US3811071A

US3811071A - Drive regulation and delay control in display systems

Info

Publication number: US3811071A
Application number: US00271576A
Authority: US
Inventors: J Ogle
Original assignee: Burroughs Corp
Current assignee: Unisys Corp
Priority date: 1972-07-13
Filing date: 1972-07-13
Publication date: 1974-05-14
Anticipated expiration: 1991-05-14
Also published as: DE2332905A1; JPS4960132A; FR2193249A1; BR7304908D0; GB1411005A; NL7309050A

Abstract

Apparatus addressing multi-position display devices directly from semiconductor integrated circuits and driving the display electrodes without exceeding the limitation on voltage excursions for the outputs of such circuits. The apparatus develops and applies to threshold-responsive display devices, including gas discharge display tubes or display panels, only the amount of voltage that is needed to operate them. Potential for operating the device is accumulated in steps until the device fires, it being applied to the display electrodes of the device in response to open-circuit input signals. The potential is regulated to maintain ionization delay in the device as a certain fraction of the display period and the required selection voltages for the electrodes of the device are minimized. The potential for driving the cathodes is developed across a capacitance common to all of them, and a regulator circuit coupled to it and to the cathode drivers automatically increases the bias until the device fires. The potential that proves to be necessary to operate a device is stored for continued operation of it. The driver for a cathode element that is frequently operated alone is coupled to the regulator circuit by a high impedance connection for increasing the energizing potential sufficiently to ensure ionization. The anodes are driven from semiconductor logic circuit often without intermediate circuit elements.

Description

United States Patent 191 Ogle DRIVE REGULATION AND DELAY CONTROL IN DISPLAY SYSTEMS [75] Inventor: James Ogle, Neshanic Station,

[73] Assignee: Burrbughs Corporation, Detroit,

Mich.

[22] Filed: July 13, 1972 [21] Appl. N0.: 271,576

[52] U.S. Cl. 315/169 TV, 315/169 R [51] Int. Cl. H05b 37/00 [58] Field of Search 315/169 R, 169 TV [56] References Cited UNITED STATES PATENTS 3,573,542 4/1971 Mayer et al..... 315/169 R 3,626,244 12/1971 Holz 315/169 R 3,665,246 5/1972 Kurahashi et al. 315/169 R Primary Examiner-Herman Karl Saalbach Assistant ExaminerLawrence J. Dahl Attorney, Agent, or Firm-Robert A. Green; Edward.

G. Fiorito; Paul W. Fish 57 ABSTRACT Apparatus addressing multi-position display devices May 14, 1974 directly from semiconductor integrated circuits and driving the display electrodes without exceeding the limitation on voltage excursions for the outputs of such circuits. The apparatus develops and applies to threshold-responsive display devices, including gas discharge d-isplay tubes or display panels, only the amount of voltage that is needed to operate them. Po-

tential for operating the device is accumulated in steps until the device fires, it being applied to the display electrodes of the device in response to open-circuit input signals. The potential is regulated to maintain ionization delay in the device as a certain fraction of the display period and the required selection voltages for the electrodes of the device are minimized.

The potential for driving the cathodes is developed across a capacitance common to all of them, and a regulator circuit coupled to it and to the cathode drivers automatically increases the bias until the device tires. The potential that proves to be necessary to operate a device is stored for'continued operation of it. The driver for a cathode element that is frequently operated alone is coupled to the regulator circuit by a high impedance connection for increasing the energizing potential sufficiently to ensure ionization. The anodes are driven from semiconductor logic circuit often without intermediate circuit elements.

6 Claims, 5 Drawing Figures DRIVE REGULATION AND DELAY CONTROL IN DISPLAY SYSTEMS BACKGROUND OF THE INVENTION This invention relates to apparatus for operating segmented-electrode display devices which are threshold- I responsive to selection signals applied to them, including gas discharge display tubes and display panels.

like and to driving display elements thereof without exceeding the voltage limitations on the circuits employed.

Various segmented-electrode display devices have been-developed in recent years for use as readout indicators for electronic calculators and the like. One such device is the PANAPLEX panel display which is a multiple-position gas discharge device having a plurality of segmented display cathodes and a plurality of associated anode electrodes. Such display panels usually include several groups of cathode segments, with like segments of the different groups being interconnected, and an anode electrode associated with each group'of cathodes.

