Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-08-02
2002-11-05
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169400, C345S068000
Reexamination Certificate
active
06476561
ABSTRACT:
This application is based on application No. H12-236231 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas discharge display device used for image display for computers, televisions, and the like, and in particular to a surface discharge AC plasma display panel.
2. Related Art
In recent years, there have been high expectations for large-screen televisions with superior picture quality such as high-definition televisions. In the field of display devices, plasma display panels (hereafter referred to as PDPs) have become the focus of attention for their ability to produce large-screen slimline televisions, with sixty-inch models already having been developed.
PDPs can be roughly divided into direct current (DC) types and alternating current (AC) types. At present, AC types, which are suitable for large-screen use, are prevalent.
A typical surface discharge AC PDP is described hereafter. A front panel and a back panel are arranged in parallel to each other with barrier ribs interposed therebetween. Discharge gas is enclosed in a discharge space which is partitioned by the barrier ribs. Scan electrodes and sustain electrodes are aligned in parallel on the front panel, and a dielectric layer is formed on the front panel so as to cover the scan and sustain electrodes. Also, address electrodes and the barrier ribs are arranged on the back panel, and red phosphor layers, green phosphor layers, and blue phosphor layers are formed between the barrier ribs.
FIG. 13
shows an electrode matrix of this PDP. In the drawing, for example, the number n of scan lines L is 4, and the number m of address lines is 6.
Pairs of scan electrodes SC
1
-SC
4
and sustain electrodes SU
1
-SU
4
are arranged in parallel at a predetermined pitch, and address electrodes A
1
-A
6
are aligned perpendicular to the scan and sustain electrodes. Discharge cells are formed at the points where the pairs of scan and sustain electrodes cross over the address electrodes. Adjacent discharge cells are separated by barrier ribs RIB
1
-RIB
7
.
To drive the PDP, drive circuits are used to apply pulses to the electrodes, which causes discharge and emission of ultraviolet light from the discharge gas. This ultraviolet light is absorbed by the particles of red, green, and blue phosphors in the phosphor layers, causing excited emission of light.
Discharge cells in an AC PDP are fundamentally only capable of two display states, ON and OFF. Accordingly, a field timesharing gradation display method is adopted whereby one field is divided into multiple sub-fields having predetermined weights and a gray scale is expressed by the combination of the sub-fields.
FIG. 14
shows a method of dividing one field when 256 gray levels are expressed. In the drawing, the horizontal direction represents time, and the areas filled in with black represent discharge sustain periods.
FIG. 15
shows an example of drive voltage waveforms which are applied to the electrodes in one sub-field, when driving the PDP according to the above method. As illustrated, one sub-field is made up of a write period, a sustain period, and an erase period.
In the write period, the sustain electrodes SU
1
-SU
n
are held at a fixed potential (0V in this example). A write pulse P
a
is selectively applied to the address electrodes A
1
-A
m
according to image data to be displayed, while a scan pulse P
scn
whose polarity is opposite to the write pulse P
a
is applied to the scan electrodes SC
1
-SC
n
.
As a result, the potential difference between the scan and address electrodes causes first write discharge, which in turn causes second write discharge between the scan and sustain electrodes (hereafter the first write discharge and the second write discharge are collectively called “write discharge”). Hence a wall charge necessary for sustain discharge to occur is accumulated.
By performing such write discharge sequentially for the scan electrodes SC
1
-SC
n
, image data to be displayed is written.
In the sustain period, AC sustain pulses P
sy
and PSX are applied in bulk to the scan electrodes SC
1
-SC
n
and the sustain electrodes SU
1
-SU
n
. This causes sustain discharge to continuously occur in the discharge cells where the wall charge has been accumulated in the write period, as a result of which an image is displayed.
In the erase period, an erase pulse P
e
is applied to all sustain electrodes SU
1
-SU
n
, to cause erase discharge. As a result, the wall charge which remains after the sustain discharge is mostly neutralized.
According to this drive method, since a great number of scan lines need to be scanned within the write period, the write discharge tends to become unstable. When the write discharge is unstable, the light emission caused by the subsequent sustain discharge becomes unstable, too.
This problem appears to be solved by setting the voltage of the write pulse at a high level. However, limitations in the performance of the data driver make it impossible to increase the voltage of the write pulse.
Accordingly, to produce an excellent image display, it is of particular importance to perform write discharge reliably within a write period.
Recently, various PDPs have been developed to improve panel brightness. Examples are a PDP whose filling pressure of discharge gas is set equal to or greater than an atmospheric pressure, and a PDP whose discharge gas contains Xe at a partial pressure of 10% or more. Such PDPs have particularly high write discharge firing voltages and so the problem of unstable write discharge is more serious. For this reason, it is difficult to drive these PDPs by the drive method shown in FIG.
15
.
To overcome this problem, a drive method that introduces a set-up period before the write period is disclosed by Japanese Laid-Open Patent Application No. H08-212930.
FIG. 17
shows an example of drive voltage waveforms according to this method. As shown in the drawing, a set-up pulse P
rn
of positive polarity is applied to the scan electrodes SC
1
-SC
n
in the set-up period.
By such applying the set-up pulse of the rectangular wave, set-up discharge takes place and as a result the wall charge remaining in the discharge cells after the erase discharge is completely neutralized. Also, priming effects that assist the subsequent write discharge to occur easily and reliably are obtained. Thus, this method is effective to stabilize the write discharge, but the level of stabilization achieved solely by this method is still insufficient, and other solutions are desired too.
To stabilize the write discharge, Japanese Laid-Open Paten Application No. H06-289811 discloses a drive method that applies a base pulse whose polarity is opposite to a write pulse, to scan electrodes in a write period.
FIG. 16
shows an example of drive voltage waveforms according to this method. In the drawing, the positive write pulse P
a
is applied to the address electrodes A
1
-A
m
. Also, a base pulse having a base voltage V
b
of negative polarity and constant wave height is applied to the scan electrodes SC
1
-SC
n
, throughout the write period, and a negative scan pulse P
sco
is superimposed on the base pulse.
When the base pulse is applied to the scan electrodes in this way, the potential difference between the address and scan electrodes and the potential difference between the scan and sustain electrodes increase by the degree of the base pulse applied. This encourages the first write discharge and the second write discharge to occur more reliably. As a result, the write discharge takes place unfailingly with no need to increase the voltage of the write pulse, with it being possible to improve the picture quality.
This base pulse applying method can drive, with a certain measure of success, a PDP whose discharge gas filling pressure is equal to or greater than an atmospheric pressure and a PDP whose discharge gas contains Xe at a partial pressure of 10% or more.
Even in this method, however, if the absolute value of the base voltage V
b
is set h
Matsushita Electric - Industrial Co., Ltd.
Price and Gess
Vu David
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