Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-06-19
2002-11-19
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C349S151000
Reexamination Certificate
active
06483495
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device comprising drive circuitry including an active element, and a pixel driving element, the drive circuitry and the pixel driving element being formed on the same substrate. More particularly, the present invention relates to a liquid crystal display device in which a common transition electrode is disposed via an insulating layer in a drive circuit region in which drive circuitry is provided.
2. Description of the Related Art
A liquid crystal display device is known as a device for displaying images. The liquid crystal display device displays images by controlling a voltage applied across liquid crystal material interposed between a base substrate and a counter substrate.
One type of a liquid crystal display device is an active matrix type liquid crystal display device. An active matrix type liquid crystal display device includes a thin film transistor (TFT) preferably used as a switching element for driving a pixel having steep on-off characteristics. Therefore, an active matrix type liquid crystal display device has high-speed response and can have a large number of pixels, resulting in a large-size and high-definition display.
Hereinafter, an active matrix type liquid crystal display device in a driver monolithic form will be described. The phrase “driver monolithic forms” means that a driver and pixel electrodes controlled by the driver are provided on the same substrate. Images are displayed on the liquid crystal display device by the driver controlling pixel electrodes.
FIG. 7
is a top view of a base substrate
550
of an active matrix type liquid crystal display device
500
in a conventional driver monolithic form.
A display region
501
is provided in a middle portion of a surface of the base substrate
550
facing a counter substrate (not shown in FIG.
7
). Referring to
FIG. 7
, a scanning driver
505
and a data driver
506
are provided around the display region
501
. A plurality of common transition electrodes
508
are provided at a further peripheral region of the base substrate
550
than the scanning driver
505
and the data driver
506
. A signal input terminal
507
provided on a portion of the peripheral region supplies power to a counter electrode (not shown) on the counter substrate through the common transition electrodes
508
. The common transition electrodes
508
are electrically connected to a peripheral portion of the counter electrode via conductive paste.
FIG. 8
is an enlarged diagram of a portion A (
FIG. 7
) of the base substrate
550
of the liquid crystal display device
500
. Referring to
FIG. 8
, in the display region
501
, a plurality of scanning signal lines
502
and a plurality of data signal lines
503
are provided in such a manner as to intersect. The pixel driving elements (e.g., TFTs) and pixel electrodes
504
are arranged in a matrix, each pair of which are provided in the vicinity of an intersection. The gate electrodes of the TFTs provided on the same row are connected to a common scanning signal line
502
. The scanning signal line
502
on each row is connected to the scanning driver
505
. The drain (or source) electrodes of the TFTs provided on the same column are connected to a common data signal line
503
. The source (or drain) electrodes of the TFTs are connected to the pixel electrode
504
. The data signal line
503
on each column is connected to the data driver
506
.
The scanning driver
505
progressively scans the scanning signal lines
502
(a scanning signal line
502
is provided in each row). The data driver
506
is controlled so that image data is progressively applied from the data signal lines
503
to the respective pixel electrodes
504
via the TFTs, thereby displaying images in the display region
501
.
Typically, the counter electrode provided on the counter substrate is a transparent electrode made of ITO (indium tin oxide) or the like. The electric resistance of the counter electrode is relatively large. Particularly in a large-sized liquid crystal display device, brightness gradation, irregular display, or the like may occur due to a delay of a polarity inversion signal caused by distributed resistance in the counter electrode and liquid crystal capacitance. To avoid this, for example, the common transition electrodes
508
are provided at a plurality of portions of the base substrate
550
. In the case of a liquid crystal display device using TAB (tape automated bonding), the pitch of the TAB is narrowed so that a common transition electrode is provided between the TABs. However, in a typical liquid crystal display device in a driver monolithic form, a plurality of the common transition electrodes
508
are provided at a further peripheral region of the base substrate
550
than the scanning driver
505
and the data driver
506
.
Recently, the miniaturization of devices is in increasing demand. An even smaller size liquid crystal display device is desired. In a liquid crystal display device, the area of the display region
501
viewed by a user should be increased as much as possible while the surrounding region of the display region
501
which has substantially no contribution to display is reduced as much as possible.
Needless to say, the same applies to the above-described active matrix type liquid crystal display device
500
in the driver monolithic form. A portion having substantially no contribution to display, in which the drive circuitry including the scanning driver
505
and the data driver
506
and the common transition electrodes
508
are provided, can be reduced with respect to the display region
501
.
However, when a plurality of the common transition electrodes
508
are provided outside the scanning driver
505
and the data driver
506
in the liquid crystal display device
500
, the width of the peripheral portion of a liquid crystal display device, which has substantially no contribution to display, is significantly increased.
Further, when conductive paste is applied to the common transition electrodes
508
using a printing process, static electrical charge tends to occur. Such static electrical charge is likely to cause fluctuation of the threshold of an active element in a circuit in the vicinity of the common transition electrode
508
. Particularly when the threshold fluctuation occurs in a switching element for sampling in the data driver
506
within the active matrix type liquid crystal display device
500
in the driver monolithic form, a sampling level to image display data is varied for each data signal line
503
, so that display quality is significantly reduced.
Further, when conductive paste is applied to the common transition electrodes
508
, excessive charge transfer occurs due to the potential (or charge quantity) difference between a glass substrate and an application device. This charge transfer is likely to cause a change in characteristics, such as threshold fluctuation, of an active element within a circuit in the vicinity of the common transition electrode
508
.
The data driver
506
includes an active element other than the switching element for sampling. For example, a logic circuit such as a shift register circuit within the data driver
506
includes an active element. The logic circuit is only required to transfer and/or identify a digital signal expressed by 0 or 1. Therefore, a certain degree of a threshold fluctuation of an active element in the logic circuit does not have a substantial influence on display quality.
The switching element for sampling needs to charge each data signal line
503
with analog image display data in a certain limited time, e.g., about 160 ns for a QVGA display format. When threshold fluctuation occurs in the switching element for sampling, the sampling level to the image display data is varied for each data signal line
503
due to a difference in a charge capability between each element. Therefore, a display quality is significantly reduced.
SUMMARY OF THE INVENTION
According to one asp
Ishiguro Ken-ichi
Kaise Yasuyoshi
Kubota Yasushi
Said Mansour M.
Shalwala Bipin
Sharp Kabushiki Kaisha
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