EP0747875A1 - Control method for a flat panel display - Google Patents

Control method for a flat panel display Download PDF

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Publication number
EP0747875A1
EP0747875A1 EP96410067A EP96410067A EP0747875A1 EP 0747875 A1 EP0747875 A1 EP 0747875A1 EP 96410067 A EP96410067 A EP 96410067A EP 96410067 A EP96410067 A EP 96410067A EP 0747875 A1 EP0747875 A1 EP 0747875A1
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EP
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Prior art keywords
polarized
anode
screen
color
phases
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EP96410067A
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German (de)
French (fr)
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EP0747875B1 (en
Inventor
Bernard Bancal
Axel Jaeger
Raynald Thevenet
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique CEA
Pixtech SA
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    • 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
    • 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
    • G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
    • G09G2310/0235—Field-sequential colour display

Definitions

  • the present invention relates to flat display screens, and more particularly to so-called cathodoluminescence screens, the anode of which carries luminescent elements separated from each other by insulating zones and capable of being excited by electronic bombardment.
  • This electronic bombardment requires that the luminescent elements are polarized and can come from microtips, from layers with low extraction potential or from a thermionic source.
  • microtip color screens To simplify the present description, below only the microtip color screens will be considered, but it will be noted that the invention relates generally to the various types of screens mentioned above and the like.
  • Figure 1 shows the structure of a color microtip flat screen.
  • Such a microtip screen essentially consists of a cathode 1 with microtips 2 and a grid 3 provided with holes 4 corresponding to the locations of the microtips 2.
  • the cathode 1 is placed opposite a cathodoluminescent anode 5 including a substrate of glass 6 constitutes the screen surface.
  • microtip screen The operating principle and a particular embodiment of a microtip screen are described, in particular, in American patent number 4,940,916 of the French Atomic Energy Commission.
  • the cathode 1 is organized in columns and consists, on a glass substrate 10, of cathode conductors organized in meshes from a conductive layer.
  • the microtips 2 are produced on a resistive layer 11 deposited on the cathode conductors and are arranged inside the meshes defined by the cathode conductors.
  • Figure 1 partially shows the interior of a mesh and the cathode conductors do not appear in this figure.
  • the cathode 1 is associated with the grid 3 which is organized in lines. The intersection of a line of the grid 3 and a column of the cathode 1 defines a pixel.
  • This device uses the electric field created between the cathode 1 and the grid 3 so that electrons are extracted from the microtips 2. These electrons are then attracted by phosphor elements 7 from the anode 5 if these are suitably polarized.
  • the anode 5 is provided with alternating bands of phosphor elements 7r, 7g, 7b each corresponding to a color (Red, Green, Blue). The strips are separated from each other by an insulator 8.
  • the phosphor elements 7 are deposited on electrodes 9, consisting of corresponding strips of a transparent conductive layer such as indium tin oxide (ITO) .
  • ITO indium tin oxide
  • the sets of red, green and blue bands are alternately polarized with respect to the cathode 1, so that the electrons extracted from the microtips 2 of a pixel of the cathode / grid are alternately directed towards the phosphor elements 7 opposite each other. colours.
  • the command to select the phosphor 7 (the phosphor 7g in FIG. 1) which must be bombarded by the electrons coming from the microtips 2 of the cathode 1 requires commanding, selectively the polarization of the phosphor elements 7 of the anode 5, color by color.
  • FIG. 2 schematically illustrates a conventional color screen anode structure. This figure partially shows, in elevation on the phosphor side, an anode 5 produced according to known techniques.
  • the strips 9 of anode electrodes, deposited on the substrate 6, are interconnected outside the useful surface of the screen, by color of phosphor elements 7, to be connected to a control system (not shown).
  • Two interconnection tracks 12 and 13, respectively anode electrodes 9g and 9b, are produced for two of the three colors of phosphor elements (for example 7g and 7b).
  • An insulation layer 14 (shown in dashed lines in FIG. 2) is deposited on the interconnection track 13.
  • a third interconnection track 15 is connected, by means of conductors 16 deposited on the insulation layer 14, to the anode electrode strips 9r intended for the phosphor elements 7r of the third color.
  • the rows of the grid 3 are sequentially polarized at a potential of the order of 80 V while the strips of phosphor elements (for example 7g in FIG. 1) to be excited are polarized under a voltage of the order of 400V, the other bands (for example 7r and 7b in FIG. 1) being at a low or zero potential.
  • the columns of cathode 1 are brought to respective potentials between a maximum emission potential and a non-emission potential (for example 0 and 30 V). We thus fix the brightness of a color component of all the pixels of a line.
  • the choice of the values of the polarization potentials is linked to the characteristics of the phosphor elements 8 and of the microtips 10. Conventionally, below a potential difference of 50 V between the cathode and the grid, there is no electronic emission and the maximum emission used corresponds to a potential difference of 80 V.
  • the conventional control mode of such a color screen consists in forming several images per second, for example 50 to 60 images per second, that is to say that there is a duration of approximately 20 milliseconds for form each image. This duration is called frame duration.
  • the lines L1 ... Li-1, Li, Li + 1 ... Ln are sequentially brought to a high potential so that all the pixels of the corresponding line are likely to be excited at a given time.
  • the column conductors of the cathodes are placed at potentials capable of giving the corresponding pixels the desired light intensity.
  • a drawback of this type of flat screen appears when, in at least one area of an image, it is desired to display for a relatively long period, ranging from a few seconds to a few minutes, a uniform color corresponding to one of the three colors.
  • the corresponding area of the screen is polarized for only one sub-frame out of three.
