Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-12-07
2004-11-16
Liang, Regina (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S094000, C345S096000, C345S099000, C345S087000, C345S214000
Reexamination Certificate
active
06819311
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving process for a liquid crystal display, and in particular to a driving process for an active matrix type liquid crystal display which is suitable for motion picture display.
2. Background Art
In recent years, liquid crystal displays (hereafter abbreviated as LCD) have increased in size and definition, and the range of images displayed is also widening, from the handling of mainly still images such as in the liquid crystal displays used with personal computers and word processors and the like, to incorporate the handling of motion pictures such as in the liquid crystal displays used as televisions and the like. An LCD is thinner than a TV equipped with a CRT (cathode ray tube), and can be installed without occupying much space, and consequently it is expected that LCDs will become widely used in average households.
FIG. 20
shows a sample construction of a conventional active matrix type LCD. The LCD comprises a first and a second glass substrate, and a liquid crystal display panel section
100
for displaying images. A number n (where n is a natural number) of scanning lines
101
and a number m (where m is also a natural number) of signal lines
102
are disposed in a grid like arrangement on top of the first glass substrate, and a TFT (thin film transistor)
103
which functions as a non linear element (switching element) is provided in the vicinity of each point of intersection between the scanning lines
101
and the signal lines
102
.
A gate electrode of the TFT
103
is connected to the scanning line
101
, a source electrode is connected to the signal line
102
, and a drain electrode is connected to a pixel electrode
104
. The aforementioned second glass substrate is then arranged in a position facing the first glass substrate, and a common electrode
105
is then formed on one surface of the glass substrate with a transference electrode of ITO or the like. Then, a liquid crystal is used to fill the space between the common electrode
105
and the pixel electrode
104
formed on the top of the first glass substrate.
The scanning lines
101
and the signal lines
102
are connected to a scanning line driving circuit
106
and a signal line driving circuit
107
respectively. The scanning line driving circuit
106
sequentially drives a large electric potential to the n scanning lines
101
, and switches the TFT
103
connected to each scanning line
101
to an ON state. With the scanning line driving circuit
106
in the scanning state, the signal line driving circuit
107
outputs a gradation voltage corresponding with the image data to one of the m signal lines, and the gradation voltage is written to the pixel electrode
104
via the TFT
103
in an ON state, and the potential difference between the common electrode
105
which is set at a uniform potential, and the gradation voltage written to the pixel electrode
104
is used to control the amount of light transmission and consequently the display. The liquid crystal display panel section
100
is driven in this manner.
FIG. 21
is a diagram showing waveforms of signals output from the scanning line driving circuit
106
and the signal line driving circuit
107
of a conventional liquid crystal display to the scanning lines
101
and the signal lines
102
respectively. In
FIG. 21
, the symbols VG
1
to VGn represent scanning signal waveforms applied to each of the scanning lines
101
. As shown in the figure, the scanning signals VG
1
to VGn apply a high electric potential to only one scanning line
101
at any one time, and the signals are output sequentially to the n scanning lines
101
. Furthermore, the symbol VD represents a signal output to a single signal line
102
, and the symbol Vcom represents a signal waveform applied to the common electrode
105
. In the example shown in
FIG. 21
, the signal VD is a signal in which the signal strength varies in accordance with each piece of image data, whereas the signal Vcom is of a uniform value and does not vary over time.
Furthermore, in such a liquid crystal display, in order to prevent the deterioration of the liquid crystal, so-called AC driving is used, and generally the device is controlled so that a DC component voltage is never applied to the liquid crystal for a long period of time. One example of an AC drive method involves making the voltage applied to the common electrode
105
uniform, and applying alternate positive polarity and negative polarity signal voltages to the pixel electrode
104
.
If motion picture display is conducted on this type of LCD, then problems of image quality deterioration, such as the residual image phenomenon, will arise. The cause of this problem is that because the response speed of the liquid crystal material is slow, when a gradation variation occurs, the liquid crystal is unable to track the gradation variation within a single field period and produces a cumulative response using several field periods. Consequently, considerable research is being conducted into various high speed response liquid crystal materials as a way of overcoming this problem.
However, the aforementioned problems such as the residual image phenomenon are not caused solely by the response speed of the liquid crystal, and have also been reported by institutions such as the NHK Broadcasting Technology Research Laboratory as being caused by the display process (for example, refer to the 1999 Conference of the Electronic Information Communication Society, SC-8-1, pp.207-208). As follows is a description of this problem of the display process, with a comparison of a CRT driving process and an LCD driving process.
FIGS. 22A and 22B
are diagrams showing comparative results for the time response of display light of a pixel in a CRT and an LCD, where
FIG. 22A
shows the time response for a CRT, and
FIG. 22B
shows the time response for an LCD. As shown in
FIG. 22A
, the CRT is a so-called in-pulse type display device where light is generated for only several milliseconds from the time the electron beam strikes the fluorescent substance of the tube surface, whereas the LCD shown in
FIG. 22B
is a so-called hold type display device where the display light is retained for one field period from the time the writing of data to the pixel has finished until the next write occurs.
When motion pictures are displayed on a CRT and an LCD with the above characteristics, the displays shown in
FIGS. 23A and 23B
results.
FIGS. 23A and 23B
are diagrams showing a sample image display in the case where motion pictures are displayed on a CRT and an LCD, where
FIG. 23A
represents a sample CRT display and
FIG. 23B
represents a sample LCD display. FIG.
23
A and
FIG. 23B
represent the case of a circular display object moving in a direction x shown in the figures. In such a case, then as shown in
FIG. 23A
, in the in-pulse type display device CRT, the display object is displayed momentarily at positions corresponding with the time, whereas in a hold type display device LCD the image of the previous field remains until immediately before a new write is performed.
When a person views the motion pictures displayed in the manner shown in
FIGS. 23A and 23B
, then the motion pictures are perceived in the manner shown in
FIGS. 24A and 24B
.
FIGS. 24A and 24B
are diagrams describing the image perceived by a person when a motion picture is displayed on a CRT and an LCD, where
FIG. 24A
represents the case of a CRT, and
FIG. 24B
represents the case of an LCD. As shown in
FIG. 24A
when a motion picture is displayed on an in-pulse type display device CRT, there is no perception at any time of a displayed image overlapping the previous image. However, when a motion picture is displayed on a hold type display device LCD, then due to effects such as the time integral effect of human sight, the currently displayed image is perceived to overlap with the previously displayed image, producing a motion blur problem.
Several improvements have been proposed for overcoming the afor
Hayama Hiroshi
Nose Takashi
Dinh Duc Q
Liang Regina
McGinn & Gibb PLLC
NEC Corporation
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