EP0414598A1 - Plasma panel display device - Google Patents

Abstract

The present invention relates to a plasma panel display device, the plasma panel being designed in a novel manner which permits in particular simplification of its manufacture and implementation. According to the invention, the plasma panel comprises electrodes (E1, E2) associated in pairs (P1 to P7), the electrodes of a given pair having directly the shape of the figure which it is desired to represent. <IMAGE>

Description

The invention relates to a display device using a plasma panel. It relates in particular to a new structure of plasma panels which in particular makes it possible to simplify manufacture and reduce costs.

Plasma panels are flat screen display devices operating on the principle of light discharge in gases. They are used for viewing alphanumeric, graphic or other images.

Generally the plasma panels include two insulating tiles defining a space filled with gas at low pressure. Most often, each slab has on its internal face a network of parallel conductive electrodes. The tiles are positioned face to face so that the electrode arrays are orthogonal, that is to say that the electrodes of a network called column electrodes are arranged in columns, and that the electrodes of the other network called line electrodes are arranged in lines. The whole is sealed using a sealing joint, a very small and uniform space being maintained between the tiles; this space is filled with a gas mixture, the essential component of which is neon, this gas being chosen for its high luminance in the visible spectrum. The column and line electrodes are crossed so that they define a matrix of gas cells each formed substantially at the intersection of line and column electrodes.

The operating principle is the selective generation (that is to say at the level of selected cells) of electric discharges in the gas. Each discharge in the gas is accompanied by an emission of light which is located at the level of each cell where an electric discharge occurs. Each cell can thus constitute an elementary source of light, the state of which can be changed (on or off): a given figure or shape is visualized by putting a succession of cells in the on state, the location of which in the matrix corresponds to the shape of the figure you want to display.

There are different types of plasma panels, in particular panels of the continuous operating type, and so-called "alternative" panels.

Given the matrix arrangement of the cells, their addressing is matrix, that is to say that for each cell this addressing is carried out by controlling two crossed electrodes at the level of the selected cell. Thus, for example, in plasma panels operating continuously in which each cell is generally defined at the intersection between only a column electrode and only a row electrode, for a given cell, it is necessary to select the column electrode and the row electrode which define this cell and apply between these two electrodes a voltage called "ignition" as long as one wants to obtain an emission of light by this cell thus selected. The ignition voltage is a voltage whose value is equal to or greater than the cell's ignition voltage, the ignition voltage being the minimum voltage to be applied between the two electrodes of a cell to obtain ionization of the gas .

In panels of the alternative operating type, the addressing of a given cell is also carried out by the control of two electrodes which are crossed at the level of this given cell, and which serve to define it. However, these so-called "alternative" panels have certain advantages, one of which is to present a memory effect which makes it possible to address the useful information only to the cell whose state it is desired to change, while the state of the others cells are simply maintained, or maintained (in the case of the on state) by repetition of alternating electrical discharges called maintenance discharges. In this type of panel plasma, the electrodes are covered with a layer of dielectric material, and they are therefore no longer in contact with the gas or with the discharge: consequently, with each discharge, an ionization of the gas causes the storage of electric charges on the insulator covering the electrodes, helping with maintenance discharges, which maintenance discharges are obtained by a maintenance voltage formed by slots which follow one another with opposite polarities.

Under these conditions, the maintenance voltage, applied between the two electrodes, has a value lower than the ignition voltage, and a voltage greater than the ignition voltage is necessary only to modify the state of a cell.

It should be noted that among the plasma panels of alternative type, some use only two electrodes to define a cell, as described for example in a French patent n ° 78 04893 in the name of THOMSON-CSF published under n ° 2 417 848 .

Also known are alternative plasma panels called "coplanar maintenance", in which three or more electrodes are used to form a cell. In this case, most often each cell of the matrix is formed substantially at the intersection between a column electrode with two parallel and coplanar maintenance electrodes, forming a pair of maintenance electrodes. With this type of plasma screen, for each cell the maintenance of the discharges, that is to say the repetition of the alternating electrical discharges previously mentioned, is ensured between the two maintenance electrodes of the same pair, and the addressing a given cell is done by generating discharges between two crossed electrodes at this cell.

