EP0457637A1 - Method for controlling the luminance of an AC plasma panel - Google Patents

Abstract

The method of the invention makes it possible especially to act on the luminance by line with a view to creating localised overbrightnesses or underbrightnesses. The method consists in controlling a "written" state or an "erased" state of cells (C1 to C36) arranged in n lines (L1 to L4), then in applying hold signals to the cells with a view to activating the cells in the "written" state. According to one characteristic of the invention, the method consists in inhibiting transmission of one or more hold signals (SE, SAE) to the cells of at least one line (L1 to L9), in such a way as to reduce the luminance of this line with respect to the other lines. <IMAGE>

Description

The invention relates to a method for adjusting the luminance of a screen of the alternating plasma panel type, making it possible in particular to act by lines or by bands in order to create localized highlights or sub-glosses of the screen.

Plasma panels of the alternative type, called in the following description "PaP.Ac", have a memory property which makes it possible to dissociate the addressing functions (command to write or erase information), maintenance of light discharges which is used to produce most of the useful light. Also, a conventional method of adjusting the overall luminance of the screen consists in adjusting the frequency of maintenance signals which carry out the maintenance of the discharges, maintenance by which cells in the "registered" state produce light.

The operation and structure of "PaP.Ac" are in themselves well known. The panels are for example of the type with two crossed electrodes to define a discharge cell, as described for example in a French patent in the name of THOMSON-CSF published with the number 2.417.848; addressing discharges and maintenance discharges being carried out between two same electrodes. These panels can also be of the coplanar maintenance type, with for example three electrodes crossed to define a cell, so that addressing discharges and maintenance discharges can take place between different electrodes, as described in particular in a European patent application EP-A-0135 382 and in a French patent application published with the number 2 629 265.

In "PaP. Ac" with coplanar maintenance or not, the addressing of a given cell (that is to say its recording or its deletion) is carried out by the selection of the two corresponding crossed electrodes, to which we apply voltage slots suitable for creating, between these two electrodes, a potential difference such that it generates a writing or erasing discharge.

A classic addressing method consists in operating line by line: in this case all the cells of a line are controlled to be put all in the same state, the "erased" state for example (semi-selective operation) and this operation is followed by a selective operation during which one or more selected cells of this same line are "registered".

The semi-selective and selective operations are carried out for each line during an addressing phase, with a time offset from one line to the next line which corresponds to the duration of a line cycle.

In each line cycle, generally the addressing phase is followed by a specific maintenance phase, so that, for each cell line, between two consecutive addressing phases, the cells in the "registered" state are activated by the service signals.

It should be noted that generally the addressing by semi-selective and selective operation and carried out by superposition of addressing slots on basic slots, as explained for example in the French patent applications in the name of THOMSON-CSF n ° 88 11 248 and No. 88 11 247, the latter patent application to be considered as part of this description.

Taking as examples the "PaP Ac" with coplanar maintenance, these panels generally comprise an array of electrodes called column electrodes, whose function is only an addressing function and which are crossed with pairs of maintenance electrodes; each pair being formed an address-maintenance type electrode having an addressing function plus a maintenance function, and an electrode having only a maintenance function. Each crossing of a column electrode with a pair of electrodes defines a cell, such that the cells are arranged in rows and columns; each row of cells corresponds to a pair of maintenance electrodes.

Selective addressing is carried out between a column electrode and a addressing-maintenance electrode; semi-selective addressing (an entire line) can be carried out between the two electrodes of the same pair. Maintenance discharges are obtained by applying maintenance signals to two electrodes of the same pair.

Usually maintenance is ensured by simultaneously creating, or at least at close times, a rising front on one of the electrodes, the addressing-maintenance electrode for example and a falling front on the maintenance only electrode: these two variations are added and generate a maintenance discharge. This is generally obtained using cyclic voltage slots which are applied to the two electrodes of the same pair with opposite polarities and which constitute the maintenance signals.

Thus voltage slots are permanently applied to all cell lines, slots which form maintenance signals during the maintenance phases, and which constitute basic slots during the addressing phases; Address slots (registering or deleting) are superimposed on these basic slots only on the address-maintenance electrode of the addressed line. The basic slots have substantially the same amplitude as the slots for maintenance signals, so that they can generate at least one light discharge.

