EP1407443A1

EP1407443A1 - Method for monitoring a plasma display panel with discharge between triad-mounted electrodes

Info

Publication number: EP1407443A1
Application number: EP02747498A
Authority: EP
Inventors: Laurent Tessier
Original assignee: Thomson Plasma SAS
Current assignee: Thomson Plasma SAS
Priority date: 2001-06-13
Filing date: 2002-06-04
Publication date: 2004-04-14
Anticipated expiration: 2022-06-04
Also published as: FR2826166B1; JP2005505788A; FR2826166A1; US20040160390A1; CN1272760C; JP4184949B2; TW588301B; KR100854045B1; CN1514991A; DE60228965D1; US7167144B2; WO2002101703A1; KR20040010698A; EP1407443B1

Abstract

The invention concerns a plasma panel display wherein the coplanar faceplate of the display panel comprising electrode triads including each two opposite side electrodes (13, 14) and a central electrode (20), and wherein during sustain operations by application of a series of sustain voltage pulses between the electrode triads, the central electrode always acts as anode. Such an arrangement, and, preferably at an adapted width of the central electrode (20), enables to enhance substantially the luminous efficacy of the display panel.

Description

PROCESS FOR DRIVING A PLASMA PANEL DISCHARGED FROM BETWEEN TRIADIC ELECTRODES.

With reference to document FR 2790583 (SAMSUNG), in particular to FIG. 4 of this document reproduced schematically below in FIG. 1, the invention relates to a method for controlling a plasma panel for viewing alternating current images, with co-planar maintenance discharges, and with memory effect, of the type comprising:

- a parallel front slab and a rear slab leaving between them a space filled with discharge gas,

- one of the slabs 12 comprising at least a first network of electrodes 5 and the other slab 11 comprising at least a second network of triads of electrodes 13, 20, 14 whose general direction is approximately orthogonal to that of the electrodes 5 of the first network,

the spaces located at the intersections of the electrodes 5 of the first array and the triads of electrodes 13, 20, 14 of the second array of electrodes constituting a matrix of zones 9 of light discharges and points of the image to be displayed,

- The electrodes of the triads 13, 20, 14 being coated with a dielectric layer 17 to obtain the conventional memory effect according to which a discharge can be generated between these electrodes by application of a voltage lower than the ignition voltage.

Generally, the walls of adjacent discharge zones are partially coated with phosphors emitting different colors when they are excited by the ultraviolet radiation of the discharges; thus, the adjacent points corresponding to these zones of different colors are associated in pixels or elements of the image to be displayed.

Generally, the discharge areas, at least those of different colors, are separated by barriers.

The memory effect mentioned above is obtained in a discharge zone 9 as soon as charges are deposited on the surface of the dielectric 17 in this zone, in particular by application of a so-called pulse. addressing between the electrode 5 and at least one of the opposite electrodes of the triad 14, 20, 13 which intersect in this zone; the dielectric layer is generally coated with a layer for protecting and emitting secondary electrons, for example based on MgO. To obtain a succession of maintenance discharges in the zones thus “addressed”, the piloting method described in this document comprises:

- conventionally, the application of at least one series of holding voltage pulses between the opposite electrodes 13, 14 of each triad so as to generate holding discharges in each of the "addressed" crossing zones 9, c ' ie that in which one wishes to maintain a discharge;

- in addition, at an instant prior (claim 3) or equal (claim 6) to that of the application of a sustain pulse of this series, application of a pulse on the central electrode 20 of said triad so to obtain: o either (claim 4) the elevation of the potential of the central electrode 20 to the level of the highest potential [central = anode] of the two opposite electrodes 13, 14 at the time of said holding pulse generating a light discharge holding, then, when said discharge decreases, lowering the potential of this central electrode 20 to the lowest potential of the two opposite electrodes 13, 14 [central = cathode]. either (claim 5) lowering the potential of the central electrode 20 to the lowest potential [central = cathode] of the two opposite electrodes 13, 14 at the time of said sustain pulse generating a sustain light discharge, then, when said discharge decreases, raising the potential of this central electrode 20 to the level of the highest potential of the two opposite electrodes 13, 14 [central ≈ anode].

The timing diagrams corresponding to the timing of the pulses and discharges are represented on the one hand in FIGS. 5 and 6 of this document, on the other hand in FIGS. 8 and 9. Still according to this document FR 2790583, the central electrode 20 must be thin so as not to increase the electrostatic capacity of the holding electrodes of each triad.

