EP1390940B1 - Display method for a coplanar plasma display panel using a pulse train with sufficiently high frequency to stabilise the discharges - Google Patents

Description

The invention relates to a method for addressing and controlling a panel. plasma display.

• une dalle arrière dotée d'un premier réseau d'électrodes,
• une dalle avant, parallèle à la première, dotée d'un second réseau de paires d'électrodes orthogonales aux électrodes du premier réseau, les électrodes de chaque paire ménageant entre elles des espaces de décharge positionnés aux croisements des électrodes du premier réseau et des paires d'électrodes du second réseau.

Document JP 10-171399 (HITACHI) describes a plasma panel of the coplanar type comprising:

• a rear panel with a first network of electrodes,
• a front plate, parallel to the first, provided with a second network of pairs of electrodes orthogonal to the electrodes of the first network, the electrodes of each pair providing between them discharge spaces positioned at the intersections of the electrodes of the first network and of the pairs electrodes of the second network.

• activation d'une décharge dans chacune des zones de croisement à activer, par application, au moins, d'une impulsion de tension d'adressage entre l'électrode de la dalle arrière et une électrode de la dalle avant qui se croisent dans cette zone,
• ré-activation d'une série de décharges dans cette zone par application d'une série d'impulsions de tension de maintien entre la même électrode de la dalle avant et l'électrode appariée de cette même dalle.

Addressing and controlling a plasma display panel of this type generally comprises the following steps:

• activation of a discharge in each of the crossing zones to be activated, by application, at least, of a addressing voltage pulse between the electrode of the rear panel and an electrode of the front panel which cross in this zone ,
• re-activation of a series of discharges in this zone by application of a series of holding voltage pulses between the same electrode of the front panel and the paired electrode of this same panel.

According to this method, the addressing discharge essentially extends perpendicular to the slabs, in the space, filled with discharge gas, which separates the tiles; maintenance discharges extend, on the contrary, essentially parallel to the tiles, along the front tile.

According to this conventional method, the instantaneous frequency of the pulses of maintenance is generally of the order of 100 to 300 kHz and conditions the panel brightness; maintenance is described as "positive" if both pair electrodes always have a positive or zero potential compared to addressing electrodes, "negative" otherwise, "bipolar" in the case where this potential is alternately positive and negative (the signals of holding electrodes of the same pair are then shifted by half a phase).

Addressing pulses can be grouped into groups of lines and are then also very close to each other.

For the addressing and control of a panel of this type, the document JP 10-171399 (HITACHI) proposes to use, in addition, very high pulses frequency, well above 10 MHz.

• adressage ou écriture (phase IV) lors de l'impulsion de tension d'adressage résultant de la différence entre le signal 107 appliqué à l'électrode Y_m et le signal 108 appliqué à l'électrode A,
• maintien bipolaire par application de signaux 101 générant des impulsions classiques « basse fréquence » de tension de maintien entre l'électrode Y_m et l'électrode appariée X,
• selon l'invention présentée dans ce document, pendant cette phase de maintien, du côté de celle des électrodes Y_m ou X qui sert de cathode, on applique en outre un signal dit « RF » de très haute fréquence 100 ; l'application de ce signal correspond ici à l'étape VII de maintien.

If, as indicated in FIG. 3 of this document, the first network of electrodes comprises electrodes A ₁ , A ₂ , ..., A ₆ , and if the second network comprises pairs (X, Y ₁ ), ( X, Y ₂ ), ..., (X, Y _n ), referring now to FIG. 1 of this document, the addressing and control of the coplanar plasma display panel then comprise the following steps:

• addressing or writing (phase IV) during the addressing voltage pulse resulting from the difference between the signal 107 applied to the electrode Y _m and the signal 108 applied to the electrode A,
• bipolar hold by application of signals 101 generating conventional “low frequency” pulses of hold voltage between the electrode Y _m and the paired electrode X,
• according to the invention presented in this document, during this holding phase, on the side of that of the electrodes Y _m or X which serves as a cathode, a signal called "RF" of very high frequency 100 is also applied; the application of this signal here corresponds to step VII of maintenance.

• qu'il convient de commencer à appliquer le signal RF 100 avant que la décharge de maintien classique correspondant à l'impulsion 101 n'ait conduit à l'inversion complète des charges sur la couche diélectrique qui recouvre les électrodes ; ainsi, il convient que le temps t_d qui sépare le front d'impulsion 101 du premier front des signaux RF soit largement inférieur au temps cumulé de la décharge de maintien et de l'inversion complète des charges ;
• qu'il convient que la demi-période t_w du signal RF 100 soit suffisamment courte pour que les charges ioniques n'aient pas le temps de rejoindre la cathode au cours d'une demi-période ; cette condition conduit généralement à des fréquences très élevées difficiles à mettre en oeuvre.