  • the color drift will be called here color drift. In practice, this means that at least one of the bands of phosphor material adjacent to the polarized bands begins to exhibit luminescence.
  • the present invention provides a new solution to the aforementioned problem of color drift.
  • Another object of the present invention is to provide such a method which also solves the breakdown problems in color screens or monochrome screens.
  • the present invention provides a method for controlling a cathodoluminescence screen consisting in providing regeneration phases during which at least part of the anodes is at low potential and the corresponding cathodes are polarized in an emission state. .
  • the screen is a color microtip screen
  • the regeneration phases are interspersed between operating phases and, during these regeneration phases, all the anodes are at low potential and the microtips and the grids are polarized in an emission state.
  • the screen is a color microtip screen
  • each anode is divided into at least two separately addressable portions
  • the regeneration phases are carried out on a first portion while an image is in progress of formation on another portion and, during a regeneration phase, a first portion of anode is at low potential and the microtips and the grids opposite are polarized in an emission state.
  • said regeneration phase is interposed between each frame.
  • said regeneration phase has a duration less than that of a color subframe.
  • the grid lines are polarized sequentially, the cathode columns being polarized at a high emission potential.
  • the grids are sequentially polarized and overlapped.
  • the screen is a monochrome screen.
  • An advantage of the present invention is that, during the regeneration phases, the anodes are at low potential and do not attract electrons. The corresponding luminescent elements are therefore not excited and, consequently, the regenerated areas of the screen remain dark and do not influence the image.
  • Another advantage of the invention is that, since anode-cathode breakdowns are avoided, the anode-cathode voltage can be increased compared to conventional designs. This results in an increase in the brightness of the screen.
  • the invention basically provides for inserting regeneration phases in an image display process.
  • all the anode bands are set to a low potential (of non-attraction of electrons) and the grids (lines) and the points (cathode columns) are polarized under conditions capable of producing a high, but not necessarily maximum, generation of electrons.
  • These regeneration phases can be provided between successive frames, between successive subframes, or periodically after a certain number of frames.
  • FIG. 5 illustrates a preferred variant of the first embodiment for controlling a microtip color screen anode according to the present invention.
  • a frame duration T provision is made for periods of color sub-frames Tr, Tg, Tb during which each of the bands of a color, red, green, blue, is sequentially polarized.
  • a dead time Td is provided corresponding to an abovementioned regeneration phase. During this time Td, none of the three sets of anode bands are polarized.
  • the cathode-grid assemblies are polarized to produce an emission of electrons.
  • the period T of FIG. 5 can be identical to the period T of FIG. 3, in which case the durations of each of the sub-frames Tr, Tg, Tb will be reduced.
  • the duration Td is preferably less than the duration of each of the color subframe periods so as not to significantly affect the brightness of the screen, if the anode-cathode voltage is not increased.
  • the grid lines are preferably scanned as indicated above, the cathode lines remaining polarized at a high emission potential.
  • This scanning can be carried out in a conventional manner as indicated in FIG. 4, each grid being sequentially polarized at its high potential.
  • An advantage of the first embodiment of the present invention is that the desired result is obtained without modifying the structural characteristics of a device for controlling a microtip screen. You just have to modify the programming of the lines, columns decoding circuits and groups of anode bands. It will also be noted that the scanning can be carried out very quickly and that the dead time can be brief compared to the duration of the color frames and subframes.
  • FIG 8 illustrates a second embodiment of the present invention.
  • the structure of the anode strips is changed so that each anode strip is divided into at least two addressable (polarizable) portions independently.
  • Each anode strip is divided into two portions 9b-9b ', 9r-9r', 9g-9g '.
  • the portions 9b, 9r and 9g are respectively connected to interconnection lines 12, 13 and 15.
  • the portions 9b ', 9r' and 9g ' are respectively connected to interconnection lines 12', 13 'and 15'.
  • the upper half (one color) of the anode is polarized and then we pass to the lower half to obtain the desired color subframe. While one half of the screen is addressed for display, a regeneration is carried out on the second half of the screen as described in relation to the first embodiment of the invention.
  • An advantage of the second embodiment of the present invention is that the desired result is obtained without dead time at the cost of a simple structural modification.
  • the invention also applies to luminescent screens whose anode potential is normally fixed. In such screens, it is also possible to provide a regeneration phase.
  • the present invention is susceptible of various variants and modifications which will appear to those skilled in the art.
  • the invention has been described in relation to a color screen to reduce the color drift, it also has the advantage of reducing anode-cathode or anode-grid breakdowns.
  • it also applies to monochrome screens in which a dead time will be provided between displays of frames, for example after each frame.
  • a monochrome screen in which the frame duration is 10 ms, the anode voltage of 250 to 300 V, and the brightness of 300 to 400 cd / m 2 , it is not possible to increase the anode voltage without having breakdowns.
  • a regeneration step of, for example, 0.3 ms is provided at the end of each frame. The inventors have noted that the anode voltage could then be increased to 600 V without any breakdown occurring. As a result, the brightness has been increased to around 1000 cd / m 2 .

Abstract

The screen has an anode (5) with luminophores (7r,7g,7b) on at least two sets of conductive strips (9) which are bombarded with electrons from micropoints (2) of the cathode (1). The control introduces phases of regeneration during which the anode is at low potential while the corresponding cathode is biased in an emissive condition. The regenerative phases are interspersed among the display phases within a repetitive cycle whereby the red, green and blue subframe periods follow one another with a regenerative period between each blue and the next red.

