Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-07-06
2003-03-04
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S098000, C345S099000, C345S100000, C345S690000, C345S208000, C345S209000, C345S210000
Reexamination Certificate
active
06529180
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, and, more particularly, to a technology applicable to image signal line driving (drain driver) of a liquid crystal display device which is capable of producing a multiple grayscale display.
An active matrix type liquid crystal display device having an active element (for example, thin film transistor) for each pixel, and in which a display is produced by selectively driving the active elements, is widely used as a notebook type personal computer. In the active matrix type liquid crystal display device, an image signal voltage (grayscale voltage in correspondence with display data; hereinafter, referred to as a grayscale voltage) is applied via the active element; and, accordingly, there is no cross talk among respective pixels, so that it is not necessary to use a special drive method for preventing cross talk as in a simple matrix type liquid crystal display device, whereby multiple grayscale display is feasible.
As one known example of the active matrix type liquid crystal display device, there is a liquid crystal display device having a liquid crystal display panel (TFT-LCD) of the TFT (Thin Film Transistor) type, a drain driver arranged on an upper side of the liquid crystal display panel, a gate driver arranged at a side face of the liquid crystal display panel and an interface unit. According to the TFT type liquid crystal display device, there are provided a grayscale voltage generating circuit, a grayscale voltage selecting circuit (decoder circuit) for selecting one grayscale voltage in correspondence with display data from among a plurality of grayscale voltages generated in the grayscale voltage generating circuit and an amplifier connected to receive the one grayscale voltage selected by the grayscale voltage selecting circuit. Such a technology is described in, for example, Japanese Application No. 8-86668.
SUMMARY OF THE INVENTION
In recent years, in a liquid crystal display device of a liquid crystal module of the TFT type, along with demands for a large screen liquid crystal display panel, there is a further demand for a high resolution formation, such as 1024×768 pixels in the XGA display mode, 1280×1024 pixels in the SXGA display mode or 1600×1200 pixels in the UXGA display mode. Therefore, the number of horizontal scans in one vertical scan period is increased; and, in accordance therewith, the write time period per one horizontal scan become shorter and shorter, and so the output delay time period (tDD) of the drain driver poses a serious problem.
For example, in the XGA display mode, the write time period per one horizontal scan is about 20 &mgr;s, and there is also a case in which the output delay time period (tDD) of the drain driver reaches 10 through 20 &mgr;s. In such a case, the pixel write voltage becomes deficient and the display quality of the image displayed on the liquid crystal display panel is significantly deteriorated.
Meanwhile, in a liquid crystal display device, there is a tendency toward large size formation and high resolution formation (multiple pixel formation). Furthermore, in order to dispense with wasteful space and produce a display device having an attractive appearance, a region other than a display region of the liquid crystal display device, that is, a frame edge portion thereof, should be reduced in size (narrow frame edge formation). For that purpose, it is necessary to further reduce the chip size of a semiconductor chip constituting a drain driver; and, in accordance therewith, the grayscale voltage selecting circuit has been constituted by a field effect type transistor (MOS transistor) of a minimum size. As a result, the current driving function of the grayscale voltage selecting circuit is lowered, and the time period (output delay time period) for determining the grayscale voltage in correspondence with display data by the grayscale voltage selecting circuit is increased, which constitutes a significant factor in the output delay time period (tDD) of the drain driver.
Further, in a liquid crystal display device, the multiple grayscale display is being advanced from a 64 value grayscale display to a 256 value grayscale display, and the voltage width per grayscale value of a plurality of grayscale voltages generated by the grayscale voltage generating circuit (that is, potential difference between contiguous grayscale voltages) is reduced. Meanwhile, with respect to an amplifier for amplifying the grayscale voltage, owing to a dispersion in the characteristic of the active element constituting the amplifier, an offset voltage is produced; and, when the offset voltage is produced in the amplifier, an error is caused in the output voltage of the amplifier, and the output voltage of the amplifier becomes a voltage different from a target value (regular grayscale voltage). This results in a problem in which a vertical streak of black or white is produced on the display screen displayed on the liquid crystal display panel, which significantly deteriorates the display quality.
The invention has been carried out in order to resolve the above-described problems of the conventional technology, and it is an object of the invention to provide a technology capable of promoting the display quality of a display image displayed on a liquid crystal display element in a liquid crystal display device.
It is another object of the invention to provide a technology enabling high speed operation and large screen formation of a liquid crystal display element in a liquid crystal display device.
The objects and novel characteristics of the invention will become more apparent from the following description and the attached drawings.
A simple explanation will be given of representatives features of the invention disclosed in the specification.
That is, according to an aspect of the invention, there is provided a liquid crystal display device comprising a liquid crystal display element having a plurality of pixels provided in a matrix arrangement and a plurality of image signal lines for applying grayscale voltages in correspondence with display data to respective pixels in a column (or row) direction to the plurality of pixels, and image signal line driving means constituted by at least a single semiconductor integrated circuit device for supplying the grayscale voltages in correspondence with the display data to the respective image signal lines. The semiconductor integrated circuit device comprises a plurality of grayscale voltage selecting means for selecting the grayscale voltages in correspondence with the display data inputted from the plurality of grayscale voltages and constituted by a transistor having a minimum size in the semiconductor integrated circuit device; a plurality of amplifiers for amplifying the grayscale voltages selected by the respective grayscale voltage selecting means and for outputting the selected grayscale voltages to the respective image signal lines; first switching means provided between the respective grayscale voltage selecting means and the amplifiers; second switching means provided between a power source line supplied with a predetermined charge voltage and the respective amplifiers; and switching controlling means for switching off the first switching means and switching on the second switching means in an initial predetermined time period of one horizontal scanning time period.
Further, according to another aspect of the invention, there is provided a liquid crystal display device comprising a liquid crystal display element having a plurality of pixels provided in a matrix arrangement and a plurality of image signal lines for applying grayscale voltages in correspondence with display data to respective pixels in a column (or row) direction to the plurality of pixels, and image signal line driving means constituted by at least a single piece of a semiconductor integrated circuit device for supplying the grayscale voltages in correspondence with the display data to the respective image signal lines
Ito Shigeru
Kataoka Noboru
Ogura Akira
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Nguyen Jimmy H.
Shalwala Bipin
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