Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
2000-05-02
2002-04-23
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S584000, C345S060000
Reexamination Certificate
active
06376986
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface discharge type plasma display panel (PDP) in which main electrodes making a pair extend in parallel as row electrodes defining rows of a screen.
It is said that a ratio of a main electrode area and a cell area (an area ratio) is better to be smaller for improving a light emission efficiency (1m/W) that is a light emission quantity (luminous flux) per a unit power consumption in a plasma display panel. In “The latest in Technology of Plasma Display,” (Mikoshiba, ED Research Co.) the following equation is disclosed.
light emission efficiency=1/(1+c×discharge current density),
where c is a constant.
Two of the reasons the light emission efficiency is improved are as follows. First, non-effective power consumed for charging a capacitance between the electrodes is reduced. Secondly, the discharge current decreases along with the decrease of the area ratio, and self-absorption of a vacuum ultraviolet light by discharge gas decreases so that excitation efficiency is enhanced.
However, if the width of the main electrode is reduced for decreasing the area ratio, the gap length of the surface discharge is increased. In this case, although the capacitance between the electrodes decreases, a discharge starting voltage increases and a voltage margin of driving decreases.
The increase of the cell number for a wide screen and a high definition causes an increase of power consumption. The reduction of the power consumption is important from a viewpoint of reducing generation of heat. It is required to satisfy both securing an operation margin for a stable display and improving the light emission efficiency.
2. Description of the Prior Art
FIG. 13
is a plan view showing the conventional electrode structure.
FIG. 14
is a perspective view showing an inner structure of the conventional plasma display panel.
The illustrated plasma display panel
9
has a structure disclosed in Japanese unexamined patent publication No. 9-50768. Main electrodes Xq, Yq, a dielectric layer
17
and a protection film
18
are provided on the front side glass substrate
11
. On the backside glass substrate
21
, there are provided address electrodes A as row electrodes, an insulator layer
24
, partitions
29
for defining a discharge space
30
, and fluorescent layers
28
R,
28
G and
28
B for color display. Each of the main electrodes Xq, Yq includes a transparent conductive film
41
q
and a metal film
42
q
. The main electrodes Xq, Yq are arranged alternately at a constant space (a surface discharge gap) in the column direction. The gap direction of the surface discharge gap, i.e., the direction in which the main electrodes Xq, Yq face each other is the column direction. The discharge space
30
is filled with a two-component gas such as neon and xenon.
In the plasma display panel
9
, the partition
29
that divides the discharge space
30
in each column has a ribbon shape meandering regularly in a plan view. As shown in
FIG. 14
, each partition
29
is meandering at a constant pitch and width in a plan view, and is arranged so that the distance between the neighboring partitions
29
becomes smaller than a constant value periodically along the column direction. The constant value is a distance that can suppress the discharge and is determined by the discharge condition such as a gas pressure. Since the partitions
29
are disposed separately, the space (a column space)
31
between the neighboring partitions is continuous over the all rows of the screen. Thus, easiness of the drive in each column by priming, uniformity of the printing state of the fluorescent layer and easiness of the exhausting process in manufacturing can be realized. In the plasma display panel
9
, a red fluorescent layer
28
R, a green fluorescent layer
28
G and a blue fluorescent layer
28
B are arranged in this order for each column. The light emission color of each row in a column is the same.
A portion (a narrowing portion)
31
B of the column space
31
in which the width in the row direction is small cannot generate the surface discharge easily, so a portion (enlarging portion)
31
A having a wide width substantially contributes the light emission. Therefore, a cell that is a display element is disposed at every two columns in each row. Noting the neighboring two rows, the column in which a cell is disposed changes alternately one by one column. Namely, cells are arranged in a staggered pattern both in the row direction and the column direction. In the plasma display panel
9
, the neighboring three cells of red, green and blue colors constitute a pixel. The arrangement format of the color display by the three colors is a triangle (delta) format. The triangle arrangement has an advantage for high definition compared with an inline arrangement since the width of the cell is larger than one third of the pixel pitch in the row direction. In addition, it can perform a high intensity display since a ratio of non-emission area of the screen is small.
In the conventional structure, the shape of the main electrodes Xq, Yq in a plan view is like linear ribbon having a constant width over the full length of the screen, and the main electrodes Xq, Yq are close to each other in the narrowing portion
31
B as well as the enlarging portion
31
A of the column space
31
. Therefore, an error discharge can be generated in the narrowing portion
31
B. If attempting to prevent the error discharge completely by setting the drive voltage, the operation margin will become small. It is also a problem that a waste of power consumption for charging a capacitance between the electrodes is large.
SUMMARY OF THE INVENTION
The object of the present invention is to prevent the interference of discharge between the rows securely without decreasing the operation margin. Another object of the present invention is to reduce a capacitance between electrodes. Still another object of the present invention is to reduce a discharge current so as to improve a light emission efficiency.
In the present invention, the shape of the main is selected so that an electrode area ratio at a narrowing portion in a column space is smaller than an electrode area ratio at an enlarging portion, and the maximum value of the electrode gap between rows at the narrowing portion is larger than the minimum value of the electrode gap at the enlarging portion (i.e., surface discharge gap length). If the electrode area ratio at the narrowing portion is small, the diffusion of the discharge along the electrode is suppressed so that the interference of the discharge in the column direction is prevented. It is the best that the main electrode is provided so that the electrode area ratio becomes zero, i.e., so as to avoid the narrowing portion. In addition, by enlarging the electrode gap between rows at the narrowing portion for a part or the entire of the opposing area of the electrodes, a capacitance between the electrodes is reduced. Thus, a waste of power consumption is reduced so that the light emission efficiency is improved.
In the present invention, the main electrode is formed in the shape having a belt-like portion extending in the row direction and a half circle portion protruding toward the enlarging portion of each column. The half circle portion opposes the other half circle portion of the neighboring main electrode so as to form a surface discharge gap, The electrode area in the cell decreases by the extent of the gap between the half circle portion and the belt-like portion. As a result, the discharge current decreases so that light emission efficiency is improved. It is not necessary to increase the surface discharge gap length for decreasing the electrode area. Namely, a predetermined operation margin can be secured. By increasing the number of lighting times per a period, the drop of the intensity due to the decrease of the discharge current can be compensated. It is preferable for the intensity to form the half circle portion with a transparent conductive film
Kosaka Tadayoshi
Namiki Fumihiro
Takagi Kazushige
Fujitsu Limited
Patel Ashok
Staas & Halsey , LLP
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