another object is to maintain full illumination of different energized electrodes of a light emitting film display of the above type regardless of the amount of repetitive usage of such electrodes.
Another object is to increase the operating life of light emitting films of the above type.
According to a preferred embodiment of the present invention, each electrode is connected in circuit with a respective inductor to form a resonant circuit, the inductors and corresponding electrodes being connected together through low impedance switching means so as to maintain all unselected electrodes at a fixed reference voltage at all times.
Also, preferably, a switching device alternately connects the inductors of the segment electrodes to voltages of different potentials so that energy stored in the inductors of both selected and unselected segments is always decaying at the same rate during the time interval when a segment electrode may be energized.
Other individual switching devices for both the segment electrodes and the digit electrodes are provided and are normally held on (conducting) so that the voltage applied across the inductors is such that the total energy stored in such inductors is equal to the energy required to drive each electrode pair to their required peak voltage necessary to cause full light emission. Now, if the two such individual switching devices in circuit with a selected electrode pair and their respective inductors are turned off simultaneously, the magnetic fields of such respective inductors collapse, causing the resonant circuits comprising the inductance and capacitance formed by theelectrode pair to resonate or ring at a frequency determined by the inductance L of the inductors and the capacitance C of the electrode pair, i.e., f =1 /21r V LC.
Since each of the unselected electrodes is connected to a common reference voltage and only one digit array is selected at a time, the capacitances thereof cannot be combined in different complex series-parallel paths which could otherwise cause unwanted light emission of such unselected pairs. That is, the voltage applied to the unselected pairs will remain constant and well below that required to luminesce. Furthermore, only a negligible DC component will be applied across the electrode pairs.
Also, since relatively different voltage potentials are alternately applied to the inductors of the segment electrodes, the energy stored in such inductors is always decaying during the time interval when a segment electrode may be energized.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates diagramatically a multiplexing arrangement of data display light emitting films embodying a preferred form of the present invention.
FIG. 2 illustrates a display panel including a typical FIG. 5 is a diagram showing the waveforms at specific points in the circuit of FIG. 1.
FIG. 6 is a schematic diagram of a modified form of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 2 and 3 in particular, a multidigit display panel, generally indicated at 11, is illustrated. Although only three digit arrays 12, 13, and 14 are shown, it should be understood that a greater number of such arrays may be incorporated in the panel, for example, twelve.
The display panel, which per se forms no part of the present invention, may comprise a glass substrate 15 (FIG. 3) to which are bonded a series of separated transparent electrodes 16 in a common layer or plane. The electrodes 16 are located side-by-side and form the digit electrodes. A transparent polycrystalline phosphor film 17 is interposed between a dielectric film 18 and a second transparent dielectric film 19, the latter being bonded to the surfaces of the digit electrodes 16. A series of separated segment electrodes 20 in a common layer, which may be opaque, are bonded to the dielectric layer 18 and are arranged in groups of eight, overlaying respective digit electrodes 16. Seven of such segment electrodes 20 form the figure 8 as seen in FIG. 2, and the eighth which may or may not be used forms a decimal point 21.
Each segment electrode 20, together with its respective digit electrode 16, form what I will term an electrode pair having a capacity C which, when an AC voltage in the neighborhood of 350 volts, peak or 700 volts peak to peak, is impressed thereacross causes the interposed portion of phosphor film 17 to emit visible light. Where digits having a height of 0.35 inches are incorporated in the panel 11, the total capacitance per segment is approximately 48 pf. (pico farads) for horizontal segments and 60 pf. for vertical segments.
As seen in FIG. 1, an inductor 22 of approximately 50 mh. (millihenries) is connected between each digit electrode 16 and a common line 29. Also, the corresponding segment electrodes 20 of the different digit arrays 12, 13, 14, etc., are connected together through respective lines 23 and each such line is connected through an inductor 24 of approximately 50 mh. to a switching device shown generally at 39, capable of alternately connecting all of the inductors 24 to the positive side of a DC power source 39b of one potential (V,) and to the negative side of a DC power source 39a and 3912 are connected to the common line 29.
