Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2002-05-22
2003-09-23
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169400, C345S060000, C345S063000
Reexamination Certificate
active
06624587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a driving technique for a plasma display panel, and more particularly to a method of driving a plasma display panel and an apparatus thereof that is capable of preventing an abnormal discharge generated at the upper and lower edges of an effective display area of the plasma display panel.
2. Description of the Related Art
Generally, a plasma display panel (PDP) radiates a phosphor using an ultraviolet with a wavelength of 147 nm generated upon discharge of an inactive mixture gas such as He+Xe, Ne+Xe or He+Ne+Xe, to thereby display a picture including characters and graphics. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development. Particularly, since a three-electrode, alternating current (AC) surface-discharge PDP has wall charges accumulated in the surface thereof upon discharge and protects electrodes from a sputtering generated by the discharge, it has advantages of a low-voltage driving and a long life.
Referring to
FIG. 1
, a discharge cell of a conventional three-electrode, AC surface-discharge PDP includes a scan/sustain electrode
12
Y and a common sustain electrode
12
Z provided on an upper substrate
11
, and an address electrode
17
X provided on a lower substrate
16
.
The scan/sustain electrode
12
Y and the common sustain electrode
12
Z are formed from a transparent electrode material, such as indium-tin-oxide (ITO). Each of the scan/sustain electrode
12
and the common sustain electrode
12
Z is provided with a metal bus electrode
13
for reducing a resistance.
An upper dielectric layer
14
and a protective film
15
are disposed on the upper substrate
11
provided with the scan/sustain electrode
12
Y and the common sustain electrode
12
Z. The protective film
15
prevents a damage of the upper dielectric layer
14
caused by a sputtering during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film
15
is usually made from magnesium oxide (MgO).
A lower dielectric layer
18
and barrier ribs
19
are formed on the lower substrate
18
provided with the address electrode
17
X. The surfaces of the lower dielectric layer
18
and the barrier ribs
19
are coated with a fluorescent material layer
20
. The address electrode
17
X is formed in a direction crossing the scan/sustain electrode
12
Y and the common sustain electrode
13
Z.
The barrier ribs
19
is formed in a direction parallel to the address electrode
17
X to prevent an ultraviolet ray and a visible light generated by the discharge from being leaked to the adjacent discharge cells. The fluorescent material layer
20
is excited by an ultraviolet ray generated upon plasma discharge to produce any one of red, green and blue visible lights. An inactive mixture gas such as He+Xe or Ne+Xe is injected into a discharge space defined between the upper and lower substrate
11
and
16
and the barrier rib
19
.
FIG. 2
shows a schematic electrode arrangement of the conventional three-electrode, AC surface-discharge PDP.
Referring to
FIG. 2
, the conventional three-electrode, AC surface-discharge PDP includes a scan electrode
12
Y and a sustain electrode
12
Z formed in a parallel to each other, and an address electrode
17
X perpendicular to the scan electrode
12
Y and the sustain electrode
12
Y. A discharge cell
30
is provided at each intersection among the address electrode
17
X and a pair of scan electrode
12
Y and sustain electrode
12
Z. Non-effective display areas
32
and
33
positioned at the outer sides of the upper and lower edges of an effective display area of the PDP are provided with dummy electrodes D. In other words, the dummy electrodes D of the upper non-effective display area
32
are provided at the upper portion of the first scan electrode Y
1
positioned at the uppermost portion of the effective display area
31
while the dummy electrodes D of the lower non-effective display area
33
are provided at the lower portion of the nth sustain electrode Z positioned at the lowermost portion of the effective display area
31
. The dummy electrodes D play a role to cause a priming discharge so that it can supply priming charged particles to the uppermost line and the lowermost line of the effective display area
31
.
In order to realize gray levels of a picture, such a PDP is driven by dividing one frame into various sub-fields having a different discharge frequency. Each sub-field is again divided into a reset period for causing a uniform discharge, an address period for selecting a discharge cell and a sustain period for implementing gray levels depending upon a discharge frequency. For instance, when it is intended to display a picture of 256 gray levels, a frame interval equal to {fraction (1/60)} second (i.e. 16.67 ms) is divided into 8 sub-fields as shown in FIG.
3
. Each of the 8 sub-fields is again divided into an address period and a sustain period. Herein, the reset period and the address period of each sub-field are equal every sub-field, whereas the sustain interval and the discharge frequency become different depending upon a brightness weighting value assigned to each sub-field. If a brightness weighting value is increased at a ratio of 2
n
(wherein n=0, 1, 2, 3, 4, 5, 6 and 7) for each successive sub-field, then each of the sustain period and the discharge frequency is twice increased in proportion to said brightness weighting value 2
n
whenever the current sub-field is transited into the next sub-field. Gray levels of a picture supplied in one frame interval can be implemented by a combination of the sustain discharge frequency differentiated for each sub-field as mentioned above.
However, the conventional PDP has a problem in that an abnormal discharge is caused by electric charges excessively accumulated at the non-effective display areas
32
and
33
positioned at the outer sides of the uppermost and lowermost portions of the effective display area
31
. If such a normal discharge is generated, then a light accompanied by the discharge is diffused into the effective display area
31
. Thus, a display quality is deteriorated. Furthermore, a picture fails to be displayed for several seconds and the discharge cell may be damaged in a serious circumstance. The abnormal discharge becomes more serious as a brightness of the PDP goes higher and a resolution of the PDP goes higher.
In order to overcome such an abnormal discharge, Japanese Laid-open Patent Gazette No. Pyung 10-64432 has been suggested a method of removing dielectric materials of the upper and lower edges of the PDP to discharge electric charges accumulated in the non-effective display areas
32
and
33
through the address electrode
17
X. Also, Japanese Laid-open Patent Gazette No. Pyung 10-69858 has been suggested a method of providing a normal turn-on area at the upper and lower edges of the PDP to cause a discharge at the normal turn-on area, thereby eliminating electric charges. However, these methods have a problem in that they are effective only when the entire area of the PDP is used as the effective display area, but fails to prevent the abnormal discharge in a case when a portion of the PDP is used as the display area.
Otherwise, Japanese Laid-open Patent Gazette No. Pyung 10-64434 has been suggested a method of mixing conductive particles within a dielectric layer provided with an address electrode to discharge electric charges accumulated in the upper and lower edges of the effective display area by utilizing the dielectric layer. This method has a problem in that it has a difficulty in keeping an electric conductivity of the dielectric layer in the baking process.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method of driving a plasma display panel and an apparatus thereof that is capable of preventing an abnormal discharge generated at the upper and lower e
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