FR2851073A1 - PLASMA DISPLAY DEVICE HAVING DRIVING MEANS ADAPTED FOR REALIZING FAST EQUALIZATION OPERATIONS - Google Patents

Abstract

Conventionally, the control means are suitable for generating charge equalization operations, then addressing, then maintenance; the invention results in the sharing of charge equalization operations into two successive steps: a step P1 for generating space charges and metastables, o a step P2 for the accelerated end of generation of charges, during which one operates in low discharge mode between the electrodes E1, E2 serving at least for addressing. Thanks to this sharing, it is possible to shorten the charge equalization operations, improve the luminous performance of the panel and / or the manufacturing yields of the plasma panels.

Description

The invention relates to a display device comprising a panel with

  plasma, of the reciprocating memory-effect type, with crossed electrodes serving at least for addressing, optionally provided with coplanar electrodes for at least the maintenance, and control means for this panel adapted to carry out operations of equalization of loads, addressing and maintenance in the discharge areas of this panel.

  An alternative plasma memory (PDP) display panel generally comprises two parallel slabs providing between them a space containing a discharge gas; between the slabs, generally on the internal faces of these slabs, such a panel comprises several electrode arrays: - generally two crossed electrode arrays, each arranged on a different slab and therefore not coplanar, and used for the addressing of discharges, at the intersections of which are defined, in the space between the slabs, zones of light discharges, and at least two parallel coplanar electrode arrays, arranged on the same slab and serving for the maintenance of discharges; these networks are covered with a dielectric layer, in particular to provide a memory effect; this dielectric layer is itself covered with a protective and secondary electron emission layer, generally based on magnesia.

  Each electrode of a maintenance network forms with an electrode of the other maintenance network a pair of electrodes delimiting between them a succession of zones of light discharges, generally distributed along a line of discharge zones. of the panel.

  The areas of light discharges form, on the panel, a two-dimensional matrix; each zone is capable of emitting light so that the matrix displays the image to be displayed.

  Generally, one of the coplanar electrode arrays serves both addressing and maintenance. In this particular case, this electrode array X, the second network of coplanar electrodes, and the orthogonal addressing electrode array Y and X will be referred to hereafter as the other. The X and Y electrode arrays thus serve lines of discharge zones, whereas the electrode network A serving only for addressing serves columns of discharge zones.

  Adjacent discharge areas, at least those that emit different colors, are generally delimited by barriers; these barriers are generally used as spacers between the slabs.

  The walls of the light discharge zones are generally partially coated with phosphors sensitive to ultraviolet radiation from the light discharges; adjacent discharge areas are provided with phosphors emitting different primary colors, so that the association of three adjacent areas forms a pixel or pixel.

  In practice, these luminophores cover the slopes of the barriers and the slab bearing these barriers, which is generally the slab carrying the electrode array used only for addressing; the address electrodes are therefore covered with phosphors.

  When the plasma panel is in operation, to display an image, a succession of displays or sub-displays is performed using the discharge zone matrix; each sub-display generally comprises the following steps: - firstly, a selective addressing step which aims to modify the electrical charges on the dielectric layer in each of the discharge zones to be activated, by applying at least one voltage pulse between the addressing electrodes intersecting in these areas; - then, a non-selective maintenance step during which a succession of voltage pulses is applied between the electrodes of the maintenance pairs so as to cause a succession of light discharges only in the zones of discharges which were previously activated.

  At the end of a sub-display, the discharge zones may be in very different states of internal electrical voltages, especially depending on whether or not these zones have been activated during this under-display; other factors contribute to this dispersion of internal stress states, such as the nature of the phosphors corresponding to these zones, the inevitable fluctuations in the dimensional characteristics of these discharge zones, the fluctuations in the surface composition of the walls of these zones, which are related to panel manufacturing processes.

  In order to homogenize the state of the internal voltages of the discharge zones to be addressed, most of the addressing steps are preceded by a step of equalizing these zones, which essentially aims to put all the discharge areas to be addressed in a same internal voltage state, whether or not they were enabled during the previous sub-display; this equalization step 10 (called "reset" in English) conventionally comprises an operation of forming electric charges ("priming" in English) followed by a charge adjustment operation also called "erasing" of these charges at the end of which, ideally, the internal voltages within each discharge zone are close to the ignition thresholds between electrodes for addressing and between maintenance electrodes.

  For each pair of addressing or maintenance electrodes of a discharge zone, it is possible to associate an external voltage applied between these electrodes and an internal voltage in the gas space separating the materials which cover these electrodes. The internal voltage generally differs from the external voltage due to the surface charges which are on the surface of the insulating materials covering the electrodes, at the interface between these dielectric materials and the gas of the discharge zone.

  These surface charges result on the one hand from a capacitive effect related to the dielectric properties of the materials which delimit the discharge zones, on the other hand from an accumulation of so-called "memory" charges produced by the preceding discharges in the gas of these areas of discharge.

  The internal ignition threshold of a discharge zone in a given direction corresponds to an internal voltage limit value along this direction above which the gas ionizes in this zone. This value depends on the characteristics of the gas in this zone, those of the materials in contact with the gas in this zone, and the geometry of the electrodes passing through this zone outside this zone.