PNP transistors 26, forming digit switching devices, are connected between respective digit electrodes 16 and a third DC power supply source 27. A diode 28 is connected in series with the collector of each transistor 26 for a purpose to be described later. Likewise, an NPN transistor 30 is connected between each segment line 23 and the common line 29. A diode 32 is connected in series with the collector of each of the transistors 30.
The use of PNP transistors for digit drivers and NPN transistors for segment drivers is arbitrary. NPN digit drivers and PNP segment drivers would function as well.
Normally, all of the transistors 26 and 30 are biased to on or conducting condition, causing a current flow through all of the inductors 22 and 24, thereby 26 and 30 are momentarily turned off by simultaneously applying proper biasing signals 138 and 139 (FIG. 5) to the bases e and e.,, respectively, thereof concurrently with switching of the device 39 from source 39b to source 39a as seen at 40 (FIG. 5). This will induce a voltage having a waveform 49 (FIG. 5) in the selected resonant circuits and will drive the selected main digit electrode 16 and secondary segment electrodes 20 to light emission. If L l/(21rf) where f is the desired drive frequency and C is the equivalent capacitance of the selected electrode pair comprising a digit electrode 16 and segment electrode 20, the connected resonant circuit will ring at the desired frequency and amplitude to cause full light emission.
The optimum potentials of the power supplies 27, 39a and 39b, depend on the resistances of the inductors 22 and 24 and the voltage drop across the transistors 26 and 30 and diodes 28 and 32. In the present embodiment, the voltage drop across the transistors 22 and 24 plus diodes 28 and 32 is approximately 0.9 volts and the voltage drop across each inductor is not more than 0.5 volts or a total of approximately 1.5 volts.
As the voltage applied to the digit electrode 16 reverses, the diode 28 becomes reverse-biased to prevent clipping of the positive half of the cycle. Likewise, as the voltage applied to the selected segment electrode 20 reverses, the respective diode 32 prevents clipping of the negative half of the cycle.
Since the selected digit electrode 16 and segment electrodes 20 are driven out of phase with each other, the peak voltage across each of the transistors, i.e., 26 and 30, is approximately one half the voltage across the selected electrode pair or pairs. In the presently disclosed embodiment, the peak voltage across the transistors 26 and 30 is approximately I75 volts each and thus the peak voltage across each selected electrode pair is 350 volts, making 700 volts peak-to-peak.
In order to avoid excessive current and unnecessary energy losses, the transistors 26 and 30 are preferably turned on during the half cycle in which the diodes 28 and 32 are back-biased. Thus, where f 25 khz, which is a period of 40 ,us, the transistors 26 and 30 are preferably turned off for approximately 30 MS. Normally, in the present multiplexing system, the different transistors 26 are in conducting condition and are turned off sequentially in a re-occurring manner to sequentially bias the different electrodes 16 to energized condition. Circuitry for performing this function may be conventional and is therefore not disclosed herein.
light emission. Also, the capacitance of each unselected electrode pair will be constant.
It will be noted that the formation of each numeral display requires from two to seven segment electrodes to be energized at a time. Therefore, if C equals the capacitance of a single electrode pair, and N equals the number of digits in the display, then the total capacitance seen by any transistor 30 is 2C for a selected digit and (N-l )C for all unselected digits or a total of (N+l )C. Since all segment electrodes are connected to the common line 29, the capacitance seen at the juncture of the inductor 22 and electrode 16 is 2C for each driven segment electrode plus C for each undriven segment electrode or 2PC (7-P)C 7+P)C where P equals the number of selected segment electrodes. Since P is never less than two or more than seven, the total range of equivalent digit electrode capacitance is 9C to 14C, not including that of the decimal point electrode 21. If the decimal point electrode capacitance is 0.2C, the total range of digit capacitance is 9.2C to 14.4C or an average of l 1.8C i 22 percent. Since a 22 percent variation in capacitance results in approximately a l 1 percent variation in voltage, (V I V (L/C) and since the voltage applied to the selected digit electrode 16 is one half of the total voltage across a selected electrode pair, the voltage uncertainty due to variations in the number of segment electrodes which are driven at any one time is approximately 5 percent, which results in a negligible change in light intensity.
