US 3662184 A
An improved pulse generator circuit primarily for multiple discharge gaseous display and/or memory panels having crosstalk eliminating means. A low level voltage signal from an addressing logic system is inductively translated to a high voltage unidirectional pulse and added to a periodic alternating sustaining voltage at selected times to control "on"-"off" states of selected discharge units. The improvements relate to utilization of an electronic switching circuit responsive to a spurious voltage signal to provide a low impedance to voltages induced or capacitively coupled to display lines associated therewith from other conductors. Consult the specification for other features and details.
Claims available in
Description (OCR text may contain errors)
I United States Patent Johnson 1 May 9,1972
William E. Johnson, Temperance, Mich.
22 Filed: Apr. 13, 1970 ] Appl. No.: 27,595
Related US. Application Data  Division of Ser, No. 752,626, July 14, 1968, Pat, No.
 US. Cl. ..307/106, 340/166 EL  lnt.Cl ..Gllcll/28  Field ofSearch ..307/106; 340/166 EL, 324, 173; 313/188  References Cited UNITED STATES PATENTS 2,869,036 1/1959 Engelbart ..340/173 2,932,770 4/1960 Livingston...
...340/l66 EL X 3,096,516 7/1963 Pendleton et al. ,..340/l66 EL X 3,173,745 3/1965 Stone et a1 340/166 EL UX 3,263,028 7/1966 Shanafelt 340/166 EL X 3,327,163 6/1967 Blank 3,343,129 9/1967 Schmrtz ..340/166 3,440,637 4/1969 Molnar et a1 3,499,167 3/1970 Baker et 211....
3,513,327 5/1970 Johnson 3,559,190 1/1971 Bitzer et al....- ..340/173 Primary E.\'aminerRobert K. Schaefer Assistant Examiner-William .1. Smith A!!0rne v-E. J. Holler and Donald K. Wedding  ABSTRACT An improved pulse generator circuit primarily for multiple discharge gaseous display and/or memory panels having crosstalk eliminating means. A low level voltage signal from an addressing logic system is inductively translated to a high voltage unidirectional pulse and added to a periodic alternating sustaining voltage at selected times to control "on-off states of selected discharge units. The improvements relate to utilization of an electronic switching circuit responsive to a spurious voltage signal to provide a low impedance to voltages induced or capacitively coupled to display lines associated therewith from other conductors. Consult the specification for other features and details.
2 Claims, 4 Drawing Figures 2,998,546 8/1961 Kuntz et a1. 340/166 EL X 2,955,231 10/1960 Aiken ...340/l66 EL X 2,995.682 8/1961 Livingston ..340/166 EL X 3,012,095 12/1961 Skellett ..340/166 EL UX L 015 oiscnTmeE PTL Fl SIM VI 20V) LINE 6V IINII 15pm PA'TENTEDMM 9:912 3,662,184.
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. INVEN'IOR WILLIAM E. JOHNSON I av 5.x Mm wmm Kwaclcimg ATTORNEY;
ELECTRONIC CIRCUITRY FOR A FLAT GASEOUS DISCHARGE DISPLAY PANEL RELATED APPLICATION This application is a divisional of U.S. Pat. application Ser. No. 752,626 filed Aug. 14, 1968, now U.S. Pat. No. 3,513,327.
THE INVENTION The present invention relates in general to a low impedance pulse generator circuit and, in particular, is related to circuits for adding a high voltage unidirectional pulse to a source of sustaining potential at selected time intervals to control operation of selected individual discharge units in a multiple unit discharge gas display and/or memory panel and preventing misfiring or spurious firings of individual discharge units.
The object of this invention is to provide a low impedance pulse generator between a low voltage addressing logic circuitry and a high voltage gaseous display and/or memory device having closely spaced conductors in conductor arrays defining a plurality of gas discharge units in a display panel.
