FR2795218A1 - METHOD FOR ADDRESSING A MEMORY EFFECT VIEWING PANEL - Google Patents

Abstract

The present invention relates to a method of addressing a memory effect display panel comprising cells defined at the intersection of arrays of crossed electrodes, the cells having two states, one "registered", the other " erased ", the method consisting for a given cycle time in applying to all the cells a sustain signal producing a sustain discharge at the level of the cells in the written state and in successively applying to the electrodes of an array a signal addressing comprising a semi-selective signal and a selective signal, the semi-selective signal being applied for at least part of the cycle time of the selective signal simultaneously to different electrodes. The invention applies to AC plasma panels of the coplanar and matrix type.

Description

The present invention relates to a method for addressing a panel of

  memory effect visualization, more particularly of a

  alternative type plasma panel.

  Plasma panels called PAP for short in the following

  description are flat viewing screens that use the emission of

  radiation in the visible or ultraviolet spectrum from a discharge

in a gas ..

  PAPs have two main families: o - PAPs of the continuous type,

- PAP of the so-called alternative type.

  PAPs of the alternative type, because of their particular structure, benefit in their operation from an effect called memory effect which makes them particularly suitable for constituting large screens with a large number of elementary cells both for professional applications and for applications. General public such as high-definition color television.

  The present invention relates to the latter type of PAP.

  There are different types of alternative PAPs: - The so-called matrix PAPs which only have two crossed electrode networks to define the cells and to address and activate each cell. These PAPs are described in particular in the

French Patent No. 2,417,848.

  - The so-called coplanar PAPs which comprise a network of two so-called maintenance electrodes on a first slab and a network of electrodes on a second slab defining with one of the maintenance electrodes address electrodes, the cells being defined at the crossing both

  networks. This type of PAP is described in particular in the European patent EP-

A-O 135 382.

  The operation of alternative or memory effect PAPs generally includes an addressing function and a maintenance function which aims to produce light energy. The maintenance function consists in applying to a set of electrodes, in general all the lines of the panel, an alternative maintenance signal substantially in a slot which has the effect of maintaining each cell in the state which has been assigned to it before. by an addressing signal. This maintenance signal generates at the level of

  cells in the state entered a maintenance release.

  Addressing is generally done by line-by-line scanning of the panel. The cells of a selected row are controlled simultaneously by a semi-selective operation, for example in erasure, this operation being followed by a selective operation during

  which cells in the row can then be entered. The semi-operation

  selective followed by selective operation is accomplished with a time shift from one line to another. On the other hand, in a known manner, the semi-selective operation can be a registration operation and the selective operation

  can be an erase operation.

  i, 5 In an alternating type plasma display panel, the discharge current is limited by a capacitor in series with each cell to avoid destruction of the display panel if the source is not limited in current. The capacitor is generally produced by covering the network of electrodes with a dielectric layer, i.e. a glass in

2o borosilicate for example.

  Erasing a cell therefore consists in removing the charges

  stored on the dielectric, at the level of the cells of the line considered.

  To obtain the erasure, a voltage is generally applied to the electrode forming the corresponding line, which generates a discharge the intensity of which is chosen so that the charges stored opposite are recombined with one another for s 'to cancel. The erasure of a cell creates a discharge current whose intensity is substantially equal to half that of the maintenance current, since there is transfer of about half of the

usual maintenance costs.

  Currently, the selective erasure operation is carried out

different ways.

  According to an embodiment known as "shuffling", a PAP AC of the matrix type receives an addressing signal of the type of that shown in dotted lines in FIG. 1, the signal in solid lines representing the discharge voltage of the gas. In this case, all the line electrodes simultaneously receive the maintenance signal shown in dashes. This signal Vef is substantially in a niche with high end stops at a potential V2 and low end stops at a potential V1 located on either side of a median potential V0 at which level, in certain cases, can be achieved. middle bearings not shown in this embodiment.

  The extreme landings are separated by rising and falling edges.

  The maintenance signal Ve, causes maintenance discharges at the level of the cells in the registered state. In the embodiment shown, the addressing signal superimposed on the maintenance signal is applied to the electrodes 0o of a network each in turn. It can for example be applied to line electrodes. However, it is conceivable that it is applied to the column electrodes. The addressing signal is broken down into a semi-selective signal and a selective signal. The semi-selective signal is, for example, the

  erase signal while the selective signal is the registration signal.

  However, in a manner known to those skilled in the art, the semiselective signals

  and selective can be reversed.

  As shown in Figure 1, the selective registration signal consists of a pulse referenced IE which is superimposed on the upper level of the maintenance signal. The semi-selective erase signal consists of an IR erase pulse generated from a low level of the maintenance signal. The IR erase pulse generates an erasure discharge at all cells in the registered state of the selected line and

  replaces the one that should have been generated by the maintenance signal.

