Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-12-24
2002-06-04
Wu, Xiao (Department: 2774)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S063000, C345S204000
Reexamination Certificate
active
06400343
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for activating cells forming the elementary image points of an image display screen. It applies advantageously in cases in which the activation of the cells demands the provision of a current of short duration and high intensity. The invention also relates to an image display device which uses this process.
2. Discussion of the Background
The activation of the cells of a display screen demands the provision of a current whose intensity is all the higher the larger the number of cells to be activated simultaneously.
These conditions are found in various types of display screen to which the invention may therefore be applied, especially plasma panels, screens with light-emitting diodes, liquid crystal screens, or else screens of the type whose elementary cells use a so-called “needle effect” phenomenon so as each to produce a beam of electrons. It should be noted that the simultaneity of actuation of the cells is more definite in screens which employ an effect termed the “memory effect”.
Taking for example the screens of plasma panels in which the activation of the cells calls for a sizable current, and more particularly plasma panels (abbreviated to “PAPs”) of the ac type all of which employ the “memory effect”, there are various types of ac PAPs: for example those which use just two crossed electrodes to define a cell, as described in French Patent FR 2,417,848; or again, ac PAPs of the so-called “coplanar sustain” type, which are known in particular in respect of the European Patent document EP-A-0,135,382, and in which each cell is defined at the crossover of a pair of so-called “sustain” electrodes, with one or more other electrodes used more particularly for addressing the cells.
The manner of operation of an ac PAP is explained below with reference to FIG.
1
. To simplify the explanations, the diagram shown in
FIG. 1
is that of a PAP with two crossed electrodes defining a cell.
The PAP comprises a network of electrodes Y
1
to Y
4
termed “row electrodes”, crossed with a second network of electrodes X
1
to X
4
termed column electrodes. To each intersection of row and column electrodes there corresponds a cell C
1
to C
16
. These cells are thus arranged in rows L
1
to L
4
and columns.
In the example of
FIG. 1
, just 4 row electrodes Y
1
to Y
4
and 4 column electrodes X
1
to X
4
are represented, which define 16 cells C
1
to C
16
serving to form the display screen
1
of the PAP, but in practice, an ac PAP can comprise 1000 or more row electrodes and as many column electrodes, serving to define 1 million or more cells.
Each row electrode Y
1
to Y
4
is linked to an output stage SY
1
to SY
4
of a row control device
2
, and each column electrode X
1
to X
4
is linked to an output stage SX
1
to SX
4
of a column control device
3
. These two control devices
2
,
3
are driven by an image management device
4
.
The row control device
2
comprises a so-called “sustain” generator
5
responsible for producing cell activation signals termed “sustain signals” SE. The sustain generator
5
delivers the sustain signals SE via an output circuit
6
, which itself distributes them to each output stage SY
1
to SY
4
so that these signals SE are applied simultaneously to all the row electrodes Y
1
to Y
4
.
It should be noted that a capacitance c PAP which symbolizes a so-called global capacitance exhibited by all PAPs has been depicted with dashed lines at the output of the sustain generator
5
.
In a PAP, the elementary cell experiences just two states: the so-called “lit” or “written” state and the so-called “unlit” or “erased” state. In the “lit” state it can produce an electric discharge which itself produces light; in the so-called “unlit” state there is no discharge produced, and hence no light emitted. ac PAPs have in common that they benefit naturally, of not their technology, from the “memory effect” mentioned above. The term “memory effect” is understood to mean the effect which allows cells having two stable states to retain one or other of these states after the signal which triggered this state has disappeared.
In ac PAPs, the “memory effect” is used with the aid of the sustain signals SE to activate the cells C
1
to C
16
which are in the “lit” state, that is to say to bring about discharges and hence emissions of light in these cells, without modifying their “lit” state or modifying the state of the cells which are in the “unlit” state.
It should be noted that the cells C
1
to C
16
are placed in the “lit” state or in the “unlit” state as a function of the image which is to be produced, by addressing operations which are usually performed row by row. For this purpose, the row control device
2
generally comprises elements (not represented) which cooperate with the row output stages SY
1
to SY
4
so as, when a given row L
1
to L
4
is addressed, to superimpose addressing-specific signals on the sustain signals SE and to do so solely for the row electrode Y
1
to Y
4
which corresponds to the row L
1
to L
4
addressed.
FIG. 2
a
represents the sustain signals SE and
FIG. 2
b
illustrates the phase relation between the inrush currents drawn by the row control device
2
and the sustain signals SE.
The sustain signals SE consist of voltage strobes following one another with a period P of the order of for example 8 to 10 microseconds.
These strobes are established on either side of a reference potential Vo which is for example earth. They vary between a negative potential V
1
, in which they exhibit a so-called negative plateau p−, and a positive potential V
2
in which they exhibit an opposite plateau to the previous so-called positive plateau p+. These positive and negative potentials V
2
, V
1
each have for example a value of 150 volts with respect to the reference potential Vo.
The reference potential Vo is applied to the column electrodes X
1
to X
4
in such a way that the sustain signals SE develop alternately positive and negative voltages, of 150 volts in the example, across the terminals of the cells C
1
to C
16
, each of these voltages giving rise to a discharge in those cells which are in the “lit” state.
These discharges in the cells C
1
to C
16
. occur slightly after each negative or positive transition Tn, Tp of the voltage of the sustain signals, of the order for example of a few hundred nanoseconds after the establishing of the positive and negative plateau. To each of these discharges in the cells there corresponds an inrush current termed the “discharge current” ID which is provided by the row control device
2
. In
FIG. 2
b
it may be seen that the discharge current ID is in fact established after each start of a positive and negative plateau. Of course, the discharge current ID changes direction depending on whether it is established on the basis of a positive plateau p+ or a negative plateau p−.
The existence is also observed of another inrush current termed the “capacitive current” Ic which is in phase with each transition Tn, Tp of the sustain signals and which corresponds to the current required to charge, alternately positively and negatively, the overall capacitance c PAP exhibited by the PAP. This global capacitance of the PAP, of non-negligible value, is constituted by various stray capacitances and the like exhibited in particular by the screen
1
itself and which are formed for example by the row and column electrodes Y
1
to Y
4
and X
1
to X
4
, the printed circuit tracks and the various connections and circuits, plus the stray capacitances exhibited by the elements responsible for deriving the sustain signals SE in the row control device
2
. Thus, for example, the global capacitance c PAP can have a value of 10 nF in the case of a screen
1
having 4 or 5 dm
2
, possessing for example 512 row electrodes and 512 column electrodes which constitute 512×512 cells. Of course, the value of the global capacitance c PAP depends greatly on the technologies employed.
The discharge current ID co
Dunand André
Zorzan Philippe
"Thomson-CSF"
Wu Xiao
LandOfFree
Method for activating the cells of an image displaying... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for activating the cells of an image displaying..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for activating the cells of an image displaying... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2912987