The invention will be described in connection with a gas discharge display panel of the type disclosed in Baker et al. application Ser. No. 686,384, filed Nov. 24, I967, now U.S. Pat. No. 3,499,167, and entitled Gas Discharge Display-Memory Device and Method; lnterfacing Circuitry and Method for Multiple Discharge Gaseous Display and/or Memory Panels disclosed in Johnson et al. application Ser. No. 699,170, filed Jan. 19, 1968; and Low Impedance Pulse Generator disclosed in Johnson application Ser. No. 752,626 filed Aug. 14, 1968. However, in a broader sense the invention has utility whenever it is desired to sense spurious pulse voltages.
Multiple discharge display and/or memory panels of the type with which the present invention may be used are characterized by a gaseous medium, usually a mixture of two gases, at a relatively high gas pressure in a thin gas chamber or space between a pair of opposed dielectric charge storage members which are backed by conductor arrays, the conductor arrays backing each dielectric member being transversely oriented to define a plurality of discrete discharge volumes and constitute a discharge unit. In some cases the discharge units may be additionally defined by. physical structure such as perforated glass plates and the like. However, in the above-identified patentapplication of Baker et al., physical barriers and isolation members have been eliminated. In both cases, charges electrons and ions) produced upon ionization of the gas at a selected discharge unit site or conductor cross-point, when proper alternating operating potentials are applied to selected conductors thereof, are collected upon the surfaces of the dielectric at specifically defined locations and constitute an electrical field opposing the electrical field which created 1 them.
. current surge through the transformer primary induces a high voltage pulse on the secondary. Secondaries of all the transformers are connected in series with a source of sustaining voltage, which, in the absence of voltage pulses induced by transformer action are insufficient to control a selected discharge unit, but is sufficient to sustain a sequence of discharges once the selected discharge unit has been fired or discharged, such being effected by a stored wall charges as described in greater detail in said Baker et al. application. Due to the small spacing (about 30 mil conductor center to conductor center) between conductors of conductor arrays defining the discharge units, energy from large pulse voltages applied to a selected conductor may be capacitively coupled to adjacent conductors and can cause cross-talk and/or spurious signals to discharge units. I
The present invention is directed to a pulse generator incorporating a solution to the problem of cross-talk or spurious pulsing of discharge units in a plasma display panel and includes a circuit responsive to spurious voltage pulses to provide a low impedance to spurious currents in conductors in such arrays in such a way as to absorb or dissipate pulse energy capacitively coupled to certain conductors and hence suppress cross-talk or avoid spurious firing or turning off of selected discharge units. Specifically, spurious voltages are sensed by a diode sensor which controls a transistor circuit to produce a low impedance to spurious currents.
The above and other advantages and features of the invention will be better understood when considered with the following specification and accompanying drawings wherein:
FIGS. 1A and 1B are diagrammatic illustrations of a gas discharge panel and associated circuits for carrying out the invention and are the same as FIGS. 1A and 1B of application Ser. No. 699,170,
FIG. 2 is an electrical schematic of a form of pulse generating circuit incorporating the invention,
FIG. 3 is a diagram used to explain the principle of the invention as applied to a gas discharge display panel.
With reference now to the drawings, FIGS. 1A and 18 (both being taken from application Ser. No. 699,170 filed Jan. 19, 1968) illustrate a gas discharge display/memory panel disclosed in the above-identified Baker et al. application, in which glass support members 10 and 11 have formed on their opposing surfaces conductor arrays 12 and 13 respectively. Dielectric members or coatings 14 and 16 have surfaces 17 and 18 respectively, which form charge storage surfaces for storage of charges (electrons and ions) generated upon discharge (ionization) of individual discharge units, respectively.
The surfaces 17 and 18 of dielectric members 14 and 16 respectively, are spaced apart by spacer 19 to form a thin gas chamber or space 20 and spacer 19 or an additional sealant may be utilized to form a complete hermatic seal for the gas chamber 20. Glass support members are sufficiently rugged to withstand the pressure of the gas within space 20 and ambient pressure and with a minimum deflection. In the disclosed panel there are no physical obstructions or structures in the gas chamber and due to the pressure, plurality of discrete discharges can occur within chamber 20 without detrimental interaction to the display or memory functions of individual discharge units, even though the conductors 12-1, 12-2, l2-N and 13-1, 13-2 13-N of the conductor arrays are spaced no more than about 30 mils center-to-center spacing.
