Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-04-19
2002-12-10
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169300, C345S060000, C345S067000, C345S068000
Reexamination Certificate
active
06492776
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for driving plasma display panels (PDP) which are used as display terminals for television sets and computers.
DESCRIPTION OF THE BACKGROUND ART
A plasma display panel (referred to as “PDP” hereinafter) is a device which displays letters or pictures by using light emitted from plasma generated during gaseous discharge. The PDP is classified into a DC-type and an AC-type depending on a driving method for providing an electric field thereto in order to make the plasma.
Since the PDP has advantageous characteristics such as large screen size of more than 40 inches, ability to display full-color images and wide viewing angle compared with other flat panel devices, it results in a rapid increase in its application area such as next generation high definition televisions (HDTV) capable of hanging on the wall and a multimedia display apparatus combining a TV and a personal computer.
There are several methods for driving the AC-type PDP. One of the methods is disclosed in U.S. Pat. No. 5,541,618, assigned to Fujitsu Limited. An Address Display period Separated (ADS) sub-field method is disclosed and used for driving the PDP in this patent. In accordance with this patent, one image frame is divided into n number of subframes. Each of the subframes includes: an addressing period subsequently providing scan pulses to all scan electrodes in order to indicate cells to be lit; and a display period having a predetermined sustain pulses and concurrently applying sustain pulses to all the scan electrodes, wherein a number of the sustain pulses is predetermined differently for each subframe. The scan pulses are continuously provided onto all the scan electrodes and address pulses are applied onto data electrodes in response to picture data to be displayed. However, according to the ADS sub-field method, since every subframe should have an addressing period for addressing all the scan lines, the display period is relatively shortened. Therefore, the brightness of an image may be decreased.
In order to prevent users from seeing flickers on the screen, the time for controlling illumination of one frame should be limited to about {fraction (1/60)} sec or less, namely 16.67 ms. In the NTSC system having 480 scan lines, if one image frame is divided into 8 number of subframes, it takes about 11 to 12 ms in addressing one image frame. Because the remaining time for the display period which TV viewer can substantially recognize the image is only 5 to 6 ms, the efficiency becomes only 30% and the brightness of the image is reduced. However, if increasing frequency of sustain pulse in order to compensate the brightness reduction, power consumption is increased and reliability of driving is also decreased.
In the case of HDTV having 1024 scan lines, because it takes about 24 to 25 ms in addressing one image frame, there is not enough remaining time for the display period. As a result, the TV viewer cannot recognize the image. Also, since pixels corresponding to scan electrodes are continuously selected for an addressing period, the reliability of driving is reduced by a result of static delay effect, which occurs in discharge firing.
One specific driving method for ADS is disclosed in EP patent No. 0,965,975A1 “Method and apparatus for driving plasma display panel”. A plasma display panel using this method has a plurality of first electrodes and second electrodes arranged parallel to each other, a plurality of third electrodes arranged to cross the first and second electrodes, and discharge cells defined within the areas in which the third electrodes cross the first and second electrodes. The electrodes are thus mutually arranged in the form of a matrix. According to a driving method for such a plasma display panel, a reset period is a period during which the distribution of wall charges in the plurality of discharge cells is uniformed. An addressing period is a period during which wall charges are produced in the discharge cells according to display data. A sustain discharge period is a period during which sustain discharge is induced in the discharge cells in which wall charges are produced during the addressing period. The driving method comprises a step of applying a first pulse as shown in prior art
FIG. 3
(−V
wx
, V
wy
) in which an applied voltage varies with time so as to induce first discharge in the lines defined by the first and second electrodes, and a step of applying a second pulse (V
ex
, −V
ey
) in which an applied voltage varies with time so as to induce second discharge as erase discharge in the lines defined by the first and second electrodes. These steps are carried out during the reset period.
FIG. 1
is a schematic diagram showing the structure of a surface discharge type PDP.
FIG. 2
is a waveform diagram illustrating an ADS driving method implemented in the PDP shown in FIG.
1
. During the addressing period, addressing discharge is induced by applying a scanning pulse successively to the Y electrodes. A voltage Vx is, conventionally applied to the X electrodes that are paired with the Y electrodes, to which the scanning pulse has been applied, to define display lines. Consequently, addressing discharge is induced. In contrast, a voltage −Vux is applied to X electrodes defining non-display lines. A potential difference from the Y electrodes is thus limited in order to prevent addressing discharge from being induced in the non-display lines. The scanning pulse is applied successively to the odd-numbered Y electrodes in order to induce addressing discharge. Thereafter, the scanning pulse is applied successively to the even-numbered Y electrodes in order to induce addressing discharge. This procedure is the same as that in the conventional method and is commonly referred to as a selective write method.
A second specific driving method for ADS is disclosed in U.S. Pat. No. 6,020,687 wherein a method for driving a plasma display panel includes carrying out an erase address operation when a display on the screen is renewed. The erase address operation includes the steps of carrying out an address preparation operation for producing the wall charge in all the discharge cells through a first step of generating a discharge only in a discharge cell in an ON-state, and a second step of generating a discharge only in a discharge cell in an OFF-state, and carrying out an operation for selectively erasing the wall charge in a discharge cell other than a discharge cell corresponding to data of the image to be displayed.
FIG. 3
shows exemplary waveforms for voltage pulses applied to the electrodes by this erase address method. The pulse for the erase address discharge (a voltage pulse synthesized from an address pulse applied to the address electrode and a scan pulse applied to the scan electrode) is applied to create an address discharge only in non-selected cells to remove the stored wall charge. Accordingly, the sustain discharge does not occur later in these cells. This method is commonly referred to as the selective erase method in the industry.
Another method for driving the PDP is Address While Display (AWD). There have been proposed many PDP driving methods that use the AWD method, such as in the article by Lim G. S. “New Driving Method for Improvement of Picture Quality in 40-inch AC PDP” Asia Display 98 pp. 591-594. In that article they adapted the new driving method to improve the picture quality that is called Distributed-Address and Sustain (DAS) method. This technique is different from the current ADS method. The address period and display period is not separated so the problem which reduces the light-emitting time in traditional ADS method is solved.
FIG. 4
shows the driving waveforms and timing diagrams, which were applied to the DAS method. The DAS method has a poor contrast ratio because the addressing method used is a non-selective write pulse followed by a selective erase pulse. Both pulses produce light output that is not part of picture data, therefore, resulting in a poor contrast ratio
Pappas George
Vu David
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