Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-07-14
2003-07-01
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S143000, C349S043000
Reexamination Certificate
active
06587174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to an active matrix type liquid crystal display, and more particularly to an active matrix type liquid crystal display having a main display area and a sub-display area which have pixel areas different from each other in size respectively.
2. Prior Art
As a conventional active matrix type liquid crystal display, there is known a liquid crystal display shown in FIG.
14
.
FIG. 14
is a plan view showing a thin film transistor (hereinafter, referred to as TFT) array substrate
140
.
On the conventional TFT array substrate
140
for the active matrix apparatus, there are formed respectively: a display area
130
in which pixel areas
132
constituting pixels are arranged in a matrix shape; leader wiring
134
and scanning line terminals
136
for scanning lines for connecting scanning lines
101
in this display area
130
to an external gate driver (not shown); and leader wiring
135
and signal line terminals
137
for signal lines for connecting signal lines
119
in the display area
130
to an external source driver (not shown).
In terms of new functions capable of being added to the conventional active matrix type liquid crystal display, there has been advocated the necessity for providing another display area
31
(hereinafter, referred to as sub-display area) aimed at displaying, for example, character information in addition to a display area
30
(hereinafter, referred to as main display area) as shown in FIG.
1
.
In this case, since high definition display is requested for the main display area
30
, the pixel area
32
is made small, but in the sub-display area
31
, it is not always necessary to cause the size of its pixel area
33
to coincide with that of the main display area because of the display object. Out of requests to display, for example, characters bigger for making them legible, design is made so as to cause the size of the pixel area
33
in the sub-display area
31
to be rather bigger than that of the pixel area
32
in the main display area
30
.
On the other hand, in the active matrix type liquid crystal display, a liquid crystal layer is pinched between a pair of substrates oppositely arranged, and this liquid crystal layer is used as a display medium. In order to prevent the liquid crystal layer from being stuck, AC voltage in which DC voltage is not superimposed is applied to the liquid crystal layer, and this is used as display voltage. This AC voltage is applied to a pixel electrode mainly constituting the pixel area from the signal line through TFT which has turned ON through gate voltage from the scanning line. A steady DC voltage is applied to an opposite electrode which opposes to this pixel electrode through the liquid crystal layer. Thus, an electric field is imparted to the liquid crystal layer to change its refractive index whereby the liquid crystal layer becomes usable as a display medium.
However, a dynamic voltage drop &Dgr;Vp occurs in potential Vp of the pixel electrode when the gate voltage is changed in order to cause TFT to be in an OFF state, resulting from: a change in the dielectric constant of the liquid crystal in response to the field intensity; existence of parasitic capacity between gate electrode and drain electrode of TFT; existence of parasitic capacity between scanning line and pixel electrodes sandwiching insulating film therebetween; existence of parasitic capacity between scanning line and capacity electrodes sandwiching insulating film therebetween; existence of parasitic capacity between signal line and pixel electrodes sandwiching insulating film therebetween; existence of parasitic capacity between signal line and capacity electrodes sandwiching insulating film therebetween; and the like.
When the gate voltage Vg is caused to change in order to cause TFT to be in an OFF state, a dynamic voltage drop &Dgr;Vp occurs in potential Vp of the pixel electrode. When the gate voltage Vg is caused to change in order to cause TFT to be in an OFF state, electric charge is distributed between capacity of the liquid crystal layer between a pair of substrates, storage capacity consisting of the scanning line, gate insulating film thereon and capacity electrode, and the parasitic capacity to cause a voltage drop &Dgr;Vp in the potential Vp of the pixel electrode.
When the voltage drop &Dgr;Vp occurs in the potential Vp of the pixel electrode as described above, a difference will occur between positive and negative voltage amplitudes at the potential Vp of the pixel electrode for driving the liquid crystal with center potential Vsc of the signal voltage Vs as a reference. If the same voltage is applied irrespective of the polarity of voltage, the liquid crystals have the same transmittance characteristic. Therefore, in, for example, a normally white, active matrix type liquid crystal display having high transmittance in a no-voltage applied state, it becomes lower in transmittance in polarity having a large voltage amplitude, and higher in polarity having a small voltage amplitude. For this reason, light and dark responsive to the transmittance are repeated, and these will be visually identified as flickers.
Variations in the dielectric constant of the liquid crystal, which is one factor for causing the voltage drop, in response to the field intensity relate to the physical properties of the liquid crystal and cannot be avoided. Also, as another factor, there are parasitic capacity of circuits, of which, existence of parasitic capacity between gate electrode and drain electrode of TFT cannot be structurally avoided in the current active matrix type liquid crystal display because gate insulating film formed between the electrodes forms capacity.
Also, the parasitic capacity between scanning line and pixel electrode cannot be structurally avoided in the current active matrix type liquid crystal display.
Thus conventionally, the potential at the opposite electrode is adjusted at the optimum such that the positive and negative voltage amplitudes for AC voltage for driving the liquid crystal are equal to each other, and the storage capacity is formed in parallel with respect to the capacity of the liquid crystal layer, whereby an attempt has been made to resolve the flickers.
Where there is, in addition to the main display area, provided a sub-display area having a pixel area different in size, there occurs a difference in voltage drop &Dgr;Vp of pixel electrode between the main and sub-display areas because the value of the liquid crystal capacity or the parasitic capacity differs depending upon the size of the pixel area. This has led to a problem that flickers become prone to be visually identified to deteriorate the display quality.
SUMMARY OF THE INVENTION
The present invention has been achieved in order to solve the above-described problems, and is aimed to provide an active matrix type liquid crystal display capable of preventing flickers from occurring by applying the same potential to the opposite electrode without dividing the opposite electrode between main and sub-display areas which have pixel areas different in size respectively.
An active matrix apparatus according to the present invention is constructed such that there is sandwiched a liquid crystal layer between a pair of substrates oppositely arranged; on the surface of one substrate, a plurality of scanning lines and a plurality of signal lines are formed to intersect each other in a matrix shape; in the vicinity of a plurality of intersected portions formed by the plurality of scanning lines and signal lines, there are formed respectively TFTs having gate electrodes connected to the scanning lines, pixel electrodes connected to the TFTs, and capacity electrodes for forming storage capacity with the scanning lines and the storage capacity; on the surface of the other substrate on the liquid crystal layer side, there is formed an opposite electrode; there are provided a main display area having a plurality of pixel areas, each of the pixel areas being enclosed with th
Akkapeddi P. R.
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Kim Robert H.
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