It is to beunderstood that the invention may be applied with equal facility and results to display/memory panels of the type where perforated plates, honeycombs or other physical structures are utilized to provide physical confinement for each individual discharge unit.
The gas may be conditioned e.g., provided with a supply of free electrons) for the ionization process by application of an initial firing potential to a selected pair of conductors for sufficient time to effect an initial discharge in a discrete gas volume, as for example a discharge at the discharge unit consisting of the crossing or shadow area of conductors 12-1 and 13-1, the dielectric on those conductors at those crossings or shadow areas and the discrete volume of gas therebetween, the volume of gas permitting photonic communication between all discharge units to that photons which strike or impact the .dielectric surfaces produce or cause the release of electrons. Alternatively, the gas may be conditioned by providing an exterior source of ultraviolet radiation for producing by photoelectric emission free electrons for the ionization process or by placing a radioactive material in the glass or gas space which likewise can effect the presence of sufficient free electrons within the gas space for ionization at uniform potentials for a given gas, pressure, panel configuration, etc. At any rate, the invention will be described further in connection with a gas volume (whether unconfined as in the above referenced Baker et al. application or confined by a honeycomb or cellular structure as in the prior art) that has been conditioned for the ionization process.
Individual discharge units may be turned on" (a sequence of momentary discharges on alternate half cycles of applied alternating potential following an initial discharge) and off (termination of the sequence) by many different wave forms, the simplest of which is the sinusoidal voltage wave form. Basically, the only condition other than the voltage wave form is that the discharge unit be conditioned such that it is responsive to the applied voltage.
The pulse generator circuit for addressing a conductor of an individual discharge unit is disclosed in FIG. 2 and includes a first transistor Q1 having base 30, collector 31 and emitter 32 electrodes with collector electrode 31 connected directly to a direct current supply V1 and the emitter electrode 32 connected to ground through resistance 33. An input logic signal 34 (about 4 volts having a duration of about 100 nanoseconds) is applied to base electrode 30. This transistor Q1 operates as an amplifier andits output is coupled from emitter 32 directly to base electrode 36 of a second transistor Q2. The emitter electrode 37 of transistor Q2 is connected directly to ground and collector electrode 38 is connected through a small series resistor 39 to primary winding 40 of a transformer T1. The upper end of the primary winding of transformer T1 is connected to relatively high direct current voltage V2 through diode D2 and a diode D1 is connected in shunt or parallel with the primary winding 40 of transformer T1.
When a logic pulse 34 from addressing logic circuit 61 is applied through coupling capacitor 61C and voltage divider resistors 61RA and 61RB to the base 30 of emitter-follower transistor 01, this transistor increases the power level sufficiently to turn on transistor O2 in a switching mode. This switching action is rapid so that a current surge flows through the primary winding 40 of transformer T1 causing a voltage pulse to be produced on the secondary winding 42. At the end of the input pulse 34, transistor Q2 will turn off stopping the current flow in the primary winding 40 of transformer T1 and a second voltage pulse on the secondary 42 of the transformer is prevented by the diode D1. The diode D1 clips the negative part of the oscillation giving it single half wave output pulse. This diode D1 also serves to protect the transistor Q2 from large transients which may occur during the turn off" operation. As a practical matter, the input logic pulse 34 is made to have a duration less than half the period to take into account the transistor stored charge which may delay the turning off time of the transistor after the input signal is removed. Addressing logic circuit 61 while complex is conventional and may be of the line scan type or random access type, either of which can supply logic pulses 34 at selected time intervals.
The secondary winding 42 of the transformer T1 is in series circuit with the sustaining signal generator 29 and the line (conductor of the conductor array) being addressed so that the two voltages are added. In order to minimize interaction, the resonant frequency of the sustaining generator and the resonant frequency of the pulse generator are preferably made different so as to reduce power drain and provide maximum signal for application to the panel. The on"-off" pulse is adjusted for about a l microsecond duration and the sustaining signal period is about microseconds, however, the circuit is not limited to these particular time ratios.