According to this document, the purpose of applying a very high frequency signal is, once the charges have formed between the electrodes after a conventional sustaining discharge, to prevent the ionic charges from reaching the cathode , and to obtain the vibration of the ionic charges between the electrodes as shown diagrammatically in FIG. 4-VII of this document; with reference to figure 5, this document teaches:

• that it is necessary to start applying the RF signal 100 before the conventional sustaining discharge corresponding to the pulse 101 has led to the complete reversal of the charges on the dielectric layer which covers the electrodes; thus, the time t _d which separates the pulse edge 101 from the first edge of the RF signals should be much less than the cumulative time of the sustaining discharge and of the complete charge reversal;
• that the half-period t _w of the RF signal 100 should be short enough so that the ionic charges do not have time to reach the cathode during a half-period; this condition generally leads to very high frequencies which are difficult to implement.

According to this document, under these conditions, a discharge is obtained stabilized by the RF signal which emits light with a light output much higher than that obtained with more conventional discharges low frequency.

For example, according to this document, when the distance between two holding electrodes at the place of discharge is of the order of 100 μm, when the discharge gas is a Ne-Xe mixture at a pressure of 0.4 10 ⁵ Pa, the above conditions are as follows: t _d <1 µs approximately; t _w <0.1 µs approximately, which corresponds to frequencies above 20 MHz.

• une première décharge, générée par une impulsion classique de maintien, destinée à créer des charges ioniques dans la zone activée,
• une décharge stabilisée, générée par un train d'impulsions à haute fréquence adaptée pour stabiliser les charges ioniques crées dans la zone activée.

According to this document, in the method for controlling the plasma display panel, each holding step comprises a succession of conventional holding discharges and stabilized discharges:

• a first discharge, generated by a conventional holding pulse, intended to create ionic charges in the activated zone,
• a stabilized discharge, generated by a train of high frequency pulses adapted to stabilize the ionic charges created in the activated zone.

Thus, the sustaining discharge is used to activate or "turn on" the discharge stabilized.

The use of high frequencies poses electronic problems important which limit the use of this process for piloting panels plasma display; to obtain stabilized discharges at lower frequency, the distance between the X electrodes and the Y electrodes of each pair, but the voltage required to obtain the discharge conventional support then increases, which has other drawbacks.

• pour appliquer le signal « basse fréquence » de maintien classique qui sert à l'amorçage d'une décharge avant application du signal « haute fréquence », on a intérêt à utiliser des électrodes suffisamment rapprochées pour limiter la tension nécessaire à l'amorçage,
• pour appliquer le signal « haute fréquence », on a intérêt à utiliser des électrodes suffisamment éloignées de manière à empêcher les ions d'atteindre l'une des électrodes pendant la durée d'une alternance et obtenir ainsi l'effet de stabilisation recherché pour une fréquence qui ne soit pas trop élevée.

More precisely :

• to apply the conventional “low frequency” holding signal which is used to start a discharge before application of the “high frequency” signal, it is advantageous to use electrodes which are close enough to limit the voltage necessary for starting,
• in order to apply the “high frequency” signal, it is advantageous to use electrodes which are sufficiently distant so as to prevent the ions from reaching one of the electrodes during the duration of an alternation and thus obtain the stabilization effect sought for a frequency that is not too high.

Document US 5233272, in particular FIG. 2, describes a panel with plasma resembling a coplanar panel, comprising, for each discharge space, an anode 40 and an auxiliary electrode 50 which are coplanar and carried by the same slab, and a cathode 60 carried by the other slab ; unlike conventional coplanar panels which are effect durable memory, no dielectric layer separates the electrodes, so that it only produces a short-lived memory pseudo-effect, ie a memory effect of conditioning by the previous discharge or by an adjacent source of primary particles; in piloting such panel, according to this document, is applied between the anode and the cathode pulses of sufficient amplitude to obtain a succession of discharges; during the application of these pulses comparable to pulses of holding, pulses are applied between the coplanar electrodes 40 and 50 higher frequency to disrupt the movements of ions and make them diffuse between the electrodes (column 2, lines 20-21 and 40-41; column 3, lines 38-39 and 57-58); this disturbance only leads to the lengthening of the path of the ions between the electrodes (column 3, line 66 to column 4, line 4), and no to the stabilization of these ions as in document JP 10-171399; the application of higher frequency pulses here aims to improve the short-term memory effect and lower the required pulse amplitude to obtain landfills (column 5); according to this document (in particular “Table” column 4) and the figures, to obtain the desired effect, it is therefore important that the distance between the electrodes between which the signal is applied higher frequency (here the anode and the auxiliary electrode) is lower than the distance between the electrodes between which the signal is applied classic maintenance type; this arrangement is opposite to that which comes to be described concerning the document JP 10-171399 when one wishes to obtain stabilization of discharges in a memory effect plasma panel sustainable.

Documents JP 11-273576, JP2000-047631, JP2000-047632 and JP2000-173482 describe structures of plasma panels specially adapted for obtaining stabilized discharges using trains high frequency pulses; but the use of panel structures specific issues poses other cost issues.

The invention aims to avoid the aforementioned drawbacks, by proposing to use a classic coplanar panel in a different way than proposed in document JP 10-171399, so as to be able to stabilize the discharges at lower frequencies, without having to increase the voltage required for ignition of stabilized discharges.