In a recently developed version of the PANAPLEX panel display, the cathode elements are deposited or formed along the front surface of an insulating base plate and planaranode electrodes are spaced closely above the cathodes. A relatively large difference in potential between an anode and one or more cathodes is required initially to ionize a display position, while a lower potential across them will sustain the discharge. It has been discovered,-however, that either theanodes or the cathodes thereof, if both are suitably biased, can be operated by signals which do not'exce'ed the maximum voltage excursions that are allowed on the outputs of some metal-oxide semiconductor (MOS) integrated circuits.

Such MOS integrated form of calculator circuits, decoder circuits, counters, registers, and the like. Substantial economies would be obtained if the display positions of such devices could be either addressed or selected directly from MOS circuits with a minimum amount of intermediate amplifying or coupling circuitry being required.

A condition precedent to the use of suchlow voltage signals is that the electrodes of the device-be biased toward discharge as much as possible without causing spurious discharges. Higher voltages also have to be made available on one set of the electrodes for initial ionization and re-ionization without violating the allowable voltage ratings on the MOS or other low voltage signal source.

The total potential required for initially ionizing and for re-ionizing the display positions in gas discharge display panels, however, varies with the gas pressure and with operating temperature. It also can vary signifi, cantly from tube to tube. A set of bias voltages provided to allow the electrodes of one lot of such devices to be addressed or driven with minimum possible signal voltages may not be sufficient or may exceed the potential required to operate another lot of tubes of the same. general type.

circuits are available in the SUMMARY OF THE INVENTION Accordingly, an object of the invention is to simplify and reduce the cost of addressing and driving multipleposition display devices or panels.

Another object is to address the display positions of gas discharge devices from semiconductor integrated circuits or the like without exceeding voltage limitations on the circuits.

A further objectof the invention is to regulate the drive voltage applied to multiple-position display devices and to control the delay in activating the display positions in them.

The invention provides apparatus for driving the display electrodes of multiple-position display devices and for addressing them directly from low voltage signal sources without exceeding the voltage limitations on the signal source. The'potential for driving the cathodes is developed across a capacitance common to all of'them and a regulator circuit coupled to the cathode 7 drivers controls the voltageso that the device will fire at the predetermined ionization delay.

A major portion of the voltage applied to the display cathodes in this system is stored between display periods for application to the selected cathodes in succeedingperiod s. This stored reference potential, and consequently the operating voltage, are adjusted automatically to compensate for differences in the potential thresholds for different units and for threshold changes caused by changes in temperature or mode of operatron.

DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS Thedisplay panels described herein are thin, flat, sheet-like members which may have substantiallyany desired shape and size, and may include substantially any number of character display positions. The panels may include any suitable ionizable gas such as neon, ar-

' gon, xenon, etc., singly or in combination, with a vapor of a metal such as mercury usually included in the gas to minimize cathode sputtering. A wide range of gas pressures may be used, for example, from about 20 to about 250 Torr at ambient temperature with about to Torr being a commonly used pressure range.

Referring to FIGS. 1-3, a display device 10 embodying the invention includes an insulating base plate 20 of glass, ceramic, or the like, with an inexpensive glass being suitable and preferred. A plurality of conductive connectors or runs 30A to 306 are formed on the top surface of the insulating plate 20. The runs 30 are parallel to each other and are aligned with the horizontal axis of the base plate. Seven such runs 30A to 30G are shown; however, more or fewer may be provided, the

A second thin layer 40 of insulating material such as glass or ceramic is formed on the conductive runs 30, preferably by a silk-screen process, and the second layer 40 includes a plurality of groups of vias or apertures 50A to 50G, each aperture exposing one of the runs 30A to 30G. Thus, each group of apertures includes aperture 50A which exposes run 30A, aperture 508 which exposes run 308, aperture 50C which exposes run 30C, etc. Four such groups of apertures are illustrated.