  In the particular case described above of three arrays X, Y, A of electrodes, six values of internal thresholds are generally associated with each discharge zone: * an internal ignition threshold between X anode and Y cathode: VIT xy 5. an internal ignition threshold between X cathode and Y anode: VIT YX * an internal ignition threshold between X anode and A cathode: VIT XA * an internal ignition threshold between X cathode and A anode: VITAX * an internal threshold ignition between Y anode and A cathode: VITYA * an internal ignition threshold between Y cathode and A anode: VIT AY The terms anode and cathode are relative to the internal potentials in the gas of a discharge zone in the vicinity of the electrodes passing through this zone: it is said that one electrode is anode relative to another if the potential in its vicinity in the gas is greater than that in the vicinity of the other electrode, this other electrode then being relatively cathode.

  The two following internal thresholds have the same value because they characterize co-planar discharges that are generated by electrodes carried by the same slab and arranged generally symmetrically with respect to each other: VIT XY = VIT YX noted VIT S The two following internal thresholds, which characterize the discharges in matrix mode, therefore between two different slabs, are however different depending on whether the electrode considered plays the role of anode or cathode: VITXA = VITYA noted VITA_ca VIT-AX = VITAY noted VIT_A_an Indeed, when the address column electrode A is in cathode, the secondary emission of the phosphor covering it being lower than that of magnesia on the surface of the dielectric covering the electrode line X or Y, discharges occur at higher voltages than when it is in the anode.

  Generally: during a charge formation operation (priming), each electrode serving both addressing and maintenance Y is at anode with respect to the other two electrodes X and A; during a charge adjustment operation (erasure), each electrode serving both for addressing and for maintenance Y is in cathode relative to the other two electrodes X and A. These operations are generally carried out by applying a difference of 5 slowly increasing potential on the one hand between the two coplanar maintenance electrodes and on the other hand between the two matrix addressing electrodes of all the discharge zones of a group to be addressed; documents FR 2417848 (THOMSON-1978) and US 5745086 (PLASMACO-1998) thus describe the application of ramped voltage signals to the electrode or electrodes 10 serving both for addressing and for maintenance during the application of a constant voltage signal to the other electrodes only addressing and only maintenance.

  US Pat. No. 5,745,086 shows that the operations of equalizing the zones of a panel are thus advantageously effected in each zone, without a strong discharge but with a series of so-called "weak" discharges between the electrodes when the slope of the signal in Applied ramp does not exceed 10 V / ps.

  These "weak" discharges compensate for the increase in external voltage applied to the electrodes by a deposition of surface charges on the walls of the zones served by these electrodes, and since there is no "strong" discharge, the voltage internal gas in these areas remains equal to or slightly less than the internal ignition threshold previously defined.

  The known advantages of low discharge equalization or "reset", also known as "positive resistance equalization", are to allow precise adjustment of the internal electrical voltages within the discharge areas by producing a low light emission. Accurate adjustment is essential to the performance and efficiency of the subsequent addressing operation. Limiting this light emission is essential for the contrast performance of the display device.

  The maximum slope of the ramp signal producing small discharges in a discharge zone is related in particular to the characteristics of the materials covering the cathode of this zone, in particular to the secondary emission coefficient of these materials, and to the quantity of charges. space and metastable elements in the gas of this area. The commonly used slope values do not exceed 5 V / ps for the priming operation where the Y electrode is at anode relative to the X and A electrodes. The total amplitude of the ramp commonly covers 200 V, the duration priming therefore reaches several tens of microseconds. This time represents time lost for the other operations to be performed during a scanning or sub-scanning, namely addressing and maintenance, which limits the performance of the display device, especially at its maximum level. resignation. In addition, certain panels may be rejected at the output of production because they have operating defects related to the existence of large discharges during the priming ramp with the usual values of slope, which increases by the same the production cost Signs.

  An object of the invention is to limit these disadvantages; the invention also aims to shorten the duration of these operations of equalizing the discharge zones or "reset" without diminishing the efficiency, ie while preserving the level of equalization of the different zones discharge.

  To this end, the subject of the invention is a display device comprising: an alternating plasma memory effect panel comprising two slabs 20 forming between them a space containing a discharge gas and two networks of crossed electrodes serving at least one to the addressing, at the intersections of which are defined in the space between the slabs, areas of light discharges, - control means adapted to apply to said electrodes voltage signals adapted to perform operations intended to equalize the loads in said discharge zones, characterized in that said control means are adapted so that, during specific equalization operations of a set of discharge zones, if each discharge zone of the panel has an external voltage (VET E2E1) matrix ignition threshold between the electrodes serving at least for addressing and crossing said zone, if Min [VETE2EI] and MaX [VETE2EIl are r espectively the minimum value and the maximum value of the matrix ignition voltage (VETE2EI) of the zones of said assembly, the potential difference VE2EI applied between the electrodes serving at least for the addressing and crossing said zones of this set increases, therefore 5 that VE2E1 has exceeded the value 1.1 x MaX [VETE2E,] during said equalizing operation, according to a so-called end-of-operation slope which is greater than the maximum growth slope of VE2E1 during the instants o VE2EI is between Min [VETE2E1J and MaX [VETE2E1l] The invention then corresponds to the case 1 or 1st embodiment described in more detail below.