• une première dalle dotée au moins d'un premier réseau d'électrodes,
• une deuxième dalle, parallèle à la première, dotée au moins d'un second réseau de paires d'électrodes dont la direction générale est approximativement orthogonale à celle des électrodes du premier réseau, les électrodes de chaque paire ménageant entre elles des zones de décharge positionnées aux croisements des électrodes du premier réseau et des paires d'électrodes du second réseau,

   ledit procédé comprenant :

• l'application d'au moins une série d'impulsions de tension de maintien de manière à générer des décharges de maintien dans chacune des zones de croisement dans lesquelles on souhaite maintenir une décharge, et
• après au moins une desdites impulsions générant une décharge de maintien, l'application, entre les deux électrodes d'une paire croisant ladite zone, d'un train d'impulsions à une fréquence suffisamment élevée pour obtenir la stabilisation de ladite décharge,

   caractérisé en ce que :

• les dites impulsions de tension de maintien sont appliquées entre l'une des électrodes de ladite paire et l'électrode de la première dalle croisant ladite zone,
• au niveau de chaque zone de décharge du panneau, la distance séparant les électrodes d'une paire est supérieure à la distance séparant l'électrode de la première dalle croisant ladite zone et l'électrode de ladite paire entre lesquelles on applique les dites impulsions de tension de maintien.

To this end, the subject of the invention is a method for controlling a plasma display panel of the coplanar type comprising:

• a first slab provided with at least a first network of electrodes,
• a second slab, parallel to the first, provided with at least a second network of pairs of electrodes whose general direction is approximately orthogonal to that of the electrodes of the first network, the electrodes of each pair providing between them discharge zones positioned at the intersections of the electrodes of the first network and the pairs of electrodes of the second network,

said method comprising:

• the application of at least one series of sustain voltage pulses so as to generate sustain discharges in each of the crossing zones in which it is desired to maintain a discharge, and
• after at least one of said pulses generating a sustaining discharge, the application, between the two electrodes of a pair crossing said zone, of a train of pulses at a sufficiently high frequency to obtain the stabilization of said discharge,

characterized in that:

• said holding voltage pulses are applied between one of the electrodes of said pair and the electrode of the first plate crossing said zone,
• at each discharge zone of the panel, the distance separating the electrodes from a pair is greater than the distance separating the electrode from the first slab crossing said zone and the electrode from said pair between which the said pulses are applied holding voltage.

Generally, the first slab is a "back" slab and the second slab is a "front" slab oriented towards the observer of the images to visualize; the electrode crossing zones form the cells of panel discharge, which can be controlled, activated or not, independently of each other, depending on the voltage pulses applied to the electrodes.

• les impulsions de maintien sont appliquées entre des électrodes de la première dalle et des électrodes de la deuxième dalle ; de préférence, on choisit d'espacer les dalles de manière à pouvoir utiliser des tensions de maintien et des composants électroniques classiques ; l'espacement est alors généralement compris entre 100 et 150 µm ; si chaque dalle est dotée d'une couche diélectrique d'une épaisseur de 40 µm, la distance séparant le réseau d'électrodes de la première dalle du réseau de paires d'électrodes de la deuxième dalle est alors comprise entre 180 et 230 µm ; une distance aussi faible que 90 µm pourrait, à la limite, être envisagée entre ces électrodes ;
• la distance séparant les électrodes d'une paire de la deuxième dalle est supérieure à la distance séparant l'électrode de la première dalle et l'électrode de la deuxième dalle entre lesquelles on applique les impulsions de maintien ; ainsi, le gap entre les électrodes coplanaires, ou distance séparant les électrodes appariées, est beaucoup plus élevé que dans l'art antérieur de manière à pouvoir stabiliser les décharges à l'aide de trains d'impulsions de plus basse fréquence que dans l'art antérieur ; un gap supérieur à 500 µm peut même être envisagé.

As the holding voltage pulses are not applied between the same electrodes as the discharge stabilization pulse trains, it is possible to increase the distance between the stabilization electrodes of the front panel without affecting the voltage necessary for maintaining; thus, a conventional coplanar structure is used, but, unlike the prior art:

• the holding pulses are applied between electrodes of the first slab and electrodes of the second slab; preferably, the tiles are chosen to be spaced so as to be able to use holding voltages and conventional electronic components; the spacing is then generally between 100 and 150 μm; if each slab is provided with a dielectric layer with a thickness of 40 μm, the distance separating the array of electrodes of the first slab from the array of pairs of electrodes of the second slab is then between 180 and 230 μm; a distance as small as 90 µm could, ultimately, be considered between these electrodes;
• the distance separating the electrodes of a pair of the second plate is greater than the distance separating the electrode of the first plate and the electrode of the second plate between which the holding pulses are applied; thus, the gap between the coplanar electrodes, or distance separating the paired electrodes, is much higher than in the prior art so as to be able to stabilize the discharges using trains of pulses of lower frequency than in the prior art; a gap greater than 500 µm can even be considered.