It should be noted that the maintenance addressing electrodes are individualized, whereas on the contrary the maintenance only electrodes simultaneously receive identical slots and are generally connected together.

• soit globalement (pour l'ensemble de l'écran) en jouant sur la fréquence des signaux d'entretien ; les luminances de chacun des points sont alors les mêmes : elles sont proportionnelles à la fréquence d'entretien ;
• soit point par point, par tramage temporel comme décrit par exemple dans les brevets français publiés avec les n° 2 519 170 et n° 2 536 565 ; on obtient ainsi des niveaux intermédiaires de luminance (appelés "teintes de gris" ) qui permettent dans les images affichées des effets de dégradé ou, dans le cas par exemple de menus informatiques, la présentation de zones uniformes à luminance réduite.

In "PaP. Ac", the luminance is usually adjusted in two distinct and complementary ways:

• either globally (for the whole screen) by playing on the frequency of the maintenance signals; the luminances of each of the points are then the same: they are proportional to the frequency of maintenance;
• either point by point, by time screening as described, for example, in the French patents published with No. 2,519,170 and No. 2,536,565; intermediate luminance levels are thus obtained (called "shades of gray") which allow in the displayed images gradient effects or, in the case for example of computer menus, the presentation of uniform zones with reduced luminance.

These two methods do not make it possible to obtain, in a simple manner, intermediate cases, such as the adjustment of the luminance by bands or by packets of lines.

The method of the invention is simple to implement and it applies as well to the adjustments of the luminance in the intermediate cases mentioned above as to adjust the overall luminance.

The process of the invention also finds a particularly interesting application in polychrome "PaP. Ac", for color balancing.

According to the invention a method for controlling an alternative plasma panel, said panel comprising a plurality of cells arranged in rows and columns, the method consisting in controlling the "written" or "deleted" state of the cells and applying maintenance signals to the cells so as to activate the cells in the "registered" state, is characterized in that it consists in inhibiting the transmission of one or more maintenance signals to the cells of at least one line so as to reduce the luminance of this line.

• la figure 1 montre de manière schématique, et à titre d'exemple non limitatif, un panneau à plasma alternatif auquel peut s'appliquer le procédé conforme à l'invention ;
• les figures 2a, 2b, 2c illustrent le fonctionnement d'un panneau à plasma coplanaire fonctionnant sous la commande du procédé de l'invention ;
• les figures 3a à 3e illustrent les possibilités offertes par le procédé de l'invention ;
• les figures 4a, 4b, 4c illustrent l'application du procédé de l'invention à la commande d'un panneau à plasma à deux électrodes croisées pour définir une cellule.

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

• Figure 1 shows schematically, and by way of nonlimiting example, an alternative plasma panel to which the method according to the invention can be applied;
• Figures 2a, 2b, 2c illustrate the operation of a coplanar plasma panel operating under the control of the method of the invention;
• Figures 3a to 3e illustrate the possibilities offered by the method of the invention;
• Figures 4a, 4b, 4c illustrate the application of the method of the invention to the control of a plasma panel with two crossed electrodes to define a cell.

FIG. 1 shows an alternative plasma panel 1 to which a preferred mode of the method of the invention can be applied.

In the nonlimiting example described, the panel 1 is of the coplanar maintenance type. It comprises a network of column electrodes X1 to X4 which are crossed in a conventional manner with pairs of maintenance electrodes P1 to P9 arranged in rows. Each pair P1 to P9 of electrodes comprises an address-maintenance electrode Y1 to Y9 and a maintenance-only electrode E1 to E9: the address-maintenance electrodes Y1 to Y9 fulfill an addressing function on the one hand in cooperation with the column electrodes X1 to X4 and, on the other hand, a maintenance function with the maintenance-only electrodes. Consequently, these address-maintenance electrodes Y1 to Y9 must be individualized and they are each connected to a separate output of a line 3 address register, which delivers SAE signals useful for addressing and maintenance. .