The rate of change of current through inductors 24 during the period T (FIG. 5) of a display cycle can be changed by changing the potential V of the power supply 39a so that the energy lost per display cycle is independent of whether a segment electrode is driven or not. That is, the potential V of power supply 39a is dictated by the losses or Q of the L-C combination (inductor 24-segment electrode 20) while the potential V, of the power supply 39b may be of any convenient voltage.
For a given V and V the duty cycle or T /T -l-T may be computed from the expression: Inductor current I V T V T /(T,+T )RVsw/R Where Vsw the voltage across the series combination of transistors 30 an diodes 32 and R the resistance of inductors 24 Although any suitable form of polarity switching device 39 may be employed to alternately apply different voltage potentials to the inductors 24 concurrently with turning off of the transistors 26 and 30, FIG. 4 illustrates one example of a device suitable for this purpose.
During the time interval T (FIG. 5), transistor 42 is biased on and transistor 43 is biased off thus applying the positive voltage V to the line common to inductors 24 (e During the time interval T the combination of transistor 43 and diode 44, provide a low impedance bidirectional current path from the junction of inductors 24 (e to the negative potential V DESCRIPTION OF ALTERNATE EMBODIMENT FIG. 6 illustrates a modified form of the invention wherein the drive circuitry, including inductors 24, for the segment electrodes 20, are similar to those shown in FIG. 1. However, the inductors 22 for the digit electrodes 16 are omitted and in lieu thereof, the unselected digit electrodes 16 are each connected through a normally on transistor 50 and resistor 51 to ground potential. A second transistor 52 and resistor 53 are connected between the electrode 16 and a DC source 54 of minus volts. The latter transistor 52 is normally biased to of condition and the base thereof is connected to a signal input 55 through a capacitor 56. A diode 57 is connected between the electrode 16 and ground to provide a low impedance path to ground during the positive half cycle of the segment drive. Resistors 53 and 51 limit current through the electrode pairs to a level below that which may cause damage to the display.
Upon application of a positive pulse 60 to a selected signal input 55 the respective transistor 50 is turned off and transistor 52 turned on to apply minus 175 volts to the corresponding electrode 16. Thus, the minus 175 volt potential, applied to thedigit electrode 16 will occur during a positive half of the voltage waveform 49 (FIG. 5) applied to the segment electrodes, resulting in a total peak voltage across the digit and segment electrodes of 350 volts to cause emission.
While the circuitry of FIG. 6 may apply a DC component across the electrode pairs, the duty cycle for the digit electrode drive circuitry is typically no more than 1% and therefore the DC component is negligible.
I claim:
1. A drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a series of main electrodes on one side and a series of groups of secondary electrodes on the other side, each of said groups being associated with a respective one of said main electrodes, comprising inductors connected in circuit with respective ones of the electrodes of one of said series, power supply means for applying an electrical potential for different ones of said main electrodes,
said power supply means including a group of main switching devices connected in circuit with respective ones of said main electrodes;
power supply means for applying an electrical potential to said secondary electrodes,
said last mentioned power supply means including a group of secondary switching devices connected in circuit with respective ones of said secondary electrodes whereby, when any of said main switching devices and any of said secondary switching devices associated with a last mentioned main switching device are simultaneously turned off, energy stored in respective ones of said electrodes to cause light emission;
at least one of said groups of switching devices having a common electrical connection.
2. A drive circuit according to claim 1 wherein both of said groups of switching devices have respective common electrical connections.
3. A drive circuit according to claim 2 wherein both of said groups of switching devices have a common electrical connection.
4. A drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a main electrode on one side and a plurality of secondary electrodes on the other side, comprising inductors connected in circuit with respective ones of said secondary electrodes,
power supply means for applying an electrical potential to said secondary electrodes,
said power supply means including a main switching device connected in circuit with said main electrode;
power supply means for applying an electrical potential to said inductors,
said last mentioned power supply means including secondary switching devices connected in circuit with respective ones of said inductors whereby, when said main switching device and any of said secondary switching devices are simultaneously turned off, energy stored in respective ones of said inductors will be transferred to respective ones of said secondary electrodes to cause light emission;
said switching devices having a common electrical connection.