• le deuxième réseau de paires d'électrodes est recouvert d'une couche diélectrique ; on obtient ainsi l'effet mémoire classique des panneaux coplanaires.
• ladite première dalle est recouverte d'une couche mince de protection et d'émission d'électrons secondaires et dotée de couches de luminophores positionnées pour absorber le rayonnement ultraviolet provenant des décharges et pour émettre un rayonnement visible au travers de la dalle orientée vers l'avant dudit panneau et ces couches présentent des épargnes au niveau des zones de croisement des électrodes de manière à découvrir au niveau de cette épargne la surface de ladite couche mince sous-jacente de protection. Dans le cas où la première dalle est la dalle arrière, au niveau de chaque zone de croisement ou de chaque cellule, la dalle arrière et, le cas échéant, les parois des barrières qui séparent ces zones, sont dotés de luminophores de différentes couleur d'émission, rouge, vert et bleu ; contrairement à l'art antérieur, les décharges de maintien sont amorcées entre la dalle avant et la dalle arrière ; pour faciliter l'amorçage au niveau de la dalle arrière, il convient que, au pied des décharges, la surface de la dalle soit en matériau susceptible d'émettre des électrons secondaires sous impact ionique, comme la magnésie (MgO) ; à cet effet, on enlève dans ces zones la couche de luminophores de manière à laisser apparaítre la couche mince sous-jacente à base de MgO.
• avant l'application de séries d'impulsions de tension de maintien, l'application d'une impulsion de tension d'adressage entre l'une des électrodes de ladite paire et ladite électrode de la première dalle de manière à produire une décharge d'adressage dans ladite zone. On peut donc utiliser des méthodes d'adressage classiques de l'art antérieur, qu'il s'agisse de méthodes où toutes les lignes du panneau sont adressées avant la première impulsion de maintien (méthodes dites « ADS » ou « ADM »), ou d'autres méthodes d'adressage bien connues de l'homme du métier.
• de préférence, la distance séparant l'électrode de la première dalle et l'électrode de la deuxième dalle entre lesquelles on applique les impulsions de maintien est inférieure à 250 µm ; en outre, la distance séparant les électrodes d'une même paire au niveau des croisements est alors de préférence supérieure ou égale à 250 µm ; de préférence, la fréquence de trains d'impulsions de stabilisation de la décharge est inférieure à 150 MHz, voire même inférieure ou égale à 60 MHz.
• l'application dudit train d'impulsions est réalisée après chacune des impulsions de maintien de ladite série, ou, au contraire, est maintenue en continu pendant le déroulement de ladite série d'impulsions de maintien ; cette dernière disposition permet avantageusement de stabiliser le maximum d'ions générés par les décharges de maintien, ce qui permet d'augmenter encore le rendement lumineux du panneau ; elle permet également de limiter les pertes électriques par commutation du circuit de puissance de haute fréquence.

The invention may also have one or more of the following characteristics:

• the second network of pairs of electrodes is covered with a dielectric layer; the classic memory effect of coplanar panels is thus obtained.
• said first slab is covered with a thin layer of protection and secondary electron emission and provided with phosphor layers positioned to absorb ultraviolet radiation from the discharges and to emit visible radiation through the slab oriented towards the front of said panel and these layers have spares at the crossover areas of the electrodes so as to discover at the level of this spares the surface of said underlying thin protective layer. In the case where the first panel is the rear panel, at each crossing zone or each cell, the rear panel and, where appropriate, the walls of the barriers which separate these zones, are provided with phosphors of different colors d 'emission, red, green and blue; unlike the prior art, the maintenance discharges are initiated between the front panel and the rear panel; to facilitate priming at the level of the rear slab, the surface of the slab should be made of a material capable of emitting secondary electrons under ionic impact, such as magnesia (MgO), at the foot of the discharges; for this purpose, we remove in these areas the phosphor layer so as to reveal the underlying thin layer based on MgO.
• before the application of series of holding voltage pulses, the application of an addressing voltage pulse between one of the electrodes of said pair and said electrode of the first plate so as to produce a discharge of addressing in said area. It is therefore possible to use conventional addressing methods of the prior art, whether these are methods where all the lines of the panel are addressed before the first holding pulse (methods known as “ADS” or “ADM”), or other addressing methods well known to those skilled in the art.
• preferably, the distance separating the electrode from the first panel and the electrode from the second panel between which the holding pulses are applied is less than 250 μm; in addition, the distance separating the electrodes of the same pair at the crossings is then preferably greater than or equal to 250 μm; preferably, the frequency of pulse stabilization pulse trains is less than 150 MHz, or even less than or equal to 60 MHz.
• the application of said train of pulses is carried out after each of the holding pulses of said series, or, on the contrary, is continuously maintained during the course of said series of holding pulses; this latter arrangement advantageously makes it possible to stabilize the maximum of ions generated by the sustaining discharges, which makes it possible to further increase the light output of the panel; it also makes it possible to limit the electrical losses by switching the high frequency power circuit.