The display panel requires a continuous signal applied to all lines, which is referred to as the sustaining signal or voltage. By continuous signal it is meant that the voltage be periodic so that it may be of the simple sinusoidal type or a complex wave shape applied for short time intervals and repeated periodically. The same sustaining voltage is applied to all X lines and a similar voltage is applied to all Y" lines but at a 180 phase relationship. These voltages, as applied to conductors of conductor arrays on the panel, are balanced with respect to ground to permit the addressing of a single discharge unit within the panel.
In order to lessen the effect of variable capacitive loading on the sustaining voltage generator 29, a capacitance 45 may be connected in shunt with the panel, the larger the panel capacitance change as more discharge units are turned on, being accommodated by a larger shunt capacitance.
As shown in FIG. 1A, each line on conductor of a conductor array is provided with a pulse generator 60 (e.g., 60-12-1 60-l2-n and 60-13-1 60-13-n) which receives a trigger input logic pulse 34) from addressing circuit 61. For example, when it is desired to address or turn on the discharge unit defined by the crossing of conductors 13-1 and 12-1, a logic pulse is applied simultaneously to pulse generator circuit 60-13-1 and 60-12-1 so that unidirectional pulses are added to the out of phase voltages, respectively, from sustaining voltage generator 29. A synchronization connection between sustaining generator 29 and addressing logic circuit 61 is provided so that the logic pulses 34 occur at proper times with respect to the sustaining voltage from sustaining voltage generator 29.
If a sinusoidal voltage on a discharge unit is raised in magnitude to the breakdown level the firing potential) the discharge unit will discharge. If the amplitude of the applied potential is reduced, the discharge unit will continue to stay on and, in fact, the discharge unit will stay on down to some minimum level of sustaining voltage at which point the discharge unit will go off so that if the applied alternating potential voltage is less than the breakdown or firing voltage but greater than the sustaining voltage level the discharge unit will continue to be in a single firing state. This difference between on and off voltage levels is utilized as an electrical memory and, as noted above, it is due to alternate storage of charges on the surfaces 17 and 18 of dielectric members 14 and 16 to constitute a discharge unit bias or memory voltage. When the discharge units are arrayed in horizontal rows and vertical columns served by horizontal and vertical conductor arrays it is important to be able to alter the state of one discharge unit while not affecting the status of others. Moreover, for simplicity purposes, it is desirable to utilize a sinusoidal signal that is at or slightly greater than the sustaining level and to utilize additive voltages on certain conductors to modify the status of selected discharge units.
In order to turn off a selected discharge unit (e.g., terminate a sequence of discharges representing the on state), the stored charges (which constitute a discharge unit bias voltage) must be eliminated or modified in such a way that the amplitude of applied voltage, which is the constant amplitude sustaining voltages 72A and 728 (see FIG. 3), will be insufficient to effect a discharge. The turn off" pulse is identical to the turn on pulse and it has been found that the time of application of the turn off pulse with respect to the sustaining voltage can effect a turn off of a discharge unit if it is applied (l) in synchronism in time such that the pulse top or peak occurs at the point of a normal discharge, e.g., point 70 (see FIG. 3), or (2) to modify the slope of the next to last discharge, or (3) by having the slopes of the pulse and applied sinusoidal voltages combined to produce a near zero slope condition at the point of the last discharge.
Thus, whenever a firing voltage (or a discharge terminating voltage) is induced in a transformer secondary 42 in additive relation to the sustaining signal generator voltage to fire a selected discharge unit, such high voltage is applied to the selected conductor pair of arrays 12 and 13 at a selected discharge unit. Adjacent conductors will not have the high voltage applied exactly thereto and may, through capacitive coupling, receive an increase voltage of sufficient magnitude as to effect a spurious firing of unselected discharge units.
