Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-09-09
2002-05-28
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S092000, C345S100000, C345S103000, C345S208000, C345S209000, C348S792000, C349S037000
Reexamination Certificate
active
06396468
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, more particularly to a liquid crystal display device adopting a driving method in which scanning signals are applied to two gate buslines simultaneously.
BACKGROUND OF THE INVENTION
In resent years, development of active-matrix liquid crystal display devices using thin-film transistors as switching elements for driving liquid crystals has been actively carried out. The following description will explain a liquid crystal display device integrated with a driver, as an example of the active-matrix liquid crystal display device.
FIG. 8
is a plan depiction of the liquid crystal display device integrated with a driver. In the liquid crystal display device integrated with a driver, as illustrated in
FIG. 8
, a gate driver
32
, a source driver
33
, and a thin film transistor (hereinafter referred to as “TFT”) array section
34
are disposed on a substrate
31
made of glass or quartz.
The gate driver
32
includes a shift register
32
a
and a buffer
32
b.
The source driver
33
includes a shift register
33
a,
a buffer
33
b,
and analog switches
39
for sampling video lines
38
.
In the TFT array section
34
, a number of gate buslines
116
running from the gate driver
32
are arranged parallel to each other. A number of source buslines
120
running from the source driver
33
are arranged to cross the gate buslines
116
at right angles. Moreover, additional capacitance common lines
114
are arranged parallel to the gate buslines
116
.
A TFT
35
, a pixel
36
, and an additional capacitor
37
are provided in each rectangular region enclosed by one gate busline
116
, two adjacent source buslines
120
, and one additional capacitance common line
114
. The gate electrode of the TFT
35
is connected to the gate busline
116
, while the source electrode thereof is connected to the source busline
120
. A liquid crystal is sealed in a space between a pixel electrode connected to the drain electrode of the TFT
35
and a counter electrode, thereby forming a pixel
36
. The additional capacitance common line
114
is connected to an electrode to which the counter electrode is connected.
As a scanning method used in such a liquid crystal display device integrated with a driver, the following methods are given. One example is a simple scanning method in which a selection signal is separately applied to each gate busline. Another example is a simultaneous two-line scanning method in which two gate buslines are simultaneously driven. Here, the simultaneous two-line scanning method will be explained with reference to FIG.
9
.
According to the simultaneous two-line scanning method, in an odd-numbered field, first, scanning signals are simultaneously applied to the first and second gate buslines G
1
and G
2
. Then, after a delay of one horizontal scanning period, scanning signals are simultaneously applied to the third and fourth gate buslines G
3
and G
4
. Thus, scanning signals are simultaneously applied to an odd-numbered gate busline and the next (i.e., even-numbered) gate busline, and then to the subsequent odd-numbered gate buslines and even-numbered gate buslines in this manner successively.
On the other hand, in an even-numbered field, first, a scanning signal is applied to the first gate busline G
1
. Then, after a delay of one horizontal scanning period, scanning signals are simultaneously applied to the second and third gate buslines G
2
and G
4
. Furthermore, scanning signals are simultaneously applied to the fourth and fifth gate buslines G
4
and G
5
. Hence, in an even-numbered field, scanning signals are simultaneously applied to a combination of adjacent gate buslines which is different from a combination of adjacent gate buslines in an odd-numbered field.
Accordingly, the simultaneous two-line scanning method requires twice the gate buslines and pixels electrodes compared to the simple scanning method in which a scanning signal is separately applied to each gate busline. However, the simultaneous two-line scanning method provides images of high resolution according to an interlace method.
In this case, since there is a need to perform a.c. driving of the liquid crystal display device, positive and negative video signals are alternately applied to a single pixel electrode every other field, i.e., a positive video signal is applied to a pixel electrode in one field and a negative video signal is applied to the pixel electrode in the next field. However, when the polarities of the video signals to be applied to pixel electrodes forming one screen are inverted every field, the flicker increases. In order to solve such a problem, for example, Japanese publication of examined patent application (Tokukohei) No. 7-113819/1985 proposes a method of inverting the phases of the video signals every two gate buslines which are to be scanned simultaneously.
In the first field, as shown in FIG.
10
(
a
), positive video signals (indicated by “+”) are applied to the pixel electrodes connected to the first and second gate buslines G
1
and G
2
which are selected simultaneously. Meanwhile, negative video signals (indicated by “−”) are applied to the pixel electrodes connected to the third and fourth gate buslines G
3
and G
4
which are selected simultaneously. Moreover, the positive video signals are applied to the pixel electrodes connected to the fifth and sixth gate buslines G
5
and G
6
which are selected simultaneously.
In the second field, as illustrated in FIG.
10
(
b
), a positive video signal is applied to the pixel electrode connected to the first gate busline, negative video signals are applied to the pixel electrodes connected to the second and third gate buslines G
2
and G
3
which are selected simultaneously, and positive video signals are applied to the pixel electrodes connected to the fourth and fifth gate buslines G
4
and G
5
which are selected simultaneously.
In the third field, as shown in FIG.
10
(
c
), video signals whose polarities are opposite to those applied in the first field are applied to the pixel electrodes connected to the respective gate buslines. In the fourth field, as shown in FIG.
10
(
d
), video signals whose polarities are opposite to those applied in the second field are applied to the pixel electrodes connected to the respective gate buslines.
In the above-mentioned method, it is possible to reduce the flicker as compared to a method in which the polarities of the video signals to be applied to the pixel electrodes of one screen are inverted between positive (+) and negative (−) every field. However, according the above-mentioned method, the polarity of the pixel electrode connected to the first gate busline G
1
changes every field in order of +, +, −,−. The polarity of the pixel electrode connected to the second gate busline G
2
changes every field in order of +, −, −, +. The polarity of the pixel electrode connected to the third gate busline G
3
changes every field in order of −, −, +, +. The polarity of the pixel electrode connected to the fourth gate busline G
4
changes every field in order of −, +, +, −. Thus, since the cycle of inverting the polarities of the video signals applied to the respective pixel electrodes is four fields, flicker is generated. As a result, the liquid crystal display device exhibits unpleasant displays.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a liquid crystal display device capable of reducing flicker even when scanning signals are simultaneously applied to two gate buslines by a gate driver.
In order to achieve the above object, a liquid crystal display device of the present invention includes:
a first substrate having gate buslines, source buslines, switching elements which are arranged in the vicinity of intersections of the gate buslines and source buslines so as to form a matrix pattern, and a pixel electrode array formed by pixel electrodes connected to t
Etoh Sunao
Matsushima Yasuhiro
Kovalick Vincent E.
Nixon & Vanderhye P.C.
Shalwala Bipin
Sharp Kabushiki Kaisha
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