The present invention relates to liquid crystal displays (LCDs), and particular to an active matrix type LCD which is suitable for motion picture display.
Because LCD devices have the advantages of portability, low power consumption, and low radiation, they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, and the like. Furthermore, LCD devices are considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions.
The first substrate includes a number n (where n is a natural number) of scanning lines 13 that are parallel to each other and that each extend along a first direction, and a number m (where m is also a natural number) of signal lines 14 that are parallel to each other and that each extend along a second direction orthogonal to the first direction. The first substrate also includes a plurality of thin film transistors (TFTs) 15 that function as switching elements. The first substrate further includes a plurality of pixel electrodes 151 formed on a surface thereof facing the second substrate. Each TFT 15 is provided in the vicinity of a respective point of intersection of the scanning lines 13 and the signal lines 14.
Each TFT 15 includes a gate electrode, a source electrode, and a drain electrode. The gate electrode of each TFT 15 is connected to the corresponding scanning line 13. The source electrode of each TFT 15 is connected to the corresponding signal line 14. The drain electrode of each TFT 15 is connected to a corresponding pixel electrode 151.
The second substrate includes a plurality of common electrodes 152 opposite to the pixel electrodes 151. In particular, the common electrodes 152 are formed on a surface of the second substrate facing the first substrate, and are made from a transparent material such as ITO (Indium-Tin Oxide) or the like. A pixel electrode 151, a common electrode 152 facing the pixel electrode 151, and liquid crystal molecules of the liquid crystal layer sandwiched between the two electrodes 151, 152 cooperatively define a single pixel unit.
The scanning lines 13 are connected to a plurality of scanning line driving circuits 11. The signal lines 14 are connected to a plurality of a signal line driving circuits 12.
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If motion picture display is conducted on the active matrix LCD 100, problems of poor image quality may occur. For example, the residual image phenomenon may occur because the response speed of the liquid crystal molecules is too slow. In particular, when a gradation variation occurs, the liquid crystal molecules are unable to track the gradation variation within a single frame period and produce a cumulative response during several frame periods. Consequently, considerable research is being conducted with a view to developing various high-speed response liquid crystal materials as a way of overcoming this problem.
Further, the aforementioned problems such as the residual image phenomenon are not caused solely by the response speed of the liquid crystal molecules. For example, when the displayed image is changed in each frame period (the period that the scanning line driving circuits 11 sequentially complete scanning from G1.1 to Gn.256 once) to display the motion picture, the displayed image of one frame period remains in a viewer's eyes as an afterimage, and this afterimage overlaps with the viewer's perception of the displayed image of the next frame period. This means that from the viewpoint of a user, the image quality of the displayed image is impaired.
It is desired to provide an active matrix LCD that can overcome the above-described deficiencies.
An active matrix liquid crystal display includes: a plurality of scanning lines that are parallel to each other and that each extend along a first direction; a plurality of signal lines that are parallel to each other and that each extend along a second direction that is orthogonal to the first direction; a plurality of thin film transistors (TFTs) each provided in the vicinity of a respective point of intersection of the scanning lines and the signal lines; a plurality of scanning line driving circuits for providing a plurality of scanning signal groups to the scanning lines, each of the scanning signal groups including an image scanning signal and a black-inserting scanning signal; a plurality of signal line driving circuits for providing gradation voltage data to the signal lines when an image scanning signal is provided to the scanning lines by the scanning line driving circuits; and a plurality of black-inserting circuits for providing a high voltage corresponding to black image data to the signal lines when a black-inserting scanning signal is provided to the scanning lines by the scanning line driving circuits.
The signal line driving circuits provide gradation voltage data corresponding with image data to the signal lines. In one embodiment, after about half of a corresponding frame time has elapsed, the black-inserting circuit provides a high voltage corresponding with black image data to the signal lines. With this mode of operation, a viewer's eyes perceive the black image during the second half of the frame time, and any afterimage of the image displayed in the first half of the frame time that would otherwise exist in the viewer's eyes is lost.