Description

La présente invention concerne les écrans plats de visualisation, et plus particulièrement des écrans, dits à cathodoluminescence, dont l'anode porte des éléments luminescents séparés les uns des autres par des zones isolantes et susceptibles d'être excités par bombardement électronique. Ce bombardement électronique nécessite que les éléments luminescents soient polarisés et peut provenir de micropointes, de couches à faible potentiel d'extraction ou d'une source thermoionique.The present invention relates to flat display screens, and more particularly to so-called cathodoluminescence screens, the anode of which carries luminescent elements separated from each other by insulating zones and capable of being excited by electronic bombardment. This electronic bombardment requires that the luminescent elements are polarized and can come from microtips, from layers with low extraction potential or from a thermionic source.

Pour simplifier la présente description, on ne considérera ci-après que les écrans couleur à micropointes mais on notera que l'invention concerne de façon générale les divers types d'écrans susmentionnés et analogue.To simplify the present description, below only the microtip color screens will be considered, but it will be noted that the invention relates generally to the various types of screens mentioned above and the like.

La figure 1 représente la structure d'un écran plat couleur à micropointes.Figure 1 shows the structure of a color microtip flat screen.

Un tel écran à micropointes est essentiellement constitué d'une cathode 1 à micropointes 2 et d'une grille 3 pourvue de trous 4 correspondant aux emplacements des micropointes 2. La cathode 1 est placée en regard d'une anode cathodoluminescente 5 dont un substrat de verre 6 constitue la surface d'écran.Such a microtip screen essentially consists of a cathode 1 with microtips 2 and a grid 3 provided with holes 4 corresponding to the locations of the microtips 2. The cathode 1 is placed opposite a cathodoluminescent anode 5 including a substrate of glass 6 constitutes the screen surface.

Le principe de fonctionnement et un mode de réalisation particulier d'un écran à micropointes sont décrits, en particulier, dans le brevet américain numéro 4 940 916 du Commissariat à l'Energie Atomique.The operating principle and a particular embodiment of a microtip screen are described, in particular, in American patent number 4,940,916 of the French Atomic Energy Commission.

La cathode 1 est organisée en colonnes et est constituée, sur un substrat de verre 10, de conducteurs de cathode organisés en mailles à partir d'une couche conductrice. Les micropointes 2 sont réalisées sur une couche résistive 11 déposée sur les conducteurs de cathode et sont disposées à l'intérieur des mailles définies par les conducteurs de cathode. La figure 1 représente partiellement l'intérieur d'une maille et les conducteurs de cathode n'apparaissent pas sur cette figure. La cathode 1 est associée à la grille 3 qui est organisée en lignes. L'intersection d'une ligne de la grille 3 et d'une colonne de la cathode 1 définit un pixel.The cathode 1 is organized in columns and consists, on a glass substrate 10, of cathode conductors organized in meshes from a conductive layer. The microtips 2 are produced on a resistive layer 11 deposited on the cathode conductors and are arranged inside the meshes defined by the cathode conductors. Figure 1 partially shows the interior of a mesh and the cathode conductors do not appear in this figure. The cathode 1 is associated with the grid 3 which is organized in lines. The intersection of a line of the grid 3 and a column of the cathode 1 defines a pixel.

Ce dispositif utilise le champ électrique créé entre la cathode 1 et la grille 3 pour que des électrons soient extraits des micropointes 2. Ces électrons sont ensuite attirés par des éléments luminophores 7 de l'anode 5 si ceux-ci sont convenablement polarisés. Dans le cas d'un écran couleur, l'anode 5 est pourvue de bandes alternées d'éléments luminophores 7r, 7g, 7b correspondant chacune à une couleur (Rouge, Vert, Bleu). Les bandes sont séparées les unes des autres par un isolant 8. Les éléments luminophores 7 sont déposés sur des électrodes 9, constituées de bandes correspondantes d'une couche conductrice transparente telle que de l'oxyde d'indium et d'étain (ITO). Les ensembles de bandes rouges, vertes, bleues sont alternativement polarisés par rapport à la cathode 1, pour que les électrons extraits des micropointes 2 d'un pixel de la cathode/grille soient alternativement dirigés vers les éléments luminophores 7 en vis à vis de chacune des couleurs.This device uses the electric field created between the cathode 1 and the grid 3 so that electrons are extracted from the microtips 2. These electrons are then attracted by phosphor elements 7 from the anode 5 if these are suitably polarized. In the case of a color screen, the anode 5 is provided with alternating bands of phosphor elements 7r, 7g, 7b each corresponding to a color (Red, Green, Blue). The strips are separated from each other by an insulator 8. The phosphor elements 7 are deposited on electrodes 9, consisting of corresponding strips of a transparent conductive layer such as indium tin oxide (ITO) . The sets of red, green and blue bands are alternately polarized with respect to the cathode 1, so that the electrons extracted from the microtips 2 of a pixel of the cathode / grid are alternately directed towards the phosphor elements 7 opposite each other. colours.

La commande de sélection du luminophore 7 (le luminophore 7g en figure 1) qui doit être bombardé par les électrons issus des micropointes 2 de la cathode 1 impose de commander, sélectivement la polarisation des éléments luminophores 7 de l'anode 5, couleur par couleur.The command to select the phosphor 7 (the phosphor 7g in FIG. 1) which must be bombarded by the electrons coming from the microtips 2 of the cathode 1 requires commanding, selectively the polarization of the phosphor elements 7 of the anode 5, color by color.

