Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-08-15
2002-11-19
Ho, Tan (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169300, C345S068000, C345S076000, C345S077000
Reexamination Certificate
active
06483251
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of driving a plasma display. More particularly, the present invention relates to a method of driving a plasma display in which each display frame comprises plural subframes and the gradation display is attained by the combination of the lit subframes.
The plasma display (PD) apparatus has good visibility because it generates its own light, is thin and can be made with a large-screen and high-speed display and, therefore, it is attracting interest as a replacement for the CRT display.
FIG. 1
is a diagram that shows the basic structure of a PD apparatus.
As shown in
FIG. 1
, in a plasma display panel (PDP)
10
, X electrodes (the first electrode: sustain electrode) X
1
, X
2
, . . . , and Y electrodes (the second electrode: scan electrode) are arranged adjacently by turns and address electrodes (the third electrode) A
1
, A
2
, . . . are arranged in the direction perpendicular to that of the X and Y electrodes. A display line is formed between a pair of the X electrode and the Y electrode, that is, between X
1
and Y
1
, X
2
and Y
2
, and so on, and a display cell (hereinafter simply referred to as cell) is formed at the point where a display line and an address electrode intersect.
The X electrodes are commonly connected to an X sustain circuit
14
, and the identical drive signal is applied to them. The Y electrodes are individually connected to a Y scan driver
12
and a scanning pulse is applied sequentially to them in the address action, which will be described later or, otherwise, the identical drive signal is applied by a Y sustain circuit
13
. The address electrodes are connected to an address driver
11
and an address signal to select an ON cell and an OFF cell, in synchronization with the scanning pulse in the address action or, otherwise, the identical drive signal is applied to them. A control circuit
15
outputs a signal that controls each above-mentioned part.
FIG. 2
is a diagram that shows the structure of a frame to describe the drive sequence in the PDP apparatus. Since the discharge of the plasma display has only two states, that is, the ON state and the OFF state, the gradation of display is represented by the number of times of light emission. Therefore, a frame corresponding to a display is divided into plural subfields as shown in FIG.
2
. Each subfield comprises the reset period, address period, and the sustain period. In the reset period, an action is carried out that brings all the cells, regardless whether the cell was ON or OFF in the preceding field, into a uniform state, for example, a state in which wall charges are eliminated or wall charges are formed uniformly. In the address period, a selective discharge (address discharge) is carried out in order to determine whether a cell is in the ON or OFF state according to the display data and wall charges needed to cause a discharge for light emission to occur in the subsequent sustain period are formed on a cell in the ON state. In the sustain period, a discharge is carried out repeatedly for light emission in the cell put into the ON state in the address period. The length of the sustain period, that is, the number of times of light emission differs from subfield to subfield, and the gradation of display can be represented by setting the numbers of times of light emission to a ratio of, for example, 1:2:4:8 . . . , and combining subfields to emit light for each cell according to the gradation.
FIG. 3
is a waveform chart that shows an example of the conventional method of driving a plasma display panel. As shown schematically, in the reset period, a pulse of the voltage Vw greater than the discharge start voltage, 300 V for example, is applied to the X electrode. The application of this pulse causes a discharge to occur in every cell regardless whether the cell was ON or OFF in the preceding subfield and wall charges are formed. When this pulse is removed, a discharge is caused to occur again by the voltage due to the wall charges themselves, and because there is no potential difference between electrodes, the space charges generated by the discharge are neutralized and a uniform state without a wall charge is realized. In the address period, a scanning pulse is applied sequentially to the Y electrode and an address pulse (address signal) is applied to the address electrode of the cell to be lit of the display line to cause a discharge 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 performed to the entire display line. In the address period, it is required that a discharge is caused to occur in the cell to which an address pulse is applied, and not in the cell to which an address pulse is not applied, and the voltage of the address pulse is determined with various error factors being taken into account. Then, in the sustain period, a sustaining pulse of the voltage Vs (approx. 170 V) is applied repeatedly to the X electrode and the Y electrode. When the sustaining pulse is applied, the cell in which wall charges are formed in the address period takes place a discharge because the voltage due to the wall charges is superposed on that of the sustaining pulse and the total voltage exceeds the discharge start voltage. The cell, in which no wall charge is formed in the address period, does not discharge. Although almost all charges are neutralized, a certain amount of ions and metastable atoms remains in the discharge space. It may be a case in which these remaining charges are used to act as a priming to cause an address discharge without fail for the next address discharge. This is called, in general, the pilot effect or the priming effect.
FIG. 4
is a diagram that shows another example of a conventional driving method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2000-75835 by the present applicant. This driving method can cause a weak reset discharge to occur and prevent the contrast from deteriorating due to the reset discharge by designing the reset pulse with a slope waveform in which voltage changes gradually. In addition, Japanese Unexamined Patent Publication (Kokai) No.2000-75835 has disclosed that it is possible to make an amount of wall charges accumulate by adjusting the voltage applied between the X electrode and the Y electrode when the reset period is completed, and it is also possible to cause a stable address discharge to occur by setting the voltage with the slope waveform to be applied to the Y electrode to a voltage between the voltage when the scanning pulse is not applied and that of the scanning pulse in the address period.
The basic structure and action of the plasma display apparatus are described as above, but various examples of modification have been proposed. In one of the modifications, for example, plural subfields with the same number of times of light emission are provided in the frame structure as shown in
FIG. 2
to make an animation display smooth. In another modification, a reset action accompanied by write discharge is carried out only in the first subfield of a frame and not in the reset action of the subsequent subfields. In another modification, a reset is carried out not in all the cells but only in the cells that were ON in the preceding subfield. In another modification, uniform wall charges are left in the reset action and the erasing address method may be used to select cells that are OFF to eliminate wall charges in the address action. In another modification, a desired amount of charges is left to be utilized in the address action by applying a voltage between the X electrode and the Y electrode from which the reset pulse is removed. Moreover, the present applicant has disclosed the plasma display apparatus employing a method called the ALIS method, in which the number of display lines is doubled without changing the number of the X electrode and the Y electrode by forming display lines in every slit between the X electrode and the Y electrode, that is, betwee
Kishi Tomokatsu
Setoguchi Noriaki
Takamori Takahiro
Fujitsu Hitachi Plasma Display Limited
Ho Tan
Staas & Halsey , LLP
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