Panel-l includes a group of cathode electrodes 60 (A to G) for each group of apertures 50. The cathodes are generally elongated bars or segments, and they are usually arrayed in a figure 8 pattern, as is well known in the art. The cathodes 60 maybe formed on insulating layer 40 by means of a silk-screen process using a conductive paste such as palladium-gold, platinumgold, palladium-silver, or the like. Each cathodeelement is in contact with one of the runs 30 exposed by one of the apertures or vias 50, and it substantially fills the aperture 50 and covers a portion of layer 40 to achieve the desired shape and size. I Y

The cathodes 60A, 608, etc. may also be formed of discrete strips of metal, preferably brazed to a conductive run 30 by means ofa mass of brazing material deposited in each of the apertures 50 in the insulating layer 40. The brazing material itself may be deposited by a silk-screen process. One suitable brazing material is a gold-germanium substance known as FORMON and sold by E. l. DuPont de Nemours & Co. The cathodes may also be formed in any other suitable manner such as by the electrolytic or electroless plating of nickel or the like or by are plasma spraying through a suitable mask.

Thus, cathodes 60 are preferably thin, flat members which do not project to any significant extent'above the top surface of insulating layer 40.

Panel 10 includes anode electrodes 90 for the groups of cathode electrodes 60. The anode electrodes comprise thin, transparent conductive films of gold, NESA, or the like formed on the lower surface 95 of the panel face plate or viewing plate 100 which is made of glass. The anode films are of the order of a few Angstroms thick and, in effect, are coplanar with the bottom surface 95 of the face plate. Thus, the anodes, for all practical purposes, do not project into the gas discharge space in the panel. The anode films are generally rectangular in shape, or are otherwise shaped, depending on the orientation of the cathodes. Anodes 90 are dimensioned and positioned so that they overlay the total area defined by the associated group of cathode electrodes. If desired, each anode 90 may be somewhat narrower and shorter than the area defined by its cathodes as shown, but in any case, the anode must overlay and r be in operative relation with a sufficient portion of each of its cathodes. Other suitable anode shapes may be 'employed, depending upon the character and symbol configuration of the cathodes to be operated.

Preferably, the spacing between each anode and its group of cathodes 60 should be of the order of 20 to 25 mils, and the spacing between each anode and the adjacent group of cathodes should be of the order of 30 to 40 mils. With this relationship at the usual pressure range, each anode is in a favorable operating position with respect to its own cathodes, but is sufficiently re-' mote from adjacent groups of cathodes so that the panel may be operatedover a suitably wide range of potentials without developing cross-talk between adjacent 'groups .of electrodes. Another factor tending to prevent cross-talk is the location of the anodes in substantially coplanar relation with the surface of the glass cover plate and not projecting into the gas space in which cathode glow takes place.

Another advantage of the close spacing of each anode to its group of cathodes, thus providing a thin volume of gas, is that metastable-state atoms produced in the gas during discharge diffuse to, and are readily neutralized at, these closely spaced surfaces. In addition, excited or charged particles are readily swept out through the anode-cathode circuit path. The tendency for cross-talk to develop is minimized by these two factors.

The top glass cover plate is of substantially the same length as the insulating layer 40 and the bottom plate 20, and it is spaced from the base plate 20 by a rectangular glass frame which isdisposed between the top glass plate 100 and the insulating layer 40. Frame 110 may be an integral part of the top and/or bottom plates. The rectangular frame serves thus to provide the desired spacing between eachanode and its associated group of cathode electrodes. The top glass plate 100 is also preferably slightly wider than the insulating layer 40 and base plate 20 so that one edge, say the upper edge, extends beyond the remainder of the panel and is accessible to permit the connection of leads to each of the anode films 90. The three

glass members

20, 100, and 110 are sealed together in any suitable-manner, for example, by means of a seal 120 formed of a glass frit or the like.

Connection to the runs 30 may be made, as an example, by means of L-shaped pins or contacts 144 which are embedded in the seal 120 at one or both ends of the panel.

The panel 10 can be filled with the desired gas atmosphere through a tubulation secured to the base plate 20 and communicating with the interior of the panel through a hole 154 in plate 20 and layer 40, and, generally, mercury is introduced from a glass capsule (not shown) held in the tubulation and suitably processed at the desired stage in the assembly process.