La figure 2 illustre schématiquement une structure d'anode d'écran couleur classique. Cette figure représente partiellement, en élévation côté luminophores, une anode 5 réalisée selon des techniques connues. Les bandes 9 d'électrodes d'anode, déposées sur le substrat 6, sont interconnectées hors de la surface utile de l'écran, par couleur d'éléments luminophores 7, pour être connectées à un système de commande (non représenté). Deux pistes d'interconnexion 12 et 13, respectivement des électrodes d'anode 9g et 9b, sont réalisées pour deux des trois couleurs d'éléments luminophores (par exemple 7g et 7b). Une couche d'isolement 14 (représentée en traits mixtes à la figure 2) est déposée sur la piste d'interconnexion 13. Une troisième piste d'interconnexion 15 est reliée, par l'intermédiaire de conducteurs 16 déposés sur la couche d'isolement 14, aux bandes d'électrodes d'anode 9r destinées aux éléments luminophores 7r de la troisième couleur.Figure 2 schematically illustrates a conventional color screen anode structure. This figure partially shows, in elevation on the phosphor side, an anode 5 produced according to known techniques. The strips 9 of anode electrodes, deposited on the substrate 6, are interconnected outside the useful surface of the screen, by color of phosphor elements 7, to be connected to a control system (not shown). Two interconnection tracks 12 and 13, respectively anode electrodes 9g and 9b, are produced for two of the three colors of phosphor elements (for example 7g and 7b). An insulation layer 14 (shown in dashed lines in FIG. 2) is deposited on the interconnection track 13. A third interconnection track 15 is connected, by means of conductors 16 deposited on the insulation layer 14, to the anode electrode strips 9r intended for the phosphor elements 7r of the third color.

Généralement, les rangées de la grille 3 sont séquentiellement polarisées à un potentiel de l'ordre de 80 V tandis que les bandes d'éléments luminophores (par exemple 7g en figure 1) devant être excitées sont polarisées sous une tension de l'ordre de 400V, les autres bandes (par exemple 7r et 7b en figure 1) étant à un potentiel faible ou nul. Les colonnes de la cathode 1 sont portées à des potentiels respectifs compris entre un potentiel d'émission maximale et un potentiel d'absence d'émission (par exemple respectivement 0 et 30 V). On fixe ainsi la brillance d'une composante couleur de tous les pixels d'une ligne.Generally, the rows of the grid 3 are sequentially polarized at a potential of the order of 80 V while the strips of phosphor elements (for example 7g in FIG. 1) to be excited are polarized under a voltage of the order of 400V, the other bands (for example 7r and 7b in FIG. 1) being at a low or zero potential. The columns of cathode 1 are brought to respective potentials between a maximum emission potential and a non-emission potential (for example 0 and 30 V). We thus fix the brightness of a color component of all the pixels of a line.

Le choix des valeurs des potentiels de polarisation est lié aux caractéristiques des éléments luminophores 8 et des micropointes 10. Classiquement, en dessous d'une différence de potentiel de 50 V entre la cathode et la grille, il n'y a pas d'émission électronique et l'émission maximale utilisée correspond à une différence de potentiel de 80 V.The choice of the values of the polarization potentials is linked to the characteristics of the phosphor elements 8 and of the microtips 10. Conventionally, below a potential difference of 50 V between the cathode and the grid, there is no electronic emission and the maximum emission used corresponds to a potential difference of 80 V.

Le mode de commande classique d'un tel écran couleur consiste à former plusieurs images par seconde, par exemple 50 à 60 images par seconde, c'est-à-dire que l'on dispose d'une durée d'environ 20 millisecondes pour former chaque image. Cette durée est appelée durée de trame.The conventional control mode of such a color screen consists in forming several images per second, for example 50 to 60 images per second, that is to say that there is a duration of approximately 20 milliseconds for form each image. This duration is called frame duration.

Comme le représente la figure 3, au cours de cette durée de trame, on procède séquentiellement à la formation de trois images correspondant chacune à une couleur. C'est-à-dire que les bandes R, G, B sont séquentiellement portées pendant des durées de sous-trames couleur Tr, Tg et Tb à des potentiels élevés pour être sélectivement actives. Classiquement, ces sous-trames couleur se suivent pratiquement sans interruption ou sont séparées de très brefs intervalles de temps pendant lesquels les lignes/colonnes sont inactives.As shown in Figure 3, during this frame time, we proceed sequentially to the formation of three images each corresponding to a color. That is to say that the bands R, G, B are sequentially brought for durations of color sub-frames Tr, Tg and Tb to high potentials to be selectively active. Conventionally, these color subframes follow each other almost without interruption or are separated by very short time intervals during which the rows / columns are inactive.

Comme l'illustre la figure 4, au cours de chacune des sous-trames couleur, les lignes L1 ... Li-1, Li, Li+1 ... Ln sont séquentiellement portées à un potentiel haut pour que tous les pixels de la ligne correspondante soient susceptibles d'être excités à un instant donné. Pendant la durée où une ligne est polarisée, les conducteurs de colonne des cathodes sont placés à des potentiels propres à conférer aux pixels correspondants l'intensité lumineuse désirée.As illustrated in FIG. 4, during each of the color subframes, the lines L1 ... Li-1, Li, Li + 1 ... Ln are sequentially brought to a high potential so that all the pixels of the corresponding line are likely to be excited at a given time. During the period when a line is polarized, the column conductors of the cathodes are placed at potentials capable of giving the corresponding pixels the desired light intensity.

Un inconvénient de ce type d'écran plat apparaît quand, dans au moins une zone d'une image, on souhaite afficher pendant une durée relativement longue, allant de quelques secondes à quelques minutes, une couleur uniforme correspondant à l'une des trois couleurs de base. Pour cela, la zone correspondante de l'écran est polarisée pendant seulement une sous-trame sur trois. Or, on s'aperçoit qu'au bout d'un certain temps, la couleur varie. Ce phénomène sera appelé ici dérive de couleur. En pratique, ceci signifie que l'une au moins des bandes de matériau luminophore adjacente aux bandes polarisées se met à présenter une luminescence.A drawback of this type of flat screen appears when, in at least one area of an image, it is desired to display for a relatively long period, ranging from a few seconds to a few minutes, a uniform color corresponding to one of the three colors. basic. For this, the corresponding area of the screen is polarized for only one sub-frame out of three. However, we realize that after a certain time, the color varies. This phenomenon will be called here color drift. In practice, this means that at least one of the bands of phosphor material adjacent to the polarized bands begins to exhibit luminescence.

