Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-03-12
2001-08-07
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S060000, C313S581000, C315S169100
Reexamination Certificate
active
06271811
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of driving a plasma display panel (PDP to be abbreviated as PDP herebelow), and in particular, to a method of driving a PDP of an alternating-current (ac) discharge memory type.
DESCRIPTION OF THE RELATED ART
In general, a PDP has various advantageous features, for example, constitution with a reduced thickness and a high display contrast ratio, possibility of a relatively large screen, a high response speed, capability of multi-color emission by use of fluorescent substances. These days, consequently, PDPs have been increasingly and widely employed in many fields of, for example, displays and color displays related to computer systems.
PDPs are classified into two types according to operations thereof, namely, PDPs of an ac discharge type in which electrodes are covered with dielectrics such that operation is indirectly conducted in an ac discharge state and PDPs of a direct-current (dc) type in which electrodes are exposed to a discharge space such that operation is achieved in a dc discharge state. Moreover, the PDPs of the ac discharge type are grouped into PDPs of a memory operation type including a discharge cell memory to drive operation thereof and PDPs of a refresh operation type in which operation is accomplished without using such a discharge cell memory. In this connection, a PDP has luminance in proportion to the number of discharges during each unitary period of time, namely, the number of voltage pulses applied thereto per unitary time. In PDPs of the refresh operation type, luminance is lowered as the display capacity is increased. Consequently, this type is primarily used for PDPs having a small display capacity.
FIG. 1
shows in a cross-sectional diagram the structure of a display cell
8
b
of a PDP conducting the ac discharge operation. As can be seen from this diagram, the display cell
8
b
includes two insulator substrates
19
and
13
which are made of glass and which respectively provide a front surface and a rear surface thereof, a scanning electrode
11
and a sustaining electrode
14
which are fabricated on the insulator substrate
13
, a data electrode
18
formed on the insulator substrate
19
to be orthogonal to the scanning electrode
11
and the sustaining electrode
14
, a discharge gas space
12
disposed between the insulator substrates
13
and
19
and filled with a discharge gas including helium, neon, xenon, or a mixture thereof, an insulation wall
12
to reserve the discharge gas space of each display cell
8
b
, a phosphor layer
16
made to convert an ultraviolet ray emitted due to discharge of the discharge gas into a visible light, a layer of dielectrics
10
to cover the scanning electrode
11
and the sustaining electrode
14
, a protective layer
15
which is made of, for example, magnesium oxide and which protects the dielectrics
10
from being damaged by the discharge, and a layer of dielectrics
17
to cover the data electrode
18
.
Referring next to
FIG. 1
, description will be given of a discharge operation of the selected display cell
8
b.
In response to a pulse voltage exceeding a discharge threshold, namely, a data pulse applied between the scanning electrode
11
and the data electrode
18
, there is caused discharge therebetween. According to the polarity of the data pulse, particles having positive or negative electric charge are attracted onto surfaces of the dielectrics
10
and
17
so as to form accumulation of charge. Due to the charge accumulation, there appears an inner voltage or a wall voltage having a polarity opposite to that of the data pulse. In consequence, as the discharge continues, the effective voltage in the cell is reduced. Even if the data pulse voltage is kept at a fixed value, the discharge cannot be kept continued and is finally stopped. Thereafter, when a pulse voltage of a polarity equal to that of the wall voltage is applied between the scanning electrode
11
and the sustaining electrode
14
, a voltage associated with the wall voltage is superimposed onto the effective voltage. Consequently, even when the sustaining pulse has a small voltage amplitude, the discharge threshold is resultantly exceeded and hence there occurs discharge. In consequence, continuously applying the sustaining pulse between the scanning electrode
11
and the sustaining electrode
14
, the discharge can be kept continued, thereby achieving a memory function. In addition, when an erasing pulse which is a pulse having a low voltage and which has a height and a width enough to cancel the wall voltage is applied to the scanning electrode
11
or the sustaining electrode
14
, the discharge can be terminated.
Incidentally, in a PDP using the ac discharge memory, to develop a stable write discharge (between the scanning and data electrode), it is effective to carry out a pre-discharge prior to the write discharge. Effect of pre-discharge is attained by optimization of wall charge of each electrode and residual of active particles (charged particles and excited particles) supplied into the discharge space. The wall charge has a relatively long life, whereas the active particles are rapidly attenuated.
FIG. 2
shows layouts of electrodes of a conventional PDP using the ac discharge memory operation.
FIG. 2
shows the electrode arrangement of a conventional PDP achieving the ac discharge memory operation in which display cells
8
b
are disposed in the form of a matrix having j rows and k columns in association with the electrode layout of the PDP panel
7
b
for the dot matrix display. As shown in
FIG. 2
, the PDP
7
b
includes scanning electrodes S
c1
, S
c2
, . . . , and S
cj
and sustaining electrodes S
u1
, S
u2
, . . . , and S
uj
which are disposed parallel to the scanning electrodes S
c1
, S
c2
, . . . , and S
cj
and data electrodes D
1
, D
2
, . . . , and D
k
which are vertical to the scanning and sustaining electrodes. In this configuration, when the phosphor layer
16
of
FIG. 1
is provided with three colors red (R), green (G), and blue (B), there can be obtained a PDP capable of displaying color images.
FIG. 3
is a signal timing chart showing examples of waveforms of driving voltages in the PDP
7
b
, namely, a waveform of a common sustaining electrode driving voltage COM applied to the sustaining electrodes S
u1
, S
u2
, . . . , and S
uj
, waveforms of scanning electrode driving pulses S
1
, S
2
, S
3
, and S
j
respectively applied to the scanning electrodes S
c1
, S
c2
, . . . , and S
cj
, and a waveform of a data electrode driving voltage DATA applied to a data electrode D
i
(1≦i≦k).
FIG. 4
is a schematic diagram showing a cycle of driving operation in the conventional example. The driving cycle includes a pre-discharge period A(
1
-
6
), a pre-discharge erasing period B(
2
-
6
). a write discharge period C(
3
-
6
), and a sustaining discharge period D(
4
-
6
). The pre-discharge period A(
1
-
6
) and the pre-discharge erasing period B(
2
-
6
) constitute a period to generate active particles and wall charge in the discharge gas space
12
, thereby attaining a stable write discharge characteristic in the write discharge period C(
3
-
6
).
Namely, in each display cell of the PDP
7
b
, the discharge and erasing operations are effected simultaneously according to a pre-discharge pulse
1
b
and a pre-discharge erasing pulse
2
b.
In the write discharge period C(
3
-
6
), a scanning pulse
3
b
is sequentially applied at an independent timing to the scanning electrodes S
c1
, S
c2
, . . . , and S
cj
so as to achieve a write discharge in a line sequential manner. To conduct a write operation in an 1
i
-th display cell
8
b
, a data pulse
6
b
is applied thereto at a timing of the scanning pulse
3
b
having the driving waveform S
1
to cause discharge between the scanning electrode S
c1
and the data electrode D
i
. When a write operation is not desired for the display cell
8
b
, the data pulse is not applied thereto. In the sustaining discharge period D(
4
-
6
), a display cell in which a write discharge has been co
Nakamura Tadashi
Sano Yoshio
Shimizu Masahiro
Ueoka Mitsuo
Foley & Lardner
Lewis David L.
NEC Corporation
Shalwala Bipin
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