Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
1999-12-07
2002-06-04
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S292000
Reexamination Certificate
active
06400079
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the plasma display panels, and more particularly to means enabling a so-called “cell conditioning” effect to be obtained.
BACKGROUND
Plasma panels (abbreviated to “PP” in the rest of this description) are image display screens of the “flat screen” type. There are two main families of PPs: PPs whose operation is of the continuous type, and those whose operation is of the alternative type. All PPs operate using the principle of an electrical discharge in a gas that results in emission of light. They generally include two insulating sheets, each carrying one or more networks of electrodes, the space between the sheets being gas-filled. The sheets are assembled together such that their networks of electrodes are mutually orthogonal. Each intersection of electrodes defines a cell which corresponds to a gas space.
FIG. 1
represents by way of example, in a partial and simplified manner, a classic structure of a color alternative PP. Various types of alternative PPs are found, among which we can mention for example: those of the type using only two crossed electrodes to define and control a cell, as described notably in a French patent published under the number 2,417,848, and those of the so-called “coplanar structure” type whose structure and operation are described for example in the European patent EP-A-0.135.382. Alternative PPs have a common characteristic in that they have an internal memory effect during operation, owing to the fact that their electrodes are covered by layer of dielectric which isolates them from the gas, in other words from the discharge.
In the example of
FIG. 1
, the PP is of the type having two crossed electrodes defining a cell. It is composed of two substrates or sheets
2
,
3
, of which one is a front sheet
2
, i.e. the sheet that is on the same side as an observer (not shown); this sheet carries a first network of electrodes called “line electrodes”, of which only 3 electrodes Y
1
, Y
2
, Y
3
are shown. The line electrodes Y
1
to Y
3
are covered with a layer
5
of a dielectric material.
The second sheet
3
forms the rear sheet. It is on the opposite side from the observer and consequently is preferably equipped with components whose function is to prevent the transmission of light towards the observer; it carries a second network of electrodes called “column electrodes”, of which only 5 electrodes X
1
to X
5
are shown in FIG.
1
. The two sheets
2
,
3
, are of a same material, generally glass. These two sheets
2
,
3
are destined to be assembled together such that the networks of line and column electrodes are mutually orthogonal.
On the rear sheet
3
, the column electrodes X
1
to X
5
are also covered with a layer
6
of dielectric material. The dielectric layer
6
is itself covered with layers forming bands
7
,
8
,
9
of luminiferous materials that correspond for example to the colors green, red and blue respectively. The luminiferous bands
7
,
8
,
9
are placed parallel to and above the column electrodes X
1
to X
5
from which they are separated by the dielectric layer
6
. The rear sheet
3
also includes barriers
11
, parallel to the luminiferous bands
7
,
8
,
9
and placed between them.
The PP is formed by the assembly of the front and rear sheets
2
,
3
, this operation forming a matrix of cells C
1
to Cn. The cells are defined at each intersection between a line electrode Y
1
to Y
3
and a column electrode X
1
to X
5
. Each cell has a discharge zone whose section corresponds substantially to so-called “useful” areas formed by the surfaces facing the two crossed electrodes. For each cell, the gas discharge causes electric charges that, in the case of an “alternative” PP, cumulate on the dielectric
5
,
6
facing the line and column electrodes; in the example shown here, this is obtained at the rear sheet
3
by means of cavities Ep
1
to Epn made in the luminiferous bands
7
,
8
,
9
substantially opposite the useful areas of the column electrodes X
1
to X
5
.
In the example shown, the intersections made by the first line electrode Y
1
with the column electrodes X
1
to X
5
defines a line of cells, each cell being in the form of a cavity: the first cell C
1
is located at the first cavity Ep
1
, the second cell C
2
at the second cavity Ep
2
, and so on until the fifth cavity Ep
5
constituting a fifth cell C
5
. The first, second and third cavities Ep
1
, Ep
2
, Ep
3
are respectively located in green
7
, red
8
and blue
9
luminiferous bands; they correspond to monochromic cells of three different colors which together can constitute a three-color cell.
The quality of the discharges in each cell, for a given value of the tension applied to the electrodes, depends on the geometry and dimensions of the cells, and the overall quality of the operation of the PP requires that these characteristics must be reproduced with low dispersion for all the cells of the PP. One of these characteristics that is particularly important is the height of the gas space formed between the front and rear sheets
2
,
3
, when these are assembled.
Generally, in color PPs (which, unlike with monochrome PPs, have luminiferous components enabling them to produce lights of different colors), one of the dimensions of the gas space formed between the sheets
2
,
3
corresponds to the distance between these sheets, this distance being defined by the height H
1
of the barriers
11
; in the rest of this description, these barriers are referred to as “carrier barriers”. During assembly of the two sheets
2
,
3
, they are separated from each other by the carrier barriers
11
that therefore play the role of spacers.
Since the carrier barriers
11
have the same height H
1
as the space separating the sheets
2
,
3
, they constitute relatively tight partitions, so that in addition to their spacing function mentioned earlier they assure another function known as “confinement”. This well-known confinement function consists notably of confining the discharge, in other words preventing its propagation into non-addressed neighboring cells, and thereby avoiding diaphonic effects between cells, and of preventing the ultraviolet radiation created by a discharge in a given cell from exciting the luminiferous material in adjacent cells, which would lead to lack of saturation of the colors, this phenomenon being known as a diaphoty effect. We note in the example shown in
FIG. 1
, that since the carrier barriers
11
are placed so as separate two luminiferous bands
7
,
8
,
9
of different colors in a so-called “triad” arrangement, they assure these confinement functions only between cells situated along the same line electrode Y
1
to Y
3
, as for cells C
1
to C
5
.
However the authors of the invention have observed that excessive confinement of cells can in some cases adversely affect the operation of the PP, especially when high speed triggering or inscription of the cells is necessary, as for example in the case of television images. The authors realize that a structure such as the one shown in
FIG. 1
, leads to total confinement of the cells, in other words to total isolation between two adjacent cells of different colors, and that this total confinement may deprive these cells of the benefits of phenomena of transfer, from one cell to another, of charges (ions or electrons of the plasma) and/or ultraviolet photons that can contribute to the triggering of a discharge in the gas.
Such transfer phenomena produce an effect known as “cell conditioning”, which can occur only if the structure of the cells leaves a path in the gas-filled space between neighboring cells, and in both directions, in other words along the line electrodes and along the column electrodes. Total confinement of a cell with respect to its two neighboring cells of different colors prevents this conditioning effect and reduces the cell activation speed.
The present invention proposes simple means of assuring in a PP the confinement and cell conditioning functions mentioned above, but without adversely affecting the consta
Baret Guy
Moi Agide
Herrera Carlos M.
Irlbeck Dennis H.
Patel Ashok
Thomson Licensing S.A.
Tripoli Joseph S.
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