  The IR erase pulse can last until the next rising edge of the maintenance signal or be shorter. It is usual in the case of AC PAPs of the color matrix type to apply several recording pulses superimposed on the upper level of the maintenance signal. With this type of addressing called "multiple pulse", the duration of the high plateau must be sufficient, which implies reducing the duration of the low plateau so as not to lengthen the addressing cycle time. This results in a reduction in the time during which the erasure is carried out since currently, the erasure pulse is generated from a low level. However, if the erasing time is too short, the charges stored at the terminals of the dielectric are not completely removed. The object of the present invention is to remedy the drawbacks mentioned above by proposing an addressing method which allows the most complete possible evacuation of the charges during erasure both for an alternative plasma panel of matrix type and of type coplanar. The present invention relates to a method of addressing a display panel with memory effect comprising cells defined at the intersection of networks of crossed electrodes, the cells having two states, one "registered", I ' another "erased", the method consisting in applying a maintenance signal io producing a maintenance discharge at the level of the cells in the registered state for a given cycle time and in successively applying to the electrodes of a network an addressing signal comprising a semi-selective signal and a selective signal, characterized in that the semi-selective signal is applied during at least part of the cycle time of the selective signal simultaneously on

different electrodes.

  According to an embodiment with addressing during the maintenance, in which the maintenance signal is a niche signal having at least two extreme steps on either side of a median potential, the semi-selective signal is applied during the minus part of the extreme level of the maintenance signal on which the selective signal is also applied. The semi-selective signal is applied during the upper or lower level of the niche maintenance signal and it consists of a portion of signal with increasing or decreasing slope, this portion starting at an intermediate potential between the median potential and the potential of the end stop and ending at the end stop. In this case, the pulses of the selective multiple-pulse signal, superimposed on the slope of the semi-selective signal, for example the erasure signal, a succession of short erasures is obtained, the amplitude of which is adjusted according to this slope. As a result, the cells receive a succession of gradually varying voltage discharges. This characteristic associated with a long discharge time makes it possible to obtain a good erasure of the cells whatever

  the structural homogeneity of said cells.

  Preferably, the pulses associated with the selective signal are adjustable in width, having fixed or variable widths which may be between 0.5 ps and less than 10, us, typically of the order of 1.5 ps and whose spacing is also adjustable in this

magnitude.

  According to another characteristic of this embodiment, a semi-selective signal is applied during the other extreme stage of the maintenance signal. This signal has the form of the semi-selective addressing signal described in French patent application no. 96 01060 in the name of

  THOMSON-CSF whose content is included in this request.

  Other features and advantages of the present invention

  will appear on reading the description given below of various

  embodiments, this description being made with reference to

  attached drawings in which: FIG. 1 already described represents a timing diagram of the addressing and maintenance signals applied on the line of a panel to

  PAP ACM type plasma according to the prior art.

  FIG. 2 schematically represents the structure of a plasma panel of the PAP ACM type to which a first mode applies

  for carrying out the method of the present invention.

  FIGS. 3a and 3b represent timing diagrams of the addressing and maintenance signals in accordance with the present invention,

applied to the PAP in Figure 2.

  Figure 4 shows a timing diagram of the signals

  addressing and maintenance according to a variant of the present invention.

  FIG. 5 is a schematic representation of a coplanar PAP to which the method of the present invention can be applied, and FIG. 6 represents the timing diagrams of the addressing and maintenance signals in accordance with the invention, applied to the

PAP electrodes in Figure 5.

  To simplify the description, in the figures, the same

  elements have the same references.

  We will first describe with reference to Figure 2, a first embodiment of an image viewing device to which the method of the present invention applies. This display device comprises a plasma display panel or PAP1 of

  matrix type and control means of this panel.

  The matrix type PAP1 display panel comprises a first array of row electrodes Y1 to Y4 crossed with a second array of column electrodes X1 to X5. A plasma cell C corresponds to each crossing of electrodes, these cells being arranged in a matrix. In the matrix type PAPs, the maintenance and addressing signals are applied between the array of row electrodes and the array of column electrodes. Thus, as shown in FIG. 2, each electrode-line

  Y1 to Y4 is connected to an ADL line addressing circuit or "driver lines".

  For large panels, there are generally several line drivers each supplying a group of lines with maintenance and addressing signals. Likewise, each column electrode X1 to X5 is connected to an ADC column addressing circuit or "column driver". The column addressing circuits generate pulses which mask those generated by the semi-selective addressing signal when written on a line selected at the C cells, this line should not be

  registered as will be explained below.

