Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
1999-11-12
2002-09-24
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S062000, C349S150000
Reexamination Certificate
active
06456344
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to an art for improving brightness irregularity on the display screen of the same.
2. Description of the Related Art
Liquid crystal display devices have been being widely spread as display terminals for information processing equipment (OA equipment) such as personal computers, because of their features of thin size and light weight as well as their high image quality which compares with Braun tubes.
Such a liquid crystal display device (i.e., a liquid crystal display module) includes, for example, transparent insulating substrates made from two glass plates or the like at least one of which has display electrodes formed on a surface confronting a surface of the other, both substrates being superposed on each other with a predetermined gap interposed therebetween. A liquid crystal sealing material is arranged in a frame-like shape (an approximately square shape) between the peripheral portions of this pair of substrates, thereby bonding both substrates to each other. A liquid crystal inlet is formed in a portion of this sealing material, and a liquid crystal (liquid crystal molecules) charged through this inlet is sealed in the inside of the sealing material between both substrates. Thus, the liquid crystal sealed between the substrates forms a liquid crystal layer. Polarizers each of which transmits only constant polarized light are arranged on the outside surfaces of both substrates (the surfaces of both substrates opposite to the liquid crystal layer), respectively. Thus, a liquid crystal display panel (also called liquid crystal element or LCD (liquid crystal display)) is finished. A light source (back light) for supplying light from the back surface of the liquid crystal display panel and displaying an image on the top surface of the liquid crystal display panel is arranged on the back surface (bottom surface) of the liquid crystal display panel. The back surface of the liquid crystal display panel represents the surface of the liquid crystal display panel opposite to a surface (front surface) thereof on which to display an image to be viewed by a user of the liquid crystal display device. Unless otherwise specified in the present specification, description will be given on the assumption that the view point (observation point) of the user is located above the liquid crystal display device.
A driving circuit board for applying a voltage according to a display image signal to the aforementioned display electrodes is arranged outside the periphery of the liquid crystal display panel. The above-described liquid crystal display panel and back light are accommodated and held in a plastic-molded case. Moreover, all of these members as well as the molded case are accommodated in a metal-made upper shield case, a metal-made lower shield case and the like, the upper shield case having a display window (which exposes the display area of the top surface of the liquid crystal display panel to the user). Thus, the liquid crystal display device is assembled.
For example, in an active matrix type of liquid crystal display panel, a gate line group and a drain line group are formed over a liquid crystal-side main surface of either one of two transparent insulating substrates made of glass or the like which are arranged to confront each other with the aforementioned liquid crystal layer interposed therebetween. The gate line group is formed to be extended in the x direction and to be juxtaposed in the y direction (in a direction intersecting the x direction), while the drain line group is insulated from the gate line group and is formed to be extended in the y direction and to be juxtaposed in the x direction.
The areas surrounded by the gate lines and the drain lines constitute pixel areas, respectively, and switching elements such as a thin film transistor (TFI) and a transparent pixel electrode are formed in each of the pixel areas.
When a scanning signal is supplied to a gate line, a thin film transistor is turned on and a video signal from a drain line is supplied to a pixel electrode via this thin film transistor which has been turned on.
Each of the drain lines of the drain line group and each of the gate lines of the gate line group are formed to be extended into at least particular peripheral portions of the transparent insulating substrate, respectively, thereby constituting external terminals in the respective peripheral portions. A plurality of driver ICs (semiconductor integrated circuits) provided with video driving circuits and a plurality of driver ICs which constitute gate scanning driving circuits are externally attached to the periphery of the substrate on which the external terminals are formed. The respective external terminals of the drain line group are connected to the video driving circuits. For this reason, the drain lines are also called video signal lines. The respective external terminals of the gate line group are connected to the gate scanning driving circuits. For this reason, the gate lines are also called scanning signal lines. The aforementioned plurality of driver ICs are respectively mounted on tape carrier packages (TCPs) and are externally attached to the periphery of the substrate.
In this construction in which TCPs provided with driver ICs are externally attached to the periphery of the transparent insulating substrate, the area (generally called “picture frame”) occupied by the region between the contour of a display area defined by the area of intersection of the gate line group and the drain line group of the transparent insulating substrate and the contour of the external frame of the transparent insulating substrate becomes larger by the area required to arrange such circuits. On the other hand, there has recently been a growing demand for liquid crystal display modules having smaller external dimensions (liquid crystal display panels having higher densities and as small external dimensions as possible).
Accordingly, in order to make the width of such picture frame as small as possible, it has been proposed to provide a construction in which video driving ICs and gate scanning driving ICs are directly mounted on a transparent insulating substrate without the use of TCP components. This mounting scheme is called the Flip-Chip-Attachment (FCA) scheme or the Chip-On-Glass (COG) scheme (both schemes will be hereinafter referred to as the FCA scheme).
A liquid crystal display device based on this FCA scheme is described in, for example, Japanese Patent Laid-Open No. 122806/1996.
SUMMARY OF THE INVENTION
FIG. 18
is a schematic front view of a conventional liquid crystal display panel based on the FCA scheme, illustrating wavy brightness irregularity which appears on the display screen of the same.
In
FIG. 18
, symbol PNL denotes a liquid crystal display panel, symbol SUB
1
a lower transparent glass substrate which constitutes part of the liquid crystal display panel PNL, symbol SUB
2
an upper transparent glass substrate which constitutes part of the same, symbol ICG a gate driver (a gate line driving IC), symbol ICD a drain driver (a drain line driving IC), and symbol LP a linear light source such as a cold-cathode fluorescent tube. A plurality of gate drivers ICG and drain drivers ICD are directly mounted on an edge portion of the transparent glass substrate SUB
1
.
In the conventional liquid crystal display device, there has been the problem that a wavy brightness irregularity WBU as shown in
FIG. 18
occurs on the display screen of the liquid crystal display panel PNL in the vicinity of the drivers ICG and ICD mounted on the substrate SUB
1
and the display quality of the liquid crystal display panel PNL lowers. The wavy brightness irregularity which makes the display screen wavily bright (white) along the periphery thereof is whitely conspicuous during a black display in particular. This wavy brightness irregularity occurs between mutually adjacent drivers as shown in
FIG. 18
by way of example. The
Nemoto Atsushi
Sasuga Masumi
Shibata Katsuhiko
Antonelli Terry Stout & Kraus LLP
Parker Kenneth
Schechter Andrew
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