• une première dalle dotée au moins d'un premier réseau d'électrodes,
• une deuxième dalle, parallèle à la première, dotée au moins d'un second réseau de paires d'électrodes dont la direction générale est approximativement orthogonale à celle des électrodes du premier réseau, les électrodes de chaque paire ménageant entre elles des zones de décharge positionnées aux croisements des électrodes du premier réseau et des paires d'électrodes du second réseau, caractérisé en ce que, au niveau de chaque zone de décharge, la distance séparant les électrodes d'une paire est supérieure à la distance séparant l'électrode de la première dalle croisant ladite zone et l'une quelconque des électrodes de ladite paire (X, Y).

The subject of the invention is also a plasma display panel of the coplanar type intended for applying the piloting method according to the invention, comprising:

• a first slab provided with at least a first network of electrodes,
• a second slab, parallel to the first, provided with at least a second network of pairs of electrodes whose general direction is approximately orthogonal to that of the electrodes of the first network, the electrodes of each pair providing between them discharge zones positioned at the intersections of the electrodes of the first network and the pairs of electrodes of the second network, characterized in that, at each discharge zone, the distance separating the electrodes from a pair is greater than the distance separating the electrode from the first slab crossing said zone and any one of the electrodes of said pair (X, Y).

It is between one of these electrodes of the pair and this electrode of the first panel that the process sustain voltage pulses are applied according to the invention.

• la distance entre le premier réseau d'électrodes et le deuxième réseau de paires d'électrodes est inférieure à 250 µm et la distance séparant les électrodes d'une même paire au niveau des croisements est supérieure ou égale à 250 µm ;
• le deuxième réseau de paires d'électrodes est recouvert d'une couche diélectrique, elle-même généralement recouverte d'une couche de protection ;
• ladite première dalle est recouverte d'une couche mince de protection et d'émission d'électrons secondaires et dotée de couches de luminophores positionnées pour absorber le rayonnement ultraviolet provenant des décharges et pour émettre un rayonnement visible au travers de la dalle orientée vers l'avant dudit panneau et ces couches présentent des épargnes au niveau des zones de croisement des électrodes de manière à découvrir au niveau de cette épargne la surface de ladite couche mince sous-jacente de protection.

The invention may also have one or more of the following characteristics:

• the distance between the first array of electrodes and the second array of pairs of electrodes is less than 250 μm and the distance separating the electrodes from the same pair at the crossings is greater than or equal to 250 μm;
• the second network of pairs of electrodes is covered with a dielectric layer, itself generally covered with a protective layer;
• said first slab is covered with a thin layer of protection and secondary electron emission and provided with phosphor layers positioned to absorb ultraviolet radiation from the discharges and to emit visible radiation through the slab oriented towards the front of said panel and these layers have spares at the crossover areas of the electrodes so as to discover at the level of this spares the surface of said underlying thin protective layer.

• les figures 1 et 2 représentent schématiquement un mode de réalisation d'un ensemble de trois zones adjacentes de décharge d'un panneau coplanaire de visualisation qui peut être avantageusement utilisé pour la mise en oeuvre de l'invention, la figure 1 en vue de dessus, la figure 2 en coupe transversale,
• la figure 3 représente une vue en coupe longitudinale d'une zone de décharge de l'ensemble représenté aux figures 1 et 2, illustrant l'étalement des décharges (flèches) selon un mode de réalisation de l'invention,
• la figure 4 représente, selon un mode de réalisation de l'invention, un chronogramme des tensions appliquées aux différentes électrodes du panneau représenté aux figures 1, 2 et 3.

The invention will be better understood on reading the description which follows, given by way of nonlimiting example, and with reference to the appended figures in which:

• Figures 1 and 2 schematically show an embodiment of a set of three adjacent discharge areas of a coplanar display panel which can be advantageously used for the implementation of the invention, Figure 1 in top view , Figure 2 in cross section,
• FIG. 3 represents a view in longitudinal section of a discharge zone of the assembly represented in FIGS. 1 and 2, illustrating the spreading of the discharges (arrows) according to an embodiment of the invention,
• FIG. 4 represents, according to an embodiment of the invention, a chronogram of the voltages applied to the different electrodes of the panel shown in FIGS. 1, 2 and 3.

• une dalle arrière (non représentée) dotée d'un réseau d'électrodes A, revêtu d'une couche diélectrique 1, dotée d'un réseau de barrières 21, 22 ;
• une dalle avant (non représentée) dotée d'un réseau de paires d'électrodes X, Y, revêtu d'une couche diélectrique 3 ;

According to a preferred embodiment, with reference to FIGS. 1 and 2, the coplanar panel used for the implementation of the invention comprises:

• a rear panel (not shown) with an array of electrodes A, coated with a dielectric layer 1, with an array of barriers 21, 22;
• a front panel (not shown) provided with an array of pairs of electrodes X, Y, coated with a dielectric layer 3;

The general direction of the X, Y electrodes of the front panel is orthogonal to that of the electrodes A of the rear panel.

The dielectric layers 1, 3 are themselves coated with a very thin secondary electronic emission and protection layer, here based on MgO (not shown).