Such a plasma panel of the alternative type with coplanar maintenance is shown in FIGS. 1 and 2, in accordance with the teaching of the European patent document EP-A-0135 382. It includes a glass slab 1, covered with a first and a second family of maintenance electrodes 2 and 3 arranged in lines, parallel and coplanar, and arranged in an alternation of an electrode 2 of the first family and an electrode 3 of the second family. Thus a succession of an electrode 2 of the first with an electrode 3 of the second family constitutes a pair of maintenance electrodes used to form the same row of cells. These electrodes are provided with recesses or projections 2a and 3a which, in the same pair of maintenance electrodes, are oriented towards each other so as to concentrate maintenance discharges DE therebetween. The assembly is covered with an insulating layer 4. Addressing electrodes 5 or column electrodes are crossed with the maintenance electrodes 2 and 3; the latter are generally arranged in lines and the addressing electrodes 5 are generally arranged in columns. The assembly is covered with an insulating layer 6 and a protective layer 7 made of MgO. A second slab 8 completes the set. A gas is contained in a space 9 formed between the slabs 1 and 8 held apart by watertight shims (not shown).

The operating principle of a plasma panel of this type is as follows: an address discharge DA is selectively generated at the intersection of a column electrode 5 with an electrode 2 of the first family of a given pair d 'maintenance electrodes (in a pair of maintenance electrodes, electrode 2 provides an addressing function and a maintenance function, and electrode 3 provides only a maintenance function). This addressing discharge results in the storage of electrical charges on the insulator covering these electrodes. These charges are then used to facilitate the maintenance discharges between the two electrodes of each pair. Maintenance discharges are those which provide most of the useful light; they are maintained using voltage slots, slots which are applied between the two electrodes of each pair of maintenance electrodes and which follow one another with opposite polarities. We finds in these plasma screens, as in those of the previous example, the existence of a memory effect which makes it possible to obtain a repetition of maintenance discharges between two electrodes for a cell previously put in the on state , by applying alternating polarity maintenance voltages to all the cells, and this without modifying the "on" or "off" state of each cell by the fact that the maintenance voltage is lower than the voltage of priming.

All these types of plasma panels have, to varying degrees, very significant advantages compared to other display means or displays of the flat screen type, for example: robustness, very long service life, quality of the display that we now know how to combine very strong contrast (good readability under any lighting up to 100,000 Lux). These qualities are certainly interesting, but they are expensive because of the technology used in plasma panels, but also because of the importance and the complexity of the electronic means necessary to control these panels.

The present invention relates to a display device using a plasma panel with a new structure, a structure which makes it possible to conserve and even increase the advantages mentioned above specific to continuous to alternative plasma panels, and which leads to a considerable simplification, in particular a significant reduction in the number of electrodes, resulting in both a technological simplification and a simplification of the electronic control means.

According to the invention, a display device by plasma panel, comprising means for producing an ignition voltage, the plasma panel comprising at least two electrodes between which the ignition voltage is applied, is characterized in that the two electrodes constitute a pair of electrodes, and in that these two electrodes extend substantially in the same general direction so as to define between them a discharge zone in the form of a figure to be represented.

By the expression "extend substantially in the same general direction", we want to define two electrodes which together reproduce the shape of the figure to be displayed and are not used to form a single point of this figure. These two electrodes can be coplanar as well as contained in different planes and can be parallel, but they are not crossed, unlike the cases of the prior art where an ignition voltage is always applied between two crossed electrodes or more precisely orthogonal.

In the present invention, the fact that a pair of electrodes is formed by associating two electrodes which extend substantially in the same general direction, and the fact that a potential difference is applied between these two electrodes which constitutes an ignition voltage, the useful length of such a pair of electrodes, that is to say the length over which a discharge can be carried out, can have directly the shape of the image or of the figure that the '' we want to display.

