Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-01-12
2001-06-26
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S068000
Reexamination Certificate
active
06252568
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive method for a plasma display panel, and particularly to a drive method for an AC memory type plasma display panel.
2. Description of the Related Art
Plasma display panels (hereinbelow abbreviated “PDP”) typically offer many features including thin construction, freedom from flicker, and a high display contrast ratio, and in addition are relatively easy to apply to large screens. They have a high response speed, and are the emissive type which can display color images using a phosphor. As a result, PDP are becoming increasingly widely used in recent years in the fields of computer-related display devices and color image display devices.
Depending on the method of operation, plasma display panels can be divided between the AC type, in which electrodes are covered by a dielectric and which are operated indirectly by AC discharge, and the DC type, in which the electrodes are exposed in a discharge space and which are operated directly by DC discharge. The AC type can be further divided between the memory type, which employs the memory of discharge cells as a drive method, and the refresh type, which doesn't make use of the discharge cell memory. The luminance of a PDP is proportional to the number of discharges, i.e., the number of repetitions of the pulse voltage. In the case of the above-described refresh type, luminance decreases with increase in the display capacity, and these displays are therefore mainly used in PDPs having a low display capacity.
FIG. 1
is a sectional view showing an example of the construction of one display cell in an AC memory type PDP. This display cell is made up of two insulator substrates
1
and
2
composed of glass, one being the front plate and the other being the rear plate; transparent scan electrode
3
and transparent sustain electrode
4
formed on insulator substrate
1
; bus electrodes
5
and
6
arranged over scan electrode
3
and sustain electrode
4
to decrease the electrode resistance; data electrode
7
formed on insulator substrate
2
orthogonal to scan electrode
3
and sustain electrode
4
; discharge space
8
between insulator substrates
1
and
2
filled with a discharge gas composed of, for example, helium, neon, or xenon, or a mixture of these gases; phosphor
11
for converting the ultraviolet rays generated by the above-described discharge of discharge gas into visible light
10
; dielectric layer
12
that covers scan electrode
3
and sustain electrode
4
; protective layer
13
composed of, for example, magnesium oxide for protecting dielectric layer
12
from discharge; and dielectric layer
14
that covers data electrode
7
.
Explanation is next presented regarding the discharge operation of a selected display cell with reference to FIG.
1
. When a pulse voltage that exceeds the discharge threshold value is applied between scan electrode
3
and data electrode
7
and discharge begins, positive and negative charges corresponding to the polarity of this pulse voltage are drawn to the surfaces of dielectric layers
12
and
14
on both sides, and charge is accumulated. The polarity of the equivalent internal voltage arising from this accumulation of charge, i.e., wall voltage, is the reverse of the polarity of the above-described pulse voltage, and the effective voltage inside the cell therefore decreases with the growth of discharge. Even if the above-described pulse voltage maintains a uniform value, discharge cannot be sustained and eventually stops. A sustaining discharge pulse, which is a pulse voltage of the same polarity as the wall voltage, is subsequently applied between neighboring scan electrode
3
and sustain electrode
4
. This voltage combines with the wall voltage portion as the effective voltage, whereby the display cell exceeds the discharge threshold value and can discharge even if the voltage amplitude of the sustaining discharge pulse is low. Discharge can be sustained in the display cell by continually applying the sustaining discharge pulse alternately between scan electrode
3
and sustain electrode
4
. This function is the memory function mentioned hereinabove. The above-described sustaining discharge can be stopped in the display cell by applying a wide low-voltage pulse or a narrow pulse, which has about the sustaining discharge pulse voltage, to scan electrode
3
or sustain electrode
4
so as to neutralize wall voltage.
FIG. 2
is a schematic plan view showing the composition of a PDP formed by arranging the display cell shown in
FIG. 1
in a matrix. In the figure, PDP
15
is a dot matrix display panel in which display cells
16
are arranged in mxn rows and columns. PDP
15
is provided with scan electrodes Sc
1
, Sc
2
, . . . , Scm and sustain electrodes Su
1
, Su
2
, . . . , Sum arranged in parallel as row electrodes. PDP
15
is also provided with data electrodes D
1
, D
2
, . . . , Dn arranged as column electrodes orthogonal to the scan electrodes and sustain electrodes.
FIG. 3
is a waveform chart of drive pulses illustrating a conventional drive method (hereinbelow referred to as the “first example of the prior art”) for the PDP shown in
FIG. 1
proposed in the “International Symposium Digest of Technical Papers of the Society for Information Display,” Volume XXVI, October 1995, pp. 807-810.
In
FIG. 3
, Wc is a sustain electrode drive pulse applied in common to sustain electrodes Su
1
, Su
2
, . . . , Sum; Ws
1
, Ws
2
, . . . , Wsm are scan electrode drive pulses applied to scan electrodes Sc
1
, Sc
2
, . . . , Scm, respectively; and Wd is a data electrode drive pulse applied to data electrode Di (1≦i≦n). One drive period (one frame) is made up of priming discharge interval A, addressing discharge interval B, and sustaining discharge interval C, and image display is obtained through repetition of these intervals.
Priming discharge interval A is the interval for generating wall charge and active particles in the discharge space so as to obtain stable addressing discharge characteristics in addressing discharge interval B. In priming discharge interval A, after applying priming discharge pulse Pp to cause all display cells of PDP
15
to discharge simultaneously, a priming discharge erasing pulse Ppe is simultaneously applied to each scan electrode to eliminate any charge of the wall charge generated by the priming discharge interval that would impede addressing discharge and sustaining discharge. In other words, priming discharge pulse Pp is first applied to Su
1
, Su
2
, . . . , Sum, and after discharge occurs in all display cells, erasing pulse Ppe is applied to scan electrodes Sc
1
, Sc
2
, . . . , Scm to bring about erasing discharge and eliminate wall charge accumulated due to the priming discharge pulse.
In addressing discharge interval B, sequential scan pulse Pw is applied to each scan electrode Sc
1
, Sc
2
, . . . , Scm. Synchronized with this scan pulse Pw, data pulse Pd is selectively applied to data electrodes Di (1≦i≦n) of those display cells that are to display, thereby bringing about addressing discharge and generating wall charge in display cells that are to display. Scan base pulse Pbw is a drive pulse that is applied to all scan electrodes in common throughout the duration of the addressing discharge interval, and is set to an amplitude whereby discharge does not occur between a scan electrode and data electrode even if data pulse Pd is applied to a data electrode.
In sustaining discharge interval C, sustaining discharge pulse Pc of negative polarity is applied to sustain electrodes, and sustaining discharge pulse Ps of negative polarity having phase delayed 180° from that of sustain electrode pulse Pc is applied to each scan electrode, thereby maintaining the sustaining discharge necessary for obtaining the desired luminance in display cells in which addressing discharge has occurred in addressing discharge interval B.
FIG. 4
is a waveform chart showing the drive method of the prior art described in Japanese Patent Laid-open No. 68946/97 (herein
Iseki Koki
Nakamura Tadashi
NEC Corporation
Piziali Jeff
Shalwala Bipin
Sughrue Mion Zinn Macpeak & Seas, PLLC
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