The network of barriers here is formed by walls 21 extending in parallel to the electrodes A of the rear panel and of walls 22 extending parallel to the electrodes X, Y of the front panel, so as to delimit zones of 4R, 4G, 4B discharges at the intersections of electrodes A on the one hand, and paired electrodes X and Y on the other hand.

The tops of the rear slab barriers support the front slab.

The barrier walls and the dielectric layer 1 of the rear panel are covered with layers of phosphors 5R, 5G, 5B, capable of emitting respectively in red, green and blue, under the excitement of ultraviolet radiation from localized landfills respectively in zones 4R, 4G, 4B; the set of three adjacent discharge areas represented in FIGS. 1 and 2 therefore corresponds to an image element or pixel of the image display panel for implementing the invention.

The electrodes A of the rear panel include a conductive bus 61 extending under the barriers over the entire height of the panel, which is provided, at level of each discharge zone, of a projecting branch 62; each bypass 62 of a given area 4R, 4G or 4B is placed next to the electrode X of the pair X, Y which crosses said zone, and extends towards the middle of this zone ; opposite the free end of each lead 62 of the electrode X, the dielectric layer 1 is devoid of phosphors, so that form a savings 7 in the layers of phosphors 5R, 5G, 5B, to discover at the level of this savings the magnesia-based surface (MgO) of the thin layer of protection and secondary electronic emission, and thus making the magnesia of this layer accessible to the discharge so that it can play the role of secondary electronic emission favorable to a decrease in ignition voltage; at the location of these savings 7, the surface of the protective layer based on MgO is therefore directly in contact with discharge zones 4R, 4G, 4B; finally, the panel has an electrode A by column of picture elements.

The paired electrodes X, Y extend over the entire width of the panel; the panel has one pair X, Y per line of picture elements; according to one variant, an electrode X can be common to two lines adjacent picture elements, as described in document US 5162701 (NEC).

Finally, according to an important characteristic of the invention, the distance between the pairs of electrodes X, Y at each picture element is greater than the distance between the electrode array A of the rear panel and that of pairs of electrodes X, Y of the front panel, that is to say greater than the sum of the distance between the slabs and the thickness of the applied layers on these networks; details are given below.

For the production of the coplanar panel which has just been described, we use conventional and known methods which will not be described here.

• d'abord, au niveau de chaque zone de décharge à activer de la ligne, application d'une impulsion de tension d'adressage entre l'électrode X de la ligne concernée et l'électrode A croisant cette zone, de manière à produire une décharge d'adressage D_A (non représentée) dans cette zone ; cette impulsion de tension est obtenue en appliquant simultanément les signaux S_AA et S_AX respectivement aux électrodes A et X ;
• ensuite et selon l'invention, toujours au niveau de cette zone, application de séries d'impulsions de tension de maintien entre la même électrode X de la ligne concernée et la même électrode A croisant cette zone, de manière à produire des décharges D_H de maintien (représentée Fig.3) dans cette zone ; ces impulsions de tension sont obtenues en appliquant alternativement les signaux positifs S_HX et S_HA respectivement aux électrodes A et X ; dans cette configuration, les électrodes A et X servent alternativement de cathode et d'anode, et le maintien est dit « bipolaire » ; d'autres configurations de maintien connues de l'art antérieur sont envisageables, comme le maintien « positif » tel que décrit dans le document EP 855692 (NEC), ou le maintien « négatif » ;
• enfin, parallèlement aux impulsions de maintien, application, entre l'électrode X et l'électrode appariée Y de la ligne concernée, d'au moins un train d'impulsions à une fréquence suffisamment élevée pour obtenir le transfert de la décharge de maintien entre ces électrodes et pour former une décharge stabilisée D_S; ce train d'impulsions est obtenu ici en appliquant un signal radiofréquence T_SY à l'électrode Y ; comme dans le document JP 10-171399, l'intervalle de temps qui s'écoule entre l'application d'une impulsion de maintien, S_HX ou S_HA, et le début de l'application du train d'impulsions T_SY, doit être inférieur au délai nécessaire à l'inversion des charges électriques résultant de cette décharge de maintien ; de préférence, contrairement au procédé décrit dans le document JP 10-171399 où les trains d'impulsions haute fréquence sont interrompus avant chaque impulsion de maintien, on applique ici le train d'impulsions haute fréquence sans interruption, jusqu'à la fin de la période de maintien relative au sous-balayage concerné ; cette disposition permet de stabiliser le maximum d'ions générés par les décharges de maintien, d'améliorer encore le rendement lumineux du panneau, et d'améliorer aussi le rendement électrique car on limite ainsi le nombre de commutations haute-fréquence consommatrices d'énergie.