L'origine de ce phénomène est mal comprise. On pense actuellement qu'il est dû au fait que des électrons s'accumulent sur les zones isolantes 8 entre les bandes de matériaux luminophores et assurent une conduction vers des bandes voisines.The origin of this phenomenon is poorly understood. It is currently thought to be due to the fact that electrons accumulate on the insulating zones 8 between the strips of phosphor materials and provide conduction to neighboring strips.

Pour éviter ce phénomène, on a proposé dans l'art antérieur diverses techniques dont l'une consiste à séparer par des intervalles de temps brefs les polarisations des bandes d'anode entre deux sous-trames couleur successives et à appliquer une impulsion de tension négative sur l'anode qui vient d'être polarisée avant de polariser positivement l'anode suivante à exciter.To avoid this phenomenon, various techniques have been proposed in the prior art, one of which consists in separating the polarizations of the anode bands between two successive color subframes by brief time intervals and in applying a negative voltage pulse. on the anode which has just been polarized before positively polarizing the next anode to be excited.

Toutefois, ce procédé qui donne des résultats satisfaisants quant à la suppression du phénomène de dérive de couleur présente l'inconvénient d'être relativement complexe à mettre en oeuvre puisqu'il complique la fourniture des tensions d'alimentation d'anode, qui sont des tensions de valeurs élevées (quelques centaines de volts) et qu'il nuit à la brillance de l'écran.However, this method which gives satisfactory results with regard to the elimination of the color drift phenomenon has the drawback of being relatively complex to implement since it complicates the supply of the anode supply voltages, which are high values (a few hundred volts) and that it affects the brightness of the screen.

Egalement, dans des écrans monochromes, des claquages se produisent souvent après une longue durée de fonctionnement.Also, in monochrome screens, breakdowns often occur after a long period of operation.

Ainsi, la présente invention propose une nouvelle solution au problème susmentionné de dérive de couleur.Thus, the present invention provides a new solution to the aforementioned problem of color drift.

Un autre objet de la présente invention est de prévoir un tel procédé qui résolve également les problèmes de claquage dans les écrans couleur ou les écrans monochromes.Another object of the present invention is to provide such a method which also solves the breakdown problems in color screens or monochrome screens.

Pour atteindre ces objets, la présente invention prévoit un procédé de commande d'un écran à cathodoluminescence consistant à prévoir des phases de régénération pendant lesquelles une partie au moins des anodes est à potentiel bas et les cathodes correspondantes sont polarisées dans un état d'émission.To achieve these objects, the present invention provides a method for controlling a cathodoluminescence screen consisting in providing regeneration phases during which at least part of the anodes is at low potential and the corresponding cathodes are polarized in an emission state. .

Selon un mode de réalisation de l'invention, l'écran est un écran couleur à micropointes, les phases de régénération sont intercalées entre des phases de fonctionnement et, pendant ces phases de régénération, toutes les anodes sont à potentiel bas et les micropointes et les grilles sont polarisées dans un état d'émission.According to one embodiment of the invention, the screen is a color microtip screen, the regeneration phases are interspersed between operating phases and, during these regeneration phases, all the anodes are at low potential and the microtips and the grids are polarized in an emission state.

Selon un mode de réalisation de l'invention, l'écran est un écran couleur à micropointes, chaque anode est divisée en au moins deux portions adressables séparément, les phases de régénération sont réalisées sur une première portion tandis qu'une image est en cours de formation sur une autre portion et, pendant une phase de régénération, une première portion d'anode est à potentiel bas et les micropointes et les grilles en regard sont polarisées dans un état d'émission.According to one embodiment of the invention, the screen is a color microtip screen, each anode is divided into at least two separately addressable portions, the regeneration phases are carried out on a first portion while an image is in progress of formation on another portion and, during a regeneration phase, a first portion of anode is at low potential and the microtips and the grids opposite are polarized in an emission state.

Selon un mode de réalisation de l'invention, ladite phase de régénération est intercalée entre chaque trame.According to one embodiment of the invention, said regeneration phase is interposed between each frame.

Selon un mode de réalisation de l'invention, ladite phase de régénération a une durée inférieure à celle d'une sous-trame couleur.According to one embodiment of the invention, said regeneration phase has a duration less than that of a color subframe.

Selon un mode de réalisation de l'invention, pendant ladite phase de régénération, les lignes de grille sont polarisées séquentiellement, les colonnes de cathode étant polarisées à un potentiel d'émission élevé.According to one embodiment of the invention, during said regeneration phase, the grid lines are polarized sequentially, the cathode columns being polarized at a high emission potential.

Selon un mode de réalisation de l'invention, plusieurs grilles sont polarisées simultanément.According to one embodiment of the invention, several grids are polarized simultaneously.

Selon un mode de réalisation de l'invention, les grilles sont polarisées séquentiellement et en recouvrement.According to one embodiment of the invention, the grids are sequentially polarized and overlapped.

Selon un mode de réalisation de l'invention, l'écran est un écran monochrome.According to one embodiment of the invention, the screen is a monochrome screen.

Un avantage de la présente invention est que, pendant les phases de régénération, les anodes sont à potentiel bas et n'attirent pas d'électrons. Les éléments luminescents correspondants ne sont donc pas excités et, en conséquence, les zones régénérées de l'écran restent sombres et n'influent pas sur l'image.An advantage of the present invention is that, during the regeneration phases, the anodes are at low potential and do not attract electrons. The corresponding luminescent elements are therefore not excited and, consequently, the regenerated areas of the screen remain dark and do not influence the image.

