Classifications

• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
  • G09G3/28—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels
  • G09G3/288—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels using AC panels
  • G09G3/291—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels using AC panels controlling the gas discharge to control a cell condition, e.g. by means of specific pulse shapes
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
  • G09G3/28—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels
  • G09G3/288—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels using AC panels
  • G09G3/291—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels using AC panels controlling the gas discharge to control a cell condition, e.g. by means of specific pulse shapes
  • G09G3/292—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels using AC panels controlling the gas discharge to control a cell condition, e.g. by means of specific pulse shapes for reset discharge, priming discharge or erase discharge occurring in a phase other than addressing
  • G09G3/2927—Details of initialising
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
  • G09G3/28—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels
  • G09G3/288—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels using AC panels
  • G09G3/298—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels using AC panels using surface discharge panels
  • G09G3/2983—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels using AC panels using surface discharge panels using non-standard pixel electrode arrangements
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J11/00—Gas-filled discharge tubes with alternating current induction of the discharge, e.g. alternating current plasma display panels [AC-PDP]; Gas-filled discharge tubes without any main electrode inside the vessel; Gas-filled discharge tubes with at least one main electrode outside the vessel
  • H01J11/10—AC-PDPs with at least one main electrode being out of contact with the plasma
  • H01J11/12—AC-PDPs with at least one main electrode being out of contact with the plasma with main electrodes provided on both sides of the discharge space
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J11/00—Gas-filled discharge tubes with alternating current induction of the discharge, e.g. alternating current plasma display panels [AC-PDP]; Gas-filled discharge tubes without any main electrode inside the vessel; Gas-filled discharge tubes with at least one main electrode outside the vessel
  • H01J11/20—Constructional details
  • H01J11/22—Electrodes, e.g. special shape, material or configuration
  • H01J11/24—Sustain electrodes or scan electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J11/00—Gas-filled discharge tubes with alternating current induction of the discharge, e.g. alternating current plasma display panels [AC-PDP]; Gas-filled discharge tubes without any main electrode inside the vessel; Gas-filled discharge tubes with at least one main electrode outside the vessel
  • H01J11/20—Constructional details
  • H01J11/22—Electrodes, e.g. special shape, material or configuration
  • H01J11/26—Address electrodes
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2310/00—Command of the display device
  • G09G2310/06—Details of flat display driving waveforms
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2310/00—Command of the display device
  • G09G2310/06—Details of flat display driving waveforms
  • G09G2310/066—Waveforms comprising a gently increasing or decreasing portion, e.g. ramp
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2320/00—Control of display operating conditions
  • G09G2320/02—Improving the quality of display appearance
  • G09G2320/0228—Increasing the driving margin in plasma displays
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2211/00—Plasma display panels with alternate current induction of the discharge, e.g. AC-PDPs
  • H01J2211/20—Constructional details
  • H01J2211/22—Electrodes
  • H01J2211/24—Sustain electrodes or scan electrodes
  • H01J2211/245—Shape, e.g. cross section or pattern

Definitions

• This invention relates to AC plasma display panels and, more particularly, to a an AC plasma display panel that emits most of its light from the positive column region of a gas discharge and, as a result, exhibits substantially improved levels of image brightness and luminous efficiency.
• PDPs Prior art AC plasma display panels
• gas discharges exhibit two distinct light emitting regions, i.e. the negative glow wherein a plasma exists with an excess of positively charged ions and the positive column wherein the plasma evidences a balance of positively charged ions and electrons.
• PDP subpixel sites operate using the same fundamental principle as a fluorescent lamp. More particularly, a PDP subpixel employs ultraviolet light generated by a gas discharge to excite visible light emitting phosphors.
• a fluorescent lamp uses the positive column region of a gas discharge to generate most of its light since the positive column has a much higher luminous efficiency than the negative glow.
• the positive column has not been previously successfully applied to AC PDPs because the limited physical space of the small subpixel sites do not easily allow sufficient room for the usually long dimensions of a positive column.
• the power in a gas discharge is divided between the two major regions: the positive column and the negative glow.
• the positive column is characterized by an equal density of electrons and ions that are of a very high density that shields out most of an applied electric field.
• the negative glow is characterized by a very high level of positive ions and a very low level of negative electrons.
• the high density of positive charge means that the electric field in the negative glow is very high. The very high electric field allows a major part of the potential applied across the gas to be dropped across the negative glow.
• the positive column and the negative glow have considerably different luminous efficiencies.
• the positive column is very efficient and the negative glow is inefficient.
• a fundamental reason for this difference is that most of the current flow in the positive column is due to electrons and most of the current flow in the negative glow is due to ions.
• Energy absorbed by electrons can be used to efficiently excite atoms that ultimately emit light.
• energy absorbed by ions eventually gets transferred to the gas atoms as kinetic energy and simply heats up the gas .
• the positive column has approximately equal numbers of electrons and ions. Since the electrons have roughly 100 times the mobility of the ions, they will conduct 100 times more of the current than the ions in the positive column. Because most of the current flow in the positive column is in _ the electrons, virtually all of the power dissipated in the positive column goes into the kinetic energy of the electrons. This kinetic energy can be transferred to the excitation of atoms with efficiencies greater than 80% if the electric field is of the correct low value. Virtually all of the excited atoms generate ultraviolet photons which can further excite the phosphors to emit the desired visible light.
• the negative glow has a high number of ions and a much smaller number of electrons. Even though the electrons have two orders of magnitude greater mobility than the ions, the ions are of such a large density that much of the power dissipated in the negative glow goes to the kinetic energy of the ions. However, the electric field in the negative glow is very high and therefore the electrons gain much higher kinetic energies than in the lower field of the positive column. The higher electron kinetic energies mean that the electrons can both excite and ionize the atoms. Electron energy used to ionize the atoms creates ions that flow to the cathode and are ultimately neutralized at the cathode surface.
• a second strategy for increasing the efficiency of the fluorescent lamp is to increase the length of the positive column. This is the reason that the common fluorescent lamp is a long tube.
• the positive column can be modeled as a resistor. Therefore the longer the positive column, the greater its resistance and the greater its power dissipation.
• the properties of the positive column allow it to be easily extended in length as long as there is sufficient voltage to establish the desired current across its resistance. This means that for a constant current, as the positive column is made _ longer, the voltage across the positive column needs to increase proportionally. Further, the longer the positive column, the more favorable is the ratio between the power dissipated in the positive column and that dissipated in the negative glow.
• Fig. 1 shows a prior art color AC PDP from U.S. Patent 5,745,086.
• This structure utilizes ultraviolet light which is generated by a gas discharge to selectively excite red, green and blue phosphors to emit the desired full color visible light.
• Figs. 2a-2c show typical cross sectional views of the subpixels in the AC PDP of Fig. 1.
• Such an AC PDP operates with AC voltages and provide write voltages which exceed the firing voltage of the ionizable gas at a given discharge site, as defined by selected column and row electrodes.
• the discharge is continuously "sustained" by applying an alternating sustain signal (which, by itself, is insufficient to initiate a discharge) .
• the technique relies upon wall charges generated on the dielectric layers of the substrates which, in conjunction with the sustain signal, operate to maintain continuing discharges .
• the wall charge states In order for an AC plasma panel to exhibit reliable operation, its wall charge states must be repeatable and standardized. More specifically, the wall charge states must exhibit repeatable values irrespective of a - previous data storage state, so that succeeding address and sustain signals reliably cooperate to assure repeatable pixel site operation.
• PDP 10 includes a back substrate 12 upon which plural column address electrodes 14 are supported. Column address electrodes 14 are separated by barrier ribs 16 and are covered by red, green and blue phosphors 18, 20 and 22, respectively.
• a front transparent substrate 24 includes a pair of sustain electrodes 26 and 28 for each row of pixel sites.
• a dielectric layer 30 is emplaced on front substrate 24 and a magnesium oxide or similar high gamma material overcoat layer 32 covers the entire lower surface thereof, including all of sustain electrodes 26 and 28.
• Fig. 1 The structure of Fig. 1 is sometimes called a single substrate AC PDP since both sustain electrodes 26 and 28, for each row, are on a single substrate of the panel.
• An inert gas mixture is positioned between substrates 12 and 24 and is excited to a discharge state by a sustain signal applied by sustain electrodes 26 and 28.
• the discharging inert gas produces ultra-violet light that excites the red, green and blue phosphor layers 18, 20 and 22, respectively to emit visible light. If the driving voltages applied to column address electrodes 14 and sustain electrodes 26, 28 are appropriately controlled, a full color image is visible through front substrate 24.
• Fig. 2d provides typical dimensions of prior art PDPs (in micrometers) for various designs. Designs F, N, M and P are designs used in practical displays by various manufacturers. Note that for these designs, the gap distance between the front substrate sustain electrodes, called the sustain - gap (SusG) is usually approximately equal to the gap distance between the front substrate and the rear substrate, referred to as the substrate gap (SubG) .
• the sustain gap is always less than the distance between the sustain electrode of one subpixel and the sustain electrode of a neighboring subpixel which is referred to as the inter pixel gap (IPG) .
• IPG inter pixel gap
• the IPG is not considerably larger than the SusG, there will be strong interaction between subpixels that will cause operational failures. More specifically, if the IPG is smaller than the SusG, then when the sustain signal is applied, the electric field across the IPG will be larger than the electric field across the SusG. This will allow a discharge to occur along the IPG which would modify the charge on the sustain dielectric layers and substantially modify the operation of the discharge along the sustain gap.
• An AC PDP has a plurality of addressable subpixel sites, each subpixel site including an address electrode positioned on one substrate and first and second sustain electrodes positioned on an opposed substrate. An intersection between the address electrode and the first sustain electrode defines a first discharge site and an intersection between the address electrode and the second electrode defines a second discharge site.
• a scan driver is active during an address phase, and applies a negative going signal to the first sustain electrode.
• An address driver applies an address signal to the address electrode which creates a discharge at the first discharge site. As a result, a positive column moves along the address electrode to the second discharge site and causes a discharge thereat which induces a wall voltage at the second discharge site in accordance with a determined subpixel value.
• a sustain driver applies a sustain signal to both the first sustain electrode and the second sustain electrode and creates a "ping pong" action of the wall charge states at the discharge sites and enables the use of positive column light emission in the PDP.
• Fig. 1 shows a prior art color AC PDP.
• Fig. 2a shows a first sectional view of the AC PDP of Fig . 1 .
• Fig. 2b shows a second sectional view of the AC PDP of Fig. 1.
• Fig. 2c shows a schematic plan view of the AC PDP of Fig. 1.
• Fig. 2d is a Table which provides measurements of both prior art PDPs and a PDP incorporating the invention.
• Fig. 3 is a schematic which illustrates the electrode arrangements of a PDP incorporating the invention.
• Fig. 3a illustrates an electrode arrangement of Fig. 3, which further incorporates electrode isolation bars.
• Fig 3b is a sectional view of a part of the electrode arrangement of Fig. 3a, helpful in enabling an understanding of the operation of the electrode isolation bars.
• Fig. 4 is a sectional view of a subpixel in the PDP of Fig. 3.
• Figs. 5a-5f illustrate the operation of the subpixel of Fig. 4.