  The object of the invention is also, according to the same principle, a display device comprising: a reciprocating plasma memory effect panel comprising two plates 15 forming between them a space containing a discharge gas, two networks of crossed electrodes at least for addressing, at the intersections of which are defined in the space between the slabs areas of light discharges, at least two arrays of electrodes serving at least for maintenance and arranged so that each discharge zone is traversed by one of the electrodes of each of these networks, - control means adapted to apply to said electrodes voltage signals adapted to perform so-called equalization operations for equalizing the charges in said zones of discharge, characterized in that said driving means are adapted so that during specific operations of equalizing a set of zones if each discharge zone of the panel has an external matrix ignition threshold voltage (VETEA2EA1) between the electrodes serving at least the addressing and crossing said zone, if Min [VETEA2EAI1 MaXIVET EA2EA1] are respectively the minimum value and the maximum value of the matrix ignition voltage (VETEA2EA1) of the zones of said assembly, if each discharge zone of the panel has an external voltage (VET ES2ESI) ignition threshold said coplanar between the electrodes serving at least to maintenance and crossing said zone, if Min [VETES2ES1] and MaX [VETES2ES1] are respectively the minimum value and the maximum value of the coplanar ignition voltage (VETES2ES1) of the zones of said set, - or the potential difference VEA2EA1 applied between the electrodes 5 serving at least for addressing and crossing said zones of this set does not exceed the value Min [VETEA2EA1] as long as the potential difference VES2ESI applied between the electrodes serving at least for maintenance and passing through said zones of this assembly do not exceed the value MaX [VETES2ESI] and grow according to a positive end-of-operation slope since the potential difference VES2ESI applied between these electrodes at least for maintenance has exceeded the MaX value [VETES2ESI], - the potential difference VEA2EA1 applied between the electrodes serving at least for addressing and crossing said zones of this set increases, since the difference in potential VES2ES1 applied between the 15 electrodes serving at least for maintenance and passing through said zones has exceeded the MaX value [VETES2ES '], according to a positive end-of-operation slope which is greater than the maximum growth slope of VEA2EA1 during the instants o VES2ES1 is between Min [VET ES2ES11 and MaX [VETES2ES1]; The invention then corresponds, either to the case 2 or the second embodiment described in more detail below, or to the case 3 or 3 embodiment described in more detail below.

  Generally, the control means are adapted to perform moreover: - selective addressing operations to selectively enable or disable discharge zones; they are performed by applying voltage pulses between the electrodes for at least addressing; non-selective maintenance operations for triggering discharges only in the previously activated discharge zones of the panel; they are performed by applying voltage pulses between the electrodes for at least maintenance.

  Such a panel is called "memory effect" because, during maintenance periods, discharges occur only in areas that have been previously activated; for this purpose, at least one of the electrodes at least one of the electrodes, which is at least for maintenance purposes, is coated with a dielectric layer which is itself covered with a protection and emission layer. secondary electrons.

  The dielectric layer provides the memory effect which allows, during maintenance operations, to trigger discharges only in the zones 5 activated; the protective layer is generally magnesia-based and has a high secondary electron emission coefficient, higher than the secondary electron emission coefficient of the material coated at each discharge zone; one of the electrodes which serves at least for addressing, this material being generally a phosphor.

  Preferably, the control means are adapted so that, during said specific charge equalization operations, in each zone of said assembly, the electrode covered with the protective layer serves as anode; the specific operations of equalization of charges are then operations of formation of charges, or of "priming" in English language; it is not therefore in this case adjustment operation or erasing charges, o this electrode covered with the protective layer generally acts on the contrary the role of cathode.

  Each equalization operation generally concerns a group of discharge zone lines of the panel, or even all of the lines; these operations are usually initiated before a selective addressing operation.

  By matrix ignition is meant the triggering of discharges between electrodes serving at least for addressing, and by coplanar ignition the triggering of discharges between electrodes serving at least for maintenance.

  In the case where the panel comprises coplanar electrode networks 25 carried by the same slab, these electrodes are used at least for maintenance; the other slab usually carries a network of electrodes mainly used for addressing, or in addition to the triggering of maintenance discharges; preferably in this case, one of the electrode arrays serving at least the addressing is merged with one of the electrode arrays serving at least the maintenance, and forms one of the arrays of coplanar electrodes; it is then this electrode array that serves as anode during the charge formation operations.

  Conventional coplanar plasma panels of the prior art are then used.

  In the case where the panel does not include coplanar electrode arrays, maintenance operations are generally performed by applying voltage pulses between electrodes also for addressing; the panel then generally comprises two electrode networks 5, one on each slab; alternatively, the maintenance operations could be performed by applying a radiofrequency field in the discharge areas, in which case the electrodes of the panel are only used for addressing.

  Thanks to the invention, it is possible to shorten the time required for the equalization operations, to devote additional time to the maintenance operations and thus to improve the luminous performances of the panel.

  Thanks to the invention, it is possible to appreciably improve the manufacturing yields of the plasma panels by reducing the rejection rates.

  Preferably, the end of operation and growth slope of the potential difference between the electrodes serving at least the addressing is greater than V4fis.

  Thus, as soon as all the matrix ignition thresholds have been crossed in case 1, as soon as all the coplanar ignition thresholds have been crossed in cases 2 or 3, the equalization operations take place much more quickly than in the prior art without losing anything on the quality of these operations and without risking strong discharges detrimental to the contrast; we can then devote more time to other piloting operations, including maintenance, which improves the display performance, especially in the case of viewing video images.

  Preferably, the end of operation and growth slope of the potential difference between the electrodes serving at least for addressing is greater than 10 V / gts. The performance of the device and the advantages of the invention are further improved.