Un autre avantage de l'invention est que, comme on évite les claquages anode-cathode, la tension anode-cathode peut être augmentée par rapport aux réalisations classiques. Il en résulte une augmentation de luminosité de l'écran.Another advantage of the invention is that, since anode-cathode breakdowns are avoided, the anode-cathode voltage can be increased compared to conventional designs. This results in an increase in the brightness of the screen.

Ces objets, caractéristiques et avantages, ainsi que d'autres de la présente invention seront exposés en détail dans la description suivante de modes de réalisation particuliers faite, à titre non limitatif, en relation avec les figures jointes parmi lesquelles :

  • les figures 1 à 4 qui ont été décrites précédemment sont destinées à exposer l'état de la technique et le problème posé ;
  • la figure 5 représente une séquence de signaux de sous-trames couleur selon un premier mode de réalisation de la présente invention ;
  • les figures 6 et 7 représentent deux variantes de séquences de signaux de lignes utilisées selon la présente invention pendant des phases de régénération ; et
  • la figure 8 représente une structure d'anode adaptée à la mise en oeuvre d'un deuxième mode de réalisation de la présente invention.
These objects, characteristics and advantages, as well as others of the present invention will be explained in detail in the following description of particular embodiments made, without implied limitation, in relation to the attached figures among which:
  • Figures 1 to 4 which have been described above are intended to show the state of the art and the problem posed;
  • Figure 5 shows a sequence of color subframe signals according to a first embodiment of the present invention;
  • Figures 6 and 7 show two variants of line signal sequences used according to the present invention during regeneration phases; and
  • FIG. 8 represents an anode structure adapted to the implementation of a second embodiment of the present invention.

Pour des raisons de clarté, les représentations des figures ne sont pas à l'échelle et les mêmes éléments ont été désignés aux différentes figures par les mêmes références.For reasons of clarity, the representations of the figures are not to scale and the same elements have been designated in the different figures by the same references.

L'invention prévoit fondamentalement d'insérer des phases de régénération dans un processus d'affichage d'image.The invention basically provides for inserting regeneration phases in an image display process.

Selon un premier mode de réalisation de la présente invention, au cours de chacune de ces phases de régénération, toutes les bandes d'anode sont mises à un potentiel bas (de non-attraction d'électrons) et les grilles (lignes) et les pointes (colonnes de cathode) sont polarisées dans des conditions propres à produire une génération élevée, mais non nécessairement maximale, d'électrons.According to a first embodiment of the present invention, during each of these regeneration phases, all the anode bands are set to a low potential (of non-attraction of electrons) and the grids (lines) and the points (cathode columns) are polarized under conditions capable of producing a high, but not necessarily maximum, generation of electrons.

Ces phases de régénération peuvent être prévues entre des trames successives, entre des sous-trames successives, ou périodiquement après un certain nombre de trames.These regeneration phases can be provided between successive frames, between successive subframes, or periodically after a certain number of frames.

Etant donné la configuration usuelle des circuits de commande d'un écran couleur à micropointes, il semble aujourd'hui plus simple de prévoir qu'une phase de régénération survient à la fin de chaque trame couleur. C'est ce qui sera décrit ci-après dans le cadre d'un mode de réalisation préféré mais ceci ne doit pas être considéré comme une limitation de la présente invention.Given the usual configuration of control circuits for a microtip color screen, it now seems simpler to provide for a regeneration phase to occur at the end of each color frame. This will be described below in the context of a preferred embodiment, but this should not be considered as a limitation of the present invention.

Par ailleurs, pendant chaque phase de régénération, étant donnée la structure des circuits de décodage et d'alimentation (drivers) associés aux lignes de grille et aux colonnes de cathode, il n'est généralement pas possible en pratique d'alimenter simultanément toutes les pointes, en mettant simultanément toutes les lignes au potentiel haut de 80 volts et toutes les cathodes au potentiel bas voisin de 0 volt (la puissance de l'alimentation serait insuffisante). Ainsi, de préférence, on procédera pendant la phase de régénération à un balayage séquentiel rapide de toutes les lignes, pour les mettre successivement, individuellement ou par groupe, au potentiel haut tandis que les cathodes sont toutes maintenues au potentiel bas.Furthermore, during each regeneration phase, given the structure of the decoding and power supply circuits (drivers) associated with the grid lines and the cathode columns, it is generally not possible in practice to simultaneously supply all the points, by simultaneously putting all the lines at the high potential of 80 volts and all the cathodes at the low potential close to 0 volts (the power of the power supply would be insufficient). Thus, preferably, during the regeneration phase, a rapid sequential scanning of all the lines will be carried out, to put them successively, individually or in groups, at the high potential while the cathodes are all kept at the low potential.

La figure 5 illustre une variante préférée du premier mode de réalisation de commande d'une anode d'écran couleur à micropointes selon la présente invention.FIG. 5 illustrates a preferred variant of the first embodiment for controlling a microtip color screen anode according to the present invention.

Au cours d'une durée de trame T, on prévoit comme précédemment, des périodes de sous-trames couleur Tr, Tg, Tb au cours desquelles chacune des bandes d'une couleur, rouge, vert, bleu, est séquentiellement polarisée. On prévoit en outre un temps mort Td correspondant à une phase de régénération susmentionnée. Pendant cette durée Td, aucun des trois ensembles de bandes d'anode n'est polarisé. Par contre, comme on l'a expliqué précédemment, les ensembles cathode-grille sont polarisés pour produire une émission d'électrons.During a frame duration T, as before, provision is made for periods of color sub-frames Tr, Tg, Tb during which each of the bands of a color, red, green, blue, is sequentially polarized. In addition, a dead time Td is provided corresponding to an abovementioned regeneration phase. During this time Td, none of the three sets of anode bands are polarized. On the other hand, as explained previously, the cathode-grid assemblies are polarized to produce an emission of electrons.

