Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-06-29
2002-07-02
Shankar, Vijay (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S204000
Reexamination Certificate
active
06414654
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of driving a plasma display panel having a plurality of scan electrodes aligned in a row direction, a plurality of data electrodes aligned in a column direction, and a plurality of sustain electrodes that are formed parallel with the scan electrodes and that are each paired with a scan electrode.
2. Description of the Related Art
As flat display panels that can be readily applied to large-screen applications, plasma display panels (hereinbelow abbreviated “PDP”) that can be used for such purposes as a display output of personal computers, display output of work stations, and wall-hung televisions can be divided between two types depending on the operating method. One type is the direct-current discharge PDP in which electrodes are exposed to discharge gas and discharge is brought about only during the application of voltage, and the other is alternating-current PDP in which electrodes are covered with a dielectric and discharge is brought about without exposing the electrodes to discharge gas. The alternating-current PDP (hereinbelow referred to as “AC-PDP”) has a memory capability in the discharge cells themselves due to the charge-storing effect of a dielectric.
FIG. 1
is a section view showing the configuration of a typical AC-PDP of the prior art. In the AC-PDP shown in
FIG. 1
, the construction described hereinbelow is formed in a space enclosed between front substrate
10
containing glass and rear substrate
11
similarly containing glass.
Scan electrodes
12
and sustain electrodes
13
are alternately formed at a prescribed spacing on front substrate
10
. Scan electrodes
12
and sustain electrodes
13
are covered with insulation layer
15
a
, and protective layer
16
that protects insulation layer
15
a
from discharge and contains, for example, MgO, is formed on insulation layer
15
a
. In addition, data electrodes
19
are formed on rear substrate
11
orthogonal to scan electrodes
12
and sustain electrodes
13
on front substrate
10
. Data electrodes
19
are covered with insulation layer
15
b
, and phosphor
18
is applied on insulation layer
15
b
to effect display by converting ultraviolet rays generated by discharge into visible light. In addition, barrier ribs
17
that both establish discharge spaces
20
and demarcate pixels are formed between insulation layer
15
a
on front substrate
10
and insulation layer
15
b
on rear substrate
11
. A gas mixture of, for example, helium, neon and xenon is charged within discharge spaces
20
as the discharge gas.
FIG. 2
is a plan view showing the arrangement of electrodes in the AC-PDP shown in FIG.
1
. In the electrode configuration of the AC-PDP shown in
FIG. 2
, m scan electrodes
12
i
(i=1, 2, . . . , m) are formed in the row direction, n data electrodes l
9
j
(j=1, 2, . . . , n) are formed in the column direction, one pixel being formed at each point of intersection. Sustain electrodes
13
i
are formed in the horizontal direction to form pairs with scan electrodes
12
i
, scan electrodes
12
i
and sustain electrodes
13
i
being mutually parallel. A color display AC-PDP is produced by separately applying phosphor
18
shown in
FIG. 1
to each pixel in the three colors Red, Green, and Blue.
FIG. 3
is a timing chart showing the waveforms of the drive voltage applied to each electrode of the AC-PDP shown in FIG.
2
. Explanation is next presented regarding the drive method of an AC-PDP of the prior art with reference to FIG.
3
.
Extinguishing pulse
21
is first applied to all scan electrodes
12
to extinguish pixels that were emitting light before the time shown in
FIG. 3
, whereby all pixels are extinguished. Next, preparatory discharge is effected by applying preparatory discharge pulse
22
to sustain electrodes
13
to force all pixels to discharge and emit light. Preparatory discharge extinguishing pulse
23
is then applied to scan electrodes
12
to extinguish the preparatory discharge of all pixels. This preparatory discharge facilitates subsequent write discharge.
After extinguishing the preparatory discharge, scan pulses
24
are applied to each of scan electrodes
12
1
-
12
m
at a staggered timing, and, synchronized to the timing of the applied scan pulses
24
, data pulses
27
that correspond to display data are applied to data electrodes
19
1
-
19
n
. The diagonal lines of data pulses
27
in
FIG. 3
indicate that the presence or absence of data pulses
27
is determined according to the presence or absence of display data. Write discharge occurs within discharge spaces
20
between scan electrodes
12
and data electrodes
19
shown in
FIG. 1
in pixels in which data pulse
27
is applied at the time of scan pulse
24
is applied, and write discharge does not occur if data pulse
27
is not applied at the time scan pulse
24
is applied.
In a pixel in which write discharge occurs, a positive charge referred to as a wall charge is stored in insulation layer
15
a
at scan electrode
12
. At this time, a negative wall charge is stored on insulation layer
15
b
on data electrode
19
. First sustain discharge occurs due to the combination of the positive potential due to the positive wall charge formed on insulation layer
15
a
on scan electrodes
12
and first sustain discharge pulse
25
of negative polarity that is applied to sustain electrodes
13
. When first sustain discharge occurs, a positive wall charge is stored in insulation layer
15
a
at sustain electrode
13
and a negative wall charge is stored in insulation layer
15
a
over scan electrode
12
, thereby forming a potential difference. The potential difference due to these wall charges combines with second sustain discharge pulse
26
applied to scan electrodes
12
, generating a second sustain discharge. Sustain discharge thus continues with the potential difference caused by wall charge formed by the x
th
sustain discharge combining with the (x+1)
th
sustain discharge pulse. The amount of emitted light is controlled by the number of times sustain discharge is continued.
If the voltages of sustain discharge pulse
25
and sustain discharge pulse
26
are adjusted in advance to a level such that discharge is not generated by these pulse voltages alone, first sustain discharge will not occur despite the application of first sustain discharge pulse
25
in pixels in which write discharge has not occurred because there is no potential due to wall charge before first sustain discharge pulse
25
is applied, and subsequent sustain discharges will also not occur.
Sustain discharge pulse
25
and sustain discharge pulse
26
are usually applied to sustain electrodes
13
and scan electrodes
12
at a frequency on the order of 100 kHz. In addition, sustain discharge pulse
25
and sustain discharge pulse
26
have phases shifted 180° to each other. The frequency of generation of sustain discharges is on the order of 200 kHz because sustain discharge pulses
25
are alternately applied to sustain electrodes
13
and scan electrodes
12
.
Explanation is next presented regarding the gray-scale display method of an AC-PDP. In an AC-PDP, the drive sequence explained in
FIG. 3
is referred to as a sub-field. Essentially, the display ON/OFF is determined by write discharge in a sub-field, and the luminance of the emitted light is determined by the number of times of sustain discharge.
FIG. 4
is a chart showing the rate of the number of sustain discharge pulses during one image display period. Gray-scale display by sub-field divisions is explained with reference to FIG.
4
. Referring to
FIG. 4
, in an usual AC-PDP, one image display period is divided into a plurality of subfields, and ON/OFF control of display is effected in each sub-field. If the number of sustain discharges varies in each sub-field and, for example, the ratio of the number of sustain discharges is made 1:2:4:8 in a four sub-field division, 16 tones can be displayed by means of the ON/OFF control of each sub-field. In other words, tones
Frenel Vanel
McGinn & Gibb PLLC
NEC Corporation
Shankar Vijay
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