  Preferably, in the case 2 or 3, while VES2ES1 is between Min [VETES2ES1] and MaX [VETES2ESI] during said equalization operations, the potential difference VES2ES applied between the electrodes serving at least the maintenance increases according to a so-called start of operation slope which is greater than 5 V / ris, preferably greater than 10 V / ps. The performance of the device and the advantages of the invention are further improved.

  Preferably, during each of said specific charge equalization operations, the potential difference (VE2E1; VEA2EA1) applied between the electrodes serving at least the addressing is homogeneous and strictly increasing when Minivet E2E1] <VE2E1 <MaX [VETE2E1], or that Min [VETEA2EAI] <VEA2EA1 <MaX [VETEA2EA1]. Strictly increasing homogeneous growth is understood to mean nonzero growth. Preferably, this growth is linear with time; we are therefore left with linear voltage ramps applied to one of the electrode networks, which is easier to implement.

  Preferably, in the case 2 or 3, during each of said specific operations of equalizing charges, the potential difference (VES2ES1) applied between the electrodes serving at least the maintenance is homogeneous strictly increasing when Min [VETES2ES1] <VES2ES1 <MaX [VETES2ES1] Strictly increasing homogeneous growth is understood to mean nonzero growth. Preferably, this growth is linear with time; we are therefore left with linear voltage ramps applied to one of the electrode networks, which is easier to implement.

  The following is a summary of the principles underlying the invention applied to "priming" operations in English: * To achieve a low discharge mode with the highest slope value As is possible between two electrodes for addressing E1 and E2, or EA1 and EA2, E1 or E11 being cathode, the initial level of conditioning of the discharge areas is raised before applying a strong slope signal between these electrodes.

  The invention therefore results in two successive steps within a single charge equalization operation: a step P1 of generation of space and metastable charges obtained by discharges or a step P2 of accelerated completion of generation of charges, corresponding to the homogenization of these charges, during which one operates in 5 mode of weak discharges between the electrodes serving at least to address El and E2, or between EA1 and EA2, with the highest possible slope , usually greater than 10 V / ps.

  The invention is applicable to plasma panels having different cell or discharge zone structures, for example of the "ACM", "ACC", or "ACC3E" type.

  * In case 1 applicable to any type of matrix panel type "ACM" with two electrodes El, E2 per cell, or ACC with 3 or more electrodes per cell (including EA1 and EA2), step PI consists of application of a low slope ramp for a time sufficient to generate discharges between the two electrodes El and E2 (EA1 and EA2 respectively), regardless of the previous state of the cells. This low slope value corresponds in fact to the slopes commonly used in the prior art, less than 10V / ps. The discharges E1-E2 (respectively EA1-EA2) thus produced serve both for conditioning the cell and for a part of the homogenization of the internal voltage to the cell, between the electrodes E1 and E2 (EA1 and EA2, respectively). ).

  * In cases 2 and 3 applicable to coplanar panels of "ACC" type comprising at least three electrodes EA1, EA2 = ES2, ES1 per cell, step PI consists in the application of a slope ramp stronger than in the prior art, generally greater than 10 V / ps between the coplanar electrodes of the cell, ES1 being in the cathode being covered with a secondary emission coefficient material greater than that covering EA1, and ES2 being EA2 (case of the standard "ACC": EA1: column, EA2 = ES2 = line "scan / sustain", ES1 = line "common"). The ES1-ES2 coplanar discharges thus produced serve both for conditioning the cell and for some of the homogenization of the internal voltage between ES1 and ES2. Cases 2 and 3 are distinguished as follows: o Case 2: no discharge occurs between EA1 and EA2 during step Pi, the ignition voltage not being exceeded internally between these electrodes. This can be achieved with various signals between EAI and EA2 (constant, ramp, or others) as long as the ignition threshold is not exceeded. During this step P1, the weak coplanar discharges are triggered and the low matrix discharges are prevented, the amplitude of the ramped signal applied to the matrix not exceeding the matrix threshold voltage at any moment.

  o Case 3: Dot discharges occur between EAI and EA2 during step PI concurrently with coplanar discharges between ESI and ES2. In this case, the slope of the signal between EA1 and EA2 must be low to allow operation in low discharge mode while a sufficient level of conditioning of the cell is not yet achieved. In this case, the slope of the signal between EAI and EA2 is less than that between ES1 and ES2.

  * Step P2 is characterized by the application of ramp signal higher slope than in the prior art, generally greater than 10V / ps, between EA1 and EA2. It does not matter, at this point, what happens between the other electrodes.

  * The steps P1 and P2 can optionally be separated by a period without discharge into the cell (for example if the applied voltages cease to grow temporarily). This period must not exceed 20 ps for the conditioning effect created during PI to be active during P2.

  The embodiments described are deduced from these general principles and from the conditions of generation of discharges between electrodes specific to each cell of the panel as related to: o variable ignition thresholds according to the cells o in the state of the surface memory charges depending on the history of the cell (on or off previously).