The maintenance only electrodes E1 to E9 only provide a maintenance function, they can therefore all be connected to the same output of a pulse generator 4, from which they receive maintenance signals SE.

The column electrodes X1 to X4 provide an addressing function, they are therefore individualized and each connected to a separate output of a column addressing register 5 delivering addressing signals SA.

The operating commands and the synchronization of the two address registers 3, 5 and of the generator 4 are managed in the traditional way by a control device 12.

Each crossing of a column electrode X1 to X4 with a pair P1 to P9 of electrodes defines a cell C1 to C36, the cells thus being arranged in rows L1 to L9 and in columns.

In the nonlimiting example of the description, only 4 columns X1 to X4 and 9 pairs P1 to P9 forming 9 rows L1 to L9 are shown, which define a screen of 36 cells, but in the spirit of the invention different numbers rows and columns can be used and the screen can have many more rows, for example 480, 1,000 or more.

In a first version of the method of the invention, a characteristic of the method consists in eliminating, that is to say in not applying, to at least one line L1 to L9 of cells, the maintenance signals SE delivered by the pulse generator 4; this being obtained by not applying these maintenance signals to the corresponding maintenance-only electrode E1 to E9.

If these signals are not applied to the electrodes E1 to E9 solely for the maintenance of all the lines L1 to L9, the maintenance discharges are eliminated and therefore the luminance of the screen is reduced overall; and this luminance is increased overall when we reapply these signals.

If we do not act on all the lines of the screen, but only on some of them, for example grouped in packets, we obtain localized effects of under-highlighting or highlighting.

For example, if the second, third, seventh and eighth maintenance-only electrodes E2, E3, E7 and E8 are not supplied with maintenance signals, maintenance discharges do not occur for the cells formed by the pairs P2, P3, P7, P8 i.e. the lines L2, L3, L7, L8. The cells of these lines produce less light and constitute areas of under-brightness on the screen, compared to the lines of cells L1, L4, L5, L9 which are normally supplied.

Thus, by removing the maintenance signals applied to certain maintenance-only electrodes, the coplanar maintenance for the corresponding lines L1 to L9 is eliminated, and the light produced by the cells of these lines is then due only to the discharges produced between the column electrodes X1 to X4 and the addressing-maintenance electrodes Y1 to Y9.

To obtain a localized highlight, for example of lines L2, L3, L7, L8, it is necessary to act in the opposite way, by applying the maintenance signals to these lines L2, L3, L7, L8 and by not applying it other lines L1, L4, L5, L6, L9.

These two luminance levels can be obtained in a simple manner, for example by actuating a simple switch I1 placed between the pulse generator 4 and the solely maintenance electrodes E1 to E9, whereas until now it was known to act on maintenance signals in a complex way by varying the frequency of these signals.

In fact, in the method of the invention, the maintenance signals SE are not suppressed but their transmission to the cells is inhibited.

The passage from one luminance level to the other can be done globally for the whole screen, it suffices to cut the general transmission of the maintenance signal SE or to establish it using the switch I1 for example.

The luminance modifications can also be carried out in packets of one or more contiguous lines as already explained above, for lines whose positions are predetermined or not.

In the case of predetermined lines, these lines can be separated from the others, and for example connect them by the same packets to the generator 4 by means, for example, of a second switch I2 for each packet, as shown in FIG. 1 with the maintenance lines E3, E4 only.

Another method consists in implanting only maintenance electrodes for the lines L1 to L9 which are desired to be brighter. For example, if it is expected that the second and third lines L2, L3 will be brighter, only the second and third maintenance-only electrodes E2, E3 are implanted and not the others.

It is also possible to act in software, with the possibility of action on all lines L1 to L9 or only some of them. For this purpose, it is possible to have in series with all the maintenance only electrodes E1 to E9, an electronic switching element, a transistor T1 to T9 for example (symbolized by a frame in dotted lines). These switching elements are connected (in a manner which is not conventional in itself) to the control device 12, by which the electrons are chosen only for maintenance electrodes E1 to E9 to which maintenance signals SE will be applied.

Another interesting possibility offered by the method of the invention applies to the adjustment of the colors of a polychrome panel. In fact, if cells of the same colors are grouped together in the same maintenance-only electrode packets, each color can be given two levels of intensity.