In addition, in the case where several pairs of electrodes are used, the selected pairs of electrodes can be controlled directly, that is to say without having to carry out an addressing matrix selection as is the case in prior art.

• - les figures 1 et 2 déjà décrites de rapportent à un panneau à plasma de l'art antérieur ;
• - la figure 3 illustre de manière schématique une forme de réalisation préférée d'un panneau à plasma conforme à l'invention ;
• - la figure 4 montre des créneaux de tension à appliquer à des paires d'électrodes montrées à la figure 3 dans le cas où ces dernières sont du type fonctionnant en alternatif ;

The invention will be better understood, and other advantages which it provides, as well as other particularities which characterize it, will appear on reading the description which follows, given by way of nonlimiting example with reference to the appended figures, among :

• - Figures 1 and 2 already described relate to a plasma panel of the prior art;
• - Figure 3 schematically illustrates a preferred embodiment of a plasma panel according to the invention;
• - Figure 4 shows voltage slots to be applied to pairs of electrodes shown in Figure 3 in the case where the latter are of the type operating in alternating mode;

FIG. 3 schematically shows a display device 10 according to the invention. The display device 10 comprises a plasma panel 11 and control means 16, 20, 21 of this plasma panel.

The plasma panel 11 is of a new type, and according to a characteristic of the invention it comprises at least one pair P1 to P7 of electrodes formed by two electrodes E1, E2 which extend one near the another on a length called useful length L1, so that this useful length draws the figure to be displayed.

In the nonlimiting example of the description, the display panel 11 comprises several pairs of electrodes, in fact 7 pairs P1 to P7 each intended to produce a plasma display which in the nonlimiting example described is a segment, this in the context of a display of the type with 7 segments which makes it possible to represent a digit from 0 to 9 by the choice of the segments which are made visible; these segments being arranged to form the number 8.

Of course, the plasma panel 11 may include many more of these pairs of electrodes P1 to P7, or have only one, and also the figure produced by such a pair of electrodes may be different and be sufficient. to itself.

Each pair P1 to P7 has first and second electrodes E1, E2, and the two electrodes of each pair are intended to be constructed to be associated, that is to say to function together so as to constitute a discharge cell whose a dimension is given by the useful length L1 of each pair of electrodes P1 to P7. The useful length L1 of each pair P1 to P7 represents the length of a discharge zone ZC (symbolized by a hatched surface at the level of the first pair P1), that is to say of a zone of light whose visible form is substantially that of the pair P1 to P7 which is activated or lit.

In the nonlimiting example described, the two electrodes E1, E2 of each pair P1 to P7 are parallel and they are coplanar, that is to say that they are carried by the same rear panel 12 (as is the case of the maintenance electrodes 2, 3 carried by the same panel 1, in the alternative plasma panel with coplanar maintenance of the prior art shown in FIGS. 1 and 2.)

Aside from the shape, connection and arrangement of the electrodes E1, E2 which constitute the pairs P1 to P7, the structure of the plasma panel 11 of the invention can be compared to that of a conventional plasma panel such as by example shown in Figure 1, and it includes: a second slab called front slab 13 (which corresponds to the slab marked 8 in Figure 1), which in Figure 3 is located in a shallower plane than that of the rear slab 12; a gas mixture is contained between the two tiles 12, 13; and in the case of alternating operation, the electrodes E1, E2 can be covered in a conventional manner with a dielectric material (not shown) which isolates them from the gas and from the discharge by means similar to those used in the prior art.

In this configuration, the segments which make it possible to constitute the pairs P1 to P7 are seen through the front panel 13.

It should be noted that the two electrodes E1, E2 which constitute a pair P1 to P7, are not necessarily coplanar: in fact, for each of the pairs P1 to P7, the first electrode E1 can for example be carried on the rear panel 12 and the second electrode E2 can be carried by the front panel 13. In the latter case, they can be arranged so that, seen through the front panel 13, they appear as if they were coplanar; but they can also be arranged so that their surface either fully or partially opposite, in which case the second electrode E2 is seen through the first electrode E1, and it is preferable that the latter is transparent.

