Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-06-29
2001-12-25
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S141000
Reexamination Certificate
active
06333769
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device and, More specifically, the invention relates to an in-plane field type liquid crystal display device.
In general, an in-plane field type liquid crystal display device is provided with a pixel electrode and a counter electrode spaced apart from the pixel electrode in each pixel area on a liquid-crystal-side surface of one of transparent substrates which are opposed to each other via a liquid crystal, and is arranged to control the optical transmittance of the liquid crystal by means of an electric field which occurs between the pixel electrode and the counter electrode.
A liquid crystal display device of an active matrix type which adopts the in-plane field mode includes, on a liquid-crystal-side surface of one of its transparent substrates, scanning signal lines extended in the x direction and juxtaposed in the y direction, counter signal lines extended in the x direction and juxtaposed in the y direction, and video signal lines extended in the y direction and juxtaposed in the x direction, and each area surrounded by scanning and counter signal lines adjacent to each other and a pair of video signal lines adjacent to each other is formed as a pixel area.
In each pixel area, a thin-film transistor driven by the supply of a scanning signal from the scanning signal line and a pixel electrode to which a video signal is supplied from one of the video signal lines via the thin-film transistor are formed.
In this case, since a voltage corresponding to the video signal on the basis of the counter electrode is applied to the pixel electrode, a reference voltage is applied to the counter electrode via the counter signal line.
In such a liquid crystal display device, since its structure is such that its thin-film transistors are easily damaged by static electricity, it is indispensable to take measures against static electricity.
As an attempt at taking measures against static electricity, there is an art in which a protection element common line is formed to surround a display area made of an assembly of pixels, and scanning signal lines and video signal lines are connected to the protection element common line via non-linear elements at the intersections of the scanning and video signal lines and the protection element common line.
For example, the art of taking measures against static electricity in a liquid crystal display device which differs in structure from the in-plane field mode is described in Japanese Patent Laid-Open No. 90428/1997.
SUMMARY OF THE INVENTION
In the above-described prior art, as measures against static electricity, scanning signal lines and video signal lines are connected to a common line via static protection elements. Although the static protection elements are formed of high-resistance elements so that static electricity flows through the static protection elements, the scanning signal lines and the video signal lines are electrically connected via the static protection elements and the common line. For this reason, it has been found out that when the liquid crystal display device is being driven by an external circuit, part of video signals from the video signal lines flow into the static protection elements as leak current and this leak current flows into the counter electrodes of the respective pixels via the common line, so that the problems that image quality is degraded and that the voltage at the video signal lines lowers occur.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an art capable of avoiding occurrence of damage due to static electricity in a liquid crystal display device of a in-plane field mode which is provided with pixel electrodes and counter electrodes on one substrate.
Another object of the present invention is to provide a liquid crystal display device capable of avoiding occurrence of leak current from scanning signal lines or video signal lines.
The above and other objects and novel features of the present invention will become apparent from the description given herein and the accompanying drawings.
A representative aspect of the invention disclosed in the present application is summarized below.
In a liquid crystal display device, pixels areas which are surrounded by scanning signal lines, video signal lines and counter signal lines are arranged on a liquid-crystal-side surface of one of transparent substrates opposed to each other across a liquid crystal, and the respective pixel areas include thin-film transistors driven by the supply of scanning signals from the scanning signal lines, pixel electrodes to which video signals from the video signal lines are supplied via the respective thin-film transistors, and counter electrodes spaced apart from the pixel electrodes and connected to the counter signal lines.
A common line is formed to surround a display area made of an assembly of the pixel areas, and the video signal lines and the scanning signal lines are connected to the common line by non-linear elements at the intersections of the video and scanning signal lines and the common line.
The common line is connected to the counter signal lines via high-resistance elements.
In the liquid crystal display device having the above-described construction, even if leak current due to scanning or video signals flows via the non-linear elements, this leak current can be prevented from flowing into the counter signal lines, by the high-resistance elements.
REFERENCES:
patent: 9-90428 (1997-04-01), None
patent: 10-10494 (1998-01-01), None
English abstract of Japanese reference 10-10494 published on Jan. 16, 1998, obtained from file 351 on the Dialog database.
Nakano Yasushi
Oritsuki Ryoji
Suzuki Nobuyuki
Antonelli Terry Stout & Kraus LLP
Dudek James A.
Hitachi , Ltd.
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