Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-03-02
2003-11-25
Mengistu, Amare (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S066000
Reexamination Certificate
active
06653993
ABSTRACT:
INDUSTRIAL FIELD OF USE
The present invention relates to a plasma display panel driving method and a plasma display panel display apparatus used as the display screen for computers, televisions and the like, and in particular to a driving method which uses an address-display-period-separated sub-field (hereafter referred to as ADS) method.
RELATED ART
Recently, plasma display panels (hereafter referred to as PDPS) have become the focus of attention for their ability to realize a large, slim and lightweight display apparatus for use in computers, televisions and the like.
PDPs can be broadly divided into two types: direct current (DC) and alternating current (AC). One example of a DC PDP is described in EPO 762,461, which discloses a PDP in which discharge cells are arranged in a matrix. AC PDPs are suitable for large-screen use and so are at present the dominant type.
High-definition television in which high resolutions of up to 1920×1080 pixels is currently being introduced and PDPs should preferably be compatible with this kind of high-definition display, just as with other types of display.
FIG. 1
is a view of a conventional alternating current (AC) PDP.
In this PDP a front substrate
11
and a back substrate
12
are placed in parallel so as to face each other with a space in between. The edges of the substrates are then sealed.
Scanning electrode group
19
a
and sustain electrode group
19
b
are formed in parallel strips on the inward-facing surface of the front substrate
11
. The electrode groups
19
a
and
19
b
are covered by a dielectric layer
17
composed of lead glass or similar. The surface of the dielectric layer
17
is then covered with a protective layer
18
of magnesium oxide (MgO). A data electrode group
14
formed in parallel strips is covered by an insulating layer
13
composed of lead glass or similar are placed on the inward-facing surface of the back substrate
12
. Barrier ribs
15
are placed on top of the insulating layer
13
, in parallel with the data electrode group
14
. The space between the front substrate
11
and the back substrate
12
is divided into spaces of 100 to 200 microns by the barrier ribs
15
. Discharge gas is sealed in these spaces. The pressure at which the discharge gas is enclosed is normally set below external (atmospheric) pressure, typically in a range of between 200 to 500 torr.
FIG. 2
shows an electrode matrix for the PDP. The electrode groups
19
a
and
19
b
are arranged at right angles to the data electrode group
14
. Discharge cells are formed in the space between the substrates, at the points where the electrodes intersect. The barrier ribs
15
separate adjacent discharge cells preventing discharge diffusion between adjacent discharge cells so that a high resolution display can be achieved.
In monochrome PDPS, a gas mixture composed mainly of neon is used as the discharge gas, emitting visible light when discharge is performed. However, in a color PDP like the one in
FIG. 1
, a phosphor layer
16
composed of phosphors for the three primary colors red (R), green (G) and blue (B) is formed on the inner walls of the discharge cells, and a gas mixture composed mainly of xenon (such as neon/xenon or helium/xenon) is used as the discharge gas. Color display takes place by converting ultraviolet light generated by the discharge into visible light of various colors using the phosphor layer
16
.
Discharge cells in this kind of PDP are fundamentally only capable of two display states, ON and OFF. Here, an ADS method in which one frame (one field) is divided into a plurality of sub-frames (sub-fields) and the ON and OFF states in each sub-frame are combined to express a gray scale is used.
FIG. 3
shows a division method for one frame when a 256-level gray scale is expressed. The horizontal axis shows time and the shaded parts show discharge sustain periods.
In the example division method shown in
FIG. 3
, one frame is made up of eight sub-frames. The ratios of the discharge sustain period for the sub-frames are set respectively at 1, 2, 4, 8, 16, 32, 64, and 128. These eight-bit binary combinations express a 256 gray scale. The NTSC (National Television System Committee) standard for television images stipulates a frame rate of 60 frames per second, so the time for one frame is set at 16.7 ms.
Each sub-frame is composed of the following sequence: a set-up period, a write period, a discharge sustain period and an erase period.
FIG. 4
is a time chart showing when pulses are applied to electrodes during one sub-frame in one related art.
In the set-up period, all the discharge cells are set-up by applying set-up pulses to all of the scan electrodes
19
a.
In the write period, data pulses are applied to selected data electrodes
14
while scan pulses are applied sequentially to the scan electrodes
19
a.
This causes a wall charge to accumulate in the cells to be ignited, writing one screen of pixel data.
In the discharge sustain period, a bulk pulse voltage is applied across the scan electrodes
19
a
and the sustain electrodes
19
b
, causing discharge to occur in the discharge cells where the wall charge has accumulated, and light to be emitted for a certain period.
In the erase period, narrow erase pulses are applied in bulk to the scan electrodes
19
a
, causing the wall charges in all of the discharge cells to be erased.
In the above driving method, light should normally only be emitted in the discharge sustain period and not in the set-up, write and erase periods. However, discharge occurring when set-up or erase pulses are applied causes the whole panel to emit light and contrast drops accordingly. Discharge occurring when the write pulses are applied also causes discharge cells to emit light, having a further detrimental effect on contrast. Consequently, there is a need to develop techniques for resolving these problems.
The above PDP driving method also should make the discharge sustain period in each frame as long as possible in order to improve luminance. Accordingly, the write pulses (scan pulses and data pulses) should preferably be as short as possible, so that writing can be performed at high speed.
High resolution PDPs have a large number of scan electrodes, so it is particularly desirable that the write pulses (scan pulses and data pulses) be narrow to enable driving to be performed at high speed.
However, in a conventional PDP, setting the write pulse narrowly causes write defects, lowering the quality of the image displayed.
If the voltage for the write pulse is high and the pulse narrow, writing may conceivably be performed at high speed without write defects. Normally, however, higher speed data drivers have lower ability to withstand voltage, so that it is difficult to realize a driving circuit which can write at both a high voltage and a high speed.
In the above PDP driving method, another important issue is driving the PDP with low power consumption. To achieve this, the inefficient power consumed in the discharge sustain period should be reduced to increase luminous efficiency.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a PDP driving method that operates at high speed, and improves contrast without causing write defects. A further object of the present invention is to provide a PDP driving method that improves luminous efficiency. Yet another object of the present invention is to provide a PDP driving method that produces high image quality and high luminance without causing flicker and roughness on the screen.
In the present invention, a staircase waveform that rises in two steps or more is used for the set-up pulses. Using this kind of waveform for the set-up pulses rather than a simple rectangular pulse improves contrast without producing write defects.
Using a staircase waveform that falls in two steps or more for the write pulses rather than a simple rectangular pulse enables high speed driving to be performed without causing write defects.
Meanwhile, using a staircase waveform that rises in two steps or more for the write pulses improves con
Hibino Junichi
Higashino Hidetaka
Nagao Nobuaki
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