Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reissue Patent
1997-03-13
2001-11-13
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S060000
Reissue Patent
active
RE037444
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique of driving a display panel composed of display elements having a memory function, and particularly, to a method of and an apparatus for driving an alternating current (AC) plasma display panel (PDP), which provides multiple intensity levels and adjusts the luminance of a full color image plane.
2. Description of the Related Art
In the AC PDP, voltage waveforms are alternately applied to sustain two discharge electrodes, to maintain discharge and to display an image by emission. Each shot of discharge lasts several microseconds after the application of a pulse. Ions, i.e., positive charge produced by the discharge are accumulated over an insulation layer on an electrode of negative voltage. Electrons, i.e., negative charges produced by the discharge accumulate over an insulation layer on an electrode of positive voltage.
At first, a pulse (a write pulse) having a high voltage (a write voltage) is applied to cause discharge and produce wall charges. Thereafter, a pulse (a sustain discharge pulse) having a low voltage (a sustain discharge voltage) whose polarity is opposite to that of the high voltage and which is lower than the high voltage is applied to enhance the accumulated wall charges. As a result, the potential of the wall charges with respect to a discharge space exceeds a discharge threshold voltage to start discharging. In this way, once the wall charges are accumulated in a cell by the write discharge, the cell can continuously discharge if sustain discharge pulses, having opposite polarities, are alternately applied to the cell. This phenomenon is called a memory effect or a memory drive. The AC PDP enables various image data to be displayed by utilizing such a memory effect.
These kinds of AC PDPs are classified into a two-electrode type employing two electrodes for carrying out selectively discharge (addressing discharge) and sustain discharge, and a three-electrode type additionally employing a third electrode to carry out addressing discharge. Among such AC PDPs, in the AC PDP displaying color images (full color images) with multiple intensity levels, i.e., a color PDP, a phosphor located within each cell is excited by ultraviolet rays generated due to a discharge between different kinds of electrodes. However, this phosphor is relatively fragile against a hitting of ions, i.e., positive charges are also generated due to the discharge. The former two-electrode type PDP has a construction such that the ions collide directly with the phosphor, and therefore the life of the phosphor is likely to become shortened. On the other hand, in the latter three-electrode PDP, a surface-discharge with high voltage is carried out between a first-electrode and a second electrode, each located in the same plane. In such a construction, the phosphor at the side of the third electrode is avoided from the direct and strong bombardment of ions, and consequently a life of the phosphors is likely to become longer. Namely, the three-electrode PDP is advantageous in displaying color (full color) image with multiple intensity levels. Accordingly, as the color PDP, the three-electrode type is currently used. The amount of emission (luminance) of the three-electrode PDP is determined by the number of pulses applied to the PDP.
FIG. 1
is a plan view schematically showing a conventional three-electrode and surface-discharge PDP.
In
FIG. 1
, numeral
1
is a panel,
2
is an X electrode,
3
1
,
3
2
, - - -
3
K
, - - -
3
1000
are Y electrodes, and
4
1
,
4
2
, - - -
4
K
, - - -
4
M
are addressing electrodes. A cell
5
is formed at each intersection where a pair of the X and Y electrodes crosses one of the addressing electrodes, to provide M×1000 cells
5
in total. Numeral
6
is a wall for partitioning the cells
5
, and
7
1
to
7
1000
are display lines.
FIG. 2
is a sectional view schematically showing the basic structure of the cell
5
. Numeral
8
is a front glass substrate,
9
is a rear glass substrate,
10
is a dielectric layer for covering the X electrode
2
and Y electrode
3
k
,
11
is a protective film of an MgO film or the like,
12
is a phosphor, and
13
is a discharge space.
FIG. 3
shows the conventional PDP of FIG.
1
and its peripheral circuits. Numeral
14
is an X driver circuit for supplying a write pulse and a sustain discharge pulse to the X electrodes
2
,
15
1
to
15
4
are Y driver ICs for supplying addressing pulses to the Y electrodes
3
1
to
3
1000
,
16
is a Y driver circuit for supplying pulses other than the addressing pulses to the Y electrodes
3
1
to
3
1000
,
17
1
to
17
5
are addressing driver ICs for supplying addressing pulses to the addressing electrodes
4
1
to
4
M
, and
18
is a control circuit for controlling the X driver circuit
14
, Y driver ICs
15
1
to
15
4
, Y driver circuit
16
, and addressing driver ICs
17
1
to
17
5
.
FIG. 4
is a waveform diagram showing a first conventional method of driving the PDP of FIG.
1
. More precisely, this figure shows a drive cycle of a conventional “sequential line driving and self-erase addressing” method.
This method selects one of the display lines to write display data thereto during the drive cycle. The Y electrode of the selected line is set to a ground level (GND: 0 V), and the Y electrodes of the other display lines (unselected lines) are set to a potential level of Vs. A write pulse
19
having a voltage of Vw is applied to the X electrode
2
, to discharge all cells of the selected line. At this time, a voltage difference between the X and Y electrodes of the selected line is Vw, and a voltage difference between the X and Y electrodes of the unselected lines is Vw−Vs. By setting Vw>Vf>Vw−Vs (where Vf is a discharge start voltage), all cells of the selected line will discharge.
As the discharge progresses, the protective film,
11
, e.g., an MgO film over the X electrode
2
of the selected line accumulates negative wall charges, and the MgO film over the Y electrode of the selected line accumulates positive wall charges. Since the polarities of these wall charges are to reduce an electric field in the discharge space, the discharge quickly converges and ends within about a microsecond.
Sustain discharge pulses
20
and
21
are alternately applied to the X and Y electrodes of the selected line, so that the accumulated wall charges are added to the voltages applied to the electrodes, to repeat sustain discharge in cells except those that are not turned ON (not in light emission).
For the cells that are not turned ON, the first sustain discharge pulse
20
a is applied to the X electrode
2
, to accumulate positive wall charges in the MgO film over the X electrode
2
of the selected line, and negative wall charges in the MgO film over the Y electrode of the selected line. In synchronism with the first sustain discharge pulse
21
a, applied to the Y electrode of the selected line, an addressing pulse (an erase pulse)
22
having a positive voltage of Va is selectively applied to the addressing electrodes of the cells not to be turned ON.
At this time, sustain discharge occurs in every cell of the selected line, and in particular, the cells that have received the positive addressing pulse
22
through the addressing electrodes cause discharge between the addressing electrodes and the Y electrode, to excessively accumulate positive wall charges in the MgO film over the Y electrode.
If the voltage Va is set such that the voltage of the wall charges exceeds the discharge start voltage, the voltage of the wall charges induces discharge when the external voltage are removed, i.e., when the potential of the X and Y electrodes is returned to Vs and that of the addressing electrodes to GND. This causes self-erase discharge to dissipate the wall charges in the cells not to be turned ON. Accordingly, from this moment, the sustain discharge pulses
20
and
21
will never cause sustain discharge in the cells not to be turned ON.
For the cells to be turned ON,
Fujitsu Limited
Staas & Halsey , LLP
Wu Xiao
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