• Fig. 6a is a plot of sustain voltage versus sustain gap illustrating the relationship between minimum sustain voltages required to establish a discharge for conventional design PDPs having relatively small sustain gaps and for PDPs constructed in accordance with the invention and exhibiting relatively large sustain gaps.
• Fig. 6b illustrates a set of sustain waveforms used with the invention.
• Fig. 7 illustrates a set of sustain waveforms that will create an errant erase operation.
• Fig. 8 illustrates a set of prior art sustain waveforms that will not operate with the invention.
• Figs 9a and 9b show prior art addressing and sustain waveforms.
• Fig. 10 shows a set of waveforms that have been found to be successful for addressing the subpixels using the principles of the invention.
• Fig. 11 shows details of pulse setup waveforms used with the invention.
• Fig. 12 shows a single erase pulse of possible amplitudes Vel, Ve2, Ve3 or Ve4 that may be applied to the YSA sustain electrodes.
• Fig. 13 illustrates prior art ramp setup waveforms.
• Fig. 14 illustrates a set of waveforms for operating the invention.
• Figs. 15a-15c show actual measured sustain voltages and currents for the address electrode, the trigger cell sustain electrode and the state cell sustain electrode in a PDP incorporating the invention hereof.
• Figs. 16a and 16b show measured gas discharge light observed from a subpixel as a function of space and time during the discharge shown in Fig. 15. -
• Fig. 17 shows an analogy of the stability of a typical plasma display subpixel.
• Fig. 18 shows the same sustain waveforms that were shown in Fig. 6b and the allowed values of wall voltages for both ON and OFF states.
• Fig. 19 shows an allowed choice of the OFF state wall voltage for the trigger cell and the state cell that is within the bounds described in Fig. 18.
• a schematic electrode layout is shown of a PDP 50 incorporating the invention.
• Fig 4 is a sectional view across subpixel 1 in Fig. 3.
• a plurality of single trace address electrodes 52 (X0 - Xn-1) are positioned and are driven, selectively, by an X address driver 53 during an address phase of operation.
• Address electrodes X0 - Xn-1 are separated by barrier ribs 54.
• Each address electrode is covered by a dielectric/phosphor coating 56.
• On lower substrate 58 are positioned a plurality of sustain loops 60, 62, 64, etc., each of which comprises a pair of parallel trace electrodes, e.g., YSBO and YSB1. All of sustain loops 60, 62, 64, etc.. are driven in common from sustain bus electrode 66, which is, in turn, connected to a sustain driver 68.
• sustain driver 68 a sustain driver 68.
• Scan/sustain driver 70 Interleaved between the sustain loops are pairs of single trace scan electrodes, e.g., YSA1, YSA2, etc.. which are individually driven by a scan/sustain driver 70.
• Scan/sustain driver 70 applies sustain signals to each of scan electrodes YSA1, YSA2,..., which act as sustain electrodes during the sustain phase.
• Scan/sustain driver 70 during an address phase, sequentially applies scan voltages to the scan electrodes in a raster scan manner.
• Each of the scan electrodes and sustain loop electrodes is covered by a dielectric coating 72 (Fig. 4) and, for example, an MgO overcoat 73.
• a dischargeable gas is maintained between upper substrate 51 and lower substrate 58.
• subpixel illumination selectively occurs between adjoining scan and sustain electrodes (along intersecting address electrodes) by virtue of positive column discharges.
• PDP 50 makes the light from the positive column dominant over the negative glow light, is that the distance between each scan electrode and adjoining sustain electrode (sustain gap) is made as long as possible in order to make the positive column as long as possible. This has the effect of increasing the power dissipated in the positive column relative to the power dissipated in the negative glow and thereby increases the relative light emitted by the positive column.
• the techniques used to operate the invention enable the sustain gap to be much greater than the substrate gap SubG.
• the - techniques allow the SusG to be larger than the inter pixel gap (IPG) without an exchange of the roles of these two gaps.
• An electrode dimension design while not necessarily optimum, has been found to operate according to the invention with a highly luminous positive column along the sustain gap in a practical AC PDP having a gas mixture of 10% xenon and 90% neon with a gas pressure of 450 Torr and an MgO cathode material 73.
• the design has a pixel pitch of 1320 um which is appropriate for a 4:3 aspect ratio VGA color PDP having 640 by 480 pixels and a 42 inch diagonal.
• the sustain electrode width is 100 um
• the sustain gap is 700 um
• the inter pixel gap is 420 um.
• the substrate gap is 110 um.
• PDP 50 can utilize subpixel dimensions similar to the INV design and still maintain acceptable plasma display sustaining and addressing operations and, in addition, generate most of the light - from the positive column.
• the invention allows two independent sustain discharges to occur along the substrate gap, the first sustain discharge being between the first sustain electrode (i.e., the scan electrode) and the address electrode, and the second sustain discharge being between the second sustain electrode and the address electrode.
• the scan electrodes perform a scan function during the address phase and perform a sustain function during a sustain phase.
• the scan driver applies sequential scan voltages to the scan electrodes, whereas during the sustain phase, a sustain signal is applied, in common, to all of the scan electrodes, which accordingly operate as sustain electrodes.
• the 700 um sustain gap is so large relative to the 110 um substrate gap that it is difficult to strike a discharge between the two sustain electrodes at a reasonably low voltage.
• the substrate gap is only 110 um and therefore it is easy to strike a discharge at a reasonably low voltage between an address electrode and a sustain electrode.
• the problem is that the sustain gap is so great that it initially appears difficult to set up a discharge along the sustain gap even though there are discharges between the sustain electrodes and the address electrode along the substrate gap.
• the sustain operation results in each subpixel - being divided into two seemingly independent cells, one cell defined by the intersection of a first sustain electrode and the address electrode and the second cell defined by the intersection of the second sustain electrode and the address electrode. It is a fundamental teaching of this invention of a technique that allows strong conductivity between these two seemingly independent plasma display cells.
• the cell that initiates the discharge will be named the trigger cell and the cell to which (i) the positive column extends and (ii) stores the pixel state, will be named the state cell.
• the term scan electrode will only be used during an address phase of operation of the invention.
• the fundamental principle is to operate the trigger cell in such a manner that when an appropriate discharge is initiated therein, a highly ionized positive column will emanate out therefrom and will move along the sustain gap (and the spanning address electrode) until it intersects with the state cell.
• This highly ionized positive column then forms a conductive channel between the trigger cell and the state cell which acts to discharge the wall charges on both the trigger cell and the state cell.
• the highly conductive channel forms and discharges the wall voltages on the dielectrics at the trigger and state cells, a highly luminous positive column discharge is formed that has greater luminance than the negative glow. The details of how this is accomplished will be discussed below.
• Figs. 5a-5f are a time sequence illustrating the - above described operation.
• a negative going pulse is applied to the trigger cell sustain electrode A so that it initiates a trigger cell discharge across the substrate gap, while the sustain electrode A acts as the cathode with respect to address electrode XA.
• the initial voltage across the trigger cell substrate gap is at least 250 volts. Under such conditions, a highly conductive positive column can occur that emanates from the trigger cell to the state cell.
• the voltage across the substrate gap is high and the discharge is growing in intensity, but has not yet reached a level of intensity that results in any significant field distortion and it has not significantly altered the initial wall charge distribution on any of the dielectric surfaces.
• the discharge has reached a level of intensity that field distortion has created a highly conductive plasma region near the trigger cell address electrode XA (acting as the anode) .
• This plasma region is the positive column.
• Near the trigger cell sustain electrode (acting as the cathode) is the negative glow region that has a high electric field and a very high ion density but a relatively low electron density. This highly conductive discharge and field distortion discharges the dielectric capacitors over both sustain electrode A and address electrode XA of the trigger cell.
• the dielectric covering the address electrode comprises a phosphor layer that is usually a powder with a low density.
• a low density powder usually has a low relative dielectric constant, causing the capacitance of the - dielectric layer covering the address electrode to be considerably less than the capacitance of the dielectric layer covering the sustain electrode. Because of these differences in capacitances, when a discharge current flows through the two capacitors, the voltage across the address electrode dielectric 56 will change much more quickly than that across sustain dielectric 72 (including MgO layer 73) .
• the voltage on the address electrode dielectric 56 becomes so negative that the regions of dielectric 56 along address electrode XA further away from the center of the trigger cell will have a more positive potential than the regions in the center of the trigger cell. Electrons from the highly conductive plasma very quickly move to these regions of more positive potential and effectively couple the energy stored in the capacitance of the extended dielectric 56 into the discharge.
• Fig. 5c shows how the positive column has extended itself away from the center of the trigger cell _ and is discharging this extended region further. Note that as the positive column extends from the center of the trigger cell, the regions of address electrode dielectric 56 in contact with the positive column become negatively charged whereas those regions not yet contacted by the positive column remain positively charged.
• time t3 (Fig. 5d) , the positive column from the trigger cell discharge has reached the state cell and the electrons from the positive column flow to the positive potential of dielectric 72 covering the state cell sustain electrode B.
• Dielectric 72 has a dielectric constant considerably higher than the dielectric constant of address electrode dielectric 56, allowing considerably more charge to flow into the state cell sustain dielectric 72 before its potential changes significantly.
• the current between sustain electrodes A and B begins to rise to very high levels and most of the energy stored in the sustain electrode dielectric capacitance of both the state cell and the trigger cell is deposited into the electron energy of the positive column.
• the positive column forms a highly luminous filament that bridges the sustain gap. This filament grows in intensity until it reaches a peak at time t4 (Fig. 5e) .
• the charge deposited by the discharge on dielectric 72 covering sustain electrode B has risen to a sufficiently large level that the voltage across the positive column is reduced to a low level and to a point where the light generation rate peaks and then begins to decrease.
• the discharge continues to decay in intensity until at time t5 (Fig. 5f) , the discharge current no longer flows. At this point the space charges created in the gas volume have flowed to all of the dielectric surfaces. If the initial voltage across the gas volume is high enough so that a sufficiently strong discharge occurs, then there is sufficient available space charge to substantially reduce the voltage across the gas to zero volts for nearly all regions of the subpixel. This means that nearly all dielectric surfaces at time t5 will be at one potential.
• the single potential of all dielectric surfaces at time t5 is signified in Fig. 5f by the equal density of positive charges on all dielectric surfaces.
• Fig. 3a shows a second embodiment of the electrode layout of Fig. 3 wherein conductive isolation bars 99 have been placed within each inter pixel gap IPG. Since the electrode topology of Fig. 3 has a larger sustain gap than inter pixel gap, it is desirable to provide an isolation means which restricts the spreading of positive column discharges across inter pixel gaps. Such a means is provided by conductive isolation bars 99. -
• Figs. 5a-5f show how the positive column moves along the sustain gap between the trigger cell and the state cell.
• the positive column moves from left to right. It is important to consider why the positive column moves to the right in this case and why it does not move to the left. If it were to move to the left then it could move across the inter-pixel gap which could cause an undesirable interaction with a neighboring pixel which could errantly change the state of the neighboring pixel. Another important consideration is why does the positive column stop once it has reached the state cell or in other words, why does the positive column not continue its spread past the state cell across the inter pixel gap and on to the large positive charge of the neighboring state cell. An additional problem with the positive column extending across either the left or the right inter pixel gap is the large amount of undesirable light generated between the pixels.