In plasma panels with coplanar maintenance discharges, discharges occur by charge transfers, through zone 9, on the internal surface of the dielectric layer 17 of the slab 11 carrying the coplanar electrodes, here the triads 13 , 2014 ; we will now describe the different charge transfer steps which give rise, if necessary, to maintenance light discharges in the case of piloting the panel as described in document FR 2790583; reference is made to the attached figures 2A to

2H1 where the zones filled with signs - _ - represent negative charges or electrons on the surface of the dielectric 17, where the gridded zones correspond to positive charges or ions on the surface of the dielectric 17: - after a conventional addressing pulse applied at an intersection of an electrode 5 of the first array and a triad of electrodes 13, 20, 14 of the second array of electrodes, between this addressing electrode 5 and at least one electrode of this triad, the load distribution illustrated in FIG. 2A, the electrode 14 being brought to + 300 V relative to the other electrodes 20 (0 V) and 13 (0 V); electrons are therefore accumulated on a lateral electrode of the triad, and ions are accumulated mainly on the central electrode of the triad.

- as in a conventional maintenance sequence, the potentials of the two side electrodes are reversed and the electrode 13 is brought to + 200 V relative to the opposite side electrode 14 (0 V); at the time of application of this first holding pulse, the potential of the central electrode 20 is then high at the level of the highest potential of the two opposite electrodes 13, 14, in this case 200 V, and the central electrode plays then the role of anode; this leads to the configuration described in FIG. 2B1 and a first main maintenance light discharge arises (see arrow) which causes the inversion of the charges shown in FIG. 2C1; during this charge reversal, the electrons spread over the width of the central electrode 20 and over that of the lateral electrode 13, which gives rise to an elongation important to the positive pseudo-column of the plasma and therefore to a discharge of good light output;

- then, when this discharge decreases, the potential of the central electrode 20 is lowered to the level of the lowest potential of the two opposite electrodes 13, 14, here 0 V, and the central electrode then plays the role of cathode, as shown in Figure 2B2; the movement of the charges which then begins (arrows) generates a first secondary holding light discharge and results in the distribution of the charges shown in FIG. 2C2; this discharge has a poor light output, because it does not give rise to a significant and significant spread of electrons;

- the second holding pulse is now applied by again inverting the potentials of the two side electrodes; the electrode 14 is now brought to + 200V relative to the opposite lateral electrode 13 (0 V); at the time of application of this second holding pulse, the potential of the central electrode 20 is then again high at the level of the highest potential of the two opposite electrodes 13, 14, ie here 200 V, and the electrode central then plays the role of anode; we arrive at the configuration described in Figure 2D1; the second main holding light discharge (see arrow) which is expected to take place almost does not take place, since the central area of the surface of the dielectric is strongly discharged and the memory effect is partly lost; the previous sequence therefore led to self-erasure; the configuration of the loads to which we end up is very little modified (Figure 2F1).

- then, the potential of the central electrode 20 is again lowered to the lowest potential of the two opposite electrodes 13, 14, here 0 V, and the central electrode then plays the role of cathode, as shown in FIG. Figure 2D2; the movement of the charges which then begins (arrows) generates a second secondary holding light discharge and results in the distribution of the charges shown in FIG. 2F2; this discharge has a poor light output, since the spread to which it gives rise here concerns the ions;

- After this first complete maintenance cycle comprising two main maintenance pulses, a second cycle is then approached; we apply thus the first sustaining pulse of the second cycle by again reversing the potentials of the two side electrodes; the electrode 13 is now brought to + 200V relative to the opposite lateral electrode 14

(0V); at the time of application of this holding pulse, the potential of the central electrode 20 is then high at the level of the highest potential of the two opposite electrodes 13, 14, ie here 200 V, and the central electrode plays the role of anode; we arrive at the configuration described in Figure 2G1; and a new main maintenance light discharge appears (see arrow) which causes the reversal of the charges represented in FIG. 2H1, identical to FIG. 2C1 representing the end of the first maintenance discharge; during this charge reversal, the electrons spread over the width of the central electrode and that of the lateral electrode 13, which gives rise to a significant elongation of the positive pseudo-column of the plasma and therefore to a good light output discharge; The second sustaining cycle then continues like the first cycle and the charge movements are identical to that of the first cycle: from the end of this first main sustaining discharge of the second cycle (FIG. 2C1 identical to 2H1), follow one another a secondary discharge of poor efficiency leading to self-erasure (FIGS. 2B2 and 2C2), a very weak main sustaining discharge (FIGS. 2D1 and 2F1), finally another secondary discharge of poor efficiency (FIGS. 2D2 and 2F2).

If necessary, other identical holding cycles then follow one another until the desired holding time has been used up, and the voltage pulses applied to the electrodes form a series of holding pulses.

It can therefore be seen that over a complete cycle comprising two main pulses and two secondary holding pulses, a single discharge has good light output; overall, the light output of the plasma panel is therefore not satisfactory when using, for coplanar maintenance, arrays of electrode triads and the control method described in document FR 2790583.