La période T de la figure 5 peut être identique à la période T de la figure 3, auquel cas les durées de chacune des sous-trames Tr, Tg, Tb seront réduites. La durée Td est de préférence inférieure à la durée de chacune des périodes de sous-trames couleur pour ne pas nuire de façon notable à la luminosité de l'écran, si la tension anode-cathode n'est pas augmentée.The period T of FIG. 5 can be identical to the period T of FIG. 3, in which case the durations of each of the sub-frames Tr, Tg, Tb will be reduced. The duration Td is preferably less than the duration of each of the color subframe periods so as not to significantly affect the brightness of the screen, if the anode-cathode voltage is not increased.

Au cours de la durée Td, on procède de préférence comme cela a été indiqué précédemment à un balayage des lignes de grille, les lignes de cathode restant polarisées à un potentiel de forte émission. Ce balayage peut être réalisé de façon classique comme cela a été indiqué en figure 4, chaque grille étant séquentiellement polarisée à son potentiel élevé.During the period Td, the grid lines are preferably scanned as indicated above, the cathode lines remaining polarized at a high emission potential. This scanning can be carried out in a conventional manner as indicated in FIG. 4, each grid being sequentially polarized at its high potential.

Pour accélérer cette phase de balayage des lignes, on pourra, ou bien, comme le représente la figure 6, mettre simultanément des groupes de lignes, par exemple trois lignes (non nécessairement adjacentes) au potentiel élevé, ou bien, comme le représente la figure 7, polariser les lignes en recouvrement. En figure 7, pour la simplicité du dessin, on a représenté les lignes polarisées en recouvrement comme étant adjacentes. En pratique, on pourra adopter d'autres solutions. Bien entendu, dans les structures des figures 6 et 7, on choisira le nombre de lignes polarisées simultanément ou le nombre de lignes polarisées en recouvrement de façon à rester compatible avec les possibilités de génération de puissance des circuits d'alimentation des colonnes et lignes.To speed up this line scanning phase, it is possible either to, as shown in FIG. 6, put groups of lines simultaneously, for example three lines (not necessarily adjacent) with high potential, or else, as shown in the figure 7, polarize the overlapping lines. In FIG. 7, for the simplicity of the drawing, the polarized lines in overlap are shown as being adjacent. In practice, we can adopt other solutions. Of course, in the structures of FIGS. 6 and 7, the number of lines polarized simultaneously or the number of lines polarized in overlap will be chosen so as to remain compatible with the possibilities of power generation of the supply circuits of the columns and lines.

La raison pour laquelle la présente invention résout le problème de dérive de couleur n'est pas expliquée théoriquement aujourd'hui par les inventeurs. Toutefois, des expériences effectuées par ceux-ci sur des images fixes ou des images mobiles présentant des zones de couleur constante, ont montré que le phénomène de dérive de couleur est complètement éliminé par la présente invention.The reason why the present invention solves the problem of color drift is not explained theoretically today by the inventors. However, experiments carried out by them on still images or moving images having areas of constant color, have shown that the phenomenon of color drift is completely eliminated by the present invention.

Un avantage du premier mode de réalisation de la présente invention est que l'on obtient le résultat recherché sans modifier les caractéristiques structurelles d'un dispositif de commande d'un écran à micropointes. Il suffit de modifier la programmation des circuits de décodage des lignes, des colonnes et des groupes de bandes d'anode. On notera également que le balayage peut être effectué très rapidement et que le temps mort peut être bref devant la durée des trames et des sous-trames couleur.An advantage of the first embodiment of the present invention is that the desired result is obtained without modifying the structural characteristics of a device for controlling a microtip screen. You just have to modify the programming of the lines, columns decoding circuits and groups of anode bands. It will also be noted that the scanning can be carried out very quickly and that the dead time can be brief compared to the duration of the color frames and subframes.

La figure 8 illustre un deuxième mode de réalisation de la présente invention. Dans ce mode de réalisation, la structure des bandes d'anode est modifiée de façon que chaque bande d'anode est divisée en au moins deux portions adressables (polarisables) indépendamment. Dans cette figure, on a utilisé les mêmes notations qu'en figure 2. Chaque bande d'anode est divisée en deux portions 9b-9b', 9r-9r', 9g-9g'. Les portions 9b, 9r et 9g sont respectivement reliées à des lignes d'interconnexion 12, 13 et 15. Les portions 9b', 9r' et 9g' sont respectivement reliées à des lignes d'interconnexion 12', 13' et 15'. Pour simplifier les explications, on supposera que les portions sont égales et que l'écran est partagé en deux dans le sens de la hauteur. Ainsi, tandis que les lignes supérieures de la grille sont séquentiellement polarisées pour l'affichage, on polarise la moitié supérieure (une couleur) de l'anode puis on passe à la moitié inférieure pour obtenir la sous-trame couleur souhaitée. Pendant qu'une moitié de l'écran est adressée pour un affichage, on procède à une régénération sur la deuxième moitié de l'écran de la façon décrite en relation avec le premier mode de réalisation de l'invention.Figure 8 illustrates a second embodiment of the present invention. In this embodiment, the structure of the anode strips is changed so that each anode strip is divided into at least two addressable (polarizable) portions independently. In this figure, the same notations were used as in Figure 2. Each anode strip is divided into two portions 9b-9b ', 9r-9r', 9g-9g '. The portions 9b, 9r and 9g are respectively connected to interconnection lines 12, 13 and 15. The portions 9b ', 9r' and 9g 'are respectively connected to interconnection lines 12', 13 'and 15'. To simplify the explanations, we will assume that the portions are equal and that the screen is split in two vertically. Thus, while the upper lines of the grid are sequentially polarized for display, the upper half (one color) of the anode is polarized and then we pass to the lower half to obtain the desired color subframe. While one half of the screen is addressed for display, a regeneration is carried out on the second half of the screen as described in relation to the first embodiment of the invention.

