Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-02-26
2003-07-22
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S691000, C345S058000, C345S099000
Reexamination Certificate
active
06597335
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a matrix-type super twisted nematic (STN) liquid crystal display device used for various office automation (OA) equipment such as a personal computer and/or a word processor, a multi-media information terminal, audio video (AV) equipment, game equipment, etc., and a method for driving the same. More specifically, the present invention relates to a liquid crystal display device in which an improved uniform display quality can be obtained, and a method for driving the same.
2. Description of the Related Art
In the above-mentioned STN liquid crystal display device, higher response is known to decrease contrast. Hereinafter, the reason for this and proposed techniques for solving this problem will be described.
In the past, in an STN liquid crystal display device, a line sequential driving system has been adopted. According to this driving system, row electrodes are successively scanned one at a time over one frame period, high scanning pulse is applied to each row electrode only once in one frame period, and in synchronization with this, a data voltage in accordance with display data of each pixel on a row electrode to be scanned is applied to column electrodes.
In a liquidcrystal display device adopting the above-mentioned driving system, a display of mainly a freeze-frame picture is intended. Therefore, such a liquid crystal display device uses liquid crystal with relatively low response. In this case, liquid crystal responds to an effective value of a voltage to be applied, and a practical contrast ratio is obtained. However, when it is attempted to realize high response of the liquid crystal by reducing the viscosity of the liquid crystal and making a liquid crystal layer thinner so as to create a display of a moving picture, according to the line sequential driving system, the liquid crystal responds to a driving waveform itself, without responding to an effective value of a voltage, and the transmittance noticeably fluctuates per frame. This phenomenon is called a frame response phenomenon, which causes a significant decrease in the contrast ratio.
In order to solve the above-mentioned problem, the following driving system is proposed. According to this system, unlike the linear sequential driving system, a plurality of low scanning pulses are applied in one frame, thereby suppressing a frame response phenomenon to prevent the contrast ratio from decreasing. Such a driving system is called a multi-line simultaneous selection driving system, which is characterized in that a plurality of row electrodes are simultaneously scanned by using an orthogonal matrix. Hereinafter, its basic operation will be briefly described.
Input data is subjected to orthogonal transformation by using an orthogonal matrix, and a data voltage based on operational data is applied to a column electrode. In synchronization with this, a scanning voltage based on a column vector of the orthogonal matrix is simultaneously applied to row electrodes to be simultaneously selected. In this way, orthogonal transformation of image data is performed on a liquid crystal panel, and an input image can be reproduced. At this time, depending upon the number of row electrodes be simultaneously selected and the scanning order, the following three driving systems are proposed. The basic principle of each driving system is as described above.
The first driving system is an active addressing system in which all the row electrodes in one screen are simultaneously scanned. This system is disclosed in T. J. Scheffer, et al., SID '92, Digest, p. 228, and Publication for Opposition No. 7-120147.
The second driving system is a sequence addressing system in which a plurality of row electrodes less than all the electrodes in one screen are classified into groups, and each group is sequentially scanned. This driving system enables the circuit size to be smaller, compared with the first driving system. This system is disclosed in T. N. Ruckmongathan et al., Japan Display '92, Digest, p. 65 and Japanese Laid-Open Publication No. 5-46127.
According to the third driving system, one screen is divided into a plurality of blocks in a row direction, and a plurality of row electrodes less than all the electrodes in each block are classified into groups, and each group is sequentially scanned, whereby all the blocks driven (Japanese Laid-Open Publication No. 6-291848). This driving system can reduce memory space, and enables the circuit size to be smaller, compared with the second driving system.
As described above, by adopting a multi-line simultaneous selection driving system in a high-response simple matrix-type liquid crystal display device, the frame response phenomenon is suppressed, and a decrease in the contrast ratio can be prevented.
Furthermore, as a gray-scale system of an STN liquid crystal display device, a pulse width modulation system (PWM system) is known, in which an operation between display data and an orthogonal function is performed per bit, and a data signal voltage with a width corresponding to a weight per bit is applied to a column electrode. This is disclosed in Japanese Laid-Open Publication No. 990914.
However, in the conventional pulse width modulation system, the number of signal changes per horizontal scanning period becomes larger than the case where a gray-scale display is not realized. This increases the frequency of a data voltage signal, so that the amount of induced distortion caused by electrode resistance and liquid crystal capacitance becomes large. As a result, an effective voltage value slightly different from the fundamental effective voltage value is applied to liquid crystal, which leads to a decrease in display quality due to, for example, cross-talk. This will be described with reference to the drawings.
As shown in
FIG. 8
, a display state of pixels is determined on a liquid crystal panel including 6 pixels in the vertical (row) direction and 2 pixels in the horizontal (column) direction. Each of column electrodes X
1
and X
2
and row electrodes Y
1
to Y
6
is determined as shown in this figure.
FIG. 9
shows driving waveforms C
1
C and C
2
C of the column electrodes X
1
and X
2
and a driving waveform R
1
C of the row electrode Y
1
in the case where the liquid crystal panel in this state is driven in the conventional manner.
As is understood from
FIG. 9
, according to the conventional driving system, display data on the column electrode X
1
is exactly the same as that on the column electrode X
2
, so that a data signal represented by the waveform C
1
C applied to the column electrode X
1
becomes exactly the same as a data signal represented by the waveform C
2
C applied to the column electrode X
2
. Thus, timing of changes in waveforms and the change directions are exactly the same between the two signals. Therefore, waveform distortion of a scanning voltage represented by the waveform R
1
C induced by a data voltage becomes relatively large as shown in FIG.
9
. Accordingly, a waveform of a voltage actually applied to liquid crystal is largely shifted from an ideal waveform without containing any waveform distortion, and an effective voltage value becomes substantially different from an ideal value.
Thus, considering the case where hundreds of column electrodes are provided, the variation in difference between the effective voltage value and the ideal value becomes large per column electrode according to the conventional driving method, which leads to a decrease in display quality due to, for example, cross-talk.
SUMMARY OF THE INVENTION
A method for driving a liquid crystal display device is provided. The device includes a plurality of row electrodes to which a scanning signal is applied; a plurality of column electrodes disposed so as to cross the plurality of row electrodes, to which a display data signal is applied; and a liquid crystal layer interposed between one of the plurality of row electrodes and one of the plurality of column electrodes, for performing a display at a crossi
Ueno Satoshi
Yasunishi Norio
Conlin David G.
Edwards & Angell LLP
Saras Steven
Sharp Kabushiki Kaisha
Spencer William C.
LandOfFree
Liquid crystal display device and method for driving the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid crystal display device and method for driving the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display device and method for driving the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3028274