It can therefore be seen that, in a series of holding pulses, the central electrode alternately plays the role of anode and cathode. Furthermore, the narrow width of the central electrode of these triads, as described and recommended in document FR 2790583, limits the possibilities of spreading the electrons and lengthening the positive pseudo-column of the plasma, which does not bring any improvement in light efficiency compared to conventional coplanar configurations, the improvement in light efficiency is not the aim pursued by this document.

The object of the invention is to propose a structure of a coplanar plasma panel and a method of controlling the holding pulses of this panel providing a significant improvement in the light output; the object of the invention is in particular to avoid the abovementioned drawbacks.

To this end, the subject of the invention is a method for controlling a plasma panel for viewing alternating current images, with co-planar maintenance discharges, and with memory effect, the said panel comprising: a slab front and a parallel rear panel providing between them a space filled with discharge gas, one of the panels comprising at least a first network of electrodes and the other panel comprising at least a second network of triad of electrodes whose direction general is approximately orthogonal to that of the electrodes of the first network, - each triad comprising two opposite lateral electrodes and a central electrode, the spaces located at the intersections of the electrodes of the first network and the triads of electrodes of the second network electrodes forming a matrix of zones of light discharges and points of the image to be viewed, the electrodes of the triads being coated with a dielectric layer, said procedure comprising at least one holding operation by applying a series of holding voltage pulses between the electrodes of each triad so as to generate holding discharges in each of the crossing zones in which it is desired to maintain a light discharge, characterized in that, during said holding operation, the central electrodes of each triad always play the role of anode. Thanks to this arrangement, the light output of the panel is significantly improved; according to the invention, and unlike the control methods described in the document FR 2790583 already cited, during the entire duration of the holding operations (or "maintenance phases"), the potential of the central electrode is always strictly greater than that of one or the other lateral electrode, so that this central electrode always plays the role of anode.

An advantageous means for making the central electrode play the role of anode during the whole holding operation (or all the maintenance phases) consists in making this electrode floating; in fact, in principle of the capacitive divider bridge, in such a configuration, the central electrode then has a potential between the potential of the two adjacent side electrodes so that this potential of the central electrode is always strictly greater than that of the one or the other side electrode; the economic advantage of such a configuration is that it does not require a specific holding power supply for the central electrodes of the panel nor switches or “drivers” for their power supply.

To obtain an even greater improvement in the light output, it is preferable, contrary to the teachings of the document FR 2790583 already cited, that the central electrode has a width which is sufficiently large to favor the spreading of the electrons and the elongation of the positive pseudocolumn. plasma during sustaining discharges; preferably, the width of this central electrode is greater than the gaps separating and insulating the adjacent electrodes of the same triad; in the case where the two gaps of the same triad have different values, the width of the central electrode is greater than the highest gap; preferably, the width of this central electrode is greater than 80 μm.

The width of this central electrode can in particular be between 100 and 200 μm. Advantageously, the central electrode can even be wider than 200 μim; in particular in this case, there is then a risk of matrix ignition of the discharges, that is to say initiation of these discharges, not between the electrodes of the triad (case of coplanar ignition), but between an electrode of the first network belonging to a slab and an electrode of a triad belonging to the other slab; one seeks to avoid the matrix ignitions because, contrary to the coplanar ignitions, they fluctuate widely from one cell to another of the panel according to the electrical characteristics of the materials of the walls of these cells, in particular phosphors, which differ from one cell to cell; these electrical characteristics include permittivity, static charge, dielectric thickness, electronic secondary emission; in order to avoid or limit this matrix ignition, preferably: the gaps separating and isolating the adjacent electrodes of the same triad are less than 80 μm, and the spacing between the slabs saving the space filled with discharge gas is greater than 130 μm.

Advantageously, the width of the central electrode is then greater than the width of each of the side electrodes. Between each series of holding pulses, selective addressing or selective clearing operations are generally carried out; before a selective addressing, one generally proceeds to a preparation operation

(or "priming" in English) and a delete operation, both semi-selective or non-selective. To this end, the invention also relates to the above method according to the invention also comprising, before or after each holding operation, a selective addressing or erasing operation applied only in each of said areas where the it is desired to maintain a light discharge during said series, by applying at least one voltage pulse between the electrode of said first network crossing said zone and at least one of the electrodes of the triad crossing said zone.

In the case of an addressing operation, this takes place before each holding operation and the corresponding addressing pulse is adapted in a manner known per se to generate electric charges on the dielectric layer in said zone and thus obtain the well-known memory effect of plasma panels.

This process corresponds to a classic control mode by selective addressing, which can be used in processes where one addresses successively lines or groups of lines of landfill areas before a maintenance phase (so-called "ADS" or "ADM") or in the processes where lines or groups of lines are addressed during the maintenance of other lines or groups of lines (case called "AWD"). In the case of an erasing operation, this takes place after each holding operation and the corresponding erasing pulse is adapted in a manner known per se to remove the electric charges on the dielectric layer in said area and end the memory effect.