5. A drive circuit according to claim 4 comprising means for alternately applying different voltage potentials to said common electrical connection.
6. A drive circuit according to claim 4 comprising means for alternately applying voltage potentials of different polarities to said common electrical connection.
7. A drive circuit according to claim 5 comprising means for concurrently operating said last mentioned means and for turning off said switching devices.
8. A drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a main electrode on one side and a plurality of secondary electrodes on the other side, comprising a main inductor connected in circuit with said main electrode,
secondary inductors connected in circuit with respective ones of said secondary electrodes,
power supply means for applying an electrical potential to said main inductor, said power means including a main switching device connected in circuit with said main inductor,
power supply means for applying an electrical potential to said secondary inductors,
said last mentioned power supply means including secondary switching devices connected in circuit with respective ones of said secondary inductors whereby, when said main switching device and any of said secondary switching devices are simultaneously turned off, energy stored in respective ones of said inductors will be transferred to respective ones of said electrodes to cause light emission,
said main and secondary switching means having a common electrical connection.
9. A drive circuit according to claim 7 wherein said main inductor is connected in series with said main electrode and said secondary inductors are connected in series with respective ones of said secondary electrodes.
10. A drive circuit according to claim 8 wherein said main switching device comprises a switching transistor connected to a point intermediate said main inductor and said main electrode, and
said secondary switching device comprises switching transistors connected to points intermediate said secondary inductors and respective ones of said secondary electrodes.
11. A drive circuit according to claim 10 comprising means for back-biasing said transistors.
12. A drive circuit according to claim 8 wherein said common electrical connection is connected to said first and second power supply means.
13. A drive circuit according to claim 8 wherein said main inductor is connected in circuit with said main electrode and said secondary inductors are connected in circuit with respective ones of said secondary electrodes to form resonant circuits, said common electrical connection being connected to a point intermediate said main inductor and said secondary switching devices.
14. A drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a plurality of main electrodes on one side and a plural ity of groups of secondary electrodes on the other side, each of said groups being associated with a respective one of said main electrodes, comprising main inductors connected in circuit with respective ones of said main electrodes,
secondary inductors connected in circuit with respective ones of said secondary electrodes,
power supply means for applying an electrical poten tial to different ones of said main electrodes,
said power supply means including main switching devices connected in circuit with respective ones of said main electrodes;
power supply means for applying an electrical potential to said secondary electrodes,
said last mentioned power supply means including secondary switching devices connected in circuit with respective ones of said secondary electrodes whereby, when any of said main switching devices and any of said secondary switching devices associated with a said last mentioned main switching device are simultaneously turned off, energy stored in respective ones of said inductors will be transferred to respective ones of said electrodes to cause light emission;
said inductors having a common electrical connection.
15. A device according to claim 14 comprising means for alternately applying different voltag'e potentials to said secondary inductors.
16. A device according to claim 14 comprising means for changing said voltage potential applied to said secondary inductors when said switching devices are turned off.

Claims (16)

1. A drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a series oF main electrodes on one side and a series of groups of secondary electrodes on the other side, each of said groups being associated with a respective one of said main electrodes, comprising inductors connected in circuit with respective ones of the electrodes of one of said series, power supply means for applying an electrical potential for different ones of said main electrodes, said power supply means including a group of main switching devices connected in circuit with respective ones of said main electrodes; power supply means for applying an electrical potential to said secondary electrodes, said last mentioned power supply means including a group of secondary switching devices connected in circuit with respective ones of said secondary electrodes whereby, when any of said main switching devices and any of said secondary switching devices associated with a last mentioned main switching device are simultaneously turned off, energy stored in respective ones of said electrodes to cause light emission; at least one of said groups of switching devices having a common electrical connection.
2. A drive circuit according to claim 1 wherein both of said groups of switching devices have respective common electrical connections.