• Fig. 3b shows a cross section of three pixels of the plasma panel with the electrodes of figure 3a.
• Figure 3b also shows the initial charge distribution on the dielectric layers at the time tO which is the same time as shown in figure 5a.
• the positive column moves from the trigger cell to the state cell in the exact way shown in figure 5. This movement occurs because the electrons from the leading edge of the positive column are attracted to the positive charge along the dielectric covering the address electrode as shown in Fig. 5c. Since the address electrode dielectric to the right of the Fig. 3b, pixel 2 trigger cell is positive, the pixel 2 positive column will move to the right. Note that the address electrode dielectric to the left of the pixel 2 - trigger cell is negative. This will repel the positive column electrons and therefore inhibit the growth of the positive column to the left of the pixel 2 trigger cell.
• the pixel 2 positive column reaches the state cell, it does not continue to move to the right to the positive charge of the pixel 3 state cell because of the negative charge on the dielectric covering the address electrode in the inter pixel gap between the pixel 2 state cell and the pixel 3 state cell.
• Dielectric surfaces that are near gas discharges have a well known characteristic that the dielectric regions farther from the main discharge activity charge up more negatively than those regions in close contact with the discharge. This phenomenon is fundamentally caused by the different velocities of the electrons and the ions in the gas. Because of the relative masses of these charged particles the electrons have approximately 100 times the velocity of the ions in a gas discharge. This means that electrons will fly out of the discharge 100 times faster than the ions. When the initial electrons fly out they will charge the dielectric surface negatively and set up a negative potential that will repel the electrons. This negative potential will attract the positive ions.
• This negative potential continues to grow until an equilibrium __ potential is reached.
• the equilibrium potential is determined by the condition that an equal number of ions and electrons flow to the surface. This equilibrium potential will repel the high velocity electrons and attract the low velocity positive ions so that the ion currents and the electron currents are equal. This equal ion and electron current condition will result in a zero sum of these opposite polarity currents. If the sum of the currents is zero, then there is no net charge flowing to the dielectric surface and the potential will stop changing. This stable potential is defined as the equilibrium potential.
• the condition for establishing the negative charge in the inter pixel gap is that there be no significant discharge activity in the inter pixel gap.
• the sustain discharges will then establish the negative charges in the inter pixel gaps as shown in figure 3b by the mechanism discussed in the previous paragraph.
• isolation bar 99 The purpose of the isolation bar 99 is to insure that there is no significant discharge activity in the inter pixel gap so that the negative charge can accumulate there. It is convenient to make the isolation bar with the same material and process as the front plate sustain electrodes. In this way the isolation bar is simply defined by a simple front plate electrode mask change.
• Figure 3a shows that the isolation bars 99 are not directly electrically connected to any other electrodes, but are left floating. This means that the potential on the shorting bars will be determined by the capacitive coupling between the isolation bars and the other electrodes in the plasma panel.
• Figure 3b shows the coupling capacitors, Cl through C5, for the isolation - bar between pixels 1 and 2. If a pulse is applied to the electrodes A in figure 3b, a fixed percentage of that pulse will also appear on isolation bar 99.
• this fixed percentage is determined by the pixel geometry's and materials dielectric properties. The exact value of this percentage is determined by the capacitive divider comprised of the parallel combination of Cl and C2 with the series combination of C3, C4 and C5 shown in figure 3b.
• the magnitudes of capacitors Cl and C2 will be relatively large because they are formed in the glass layers of the front substrate glass and the dielectric glass which have high relative dielectric constants.
• the magnitude of the series combination of C3, C4 and C5 will be relatively low since series combinations of capacitors are always smaller than the smallest capacitor which in this case is C3.
• this fixed percentage is important - for the proper operation of the isolation bar. As stated above it is necessary for there to be no significant discharge activity in the inter pixel gap. Since the isolation bar is very similar to the sustain electrodes, if the voltage pulses on the isolation bars are too high then an undesirable sustain discharge could occur to the isolation bar. It is therefore necessary to design the plasma display materials, electrode geometry's and sustain pulse amplitudes in such a way that when the sustain pulses are applied to the normal sustain electrodes that the fixed percentage discussed above is sufficiently low so that the pulsed potential that results on the isolation bar is below the voltage at which the sustain discharges can occur on the isolation bar. This minimum sustain voltage measured on the isolation bar is designated Vsminib.
• the isolation bar pulsed potential on the isolation bar is below Vsminib, there will be no significant discharge activity along the isolation bar and therefore there will be no significant discharge activity in the inter pixel gaps. This will allow the negative charge to build up in the inter-pixel gap which will repel the movement of the positive column across the inter pixel gap. This will eliminate the undesirable errant discharges to neighboring pixels or undesirable inter-pixel light.
• the isolation bar pulsed potential remains below Vsminib, the isolation bar has the desired effect of acting like a shield for the electric fields from the sustain electrodes that extend into the inter pixel gap. It acts like this shield primarily because of the negative charge on the dielectric layers shown in the inter pixel gap of figure 3b that accumulates due to - lack of discharge activity.
• U. S. patent 3,666,981 to Lay documents the usage of electrostatic isolation bars to prevent discharges from spreading out to neighboring cells on dual substrate monochrome PDPs.
• the isolation bars are placed between every sustain electrode on both the front and the back substrates.
• the isolation bars are placed on only one substrate and only between every other sustain electrode. More specifically, this invention requires that the isolation bars be placed between only the sustain electrodes that are at the same potential during the sustain operation. This is shown in figures 3a and 3b.
• one isolation bar is between the two A sustain electrodes and another isolation bar is between the two B sustain electrodes .
• both A sustain electrodes are at the same potential and both B sustain electrodes are at the same sustain potential.
• the potential on the A electrodes is frequently different than the potential on the B electrodes.
• This invention would not work properly if the isolation bars were placed between sustain electrodes that are at a different potential during the sustain period. For instance if isolation bars were placed between the A and B electrodes of Fig. 3b there would be very significant problems. First of all the region between the sustain electrodes A and B is across the sustain gap which is where the main discharge of the panel occurs.
• Isolation bars in the region of the sustain gap will of course have the undesirable property of blocking the most significant light emission of the panel.
• the placement of ⁇ the isolation bars in the sustain gap would interfere with the electric field in the sustain gap and would also possibly interfere with the movement of the positive column from the trigger cell to the state cell .
• the pulsed potential that appears on an isolation bar placed between the A and B electrodes will be much different compared to the pulsed potential of isolation bars placed between two sustain electrodes that are always at the same potential during the sustain period. Since the A and B sustain electrodes are frequently at different potentials during the sustain waveform the isolation bar between the A and B electrodes would float to a lower potential when a sustain pulse is applied to either sustain electrode than the potential of an isolation bar placed between pulsed equipotential sustain electrodes. The reason for this is a differing capacitive divider ratio for the two different cases. For the case of the isolation bar between the A and B electrodes, the isolation bar will be pulsed to less than 50% of the amplitude of the pulse applied to either sustain electrode.
• the isolation bar will be pulsed to significantly greater than 50% of the pulse amplitude applied to the sustain electrodes.
• Another problem with placing the isolation bars between the A and B sustain electrodes is the significant increase in capacitance between the A and B sustain electrodes.
• the isolation bars are placed between the sustain electrodes of equal potential according to the principles of this invention, there is a minimal increase in the capacitance between the A and_ B sustain electrodes. This significantly reduced capacitance will significantly reduce the power dissipated in the circuits that must drive the panel capacitance.
• a PDP has been successfully operated where the inter pixel gap was set to be approximately equal to the sustain gap, isolation bars 99 were centered in the inter pixel gaps and the width of each isolation bar 99 was approximately 50% to 80% of the inter pixel gap.
• Curve A is similar to the classic U shaped gas discharge Paschen curve and defines how the minimum sustain voltage required by the prior art to just sustain a cell discharge between the two sustain electrodes (i.e., Vsmin) behaves as the sustain gap is varied.
• the Vsmin voltage increases because the electric field decreases due to the larger sustain gap distance which causes fewer ionizations per - volt.
• the Vsmin voltage increases because there are fewer electron collisions with gas atoms which causes fewer ionizations per volt.
• Curve B is defined as the minimum sustain voltage required to achieve a sufficiently strong discharge at a trigger cell, initially having an ON state wall voltage, which creates a positive column that travels to an adjacent state cell so as to successfully establish the state cell wall voltage to the ON state.
• curve B is much more weakly dependent on the sustain gap than is curve A. This is primarily because the initiation voltage of the curve B trigger cell discharge should be independent of the sustain gap since the trigger cell discharge initially occurs across the substrate gap and not the sustain gap, as does the curve A discharge.
• the curve B voltage increases only slightly with sustain gap because the trigger cell discharge must increase in strength slightly for the positive column to extend to the state cell for the longer sustain gaps.
• curves A and B allow sustain operation according to the invention for sustain gaps larger than the intersection point of the two curves (i.e., the critical sustain gap). Use of the larger gaps allows operation below the Vsmin of - curve A (i.e., portion C of curve A), yet at a sustain voltage above curve B so that the invention discharge mode will successfully sustain the sub-pixels.
• Electrode waveforms will hereafter be described that allow a stable sequence of plasma display subpixel discharges and allow a subpixel to be in either the ON state or the OFF state. These waveforms and conditions are necessary in order to achieve inherent memory in the AC PDP display subpixels.
• Fig. 6b shows one set of sustain waveforms that has been found to work well and that allow the subpixels to be in either the on state or the off state. Also shown in Fig. 6b are the wall voltage levels for both the on state and the off state. The wall voltage drawn for a given sustain electrode occurs due to charge on the dielectric covering the given sustain electrode and the charge on the address electrode dielectric that intersects the given sustain electrode.
• Fig. 6b shows five sustain discharges which are labeled tdl through td5. - Sustain pulses with amplitudes Vs are sequentially applied as shown in Fig. 6b. Referring to the cell structures of Fig. 3, Fig. 5 and the waveforms of Fig. 6b, at tfl the YSA sustain electrode falls and creates a discharge at tdl between the YSA sustain electrode and the address electrode XA.
• each trigger discharge initiated in a trigger cell generates a positive column that moves from the trigger cell along the address electrode to the state cell.
• a given physical - cell has a designation of state cell or trigger cell that is different at times tdl and td2.
• the trigger cells are positioned between the address electrode and sustain electrode YSA, whereas at time td2 the trigger cells are positioned between the address electrode and sustain electrode YSB.
• the state cells are positioned at sustain electrode YSB whereas, at time td2 the state cells are positioned at sustain electrode YSA.
• Fig. 5f of wall charge distribution at time t5 shows that at the end of the discharge, all of the dielectric surfaces are at the same potential due to the large number of charged particles generated during the discharge. After each discharge, the wall voltage adjusts to a level very close to the sustain voltage level. This of course means that the voltage across the substrate gap is near zero.