This process corresponds to a classic control mode by selective erasure.

Preferably, the selective voltage pulse is applied between the electrode of said first network crossing said zone and the central electrode of the triad crossing said zone.

By thus transferring all of the selective addressing or erasing operations to the central electrodes, the lateral electrodes of series of adjacent discharge zones can be grouped together, even to the point of using common electrodes, for example as lateral electrode lower of a triad corresponding to a line n and as the upper lateral electrode of the triad corresponding to the next adjacent line (n + 1); thus, the invention also relates to a method according to the invention in which, all of the zones served by the same triad forming a line of said panel, on any two adjacent lines crossed respectively by a first triad on the one hand and by a second triad on the other hand, the lateral electrode of the first triad is electrically connected to the same potential as the lateral electrode closest to the second triad.

Preferably, said two electrodes connected electrically form an electrode common to two adjacent lines.

The subject of the invention is also a plasma panel capable of being used for implementing the method according to the invention, comprising: a parallel front panel and a rear panel providing between them a space filled with discharge gas, one of the slabs comprising at least a first network of electrodes and the other slab comprising at least a second network of triads electrodes whose general direction is approximately orthogonal to that of the electrodes of the first network, each triad comprising two opposite lateral electrodes and a central electrode, - the spaces located at the intersections of the electrodes of the first network and the triads of electrodes of the second network electrodes forming a matrix of light discharge zones and points of the image to be displayed, the electrodes of the triads being coated with a dielectric layer, - means for controlling the discharges in each of said crossing zones using, in particular , holding operations, characterized in that said control means are adapted so that, during holding operations, the central electrode always plays the role of anode. In the above-mentioned case where the central electrodes are floating and without external connections, the panel does not include a specific holding power supply for these electrodes nor switches or “drivers” for their power supply.

Preferably, the width of the central electrode is greater than the gaps separating and insulating the adjacent electrodes of the same triad; in practice, the width of the central electrode is greater than 80 μm; other preferences concerning the geometry of the electrodes and / or of the cells of the panel have been previously mentioned, in particular the advantageous case where the width of the central electrode is greater than the width of each of the side electrodes.

Preferably, all of the zones served by the same triad forming a line of the panel, on any two adjacent lines crossed respectively by a first triad on the one hand and by a second triad on the other hand, the lateral electrode of the first triad is electrically connected to the same potential as the side electrode closest to the second triad; preferably, said two electrodes connected electrically form an electrode common to two adjacent lines. 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:

- Figure 1, already described, is a schematic sectional view of a cell with three coplanar electrodes of a plasma panel of the prior art, with the same references as Figure 4 of the document FR 2790583;

- Figures 2A to 2H1 (not Figure 2E), already described, illustrate the evolution of electrical charges and the emergence of light discharges in a cell of Figure 1, when driven according to the prior art as described in document FR 2790583;

- Figures 3A to 3F illustrate the evolution of electrical charges and the emergence of light discharges in a cell similar to that of Figure 1 but with a larger central electrode according to the invention, when it is controlled in a mode of realization of the invention; FIG. 4 schematically illustrates, by four chronograms referenced 20, 13, 14 and 5, the evolution, over time, of the potential applied to the electrodes of a coplanar triad (lateral electrodes 13, 14 and central electrode 20) and the addressing electrodes 5 according to an embodiment of the invention; FIGS. 5A to 5C illustrate the spreading of the discharges in a cell with two coplanar electrodes of a plasma panel of the prior art, as a function of the width of the coplanar electrodes and of the gap separating these electrodes;

- Figure 6 shows a top view and two side sectional views of a group of three adjacent cells of different colors of a plasma panel according to a particular embodiment of the invention, where each side electrode of a triad is common to two adjacent lines of the panel and is made of transparent conductive material;

- Figure 7 shows a top view similar to that of Figure 6, with the difference that the side electrodes are formed of opaque conductor grids; - Figure 8 shows a variant of Figure 6 with a large central electrode with buses arranged at the discharge initiating edges of this electrode;

- Figure 9 shows a variant of Figure 7 with a large central electrode;

