Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-02-28
2004-02-10
Shankar, Vijay (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C315S169400
Reexamination Certificate
active
06690342
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a plasma display device employing a plasma display panel (hereinafter referred to as a PDP), and in particular to a technology useful for increasing luminous efficiency.
Recently, plasma display devices employing an AC surface-discharge PDP are beginning to be mass-produced as a large-screen thin color display devices.
Presently, AC surface-discharge PDPs having a three-electrode structure as shown in
FIG. 13
are widely used. In the AC surface-discharge PDP of
FIG. 13
, a discharge space
33
is formed between a pair of opposing glass base plates, a front base plate
21
and a rear base plate
28
. The discharge space
33
is filled with a discharge gas (usually a mixture of gases such as He, Ne, Xe, Ar and others) at several hundreds or more of Torrs.
A plurality of pairs of X and Y electrodes for sustain discharge are disposed on the underside of the front base plate
21
serving as a display screen, for sustain discharge mainly for light emission for forming a display.
Usually, each of the X and Y electrodes is made of a combination of a transparent electrode and an opaque electrode to supplement conductivity of the transparent electrode.
The X electrodes are comprised of transparent X electrodes
22
-
1
,
22
-
2
, . . . and corresponding opaque X bus electrodes
24
-
1
,
24
-
2
, . . . , respectively, and the Y electrodes are comprised of transparent Y electrodes
23
-
1
,
23
-
2
, . . . and corresponding opaque Y bus electrodes
25
-
1
,
25
-
2
, . . . , respectively. It is often that the X electrodes are used as a common electrode and the Y electrodes are used as independent electrodes.
A discharge gap Ldg between the X and Y electrodes in one discharge cell are designed to be small such that a discharge breakdown voltage is not excessively high, and a spacing Lng between two adjacent cells is designed to be large such that unwanted discharge is prevented from occurring between two adjacent cells.
The discharge sustain X and Y electrodes are covered with a front dielectric substance
26
which, in turn, is covered with a protective film
27
made of material such as magnesium oxide (MgO).
The MgO protects the front dielectric substance
26
and lowers a discharge breakdown voltage because of its low sputtering yield and high secondary electron emission coefficient.
Address electrodes
29
(hereinafter referred to merely as an A-electrode) for addressing cells are disposed on the upper surface of the rear base plate
28
in a direction perpendicularly to the discharge sustain X and Y electrodes.
The address electrodes
29
are covered with a rear dielectric substance
30
, separation walls
31
are disposed between the A-electrodes on the rear dielectric substance
30
.
A phosphor
32
is coated in a cavity formed by the surfaces of the separation walls
31
and the upper surface of the rear dielectric substance
30
.
In this configuration, an intersection of a pair of discharge sustain electrodes with an A-electrode corresponds to one discharge cell, and the discharge cells are arranged in a two-dimensional fashion.
In a color PDP, a trio of three discharge cells coated with red, green and blue phosphors, respectively, forms one pixel.
FIG.
14
and
FIG. 15
are cross-sectional views of one discharge cell of
FIG. 13
viewed in the directions of the arrows D
1
and D
2
, respectively. In
FIG. 15
, the boundary of the cell is approximately represented by broken lines.
Now operation of the PDP will be explained.
The principle of generation of light by the PDP is such that discharge is started by a pulse applied between the X and Y electrodes, and ultraviolet rays generated by excited discharge gases are converted into visible light by the phosphor.
As shown in a block diagram of
FIG. 16
, the PDP
100
is incorporated into a plasma display device
102
.
In
FIG. 16
, a driving circuit
101
receives signals for a display image from a video signal source
103
, converts the signals into driving voltages as shown in
FIGS. 17A
to
17
C, and then supplies them to respective electrodes of the PDP
100
.
FIG. 17A
is a time chart illustrating a driving voltage during one TV field required for displaying one picture on the PDP shown in FIG.
13
. Portion of
FIG. 17A
illustrates that one TV field
40
is divided into sub-fields
41
to
48
having different numbers of light emission more than one from one another. Gray scales are generated by a combination of one or more selected from among the eight sub-fields.
Suppose eight sub-fields are provided which have gray scale brightness steps in binary number step increments, then each discharge cell of a three-primary color display device provides 2
8
(=256) gray scales, and as a result the three-primary color display device is capable of displaying about 16.78 millions of different colors.
Portion II of
FIG. 17A
illustrates that each sub-field comprises a reset discharge period
49
for resetting a discharge cell to an initial state, an address period
50
for addressing a discharge cell to be made luminescent, and a light-emission period (also called a discharge sustain period)
51
.
FIG. 17B
illustrates waveforms of voltages applied to the A-electrode
29
, the X electrode and the Y electrode during the address period
50
shown in
FIG. 17A. A
waveform
52
represent a voltage V
0
applied to one of the A-electrodes
29
, a wave form
53
represent a voltage V
1
applied to the X electrode, and waveforms
54
and
55
represent voltages V
21
and
22
applied to ith and (i+1)st Y electrodes.
As shown in
FIG. 17B
, when a scan pulse
56
is applied to the ith Y electrode, in a cell located at an intersection of the ith Y electrode with the A-electrode
29
supplied with the voltage V
0
, first an address discharge occurs between the Y electrode and the A-electrode, and then an address discharge occurs between the Y electrode and the X electrode.
No address discharges occur at cells located at intersections of the X and Y electrodes with the A-electrode at ground potential.
The above applies to a case where a scan pulse
27
is applied to the (i+1)st Y electrode.
In the cell where the address discharges have occurred, charges (wall discharges) are generated on the surface of the dielectric substance
26
and the protective film
27
covering the X and Y electrodes by the discharges, and consequently, a wall voltage Vw (V) occurs between the X and Y electrodes as shown in FIG.
15
.
In
FIG. 15
, reference numeral
3
denotes electrons,
4
is a positive ion,
5
is a positive wall charge, and
6
are negative wall charges.
The presence and absence of the wall charges corresponds to the presence and absence of sustain discharge during the succeeding light-emission period
51
, respectively.
FIG. 17C
illustrates pulse driving voltages (or voltage pulses) applied to the X and Y electrodes serving to sustain discharge and a driving voltage applied to the A-electrode, all at the same time during the light-emission period
51
shown in FIG.
17
A.
The Y electrode is supplied with a pulse driving voltage of waveform
58
, the X electrode is supplied with a pulse driving voltage of waveform
59
, the magnitude of the voltages of the waveforms
58
and
59
being V
3
(V).
The A-electrode
29
is supplied with a driving voltage of waveform
60
which is kept at a constant voltage V
4
during the light-emission period
51
. The voltage V
4
may be ground potential.
The pulse driving voltage of the magnitude V
3
is applied alternately to the X electrode and the Y electrode, and as a result reversal of the polarity of the voltage between the X and Y electrodes is repeated.
The magnitude V
3
is selected such that the presence and absence of the wall voltage generated by the address discharge correspond to the presence and absence of the sustaining discharge, respectively.
In the discharge cell where the address discharge has occurred, discharge is started by the first voltage pulse, and continues until wall charges of the opposite polarity accumu
Kajiyama Hiroshi
Kawanami Yoshimi
Kunii Yasuhiko
Shibata Masayuki
Suzuki Keizo
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Said Mansour M.
Shankar Vijay
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