3. A drive circuit according to claim 2 wherein both of said groups of switching devices have a common electrical connection.
4. A drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a main electrode on one side and a plurality of secondary electrodes on the other side, comprising inductors connected in circuit with respective ones of said secondary electrodes, power supply means for applying an electrical potential to said secondary electrodes, said power supply means including a main switching device connected in circuit with said main electrode; power supply means for applying an electrical potential to said inductors, said last mentioned power supply means including secondary switching devices connected in circuit with respective ones of said inductors whereby, when said main switching device and any of said secondary switching devices are simultaneously turned off, energy stored in respective ones of said inductors will be transferred to respective ones of said secondary electrodes to cause light emission; said switching devices having a common electrical connection.
5. A drive circuit according to claim 4 comprising means for alternately applying different voltage potentials to said common electrical connection.
6. A drive circuit according to claim 4 comprising means for alternately applying voltage potentials of different polarities to said common electrical connection.
7. A drive circuit according to claim 5 comprising means for concurrently operating said last mentioned means and for turning off said switching devices.
8. A drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a main electrode on one side and a plurality of secondary electrodes on the other side, comprising a main inductor connected in circuit with said main electrode, secondary inductors connected in circuit with respective ones of said secondary electrodes, power supply means for applying an electrical potential to said main inductor, said power means including a main switching device connected in circuit with said main inductor, power supply means for applying an electrical potential to said secondary inductors, said last mentioned power supply means including secondary switching devices connected in circuit with respective ones of said secondary inductors whereby, when said main switching device and any of said secondary switching devices are simultaneously turned off, energy stored in respective ones of said inductors will be transferred to respective ones of said electrodes to cause light emission, said main and secondary switching means having a common electrical connection.
9. A drive circuit according to claim 7 wherein said main inductor is connected in series with said main electrode and said secondary inductors are connected in series with respective ones of said secondary electrodes.
10. A drive circuit according to claim 8 wherein said main switching device comprises a switching transistor connected to a point intermediate said main inductor and said main electrode, and said secondary switching device comprises switching transistors connected to points intermediate said secondary inductors and respective ones of said secondary electrodes.
11. A drive circuit according to claim 10 comprising means for back-biasing said transistors.
12. A drive circuit according to claim 8 wherein said common electrical connection is connected to said first and second power supply means.
13. A drive circuit according to claim 8 wherein said main inductor is connected in circuit with said main electrode and said secondary inductors are connected in circuit with respective ones of said secondary electrodes to form resonant circuits, said common electrical connection being connected to a point intermediate said main inductor and said secondary switching devices.
14. A drive circuit for a capacitive light emitting film display wherein a phosphor film is interposed between a plurality of main electrodes on one side and a plurality of groups of secondary electrodes on the other side, each of said groups being associated with a respective one of said main electrodes, comprising main inductors connected in circuit with respective ones of said main electrodes, secondary inductors connected in circuit with respective ones of said secondary electrodes, power supply means for applying an electrical potential to different ones of said main electrodes, said power supply means including main switching devices connected in circuit with respective ones of said main electrodes; power supply means for applying an electrical potential to said secondary electrodes, said last mentioned power supply means including secondary switching devices connected in circuit with respective ones of said secondary electrodes whereby, when any of said main switching devices and any of said secondary switching devices associated with a said last mentioned main switching device are simultaneously turned off, energy stored in respective ones of said inductors will be transferred to respective ones of said electrodes to cause light emission; said inductors having a common electrical connection.
15. A device according to claim 14 comprising means for alternately applying different voltage potentials to said secondary inductors.
16. A device according to claim 14 comprising means for changing said voltage potential applied to said secondary inductors when said switching devices are turned off.