• the waveforms of Fig. 6b are designed so that the trigger cell discharges are always initiated by a negative-going sustain voltage transition. This is important because it means that the cathode of the trigger cell discharge is always the dielectric surface that covers the sustain electrode and not the dielectric surface that covers the address electrode. These two surfaces usually have considerably different properties when used as cathodes. For instance, in experimental subpixels that were measured, the initial discharge breakdown voltage, Vb-, when the trigger cell sustain voltage was the cathode, was measured to be approximately 200 volts, but the same cell breakdown voltage, Vb+, was measured to be approximately 300 volts when the address electrode was the cathode.
• the sustain dielectric is usually coated with a high secondary emission material such as MgO and the address dielectric is coated with or is made entirely of some suitable phosphor material.
• the high secondary emission material such as MgO has a high gamma coefficient which means that it emits a high number of secondary electrons when it is bombarded with positive ions from a gas discharge. This gives the discharge a relatively low voltage characteristic which is desirable to reduce circuit costs and power dissipation in the negative glow region of the ⁇ discharge.
• the phosphor material that covers the address electrode is designed to efficiently convert ultraviolet light to visible light.
• the phosphor generally does not have a high secondary emission material, such as MgO, because such materials usually absorb the ultraviolet light generated by the gas discharge which would give the display poor luminous efficiency.
• MgO secondary emission material
• the cathode of the trigger cell sustain discharge be the dielectric surface that covers the sustain electrodes and not the dielectric that covers the address electrodes. This is achieved by initiating the trigger cell discharge with the negative-going edge of the sustain pulses, as shown for all of the discharges in Fig. 6b.
• Figs 9a and 9b show prior art addressing and sustain waveforms from U.S. Patent 5,746,086.
• the prior art breaks a frame time into multiple subfields, as shown in Fig. 9a.
• Fig. 9b shows that each subfield is broken into various periods.
• the Fig. 9b prior art steps 1, 2 and 3 will be called the setup period and the prior art step 4 will be called the address period.
• the last period will be called the sustain period. While this invention, in a preferred embodiment, employs such an addressing/sustain operation, the waveforms and their points of application differ markedly.
• the setup period has the purpose of placing all of the subpixels in the panel in a well established wall voltage state that is appropriate for the proper - operation of the address period.
• the setup period also serves to prime the subpixels in the OFF state so that the address period discharge will be well primed and will therefore occur properly.
• the address period has the purpose of changing the state of a subpixel if there are coincident address pulses on both the YSA electrode and the XA electrode that define the subpixel.
• the sustain period has the purpose of generating light from the subpixels that are in the ON state and not generating light from subpixels that are in the OFF state.
• Fig. 10 shows a set of waveforms that have been found to be successful for addressing the subpixels using the principles of the invention. These waveforms are designed to prime and then set all of the subpixels in the PDP to the OFF state during the setup period and to turn the selected subpixels to the ON state during the address period. A similar set of waveforms, not shown here, could be designed utilizing the principles taught in this invention that sets all of the subpixels in the panel to the ON state during the setup period and then turns the selected subpixels to the OFF state during the address period.
• the sustain period operation has been covered extensively above and are the same as presented in Fig. 6b. It is next appropriate to discuss the setup period.
• the pulse setup waveforms will be presented first.
• Fig. 11 shows details of the pulse setup waveforms. These waveforms are divided into a bulk - write and a bulk erase.
• the bulk write has the function of placing both the OFF cells and the ON cells into the ON state.
• all of the subpixels in the panel have one ON state set of wall voltages.
• All trigger cells in the panel have one well defined wall voltage and all state cells in the panel have another well defined wall voltage.
• all of the subpixels are placed in the OFF state so that there will be no discharge during the sustain period that follows the setup period, unless a selective write occurs during the address period.
• the bulk write is accomplished by placing such a large negative pulse on the YSA sustain electrodes that all of the trigger cells discharge regardless of whether the subpixel is initially either in the ON state or the OFF state.
• This large negative bulk write pulse causes the positive column to spread from each trigger cell to an adjoining state cell so that the voltage across the substrate gap of the state cell is reduced to zero and all of the state cells in the PDP are placed into the ON state.
• the bulk erase pulse is designed to place the bulk erase state cell at exactly the desired wall voltage level needed for proper selective addressing.
• Fig. 12 shows how this operates. At time trel, a single erase pulse, of possible amplitudes Vel, Ve2, Ve3 or Ve4, is applied to the YSA sustain electrodes. Note that Fig. 12 shows four different waveform rows, each having a different possible value of Ve.
• the YSB sustain voltage falls and causes a trigger discharge in the trigger cells. This happens in all of the trigger cells in the PDP since it is assumed that a bulk write placed all of the - subpixels in the ON state just prior to time trel.
• the positive column from all of the trigger cell discharges spread to all of the state cells and reduces the voltage across all of the state cell substrate gaps to zero. Because of this, each state cell wall voltage moves to a value nearly equal to the applied erase pulse amplitude of Vel, Ve2, Ve3 or Ve4, as shown for each of the four cases in Fig. 12.
• This novel property of the invention allows the wall voltage of a state cell to be conveniently set to any desired level in accord with the potential applied thereto, and is used in the addressing operation.
• Vel is the same pulse amplitude as a high level of the YSA sustain pulse which is at Vs volts. Setting the state cell wall voltage to Vel sets all of the state cells to the ON state.
• Ve4 is the same as the low level of the YSA sustain pulse. Setting the erase pulse to Ve4 sets all of the state cells to the OFF state.
• the Ve4 case of Fig. 12 initiates a trigger cell discharge when the state cell sustain voltage is at the low level which causes the trigger cell positive column to reduce the voltage across the state cell substrate gap to zero, thereby placing the state cell in the OFF state.
• the final wall voltage is very closely equal to the value of Ve which is easily controlled. Note that it is the value of Ve that is applied to the state cell which, in Fig. 12, is at the YSA sustain electrode at time tfel, and determines the final value of the wall voltage after the bulk erase operation.
• the exact value of the initial voltage across the trigger cell substrate gap does not determine the value of the final wall voltage of the state cell as long as the trigger cell substrate gap has enough initial voltage to initiate a proper trigger cell discharge that will extend its positive column to the state cell.
• the prior art erase discharge does not have this same independence.
• Fig. 13 Prior art ramp setup waveforms are shown in Fig. 13 (as taught in US patent number 5,745,086).
• a slowly rising or falling ramp is used to cause a weak discharge in a gas that has a positive resistance characteristic. This allows the wall voltage to slowly follow the ramp and maintains the voltage across the gas very close to the breakdown voltage of the gas.
• the rising ramp of Fig. 13 serves the purpose of the bulk write which places both the ON and the OFF subpixels in a single well established wall voltage - state.
• the falling ramp of Fig. 13 serves the purpose of the bulk erase which places all of the subpixels in an off state with a well established wall voltage level.
• the advantage of the ramp setup waveforms of Fig. 13 over the pulse setup waveforms of Figs. 11 and 12 is the significantly lower amount of light that the ramp setup waveforms generate compared to the pulse waveforms which allows the ramp waveforms to have a display with a significantly enhanced contrast, as described in the '086 patent.
• the advantage of the pulse setup waveforms of Figs. 11 and 12 over the ramp waveforms of Fig. 13 is the reduced amount of time that the pulse setup waveforms take, compared to the ramp waveforms .
• the prior art ramp waveform shown in Fig. 13 utilizes a positive resistance discharge between the YSA and the YSB sustain electrodes.
• the YSB sustain dielectric is the cathode
• the YSA sustain dielectric is the cathode.
• the setup period waveforms it is necessary for the setup period waveforms to establish the wall voltages of both the trigger cell and the state cell to the OFF state range or else the subpixel can errantly turn ON during the sustain period, even without a selective address pulse during the address period. Because of the independence of the discharges during the ramp, it is sometimes desirable to apply the ramp waveforms to both the YSA and the YSB electrodes, as shown in the invention waveforms shown in Fig. 14.
• the first operation of the Fig. 14 setup period is the bulk erase which places all of the ON subpixels to the OFF state. This is accomplished with the same technique shown in Fig. 12 (case 4) whereby the positive column from the YSA trigger cell goes to the state cell while the YSB voltage is low. This places the wall voltages of both the trigger cells and the state cells to the level of the low sustain voltage.
• This bulk erase only causes a discharge in subpixels that were in the ON state during the sustain period.
• the subpixels that are OFF during the sustain period will have some unknown wall voltage.
• the setup waveforms - For consistent addressing operation during the address period, it is desirable for the setup waveforms - to place all cells at a fixed, well established OFF state wall voltage.
• the ramp waveforms of Fig. 14 accomplish this.
• the ramp waveforms shown in Fig. 14 are considerably different than those shown in Fig. 13.
• One major difference is that the initial ramp of Fig. 13 is positive-going and the initial ramp of Fig. 14 is negative-going. It is important for the initial ramp of this invention to be negative-going in order to achieve stable operation. This insures that the initial falling ramp discharge has the sustain electrode dielectric as the cathode and is necessary so that the high secondary emission surface (such as MgO) can create a stable discharge.
• the positive resistance discharge that occurs due to the ramp is similar to a constant current DC discharge.
• the constant current that passes through this positive resistance discharge is proportional to the ramp rate in volts per microsecond of the applied ramp.
• the discharge in the positive resistance mode adjusts itself so that the voltage across the substrate gap is exactly at the breakdown voltage of the discharge. Recall that for the MgO cathode of the measured devices, this is approximately 200 volts and that for the measured phosphor cathodes, approximately 300 volts.
• the discharge current will increase until enough charge builds up on the dielectric layers to reduce the voltage across the substrate gap back - down to the breakdown voltage. If the substrate gap voltage is below the breakdown voltage, the discharge current decreases to a point where it does not discharge the capacitance of the dielectric layers at such a high rate and the changing ramp voltage placed on the external electrode causes the magnitude of the voltage across the substrate gap to increase until it reaches the breakdown voltage. Once the breakdown voltage is reached, the discharge attains a constant stable level with time, where the rate of increase of the ramp voltage is exactly balanced by the rate of increase of voltage across the dielectric layers. Unfortunately, the above mentioned stable positive resistance discharge may not occur if there is insufficient priming of the discharge.
• the increasing ramp voltage may cause the voltage across the substrate gap to increase to considerably above the breakdown voltage before any discharge occurs. If this gap voltage rises to too high of a level above the breakdown voltage, then when the low level of priming finally does allow the discharge to initiate, the current growth rate will be so high that significant space charge field distortion will occur so that a negative resistance discharge will occur. This will cause a very strong discharge that will reduce the substrate gap voltage to well below the breakdown voltage and will cause the discharge current to rapidly decay to a very low level.
• This pulsed type of discharge, caused by low priming is not desirable for setup waveforms because it generates a high level of discharge light and it does not place the wall voltage at a well established constant level.
• the final level of the wall voltage after a discharge in this low priming case is determined by - many factors. It is somewhat random in nature since the strength of the discharge is determined by how high the continually increasing voltage across the substrate gap is above the breakdown voltage at the instant when the randomly accruing priming particles initiate the discharge.
• a sufficiently high level of priming allows the discharge to initiate when the continually increasing applied ramp voltage places the substrate gap voltage just slightly above the breakdown voltage. Because the gap voltage is only slightly above the breakdown voltage, the rate of current rise does not cause space charge field distortion to set in before the charge builds up on the dielectric to reduce the substrate gap voltage back down to the breakdown voltage.