In order to simplify the description and reveal the differences and advantages which the invention presents compared to the prior art, identical references are used for the elements which perform the same functions. The plasma panel according to the invention is identical to that previously described (FIG. 1) and to that described in the document FR 2790583 (FIG. 4), with the difference that is essential for optimizing the light output, that the electrode central 20 of each triad is wide enough to favor the elongation of the positive pseudo-column of the plasma and the spreading of the electrons during a light discharge; in practice, the width of this central electrode is greater than the gap which separates the electrodes between them; thus, the width of this central electrode is greater than 50 μm, preferably greater than 80 μm; the width of the central electrode of each triad is generally between 100 and 200 μm approximately. We will now describe the process for controlling the plasma panel according to the invention, in particular in a holding phase according to the invention, with reference to FIGS. 3A to 3F which represent the evolution of the charges at the surface of the dielectric layer 17, with the same representation conventions as for FIGS. 2A to 2H1: - during a conventional addressing pulse applied to a crossing of an electrode 5 of the first network and a triad of electrodes 13, 20, 14 of the second network of electrodes, between this addressing electrode 5 and at least one electrode of this triad, the charge distribution illustrated in FIG. 3A is obtained, after the addressing discharge, the lateral electrode 14 being brought to + 300 V compared to the other side 13 (0 V) or central 20 (0 V) electrodes; electrons are therefore accumulated on a lateral electrode of the triad, and ions are accumulated mainly on the central electrode of the triad, which is wider than in the prior art. - as in a conventional maintenance sequence, the potentials of the two lateral electrodes are reversed and the electrode 13 is brought to + 200V relative to the opposite lateral electrode 14 (0 V); at the time of application of this first holding pulse, the potential of the central electrode 20 is then raised to the level of the highest potential of the two opposite electrodes 13, 14, ie here 200 V and is maintained at this value until 'at the end of the first sustaining pulse unlike the prior art; the central electrode then plays the role of anode; this leads to the configuration described in FIG. 3B and, as in the prior art, a first main maintenance light discharge arises (see arrow) which results in the reversal of the charges shown in FIG. 3C; during this charge reversal, the electrons spread over the central electrode 20 which is much wider than in the prior art and over the lateral electrode 13, which gives rise to a greater elongation than in the prior art of the positive pseudo-column of the plasma and therefore to a discharge of better light yield;

- The second holding pulse is then applied directly by again reversing the potentials of the two side electrodes; the electrode 14 is now brought to + 200 V relative to the opposite lateral electrode 13 (0 V); at the time of the application of this second holding pulse, the potential of the central electrode 20 is always maintained at the level of the highest potential of the two opposite electrodes 13, 14, ie here 200 V; the central electrode always plays the role of anode; this leads to the configuration described in FIG. 3D and a second main holding light discharge (see arrow) is triggered which results in the inversion of the charges represented in FIG. 3F with a transient state represented in FIG. 3E; during this charge reversal, the electrons spread out again on the central electrode 20 which is much wider than in the prior art and on the lateral electrode 14, which gives rise to a greater elongation of the positive pseudo-column of the plasma and therefore at a higher light output discharge;

- After this first complete holding cycle comprising only two main holding pulses, a second cycle is then approached; we then apply a first main pulse to maintain the second cycle by again reversing the potentials of the two lateral electrodes but always without changing the potential of the central electrode 20; electrode

13 is now brought to + 200V relative to the opposite side electrode

14 (0 V) and the central electrode 20 always plays the role of anode; this configuration results in the reversal of the loads already shown in the figure

3C, representing the end of the first sustaining discharge of the second cycle, and the discharge obtained has a very good light output as for the first cycle.

The second holding cycle then continues like the first cycle and the movements of the charges are identical to those of the first cycle: from the end of this first holding discharge of the second cycle

(FIG. 3C), a second discharge for maintaining the second cycle occurs

(Figures 3D to 3F) also showing very good light output.

It can therefore be seen that the series of holding pulses only cause discharges with very good light yields; overall, the light output of the plasma panel is therefore appreciably improved and optimized, thanks to a control system where the central electrode always plays the role of anode and thanks to the width of the central electrode, greater than in l prior art.

According to the invention, the elongation of the discharge which is obtained makes it possible, in each zone, to increase, within the plasma, the volume of the pseudo-positive column where a weak electric field prevails and where the emission of ultraviolet photons is generated with very good yield.

In the prior art plasma panels provided with pairs of coplanar electrodes 3, 4 for holding as shown diagrammatically in FIG. 5A, at least two means are known to improve the light output:

- by increasing the width of the electrodes of each pair, so as to obtain an elongation of the discharge as shown in the figure 5B; but the risks of interference between different discharge zones (“crosstal” in English) impose an upper limit on this width, and therefore on improving the light output;

- by increasing the gap which separates the coplanar electrodes from a pair, in order to limit the electric field in the discharge zones; we then obtain an elongation of the discharge path in the depth of each zone as shown in Figure 5C, because the field lines then take approximately the form of semicircles (unlike Figure 5B where the gap is too small) ; but this increase in the gap adversely modifies the conditions for igniting landfills (Paschen law), requires high ignition voltages, and leads to prohibitive additional costs in terms of electronic components; the need to be able to drive the panel with sufficiently low voltage pulses therefore considerably limits the increase in the gap. The invention allows these two means to be used while avoiding these limitations; the central electrode makes it possible to space the two opposite coplanar electrodes without modifying the conditions of ignition of the discharges. The invention also has the following advantages:

- as the central electrode is maintained at the same potential during the entire maintenance phase, the control system of the panel is therefore very simple to implement, therefore very economical;

- As the central electrode is wider than in the prior art, this electrode is easy to produce at low cost.