  The invention will be better understood on reading the description which will follow, given by way of nonlimiting example, and with reference to the appended figures in which: FIG. 1 describes a timing chart for the application of potential differences between the electrodes of a matrix panel during a charge generation operation according to a first embodiment of the invention; FIG. 2 describes a timing diagram for applying potential differences between the electrodes for addressing and between the electrodes for maintaining a coplanar panel during a charge generation operation according to a second embodiment. of the invention; FIG. 3 depicts a timing chart for applying potential differences between the electrodes for addressing and the electrodes for servicing a coplanar panel during a charge generation operation according to a third embodiment. of the invention; FIG. 4 is a general time chart of application of voltage to the three electrode arrays of a conventional coplanar panel during a charge creation operation, to illustrate, according to the detailed example given in the description, the interest of the invention compared to the chronograms of the prior art; FIGS. 5 to 7 describe the strong discharges that are unfortunately obtained when applying to the three electrode arrays voltages according to a fast timing diagram but outside the scope defined by the invention; - Figure 8 illustrates the advantage provided by the invention, namely the absence of strong discharges while applying a fast timing to the three electrode networks.

  Various general embodiments of the invention will now be described; the first embodiment applies to so-called "matrix" plasma panels which comprise only two electrode arrays E1, E2, one on each slab, which serve both for addressing and for landfill maintenance; the other embodiments apply to "coplanar" type plasma panels which comprise two maintenance electrode arrays ES1, ES2 on the same coplanar slab and two addressing electrode arrays, EA1 on the so-called facing slab opposite the coplanar slab and EA2 on the coplanar slab. These other embodiments apply to conventional coplanar panels where a coplanar electrode array serves both addressing and maintenance, which means that EA2 is then confused with ES2.

  The electrodes which are used for maintenance, E2 or ES1 and ES2, are coated with a dielectric layer itself covered with a material such as magnesia having a high coefficient of secondary electron emission, in any case more high that the material covering the electrodes El or EA1 of the addressing tile; the material covering the electrodes E1 or EA1 is generally a luminophore; by extension, the slab supporting these electrodes 10 and the magnesia layer is called a maintenance slab, or coplanar slab in the case of coplanar panels.

  A matrix panel includes a large number of discharge areas; after a scanning or sub-scanning of images, each zone of the panel has an external ignition threshold voltage, VETE2E1 in the case of a charge creation operation o E2, of the maintenance panel, plays the anode role. Min [VET E2E1] is called the minimum ignition voltage value of all the zones of the panel, and Max [VET E2E1] the maximum ignition voltage value of all the zones of the panel.

  A coplanar panel has a large number of landfill zones; after a scanning or sub-scanning of images, each zone of the panel has a matrix ignition threshold external voltage, VETEA2EA1, and an external coplanar ignition threshold voltage, VETES2ES1, this in the case of an operation of creation of charges o EA2 and ES2, of the coplanar slab, play the role of anodes. We call Min [VETEA2EAI] and Min [VETES2ES1I] the minimum value of, respectively, the matrix ignition voltage and the coplanar ignition voltage of all the zones of the panel, and MaX [VET EA2EA1] and MaX [ VETES2ES1] the maximum value of, respectively, the matrix ignition voltage and the coplanar ignition voltage of all the zones of the panel.

  All embodiments of the invention presented below relate to charge creation or priming operations; according to an essential characteristic of the invention, each of these operations comprises a step Pi called start of creation of charges and conditioning, duration -c, followed by a step P2 called accelerated end of creation of charges, duration t2, the duration separating the end of the first step and the beginning of the second step should not exceed 20 ts if one wants to take full advantage of the conditioning of the discharge zones in the second step P2.

  Referring to FIG. 1 to describe the charge generation operations of a matrix panel, the following external voltages are distinguished successively between the electrodes E2 (anode) and E1 (cathode): VE2EIPPST at the beginning of step Pi VE2ElP2_ST at the beginning of step P2, VE2E1_P2_-ND at the end of step P2.

  Referring to FIGS. 2 and 3 to describe the charge creation operations of the coplanar panels, the following external voltages 15 are successively distinguished between the addressing electrodes EA2 (anode) and EAI (cathode) on the one hand, and between the maintenance electrodes ES2 (anode) and ES1 (cathode) on the other hand: VEA2EA1_PIST and VES2ESlPIST at the beginning of step PI, - VEA2EA1_PLND and VES2ES1 pl ND at the end of step PI, 20 - VEA2EA1_P2_ST and VES2ES1lP2_ST at the beginning of step P2, - VEA2EA1_P2_ND and VES2ESlP2_ND at the end of step P2.

  In order to simplify the description, in the various embodiments, identical references are used for the elements which provide the same functions.

  1st embodiment: case of a matrix or coplanar panel.

  Referring to Figure 1, the two steps P1 and P2 are defined as follows: - VE2EI PI ST <Min [VET E2EIV; thus, at the beginning of step Pi, the ignition threshold of the discharges is not exceeded in any of the cells of the panel regardless of their state of charge resulting from operations during previous scans or subscans; preferably, VE2EI_PIST> 0.9 x Min [VETE2E1], so that weak discharges are started in areas of the panel from the beginning of the conditioning step PI; - VE2E-_PIND> Max [VETE2E1]; thus, the ignition threshold of the discharges is exceeded in each cell of the panel at the end of the conditioning step PI, regardless of their state of charge resulting from previous operations, so as to create an initial packaging; preferably, VE2E1_-PND <1.1 x MaX [VET E2E1], so as not to unnecessarily prolong the period PI of slow growth potential and to start as soon as possible period P2 rapid growth potential; - VE2ElP2_ST = VE2E1__ pND, so that the two stages PI and P2 are linked without transition; - VE2ElP2_ND is defined identically to the prior art, ie so as to obtain, at the end of step P2, the desired level of charge formation in all discharge areas of the panel.