• This sufficiently high level of priming allows a stable positive resistance discharge to occur that is very suitable for the setup operation because it produces a low level of light and it places the wall voltage at a well established constant level.
• priming Because of the importance of priming to the stability of the ramp discharge, it is necessary to discuss the mechanisms of priming. There are basically two sources of priming. The first one is active particles in the gas such as electrons, ions and metastable atoms that exist for some period after a gas discharge. The second priming source is the cathode surfaces which may emit electrons for some significant period after the discharge. Both of these priming sources start the discharge by generating free electrons in the gas that can be accelerated by the electric field to create ionizing avalanches. It is frequently only necessary to generate one free electron to initiate a discharge. -
• the two sources of priming have considerably different intensities and production rates.
• the first source has generally higher priming intensity, but it generally lasts for a shorter period than the second source.
• the decay of the first source occurs because the electric field in the gas causes the free electrons and ions in the gas to drift to the walls where the electrons are captured and the ions are neutralized to become simple gas atoms.
• the metastable atoms slowly diffuse to the walls where they are de-excited to become simple gas atoms.
• the rate of priming decay for these processes depends on many factors, such as gas type, gas mixture, gas pressure, discharge cell dimensions and applied voltage. For measured discharge conditions, all of the first source particles were generally observed to decay within 25 to 50 microseconds. The second priming source can decay much more slowly.
• exoemission The mechanism for exoemission is complicated and is not well understood. However it has been shown to be very strongly dependent on the cathode material. MgO has been found to have good exoemission and can emit electrons for many milliseconds after a gas discharge. Alternatively, the phosphor layer that covers the address electrodes has been found to have very poor exoemission.
• the Fig. 14 waveforms for the setup period have an initial negative-going ramp which is of different polarity than the positive-going ramp of Fig. 13. This negative-going ramp is necessary to insure that the MgO surface of the sustain electrode is the cathode which - allows the good exoemission to properly prime the negative-going ramp discharge and insure a stable positive resistance discharge. (If the setup period was to initially use a positively going ramp then the phosphor surface that covers the address electrode will be the cathode which because of its poor exoemission will not properly prime the positive going ramp discharge and therefore allow a highly unstable negative resistance type of discharge to occur during the ramp) .
• positive or negative-going ramps may have stable discharges as long as at least one of the priming sources provides sufficient priming. For instance a positively or negatively going ramp will provide a stable positive resistance discharge if a discharge has occurred shortly before the ramp so that the first priming source due to priming particles in the gas can cause sufficient priming.
• both positive and negative-going ramps gave a stable positive resistance discharge by means of the first priming source, as long as the ramp discharge was initiated within approximately 25 to 50 microseconds of a normal sustain discharge.
• the second priming mechanism was present and so only the negative going ramp which utilizes the exoemission from the MgO, yielded a stable positive resistance discharge.
• the requirement that the initial ramp of the setup period be negative going is necessary for the invention disclosed here, but is not always necessary for prior art designs. The reason is that for most prior art designs the application of the ramp causes a discharge across the sustain gap, whereas for the invention, the - application of the ramp causes a discharge across the substrate gap. Since both of the electrodes that bound the sustain gap are sustain electrodes, a prior art sustain gap discharge will have MgO as a cathode for both a positive going ramp and a negative going ramp. Thus, the prior art setup discharge can have a positive going or a negative going ramp and still utilize the exoemission priming to cause a stable positive resistance discharge. In this invention, the large size of the sustain gap compared to the substrate gap makes the substrate gap discharge occur first at a considerably lower voltage so that only ramp discharges across the substrate gap are practical.
• the substrate gap has one cathode of MgO and the other cathode of phosphor material, it is critical for the initial setup discharge of the invention to be negative-going in order to have a stable positive resistance discharge.
• an initial negative going ramp is applied to both the YSA and the YSB sustain electrodes in order to establish well defined wall voltages for both the trigger cells and the state cells that are initially in either the ON or the OFF states.
• This initial negative-going ramp needs to go sufficiently negative to cause stable positive resistance discharges that place both the initially ON subpixels and the initially OFF subpixels in the same wall voltage state, at time tsul of the setup period, for both the state cells and the trigger cells.
• Vsn The maximum negative excursion voltage of the ramp, Vsn is adjusted to approximately 200 volts for the INV design of Table 1. This is consistent with the measured 200 volt breakdown voltage Vb- of the substrate gap when the MgO is the cathode. If this Vsn - voltage is increased above 200 volts, there is no adverse addressing effect other than an increase of the undesirable background glow of the OFF subpixels. If this Vsn voltage is reduced in magnitude below the 200 volt level, then the wall voltage levels of the ON and OFF states will not be at the same level at time tsul.
• the initial negative going ramp in Fig. 14 causes an appropriate priming discharge that places all of the cells at a well established wall voltage level at time tsul.
• setup period there are some additional requirements for the setup period to function satisfactorily.
• One of these requirements is that subpixels that remain OFF for multiple successive subfields must always discharge during the setup period or else they will not be properly primed during the address period. Since OFF subpixels do not generally discharge during the address period or the sustain period, it is common that the wall voltage of OFF subpixels at the end of one setup period will be the same wall voltage for the beginning of the next subfield setup period.
• the initial negative going ramp of Fig. 14 causes a positive resistance discharge of the OFF subpixels that, in turn, causes their wall voltages to decrease as shown in Fig. 14. It is necessary for there to be a positive going ramp, after the initial negative going ramp, in order to raise the wall voltage back in the positive direction so that the condition stated above of having the OFF subpixel wall voltage at the end of the setup period be the same as that at the beginning of the setup period. If there were no further pulses during the setup period after the initial negative going ramp, the decreased wall voltage level at the end of the setup period would prevent discharges from occurring in following setup periods because the - initial negative going pulse would not put a voltage greater than the breakdown voltage across the substrate gaps of the cells. This condition would not provide the necessary setup period priming.
• this large tsu2 transition have a change in voltage slightly less than the sum of the breakdown voltage Vb- of the substrate gap when the sustain dielectric is the cathode and the breakdown voltage Vb+ of the substrate gap when the address - dielectric is the cathode.
• the breakdown voltage Vb- is about 200 volts and the breakdown voltage Vb+ is about 300 volts.
• the tsu2 transition should be slightly less than 500 volts.
• An appropriate value for this design is 450 volts.
• This tsu2 transition voltage is carefully chosen in order to reduce the time difference between the end of the initial negative going ramp discharge at time tsuO and the start of the positive going ramp discharge at time tsu3. If the voltage across the substrate gap at time tsul is Vb- volts, then a transition at time tsu2 of Vb- volts plus Vb+ volts will place a voltage of Vb+ volts across the substrate gap.
• the discharge will perhaps be stronger than that desired for a stable positive resistance discharge during the positive going ramp. This may cause an unstable negative resistance discharge which - is undesirable for a low luminance stable setup discharge. Because the exact values of the Vb- and the Vb+ voltages may vary from one subpixel to the next for the many subpixels in a PDP, it is desirable to appropriately reduce the tsu2 transition voltage so that it is always less than the lowest value of the sum Vb- plus Vb+ that may occur for any substrate gap cells in the panel. This is why 450 volts was chosen for the experimental INV design.
• the Fig. 14 setup waveforms are very similar for both the YSA and the YSB sustain electrodes during the initial negative going ramp and the sustain transition at time tsu2. However for the remainder of the setup period after time tsu2, the two sustain electrode waveforms are different because of differing requirements of the trigger and state cells.
• the cell between the address electrode and the YSA sustain electrode is the trigger cell and the cell between the address electrode and the YSB sustain electrode is the state cell. Therefore the setup period YSA waveform sets up the trigger cell and the setup period YSB waveform sets up the state cell.
• the setup period waveforms need to set the trigger cell wall voltages to a stable, well established level so that during the address period, a low voltage level on the XA electrode that intersects a YSA address pulse-selected subpixel will leave that subpixel in the OFF state and a high voltage level on the XA electrode will cause the selected subpixel to switch to the ON state.
• the requirement to remain in the OFF state is met by placing the YSA wall voltage, at time tsu5, at a level within the range of OFF state wall voltages.
• the second negative going ramp performs the same fundamental function as the negative going ramp shown in Fig. 13.
• the second negative going ramp causes a stable positive resistance discharge at the Vb- breakdown voltage of the trigger cell substrate gap so that the peak negative excursion voltage Vsn2 of the second negative-going ramp plus the Vb- breakdown determines the OFF state wall voltage at time tsu5. If there is no discharge activity during the address period or the sustain period, then the OFF state wall voltage level established at time tsu5 remains during the address period and the sustain period.
• the state cell wall voltage has differing requirements from the trigger cell. Note that there is no second negative-going ramp for the YSB sustain waveform which intersects with the state cell during the ramp parts of the setup period. Instead the YSB positive-going ramp simply rises from the transition at time tsu2 to the voltage level Vsp at time tsu4. YSB remains at voltage level Vsp after time tsu4 and also for the entire address period.
• One effect of this YSB positive going ramp waveform is to place the Vb+ breakdown voltage across the substrate gap of the state cell. The amplitude of Vsp is adjusted to place the wall voltage at time tsu4 at a level within the range of OFF state wall voltages.
• the state cell wall voltage at time tsu4 is equal to Vsp minus Vb+.
• the state cell positive-going ramp applied to the YSB waveform gives a stable positive resistance discharge as long as there is sufficient priming from particles in the substrate gap generated from the initial negative going ramp. This works properly, as discussed above, if the time - difference between tsu3 and tsuO is less than the priming particle decay time.
• the positive column will not extend from the trigger cell to the state cell during address time ta, even though there is a very strong discharge across the trigger cell substrate gap. Without this extension of - the positive column from the trigger cell discharge to the state cell during the time ta address discharge, the subpixel will not be in the ON state when the sustain period occurs and so it will errantly not emit the desired light.
• the ramp-generated positive resistance discharge of the trigger cell operates independently of the ramp generated positive resistance discharge of the state cell, since there can be no positive column to couple the trigger cell and the state cell.
• the positive resistance discharges of the trigger cell and the state cell place their wall voltages at a well established level across their respective substrate gaps, there is still significant freedom for there to be a large difference in wall voltage between the trigger cell and the state cell.
• the ramp waveform- generated positive resistance discharges can easily control the wall voltage measured across the substrate gap of this invention.
• the positive resistance discharges will not necessarily control the wall voltage measured across the sustain gap to a well established level because of the independence of the positive resistance discharges of the trigger cell and the state cell.
• the distribution of wall voltage across the sustain gap is important for determining if the trigger cell discharge positive column will emanate from the trigger cell to the state cell during the address discharge of Fig. 14.
• a reason why the trigger cell positive column of the sustain discharge shown in Fig. 5 moves to the state cell is that the electrons from the leading edge of the expanding positive column (e.g., Fig. 5, times tl and t2) find a surface along the address electrode which has a positive potential relative to the positive column in a direction away from the trigger cell. These leading edge positive column electrons rapidly move to this positive potential region and thereby cause a further expansion of the positive column.
• the negative-going trigger cell sustain electrode that initiates the sustain trigger cell discharge causes the trigger discharge positive column leading edge potential to be negative relative to the nearly uniform address dielectric potential of Fig. 5a.