For example: the cells of lines L1, L4, L7 can correspond to the blue color B; the cells of lines L2, L5, L8 in the color red and the cells of lines L3, L6 and L9V in the color green. If these three groups of lines are connected to generator 4 each via a switch (not shown), two intensity levels can be obtained for each color.

The fact of not transmitting to some or all of the maintenance only electrodes E1 to E9, the maintenance signals SE delivered by the generator 4, has the effect of reducing the potential difference generated between the two electrodes of the pairs P1 to corresponding P9, that is to say to reduce the amplitude of the rising or falling edges previously mentioned, to the point that no discharge occurs between these two electrodes.

Also, according to another version of the method of the invention, the above-mentioned effect is obtained by acting on at least one of the address-maintenance electrodes Y1 to YE9 by not transmitting to this electrode a part SAE signals useful for maintenance.

FIGS. 2a, 2b and 2c to be read at the same time, illustrate by way of nonlimiting example the maintenance signals applied to the pairs P1 to P9: FIG. 2a represents the signals SAE applied to the address-maintenance electrodes Y1 to Y9; FIG. 2b represents the signals SE applied to the maintenance only electrodes E1 to 9 and FIG. 2c illustrates the differences in potential SAE-SE generated between the two electrodes of the same pair P1 to P9 by the application of these signals or of one of these signals.

At an instant t0: the signal SAE is at a potential + V1 stable, positive with respect to a reference voltage VR; the signal SE is at a stable potential -V2 negative with respect to the reference voltage VR; the SAE-SE potential difference is positive with a value + V3 equal to the sum of the voltages V1 and V2 (V3 = V1 + V2).

At an instant t1, the signal SAE goes to a negative potential -V1 and generates a negative variation of the potential difference SAE-SE which goes to a value V5 corresponding to V2-V1 (V5 = V2 - V1).

At an instant t1 ′ which follows and which is close to instant t1, the signal SE reverses and passes from the negative voltage -V2 to a positive voltage + V2, which generates a new negative variation of the difference SAE- SE which passes to a negative value - V3, variation which is added to that already produced at time t1 and which generates a discharge of maintenance (not illustrated).

At time t2, the signal SE reverses and goes to -V2, which causes a positive variation of the difference SAE-SE which goes to the value V5 (V5 = V2 - V1).

At an instant t2 ′ close to t2, the signal SAE goes from -V1 to + V1 and causes a new positive variation of the difference SAE-SE which goes to + V3, from which results a new maintenance discharge.

At time t3, there are variations comparable to those produced at time t1: the signal SAE goes to -V1 and the difference SAE-SE goes to the value V5.

In conventional operation, at a time t3 ′ close to time t3, a positive square wave of the signal SE (represented by dotted lines) must occur which must cause the same effects at that time t3 ′ and at a time t4 as those mentioned for times t1 ′ and t2.

If, in accordance with the invention, this voltage square wave of the signal SE is not transmitted to one or more maintenance electrodes E1 to E9, the maintenance discharges of the instants t3 ′ and t4 are eliminated for the pairs P1 to P9 corresponding. Indeed, because at each of these instants t3 ′ and t4 there is only one edge coming from the SAE signal, the maintenance is "truncated" and if the voltages are correctly adjusted, the light discharge is not not produce.

Also, the difference signal SAE-SE is maintained at the value V5 (V5 = V2 - V1) from the instant t3 until an instant t4 ′ where it changes to + V3, due to the positive variation of the signal SAE which then went to + V1.

This does not affect the proper functioning of the discharge cell in the next cycle (the memory necessary for proper functioning is preserved) and we can find at times t5, t5 ′, t6, t6 ′ which follow the same operation as at times t1, t1 ′, t2, t2 ′.

However, as mentioned above, it is possible to act in a similar manner at the address-maintenance electrodes Y1 to Y9, by not transmitting the SAE signal to one or more of these electrodes in a manner to generate one or more successive "truncated interviews", the inhibition of the transmission of the SAE signal then being carried out for example directly in the address register line 3.