The invention relates to panel-type segment display devices which include a plurality of groups of cathode electrodes which comprise elongated bars'or segments arrayed in a pattern so that the cathodes of each group can be selectively energized to display a character. For reasons of economy, corresponding electrodes in each group, usually cathodes, have a common conductor. The anodes are separately energizable and the panel is operated in a multiplex mode of operation. In this mode of operation, operating potential is applied to selected cathode conductors at time t, and thus to selected'cathode segments, and the first anode is energized and a first character is displayed by the energized cathode segments in the first group. At time t,,, operating potential is applied to the same or other cathode conductors and to the second anode and a second character isdisplayed by the second group of cathodes. This same operation is carried out for each character position, and it is repeated continually along the entire display panel at a suitable frequency so that stationary but changeable characters can be displayed.

The display system of FIG. 2 incorporates improved operating apparatus for a multiple-position display device having several groups of cathode segments or elements 60 (A-D) interconnected by cathode conductors 30 (A-D) and a plurality of associated anode electrodes 90. A digit selecting or addressing switch 200 is connected between a voltage supply terminal 190 labeled V and each of the anode electrodes 90. The

anode switches are all identical and only one of them is illustrated in detail. The cathode circuit includes current drivers 250 A-D) connected to the corresponding cathode electrodes 60 (A-D) by leads 290 and to capacitor 175 ofa biasing circuit by bus 170. Capacitor 175 is connected at its other end to voltage supply terminal 190 and is in electrical series with emitter resistor 167 of transistor 165, the collector of which is connected to a negative voltage supply terminal 150 labeled V Transistor 165 serves as the'pass element of a bias regulator circuit including feedback bus 160 and is coupled to capacitor 175 which maintains bias potential on bus 170 for the cathode drivers.

The voltage switches 200 for addressing anodes 90 and thereby selecting a digit or display position in panel 10 are each controlled by a metal-oxide semiconductor (MOS) transistor 210 having a gate terminal 205. These MOS transistors 210 may all be formed on the same MOS integrated circuit chip, and may be part of a complex multiple-function integrated circuit. Similarly, anode switch transistors 210 may be field-effect transistor (FET) units or other suitable low voltage units. The source electrodes of transistors 210 are connected to V terminal 190. The drain electrodes 215 are connected directly to the anode electrodes. A biasing resistor 220, which holds the anode'below operating potential normally, and a reverse-biased clamping diode are connected between it and a bias terminal 240. The anodes can thus receive the full voltage swing from V to the most negative voltage that can be applied to terminal 240 without violating the rated voltage limitations on the MOS or FET transistors 210.

The cathode circuit consists of segment current drivers 250 (A-D) and a bias voltage regulator including transistor 165 connected in series with capacitor 175, which stores the bias voltage for the drivers. Cathode drivers 250 and transistor 165 operate together as a feedback loop to develop bias voltage across capacitor 175 by conducting current out of it throughthe collector-emitter circuit of transistor '1 65 until the associated display device becomes activated.

The current drivers 250 for the cathodes are controlled by MOS transistors 260 or the like, which also may form part of a complex integrated circuit such as a calculator chip or the like. Furthermore, cathode input transistors 260 may be formed on the same integrated circuit chip as anode switch transistors 210 even though the anodes and cathodes, themselves, are operated at different voltage levels that exceed the rated voltage limitations of customary integrated circuits. Capacitors 265 couple the cathode input switches 260 6 to cathode current drivers 285, while isolating both the anode switches 210 and the cathode input switches 260 from the voltage levels on the cathode drivers. The anode switches 210 and the cathode input switches 260 are thus operated from the same bias point (anode voltage level V,,) and may be formed on the same integrated circuit chip.

The source electrodes of input transistors 260 for the cathode drivers' are connected to V terminal 190. Their drain electrodes are coupled at junction 262 to the emitter electrodes of cathode driver transistors 285 by capacitors 265 and are coupled to a negative voltage terminal 280 labeled V by resistors 275. The emitter electrodes of driver transistors 285 are also connected to voltage bus 170' by diodes 270. The collector electrodes are connected by leads 290 to connectors 30 (A-D) of cathode electrodes 60 (A-D) of the display device and to pull-up bias resistors 295, which hold the cathodes above their operating potential normally. The other ends of cathode bias resistors 295 are connected to a bus 180 which is coupled to V terminal 190 by a reverse-biased Zener diode 185 through leads 187 and 189. The base electrodes of cathode driver transistors 285 are connected to bus. which connects to the base electrode of transistor of the bias voltage regulator.