Other advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:
Reference will now be made to the drawings to describe the present invention in detail.
The first substrate includes a number n (where n is a natural number) of scanning lines 23 that are parallel to each other and that each extend along a first direction, and a number m (where m is also a natural number) of signal lines 24 that are parallel to each other and that each extend along a second direction orthogonal to the first direction. The first substrate also includes a plurality of TFTs (thin film transistors) 25 that function as switching elements. The first substrate further includes a plurality of pixel electrodes 251 formed on a surface thereof facing the second substrate. Each TFT 25 is provided in the vicinity of a respective point of intersection of the scanning lines 23 and the signal lines 24.
Each TFT 25 includes a gate electrode, a source electrode, and a drain electrode. The gate electrode of the TFT 25 is connected to the corresponding scanning line 23. The source electrode of the TFT 25 is connected to the corresponding signal line 24. The drain electrode of the TFT 25 is connected to a corresponding one of the pixel electrodes 251.
The second substrate includes a plurality of common electrodes 252 opposite to the pixel electrodes 251. In particular, the common electrodes 252 are formed on a surface of the second substrate that faces the first substrate, and are transparent electrodes made of ITO or the like. A pixel electrode 251, a common electrode 252 facing the pixel electrode 251, and liquid crystal molecules of the liquid crystal layer sandwiched between the two electrodes 251, 252 cooperatively define a single pixel unit.
The scanning lines 23 are connected to the scanning line driving circuits 21. The signal lines 24 are connected to the signal line driving circuits 22 and the black-inserting circuits 28.
The scanning line driving circuits 21 sequentially apply the scanning signal groups 29 (G1.1 to Gn.256) to the scanning lines 23. When the image scanning signals 291 are provided to the scanning lines 23 by the corresponding scanning line driving circuits 21, the TFTs 25 respectively connected to the scanning lines 23 are activated by the image scanning signals 291. Then the signal line driving circuits 22 provide gradation voltage data (VD) corresponding with image data of an external circuit to the signal lines 24, and the gradation voltage data are written to the pixel electrodes 251 via the activated TFTs 25. The potentials of the common electrodes 252 are set at a uniform potential. The gradation voltage data written to the pixel electrodes 251 are used to control the amount of light transmission of the corresponding pixel units and consequently provide an image display for the active matrix LCD 200. When the black-inserting scanning signals 292 are provided to the scanning lines 23 by the corresponding scanning line driving circuits 21, the TFTs 25 respectively connected to the scanning lines 23 are activated by the black-inserting scanning signals 292. Then the black-inserting circuits 28 provide a high voltage corresponding with black image data to the signal lines 24, and the black image data are written to the pixel electrodes 251 via the activated TFTs 25. The black image data written to the pixel electrodes 251 are used to control the amount of light transmission of the corresponding pixel units and consequently provide a black image display for the active matrix LCD 200.
Unlike with the above-described conventional active matrix LCD 100, the signal lines 24 of the active matrix LCD 200 are connected to the plurality of signal line driving circuits 22 and the plurality of black-inserting circuits 28. The signal line driving circuits 22 provide gradation voltage data corresponding with image data to the signal lines 24. After about half of the frame time, the black-inserting circuits 28 provide a high voltage corresponding with black image data to the signal lines 24. With this mode of operation, a viewer's eyes perceive the black image during the second half frame time B, and any afterimage of the image displayed in the first half frame time A that would otherwise exist in the viewer's eyes is lost. Accordingly, there is no afterimage that can overlap with the viewer's perception of the displayed image of the next frame period. This means that from the viewpoint of a user, the image quality of the displayed image is clear.
In alternative embodiments, for example, each of the scanning signal groups 29 can have a duration equal to two fifths of the frame time. In other examples, the duration of an image scanning signal can be equal to, longer than, or shorter than the duration of a black-inserting scanning signal.
It is to be further understood that even though numerous characteristics and advantages of preferred embodiments have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Number | Date | Country | Kind |
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93140469 | Dec 2004 | TW | national |