Thus in the prior art, the instant t8 ′ would correspond to a positive variation of the signal SAE from -V1 to + V1, and the following instant t9 would correspond to a negative variation of this signal from + V1 to -V1, these variations being shown in Figure 2a in dotted lines. However, in accordance with the invention, this signal is not applied to at least one of the addressing-maintenance electrodes Y1 to Y9, so that for the corresponding pair P1 to P9 a "truncated maintenance" is carried out: there is no there are no light discharges at the instant t8 ′, that is to say that the difference SAE-SE remains at the value V5 = V2 - V1 from an instant t8 to an instant t10 despite the existence of variations of the signal SE at time t8.

Of course, the principle of "truncated maintenance" by the SAE signal applied to the address-maintenance electrodes can apply to the entire panel. But it can also be applied selectively electrode by electrode, or packet by packet of electrodes: we find all the possibilities already mentioned above with regard to electrodes only maintenance, but with greater ease for finer adjustments by adjusting the number of edges removed.

FIGS. 3a to 3e illustrate by way of nonlimiting example a case where the maintenance, for three pairs of electrodes P1, P2, P3 for example, is carried out differently for each pair by playing on the signals SE applied to the electrodes only for maintenance E1, E2, E3.

FIG. 3a represents addressing signals SA applied to the column electrodes X1 to X9; FIG. 3b represents the SAE signals applied simultaneously and in the same way to all the address-maintenance electrodes Y1 to Y9; FIGS. 3c, 3d, 3e respectively represent signals SE1, SE2, SE3 applied to the first, second and third electrodes only for maintenance E1, E2, E3.

The transmission of the maintenance signals SE1 to the electrode E1 has been totally inhibited: in this case the light discharges from line L1 are reduced to those generated only between the column electrodes and the address-maintenance electrodes, and the luminance of this line is minimum, for example Lmin equals 30 cd / m².

The maintenance signals SE2 transmitted to the second electrode only for maintenance E2 are at the maximum number, and consequently, the luminance of the second line L2 is maximum, for example Lmax equal 100 cd / m².

The maintenance signals SE3 transmitted to the third electrode only for maintenance E3 are in an intermediate number, 2 of 5 for example: in this case the luminance of the third line L3 is equal to the minimum luminance Lmin + 2/5 of Lmax-Lmin, i.e. 58 cd / m².

It should be noted that the invention can also be applied to non-coplanar panels, that is to say to panels comprising only two electrodes crossed to form a cell. Such a plasma panel could be represented by FIG. 1 by removing all the maintenance-only electrodes. For such a plasma panel, the line electrodes would be grouped for example into two packets, one of which would receive the maximum number of maintenance signals and the other of which would receive 2 signals out of 5, the lines with higher luminance would for example have 30 cd / m² and the lines with lower luminance would have about 12 cd / m².

But in the case of these panels with two electrodes per cell and unlike the case of coplanar panels, the luminance adjustment per line interferes with the addressing function: insofar as the addressing function is provided by the same type of 'electrodes than the one on which the elimination of maintenance fronts relates, it is necessary that the adjustment of the maintenance takes place outside the addressing cycles.

The addressing cycles represent in practice a significant part of frame time, for example, for a screen of 480 lines refreshed every 20 ms, the addressing occupies approximately 480 x 20 µs / line, or 9.6 ms which represent 48% of the total time. As a result, the possibilities for adjusting the maintenance are relatively limited. This constraint can be circumvented by inserting maintenance cycles of reduced duration between the addressing phases.

Figures 4a, 4b, 4c illustrate such an organization, which can be applied particularly, but not exclusively, in the case of alternative plasma panels with two crossed electrodes per cell.

FIG. 4a represents SX addressing signals applied to the column electrodes. FIG. 4b represents addressing signals and maintenance signals applied to a line electrode, corresponding to a line Li for which the maximum luminance is desired. FIG. 4c shows addressing and maintenance signals applied to the line electrode of a following line Li + 1 for which a reduced luminance is desired.

In the signals applied to each of the lines, there are addressing phases PA between which are inserted maintenance phases PE.