Except for diode D2, the circuit of FIG. 2 as thus far described is essentially disclosed in the above mentioned Johnson et al. application Ser. No. 699,170. The circuit of the present invention includes diode D2 and a switching transistor means comprising transistor Q3 and transistor Q4 which circuit is operative to sense voltages induced in primary winding 40 from secondary winding 42. Diode D2 has its anode 78 connected to the positive terminal of direct current V2 and its cathode 79 is connected to upper end 77 of primary winding 40.'Emitter 86 of transistor Q4 is connected to cathode 79 of diode D2 while base electrode 82 of transistor O4 is connected directly to anode 78 of diode D2. Collector electrode 87 of transistor Q4 is connected directly to base electrode 83 of transistor Q3 and collector electrode 81 of transistor O3 is directly connected to base electrode 82 of transistor Q4. It will be recognized that this connection of transistors Q3 and Q4 is essentially a PNPN device and that for opposite polarity operation transistor Q4 may be an NPN type transistor, transistor Q3 may be a PNP type transistor and the direction of diodes D1 and D2 would be reversed.
Voltages induced in primary winding 40 from secondary winding 42 which cause the upper end 77 of winding 40 to be negative withrespect to the lower end 76 find a low impedance path through shunt diode D1 and this low impedance is reflected to the primary as alow impedance.
Voltages induced in primary winding 40 which appear as positive potentials at the upper end 77 of this winding tend to reverse bias diode D1 which then appears as a high impedance to such voltages. However, diode D2 is likewise reverse biased by such voltage so this positive voltage appears as a potential difference across diode D2 and this voltage is applied to the emitter 86-base 82 circuit of transistor Q4 and forward biases transistor Q4 to conduction. Collector 87 of transistor Q4 .could be connected to the lower end 76 of primary winding 40 to provide a low impedance shunt circuit on primary winding 40. However, for purposes of efficiency and peak power capability transistor, Q3 is utilized with transistor Q4 as a PNPN device. Thus, collector 81 of transistor Q3 is directly connected to the base 82 of transistor Q4 and collector 87 of transistor Q4 is directly connected to base 83 of transistor Q3 and emitter 80 of transistor Q3 is connected directly to end 76 of primary winding 40. With this circuit, positive potentials induced in primary winding 40 are sensed across diode D2 (as well as across diode D1) which detects currents attempting to flow in the reverse direction. Reverse voltage appearing across diode D2 also appear at the emitter 86 base 82 circuit of transistor Q4 to immediately render both transistors Q3 and Q4 heavily conductive because of the PNPN connections described above. The conductive condition of the transistor pair is, in effect, a very low impedance on primary winding 40 which is reflected to secondary winding 42. The result is that with respect to voltages or currents applied to or at secondary 42, which induce voltages in primary 40, see a very low impedance and hence there is a low voltage drop across the secondary.
The usefulness of this circuit in connection with a gas discharge panel of the types referred to above is illustrated in FIG. 3. In FIG. 3 a gas discharge panel shown as a dotted rectangle and has conductor arrays 12 and 13, cross-points of conductors 12 with conductors 13 locating and defining a particular discharge unit in the panel. The sustaining voltage sources are shown as 29A and 293 which are 180 out of phase and apply their respective voltages to conductors 12-1, I2-2 12-n and conductors 13-1, 13-2 l3-n, respectively, through the secondary windings of transformers T12-1, T12-2 Tl2-n and Tl3-l, T13-2 T13-n, respectively, each of which corresponds to secondary winding 42 shown in FIG. 3. Each switches S12-1, SI2-2 S12-n and 513-1, S13-2 S13- n correspond to switching transistor Q2 (FIG. 2) and are selectively operated in accordance with logic pulses 34 from addressing circuit 61, one of switches 813-1, 813-12 and of switches 812-1, 812-2 S12-n being actuated simultaneously to locate and electrically manipulate a selected discharge unit or cross-point. Batteries labeled V correspond to direct current source V2 (FIG. 2) it being understood that a single source of direct current is utilized, separate batteries being shown for purposes of explanation.
