Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-05-30
2002-08-13
Hjerpe, Richard (Department: 2774)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S204000, C345S205000, C345S090000, C345S098000, C345S100000, C349S043000, C349S139000
Reexamination Certificate
active
06433765
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display, and more particularly concerns an active-matrix driving-type liquid crystal display that is preferably used in the field of flat panel displays.
BACKGROUND OF THE INVENTION
Conventionally, liquid crystal displays using a nematic liquid crystal have been widely used in watches, calculators and other articles as segment-type liquid crystal displays. In recent years, thanks to their features such as thinness, light-weight and low power consumption, the liquid crystal displays of this type have been used as various displays for word processors, personal computers and navigation systems, and have rapidly broaden their markets. In particular, much attention has been focused on liquid crystal displays of the active-matrix type in which active elements such as TFTs (Thin Film Transistors) are used as switching elements, with pixels arranged in a matrix format.
There have been ever-increasing demands for the liquid crystal displays of this type in wider fields including displays of note-type or desktop-type personal computers, portable televisions and space-saving televisions, and displays of digital cameras and digital video cameras, because they have advantages, such as a great reduction in thickness (depth), easiness for providing full-color devices and smaller power consumption, as compared with, for example, CRTs (Cathode Ray Tube).
A conventional active-matrix-type liquid crystal display of the light-transmission type is constituted by a light-transmitting active-matrix substrate on which an active-matrix circuit consisting of TFTs is formed, an opposing substrate having common electrodes formed thereon that is aligned face to face with the active-matrix substrate, and a liquid crystal layer that is interpolated between the active-matrix substrate and the opposing substrate.
FIG. 23
is a circuit diagram that schematically shows one example of the active-matrix circuit on the active-matrix substrate. A plurality of pixel electrodes
91
are formed on the active-matrix substrate in a matrix format. Normally, the pixel electrodes
91
are arranged in the row direction and column direction, with several hundreds pixels being aligned in each direction.
Moreover, common electrodes (not shown) are formed on the opposing substrate, not shown, in a manner so as to face the pixel electrodes
91
through the liquid crystal layer, and a voltage is applied to the liquid crystal layer by the pixel electrodes
91
and the common electrodes. Here, in general, the common electrodes are formed virtually on the entire surface of the opposing substrate.
Furthermore, TFTs
92
, which are active elements serving as switching means for selectively driving the pixel electrodes
91
, are formed on the active-matrix substrate, and connected to the pixel electrodes
91
. In order to provide color display, color filter layers (not shown) of red, green, blue, etc. are formed on the opposing substrate, the active-matrix substrate or another member.
Scanning lines
93
are connected to the gate electrodes of the TFTs
92
, and gradation signal lines
94
are also connected to the source electrodes of the TFTs
92
. The scanning lines
93
and the gradation signal lines
94
are allowed to pass around the pixel electrodes
91
arranged in the matrix format, and placed so as to intersect each other. Gate signals are inputted through the scanning lines
93
so that the TFTs
92
are controlled and driven. Moreover, at the time of driving the TFTs
92
, data signals are inputted to the pixel electrodes
91
through the gradation signal lines
94
. Here, scanning signal input terminals
93
a
are connected to ends of the scanning lines
93
, and data signal input terminals
94
a
are connected to ends of the gradation signal lines
94
.
Moreover, the drain electrodes of the TFTs
92
are connected to the pixel electrodes
91
, and also connected to added capacitances
95
. Then, each electrode on the opposing side of the added capacitance
95
with respect to the insulating layer is connected to each of common electrodes
96
. The added capacitance
95
is used for holding a voltage that is applied to the liquid crystal layer.
In the active-matrix-type liquid crystal display, the liquid crystal layer sandwiched between the active-matrix substrate and the opposing substrate is normally set to have an average thickness of 3.0 to 4.5 &mgr;m; thus, a liquid crystal capacitance is formed by the pixel electrodes
91
, the common electrodes and the liquid crystal layer. Here, the added capacitances
95
are connected in parallel with the liquid crystal capacitance.
In the active-matrix-type liquid crystal display having the above-mentioned arrangement, however, the scanning lines
93
and the gradation signal lines
94
are arranged to intersect each other on the same substrate, and these large number of intersections are highly susceptible to short-circuiting and the resulting defects. This has caused a reduction in the yield and high costs.
In order to solve the problem with such a construction having intersecting scanning lines and gradation signal lines on the same substrate, a liquid crystal display, for example, as shown in
FIG. 24
, has been proposed. This liquid crystal display has a construction explained as follows:
A number of switching elements
101
with three terminals, constituted by amorphous silicon semiconductors, are installed on one of substrates
100
in a matrix format. Here, a scanning line
102
is connected to one terminal of the switching element
101
for each line, and a reference signal line
103
is connected to another terminal of the switching element
101
for each line. Moreover, a pixel electrode
104
is connected to the other terminal of each of the switching elements
101
.
A plurality of gradation signal lines
106
are placed in a direction orthogonal to the scanning lines
102
on an opposing substrate
105
that is placed in a manner so as to face the substrate
100
. The gradation signal lines
106
also function as opposing electrodes at portions facing pixel electrodes
104
.
In this arrangement, the scanning lines and the gradation signal lines are not made to intersect each other on the same substrate, and placed on respectively different substrates; therefore, it is possible to reduce the rate of occurrence of line defects. Thus, it becomes possible to improve the yield and also to reduce costs. Additionally, hereinafter, the construction of a liquid crystal display shown in
FIG. 23
is referred to as the present construction, and the construction of a liquid crystal display shown in
FIG. 24
is referred to as “opposing source construction”.
As described above, there have been ever-increasing demands for large-size panels and high-precision devices with respect to liquid crystal displays. One of the major problems with the achievement of the large-size panels and high-precision devices is degradation in the display quality due to signal delays. Here, the signal delays refer to signal delays in the common signal line in the case of the present construction, and also refer to signal delay in the reference signal line in the opposing source construction.
As the panel size increases, the signal wire becomes longer, thereby increasing the resistivity of the signal wire itself and the parasitic capacitance imposed on the signal wire. Since the size of the signal delay is in proportion to a product of the resistivity of the signal wire and the load capacitance, the enlargement of the panel size, which increases both the resistivity of the signal wire and the load capacitance, causes a great signal delay. Consequently, in a certain area inside the display area in the liquid crystal display, there might be a failure in which a desired voltage is not applied to the liquid crystal within a writing period, resulting in a state in which the liquid crystal is not sufficiently charged, that is, an insufficient charge-supply state. This state causes so-called shadowing, resulting in degradation in the dis
Fujiwara Kouji
Ichioka Hideki
Inoue Naoto
Okada Hisao
Tanaka Keiichi
Hjerpe Richard
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Tran Henry N.
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