  During the step P1, the speed of growth of the potential VE2E1 between the electrodes, or the instantaneous value of the slope dVE2E1 / dT, is in accordance with the prior art, ie less than 5 V4is for the whole duration c this step; conversely, according to the invention, during step P2, the growth velocity of the VE2EI potential between the electrodes, or the instantaneous value of the slope dVE2E1 / of n is much greater than the prior art during any the duration 2 of this step, preferably greater than 10 V / bts.

  Overall, according to the invention, the potential between the electrodes grows much faster at the end of the charge generation period, during step P2, than at the beginning of this period, during step P1; the time of the charge creation operations is then very substantially reduced without any loss in the quality of these operations.

  2nd embodiment: case of a coplanar panel.

  With reference to FIG. 2, the two steps PI and P2 are defined as follows: - VES2ES1_PIST <Min [VET ES2ES1]; thus, at the beginning of step Pi, the ignition threshold of the coplanar discharges is not exceeded in any of the cells of the panel regardless of their state of charge resulting from previous operations; preferably, VES2ES1_P1_ST> 0.9 x Min [VETES2ES1], so that weak coplanar discharges are started in areas of the panel from the beginning of step P1; - VES2ES1I_ P ND> MaX [VETES2ES1]; thus, at the end of step P1, the ignition threshold of the coplanar discharges is exceeded in each cell of the panel, whatever their state of charge resulting from the previous operations, so as to create an initial conditioning; preferably, VES2ES1 Pl ND <1.1 x MaX [VETES2ES1], so as not to unnecessarily prolong the period P1 and to start the P2 period as soon as possible; - VEA2EA1_P1 <Min [VETEA2EA1], which means that, at each instant T of the conditioning step P1, the potential difference between the electrodes for the addressing VEA2EA1_P1 is kept lower than Min [VET EA2EA1], so there is no matrix discharge in the panel during this step; Note that this inequality is verified at any time P1, knowing that VET EA2EA1 can vary during P1 depending on the charges created in the vicinity of the electrodes.

  - VEA2EAIP2_ ST <Min [VETEA2EA1]; thus, at the beginning of step P2, the firing threshold of the matrix discharges is not exceeded in any of the cells of the panel regardless of their state of charge resulting from previous operations; Preferably, VEA2EA1 P2 ST> 0.9 x Min [VET EA2EA1], so that weak matrix discharges are started in areas of the panel from the beginning of step P2.

  - VEA2EAI P2 ND is defined identically to the prior art, ie so as to obtain the desired charge formation level in all the discharge zones of the panel.

  During step P1, the growth rate of the potential VES2ES1 between the maintenance electrodes, or the instantaneous value of the slope dVEs2EsIl / dtc is much greater than the prior art, preferably greater than 10 V / ps; during this step P1, the growth rate of the potential VEA2EA1 may be zero, low or high, provided that this potential remains below Min [VET EA2EAI].

  During step P2, the growth rate of the potential VEA2EA1 between the addressing electrodes, or the instantaneous value of the slope dVEA2EAI / d-c is much greater than the prior art, preferably greater than 10 V / ps; during this step P2, the growth rate of the potential VES2ESI may be zero, low or high.

  Overall, according to the invention, the charge creation operation is carried out by exceeding all the coplanar discharge thresholds before starting to exceed the first matrix discharge threshold, so that a conditioning of the gas is obtained before start the dot dumps; this is advantageous because the coplanar discharges take place on the high secondary electron emission coefficient material which coats the electrodes of the coplanar slab, thereby generating weak coplanar discharges ES1-ES2 with a steep slope during step PI; the packaging thus produced during this step P1 then makes it possible to generate, during step P2, EAI-EA2 weak matrix discharges with a greater slope than in the prior art, despite the generally poor secondary emission properties of the material, generally the luminophores, which covers the electrodes 15 of the address plate, this material being used here in cathode; thanks to the invention, it is thus possible to very substantially reduce the time of charge creation operations or to obtain proper operation with panels having poor phosphor secondary emission properties without losing the quality of these operations. 3rd embodiment: case of a coplanar panel.

  This embodiment differs from the previous one in that "limited" matrix discharges are "tolerated" during the coplanar conditioning period.

  With reference to FIG. 3, the two steps P1 and P2 are defined as follows: - VES2ESI_PIST <Min [VETES2ES1] and VEA2EA1_PIST <Min [VETEA2EA1] thus, at the beginning of step Pi, the ignition threshold of the discharges, coplanar or matrix, is not exceeded in any panel cells regardless of their state of charge resulting from previous operations; preferably, VES2ES1I P ST> 0.9 x Min [VET ES2ES1] and / or VEA2EA1_PIST X 0.9 x Min [VETEA2EAI], so that discharges, coplanar or matrix, start from the beginning beginning of step PI; VES2ESIPND> MaX [VETES2ESI] and VEA2EAIPIND> Min [VETEA2EAI]; thus, at the end of step PI, the ignition threshold of the coplanar discharges is exceeded in each cell of the panel whatever the state of charge resulting from the preceding operations, as well as the ignition threshold of the matrix discharges in all or part of these cells, so as to create an initial conditioning; - VEA2EA1_P2_ND is defined identically to the prior art, ie so as to obtain the desired level of charge formation in all discharge areas of the panel.