In a manner which is in itself conventional, each addressing phase comprises a basic erasure slot CBe within an erasure cycle CE, followed by an enrollment cycle CI comprising a basic slot CBi registration. The addressing phases PA1, PA2 have a duration of the order of 20 µs and in the case for example of a panel of 480 lines, the time available for the PE maintenance phases is 21.6 µs; this authorizes a maximum of 4 consecutive maintenance cycles CS1 to CS4 each having a shorter duration than an erasure or CE registration cycle, C1, which allows 5 levels of luminance.

In the case of the line Li (FIG. 4b), it is assumed that the first addressing phase PA1 is used for addressing this line, and consequently and in a conventional manner, on the one hand, an erasure pulse IE is superimposed on the erasure slot Cbe and, on the other hand, a registration pulse Ii is superimposed on the basic inscription slot CBi. The first addressing phase PA1 is followed, for the line Li, by the 4 maintenance cycles CS1 to CS4. Then the maintenance phase PE1 is followed by a second addressing phase PA2, and so on.

In the nonlimiting example shown in FIG. 4c, the line Li + 1 also sees the addressing phase PA1, followed by a maintenance phase PE1, itself followed by a second addressing phase PA2, etc ...; the addressing of the line Li + 1 being carried out during the second addressing phase PA2.

According to the invention, in order to reduce the luminance of the line Li + 1, the number of maintenance cycles CS1 to CS4 transmitted is less than that which is transmitted for the line Li.

Of course, this last version of the process of the invention can also apply to the case of panels with polychrome plasma, to electronically balance colors.

It should be noted that the names of "row" and "column" given to the electrodes do not necessarily prejudge the horizontal or vertical orientation of these electrodes, even if most often a horizontal row of cells is called "row".

Claims (10)

1 - Method for controlling an alternative plasma panel, said panel (1) comprising a plurality of cells (C1 to C36) arranged in rows (L1 to L9) and in columns, the method consisting in controlling the "registered" state "or the" erased "state of the cells and to apply maintenance signals to the cells so as to activate the cells in the" registered "state, characterized in that it consists in inhibiting the transmission of one or several maintenance signals (SE, SAE) to the cells (C1 to C36) of at least one line (L1 to L9) so as to reduce the luminance of this line. 2 - Method according to claim 1, characterized in that it consists in inhibiting the transmission of maintenance signals to several lines (L1 to L9) or packets of lines so as to constitute zones having different luminances. 3 - Method according to claim 2, characterized in that it consists in inhibiting the transmission of signals (SE, SAE) simultaneously to several lines (L1 to L9) and differently between at least two lines. 4 - Method according to claim 1, characterized in that it consists in inhibiting the transmission of maintenance signals (SE, SAE) in the same way for all the lines (L1 to L9) of the panel (1). 5 - Method according to one of the preceding claims, the plasma panel being of the coplanar maintenance type having addressing-maintenance electrodes (Y1 to Y9) and only maintenance electrodes (E1 to E9), characterized in that that it consists in intervening on the transmission of the maintenance signals (SAE) applied to the address-maintenance electrodes. 6 - Method according to one of the preceding claims, the plasma panel being of the coplanar maintenance type comprising column electrodes (X1 to X4) crossed with addressing-maintenance electrodes (Y1 to Y9) and with maintenance-only electrodes (E1 to E9), characterized in that it consists in intervening in the transmission of the maintenance signals (SE) applied to the electrodes maintenance only (E1 to E9). 7 - Method according to claim 6, characterized in that it consists in providing at least one line (L1 to L9) with lower luminance and in carrying out this line with only a crossed addressing-maintenance electrode (Y1 to Y9) with the column electrodes (X1 to X4). 8 - Method according to claim 6, characterized in that it consists in having at least one switching element (10) in series with the supply of maintenance signals of at least one maintenance-only electrode (E1 to E9). 9 - Method according to any one of claims 1 to 4, characterized in that the plasma panel is of the type with two crossed electrodes to define a cell. 10 - Method according to one of the preceding claims, characterized in that the plasma panel is of the polychrome type comprising cells having at least two different colors, and in that it consists in arranging the cells so that each line ( L1 to L9) is formed by cells of the same color.

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