The electrodes E1, E2 of each pair P1 to P7 are connected to the control means 16, 20, 21 which control the on or off state of each of the pairs of electrodes P1 to P7 contained in the plasma panel 11.

The control of the on or off state of a pair P1 to P7 is obtained by applying or not applying an ignition voltage to the selected pairs P1 to P7, this ignition voltage being applied in a " direct "; the term "direct" being used as opposed to the case of the prior art in which the switching on or off of a given cell is obtained by superimposing, by matrix addressing, a voltage pulse on voltage slots which are applied to all cells.

The control means comprise a voltage generator 16 which produces an ignition voltage VA. The ignition voltage is a direct voltage if the electrodes E1, E2 are in contact with the gas, and this ignition voltage and an alternating voltage if the electrodes E1, E2 are isolated from the gas by a dielectric material, it is ie if the plasma panel 11 is of the alternative type. Assuming that the panel 11 is of the alternative type, the voltage generator 16 can be formed using a simple oscillator assembly (not shown) and it can deliver, by a first output 17, a succession of voltage slots CT which, with respect to a reference voltage VR delivered by a second output 18, follow one another with opposite polarities.

The voltage slots CT are applied to the electrodes E1, E2, via a control circuit 20 whose function is to connect the electrodes E1, E2 of the pairs P1 to P7 selected to the generator 16 of ignition voltage. Such a function is in itself conventional and it can be performed in a large number of different ways, depending on the particular characteristics sought; this function has has been symbolized in the figure by connecting the output 17 of the voltage generator 16 to one of the electrodes of each pair P1 to P7, by means of a switch I1 to I7 for each pair P1 to P7. The switches I1 to I7 can for example be in themselves conventional MOS type transistors, each controlled by a coding device 21 as symbolized by links 22 in dotted lines, the coding device 21 having the function of determining the segments or pairs P1 to P7 which should be lit to form the desired figure.

In the nonlimiting example described, to facilitate and simplify the electrical connection of the pairs of electrodes P1 to P7, at least one of the two electrodes E1, E2 of a pair is connected to an electrode of at least one other of these pairs of electrodes. Thus, in the example of FIG. 3, the second electrodes E2 of the first four pairs of electrodes P1, P2, P3, P4 are connected together in the plasma panel 11 by internal connection conductors Ci and leave this the latter by a first common link LC1, and the second electrodes E2 of the fifth, sixth and seventh pairs P5, P6, P7 are also connected to each other and leave the panel 11 by a second common link LC2; this, in contrast to the first electrodes E1 which are each supplied by a particular connecting conductor CL. The two common links LC2 are connected to the second output 18 of the voltage generator 16, a second output which delivers the reference voltage VR.

The switches I1 to I7 are each connected by a first side 24 respectively to the first electrode E1 of each of the pairs P1 to P7; the other side 25 of all the switches I1 to I7 is connected to the first input 17 of the voltage generator 16.

Under these conditions, it suffices to close the switch I1 to I7 corresponding to the pair or pairs P1 to P7 selected to apply the ignition voltage VA to these selected pairs and cause them to ignite (the absence of ignition voltage at Moon of these pairs causes its extinction).

Of course, one or more pairs of electrodes P1 to P7 can be used for different displays than that of the 7-segment type, and can be applied in a particularly advantageous manner to indoor or outdoor displays, especially in large letters and / or large numbers, for example sports displays, motorway traffic signs, etc.

Such applications, of the general public type, are facilitated with a display device in accordance with the invention because the new design of the plasma panel 11 makes it possible to simplify the technology, and to simplify the implementation and consequently of reduce manufacturing and operating costs.

In technology:
- It is possible to free the front panel 13 from all electrodes, so that the function of this front face 13 is reduced to that of a simple sealing surface with possibly an optical quality suitable for the intended use, by example for surface quality, filtration or coloring. In addition, the discharge zones or light zones of such a display can be of a relatively large surface (larger than cm 2) compared to what is known in the prior art for plasma panels, also a micro-defect on the surface of the front panel 13 may not be considered as prohibitive on the final product, and allows for example to integrate directly during manufacture a front face with a desired optical quality as mentioned above.