This system allows direct addressing or selection of the anodes of a display device from transistors 210 of an MOS circuit chip or the like, and keeps the voltage swing on the digit output terminals 215 of the integrated circuit chip strictly within customarily specified voltage limits for them. Frequently specified voltage limitations on such circuits range from a conservative 20 or 25 volts to approximately 30 volts or more. The system also is operated by open circuit (negative going) selection signals for the cathode segments, which in the case of MOS data sources are open drain inputs.

Cathode drivers 250 (AD) are selectively enabled when the normally-conducting transistors 260 of the MOS data source are opened (turned off). This unclamps the input side of coupling capacitor 265 which is pulled negative by resistor 275 as shown in waveform 300 of FIG. 3, it having been held normally at V by that transistor. This signal current into resistor 275 appears as emitter current in driver transistor 285 via coupling capacitor 265and is considerably larger than the collector pull-up current through cathode bias resistors 295. The collectors, therefore, go increasingly negative during ionization delay until transistors 285 become saturated, as indicated by waveform 350 of FIG. 3. Most of the emitter current of transistors 285 is then drawn from their base electrodes and through bus l60-and the regulator 165. The sum of the base currents of all the selected cathode segment drivers 250 (A-D) is conducted by resistor 155 and the base of transistor 165 which causes a proportionately larger current in emitter resistor 167 and charges capacitor more negative.

The ratio between emitter resistor 167 and feedback resistor 155 of regulator transistor 165 determines the approximate proportion between the re-ionization delay and the digit display period at which the system will stabilize. Under typical display conditions with a 200 microsecond digit displayperiod, a segment reionization delay of about 20 to 40 microseconds, for example, is usually suitable. After the device fires, transistor 285 comes out of saturation and the major part of its emitter current is then drawn from the associated cathode via conductor 30 (A-D) and the collector of the transistor to coupling capacitor 265. Resistors 275 will limit the current thus conducted from the display and capacitors 265 are discharged thereby. Thevoltage on bias storage capacitor 175 will change little once breakdownoccurs in the device since the feedback curtire display period. The recharging current in coupling capacitor 265 will be less and capacitor 175 thus will not be discharged as much as it was charged, but will This feedback-controlled voltage is stable once display device 10 becomes activated, since the charging of capacitor 175 is governed primarily by the reionization delay, which decreases as 'the voltage goes more negative and will increase should it be too positive. The proportion between feedback resistor 155 and emitter resistor 167 of regulator transistor 165 determines this operating point and establishes the bias voltage that is stored across capacitor 175. The operating bias is thus regulated to maintain the ionization delay as a predetermined fraction of the digit period. This allows operation with smaller signals than would be required for faster ionization, yet ensures that ionization will occur at all selected cathodes.

The apparatus responds effectively 'to the operation of the device because capacitor 175 is charged to increase the driving potential for the selected cathodes until the device fires and is discharged between display periods by an amount proportional only to the number of segments that were selected.

The potential acrosscapacitor 175 is applied to cathode drivers 250 by bus 170 as bias potential. This is the potential to which coupling capacitors 265 of the cathode drivers are recharged between display periods and,

hence, the initial bias potential for the drivers during each display period. This potential is changed by regulator transistor 165, as thethreshold potential of the device also changes. This compensates for the threshold potential of different devices being different or changing with temperature or mode of operation.

The drawing of FIG. 3 reflects the operation of the display system of FIG. 2. Waveform 300 represents the voltage excursions at input junction 262 of a cathode driver 250. Two

cycles

301 and 302 are illustrated, both of which begin at V and are pulled rapidly negative by resistor 175 until transistor 285 conducts, charges distributed capacitances, in the circuit, and then becomes saturated at time t2.

Input waveforms

301 and 302 are pulled farther negative at a slower rate as current in the base-emitter circuit of transistor 285 begins to discharge coupling capacitor 265 during the remaining ionization delay until the device fires.