Referring to FIG. 4, we will now describe a complete example of the “ADS” type of diagram of a complete cycle of addressing and maintaining the discharge zones of a plasma panel according to the invention:

- In a first non-selective phase I, called preparation or “priming” in English, a uniformly increasing voltage is applied to the central electrode 20 of the second coplanar network, greater than that of the addressing electrode 5 of the first network, so as to generate a so-called “positive resistance” discharge between the central electrode 20 and a side electrode and thus produce the so-called “primary” electrical charges necessary for the addressing phase, while generating a minimum of light emission to maintain good image contrast;

in a second phase II, always non-selective, called erasing phase, without modifying the voltage of the addressing electrode 5, a uniformly decreasing voltage is applied to the central electrode 20 and to only one of the side electrodes a constant voltage adapted to be permanently greater than that of the central electrode 20, so as to produce a discharge of low light emission to erase the electric charges stored on the surface of the dielectric layer 17 during the previous preparation operation;

- In a third phase III, this time called selective addressing, while maintaining the voltage of the lateral electrode 14 at the same potential as in the previous phase and by applying to the other lateral electrode 13 a voltage identical to that most low of the addressing electrode 5, while maintaining, apart from the addressing pulses, the voltage of the central electrode 20 between that of the two lateral electrodes 13, 14, addressing pulses of a leaves simultaneously with the different electrodes 5 of the first network and on the other hand successively with the different central electrodes 20 of the second network, so as to obtain a deposit of electric charges on the surface of the dielectric 17 in the areas where it is desired to maintain discharges electric in the next maintenance phase;

in a last non-selective last phase IV of maintenance, after having applied approximately the same positive voltage Ve to the three coplanar electrodes 13, 20, 14 while maintaining the addressing electrodes 5 of the first network at a zero voltage, alternately applying a zero voltage at each lateral electrode 13, 14 without modifying the voltage of the central electrode 20; thus, this central electrode 20 plays the role of anode throughout the holding phase; the voltage Ve is adapted in a manner known per se to obtain discharges in the previously addressed areas without obtaining them in the unaddressed areas.

After this last maintenance phase, a new addressing and maintenance cycle can resume in a manner known per se for the display of images on an alternating plasma panel with memory effect. Thus, according to an advantageous variant of the invention, all of the selective addressing or erasing operations are transferred to the central electrode; thanks to this improvement, it is possible to group and electrically connect each lateral electrode of a triad to the lateral electrode closest to the adjacent triad on the slab.

These two connected electrodes may even no longer form a single electrode 21, so that the total number of electrodes of the triad network is reduced by a third; thus, the total number of electrodes of the second array of electrodes, or array of coplanar discharges, is identical, except for one electrode, to the total number of electrodes of the coplanar arrays of the prior art, which are arrays of pairs electrodes; the manufacture of the panels of plasma panels and that of the control means according to this variant are therefore no more expensive than that of plasma panels with only two coplanar electrodes of the prior art. We will now describe an embodiment of a plasma panel according to this advantageous variant, with reference to FIGS. 5 and 6 which represent the plasma panel discharge zones, where each pixel P comprises three adjacent discharge zones 9R, 9G, 9B, separated by barriers 16 extending from the dielectric layer 15 of the rear panel carrying the first array of electrodes 5 to the dielectric layer 17 of the front panel carrying the electrode triads 13, 20, 14; the adjacent triads 13, 20, 14 on the one hand and 13 ', 20', 14 '(not shown) on the other hand are separated from each other by barriers 6 orthogonal to the barriers 16; the electrodes 5 of the first network are here offset and positioned under the barriers 16, and are provided with leads 51 positioned at each discharge zone 9R, 9G, 9B, and extending towards the middle of this zone; preferably, the electrodes 5 of the first network are provided with means for promoting the formation of maintenance discharges between each lateral electrode 13, 14 of a triad and the central electrode 20 of this same triad: thus, it is preferably found two branches 51 per discharge zone, positioned on either side of the central electrode 20; the barriers 6, 16 delimit with the dielectric layers 15, 17 discharge cells; the walls of the discharge cells 9R, 9G, 9B, except that of the front panel, are coated with phosphors of different colors, respectively red, green and blue, adapted to emit radiation of these colors when excited by ultraviolet radiation from landfills; in the areas above the electrodes, the dielectric layers are generally coated with a thin layer of protection and emission of secondary electrons, generally based on MgO.