US00390097A 1973-08-20 1973-08-20 Drive circuitry for light emitting film displays Expired - Lifetime US3833833A (en)

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Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2715154A1 (en) * 1976-04-06 1977-10-20 Smiths Industries Ltd DISPLAY DEVICE FOR DISPLAYING SEVERAL CHANGING SIZES
US4096412A (en) * 1975-08-01 1978-06-20 Citizen Watch Company, Limited Driver circuit for electrochromic display device
US4129804A (en) * 1977-06-06 1978-12-12 Rca Corporation Image display device commutator
US4190836A (en) * 1976-11-15 1980-02-26 Hitachi, Ltd. Dynamic drive circuit for light-emitting diodes
US4230265A (en) * 1979-05-07 1980-10-28 Transaction Technology, Inc. Adaptive threshold optical reader
US4658186A (en) * 1983-12-27 1987-04-14 Sanyo Electric Co. Control apparatus for fluorescent display tube
EP0492362A1 (en) * 1990-12-28 1992-07-01 Stanley Electric Co., Ltd. Driving circuit for electroluminescent element
US6337543B1 (en) * 1999-12-20 2002-01-08 Gl Displays, Inc. High power cold cathode gas discharge lamp using sub-electrode structures
US6515433B1 (en) 1999-09-11 2003-02-04 Coollite International Holding Limited Gas discharge fluorescent device
US20050104531A1 (en) * 2003-10-20 2005-05-19 Park Joong S. Apparatus for energy recovery of a plasma display panel
EP1795052A1 (en) * 2004-09-13 2007-06-13 Semiconductor Energy Laboratory Co., Ltd. Light emitting device
US20090033648A1 (en) * 2004-10-29 2009-02-05 George Podd Light film device
US8552440B2 (en) 2010-12-24 2013-10-08 Semiconductor Energy Laboratory Co., Ltd. Lighting device
US8575631B2 (en) 2010-12-24 2013-11-05 Semiconductor Energy Laboratory Co., Ltd. Lighting device
US8735874B2 (en) 2011-02-14 2014-05-27 Semiconductor Energy Laboratory Co., Ltd. Light-emitting device, display device, and method for manufacturing the same
US8742405B2 (en) 2011-02-11 2014-06-03 Semiconductor Energy Laboratory Co., Ltd. Light emitting unit, light emitting device, and lighting device
US8772795B2 (en) 2011-02-14 2014-07-08 Semiconductor Energy Laboratory Co., Ltd. Light-emitting device and lighting device
US9214101B2 (en) 2013-02-14 2015-12-15 Mark Richmond Backlit graphic display device
US9343003B2 (en) * 2004-10-29 2016-05-17 George O. Podd Backlit graphic display device with device-to-surface mounts
US9516713B2 (en) 2011-01-25 2016-12-06 Semiconductor Energy Laboratory Co., Ltd. Light-emitting device
US9905632B2 (en) 2010-12-28 2018-02-27 Semiconductor Energy Laboratory Co., Ltd. Light-emitting unit, light-emitting device, and lighting device

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4096412A (en) * 1975-08-01 1978-06-20 Citizen Watch Company, Limited Driver circuit for electrochromic display device
DE2715154A1 (en) * 1976-04-06 1977-10-20 Smiths Industries Ltd DISPLAY DEVICE FOR DISPLAYING SEVERAL CHANGING SIZES
US4190836A (en) * 1976-11-15 1980-02-26 Hitachi, Ltd. Dynamic drive circuit for light-emitting diodes
US4129804A (en) * 1977-06-06 1978-12-12 Rca Corporation Image display device commutator
US4230265A (en) * 1979-05-07 1980-10-28 Transaction Technology, Inc. Adaptive threshold optical reader
US4658186A (en) * 1983-12-27 1987-04-14 Sanyo Electric Co. Control apparatus for fluorescent display tube
EP0492362A1 (en) * 1990-12-28 1992-07-01 Stanley Electric Co., Ltd. Driving circuit for electroluminescent element
US6515433B1 (en) 1999-09-11 2003-02-04 Coollite International Holding Limited Gas discharge fluorescent device
US6337543B1 (en) * 1999-12-20 2002-01-08 Gl Displays, Inc. High power cold cathode gas discharge lamp using sub-electrode structures