On the other hand, such a display is formed of electrodes E1, E2, the surface of which can be very large and which therefore can be easily produced in large series, in particular by screen printing.

In addition, a display panel 11 according to the invention can also produce a display in the range of colors. blue, red, green, it suffices for this for example to have one or more layers of phosphors on the front face 13.

In terms of implementation: this implementation is simplified compared to the traditional plasma panel, by the fact that all the "matrix addressing" part is eliminated. If the two electrodes E1, E2 of each pair P1 to P7 are arranged in a coplanar manner, they do not however use the conventional memory effect of an alternating plasma panel. It is therefore no longer necessary to have complicated voltage signals, with superposition of voltage slots as in a conventional plasma panel, but simply to have voltage slots having a sufficient amplitude to create the discharge, that is to say ie having a value equal to or greater than the ignition voltage; and under these conditions a simple oscillator therefore proves sufficient to constitute the voltage generator 16 which produces the ignition voltage VA.

It should be noted that for each pair P1 to P7, an electrode E1 or E2 can be used to constitute two pairs of electrodes, and that these two pairs of electrodes can be actuated either simultaneously or separately. For greater clarity in FIG. 3, this embodiment is illustrated on the latter by only an additional electrode Ea which in the example is associated with the second electrode E2 of the fourth pair P4, to form an additional pair Pa d ' electrodes; this additional electrode Ea is disposed along this second electrode E2 and opposite the first electrode E1 of this same fourth pair P4. The additional electrode Ea is connected to an additional switch IA, itself connected to the output 17 of the voltage generator 16.

It is thus possible, by closing the additional switch IA, to illuminate the additional pair Pa formed by the additional electrode Ea and the second electrode E2 of the fourth pair P4; it is also possible, as before, to obtain the illumination of the fourth pair P4 by closing the fourth switch 14, but it is also possible to set the simultaneously on state, the additional pair and the fourth pair Pa, P4, by simultaneously closing the additional switch IA and the fourth switch I4. Such an arrangement can be applied to the other pairs of electrodes P1 to P7, and it allows in particular to modify the luminance of a figure. However, this arrangement can also be applied advantageously in the case where phosphors (not shown) are arranged facing these pairs of electrodes: for example, the front panel 13 can carry a strip of phosphors in vis-à-vis the additional pair Pa and carry a strip of phosphors opposite the fourth pair P4, for example a strip of phosphors 31 emitting in the green for the fourth pair P4 and a strip of phosphors 30 emitting in red for the additional pair Pa. Thus by closing the fourth switch I4 we obtain a green color and by closing the additional switch IA we obtain a red color, and by closing these two switches, we obtain yellow. A similar arrangement can be applied to the other pairs of electrodes.

FIG. 4 illustrates by way of nonlimiting example, the shape of the ignition voltage to be applied to the electrodes E1, E2 of a pair P1 to P7 to be ignited. The ignition voltage is constituted by pulse trains TI1, TI2 each formed by slots of voltages CT +, CT- which follow one another with opposite polarities with respect to the reference voltage VR. The voltage slots have a positive and negative amplitude respectively + VA and -VA sufficient so that at each voltage transition from + to - or from - to +, a discharge is created in itself known. The intensity of the discharge can be adjusted by modifying the amplitude of the voltage slots between a maximum amplitude or value + VM, -VM and a minimum value + Vm, - Vm (minimum value which corresponds to the ignition voltage) ; it can also be adjusted with the number of voltage slots between two successive pulse trains TI1, TI2.

As mentioned above, the principle of electrodes associated in pairs can be applied in the case of display other than of the 7-segment type, and each pair P1 to P7 can define a figure different from that of a segment. straight. A pair P1 to P7 makes it possible in particular to represent a line of any straight, curved, sawtooth shape, etc., provided that such a shape is given to the discharge zone ZC (shown in FIG. 3) that this pair. The shape of the discharge zone ZC is in turn defined by the two electrodes E1, E2 which constitute this pair, these two electrodes being considered together and having similar shapes, the discharge zone ZC is delimited on the one hand by external longitudinal edges BL1, BL2, and on the other hand end edges BE1, BE2 of the two electrodes E1, E2 of the same pair.