Waveform 301 represents operation at equilibrium, in which the ionization delay equals the predetermined portion of the display period. Waveform 302 represents instead accumulate negative biasing charge until the device fires. I

operation of the device in which the ionization delay exceeds the predetermined fraction of the display period. At time t3 breakdown occurs at the selected display position, at which point cathode driver 285 comes out of saturation and the base currents of the selected drivers which are summed in feedback resistor decrease greatly. This causes a corresponding voltage shift in the emitter circuits of the drivers and at input junction 262 of the drivers. The input waveforms then continue to decrease as coupling capacitors 265 are discharged until the end of the display period at time t.,. The input waveforms then return to

V Voltage waveforms

310 and 320 appear on feedback busconnected to the base electrodes of cathode driver transistors 285 and to the base electrode of regulator transistor 165. They reflect the feedback current in the base of pass element and in base resistor 155 during ionization delay between times t2 and t3 and during operation of the device until t4. The amplitude of the feedback current during cycle 311 or cycle 312 will depend on how many different cathode segments are being driven by cathode drivers 250 (AD) during the particular cycle. Waveform 310 represents operation of a few cathodes and waveform 320 represents operation of most of the cathodes. Bias capacitor 175 will be charged more negatively byhigher feedback currents, but will be discharged proportionately at the end of the cycle when the corresponding number of coupling capacitors 265 are recharged into it.

Waveforms

330 and 340 represent the voltage excursions on bias voltage bus connected to capacitor and to the coupling capacitors 265 by diodes 270. Wavefrom 330 represents the excursion if only one or two different cathodes are being driven. Waveform 340 represents the larger voltage excursion when several or all of the different cathode segments or elements are being driven.

Voltage waveform 350 represents the voltage pattern that are applied to the cathode electrodes on leads 290. When driver 285 begins to conduct its collector and the associated cathodes go negative. At time t2 driver 285 saturates and its collector therefore follows the voltage on its base until the driver fires at time t3. The cathode voltage between times t3 and t4 is relatively constant as the voltage drop across a fired display position until the end of the display period. These

output waveforms

351 and 352 that are applied to cathode leads 290 beginaand end at a voltage determined by pull-upresistors 295 and zener diode connected between them and V terminal 190.

Since the ionization delay in segmented gas discharge devices depends in part on how many cathode segments are energized, a specialized cathode driver for single segment displays may be desirable. The middle bar or segment in a figure eight pattern is often operated alone as a minus sign, for example. In the cathode circuit of FIG. 4 cathode drivers 250A through 250D, etc., are the same as those of the system of FIG. 2, but cathode driver 250G is connected differently to the regulator circuit and may have a higher value cathode pull-up resistor 297 for easier driving, if desired.

In the cathode driver 2506 of FIG. 4 for cathodes 60G, a resistor 287 and a capacitor 289 are coupled in parallel between the base of its driver transistor 285 and feedback bus 160 of the regulator. When its driver transistors 285 saturates during ionization delay the base current in resistor 287 allows the base, and conseers provide to avoid the unbalancing the regulator when ionization occurs'readily, as when a cathode segment 60G is energized with several others in a multiplesegment'character or symbol. This ensures that the charging and discharging of bias storage capacitor 175 remains approximately equal at the designed ionization delay interval even though a special driver 2506 is being operated with the others. Otherwise, capacitor 175 would be inadequately charged.

In the special driver for the minus symbol cathode of FIG. 5, damping is provided in the circuit by capacitor 277 coupled between the drain electrode of input transistor 260 and negative bias terminal 280. This dampens initial saturation of its driver transistor 285 and if its feedback to the regulator to allow ionization to occur in the display at the lowest possible voltage. It also aids in preventing unbalancing of the bias circuit upon rapid ionization. Coupling. capacitor 289 is eliminated, or not, as desired. The special minus symbol cathode driver 2506 of FIG. isotherwise similar to that illustrated in FIG. 4.

Also, a forward-biased diode 154 may be connected between the base of regulator transistor 165 and a voltage divider formed of

resistors

152 and 182 connected between V,; terminal 150 and zener diode 185, for example. This causes transistor 165 to follow variations in the V power source and to keep capacitor 175 charged to a minimum level independent of whether the display has been recently operated. This limits transient power demands of regulator transistor 165 when the display is first operated or operated after a long in.-

ac tivate period.

