Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1998-03-23
2002-11-05
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S060000, C348S558000
Reexamination Certificate
active
06476801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma display device which controls signal processing in response to the signal format of an input signal.
2. Description of the Background Art
A plasma display panel (PDP) has been hithertofore known as one of the flat panel displays and received much attention as an alternative to a cathode ray tube (CRT).
Displaying an input video signal on a PDP requires the conversion of the video signal into pixel-by-pixel digital image data. Each pixel corresponds to a discharge cell which is a unit of discharge in the PDP. Gradation control at each discharge cell is such that a field is divided into subfields based on the number of gradation levels and luminescence or non-luminescence in each of the subfields is controlled. For example, if digital data indicative of a gradation level at each discharge cell is 6-bit digital data (64-level gradation), one field is divided into six subfields, and luminescence or non-luminescence in each of the six subfields is controlled depending on whether each bit is “1” or “0”. The luminance at each discharge cell corresponds to the digital data by setting the ratio of the number of sustain pulses in each of the subfields to 2
5
(MSB) to 2
0
(LSB). Thus, the increase in the number of subfields increases the number of gradation levels to achieve smooth display having improved gradation properties.
The luminescence or non-luminescence at each discharge cell is controlled in a manner described below. First, a priming pulse is applied to force a discharge to be produced at all discharge cells and to erase wall charges. Then, a scan pulse is applied to a scan electrode and an address pulse is selectively applied to an address electrode depending on display data to control whether to provide wall charges or not. This determines whether to cause luminescence at the associated discharge cell using a subsequent sustain pulse or not. At this time, reliable luminescence and enhanced display stability are achieved by increasing the pulse width of the scan pulse to prolong write time for providing the wall charges.
The division of one field into subfields for display control at each discharge cell as above described presents a problem in that a pseudo contour is produced when a moving picture is displayed. Specifically, an observer that follows a moving picture with his or her eyes finds the pseudo contour produced in a section of an image where the gradation should change smoothly. To prevent this, it has been proposed to subdivide a predetermined number of subfields to alleviate the moving picture pseudo contour.
The above described control accomplishes multi-level gradation display, high-luminance display, stable luminescence, prevention of moving picture pseudo contours and the like in the PDP image display.
The time required for one field is a fixed value determined by an input signal dependent upon a signalling system such as NTSC, PAL, and VGA, and is generally 16 to 20 msec. The above described control must be performed within this limited length of time. Unfortunately, time is insufficient for the control that satisfies overall performance. Specifically, the increase in the number of subfields, the elongation of the write time, and the subdivision of the subfields require accordingly longer time for one-field display, resulting in the insufficient execution of the above described control.
Further, signals are classified depending on the signal format, for example, into an interlaced scanning signal (referred to hereinafter as an “interlace signal”) and a non-interlaced scanning signal (referred to hereinafter as a “non-interlace signal”). The PDP which fundamentally uses the non-interlace signals for display is required to perform an interpolation process on the interlace signals to convert the interlace signals into the non-interlace signals. The interpolation process includes, for example, producing an intermediate horizontal line signal from two horizontal line signals, an upper and a lower. Disclosed in Japanese Patent Application Laid-Open No. P05-216433A (1993) is a simple process for driving the PDP so that one field of the interlace signal is displayed in a pair of lines, thereby to display the interlace signal, without using the conversion into the non-interlace signal by signal processing. This technique enables a pair of lines to be written at a time, reducing the time required for the write operation by half, but renders a displayed image rough on the whole since the same signal is displayed in the pair of lines. The use of this drive process requires the PDP to be used specifically for an interlace signal input and to fail to display the non-interlace signals such as VGA.
The time required for one field differs depending on the signal format of the input signal such as an NTSC system, a PAL system, VGA, and XGA. The level of the luminance in the plasma display is generally proportional to the frequency of the sustain pulse. Thus, changes in vertical synchronization frequency change the frequency of the sustain pulse depending on the signal format of the input signal, thereby changing the maximum luminance.
The amount of power consumption in the plasma display is proportional to the product of an APL (Average Picture Level) and the luminance. The APL is defined to mean a numerical value obtained by averaging the gradation levels (%) of all cells. For instance, the APL is 0% if black is displayed on the full screen, and is 100% if the highest gradation level of white is displayed on the full screen. The APL of a typical image is said to be an average of about 30 to 40%.
Thus, the increase in the frequency of the sustain pulse for higher luminance is not a problem for a typical screen but results in the increase in power consumption for a special screen, for example, a screen on which white is fully displayed. Countermeasures against this problem include APC (Automatic Power Control) which controls the luminance depending on the APL to suppress the power consumption at a fixed level or lower. This method is capable of suppressing maximum power consumption at a fixed level or lower on a typical screen while maintaining a high luminance, but presents another problem when a graphic signal (VGA, XGA and the like) from a personal computer is displayed. When a fixed screen (still picture) having a low APL is displayed in the form of a graphic signal, particular cells that continue high-luminance display are deteriorated, resulting in burning (image sticking on the screen).
Furthermore, in the PDP, a priming discharge (discharge at all cells) based on a priming pulse is carried out, for example, once for each subfield in order to enhance the discharge stability of the PDP. However, the priming discharge involves applying discharges to all discharge cells on the full screen at once to cause luminescence corresponding to a certain gradation level, resulting in low contrast. On the other hand, the decrease in the frequency of generation of the priming pulse leads to low discharge stability.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a plasma display device comprises: control signal output means for outputting a control signal responsive to the signal format of an input video signal; and driving means for driving a plasma display panel based on the control signal outputted from the control signal output means.
Preferably, according to a second aspect of the present invention, the plasma display device of the first aspect further comprises: signal format identifying means for identifying the signal format of the input video signal, the signal format identifying means applying to the control signal output means an identification output responsive to the signal format of the input video signal.
Preferably, according to a third aspect of the present invention, in the plasma display device of the second aspect, the control signal output means includes selecting means for selecting one of a plurality of previously determined pieces of
Bell Paul A.
Birch & Stewart Kolasch & Birch, LLP
Mitsubishi Denki & Kabushiki Kaisha
Saras Steven
LandOfFree
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