Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-07-06
2003-02-25
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S060000, C345S067000, C315S251000, C315S169300, C315S169400
Reexamination Certificate
active
06525703
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Fields of the Invention
The present invention relates to a control process for addressing an AC type plasma panel. For components used for addressing operations, its implementation makes it possible in particular to reduce the performance required from these components and hence to reduce their cost. The invention also relates to a plasma panel operating according to this process.
2. Discussion of the Background
Plasma panels or plasma screens, abbreviated to “PAPs” in the subsequent description, are flat display screens which use the emission of radiation in the visible or ultra-violet spectrum from a discharge in gases.
PAPs consist mainly of two large families, PAPs of the so-called DC type and PAPs of the so-called AC type. PAPs of the AC type, owing to their particular structure, benefit operationally from an effect referred to as the “memory effect” which renders them especially suitable in constructing large screens with a large number of elementary cells, both for professional applications and those aimed at the general public, such as for example high-definition colour television.
There are various types of AC PAP:
for example PAPs which use only two electrodes crossed to define a cell and to carry out its addressing and its activation, as described in French Patent 2 417 848:
or else AC PAPs of the so-called “coplanar sustain” type, known in particular through the European Patent document EP-A-0135 382, and in which each cell is defined at the crossing of a pair of so-called sustain electrodes with one or more other electrodes used more particularly for addressing the cells.
With AC PAPs, the addressing functions and those aimed at producing the light energy are separated: the production of light results from the “parallel” application to all the cells of a square-wave strobe signal referred to as the “sustain signal”.
By contrast, the addressing of the cells demands that it be possible to control each line and each column of cells in an individualized manner. The electronic means serving to carry out these individualized controls are relatively complex and expensive, this being all the more penalizing as the market for PAPs moves towards ever larger panels.
The operation of an AC PAP is explained further hereafter with reference to FIG.
1
. To simplify the explanations, the diagram shown in
FIG. 1
is that of a PAP with two electrodes crossed to define a cell.
The PAP comprises a screen
1
formed with the aid of a network of electrodes Y
1
to Y
6
referred to as “line electrodes”, which is crossed with a second network of electrodes X
1
to X
6
referred to as column electrodes. To each intersection of line and column electrodes there corresponds a cell C
1
to C
36
. These cells are thus arranged along lines L
1
to L
6
and columns CL
1
to CL
6
. In the example of
FIG. 1
, only
6
electrodes of each type are represented, but a PAP can include 1000 or more line electrodes and as many column electrodes, defining 1 million or more cells.
Each line electrode Y
1
to Y
6
is linked to a line output stage SY
1
to SY
6
of a line management device
2
, and each column electrode X
1
to X
6
is linked to a column output stage SX
1
to SX
6
of a column management device
3
. The operation of these two management devices
2
,
3
is controlled by an image management device
4
.
The line management device
2
comprises:
at least one circuit referred to as a sustain amplifier A
1
, producing signals referred to as “sustain signals” SE serving in activating the cells C
1
to C
36
; given the sizeable power under which the SE signals may possibly have to be delivered, they may be supplied with the aid of a first and of a second amplifier A
1
, A
2
as in the example shown;
it also includes in the non-limiting example represented, a first and a second line control circuit
6
,
7
(which correspond to the circuits referred to as “line drivers” by experts in the field). In the simplified representation shown in
FIG. 1
of the first and of the second line control circuit
6
,
7
, these latter respectively each comprise three switching stages M
1
to M
3
and M
4
to M
6
each linked to the input of a line output stage SY
1
to SY
3
and SY
4
to SY
6
, in such a way that the first circuit
6
controls the first three line electrodes Y
1
to Y
3
and that the second circuit
7
controls the following three electrodes Y
4
to Y
6
.
Each line control circuit
6
,
7
is linked to one of the amplifiers A
1
, A
2
, from which it receives the sustain signals SE, and its function is in particular: on the one hand, to forward these signals SE in such a way that they are applied simultaneously to all the line electrodes Y
1
to Y
6
which it controls; its function is on the other hand, for the electrode or electrodes selected for an addressing operation, to superimpose either a so-called write pulse IS or a so-called erase pulse IE onto the sustain signals SE, depending on the type of addressing to be carried out.
The column management device
3
has in particular the function of applying, to the column electrodes X
1
to X
6
, a reference potential, with respect to which so-called masking pulses IM are applied to some of these electrodes during addressing operations. To this end, it employs a column control circuit
8
, similar for example to the line control circuits
6
,
7
, and comprising in the example,
6
switching stages M
7
to M
12
each linked to a column output stage SX
1
to SX
6
, and which are responsible for formulating and switching the masking pulses.
In a PAP, each cell includes a gas-filled space. By applying a sufficient voltage referred to as the “turn-on voltage” VA between the two electrodes which define a given cell, an electric discharge is caused in the gas, giving rise to the emission of light by this cell. In an AC PAP, the electrodes are covered with a dielectric material. Accordingly, with each discharge into the gas, electric charges accumulate on the dielectric near the electrodes which define a cell within which the discharge occurs. These electric charges persist after the discharge and constitute an electric field referred to as the “internal memory field” specific to each cell, and make it possible, in respect of the cell which possesses it, to cause a discharge with the application of a voltage below the turn-on voltage. This effect constitutes the “memory effect” already mentioned. The cells which posseses such charges are said to be in the “written” or “on” state. To produce a discharge, the other cells demand a voltage equal to the turn-on voltage, they are said to be in the “erased” or “off” state.
The effect of applying the sustain signals SE is to activate the cells C
1
to C
36
which are in the “written” state, that is to say to cause discharges in these cells, without modifying their state or the state of the cells which are in the “erased” state. The cells are set to the “written” state or the “erased” state depending on an image to be displayed, by addressing operations which are often carried out line by line, that is to say for all the cells C
1
to C
36
belonging to the same line L
1
to L
6
(or stated otherwise, for all the cells defined along the same line electrode Y
1
to Y
6
), and then subsequently for all the cells of another line.
FIG. 2
a
represents sustain signals SE of a common type, which are intended to be applied to all the line electrodes Y
1
to Y
6
. They consist of negative voltage strobes
9
and positive voltage strobes
10
established on either side of a reference potential V
0
(which is often the potential of earth), and which follow one another with opposite polarities. They vary between a negative potential V
1
where they exhibit a so-called negative porch p−, and a positive potential V
2
where they exhibit a so-called positive porch p+. These negative and positive potentials V
1
, V
2
have for example a value of 150 volts, which is added to the voltage produced by the internal memory field, so as to reach substantially the turn-on voltage value VA. Acc
Salavin Serge
Zorzan Philippe
Hjerpe Richard
Nguyen Frances
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Thomson Tubes Electroniques
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