Although the preferred embodiments of the invention have been described in detail, it should be understood that the present disclosure has been made by way of example only. Many modifications and variations of the invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the-appended claims, the invention maybe practiced otherwise than as specifically disclosed.

What I claim is: '1. A system for operating a multiple position flat panel display device which comprises a base plate and face plate spaced apart and hermeti-- cally sealed together along a perimeter to form an envelope which is filled with an ionizable gas, a plurality of conductive runs on said base plate, and a plurality of groups of cathode segments on said base plate but insulated from said conductive runs, with each run being connected to one cathode segment in each group, each said group of cathode segments comprising a character position, and an anode electrode for each of said groups of cathode segments,

said system comprising a power supply,

a separate anode driver coupled to each of the anode electrodes for applying positive-going signals to the anode electrodes as each character position is energized, Y

a separate cathode driver having its output coupled to each of said conductive runs for applying negative-going signals to selected ones ofthe cathode electrodes concurrent with energization of the associated anode electrode to display a character at each character position,

a source of input signals coupled to each cathode driver,

a first bus coupled between said power supply and through separate resistive paths to the output of each said cathode driver,

a second bus connected to the input of each said cathode driver, 7

a third bus coupled to a portion of each said cathode driver for maintaining bias potential thereon,

an active circuit element coupled between said second and third buses for maintaining bias potential on said third bus,

a capacitor connected between said first and second buses for receiving current from said active circuit element and storing charge, and then applying operating bias'potential to each of the cathode drivers, and

impedance means coupled between said capacitor and said active circuitelement for charging the capacitor proportionally to the number of cathode segments energized in each said group at each character position to regulate the potential across it so that the firing threshold of the cathodes at the selected position in the device is exceeded and the cathodes exhibit cathode glow.

2. The system defined in claim 1 wherein said active circuit element comprises a first transistor having base, emitter, and collector electrodes with its emitter connected through a first resistiv e path to said capacitor and to said third bus, and its base electrode connected through a second resistive path to said third bus, and its collector electrode connected to a source of bias potential, and

each said cathode driver comprises a second transistor having base, emitter, and collector electrodes, its base electrode being connected to the base electrode of said first transistor, its emitter electrode being connected both through a capacitor to said source of input signals and through a diode to said third bus, and its collector electrode being connected to oneof said conductive runs and through one of said resistive paths to said first bus.

3. A system for operating a multiple position flat panel display device which comprises a base plate and face plate spacedapart and hermetically sealed together along a perimeter to form an envelope which is filled with an ionizable gas, a plurality of conductive runs on said base plate, and a plurality of groups of cathode segments on said base plate but insulated from said conductive runs, with each run being connected to one cathode seg ment in each group, each said group of cathode segments comprising a character position, and an anode electrode for each of said groups of cathode segments,

said system comprising a power supply,

a first bus extending from said power supply,

a second bus, a third bus, and a fourthbus,

a capacitor connected between said second and third buses,

a first transistor Connected between said third and fourth buses and having base, emitter, and collector electrodes,

said first transistor and its associated circuitry sensing the number of cathodes energized and to be turned on at any one character position and passing a charging current, proportional to said number of cathodes, to said capacitor, the charge developed therein being applied to said second bus and to said cathode runs and to the associated cathode segments, and

a cathode driver circuit for each of said conductive runs and for each said one cathode, segment in each said group of cathode segments,

, each said driver circuit including a source of input signals, and a second transistor having base, emitter, and collector electrodes, the emitter electrode being coupled both to said source of input signals and to'said third bus, the base electrode being connected to said fourthbus, and the collector electrode being connectedboth to said second bus and to one of said conductive runs, whereby when a source of input signals is operated and applies a signal to the second transistor in the associated cathode drive circuit, said second electrode of said first transistor, and a second resistor coupled between said third bus and one side of said capacitor and the emitter electrode of said first transistor, said first resistor sensing current flow in the cathode segments energized by said signal sources.