US7355350B2 (en) 2003-10-20 2008-04-08 Lg Electronics Inc. Apparatus for energy recovery of a plasma display panel
US20050104531A1 (en) * 2003-10-20 2005-05-19 Park Joong S. Apparatus for energy recovery of a plasma display panel
US7518574B2 (en) 2003-10-20 2009-04-14 Lg Electronics Inc. Apparatus for energy recovery of plasma display panel
US20110140617A1 (en) * 2004-09-13 2011-06-16 Semiconductor Energy Laboratory Co., Ltd. Light emitting device
US7999463B2 (en) 2004-09-13 2011-08-16 Semiconductor Energy Laboratory Co., Ltd. Light emitting device
US20080001512A1 (en) * 2004-09-13 2008-01-03 Semiconductor Energy Laboratory Co., Ltd. Light Emitting Device
EP1795052A4 (en) * 2004-09-13 2010-11-17 Semiconductor Energy Lab Light emitting device
US20110089814A1 (en) * 2004-09-13 2011-04-21 Semiconductor Energy Laboratory Co., Ltd. Light emitting device
US20110089823A1 (en) * 2004-09-13 2011-04-21 Semiconductor Energy Laboratory Co., Ltd. Light emitting device
EP1795052A1 (en) * 2004-09-13 2007-06-13 Semiconductor Energy Laboratory Co., Ltd. Light emitting device
US8912718B2 (en) 2004-09-13 2014-12-16 Semiconductor Energy Laboratory Co., Ltd. Light emitting device with a plurality of circuits connected in parallel
US8436531B2 (en) 2004-09-13 2013-05-07 Semiconductor Energy Laboratory Co., Ltd. Lighting device having plural light emitting layers with carrier generation layer therebetween
US8436532B2 (en) 2004-09-13 2013-05-07 Semiconductor Energy Laboratory Co., Ltd. Lighting device with plural light emitting elements
US8487530B2 (en) 2004-09-13 2013-07-16 Semiconductor Energy Laboratory Co., Ltd. Lighting device having plural light emitting layers which are separated
US8487529B2 (en) 2004-09-13 2013-07-16 Semiconductor Energy Laboratory Co., Ltd. Lighting device with plural light emitting elements
US9343003B2 (en) * 2004-10-29 2016-05-17 George O. Podd Backlit graphic display device with device-to-surface mounts
US20090033648A1 (en) * 2004-10-29 2009-02-05 George Podd Light film device
US8575631B2 (en) 2010-12-24 2013-11-05 Semiconductor Energy Laboratory Co., Ltd. Lighting device
US8975647B2 (en) 2010-12-24 2015-03-10 Semiconductor Energy Laboratory Co., Ltd. Lighting device
US8552440B2 (en) 2010-12-24 2013-10-08 Semiconductor Energy Laboratory Co., Ltd. Lighting device
US9905632B2 (en) 2010-12-28 2018-02-27 Semiconductor Energy Laboratory Co., Ltd. Light-emitting unit, light-emitting device, and lighting device
US9516713B2 (en) 2011-01-25 2016-12-06 Semiconductor Energy Laboratory Co., Ltd. Light-emitting device
US8742405B2 (en) 2011-02-11 2014-06-03 Semiconductor Energy Laboratory Co., Ltd. Light emitting unit, light emitting device, and lighting device
US9349990B2 (en) 2011-02-11 2016-05-24 Semiconductor Energy Laboratory Co., Ltd. Light emitting unit, light emitting device, and lighting device
US8772795B2 (en) 2011-02-14 2014-07-08 Semiconductor Energy Laboratory Co., Ltd. Light-emitting device and lighting device
US8871536B2 (en) 2011-02-14 2014-10-28 Semiconductor Energy Laboratory Co., Ltd. Light-emitting device, display device, and method for manufacturing the same
US8735874B2 (en) 2011-02-14 2014-05-27 Semiconductor Energy Laboratory Co., Ltd. Light-emitting device, display device, and method for manufacturing the same
US9281497B2 (en) 2011-02-14 2016-03-08 Semiconductor Energy Laboratory Co., Ltd. Light-emitting device, display device, and method for manufacturing the same
US9214101B2 (en) 2013-02-14 2015-12-15 Mark Richmond Backlit graphic display device

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