With regard to the delimitation of the zones ZC, it should be noted that one can avoid an extension of the discharges, along the conductors CL, LC1, LC2 (in the case in particular where the ignition voltage is high), in realizing physical barriers made of dielectric material which each make it possible to isolate an electrode E1, E2, from its supply conductor, in a conventional manner in itself. A tell barrier is symbolized in FIG. 3 with the reference 60, at the level of the second pair P2 where it isolates, on the plane of the discharge, the first electrode E1 from its connection conductor CL. Such a barrier 60 extends perpendicular to the conductor on which it is placed, with a length greater than the width (not shown) of the conductor; and, between the two slabs 12, 13, the barrier 60 has a height substantially equal to the thickness (not shown) that the gas comprises between these two slabs.

In the nonlimiting example shown in FIG. 3, each of the pairs of electrodes P1 to P7 is intended for represent a figure which forms a segment of a complete figure, so that the pairs of electrodes P1 to P7 constitute the same group of electrodes, but of course, in accordance with the invention, the plasma panel 11 can comprise pairs of electrodes (or groups of pairs of electrodes) each intended to form a distinct figure although being in the same enclosure constituted by the tiles 12, 13.

In the case illustrated by the additional electrode Ea which makes it possible to form the pair of additional electrodes Pa, it can be seen that the second electrode E2 is common to the additional pair Pa and to the fourth pair P4. It should be noted, however, that this configuration is very different from that which sometimes exists in a liquid crystal display device, because in addition to the differences in operation due to the differences in physical phenomena involved, in the configuration of the invention the electrode is common to only two pairs which define the same figure or same image area, and which in the example of FIG. 3 serve to constitute the same segment. In the liquid crystal type display device, a single very large electrode is used, carried on a slab, and which cooperates with as many individual electrodes as there are segments to be represented, these individual electrodes being laid on the opposite slab opposite the very large surface electrode. Consequently, in the liquid crystal display device, one of the two electrodes of each segment is merged with one of the two electrodes of all the other segments, while in the configuration of the invention all the electrodes are physically distinct from each other.

Claims (7)

1 - Display device by plasma panel, comprising means (16) for producing an ignition voltage, the plasma panel (11) being of the alternating type and comprising at least two electrodes (E1, E2) between which is applied the ignition voltage, characterized in that the two electrodes (E1, E2) constitute a pair (P1 to P7) of coplanar electrodes, and in that they extend substantially in the same general direction so as to together define a discharge zone (ZC) having the shape of a figure to be represented. 2 - Display device according to claim 1, characterized in that the plasma panel (11) comprises several pairs of electrodes (P1 to P7, Pa). 3 - Display device according to one of the preceding claims, characterized in that the electrodes (E1, E2) of the same pair (P1 to P7, Pa) are substantially parallel. 4 - Display device according to one of the preceding claims, characterized in that it comprises a control circuit (20) by means of which a first electrode (E1) of each pair (P1 to P7) is connected individually at a first outlet (17) means (16) which produce the ignition voltage. 5 - Display device according to claim 4, characterized in that the second electrodes (E2) nde each pair (P1 to P7) are interconnected and are connected to a second output (18) means (16) which produce ignition voltage. 6 - Display device according to one of the preceding claims, characterized in that at least one electrode (E1, E2) of at least one pair (P1 to P7) of electrodes is common to two pairs of electrodes , the common electrode (E2) cooperating with an additional electrode (EA) connected to the means (16) to produce the ignition voltage via the circuit control (20), so as to constitute two pairs of electrodes (PA, P1 to P7) for the same figure to be represented, one or the other or the two pairs of electrodes being able to be activated. 7 - Display device according to one of the preceding claims, characterized in that the ignition voltage is applied to the two electrodes (E1, E2) of the same pair of electrodes (P1 to P7, Pa) of a "direct" way.

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