  During step P1, the rate of growth of potential VES2ES, between the maintenance electrodes, or the instantaneous value of slope dVES2ES, / dr is much greater than the prior art, preferably greater than 10 Vffs; during this step PI, the rate of growth of the potential VEA2EAI is in accordance with the prior art, ie less than 5 V / fis.

  During step P2, the growth rate of the potential VEA2EA1 between the addressing electrodes, or the instantaneous value of the slope dVEA2EA1 / d-r is much greater than the prior art, preferably greater than 10 V4ts; during this step P2, the growth rate of the potential VES2ESI may be zero, low or high.

  Thanks to the invention, it is thus possible to very substantially reduce the time of charge creation operations or to obtain correct operation with panels having poor phosphor secondary emission properties without losing the quality of these operations.

  4th embodiment: case of a coplanar or matrix panel.

  This mode provides that the conditioning generated during PI is created in all or part of the cells by a strong discharge, and in the other cells by weak discharges. This is not the preferred mode unless the heavy discharge is a maintenance drain.

  5th embodiment: case of a coplanar panel or matrix.

  The fifth embodiment adds to the four preceding modes the possibility of including between the steps P1 and P2 a period without discharge for all or part of the cells, this period not exceeding a duration of 20 ps for the conditioning effect of PI is still active at the start of discharges during P2. The practical realization of a period without discharge is known in the prior art and will not be described here in detail: the internal tensions must be kept below the ignition thresholds.

  The various embodiments which have just been described by way of non-limiting illustration of the invention allow, during the operations of equalization or "reset" of the panels, an increase in the speed of growth of the potentials applied between the electrodes with respect to the prior art; the invention therefore makes it possible either to reduce the time allocated to the priming operation and to use it for addressing or maintenance, which makes it possible to improve the fidelity or the peak luminance of the panel; * to increase the yield of panel manufacture by avoiding the rejection of panels with strong discharges during priming with a usual slope; Finally, it is obvious to one skilled in the art to apply the invention to other possible cases of use of ramp signals in the control of plasma panels, without departing from the scope of the claims below.

  EXAMPLE OF THE INVENTION AND COMPARATIVE EXAMPLES On the same coplanar plasma panel having three electrode arrays, two X and Y coplanar on the front slab, including an A on the back slab for addressing, will apply different types of charge equalization or "reset" signals and evaluate their impact on discharges during the application of these signals.

  Such a coplanar board is known from the prior art and has been described in the introduction to this document, with the same references X, Y and A for the electrodes.

  FIG. 4 shows the timing diagrams of the voltage signals applied to the various electrodes X, Y and A of the panel during a charge forming operation or "priming": to the electrodes Y for maintenance and addressing (corresponding at the EA2 electrodes, here confused with ES2 of the general embodiments previously described), a linear voltage ramp characterized by a ramp vertex level Vpy, in this case 400 V, is applied; during this time, a constant signal VpX is applied to the maintenance-only X electrode (often referred to as "common"), and a constant signal VA = 0 to the addressing electrode A located on the other slab. These signals make it possible to illustrate the response of a panel to a ramp too strong with or without use of the invention.

  During each charge-forming or "priming" operation, the intensity of the so-called "strong" discharges Ds which can occur can be recorded by means of a photosensitive sensor placed in front of a set of discharge zones of the screen. accidentally, and which are unacceptable in normal use.

  The recordings obtained correspond to FIGS. 5 to 7; all these recordings are made under the same load forming operation conditions, in particular for applying the linear ramp signal, except for the value of the constant polarization signal VpX of the coplanar electrode X. FIG. 5: Vpx = + 100 V: the internal ignition threshold between the electrodes 20 serving at least for maintenance Y and X is then reached later than the internal ignition threshold between the addressing electrodes Y and A; we therefore privilege matrix discharges; there are many strong discharges Ds due to an excessive value of slope in the absence of prior conditioning of the cells; - Figure 8: Vpx = 120 V: the internal ignition threshold between the Y and A addressing electrodes is then reached later than the internal ignition threshold between the electrodes for at least Y and X maintenance; we therefore favor the start of coplanar discharges; the absence of strong discharges Ds is observed thanks to the prior conditioning of the cells by the weak coplanar discharges; such a configuration illustrates the invention.

  Figures 6 and 7 correspond to intermediate situations, where VpX is equal to 0 V and -80 V respectively, and where an unacceptable residue of strong discharges Ds is observed.

  During each charge-forming operation, the potential difference between the electrodes for at least the maintenance Y and X and the potential difference between the electrodes for the Y and A addressing therefore increase according to the same linear slope and the it is in a situation comparable to one of the 5 cases shown in Figure 2 corresponding to the second general embodiment of the invention described above; according to the invention as illustrated by FIG. 8, the charge-forming operation therefore starts with a first step P 0 where the coplanar discharges are sufficiently privileged, by polarizing the coplanar electrode X sufficiently with respect to the addressing electrode A; from a certain level of voltage between the electrodes used for addressing Y and A, matrix discharges inevitably occur because we exceed the thresholds of matrix ignitions, without generating this time of strong discharges because we has previously "conditioned" the discharge zones by coplanar discharges. The respective polarizations of X and A therefore determine the PI step characterized by coplanar discharges only creating an initial conditioning of each cell. The intermediate situations of FIGS. 6 and 7 correspond to simultaneous activation of coplanar and matrix discharges in certain cells. Since the slope applied between Y and A is as high as that applied between Y and X, insufficient conditioning results in strong discharges. To avoid strong discharges Ds, a solution according to the invention would be to apply a lower initial slope between the electrodes Y and A, as in the 3rd general embodiment of the invention described above.