  As shown in FIG. 2, the line addressing circuit ADL receives the maintenance signal from a generator of maintenance signals GSE. This maintenance signal is constituted by a signal in slots between two extreme voltage levels Vl and V2 having a low level of duration T1 and an upper level of duration T2, the time T1 being less than the time T2 in the embodiment shown . The ADL-line addressing circuit also receives the addressing signal which is superimposed on the maintenance signal from a signal generator

GSAL line addressing.

  In the embodiment shown in FIG. 2, the operation of the ADL-line addressing circuits is symbolized by switches Il, 12, 13, 14 which can switch between the LSE line bringing the maintenance signal and the LSAL line bringing the addressing signal. The state of the switches is controlled by a GB signal from a not shown scanning generator. In FIG. 2, the switches 11, 12, 13, 14 are positioned so as to receive the signal LSE, namely the lines Y1, Y2, Y4 are in maintenance. Conversely, the switch 13 is toggled so as to receive the LSAL addressing signal formed by selective and semi-selective signals, so that the line Y3 is the

addressed line.

  As shown in FIG. 2, the addressing circuit-

  ADC columns are also schematically constituted by switches' 1, 1'2, 1'3, 1'4, 1'5. These switches can receive an LCAC addressing signal from the GSAC column addressing generator or be grounded, as shown by line M. The state of switches' 1 to 1'5 is controlled by a corresponding signal V to the video content of the addressed line. In the embodiment shown, the switches 1'1, 1'2, 1'5 are grounded so that the cells located at the intersection of the row Y3 and the columns Xl, X2, or X5 are in the state "on" symbolized by a "*" while the switches 1'3 and 1'4 are connected so as to receive the LSAC signal from the column addressing generator GSAC so that the C cells being at the crossroads of the line Y3 and columns X3, X4 are in the "off" state symbolized by an "O". The cells of the other lines are

  in the maintained state as symbolized by an "S".

  We will now describe, with reference to FIGS. 3a and 3b, the shape of the addressing and maintenance signals in accordance with the present invention applied to a PAP of the matrix type as shown in FIG. 2. The addressing described with reference to Figures 3a and 3b will be a "multiple pulse" addressing. However, it is obvious to those skilled in the art that the present invention can also be applied to single pulse addressing. In this case, the maintenance signals applied to the lines YA therefore consist of slots comprising a low plateau of duration T1 at a voltage V1 followed by a high plateau at a voltage V2 of duration T2. The maintenance signal shown does not have an intermediate plateau at the level of the average voltage VO but the present invention could also be applied to maintenance signals having this intermediate plateau as described in

  Patent application No. 96 01 060 filed in the name of THOMSON-CSF.

  In known manner, this maintenance signal is superimposed on an addressing signal of the type consisting of a semi-selective signal which, in the embodiment shown, is an erasure signal and a selective signal which , in the embodiment shown, is a registration signal.

  According to the present invention, the semi-selective signal.

  of erasure is constituted by a signal applied during the upper stage of the maintenance signal, namely during the period T2, that is to say during the

  same cycle time as that receiving the selective registration signal.

  As shown in FIG. 3a, this semi-selective erasure signal consists of an increasing ramp r which starts from a voltage V3 slightly higher than the intermediate voltage V0 and rises

  up to voltage V2 of the upper bearing.

  As shown in FIG. 3a, during the time T2 which also corresponds to the selective addressing time, the driver-column ADC sends on the selected columns pulses IS1, IS2 ... as 0o as represented by Vx. Thus, on a matrix PAP, one will obtain at the terminals of the addressed cells a Ya-Vx signal as represented in FIG. 3b. During the erasure period, a continuous slope is not obtained but randomly a succession of short erasures I'S1, I'S2 etc, having an amplitude adjusted according to the slope r. The cells are therefore treated by a succession of gradually varying voltage discharges. This type of erasure discharge makes it possible to cover the various cases of homogeneity of cell structure and has sufficient time for the discharges to be stabilized before the

next maintenance window.

  As shown in FIG. 3b, there is obtained after the erasing period P a writing period P ′ with multiple pulses of known type. The pulses L'S1, I'S2 have been represented with a constant width. However, it is obvious to those skilled in the art that they can have a variable width, in particular a width between 0.5 ps and less than 10 ps, typically 1.5 ps. In addition, the spacing between

  pulses can also be adjustable in the same order of magnitude.

