Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-08-06
2002-12-03
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C345S060000
Reexamination Certificate
active
06489727
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to plasma display apparatuses, and particularly relates to a plasma display apparatus having an improved display contrast.
2. Description of the Related Art
Plasma display panels have two glass plates on which electrodes are formed, and discharge-purpose gas fills the gap of the order of 100 microns between the two glass plates. Voltages higher than the discharge threshold voltage are applied between the electrodes to start gas discharge, and ultraviolet light generated from the discharge induces the light emission of photo florescent provided on the plate, thereby effecting screen displaying.
FIG. 1
is a diagram showing a schematic configuration of a plasma display apparatus.
A display panel
10
includes first electrodes
14
and second electrodes
15
disposed in parallel, and further includes third electrodes
16
disposed in perpendicular thereto. The first electrodes
14
and the second electrodes
15
are used to provide sustain discharge for display-purpose light emission. Voltage pulses are applied between the first electrodes
14
and the second electrodes
15
, thereby carrying out sustain discharge. Either one of the first electrodes
14
and the second electrodes
15
serve as scan-purpose electrodes for writing display data. The third electrodes
16
are used to select display cells
17
that are to emit light. A voltage for writing discharge is applied between the third electrodes
16
and either one of the first electrodes and the second electrodes, so as to select discharge cells. The first electrodes
14
, the second electrodes
15
, and the third electrodes
16
are connected to a first driving circuit
11
, a second driving circuit
12
, and a third driving circuit
13
, respectively, which serve to generate voltage pulses for specific purposes.
FIG. 2
is a drawing showing details of the display panel unit
10
of the apparatus shown in FIG.
1
.
The first electrodes
14
serving as X electrodes and the second electrodes
15
serving as Y electrodes are laid out in parallel. Electrodes for display lines L
1
through L
4
are only shown in this figure. The third electrodes
16
serving as address electrodes are further formed together with shields
18
for separating the discharge cells. Details of discharge operations will be described later.
FIG. 3
is a drawing showing a frame configuration for explaining driving sequences.
Discharge of a plasma display panel can only assume either one of the “on” state and the “off” state, so that the density, i.e., the gray scale, is represented by the number of repeated light emissions. In order to efficiently implement this, a frame is divided into 10 sub-fields, for example. Each sub-field is comprised of a reset period, an address period, and a sustain discharge period. During the reset period, all cells are equally initialized regardless of lighting status in the previous sub-fields, e.g., are placed in the condition in which wall charge is erased. During the address period, selective discharge (addressing discharge) is performed to select the on/off states of cells in accordance with the display data, thereby generating wall charge that places cells in the “on” state. During the sustain discharge period, discharge is repeated in the cells where addressing discharge was performed, thereby emitting light. The length of the sustain discharge period, i.e., the number of repeated light emissions, differs from sub-field to sub-field. For example, the number of repeated light emissions may be determined such that ratios between sub-fields from the first sub-field to the tenth sub-field are 1:2:4:8: . . . :512. Sub-fields are selected in accordance with the luminance level of the display cell so as to be subjected to gas discharge, thereby achieving a desired gray scale display.
FIG. 4
is a drawing showing the way the reset discharge emits light.
When “black” is displayed in plasma display panels, it is desirable not to have any electrical discharge. Under the conditions where almost no ions, metastable atoms, or the like are present in the cell space, however, addressing discharge may not take place even when the required voltage is applied between the electrodes. In order to avoid this, all cells are periodically subjected to gas discharge.
There are two methods for such periodic discharge. One is to carry out discharge stronger than a predetermined intensity at the time of a start of the first sub-field, as shown in
FIG. 4
, (a). The other is to carry out small-scale discharge during the reset periods of all the sub-fields, as shown in
FIG. 4
, (b). These methods can provide a darkroom contrast of about 300:1 to 600:1. To be specific, the brightness of a black portion will be less than 1 cd/m
2
. Further, these two methods may be combined such that the resetting of a small-scale light emission is performed once in each frame or once in each field. In this case, a darkroom contrast of about 3000:1 is achieved. However, a complete darkness cannot be obtained, and an issue of stable operation still remains to be addressed.
FIG. 5
is a drawing showing waveforms for driving the first sub-field (e.g., SF
1
in
FIG. 4
, (a)) of a given frame.
During the reset period, a voltage, e.g., 300 V (Vw of
FIG. 5
, (b)), higher than the discharge threshold voltage is applied as a pulse to the X electrodes. This pulse causes gas discharge at all the cells regardless of the lighting status thereof in the preceding sub-field, thereby creating wall charge. When this pulse is gone, discharge starts again because of a voltage generated by the wall charge. Since no voltage difference exists between the electrodes, however, space charge generated by the discharge is neutralized to create the uniform condition of no wall discharge. Although most of the charge is neutralized, some ions and metastable atoms remain in the discharge space, serving as seeds to reliably generate addressing discharge. This is generally referred to as a seeds effect or priming effect.
During the address period after this, a scan pulse (Vy of
FIG. 5
, (c)) is applied to the Y electrodes serving as scanning electrodes, and address pulses (Va of
FIG. 5
, (a)) are applied to the address electrodes of the cells that are to emit light, thereby effecting gas discharge. This discharge spreads to the space on the side of the X electrodes, thereby generating wall charge between the X electrodes and the Y electrodes. This scanning is performed with respect to all the display lines.
During the sustain discharge period, sustain pulses of a voltage Vs (about 170 V) are repeatedly applied. At the cells where wall charge is in place by the addressing discharge, the sustain pulse voltage is added to the voltage of wall charge, thereby exceeding the discharge threshold voltage and starting actual discharge. At the cells where no addressing discharge was performed, no discharge is initiated since there is no wall charge.
FIG. 6
is a drawing showing waveforms for driving a sub-field during which no reset discharge of
FIG. 5
is performed.
The sub-field shown in
FIG. 6
corresponds to SF
1
through SF
10
of
FIG. 4
, (b). During the reset period, an erase pulse of a voltage Vb (
FIG. 6
, (b)) having a gentle slope is applied to all the cells. This causes discharge at the cells that emitted light in the preceding sub-field, thereby erasing wall discharge. Operations during the address period and the sustain discharge period are the same as those of FIG.
5
.
FIG. 7
is a drawing showing another configuration of a display panel unit different from that of FIG.
2
.
In a display panel unit
10
A of
FIG. 7
, X electrodes and Y electrodes serving as display electrodes are provided in turn at equal intervals so as to cross address electrodes A
1
through A
4
. All gaps between the electrodes are utilized as display lines (L
1
, L
2
, . . . ). This configuration is called an ALIS (alternate lightning of surfaces) method, and is disclosed in Japanese Patent No. 2801893. Since all the gaps
Fujitsu Hitachi Plasma Display Limited
Staas & Halsey , LLP
Vu David
LandOfFree
Plasma display with improved display contrast does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Plasma display with improved display contrast, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Plasma display with improved display contrast will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2976004