Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-06-04
2001-07-10
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S043000, C349S139000, C349S138000
Reexamination Certificate
active
06259493
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal apparatus.
FIG. 4
is a plan view showing a reflection liquid crystal display apparatus
100
associated with the present invention.
FIG. 5
is a longitudinal sectional view taken along a line B—B in FIG.
4
. This apparatus includes an array substrate
110
on which thin-film transistors (to be referred to as TFTs hereinafter)
114
are arranged as switching elements in the form of a matrix, a counter-substrate
130
on which a transparent counter-electrode
136
is formed, and a liquid crystal layer
150
sandwiched between the substrates
110
and
130
.
On the array substrate
110
, a plurality of scanning lines
113
and a plurality of signal lines
119
run. The scanning lines
113
run along the column direction. The gates of TFTs
114
of each row are commonly connected to one scanning line
113
. The signal lines
119
run in the row direction perpendicular to the column direction. One terminal of the source and drain of each TFT
114
of each row is commonly connected to one signal line
119
. The other terminal of each TFT
114
forms a capacitance for storing a signal together with a signal storage capacitance line
116
through an insulating film, and is connected to a reflection pixel electrode
120
(to be described later) through a contact
125
.
An organic insulating layer
118
is formed on the upper surfaces of the scanning lines
113
, the signal storage capacitance lines
116
, and the TFTs
114
. The reflection pixel electrodes
120
are formed on the upper surface of the organic insulating layer
118
in correspondence with the respective pixels.
A color filter
134
and the common electrode
136
are stacked on the upper surface of a substrate
132
. Red, blue, and green portions are arranged on the color filter
134
in nits of pixels. An optical film
188
such as a retardation plate or polarizing plate is bonded to the opposite surface of the substrate
132
to the liquid crystal layer
150
.
As described above, the reflection liquid crystal display apparatus
100
has the reflection pixel electrodes
120
formed on the upper surfaces of the TFTs
114
and signal storage capacitance lines
116
through the organic insulating layer organic insulating layer
118
. This can increase the area of the reflection pixel electrodes
120
by which light incident from above in
FIG. 4
is reflected. As a consequence, a bright image can be displayed even in a dark place without any backlight.
The following problem, however, arises in the above liquid crystal display apparatus. As shown in
FIG. 6A
, when a raster window
302
is displayed on a green halftone background
301
, vertical crosstalk occurs at an end portion of the window
302
. Referring to
FIG. 4
, since the reflection pixel electrode
120
and the signal line
119
oppose through the organic insulating layer
118
, they are coupled via a capacity. However, only one signal line
119
that is connected to a given reflection pixel electrode
120
is coupled via a capacity to this electrode
120
.
For this reason, even on the green halftone background
301
to be uniformly display in green, owing to capacitive coupling, the signal lines
119
have different influences on the reflection pixel electrode
120
at a pixel
303
adjacent to a lower portion of the raster window
302
and a pixel
304
spaced apart from the raster window
302
. More specifically, at the pixel
304
adjacent to the raster window
302
in the vertical direction, since a signal potential is applied to the signal line
119
to display the raster window
302
, the reflection pixel electrode
120
is influenced by the signal line
119
through the capacitive coupling.
Assume that a voltage VP
1
is applied to the pixel
303
owing to the influence of the raster window
302
, and a prescribed voltage VP
0
is applied to the pixel
304
, as shown in FIG.
6
B. The pixel potentials respectively applied to the pixels
303
and
304
change with time, as shown in FIG.
7
.
Let Vsg be the signal potential for a halftone image, Vsb be the signal potential for a black image, and Vsw be the signal potential for raster window display. In addition, let Pco be the coupling factor between a given pixel and a signal line connected thereto through a TFT, and Pci be the coupling factor between the ith signal line adjacent to this signal line and the corresponding pixel. Then, the voltages VP
1
and VP
0
can be expressed as
VP
0
=Vsg (1)
VP
1
=
Vsg+Pc
0
(
Vsb−Vsg
)+
Pc
1
(
Vsw−Vsg
)+
Pc
2
(
Vsb−Vsg
)+
Pc
3
(
Vsw−Vsg
)+ . . . =
Vsg+
(
Pc
0
+
Pc
2
+
PC
4
+ . . . )(
Vsb−Vsg
)+(
Pc
1
+
Pc
3
+
PC
5
+ . . . )(
Vsw−Vsg
) (2)
As a result, since the effective voltage at the pixel electrode
120
at the pixel
303
differs from that at the pixel electrode
120
at the pixel
304
, and a luminance difference is produced, crosstalk occurs. This problem also arises in a transmission liquid crystal display apparatus.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a liquid crystal display apparatus which can prevent crosstalk.
According to the present invention, there is provided a liquid crystal display apparatus comprising an array substrate including a substrate, a plurality of scanning lines formed on the substrate to run in a column direction, a plurality of signal lines formed on the substrate to run in a row direction, a plurality of switching elements formed near intersections of the signal lines and the scanning lines, and a plurality of pixel electrodes which are respectively connected to the switching elements and run in both the row and column directions, a counter-substrate opposing the array substrate, and a liquid crystal sandwiched between the array substrate and the counter-substrate, wherein each of the signal lines is alternately overlapped with pixel electrodes in a predetermined row and pixel electrodes in a row different from the predetermined row.
In this case, the pixel electrode may be a reflection electrode.
It is preferable that the area of the signal line overlapped with the pixel electrode in the predetermined row be substantially equal to that of the signal line overlapped with the pixel electrodes in the row different form the predetermined row.
The pixel electrodes are formed on an insulating interlayer formed on the switching elements.
The insulating interlayer may be made of an organic resin.
In addition, according to the present invention, there is provided a liquid crystal display apparatus comprising an array substrate including a substrate, a plurality of scanning lines formed on the substrate to run in a column direction, a plurality of signal lines formed on the substrate to run in a row direction, a plurality of switching elements formed near intersections of the signal lines and the scanning lines, and a plurality of pixel electrodes which are respectively connected to the switching elements and run in both the row and column directions, a counter-substrate opposing the array substrate, and a liquid crystal sandwiched between the array substrate and the counter-substrate, wherein each of the pixel electrodes is overlapped with a plurality of signal lines, and total widths of portions of the signal lines are overlapped with the pixel electrode.
The pixel electrode may be a reflection electrode.
It is preferable that the areas of the plurality of signal lines overlapped with the pixel electrode be substantially equal to each other.
According to the above liquid crystal display apparatus of the present invention, since each signal line is overlapped with the pixel electrodes in a predetermined row and the pixel electrodes in a row different from the predetermined row, a plurality of pixel electrodes are capacitively coupled to each signal line. This can reduce luminance differences between the pixel electrodes and prevent crosstalk.
REFERENCES:
patent: 5659375
Hanazawa Yasuyuki
Nagayama Kohei
Nakamura Takashi
Kabushiki Kaishi Toshiba
Pillsbury & Winthrop LLP
Sikes William L.
Ton Toan
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