  In FIG. 4, another embodiment of

  the present invention according to which the long erasing described above is added

  above a short erase pulse during period T1 of the maintenance window, this erase pulse being of the type

  described in French patent application No. 96 01 060 of THOMSON-

  CSF. In the embodiment shown in FIG. 4, the semi-selective erasure addressing signal comprises a part V ′ of signal with decreasing slope during the low plateau V1 of the maintenance signal, this part starting at an intermediate potential V4 referenced with respect to the potential V1 of the bottom bearing, comprised between the potential V1 of the bottom bearing and the median potential V0 and ending substantially at the level of the potential V1 of the bottom bearing. This conventional erasure signal is followed by a semi-selective erasure addressing signal of the type described with reference to FIGS. 3a and 3b. It is obvious to those skilled in the art

  that other forms may be given to the semi-addressing signal

  selective erasure such as those described in the request for

patent mentioned above.

  We will now describe with reference to FIGS. 5 and 6, another embodiment of the present invention applying more

  particularly to plasma panels of the coplanar type.

  As shown in FIG. 5, a coplanar type PAP comprises a screen formed by a set of two networks of parallel electrodes Yel, YeN and YeT, Y'eN called electrodes-crossed lines with a second network of electrodes X ' I to X'N called column electrodes. At each intersection of row and column electrodes corresponds a cell Ce which is delimited by barriers B. In the case of a coplanar PAP, the two networks of parallel row-electrodes constitute maintenance electrodes between which the maintenance signals, while between an array of row electrodes and the array of column electrodes

  the addressing signals are applied.

  As shown in FIG. 6, in accordance with the present invention, the network of maintenance electrodes Yel to YeN receives pulses in a slot having a low level of duration T'1 followed by a high level 2 of duration T'2 whose duration corresponds to the time necessary for a selective registration operation then a pulse of duration T'3 and again a low plateau of duration T'I. The set of durations T'I, T'2,

T'3 corresponds to a basic cycle.

  According to the present invention and as shown in FIG. 6 by Ye, the second network of maintenance electrodes Y'el to Y'eN receives addressing pulses which, according to the present invention, comprises during the first stage high of duration T'2, an erasure signal VE of duration slightly less than T'2 but longer than the duration T'I during which the erasure signal is normally applied. One thus obtains between the two parallel networks of electrodes-lines Yel to YeN and Y'el to Y'eN a signal as represented by Y'e - Ye in FIG. 6. During a period T'2 different from the cycle of base, a selective registration signal is applied giving the impetus. The electrode array X 'receives the pulses IS'1, IS'n in a known manner. Thus, with the present invention, the duration T'1 can be reduced significantly compared to the conventional duration since this time is no longer used for erasure. Because of this, the basic cycle

is also reduced.

  In fact, the realization of the signals allowing the implementation of the present invention implies certain constraints due to the fact that the semi-selective erasing signal has, in particular in the case of AC plasma panels of matrix type, an inverted voltage value compared to that of the selective registration signal. This requires high-voltage control devices or "drivers" operating in both positive and negative. One solution allowing an easy implementation of the present invention consists in using an amplifier per control circuit and in integrating this semi-selective erasure signal with the maintenance signal. The same type of constraint also applies to a

  coplanar type plasma panel.

]!

Claims (9)

  1. A method for addressing a memory effect display panel comprising cells defined at the intersection of networks of crossed electrodes, the cells having two states, one "registered", the other "erased" , the method consisting during a given cycle time in applying to all the cells a maintenance signal producing a maintenance discharge at the level of the cells in the registered state and in applying successively to the electrodes of a network a signal addressing! 0 comprising a semi-selective signal and a selective signal, characterized in that the semi-selective signal is applied during at least part of the cycle time of the selective signal, simultaneously on different electrodes. 2. Method according to claim 1, characterized in that, in the case of an addressing during the maintenance with a maintenance signal constituted by a signal in slots having at least two extreme steps on either side of a median potential, the semi-selective signal is applied during at least part of the extreme stage of the signal   maintenance to which the selective signal is also applied.   3. Method according to claim 2, characterized in that the semi-selective signal is applied during the high level or the low level of the niche maintenance signal.   4. Method according to any one of claims 2 or 3,   characterized in that the semi-selective signal is constituted by a portion of signal with increasing slope, this portion starting at an intermediate potential between the median potential and the potential of the extreme plateau and   ending at the extreme landing.   5. Method according to any one of claims 1 to 4,   characterized in that the semi-selective signal obtained at the level of the cells forms a succession of pulses whose amplitude is variable gradually.   6. Method according to claim 5, characterized in that the pulses have variable widths of the order of 0.5 ps to less from p1 0 s.   7. Method according to any one of the claims   previous, characterized in that an additional selective signal is   applied during the other extreme step of the maintenance signal.   8. Method according to any one of claims   previous, characterized in that it applies to plasma panels Matrix type AC.   9. Method according to any one of claims 1 to 7,   characterized in that it applies to AC plasma panels of the type coplanar.