Computer graphics processing and selective visual display system – Display driving control circuitry – Waveform generator coupled to display elements
Reexamination Certificate
2003-06-03
2004-05-11
Chang, Kent (Department: 2673)
Computer graphics processing and selective visual display system
Display driving control circuitry
Waveform generator coupled to display elements
C345S060000
Reexamination Certificate
active
06734844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma display panel (PDP) and more particularly, to a method of driving a PDP having a preliminary discharge period for applying a preliminary discharge pulse or pulses to scan electrodes, a scan period for applying successively scan pulses to the individual scan electrodes, and a sustain period for applying sustain pulses to the scan electrodes.
2. Description of the Prior Art
PDPs have a lot of advantages such that they can be readily fabricated as large-sized flat display panels, and they can provide a wide field angle of view and quick response. Thus, in recent years, they have been used for flat display devices of various computers, wall-mounted television (TV) sets, public information display panels, and so on.
PDPs are generally classified into two groups with respect to their driving method; the direct current (dc) discharge type and the alternate current (ac) discharge type. In the dc-discharge type, the electrodes are exposed to the discharge space (i.e., the discharge gas) and the PDP is driven by using the dc discharge. The dc discharge is kept for the period when the dc driving voltage is applied. On the other hand, in the ac-discharge type, the electrodes are covered with the dielectric layer not to be exposed to the discharge space (i.e., the discharge gas) and the PDP is driven by using the ac discharge. The discharge is kept by the repetitive polarity reversal of the ac driving voltage.
Since the invention relates to the ac-discharge type PDP, the explanation will be made to only the ac-discharge type PDP.
The ac-discharge type PDP is classified into two groups with respect to the electrode count in each discharge cell or pixel; the two-electrode type and the three-electrode type. A typical example of the three-electrode type PDPs is shown in
FIGS. 20 and 21
.
FIG. 20
shows the configuration of the discharge cell of the three-electrode type PDP.
FIG. 21
shows the layout of the electrodes of this PDP.
As shown in
FIGS. 20 and 21
, this PDP includes front substrate
20
and a rear substrate
21
fixed together to be opposite to each other. These substrates
20
and
21
, each of which are usually made of a glass plate, are arranged parallel to and apart from each other by a specific distance.
A plurality of scan electrodes
22
(i.e., S
1
, S
2
, . . . , Sm) are formed to be parallel to each other on the inner surface of the front substrate
20
, where m is an integer greater than unity. A plurality of common electrodes
22
(i.e., C
1
, C
2
, . . . , Cm) are formed to be parallel to each other on the same inner surface of the front substrate
20
. The scan electrodes
22
and the common electrodes
23
extend in the same direction (the lateral direction in
FIG. 21
) alternately. A transparent dielectric layer
24
is formed on the inner surface of the substrate
20
to cover the scan electrodes
22
and the common electrodes
23
. On the dielectric layer
24
, a protection layer
25
, which is made of MgO, is formed to protect the layer
24
from the discharge.
On the other hand, a plurality of data electrodes
29
(i.e., D
1
, D
2
, . . . , Dn) are formed to be parallel to each other on the inner surface of the rear substrate
21
, where n is an integer greater than unity. The data electrodes
29
are perpendicular to the scan electrodes
22
and the common electrodes
23
. A white dielectric layer
28
is formed on the inner surface of the substrate
21
to cover the data electrodes
29
. On the dielectric layer
28
, a phosphor layer
27
is formed to emit visual light.
A plurality of partition walls (not shown) are formed to extend parallel to the data electrodes
29
in the space between the front and rear substrates
20
and
21
. These walls serve to form the discharge spaces
26
between the substrates
20
and
21
and the display cells or pixels
31
. The cells
31
are arranged in a matrix array. A specific discharge gas such as He, Ne, Xe, or the like is confined into the spaces
26
.
The above-described PDP configuration has been disclosed in various documents, an example of which is the paper, Society for Information Display (SID) 98 Digest, entitled “Cell Structure and Driving Method of a 25-in. (64-cm) Diagonal High-Resolution Color ac Plasma Display”, pp. 279-281, May 1998.
Next, a prior-art driving method of the three-electrode, ac-discharge type PDP shown in
FIGS. 20 and 21
is described below. This method is one of the so-called Address Display period Separated sub-field (ADS) methods, which has formed the main stream of methods of this sort.
FIGS. 1A
to
1
E are waveform charts for explaining this prior-art driving method during one of the sub-fields T
1
. The sub-field T
1
is formed by a preliminary discharge period T
2
, a scan period T
3
, and a sustain period T
4
.
In the preliminary discharge period T
2
, a preliminary discharge pulse
114
(which is negative here) is commonly applied to the common electrodes
23
(i.e., C
1
to Cm). Thus, the difference in wall-charge formation state in the preceding, adjoining sub-field T
1
is reset or eliminated for initialization. At the same time as this, ac discharge is caused in all the discharge cells
31
to eliminate the data contained therein, thereby enabling the next writing discharge to occur at a low applied voltage, i.e., enabling the “priming effect” to occur. As a result, the preliminary discharge pulse
114
needs to have an amplitude or voltage level greater than those of the scan pulses and the sustain pulses described later.
One preliminary discharge pulse
114
is used in FIG.
1
A. However, two roles of eliminating the difference in wall-charge formation state and of causing the priming effect may be performed by respective pulses. Specifically, a sustain-discharge elimination pulse for resetting the state in the prior sub-field may be applied to the common electrodes
23
(i.e., C
1
to Cm) and then, a priming pulse for generating the priming effect in all the cells
31
may be applied thereto. In this case, the count of the sustain-discharge elimination pulses is not limited to unity. It may be two or more.
The priming effect is not necessary for every sub-field. In some driving methods, only a single priming pulse is applied during several successive sub-fields. The priming pulse activates all the cells
31
to emit light independent of whether the cells
31
have displayed information or not. Therefore, if the count of the priming pulses is decreased, the luminance at the time when the cells
31
display black color can be suppressed.
If the preliminary discharge pulse
114
as shown in
FIG. 1A
is used, to cause a single priming operation during several successive sub-fields, the voltage level or amplitude of the pulse
114
may be set to be low enough for performing only the resetting operation. In this case, to ensure the resetting operation, another pulse or pulses may be applied several times, instead of the pulse
114
.
Subsequent to the preliminary discharge pulse
114
, a preliminary-discharge elimination pulse
115
(which is negative here) is commonly applied to the scan electrodes
22
(S
1
to Sm) in the preliminary discharge period T
2
. Thus, the wall charge, which have been induced in the dielectric layers
24
and
28
by preliminary discharge due to the preliminary discharge pulse
114
, are eliminated or controlled to desired amount.
In
FIGS. 1B
to
1
D, one preliminary-discharge elimination pulse
115
is applied, two or more pulses
115
may be applied to the scan electrodes
22
to ensure the roles of the scan pulses and the sustain pulses, to suppress the fluctuation of the light-emitting state in all the cells
31
, and to cope with the load fluctuation for displaying behavior. The preliminary-discharge elimination pulse or pulses
115
may be applied to other electrodes than the scan electrodes
22
also.
Then, in the scan period T
3
, scan pulses
109
(which are negative here) are successively applied to the respective, scan electrodes
22
(i.e.,
Chang Kent
Katten Muchin Zavis & Rosenman
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