Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-08-31
2003-12-23
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169400, C345S060000
Reexamination Certificate
active
06667579
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a plasma display panel and a method of driving same. More particularly, the present invention relates to a technology to improve the display contrast while maintaining the performance stability in a plasma display panel of ALIS (Alternate Lighting of Surfaces) method in which every space between adjacent sustain electrodes is used as a display line.
A plasma display panel is a device in which a space of about 100 micron width between two glass substrates on which electrodes are formed is filled with mixed gases, consisting of gases such as Ne and Xe, for discharge, a voltage greater than the discharge start voltage is applied to cause a discharge to occur, and fluorescent materials formed on the substrates are activated, to emit light, by the ultraviolet rays generated by the discharge.
FIG. 1
is a diagram that shows the structure of a display apparatus employing a plasma display panel. In a display panel
10
, first electrodes
1
and second electrodes
2
arranged in parallel are formed, and third electrodes
3
are formed so as to be perpendicular to them. The first and the second electrodes are used mainly to perform a sustain discharge for display light emission, and the first electrodes are referred to as X electrodes, and similarly the second electrodes, as Y electrodes, here. A sustain discharge is performed by applying a voltage pulse repeatedly between the X electrode and the Y electrode. Moreover, some electrodes serve as a scanning electrode when display data is written. (In this example, the Y electrode is the scanning electrode.) On the other hand, the third electrode is used to select a display cell that is made to emit light in each display line, and a voltage is applied to perform a write discharge to select a cell to be made to discharge between the first or the second electrode and the third electrode. The third electrode is referred to as an address electrode here. These electrodes are connected to drive circuits to generate a voltage pulse to meet each purpose. As shown schematically, the X electrodes are connected to an X electrode drive circuit
12
and common drive signals are applied to the X electrodes. The X electrode drive circuit
12
has an X sustain pulse circuit
13
and an X reset voltage generate circuit
14
. The Y electrodes are connected to a Y electrode drive circuit
15
. The Y electrode drive circuit
15
has a scanning driver
16
, a Y sustain pulse circuit
17
, and a Y reset/address voltage generate circuit
18
. The address electrodes are connected to an address driver
11
. Because a display apparatus employing the plasma display panel is described in detail in EP 0 762 373 A2, and so on, which will be described later, no description is provided here.
FIG. 2
is a diagram to describe in detail the display panel part of the apparatus shown in FIG.
1
. The plural X electrodes
1
and the plural Y electrodes
2
are arranged in parallel. Display lines L1 through L4 are shown here. In addition, partitioning walls
5
are formed to separate the address electrodes
3
and the display cells. Therefore, each display cell is separated by the partitioning wall
5
in the direction that the X electrodes and the Y electrodes extend.
FIG. 3
is a diagram that shows the structure of a frame to illustrate the drive sequence of the apparatus shown in FIG.
1
. Because the discharge of a plasma display panel has only two values, that is, ON or OFF, the degree of brightness, that is, the gradation scale is represented by number of light emissions. For more efficient performance, a frame is divided into plural subfields, for example, 10 subfields. Each subfield comprises a reset period, an address period, and a sustain discharge period (also referred to as sustain period). In the reset period, an action is carried out to set all the cells to a uniform state, for example, a state in which wall charges are eliminated, regardless of the state of the cell whether ON or OFF in the preceding subframe. In the address period, a selective discharge (address discharge) is carried out to determine whether the cell is ON or OFF according to the display data, and wall charges to set a cell into the ON state are formed. In the sustain discharge period, a discharge is carried out repeatedly on the cell in which the address discharge is performed to emit a specified light. The length of the sustain discharge period, that is, the number of light emissions, differs from subfield to subfield. For example, an arbitrary gradation scale display can be attained by specifying the ratio of numbers of light emissions in the subfields 1 through 10 to 1:2:4:8 . . . , and making each cell emit light after selecting subfields according to the brightness of the cell for display.
FIG. 4
is a diagram that shows the light emission state of the reset discharge to illustrate the display contrast. To raise the display contrast, it is advisable to suppress the discharge intensity of the display cells for black display as much as possible. Therefore, it is preferable to prevent the discharge that does not have relation to display from occurring. The address discharge, however, may not be made to occur even if the specified voltage is applied between electrodes, if there is not a certain amount of suitable ions or metastable atoms. Therefore, the reset discharge is carried out in all the cells periodically. There are two methods to carry out the reset discharge in all the cells. One method is that, as shown in FIG.
4
(A), a discharge of certain level is carried out when the first subfield at the top of a frame (or a field) is initiated, and in this case, the all the cells reset discharge is not carried out in the second subfield and latter ones. This has been disclosed in Japanese Patent No. 2756053. The other method is that, as shown in FIG.
4
(B), a discharge of a small level is carried out in the reset period of all the cells. By using these methods, a display contrast of a ratio about 300:1 to 600:1 can be attained in a dark room. Concretely, the brightness is 1 cd/m
2
or less. Moreover, there may be another method, a combination of the two methods, that is, a reset with no or little light emission is carried out once in a frame or a field.
FIG. 5
is a diagram that illustrates the drive waveforms of the apparatus in
FIG. 1
, which is the example disclosed in Japanese Patent No. 2772753. In the reset period, a pulse of a high voltage, for example 300 V, greater than the discharge start voltage, is applied to the X electrode. By applying a pulse, a discharge is caused to occur in all the cells, regardless of the lighting state in the preceding subfield, and the wall charges are formed. When the pulse is removed, a discharge is caused to occur again by the voltage due to the wall charges themselves, but the space charges generated by the discharge are neutralized and a uniform state in which no wall charge exists can be established, because there is no voltage difference between electrodes. Although almost all charges are neutralized, a certain amount of ions and metastable atoms remains in the discharge space and works as a priming fire to cause the address discharge to occur without fail. This is called, in general, the pilot effect or the priming effect. In the address period, a scanning pulse is applied to the Y electrode, which is an electrode for scanning, and an address pulse is applied to the address electrode of the cell to be made to emit light and a discharge is caused to occur. This discharge propagates to the X electrode side and wall charges are formed between the X electrode and the Y electrode. This scanning is carried out on all the display lines. Then, in the sustain discharge period, a sustain pulse of Vs voltage (about 170 V) is applied repeatedly. The cell on which wall charges are formed by the address discharge initiates a discharge, because the voltage of the wall charges are added to the sustain pulse voltage and the total voltage becomes more than the discharge start voltage. The cell in which n
Kanazawa Yoshikazu
Setoguchi Noriaki
Fujitsu Hitachi Plasma Display Limited
Staas & Halsey , LLP
Vu Jimmy T.
Wong Don
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