• the sustain trigger cell positive column will always find an address dielectric potential region that has a more positive potential in the direction away from the trigger cell. This potential condition will always allow the sustain discharge trigger discharge positive column to readily extend to the state cell.
• a second negative-going pulse on the YSA electrode between times tsu4 and tsu5 acts to move ⁇ " the trigger cell dielectric potentials sufficiently negative so that during the selective address discharge at time ta, the potential of the leading edge of the positive column is sufficiently negative relative to the state cell dielectric potential that the trigger cell positive column readily moves to the state cell. It has been found that if the value of Vsp is not sufficiently positive and the value of Vsn2 is not sufficiently negative, then a reliable selective address operation possibly will not occur even though there is a strong trigger cell discharge, because the selective address trigger cell discharge positive column does not reliably move to the state cell.
• the waveforms for the selective address discharge are shown in Figs. 10, 11 and 14.
• the fundamental principle of the selective addressing operation is somewhat similar to that used in the sustain operation. Simply stated, a discharge initiated in a trigger cell causes a positive column to move to the state cell and thereby change the state of the subpixel. In this case the trigger cell intersects the YSA sustain electrode and the state cell intersects the YSB sustain electrode.
• the major difference is that the determination of the occurrence of the discharge of the trigger cell, during selective addressing, does not depend on its initial wall voltage since the properly adjusted setup waveforms will have established all of the trigger cell wall voltages at a fixed level somewhere within the allowed OFF state range. This insures that if there is no address discharge during the address period that the subpixel will be in the OFF state when the sustain period is initiated.
• the trigger discharge of the selective address operation is initiated by a coincidence of the negative going scan pulse that is sequentially applied to each YSA electrode (in the normal sequential scan method) and a positive going address pulse on the XA address electrode.
• a given subpixel When the scan pulse is applied to a given YSA electrode as a negative-going pulse, a given subpixel will have a trigger cell discharge or not depending on the voltage level of the intersecting XA address electrode. If the XA address electrode pulse is low, there will be no trigger cell discharge and the state of the subpixel will not change during the address period. Accordingly, the subpixel remains in the OFF state and does not discharge during the sustain period. If the XA address electrode voltage is high during the negative-going YSA pulse, the trigger cell of the selected subpixel discharges. The discharge causes the positive column to extend from the trigger cell to the state cell and thereby places the state cell wall - voltage to the ON state as shown in Fig. 10, 11, and 14. At the initiation of the sustain period, the ON state subpixel discharges and emits the desired amount of light during the sustain period.
• the above addressing operation requires the following conditions. First, all the setup period waveforms must set the wall voltages of all of the trigger cells and the state cells to a level somewhere within the OFF cell wall voltage range. This assures that a subpixel that is not selectively written during the address period does not begin to discharge in the ON state during the following sustain period. Second, the OFF state wall voltage of the trigger cell should be placed at a well established level in order to minimize the amplitude of the address pulses applied to the XA and the YSA electrodes. Matrix addressing requires one address driver circuit for each electrode in a matrix display and usually means thousands of address circuits in a typical television or computer monitor display. In order to reduce the cost of the display system it is desirable to reduce the voltage amplitude of the address pulses.
• the trigger cell wall voltage is properly established during the setup period, then minimum level address pulses are possible. It is most desirable to minimize the voltage on the XA address electrode circuit drivers since these are usually the most numerous. For instance in a 640x480 VGA color display, there are 1920 XA address electrode drivers and only 480 YSA scan electrode address drivers. The voltage on the XA electrodes can be minimized by properly adjusting the trigger cell - wall voltage during the setup period and the low voltage level of the negative-going YSA scan pulse.
• the polarity of the YSA scan pulses and the XA address pulses is such that, during the address period trigger cell discharge, the YSA sustain electrode is the cathode and insures that the high secondary emission surface (such as MgO) will be a cathode that makes the trigger discharge the lowest possible voltage.
• the amplitude of the negative-going YSA scan pulse determines the OFF voltage of the trigger discharge.
• the magnitude of the YSA scan pulse voltage should be equal to or greater than the XA address pulse amplitude so that half selection errors will not occur. These errors may occur if smaller magnitude YSA pulses - are used and so that subpixels with the high level of YSA (nonselected) and the high level of XA (selected) will have a voltage across the trigger cell sustain gap that is above the threshold for changing the state of the subpixel. It is desirable to make the YSA pulse voltage significantly greater than this minimum in order to have an appropriate safety factor for variations in panel manufacturing dimensions.
• the sustain electrodes of the panel front plate are drawn along the horizontal direction. Note that the sustain gap shown is considerably larger than the inter pixel gap.
• a key feature of this design is the assignment of the YSA and YSB electrodes. Note that the YSA electrodes are grouped as two adjacent electrodes and that the YSB electrodes are also grouped as two adjacent electrodes. This means that the fundamental repeating sequence of electrodes is two YSA electrodes followed by two YSB electrodes. This is considerably different from the prior art design wherein the YSA and YSB electrodes were alternated. The fundamental repeating sequence of the - prior art designs is one YSA electrode followed by one YSB electrode. In the prior art design, one subpixel had one YSA electrode and one YSB electrode.
• Fig. 3 shows four subpixels, i.e., subpixels 1, 2, 3 and 4.
• the X-dimension boundaries of these subpixels are defined by barrier ribs 54.
• the Y dimension boundaries are arbitrarily defined as the mid-points of the inter pixel gap. Note that adjacent YSB electrodes are shorted at both sides of the panel and form a continuous loop. Note also that all YSB electrodes are connected directly to YSB bus electrode 66.
• the continuous loop has the advantage that if a loop has a manufacturing defect of a single open then it will not cause a perceived open line in the panel since the broken line has a conduction path from both the left and the right end of the open point to connect to the YSB bus electrode. This double conduction path redundancy increases panel yield without any other cost penalties.
• the YSA electrodes connect to interconnect pads on the right side of Fig. 3. This allows scan address driver 70 to be connected to the panel. These YSA electrodes cannot be looped, because the addressing operation requires that adjacent YSA electrodes have differing potentials.
• the major problem of the prior art that prevents the inter pixel gap from being less than the sustain gap is resolved by the PDP design of Fig. 3 by insuring that during the sustain operation, there is no electric field across the inter pixel gap. Since for a given time during the sustain period, all of the YSA electrodes are at the same potential and all YSB ⁇ electrodes are at a same potential (that is frequently different than the YSA potential) , there is no potential difference across the inter pixel gaps.
• each such gap is bounded by either a pair of YSA electrodes or a pair of YSB electrodes.
• the sustain gaps are all bounded by one YSA electrode and one YSB electrode so that during the sustain operation, the waveforms of Fig. 6b can be applied for a successful sustain operation according to the principles of this invention.
• Fig. 6b waveforms are applied to a PDP having the front panel electrodes of Fig. 3, then during the discharge at time tdl, the cells that are defined by the YSA electrodes will be trigger cells and those defined by the YSB electrodes will be state cells.
• subpixel 1 will have its lower cell, at YSA1, as the trigger cell and subpixel 1 will have its upper cell, at YSBl, as the state cell.
• Subpixel 2 has a reverse arrangement at time tdl with its upper cell, at YSA2, being the trigger cell and its lower cell, at YSB2, being the state cell.
• Figs. 15a-15c show actual measured sustain voltages and currents for the address electrode, the trigger cell sustain electrode and the state cell sustain electrode in an array of 1920x2 subpixels driven in a 42 inch diagonal AC PDP having the dimensions of the INV design shown in Table 1 and operating according to the invention.
• Fig. 15a shows both the YSA electrode voltage which, in this case is the sustain electrode that defines the trigger cell, and the YSB electrode voltage which, in this case is the sustain electrode that defines the state cell.
• the XA voltage, which is applied to the address electrode, is not shown in Fig. 15 since it is at a constant 0 volts during the sustain operation.
• Figs. 15b and 15c show the currents flowing in the YSA, YSB and XA electrodes.
• Fig. 15c shows the same data as Fig. 15b but with an expanded time scale.
• the polarities of the three currents shown in Figs. 15b and 15c are arbitrarily chosen so that their values can - easily be compared when the discharge currents appear. Note that for the discharge current polarities shown in Figs. 15b and 15c, it is always true that the YSA current equals the sum of the YSB current and the XA current, due to the continuity of current principle and the three terminal nature of the PDP subpixel shown in Fig. 5.
• the times tO through t5 which correspond to the time labels of Fig. 5, are labeled on Figs. 15b and 15c.
• Fig. 15c shows a small discharge that is initiated in the trigger cell that peaks at time t2.
• This trigger cell discharge shows up as equal currents in both the trigger cell sustain electrode YSA and the address electrode XA for times before t2.
• the trigger cell discharge current decreases until the positive column extends to the state cell at time t3.
• the discharge current between the trigger cell sustain electrode YSA and the state cell sustain electrode YSB are equal because the highly conductive positive column connects the dielectric surfaces of these two sustain electrodes and so the address dielectric does not exert any further significant discharge current or influence on the discharge across the sustain gap.
• this current decays to the point where there is no longer any apparent discharge activity at time t5.
• Figs. 16a and 16b show the measured gas discharge light observed from a subpixel as a function of space and time during the discharge shown in Fig. 15.
• the space dimension is along a line which is parallel to the address electrode and drawn down the center of the subpixel between the trigger cell and the state cell. This line is shown as section A-A in Fig. 2c.
• This light is observed at near infrared wavelengths of approximately 828 nanometers and it comes from excited levels of the xenon atoms in the gas discharge.
• An appropriate optical filter is used to block the visible light from the phosphors which usually has substantial delay and thereby confuses the understanding of the discharge activity.
• the infrared light is commonly used to demonstrate areas where there is a significant amount of excitation of the xenon gas atoms and so it also reasonably approximates the regions where the vacuum ultraviolet light from the xenon should be generated. It is of course the vacuum ultraviolet light that is the desired output energy of the gas discharge that is used to excite the phosphors to emit the desired colored visible light from the plasma display.
• Fig. 16b shows the early discharge activity for the trigger cell. Note that the spatial light distribution is plotted for time increments of .02 microseconds and that the labeled times correspond exactly to the time axis of the voltages and currents shown in Fig. 15.
• Fig. 16a shows the later discharge activity when the positive column extends from the - trigger cell to the state cell.
• Fig.s 16a and 16b are scaled differently but that the arbitrary light intensity units are the same for both Fig.s.
• the trigger cell sustain electrode is centered at 1000 micrometers and the state cell sustain electrode is centered at 200 micrometers.
• the sustain electrodes are made of opaque chrome-copper-chrome material and so they block the light for their width of 100 micrometers. They also reflect light that is scattered back from outside of the plasma panel.
• Fig. 16b shows the first discharge activity at the trigger cell at .77 microseconds to be centered about the trigger cell sustain electrode. As time advances this trigger cell discharge activity increases in amplitude and also extends out away from the center of the trigger cell as the positive column advances toward the state cell. At .89 microseconds, which corresponds to time t3 in Fig.s 5 and 15c, the positive column has just reached the state cell and so the subsequent times shown in Fig. 16a show a substantial amount of light all along the sustain gap. At .95 microseconds, which corresponds to time t4, the light from the positive column discharge along the sustain gap has reached its peak.