To implement this coplanar panel in accordance with the invention, the electrodes are connected to a voltage supply system for the column electrodes A of the first network and the paired electrodes X, Y of the second network; a supply system of this type is known in itself and will not be described here; in a conventional manner, using this system, images are displayed on the panel, by scanning this panel line by line, or group of lines by group of lines; in a conventional manner, each scan is itself subdivided into several sub-scans, which make it possible to obtain the desired number of gray levels; with reference to FIGS. 3 and 4, each underscan comprises at least the following steps:

• first, at each discharge zone to be activated on the line, application of an addressing voltage pulse between electrode X of the line concerned and electrode A crossing this zone, so as to produce a address discharge D _A (not shown) in this area; this voltage pulse is obtained by simultaneously applying the signals S _AA and S _AX respectively to the electrodes A and X;
• then and according to the invention, still at this zone, application of series of holding voltage pulses between the same electrode X of the line concerned and the same electrode A crossing this zone, so as to produce discharges D _H holding (shown in Fig.3) in this area; these voltage pulses are obtained by alternately applying the positive signals S _HX and S _HA respectively to the electrodes A and X; in this configuration, the electrodes A and X serve alternately as cathode and anode, and the maintenance is said to be “bipolar”; other hold configurations known from the prior art can be envisaged, such as “positive” hold as described in document EP 855692 (NEC), or “negative” hold;
• finally, in parallel with the holding pulses, application, between the electrode X and the paired electrode Y of the line concerned, of at least one train of pulses at a frequency high enough to obtain the transfer of the sustaining discharge between these electrodes and to form a stabilized discharge D _S ; this train of pulses is obtained here by applying a radio frequency signal T _SY to the electrode Y; as in document JP 10-171399, the time interval which elapses between the application of a holding pulse, S _HX or S _HA , and the start of the application of the train of pulses T _SY , must be less than the time required to reverse the electrical charges resulting from this sustaining discharge; preferably, unlike the process described in document JP 10-171399 where the high frequency pulse trains are interrupted before each holding pulse, the high frequency pulse train is applied here without interruption, until the end of the holding period relative to the subscan concerned; this arrangement makes it possible to stabilize the maximum of ions generated by the sustaining discharges, to further improve the light efficiency of the panel, and also to improve the electrical efficiency since this thus limits the number of high-frequency switching operations consuming energy. .

The embodiment of the invention which has just been described results in a succession of discharges D _A , then the series D _H , D _S , as shown in the last timing diagram of FIG. 4; it can therefore be seen that the holding discharges D _A serve to ignite or reinforce the stabilized discharges D _S.

Because the savings 7 release a protective layer surface to MgO base directly in contact with the discharge zones, the voltage of maintenance necessary to obtain a discharge retains a value classic; moreover, the presence of these savings makes it possible to limit damage to the phosphor layers.

Through the use of high frequency pulses and stabilization of the resulting discharges, a very significant improvement in the light output of the panel.

• une distance suffisamment faible entre les électrodes X et A ; pour pouvoir utiliser des valeurs classiques de tension de maintien compatibles avec les composants électroniques usuels des panneaux à plasma, cette distance est généralement comprise entre 180 et 230 µm ; des valeurs plus faibles peuvent être envisagées ;
• une distance suffisamment élevée entre les électrodes X et Y pour pouvoir utiliser des fréquences plus basses pour stabiliser les décharges ; cette distance est de préférence supérieure ou égale à 250 µm ; une distance comprise entre 500 µm et 1000 µm est également envisageable pour abaisser encore les fréquences de stabilisation des décharges ; une valeur élevée du « gap » entre les électrodes coplanaires permet avantageusement d'éviter l'utilisation de matériaux conducteurs transparents pour ces électrodes, car un tel gap offre une ouverture optique suffisante au travers de la dalle avant ; on aboutit ainsi à des électrodes coplanaires étroites et opaques, donc économiques, telles que représentées à la figure 1.

As, according to the invention, the sustaining discharges D _H and the stabilized discharges D _S do not extend between the same electrodes (X and A for the first, X and Y for the second), it is possible to choose independently:

• a sufficiently small distance between the electrodes X and A; in order to be able to use conventional holding voltage values compatible with the usual electronic components of plasma panels, this distance is generally between 180 and 230 μm; lower values can be considered;
• a sufficiently large distance between the electrodes X and Y to be able to use lower frequencies to stabilize the discharges; this distance is preferably greater than or equal to 250 μm; a distance of between 500 μm and 1000 μm is also conceivable in order to further lower the stabilization frequencies of the discharges; a high value of the “gap” between the coplanar electrodes advantageously makes it possible to avoid the use of transparent conductive materials for these electrodes, since such a gap offers sufficient optical opening through the front panel; this results in narrow and opaque coplanar electrodes, therefore economical, as shown in FIG. 1.

With a gap between 500 µm and 1000 µm between the electrodes coplanar X and Y, using a discharge gas of composition and conventional pressure, we generally manage to stabilize discharges by below 100 MHz, especially between 60 MHz and 30 MHz.

Preferably, the frequency of the holding pulses S _HX , S _HA is generally between 1 kHz and 50 kHz.

Thus, thanks to the invention, it is possible to use panels coplanar to obtain stabilized plasma discharges while using conventional holding voltages and stabilization frequencies relatively low with simple and inexpensive adaptations, as the widening of the gap between the coplanar electrodes.

Other types of coplanar panel than those which have been described can be used to implement the invention, such as panels including more electrode arrays, panels where the line electrodes are common to two adjacent lines of areas of landfills, panels where the landfill areas are arranged in staggered as in document US 5825128 (FUJI), panels where the pairs of coplanar electrodes are located on the rear side as described in document EP 945890 (THOMSON).

