Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-03-13
2003-11-25
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C345S060000
Reexamination Certificate
active
06653795
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a technique for driving a plasma display panel, and more particularly to a plasma display panel driving method and apparatus that is capable of driving a plasma display panel at a higher speed as well as improving the contrast.
2. Description of the Related Art
Generally, a plasma display panel (PDP) radiates a fluorescent body by an ultraviolet with a wavelength of 147 nm generated during a discharge of He+Xe or Ne+Xe gas 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, a three-electrode, alternating current (AC) surface-discharge type PDP has advantages of a low-voltage driving and a long life in that it can lower a voltage required for a discharge using wall charges accumulated on the surface thereof during the discharge and protect the electrodes from a sputtering caused by the discharge.
Referring to
FIG. 1
, a discharge cell of the three-electrode, AC surface-discharge PDP includes a scanning/sustaining electrode
30
Y and a common sustaining electrode
30
Z formed on an upper substrate
10
, and an address electrode
20
X formed on a lower substrate
18
.
The scanning/sustaining electrode
30
Y and the common sustaining electrode
30
Z include a transparent electrode
12
Y or
12
Z, and a metal bus electrode
13
Y or
13
Z having a smaller line width than the transparent electrode
12
Y or
12
Z and provided at one edge of the transparent electrode, respectively. The transparent electrodes
12
Y and
12
Z are formed from indium-tin-oxide (ITO) on the upper substrate
10
. The metal bus electrodes
13
Y and
13
Z are formed from a metal such as chrome (Cr), etc. on the transparent electrodes
12
Y and
12
Z so as to reduce a voltage drop caused by the transparent electrodes
12
Y and
12
Z having a high resistance. On the upper substrate
10
provided with the scanning/sustaining electrode
30
Y and the common sustaining electrode
30
Z, an upper dielectric layer
14
and a protective film
16
are disposed. Wall charges generated upon plasma discharge are accumulated in the upper dielectric layer
14
. The protective film
16
protects the upper dielectric layer
14
from a sputtering generated during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film
16
is usually made from MgO. The address electrode
20
X is formed in a direction crossing the scanning/sustaining electrode
30
Y and the common sustaining electrode
30
Z. A lower dielectric layer
22
and barrier ribs
24
are formed on the lower substrate
18
provided with the address electrode
20
X. A fluorescent material layer
26
is coated on the surfaces of the lower dielectric layer
22
and the barrier ribs
24
. The barrier ribs
24
are formed in parallel to the address electrode
20
X to divide the discharge cell physically and prevent an ultraviolet ray and a visible light generated by the discharge from being leaked into the adjacent discharge cells. The fluorescent material layer
26
is excited and radiated by an ultraviolet ray generated upon plasma discharge to produce a red, green or blue color visible light ray. An inactive mixture gas, such as He+Xe or Ne+Xe, for a gas discharge is injected into a discharge space defined between the upper/lower substrate
10
and
18
and the barrier ribs
24
.
Such a three-electrode AC surface-discharge PDP drives one frame, which is divided into various sub-fields having a different emission frequency, so as to realize gray levels of a picture. Each sub-field is again divided into a reset interval for uniformly causing a discharge, an address interval for selecting the discharge cell and a sustaining interval for realizing the gray levels depending on the discharge frequency. 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 msec) in each discharge cell
1
is divided into 8 sub-fields SF
1
to SF
8
as shown in FIG.
2
. Each of the 8 sub-field SF
1
to SF
8
is divided into a reset interval, an address interval and a sustaining interval. The reset interval and the address interval of each sub-field are equal every sub-field, whereas the sustaining interval and the discharge frequency are increased at a ration of 2
n
(wherein n=0, 1, 2, 3, 4, 5, 6 and 7) at each sub-field. Since the sustaining interval becomes different at each sub-field as mentioned above, the gray levels of a picture can be realized.
Such a PDP driving method is largely classified into a selective writing system and a selective erasing system depending on an emission of the discharge cell selected by the address discharge.
The selective writing system turns off the entire field in the reset interval and thereafter turns on the discharge cells selected by the address discharge. In the sustaining interval, a discharge of the discharge cells selected by the address discharge is sustained to display a picture.
In the selective writing system, a scanning pulse applied to the scanning/sustaining electrode
30
Y has a pulse width set to 3 &mgr;s or more to form sufficient wall charges within the discharge-cell.
If the PDP has a resolution of VGA (video graphics array) class, it has total 480 scanning lines. Accordingly, in the selective writing system, an address interval within one frame requires total 11.52 ms when one frame interval (i.e., 16.67 ms) includes 8 sub-fields. On the other hand, a sustaining interval is assigned to 3.05 ms in consideration of a vertical synchronizing signal Vsync.
Herein, the address interval is calculated by 3 &mgr;s(a pulse width of the scanning pulse)×480 lines×8(the number of sub-fields) per frame. The sustaining interval is a time value (i.e., 16.67 ms−11.52 ms−0.3 ms−1 ms−0.8 ms) subtracting an address interval of 11.52 ms, once reset interval of 0.3 ms, and an extra time of the vertical synchronizing signal Vsync of 1 ms and an erasure interval of 100 &mgr;s×8 sub-fields from one frame interval of 16.67 ms.
The PDP may generate a pseudo contour noise from a moving picture because of its characteristic realizing the gray levels of the picture by a combination of sub-fields. If the pseudo contour noise is generated, then a pseudo contour emerges on the screen to deteriorate a picture display quality. For instance, if the screen is moved to the left after the left half of the screen was displayed by a gray level value of 128 and the right half of the screen was displayed by a gray level value of 127, a peak white, that is, a white stripe emerges at a boundary portion between the gray level values 127 and 128. To the contrary, if the screen is moved to the right after the left half thereof was displayed by a gray level value of 128 and the right half thereof was displayed by a gray level value of 127, then a black level, that is, a black stripe emerges on at a boundary portion between the gray level values 127 and 128.
In order to eliminate a pseudo contour noise of a moving picture, there has been suggested a scheme of dividing one sub-field to add one or two sub-fields, a scheme of re-arranging the sequence of sub-fields, a scheme of adding the sub-fields and re-arranging the sequence of sub-fields, and an error diffusion method, etc. However, in the selective writing system, the sustaining interval becomes insufficient or fails to be assigned if the sub-fields are added so as to eliminate a pseudo contour noise of a moving picture. For instance, in the selective writing system, two sub-fields of the 8 sub-fields are divided such that one frame includes 10 sub-fields, the display period, that is, the sustaining interval becomes absolutely insufficient. If one frame includes 10 sub-fields, the address interval becomes 14.4 ms, which is calculated by 3 &mgr;s(a pulse width of the scanning puls
Cho Jang Hwan
Kang Seong Ho
Kim Gop Sick
Lee Eung Kwan
A Minh D
Fleshner & Kim LLP
LG Electronics Inc.
Wong Don
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