• this intense light at .95 microseconds does not show the usual prior art strong peak near the cathode, which at this time is the trigger cell sustain electrode, but rather this discharge shows the intense light is all along the sustain gap which is indicative of a positive column discharge.
• Other evidence of positive column activity not shown in Fig. 16 is the narrow filament nature of the discharge. This - discharge that extends across the sustain gap appears as a narrow filament that measures with a half width of approximately 50 micrometers. This is especially narrow considering that the this discharge has the room of more than 300 micrometers in the space between the barrier ribs in which it could move. Again such a narrow filamentary nature is indicative of the positive column and not a negative glow.
• this intense filamentary discharge exhibits striations which are shown in Fig. 16a as the many undulations of the light along the sustain gap especially evident at .95 microseconds in the half of the sustain gap nearest the trigger cell.
• These undulations in Fig. 16a may be confused for noise, however they are not noise but are the actual measured light output.
• the noise level is much smaller than one arbitrary unit, as is evidenced by the noise observed on the state cell side of Fig. 16b.
• the undulations shown in Fig. 16a due to the striations have peak to peak amplitudes greater than 10 arbitrary units. Again striations are indicative of positive columns and are generally not observed in negative glows. It is clear that the discharge measured in Fig.s 15 and 16 has most of its light coming from an intense positive column and only a very small amount from the negative glow. Dielectric Capacitance Considerations
• the YSA to XA trigger cell substrate discharge that peaks at time t2 has a considerably smaller peak amplitude than the YSA to YSB sustain gap discharge that peaks at time t . It is also useful to compare the charge transferred for these two discharges. The charge can be found by time - integrating the currents shown in Fig. 15c. This is the same as taking the area under the curves.
• the YSA to YSB sustain gap discharge transferred 1.7x10-8 Coulombs in the period between time tO and time t5
• the YSA to XA trigger cell substrate gap discharge transferred 1.1x10-9 Coulombs in the period between time tO and time t3. This shows a 15 to 1 ratio of the sustain gap discharge charge to the trigger cell substrate gap charge. This high ratio is important to the successful operation of the PDP.
• the basic reason for this high charge ratio is low capacitance of the dielectric layer covering the address electrode when compared to the capacitance of the dielectric covering the sustain electrode.
• the address dielectric comprises a powdered phosphor layer that has a low density and therefore a low relative dielectric constant
• the sustain dielectric is usually a high density glass layer that has a high relative dielectric constant.
• the capacitance of the address electrode dielectric should be considerably smaller than the capacitance of the sustain electrode dielectric.
• Each of these capacitance's are proportional to the area of the electrode times the relative dielectric constant of the dielectric material. Also these capacitance's are inversely proportional to the thickness of the dielectric.
• the capacitance of the sustain dielectric is usually adjusted to achieve a given level of luminance from the main discharge. This suggests that the address dielectric capacitance should be adjusted to achieve a high charge ratio. This means that the address dielectric should be made of a thick material with a relatively low relative dielectric constant. In addition the area of the address electrode should be made small.
• Fig. 17 shows an analogy of the stability of a typical plasma display subpixel.
• the analogy is that - of a ball which rolls on a shaped surface.
• This ball can be in two stable states, as shown in Fig. 17. There is a high state where the ball can rest at the bottom of a high valley and there is a low state where the ball can rest anywhere along a long flat plane. Note that the lateral position of the high state is very clearly defined since if the ball is initially positioned within the high valley but not at the bottom of the valley then the forces of gravity will act to roll the ball to the lowest point of the high valley. Alternatively the lateral position of the ball in the low state is very poorly defined.
• the low state is a long flat plane, if the ball is initially positioned at a flat portion of the plane it will tend to remain at its initial position since the force of gravity will not push it laterally. Since there are many such initial positions the lateral position of the low state is very poorly defined. All that is certain about the equilibrium lateral position of a ball in the low state is that it is somewhere along the long flat plane.
• the analogy of the ball on a shaped surface is very similar to the stability situation of plasma display subpixels.
• the ON state of the plasma display subpixel is analogous to the ball in the high state of Fig. 17 and the OFF state of the plasma display subpixel is analogous to the ball in the low state of Fig. 17.
• the lateral position of the ball in Fig. 17 is analogous to the wall voltage of the plasma display subpixel at any given period of time between _ discharges.
• the plasma display discharge activity is analogous to the force of gravity.
• a plasma display subpixel in the OFF state does not have a well established equilibrium wall voltage value.
• the equilibrium wall voltage values of the OFF state generally do not have discharges of any significant strength, there is no significant force from discharge activity to change the wall voltage from one sustain pulse to the next. If the OFF state subpixel has a wall voltage analogous to the side walls of the long flat plane, then the sustain pulses will cause a weak discharge or discharges that will force the wall voltage back to the long flat plane where there will be no subsequent discharge activity.
• Fig. 18 shows the same sustain waveforms that were shown in Fig. 6b and the allowed values of wall voltages for both the ON and OFF states.
• the ON state wall voltage has a single equilibrium value.
• the OFF state has a range of allowable wall voltages.
• the wall voltages are defined for both the YSA and the YSB electrodes. These two wall voltages are meant to define the voltage across the substrate gaps between the respective sustain - electrodes and the address electrodes. At any given time the YSA or YSB wall voltages are assigned to either the trigger cell or the state cell of the subpixel.
• These two wall voltages can be independent and are coupled only if there is a conductive positive column that bridges across the sustain gap between the trigger cell and the state cell. In the case of the OFF state, where there is no conductive positive column, the wall voltages of the two cells are completely independent. In the case of the ON state, the conductive positive column couples the trigger cell and the state cell wall voltages so that during the period between discharges, one wall voltage is at a high level while the other wall voltage is at a low level.
• the actual value of the equilibrium ON state wall voltage is determined by the principle that after the highly conductive discharge there are a sufficient number of electrons and positive ions in the substrate gap that flow to the walls to nearly completely reduce the voltage across the substrate gap to zero as shown in Fig. 5f. If the substrate gap voltage is zero then the wall voltage is equal to the sustain voltage. Fig. 18 shows the ON state wall voltage is nearly identical to the sustain voltage after the discharges.
• the range of the OFF state wall voltages is bounded by the two wall voltages Vrl and Vr2. If the OFF state wall voltage ventures outside of the Vrl to Vr2 range, then weak discharges will serve to return the wall voltages back to the Vrl to Vr2 range just as gravity would return the low state ball of Fig. 17 to the long flat plane if the ball ventured to the left or right lateral side walls adjacent to the plane.
• Vrl is determined by the point where ⁇ a weak discharge is initiated when the sustain voltage is low. For example, in Fig. 18 this corresponds to the time between tfl and trl for YSA and to the time between tf2 and tr2 for YSB.
• the dielectric covering the sustain electrode becomes the cathode. Since this dielectric usually has a high secondary emission material such as MgO, the substrate gap voltage at which a weak discharge might be initiated is relatively small.
• Vrl voltage was measured to be approximately 200 volts above the low level of the sustain voltage.
• the value of Vr2 is determined by the point where a weak discharge is initiated when the sustain voltage is high. For example, in Fig. 18 this corresponds to the time between trl and tf3 for YSA and to the time between trO and tf2 for YSB.
• the sustain electrode When the sustain voltage is high, the sustain electrode becomes the anode and the address electrode becomes the cathode. Since the phosphor layer covering the address electrode usually has no high secondary emission material such as MgO, the substrate gap voltage at which a weak discharge might be initiated is relatively high.
• this Vr2 voltage was measured to be approximately 300 volts below the high level of the sustain voltage.
• the substrate gap breakdown voltage is less when the sustain electrode is the cathode than when the address electrode is the cathode. This is because the dielectric covering the sustain electrode has a high secondary emission material such as MgO whereas the phosphor layer covering the address electrode usually has no high secondary emission material.
• the minimum value of the OFF state wall voltage range, Vr2 allows the minimum value of the OFF state wall voltage range, Vr2, to be at a value below the lowest value of the sustain voltage as shown on Fig. 18.
• the sustain voltage used for the data of Fig.s 15 and 16 for the INV design, had a value Vs of 260 volts and the Vr2 was measured to be 300 volts, so that the OFF state wall voltage can in this case be 40 volts below the minimum level of the sustain voltage.
• the maximum value of the OFF state wall voltage range, Vrl cannot be greater or equal to the highest level of the sustain voltage since such an OFF state voltage would be coincident with the ON state wall voltage which would cause the OFF state to errantly discharge when the sustain voltage falls to the low level.
• Fig. 18 shows an allowed choice of the OFF state wall voltage for the trigger cell and the state cell that is within the bounds described in Fig. 18 and where, for certain periods, the OFF state wall voltage is equal to the ON state wall voltage.
• the OFF state wall voltage and the ON state wall voltage are shown in Fig. 19 to be the same for the YSA sustain electrode which, during this period intersects with the trigger cell.
• the OFF state wall voltage and the ON state wall voltage are the same for the YSB sustain electrode which during this period intersects with the trigger cell. It is obvious that any cell in which the OFF state and the ON state wall voltages are at the same level for long periods without significant discharge activity, cannot hold any useful information about the state of the subpixel.
• the trigger cells hold no useful information about the state of the subpixel after the discharge that they may have triggered.
• the state cells in Fig. 19, one of which intersects the YSA electrode in the period between td2 and td3 and the other of which intersects the YSB sustain electrode during the period between tdl and td2, do have differing wall voltage levels for the ON and OFF states. Therefore the state cells can hold information about the state of the subpixel and this is the reason they are named state cells.
• a given physical cell will hold the state of the subpixel information only during the half of the sustain cycle when it is the state cell.
• a state cell in the ON state will discharge when it turns into a trigger cell during the trigger cell sustain pulse.
• a state cell in the OFF state will not discharge when it turns into a trigger cell during the trigger cell sustain pulse.
• the YSA sustain voltage falls at tfl and the trigger discharge is initiated at tdl. Sometime after the completion of the discharge at time trl, the YSA sustain voltage rises. After a short period, the YSB sustain waveform falls at time tf2 and the trigger discharge is initiated at time td2.
• trl should occur before or at the same time as the fall of the YSB sustain voltage at time tf2. If the discharge at time td2 occurs before the rise of the YSA sustain voltage at trl, it is likely that the subpixel will be erroneously erased. This erasing action is shown in Fig. 7. The fall of the YSB sustain voltage at time tf2 will cause a discharge at the trigger cell at time td2 that initiates a positive column that extends into the state cell at time td2.
• the sustain voltage YSA which is applied to the state cell, is still at the low level as shown in Fig. 7 time td2, then the voltage across the substrate gap of the state cell is very near zero just before the trigger cell discharge. Then, when the trigger cell positive column extends into the state cell, there is no significant change of the wall voltage of the state cell (as shown in Fig. 7) for the YSA wall voltage at time td2.
• the YSA sustain voltage eventually rises at time trl, the voltage across the state cell substrate gap is at the same level as the OFF state level.
• the trigger cell will not fire at time td3 because the wall voltage of the trigger cell is at the OFF level, and so there is insufficient voltage across the trigger cell substrate gap to initiate a discharge. Note that once the subpixel is erased (at Fig. 7 time td2), there are no subsequent discharges during the remaining sustain pulses and the subpixel is placed in the OFF state by the erroneous erase at time td2.