Other addressing modes than that which has been described can be used to implement the invention, in particular those which envisage a stage prior activation (or "priming" in English) and / or deletion.

Claims (13)

1. A method of driving a coplanar-type plasma display panel comprising:

   a first plate provided at least with a first array of electrodes (A),

   a second plate, parallel to the first, provided at least with a second array of pairs of electrodes (X, Y), the overall direction of which is approximately orthogonal to that of the electrodes (A) of the first array, the electrodes of each pair (X, Y) leaving between them discharge regions (4R, 4G, 4B) positioned at the intersections of the electrodes (A) of the first array and of the pairs of electrodes (X, Y) of the second array,

   said method comprising

   the application of at least one series of sustain voltage pulses so as to generate sustain discharges (D_H) in each of the intersection regions (4R, 4G, 4B) in which it is desired to sustain a discharge, and

   after at least one of said pulses generating a sustain discharge, the application, between the two electrodes of a pair crossing said region, of a pulse train (T_SY) with a frequency high enough to stabilize said discharge,

   characterized in that:

   said sustain voltage pulses (S_HA, S_HX) are applied between one (X) of the electrodes of said pair and the electrode (A) of the first plate crossing said region ;

   in each discharge region of the panel, the distance separating the electrodes of a pair (X,Y) is greater than the distance separating the electrode (A) of the first plate crossing said region and the electrode (X) of said pair between which said sustain voltage pulses (S_HA,S_HX) are applied.
2. The method as claimed in claim 1, characterized in that the second array of electrodes (X, Y) is covered with a dielectric layer (3)
3. The method as claimed in claim 2, characterized in that, since said first plate is covered with a thin protective and secondary-electron-emitting layer and provided with phosphor layers (5R, 5G, 5B) that are positioned to absorb the ultraviolet radiation coming from the discharges and to emit visible radiation through the plate facing the front of said panel and these layers (5R, 5G, 5B) have a break (7) in each region of intersection of the electrodes (4R, 4G, 4B) so as to expose, in this break (7), the surface of said thin subjacent protective layer.
4. The method as claimed in any one of the preceding claims, characterized in that it also comprises, before the application of series of sustain voltage pulses, the application of an address voltage pulse (S_AA, S_AX) between one (X) of the electrodes of said pair and said electrode (A) of the first plate so as to produce an address discharge (D_A) in said region.
5. The method as claimed in any one of the preceding claims, characterized in that :

   the distance separating the electrode (A) of the first plate from the electrode (X) of the second plate between which the sustain pulses are applied is less than 250 µm;

   the distance separating the electrodes (X,Y) of the same pair at said intersections (4R, 4G, 4B) is greater than or equal to 250 µm
6. The method as claimed in Claim 5, characterized in that said frequency of discharge-stabilizing pulse trains (T_SY) is less than 150 MHz.
7. The method as claimed in Claim 6, characterized in that said frequency of discharge-stabilizing pulse trains (T_SY) is less than or equal to 60 MHz.
8. The method as claimed in any one of Claims 1 to 7, characterized in that said pulse train (T_SY) is applied after each of the sustain pulses (S_HX, S_HA) of said series.
9. The method as claimed in any one of Claims 1 to 7, characterized in that said pulse train (T_SY) continues to be applied throughout the application of said series of sustain pulses.
10. A coplanar-type plasma display panel that can be used to implement the drive method as claimed in any one of the preceding claims, comprising:

    a first plate provided at least with a first array of electrodes (A);

    a second plate, parallel to the first, provided at least with a second array of pairs of electrodes (X, Y), the general direction of which is approximately orthogonal to that of the electrodes (A) of the first array, the electrodes of each pair (X, Y) making between them discharge regions (4R, 4G, 4B) positioned at the intersections of the electrodes (A) of the first array with the pairs of electrodes (X, Y) of the second array;

       characterized in that, in each discharge region, the distance separating the electrodes of a pair (X, Y) is greater than the distance separating the electrode (A) of the first plate intersecting said region from any one of the electrodes of said pair (X, Y).
11. The panel as claimed in claim 10, characterized in that the distance between said first array of electrodes (A) and said second array of pairs of electrodes (X, Y) is less than 250 µm and in that the distance separating the electrodes (X, Y) of the same pair at said intersections (4R, 4G, 4B) is greater than or equal to 250 µm.
12. The panel as claimed in claim 11, characterized in that the second array of electrodes (X, Y) is covered with a dielectric layer (3).
13. The panel as claimed in claim 12, characterized in that, since said first plate is covered with a thin protective and secondary-electron-emitting layer and provided with phosphor layers (5R, 5G, 5B) that are positioned to absorb the ultraviolet radiation coming from the discharges and to emit visible radiation through the plate facing the front of said panel, these layers (5R, 5G, 5B) have a break (7) in each region of intersection of the electrodes (4R, 4G, 4B) so as to expose, in this break (7), the surface of said thin subjacent protective layer.

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