Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
1999-11-17
2003-04-01
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S582000, C313S584000, C315S169400
Reexamination Certificate
active
06541914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma display panel (PDP), and more particularly, to a discharge electrode and a phosphor for a PDP, which displays a color image.
2. Background of the Related Art
Generally, a PDP and a liquid crystal display (LCD) have lately attracted considerable attention as the most practical next display of panel displays. In particular, the PDP has higher luminance and wider visible angle than the LCD. For this reason, the PDP is widely used as a thin type large display such as an outdoor advertising tower, a wall TV, and a theater display.
The PDP performs display operation in such a manner to emit a phosphor using ultraviolet rays generated by gas discharge. Such a PDP includes an AC PDP having a dielectric layer on an electrode surface and a DC PDP in which an electrode surface is exposed to a discharge space. In the AC PDP, the phosphor is formed on the dielectric layer. In the DC PDP, the phosphor is formed on the electrode.
FIG. 1
shows a structure of a related art AC PDP of three-electrode area discharge type. As shown in
FIG. 1
, the related art AC PDP of three-electrode area discharge type includes an upper structure, a lower structure, and a discharge area
5
. The upper structure includes an upper electrode
4
having a Y electrode and a Z electrode on the same plane of a front glass substrate
1
, a dielectric layer
2
formed on the upper electrode
4
by printing, and a passivation layer formed on the dielectric layer
2
. The lower structure includes an X electrode
12
formed on a rear glass substrate
11
of the upper structure to cross the upper electrode
4
, an isolation wall
6
formed between the X electrode and the X electrode to prevent crosstalk between adjacent cells, and phosphors
8
,
9
and
10
formed around the isolation wall
6
and the X electrode
12
. The discharge area
5
is formed by sealing an inert gas in a space between the upper structure and the lower structure. For reference, in
FIG. 1
, the upper substrate is rotated by 90°.
The AC PDP of three-electrode area discharge type generates opposite discharge between the X electrode and the Y electrode if a driving voltage is applied between the X electrode and the Y electrode. As a result, wall charge occurs on a surface of the passivation layer of the upper structure. If discharge voltages having opposite polarities are continuously applied to the Y electrode and the Z electrode while the driving voltage applied to the X electrode is broken, area discharge occurs in the discharge area on surfaces of the passivation layer
3
and the dielectric layer
2
due to potential difference which is generated between the Y electrode and the Z electrode by wall charge. This area discharge generates ultraviolet rays
7
from the inert gas of the discharge area. The ultraviolet rays
7
excite the phosphors
8
,
9
, and
10
. The excited phosphors
8
,
9
and
10
are emitted to display color.
In other words, electrons in the discharge cell are accelerated to negative electrode by the driving voltage. The accelerated electrons come into collision with the inert mixing gas filled in the discharge cell at a pressure of 400~600 torr. The inert mixing gas is a penning mixing gas containing He as a main component and further containing Xe and Ne. The inert gas is excited by the collision to generate ultraviolet rays having a wavelength of 147 nm. The ultraviolet rays come into collision with the phosphors
8
,
9
and
10
surrounding the lower electrode
12
and the isolation wall
6
, so that light of a visible right ray region is emitted.
The PDP discharges a cell having pixels by controlling the voltages applied to the X, Y and Z electrodes. The intensity of light emitted by this discharge varies discharge time of the cell. In other words, gray scale required to display and image displays the image within the time required to display the entire image, for example, 1/30 seconds in case of NTSC TV signal, by varying the time length of discharge for each cell. At this time, the luminance of the screen is determined by brightness when each cell is discharged to the utmost. To obtain the highest luminance in the PDP screen, it is necessary to maintain the discharge time of the cell to the utmost within the time required to display one screen.
FIG. 2
is a block diagram showing a structure of a PDP having a driving circuit, in which a panel, an X electrode drive
10
, a Y electrode driver
20
and a Z electrode driver
30
are shown.
The X electrode
12
formed in each cell of the PDP in
FIG. 1
is connected to the X electrode driver
10
so that an address voltage is applied to the X electrode
12
. The Y electrode
25
is connected to the Y electrode driver
20
so that a scan voltage is applied to the Y electrode
25
. The Z electrode
35
is connected to the Z electrode driver
30
so that a sustain voltage is applied to the Z electrode
35
.
The X, Y and Z electrodes constitute a matrix arrangement. The matrix arrangement acts as a display area
50
of the PDP. The Y electrode
25
and the Z electrode
35
in
FIG. 2
correspond to the upper electrode
4
in FIG.
1
.
FIG. 3
shows waveforms of pulses applied to the respective electrodes of the PDP, in which the respective pulses show different waveforms in a reset period, an address period and a sustain period.
A reset pulse
21
of the scan voltage output from the Y electrode driver
20
is simultaneously applied to all of Y electrodes
25
in each discharge cell of the PDP. The Y electrode driver
20
inserts a scan pulse
22
into a sustain pulse
80
of the scan voltage applied to the Y electrode
25
so as to generate opposite discharge against the X electrode
20
referring to scan data. At this time, an address pulse
60
output from the X electrode driver
10
is applied to the X electrode
12
. The sustain voltage applied to the Z electrode
35
has a phase opposite to the sustain pulse
80
of the scan voltage and has the same period as the sustain pulse. The address pulse
60
applied to the X electrode
12
is synchronized with the scan pulse
22
applied to the Y electrode
25
and has a phase opposite to the scan pulse. Accordingly, the X electrode
12
and the Y electrode
25
generate opposite discharge by voltage difference between the address pulse
60
and the scan pulse
22
. The Y electrode
25
and the Z electrode
35
generate area discharge by voltage difference between the sustain pulse of the scan voltage and the sustain voltage. Then, if the address pulse
60
is applied to the scan voltage, area discharge stops, thereby turning off the discharge cell.
In case of opposite discharge, a red phosphor, a blue phosphor and a green phosphor formed in each discharge cell are emitted by different voltage levels, respectively. In other words, a discharge voltage in which ultraviolet rays for emitting the red phosphor are generated, a discharge voltage in which ultraviolet rays for emitting the blue phosphor are generated, and a discharge voltage in which ultraviolet rays for emitting the green phosphor are generated differ from one another because dielectric constants of the respective phosphors differ from one another. Therefore, the opposite discharge time and luminance are varied depending on the respective phosphors formed in the discharge cells of the PDP even if the same discharge voltage is applied to the respective discharge cells.
FIG. 4
shows an equivalent circuit of discharge cells of the PDP to which the discharge voltage is applied.
It is assumed that the phosphors are deposited on the electrode of the upper substrate in the same manner as the related art three-electrode area discharge type.
In
FIG. 4
, a voltage Vs is an externally applied voltage to the discharge cell, C
1
is a capacitance of the upper substrate in the cell to be discharged, Cg is a capacitance of the discharge space, Cp is a capacitance of the phosphor to be emitted, and C
2
is a capacitance of the lower substrate in the cell to be discharged excluding Cp.
The
Fleshner & Kim LLP
Guharay Karabi
LG Electronics Inc.
Patel Nimeshkumar D.
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