5. The system defined in claim 3 wherein, in each cathode driver circuit, the emitter of the second transistor is connected both through a diode to said third bus and through a capacitor to its source of input signals.

6. The system defined in claim 3 wherein, in each cathode driver circuit, the collector of the second transistor is connected through a resistor and diode to said second bus.

Claims

1. A system for operating a mulTiple position flat panel display device which comprises a base plate and face plate spaced apart and hermetically sealed together along a perimeter to form an envelope which is filled with an ionizable gas, a plurality of conductive runs on said base plate, and a plurality of groups of cathode segments on said base plate but insulated from said conductive runs, with each run being connected to one cathode segment in each group, each said group of cathode segments comprising a character position, and an anode electrode for each of said groups of cathode segments, said system comprising a power supply, a separate anode driver coupled to each of the anode electrodes for applying positive-going signals to the anode electrodes as each character position is energized, a separate cathode driver having its output coupled to each of said conductive runs for applying negative-going signals to selected ones of the cathode electrodes concurrent with energization of the associated anode electrode to display a character at each character position, a source of input signals coupled to each cathode driver, a first bus coupled between said power supply and through separate resistive paths to the output of each said cathode driver, a second bus connected to the input of each said cathode driver, a third bus coupled to a portion of each said cathode driver for maintaining bias potential thereon, an active circuit element coupled between said second and third buses for maintaining bias potential on said third bus, a capacitor connected between said first and second buses for receiving current from said active circuit element and storing charge, and then applying operating bias potential to each of the cathode drivers, and impedance means coupled between said capacitor and said active circuit element for charging the capacitor proportionally to the number of cathode segments energized in each said group at each character position to regulate the potential across it so that the firing threshold of the cathodes at the selected position in the device is exceeded and the cathodes exhibit cathode glow.

2. The system defined in claim 1 wherein said active circuit element comprises a first transistor having base, emitter, and collector electrodes with its emitter connected through a first resistive path to said capacitor and to said third bus, and its base electrode connected through a second resistive path to said third bus, and its collector electrode connected to a source of bias potential, and each said cathode driver comprises a second transistor having base, emitter, and collector electrodes, its base electrode being connected to the base electrode of said first transistor, its emitter electrode being connected both through a capacitor to said source of input signals and through a diode to said third bus, and its collector electrode being connected to one of said conductive runs and through one of said resistive paths to said first bus.

3. A system for operating a multiple position flat panel display device which comprises a base plate and face plate spaced apart and hermetically sealed together along a perimeter to form an envelope which is filled with an ionizable gas, a plurality of conductive runs on said base plate, and a plurality of groups of cathode segments on said base plate but insulated from said conductive runs, with each run being connected to one cathode segment in each group, each said group of cathode segments comprising a character position, and an anode electrode for each of said groups of cathode segments, said system comprising a power supply, a first bus extending from said power supply, a second bus, a third bus, and a fourth bus, a capacitor connected between said second and third buses, a first transistor connected between said third and fourth buses and having base, emitter, and collector electrodes, said first transistor and its associated circuitry sensing thE number of cathodes energized and to be turned on at any one character position and passing a charging current, proportional to said number of cathodes, to said capacitor, the charge developed therein being applied to said second bus and to said cathode runs and to the associated cathode segments, and a cathode driver circuit for each of said conductive runs and for each said one cathode segment in each said group of cathode segments, each said driver circuit including a source of input signals, and a second transistor having base, emitter, and collector electrodes, the emitter electrode being coupled both to said source of input signals and to said third bus, the base electrode being connected to said fourth bus, and the collector electrode being connected both to said second bus and to one of said conductive runs, whereby when a source of input signals is operated and applies a signal to the second transistor in the associated cathode drive circuit, said second transistor is driven to saturation before the associated cathode turns on and current flows through said first transistor to charge said capacitor proportionally to the number of cathodes to be turned on, said charge being applied as a generally negative potential to said second bus and to the associated cathodes to be turned on.

4. The system defined in claim 3 and including a first resistor coupled between said third bus and the base electrode of said first transistor, and a second resistor coupled between said third bus and one side of said capacitor and the emitter electrode of said first transistor, said first resistor sensing current flow in the cathode segments energized by said signal sources.