• Fig. 7 shows how a single erroneous erase can occur
• Fig. 8 which are similar to the waveforms of Fig. 6b except that the waveforms are simply inverted. These Fig. 8 waveforms were found to not properly sustain the panel with the INV design dimensions shown in Table 1.
• the positive column generated in a trigger cell of the Fig. 8 waveforms does not move to discharge the state cell.
• the trigger cell intersects YSA at time tfl. If a trigger discharge were to occur, the positive column would move to the state cell that intersects sustain electrode YSB. However since YSB is at the low state at time tfl, the wall voltage of the state cell will be adjusted to equal the low value of the YSB sustain voltage which corresponds to an OFF state. In other words an erase would occur. A similar erase operation will occur at time tf2. Since any trigger cell discharge causes subpixels to be erased there is no possibility for the positive column discharge mode to exist across the sustain gap for the waveforms of Fig. 8.
• Vsmin a minimum sustain - voltage of about 170 volts
• the geometries of the invention, INV in Table 1 which utilizes the same MgO cathode material as the prior art design, has a Vsmin of about 250 volts.
• the reason for this very large Vsmin difference is the difference in the ON state sustain discharge modes.
• the ON state sustain discharge of the invention is initiated by a discharge across the substrate gap of the trigger cell, with sufficient amplitude so that the positive column extends from the trigger cell to the state cell.
• Vsmin is determined by the condition that the trigger cell discharge is just sufficiently intense to have a strong enough discharge to cause the positive column to extend to the state cell and significantly change the wall voltage of the state cell.
• the ON state sustain discharge initially occurs across the sustain gap between the two sustain electrodes and there is no significant discharge activity across the substrate gaps.
• the prior art dimensions have an approximately one-to-one ratio of the sustain gap to the substrate gap as shown by the ratio of SusG/SubG shown in Table 1.
• This allows a large electric field to be generated across the sustain gap at the beginning of the ON state sustain discharge. This large electric field is caused by the contribution of the applied sustain voltages plus the charge on the dielectric of the YSA sustain electrode plus the charge on the dielectric of the YSB sustain electrode.
• the large electric field across the sustain gap ⁇ causes the prior art ON state sustain discharge to develop along the sustain gap.
• the sustain voltages typically used in prior art geometries range between 170 volts and 200 volts
• the substrate gap breakdown voltage which is approximately 200 volts when the MgO is the cathode and approximately 300 volts when the phosphor is the cathode.
• the existence of this major distinction of the ON state sustain discharge modes between the invention described here and the prior art can easily be measured by looking at the address electrode currents for the two ON state sustain discharges. Fig.
• This - discharge does not occur in the prior art ON state sustain discharge because its sustain gap is much smaller than the sustain gap of this new invention.
• This smaller sustain gap of the prior art allows the strong ON state discharge to develop across the high electric field between the two sustain electrodes before any significant discharge between a sustain electrode and the address electrode can develop.
• the considerably larger sustain gap of the new invention makes the electric field across the sustain gap so low that an initial discharge between the two sustain electrodes cannot occur.
• the sustain voltage Vs of the invention must be increased over that of the prior art.
• the invention sustain gap is so large relative to the substrate gap that even with an increased sustain voltage Vs, the electric field across the sustain gap is too small to directly initiate a discharge across the sustain gap. Instead the electric field across the substrate gap is much larger than across the sustain gap, and the discharge across the substrate gap occurs at a much lower voltage than across the sustain gap in the new invention. This is why the trigger cell discharge across the substrate gap at time tl of Fig. 15 appears before any discharge across the sustain gap.
• the cathode of the sustain discharge is always one of the high secondary emission dielectric layers covering one of the sustain electrodes. This means that it is not important whether the sustain voltage is high or low when the ON state sustain discharge occurs since both sustain electrodes have - high secondary emission dielectrics that can serve as a low voltage cathode.
• the ON state sustain discharge occur when the sustain electrode of the trigger cell is negative so that the high secondary emission dielectric of the trigger cell sustain electrode is the cathode. If the trigger cell discharge of the invention was to occur when the sustain electrode was positive, then the low secondary emission dielectric that covers the address electrode of the trigger cell would be the cathode and an undesirable high voltage discharge could occur.
• a further difference between the prior art and this invention is the nature of the sustain pulse transition timing. Recall that for this new invention that, referring to Fig. 6b, it is important that the rise of the sustain voltage YSA at time trl occur before the beginning of the discharge at time td2 or if an appropriate safety factor is desired, then trl should occur before or at the same time as the fall of the YSB sustain voltage at time tf2. If the discharge at time td2 occurs before the rise of the YSA sustain voltage at trl, then it is likely that the subpixel will be erroneously erased as shown in Fig. 7. Or in the extreme case of the Fig. 8 waveforms the subpixels will be erased every half sustain cycle for the new invention .
• the prior art ON state sustain discharge does not have this same restriction. There is usually no restriction as to when the trl rise occurs in the prior art ON state sustain discharge. In fact most prior art systems in use today use waveforms similar to those of Fig. 8. This is because the prior art initial sustain _ discharge occurs across the sustain gap so that if the rise of YSA does not occur before the fall of YSB at tf2, there will not be sufficient voltage across the sustain gap or the substrate gap to initiate any discharge. If the trl rise of YSA occurs after the fall of YSB at tf2, the prior art ON state sustain discharge will be initiated by the trl rise of YSA and not the fall of YSB at tf2. Thus there is no opportunity for the ON state sustain discharge mode of the prior art to be erroneously erased by the phasing of the sustain pulse edges.
• the inverted waveforms of Fig. 8 will sustain a prior art design correctly at a approximately the same low sustain voltage as the waveforms of Fig. 6b.
• the invention described here works properly with the Fig. 6b waveforms but does not work with the Fig. 8 waveforms.
• the first major advantage of the invention is luminous efficiency.
• a PDP designed according to the invention has achieved a higher luminous efficiency than a similar panel designed according to the prior art. It is believed that this higher luminous efficiency is due to the use of the more efficient positive column compared to the lower efficiency negative glow. High luminous efficiency is important because it can be used to obtain brighter panels, lower power panels or longer life panels.
• Table 1 the prior art designs have used two types of electrodes: transparent and opaque. Transparent electrodes are usually made of materials such as tin oxide or indium tin oxide and are designed to allow the discharge light to easily escape through the electrode. Opaque electrodes must be made narrow so that they do not block too much discharge light.
• transparent electrodes are that a wide electrode can be used to increase the dielectric capacitance and therefore increase the brightness of the panel. If a similar wide electrode is used with opaque electrodes, most of the light, which in the prior art comes from the negative glow, is generated under the electrode and a large portion thereof is blocked.
• opaque electrode is that panel manufacturing cost is lower because transparent electrodes require a two step process of depositing a wide transparent electrode and then depositing an additional narrow opaque and highly conductive electrode on top of the transparent electrode in order to greatly reduce the resistance of the electrode to an acceptable level.
• the simple opaque electrode design only requires the one step of depositing the opaque electrode to achieve the low resistance and so it is lower cost. Because the invention generates most of its light from the positive column, light from the negative glow is not very important and so a transparent electrode is not needed to achieve high brightness.
• the data of Fig. 16 was taken from a panel that has opaque electrodes and so it is clear that the opaque electrodes do not block a very significant amount of the light. Thus the invention facilitates the use of opaque electrodes that are lower in cost than the transparent electrodes commonly used in prior art.
• Another advantage of this invention is a lower electrode capacitance than for prior art designs. - Because the sustain gap is larger in this invention, the electrode capacitance between sustain electrodes is necessarily lower.
• Fig. 3 further reduces the capacitance that the sustainer must drive. This is because in the prior art with simple alternating YSA and YSB sustain electrodes, every YSA electrode has a YSB electrode on either side of it and each of these two YSB electrodes has a capacitance associated with it. In the Fig. 3 design, a given YSA electrode has a YSA electrode on one side and a YSB electrode on the other side. The capacitance between the YSA electrode and its YSA neighbor is not important because the sustain voltage generator does not have to drive these capacitances to different potentials. Only the capacitance between the YSA electrode and its single YSB neighbor needs to be driven by the sustainer. This means that the Fig.
• the invention will have an extended life due to reduced phosphor degradation.
• Two of these degradation mechanisms are due to the sputtering from the highly energetic ions of the negative glow.
• sputtering ions can directly degrade the phosphors by bombarding them with the high energy ions.
• the phosphors can be degraded by coating them with UV opaque MgO that is sputtered from the MgO cathodes of the sustain dielectric by the high energy ions of the negative glow.
• the invention does not have these problems to the same degree as the prior art because the damaging energetic ions remain in the region of the negative glow. Such highly energetic ions are not produced by the positive column. Since most of the light from the invention comes from the positive column, the phosphor regions that are near the positive column are much more important for light emission than the phosphor regions near the negative glow. Thus, even if the invention has the same degradation rate of the phosphors near the negative glow as the prior art displays, the invention will have extended phosphor life because most of its light comes from the phosphors near the positive column that do not degrade from negative glow sputtering. _
• One seeming disadvantage of the new invention is its higher sustain voltage, when compared to prior art.
• a typical minimum sustain voltage of the prior art P design in Table 1 is 170 volts.
• the minimum sustain voltage measured on the INV design was 250 volts.
• the higher voltage sustain circuits may be more costly for the invention than for the prior art.
• a higher voltage sustainer for the new invention will cost more than the prior art sustainer.
• the invention has a higher luminous efficiency, then for the same brightness between the invention and the prior art, the power requirements of the invention will be less and a lower sustain current will be needed just due to the reduced power requirement. There will also be an additional sustain current reduction due to the use of higher sustain voltage.
• the dl/dt of the invention is less than the dl/dt of the prior art. This is due to the growth rate of the current of the invention being limited by the growth rate of the long positive column and the growth rate of the prior art being limited by the growth rate of the much shorter negative glow. Since the long positive column grows slower the dl/dt of the invention is less than that of the prior art.
• a panel designed according to the invention can have a considerably higher luminance per discharge than one designed along the lines of the prior art. This means that it is possible to make some other desirable compromises in the design.
• the brightness of AC plasma display panels is generally proportional to the sustain frequency. This means that if the same luminance is desired for both the prior art and the invention PDP, then the average sustain frequency of the invention can be much lower than that of the prior art. This has the advantage of saving critical time in the subframe waveforms shown in Fig. 10. If the average sustain frequency of the invention is lowered, but the peak sustain frequency is maintained, then the length of time needed for the Fig.
• sustain period can be reduced. This has the advantage of allowing the extra - time to be used for a longer address period or for more subfields per frame time. A longer address period is desirable if a PDP has more scan lines. This is important for higher resolution panels. More subfields per frame is important for improving the number of gray levels or increasing the image quality. The major point is that the performance of the display can be increased by reducing the average sustain frequency in this new invention.

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• 1999
  • 1999-05-12 US US09/310,446 patent/US6184848B1/en not_active Expired - Lifetime
  • 1999-08-30 WO PCT/US1999/019714 patent/WO2000017846A1/en not_active Ceased
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