A momentary closing of any switch causes a current surge through the primary winding of the associated transformer which current surge induces a high voltage pulse in the secondary winding of the associated transformer which is added to the sustaining voltage V,/2 for the conductor being driven. Suppose it is desired to manipulate the discharge unit marked X which is defined or located at the crossing point of conductor 12-2 and 13-2. Momentarily, switch S12-2 is closed and simultaneously switch 813-2 is closed, both switch closings being effected by addressing circuit 61. Current surges through the primaries of transformers T12-2 and Tl3-2 induce voltage pulses in their secondaries which are added to the sustaining voltages to fire or control the discharge at point X," as described in said Johnson et al. application. Because of the closeness of conductors 12-1 and 12-n to conductor 12- 2 and the closeness of conductors 13-1 and 13-n to conductor 13-2 spurious voltage pulses may be coupled to these adjacent conductors as well as others by the distributed capacitances C between the conductors. In order to assure that such spurious voltage pulses do not effect undesired manipulation of discharge units along the adjacent conductors, each pulse circuit.60-13-1, 60-13-2 60-13-n and 60-12-1, 60-12-2 60- 12-n includes means for reducing the impedance thereof in response to the presence of spurious voltages. Sensing and switching circuits 112-1, 112-2...1l2-n and sensing and switching circuits 113-1, 1 13-2...113-n sense voltages induced in primary windings of transformers T12-1, T12-2...T12-n and Tl3-1, Tl32...T13-n, respectively, and effect a switching or shunting action to such induced voltages and appear as low impedances thereto, which low impedances are reflected into the transformer secondaries. In this way, any voltage coupled to an adjacent conductor produces only a low voltage drop at each secondary winding which is of insufficient magnitude even when added to the sustaining voltage at a given conductor to effect a discharge or control at an unselected discharge unit. Sensing and switching circuits 112 and 113, as shown in FIG. 3, include diodes D1 and D2 and transistors Q3 and Q4.
In addition to providing a low impedance for spurious pulse voltages, the circuit is also effective in reducing the transformer impedance with respect to the currents due to sustaining voltages V /2.
While the invention has been described in connection with a gas discharge panel, it may be used in other situations when it is desired to produce a low impedance effect to voltage pulses or signals.
In FIG. 2, typical components values, transistor and diode types are exemplary for voltage values shown.
The invention is not to be limited to the precise form shown in the drawings for obviously many changes may be made, some of which are suggested herein, within the scope of the following claims.
1. In a system for voltage pulsing selected row-column conductor pairs of a discharge panel having crossed conductor matrix dielectrically isolated from a thin gas discharge medium to manipulate the discharge condition of the discrete gas volume at a selected row-column conductor pair without interfering with the discharge condition of discrete gas volumes discharge sites defined by unselected adjacent row-column conductors of said matrix, sustaining voltage generator means for supplying balanced periodic alternating sustaining voltages in polarity opposition to all row and column conductors, respectively, pulse generator means for supplying discharge condition manipulating voltage pulses to selected row-column conductor pairs, including means providing a low impedance in circuit with row and column conductors adjacent to said selected row-column conductor pair to dissiplate energy coupled to said adjacent row-column conductors from said selected row-column conductor pair, the improvements in said sustaining voltage generator means comprising,
an independent and separate pair of sustaining voltage sources which are of relatively opposite electrical polari-,
ty, each said source generating equal amplitude and opposite polarity sustainer voltages pulses means including said pulse generator means, for applying said sustainer voltages to said matrix conductors, respectively, means intermediate said independent and separate pair of sustaining voltage sources constituting a common ground reference point intermediate said pair of sources so that i said sustainer voltages and pulses from said pulse generator means, as applied to conductor arrays on the panel,
are balanced with respect to said common ground reference point to permit manipulation of the discharge condition of any selected discrete gas volume within said panel by said pulses from said pulse generator means.
2. The invention defined in claim 1 wherein each said pulse generator means includes transformer means having primary windings for carrying current pulses corresponding to said