Un avantage du deuxième mode de réalisation de la présente invention est que l'on obtient le résultat recherché sans temps mort au prix d'une modification structurelle simple.An advantage of the second embodiment of the present invention is that the desired result is obtained without dead time at the cost of a simple structural modification.

L'invention s'applique également à des écrans luminescents dont le potentiel d'anode est normalement fixe. Dans de tels écrans, on pourra également prévoir une phase de régénération.The invention also applies to luminescent screens whose anode potential is normally fixed. In such screens, it is also possible to provide a regeneration phase.

Bien entendu, la présente invention est susceptible de diverses variantes et modifications qui apparaîtront à l'homme de l'art. En particulier, bien que l'invention ait été décrite en relation avec un écran couleur pour réduire la dérive de couleur, elle présente également l'avantage de réduire les claquages anode-cathode ou anode-grille. Ainsi, elle s'applique également à des écrans monochromes dans lesquels un temps mort sera prévu entre affichages de trames, par exemple après chaque trame.Of course, the present invention is susceptible of various variants and modifications which will appear to those skilled in the art. In particular, although the invention has been described in relation to a color screen to reduce the color drift, it also has the advantage of reducing anode-cathode or anode-grid breakdowns. Thus, it also applies to monochrome screens in which a dead time will be provided between displays of frames, for example after each frame.

Dans un exemple d'écran monochrome, dans lequel la durée de trame est de 10 ms, la tension d'anode de 250 à 300 V, et la luminosité de 300 à 400 cd/m2, il n'est pas possible d'augmenter la tension d'anode sans avoir de claquages. Selon l'invention, une étape de régénération de, par exemple, 0,3 ms est prévue à la fin de chaque trame. Les inventeurs ont constaté qu'alors la tension d'anode pouvait être augmentée jusqu'à 600 V sans qu'il ne se produise de claquage. En conséquence, la luminosité a été augmentée jusqu'à environ 1000 cd/m2.In an example of a monochrome screen, in which the frame duration is 10 ms, the anode voltage of 250 to 300 V, and the brightness of 300 to 400 cd / m 2 , it is not possible to increase the anode voltage without having breakdowns. According to the invention, a regeneration step of, for example, 0.3 ms is provided at the end of each frame. The inventors have noted that the anode voltage could then be increased to 600 V without any breakdown occurring. As a result, the brightness has been increased to around 1000 cd / m 2 .

Claims (7)

Procédé de commande d'un écran à cathodoluminescence, caractérisé en ce qu'il consiste à prévoir des phases de régénération pendant lesquelles une partie au moins des anodes est à potentiel bas et les cathodes correspondantes sont polarisées dans un état d'émission.Method for controlling a cathodoluminescence screen, characterized in that it consists in providing regeneration phases during which at least part of the anodes are at low potential and the corresponding cathodes are polarized in an emission state. Procédé selon la revendication 1, caractérisé en ce que les phases de régénération (Td) sont intercalées entre des phases d'affichage et en ce que, pendant ces phases de régénération, toutes les anodes sont à potentiel bas, les micropointes et les grilles étant polarisées dans un état d'émission.Method according to Claim 1, characterized in that the regeneration phases (Td) are inserted between display phases and in that, during these regeneration phases, all the anodes are at low potential, the microtips and the grids being polarized in an emission state. Procédé selon la revendication 1, dans lequel l'écran est un écran à micropointes, caractérisé en ce que chaque anode est divisée en au moins deux portions adressables séparément, en ce que les phases de régénération sont réalisées sur une première portion tandis qu'une image est en cours de formation sur une autre portion et en ce que, pendant une phase de régénération, une première portion d'anode est à potentiel bas et les micropointes et les grilles en regard sont polarisées dans un état d'émission.Method according to claim 1, in which the screen is a microtip screen, characterized in that each anode is divided into at least two separately addressable portions, in that the regeneration phases are carried out on a first portion while a image is being formed on another portion and in that, during a regeneration phase, a first portion of anode is at low potential and the opposite microtips and grids are polarized in an emission state. Procédé selon la revendication 2, caractérisé en ce que ladite phase de régénération est intercalée entre chaque trame.Method according to claim 2, characterized in that said regeneration phase is inserted between each frame. Procédé selon la revendication 1, caractérisé en ce que pendant ladite phase de régénération les lignes de grille sont polarisées séquentiellement, les colonnes de cathode étant polarisées à un potentiel d'émission élevé.Method according to claim 1, characterized in that during said regeneration phase the grid lines are polarized sequentially, the cathode columns being polarized at a high emission potential. Procédé selon la revendication 5, caractérisé en ce que plusieurs grilles sont polarisées simultanément.Method according to claim 5, characterized in that several grids are polarized simultaneously. Procédé selon la revendication 5, caractérisé en ce que les grilles sont polarisées séquentiellement et en recouvrement.Method according to claim 5, characterized in that the grids are sequentially polarized and overlapped.
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WO2001009870A1 (en) * 1999-08-02 2001-02-08 Motorola Inc. Method for improving life of a field emission display
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US5872551A (en) 1999-02-16
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