Claims (5)

  1. Display device comprising: an alternating plasma memory effect panel comprising two slabs forming between them a space containing a discharge gas and two crossed electrode arrays (E2, E1) serving at least one of addressing, at the intersections of which are defined in the space between the slabs, areas of light discharges, control means adapted to apply to said electrodes voltage signals adapted to carry out operations intended to equalize the charges in said zones; discharge device, characterized in that said control means are adapted so that, during specific equalization operations of a set of discharge zones, if each discharge zone of the panel has an external voltage 15 (VETE2E1) threshold of matrix ignition between the electrodes serving at least for the addressing (E2, El) and crossing said zone, if Min [VETE2E1] and Max [VETE2E1] are respectively the minimum value and the maximum value of the matrix ignition voltage (VET E2E1) of the zones of said assembly, the potential difference VE2E1 applied between the electrodes serving at least for addressing and crossing said zones of this set increases, therefore VE2E1 has exceeded the value 1.1 x Max [VETE2E1] during said equalizing operation, according to a so-called end of operation slope which is greater than the maximum growth slope of VE2E1 during the instants o VE2EI is understood between Min [VETE2El] and MaX [VETE2El] 2.- Display device comprising: - a reciprocating plasma memory effect panel comprising two slabs forming between them a space containing a discharge gas, two networks of crossed electrodes (EA2 , EA1) serving at least for the addressing, at the crossings of which are defined, in the space between the slabs, areas of light discharges, at least two electrode arrays (ES2, ESI) serving at least to the Caring n and arranged in such a way that each discharge region is traversed by one of the electrodes (ES2, ES1) of each of these networks; - control means adapted to apply to said electrodes (EA2, EA1, ES2, ESI); voltage signals adapted to perform so-called equalization operations intended to equalize the charges in said discharge zones, characterized in that said control means are adapted so that, during specific operations of equalization of a set of discharge zones, if each discharge zone of the panel has an external matrix ignition threshold voltage (VET_EA2EA1) between the electrodes (EA2, EAI) serving at least for addressing and crossing said zone, if Min [VET EA2EA1] Max [VETEA2EA1] are respectively the minimum value and the maximum value of the matrix ignition voltage (VETEA2EA1) of the zones of said assembly, if each discharge zone of the panel has an external voltage (VET ES2ES1) of so-called coplanar ignition threshold between the electrodes (ES2, ESI) serving at least for maintenance and passing through said zone, if Min [VET-ES2ESI] and Max [VETES2ES1] are respectively the minimum value and the maximum value of the coplanar ignition voltage (VETES2ES1) of the zones of said set, - or the potential difference VEA2EAI applied between the electrodes (EA2, EA1) serving at least for the addressing and crossing said zones of this set does not exceed the value Min [VET EA2EA1] as long as the potential difference VES2ES1 applied between the electrodes (ES2, ESI) serving at least the maintenance and traversing said zones of this set does not exceed the value 25 MaXEVET ES2ES1] and grows according to a positive slope. so-called end of operation when the potential difference VES2ES1 applied between these electrodes (ES2, ES1) serving at least the maintenance has exceeded the value Max [\ VET ES2ES1I '- the potential difference VEA2EAI applied between the electrodes (EA2, EA1) serving at least for addressing and crossing said zones of this assembly 30 increases, since the potential difference VES2ESI applied between the electrodes (ES2, ESI) serving at least for the maintenance and crossing said zones has exceeded the value Max [VET ES2ESI] 'according to a positive end-of-operation slope which is greater than the maximum growth slope of VEA2EA1 during the instants o VES2ES1 is between Min [VETES2ES1] and MaX [VETES2ESI ]; 3.- Device according to claim 1 or 2, characterized in that said end slope of operation and growth of the potential difference between the electrodes for at least addressing is greater than 5 V / ps.   4.- Device according to claim 3 characterized in that said end slope of operation and growth of the potential difference between the electrodes 10 serving at least for addressing is greater than 10 V / sec.   5.- Device according to any one of the preceding claims when it depends on claim 2 characterized in that, when VES2ES1 is between Min [VETES2ESl] and Max [VET ES2ES1], the potential difference 15 VES2ES1 applied between ' electrodes for at least maintenance grows according to a so-called start of operation slope which is greater than 5 V / pls.   6.- Device according to claim 5 characterized in that said slope of operation start and growth of the potential difference between the electrodes for at least the maintenance is greater than 10 V / sec.   7. Device according to any one of the preceding claims, characterized in that, during each of said specific charge equalization operations, said potential difference (VE2E1; VEA2EA1) applied between the electrodes serving at least for the addressing is homogeneous strictly increasing when Min [VETE2EI] <VE2E1 <MaX [VETE2E1], or that Min [VETEA2EA1] <VEA2EA1 <MaX [VETEA2EA1] '8.A device according to any one of the preceding claims when dependent on claim 2 , characterized in that, during each of said specific charge equalization operations, said potential difference (VEs2ESl) applied between the electrodes serving at least the maintenance is homogeneous strictly increasing when Min [VET-ES2ESI] <VES2ESI <MaX [VET ES2ES1]