According to the advantageous variant of the invention which has just been described, the lower lateral electrode 14 of the first triad, corresponding to a line n of the panel, is connected to the same bus 22 'as the upper lateral electrode 13' of the second triad, adjacent to the first, corresponding here to the next line (n + 1) of the panel; as each lateral triad electrode is shared between two adjacent lines, if N is the total number of lines of the panel, there are only 2N + 1 electrodes in total in the coplanar network or second network, which simplifies the manufacture of the panel, each electrode being served by a central bus 20, 20 ', or by a side bus 22, 22'; the side buses 22, 22 'are opaque and positioned here at the top of the barriers 6, so as not to obscure the emission of visible light from the discharge zones 9R, 9G, 9B.

A side bus 22 'then forms, with the two side electrodes 14 and 13' to which it is connected, a single and same electrode 21; the whole of the second network of electrodes or network of lines, is formed of alternations of central electrodes 20, 20 ′ which are used for selective addressing or erasing operations, and of electrodes 21, common to two lines adjacent discharge areas, which are not used for selective addressing or erasing operations.

According to the embodiment described in Figure 6, the electrodes 13, 14, 13 'are made of transparent conductive material, for example tin oxide (SnO) or mixed oxide of tin and indium ("ITO "), So as not to absorb the visible light coming from the discharge zones 9R, 9G, 9B. According to an alternative embodiment of the same type of plasma panel shown in Figure 7, the central electrodes 20, 20 'or side 21 are formed of a sub-array of opaque conductors arranged in a grid; for example : - the central electrode 20, 20 ′ comprises two opaque parallel conductors

201, 203 each having a front delimiting one of the gaps and electrically connected to each other by opaque transverse branches 202 arranged at the center of each cell 9R, 9G, 9B; - the electrode 14 supplying the cells 9R, 9G, 9B and the electrode 13 'supplying the cells 9'R, 9'G, 9'B of the neighboring line, both connected to the same bus 22' to form the electrode 21 common to two successive lines, each comprising an opaque lateral conductor 140 having a front delimiting a gap and, arranged parallel to the conductors 201, 203 of the central electrode 20; each lateral conductor 140 is electrically connected to the bus 22 ′ by means of opaque Y-shaped branches, arranged in the center of each cell 9R, 9G, 9B, 9'R, 9'G,

9'B; each Y-shaped lead comprises a main conductor 141 for the "foot" of the Y, and two secondary conductors 142, 143 forming the "branches" of the Y; these branches are connected to the bus 22 'via the “branches” 142, 143, while they are connected at the other end to the lateral conductor 140 via the “feet” 141; such a Y-shaped arrangement of the branches is advantageous for the development of the discharge length during discharge, and, consequently, for the light output of the panel.

The grid arrangement of opaque conductors of the central electrodes 20, 20 'and / or side 21 is more economical, because it avoids the costly implementation of transparent conductive materials, as in the previous embodiment of Figure 6; the conductors and the branches which form the grids are of a width which is sufficiently small to limit the occultation of the cells or discharge zones but sufficiently large to obtain the electrical conductivity necessary for obtaining the discharges.

Other forms of grids can be used, such as that of the electrode 13 of FIG. 7, comprising three parallel conductors 131, 132, 133 interconnected by transverse branches 134 arranged above the barriers 16 to limit the cell occultation.

FIG. 8 represents a variant of FIG. 6 (identical references of the components) with a central transparent electrode 20 whose width is greater than that of each of the side electrodes 13 or 14, and which is further provided with two opaque conductive buses 201, 203 which are arranged at the discharge initiating edges of this electrode; as the thickness of such conductive buses is generally greater than the thickness of the transparent part of the electrode, generally based on ITO, the thickness of the dielectric layer covering these buses is less than the thickness of the dielectric layer covering the transparent part of the electrode; thus, the thickness of the dielectric layer being less at the level of the priming edges of the central electrode relative to the thickness between outside the priming edges, it is possible to advantageously lower the discharge priming voltage, to avoid a matrix start of the discharges, to favor coplanar initiation in accordance with one of the aims of the invention.

FIG. 9 represents a variant of FIG. 7 (identical references of the components) with a central electrode 20 whose width is advantageously greater than that of each of the lateral electrodes 13 or

14; the opaque transverse branches 202 of the central electrode 20 and those 134 of the side electrodes 13, 14 are here arranged on the barriers 16 delimiting the cells; they may extend slightly along these barriers. The present invention has been described with reference to a conventional alternating plasma panel and to a control mode in which the sustaining discharges involve an inversion of charges on the surface of the dielectric; it is obvious to those skilled in the art that it can be applied to other types of display panels and to other control modes without departing from the scope of the claims below; the invention thus applies in particular to plasma panels with high frequency or radio frequency control, where the sustaining discharges are, at least partially, stabilized between the electrodes.

