Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-08-10
2004-04-27
Chang, Kent (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S089000, C345S209000, C345S210000, C345S690000
Reexamination Certificate
active
06727877
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a liquid crystal display device, and more particularly to an active matrix type in-plane switching liquid crystal display device.
2. Description of the Related Art
Recently, there has been developed an in-plane switching type liquid crystal display device in which molecular axes of aligned liquid crystal molecules are rotated in a plane parallel to a substrate, to thereby display images.
In an in-plane switching type liquid crystal display device, since a viewer looks only at minor axes of liquid crystal molecules even if he/she turns his/her viewpoint, an angle of visibility is not dependent on an inclination of liquid crystal molecules. Hence, an in-plane switching type liquid crystal display device can present a wider angle of visibility than a conventional liquid crystal display device such as a twisted nematic (TN) mode liquid crystal display device where an electric field is generated between substrates sandwiching a liquid crystal layer therebetween in a direction perpendicular to the substrates.
In an in-plane switching type liquid crystal display device, a plurality of scanning lines and signal lines are arranged on one of transparent substrates sandwiching a liquid crystal layer therebetween. Thin film transistors (TFTs) are arranged at intersections of the scanning and signal lines. Sources of the thin film transistors are electrically connected to pixel electrodes. Opposing electrodes are positioned in facing relation with the pixel electrodes.
When an image is displayed on a display screen in in-plane switching type liquid crystal display device, a voltage is applied to the scanning lines for successively turning the thin film transistors on, and then, a voltage having a magnitude determined in accordance with a gradation to be displayed is applied to an associated pixel electrode through the thin film transistor from a data line. As a result, there is produced an electric field between the pixel and opposing electrodes in parallel with the transparent substrates. The thus produced electric field varies a direction of alignment of liquid crystal molecules in the liquid crystal layer, and resultingly, vary optical characteristics of liquid crystal, ensuring a desired gradation.
The above-mentioned in-plane switching type liquid crystal display device is accompanied with a problem that flicker occurs when a certain image is displayed for a certain period of time, and thereafter, the image is switched into another image in which all pixels are arranged to be in the same gradation.
For instance, it is assumed that a liquid crystal display device is driven in accordance with a dot inversion driving method in which a voltage for driving a positive polarity and a voltage for driving a negative polarity are switched to each other in each of pixels at a predetermined interval. In this case, the above-mentioned problem occurs in particular when a checker pattern in which black-displaying pixels B (minimum gradation) and white-displaying pixels W (maximum gradation) are alternately arranged in a matrix, as illustrated in
FIG. 7
, is displayed in a certain period of time, and thereafter, all pixels are switched into images having the same gradation.
For another instance, it is assumed that a liquid crystal display device is driven in accordance with a line inversion driving method in which a voltage for driving a positive polarity and a voltage for driving a negative polarity are switched to each other in every lines at a predetermined interval. In this case, the above-mentioned problem occurs in particular when a stripe pattern in which black-displaying and white-displaying pixels are alternately arranged in every two lines is displayed in a certain period of time, and thereafter, all pixels are switched into images having the same gradation.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems in the conventional liquid crystal display devices, it is an object of the present invention to provide an in-plane switching type liquid crystal display device which is capable of reducing flickers in a display screen It is also an object of the present invention to provide a method of driving a liquid crystal display device which method is capable of reducing flickers in a display screen.
In one aspect of the present invention, a liquid crystal display device includes (a) a first substrate, (b) a second substrate, (c) a liquid crystal layer sandwiched between the first and second substrates, (d) a plurality of scanning lines arranged on the first substrate, (e) a plurality of signal lines arranged on the first substrate, (f) a plurality of first switches arranged at intersections of the scanning lines and the signal lines, (g) a plurality of pixel electrodes each electrically connected to each of the first switches, (h) a plurality of opposing electrodes each arranged in parallel with each of the pixel electrodes, and (i) a signal line driver which switches a first voltage for driving a positive pole and a second voltage for driving a negative pole at a predetermined interval in accordance with a gradation, and outputs the positive or negative driving voltage to the signal lines, the signal line driver compensating for the first and second voltages such that averages of the first and second voltages in each of gradations are different from one another.
For instance, the signal line driver may be designed to compensate for the first and second voltages such that an average of the first and second voltages is smaller in a higher gradation.
For instance, the signal line driver may be designed to compensate for the first and second voltages such that a difference between an average of positive and negative voltages to be applied to the pixel electrode in association with a gradation and a voltage of the opposing electrode associated with the pixel electrode is kept substantially constant irrespective of the gradation.
For instance, such a voltage may be applied to the opposing electrodes that a flicker is not allowed to occur in a display where pixels displaying intermediate gradation and pixels displaying black are alternately arranged. For instance, the signal line driver may be designed to compensate for the first and second voltages such that a difference between an average of the first and second voltages, associated with a maximum gradation, and an average of the first and second voltages, associated with a minimum gradation, is in the range of −1.0 to 0.0 volts both inclusive.
For instance, the signal line driver may be designed to compensate for the first and second voltages such that a difference between an average of the first and second voltages, associated with a maximum gradation, and an average of the first and second voltages, associated with a minimum gradation, is in the range −0.9 to −0.2 volts both inclusive.
For instance, the signal line driver may be designed to compensate for the first and second voltages such that a difference between an average of the first and second voltages, associated with a maximum gradation, and an average of the first and second voltages, associated with a minimum gradation, is in the range of −0.5 to −0.3 volts both inclusive.
It is preferable that the liquid crystal display device further includes a light barrier which does not allow a light to reach the first switches.
It is preferable that liquid crystal in the liquid crystal layer has a specific resistance in the range of 4.5×10
10
&OHgr; cm and 2.0×10
13
&OHgr; cm both inclusive, preferably in the range of 3.0×10
11
&OHgr; cm and 1.0×10
13
&OHgr; cm both inclusive, and more preferably in the range of 5.0×10
11
&OHgr; cm and 2.0×10
12
&OHgr;cm both inclusive.
There is further provided a liquid crystal display device includes (a) a first substrate, (b) a second substrate, (c) a liquid crystal layer sandwiched between the first and second substrates, (d) a plurality of scanning lines arranged on the first substrate, (e) a pl
Chang Kent
NEC LCD Technologies Ltd.
Sheng Tom
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