Claims

1.- Method for controlling a plasma panel for viewing alternating current images, with co-planar maintenance discharges, and with memory effect, the said panel comprising: a parallel front panel and a rear panel providing between they a space filled with discharge gas, one of the slabs (12) comprising at least a first network of electrodes (5) and the other slab (11) comprising at least a second network of triads of electrodes (13 , 20, 14) whose general direction is approximately orthogonal to that of the electrodes (5) of the first network, each triad comprising two opposite lateral electrodes (13, 14) and a central electrode (20), - the spaces located at the intersections of the electrodes (5) of the first network and triads of electrodes (13, 20, 14) of the second network electrodes forming a matrix of zones (9) of light discharges and points of the image to be viewed, the electrodes of the triads ( 13, 20, 14) being coated of a dielectric layer (17), said method comprising at least one holding operation by applying a series of holding voltage pulses between the electrodes of each triad so as to generate holding discharges in each of the zones of crossing (9) in which it is desired to maintain a light discharge, characterized in that, during said holding operation, the central electrodes of each said triad (20) always play the role of anode.

2.- Method according to claim 1, characterized in that the width of said central electrode (20) is greater than the gaps separating and isolating the adjacent electrodes of the same triad.

3.- Method according to claim 2, characterized in that the width of said central electrode (20) is greater than 80 microns.

4.- Method according to claim 3, characterized in that the width of said central electrode (20) is between 100 and 200 microns.

5.- Method according to claim 3 characterized in that the width of said central electrode (20) is greater than the width of each of said side electrodes (13, 14).

6.- Method according to any one of the preceding claims, characterized in that it also comprises, before or after each holding operation, a selective addressing or erasing operation applied only in each of said areas where it is desired maintain a light discharge during said series, by applying at least one voltage pulse between the electrode of said first network crossing said zone and at least one of the triad electrodes crossing said zone.

7.- Method according to claim 6 characterized in that said selective voltage pulse is applied between the electrode of said first network crossing said zone and the central electrode of the triad crossing said zone.

8.- Method according to claim 7 characterized in that, all of the zones (9R, 9G, 9B, ...) served by the same triad (13, 20, 14; 13 ', 20', 14 ') forming a line of said panel, on any two adjacent lines crossed respectively by a first triad (13, 20, 14) on the one hand and by a second triad (13 ', 20', 14 ') on the other hand, the lateral electrode (14) of the first triad is electrically connected to the same potential as the lateral electrode (13 ') closest to the second triad.

9. Plasma panel capable of being used for implementing the method according to any one of the preceding claims, comprising: a parallel front slab and a rear slab forming between them a space filled with discharge gas, one of the slabs (12) comprising at least a first array of electrodes (5) and the other slab (11) comprising at least a second network of triads of electrodes (13, 20, 14) whose general direction is approximately orthogonal to that of the electrodes (5) of the first network, each triad comprising two opposite lateral electrodes (13, 14) and a central electrode ( 20), - the spaces located at the intersections of the electrodes (5) of the first array and the triads of electrodes (13, 20, 14) of the second array of electrodes forming a matrix of zones (9) of light discharges and points of the image to be displayed, the electrodes of the triads (13, 20, 14) being coated with a dielectric layer (17), means for controlling the discharges in each of said crossing zones (9) using, in particular, d maintenance operations, characterized in that e said control means are adapted so that, during maintenance operations, the central electrode (20) always plays the role of anode.

10.- plasma panel according to claim 9 characterized in that the width of said central electrode (20) is greater than the gaps separating and insulating the adjacent electrodes of the same triad.

11.- plasma panel according to claim 10 characterized in that the width of said central electrode (20) is greater than 80 microns.

12.- plasma panel according to claim 11 characterized in that the width of said central electrode (20) is between 100 and 200 microns.

13.- plasma panel according to claim 11 characterized in that the gaps separating and insulating the adjacent electrodes of the same triad are less than 80 μm and in that the spacing between the slabs leaving said space filled with discharge gas is greater than 130 μm.

14.- plasma panel according to claim 13 characterized in that the width of said central electrode (20) is greater than 200 microns.

15.- Panel according to any one of claims 11 to 14 characterized in that the width of said central electrode (20) is greater than the width of each of said side electrodes (13, 14).

16.- plasma panel according to any one of claims 9 to 15 characterized in that all of the zones (9R, 9G, 9B, ...) served by the same triad (13, 20, 14; 13 ' , 20 ', 14') forming a line of said panel, on any two adjacent lines crossed respectively by a first triad (13, 20, 14) on the one hand and by a second triad (13 ', 20', 14 ') on the other hand, the lateral electrode (14) of the first triad is electrically connected to the same potential as the lateral electrode (13 ') closest to the second triad.

17.- plasma panel according to claim 16 characterized in that said two electrodes (14, 13 ') electrically connected form an electrode (21) common to two adjacent lines.