Patent Application
20080024417
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
The compensation circuit 305 provides a common voltage compensation signal to the common electrode substrate 307a according to a value control signal output from a timing controller 303 and a polarity control signal in conjunction with a latch pulse signal. The latch pulse signal is a control signal for controlling the output of a source driver, and is generally provided by the timing controller 303. Therefore, the common electrode substrate 307a receives the common voltage compensation signal as well as the common voltage signal so as to compensate the voltage change in the common voltage of the common electrode substrate 307a owing to the coupling effect generated by the parasitic capacitor.
In the present embodiment, the timing controller 303 comprises a buffer 309, a data analyzer 311, a lookup table 313, and a polarity selector 315. The buffer 309 is used for receiving and registering the image signal, wherein the image signal is comprised of continuous frames, and each frame comprises a plurality of horizontal line signals. Each horizontal line signal has a plurality of pixel data, and two adjacent pixel data of the pixel data have opposite polarities. The data analyzer 311 receives the image signal output from the buffer 309 and performs an analysis of the gray scale distribution of each of the horizontal line signals of the image signal respectively.
In addition, the data analyzer 311 is respectively electrically connected to the lookup table 313, the polarity selector 315, and the compensation circuit 305. The data analyzer 311 compares the analysis result of the gray scale distribution with a plurality of common voltage compensation values built in the lookup table 313, and selects a common voltage compensation value from the lookup table 313 to output a corresponding value control signal to the compensation circuit 305. The analysis result of the gray scale distribution made by the data analyzer 311 is also provided to the polarity selector 315 in order to select the polarity of the horizontal line signal, and a corresponding polarity control signal is output from the polarity selector 315 to the compensation circuit 305.
Therefore, the value and the polarity of the common voltage compensation signal provided by the compensation circuit 305 are respectively determined by the value control signal and polarity control signal output from the timing controller 303, and the timing of the common voltage compensation signal is determined by the latch pulse signal. Generally, the time of sending the common voltage compensation signal is at the falling edge of the latch pulse signal.
As is known to all, display panel driving methods are generally categorized as frame inversion, column inversion, row inversion and dot inversion. The degradation of the display quality resulting from the property degradation of the liquid crystal molecules can be avoided by changing the polarities of the voltage driving the liquid crystal molecules. The present invention is suitable for liquid crystal displays employing driving methods such as dot inversion or column inversion.
Moreover, the driving method of a display panel is generally categorized as normally white or normally black. When the display panel is driven in a normally white method, the voltage difference between the white signal applied to the panel and the common voltage is relatively small, while the voltage difference between the black signal and the common voltage is relatively large, therefore the black signal will greatly influence the common voltage due to the coupling of the parasitic capacitance. Contrarily, when the display panel is driven in a normally black method, the white signal will greatly influence the common voltage. The present invention will be described as below by taking a display panel that is driven in a normally white, dot inversion method as an example. Any one skilled in the art can easily employ the inventive spirit of the present invention to display panels that are driven in a normally black method or in a column inversion method.
For example, when the gate line 41 is actuated with a pulse signal, a horizontal line signal is sent to the pixel through the source lines 401˜413, wherein the horizontal line signal comprises the pixel data, P(401,41), P(402,41), P(403,41), . . . , P(413,41), and two adjacent pixel data of the pixel data P(401,41)˜P(413,41) have opposite polarities. Then, when the gate line 42 is actuated, another horizontal line signal comprising pixel data P(401,42)˜P(413,42) is sent to the pixel, wherein two adjacent pixel data of the pixel data P(401,42)˜P(413,42) have opposite polarities. And the adjacent pixel data in the pixel data P(401,42)˜P(413,42) and the pixel data P(401,41)˜P(413,41) at corresponding positions also have opposite polarities. Therefore, the pixel data polarity distribution as shown in
Moreover, if the polarity distribution of the pixel data shown in
Furthermore, taking an 8-bit gray scale (256 color scale) as an example, the gray scale value thereof is from 0 (all black) to 255 (all white). Since the black signal greatly influences the common voltage when the display panel is driven in a normally white method, only the amount of the odd pixel data (or the even pixel data) whose gray scale value falls in the abovementioned gray scale value range is counted. In this embodiment, the gray scale value range is, for example, from 0 to 50.
When the amount of the odd pixel data that is in the gray scale value range equals to the amount of the even pixel data of the horizontal line signal in the gray scale value range, there is no need to compensate the common voltage. That is because the influences on the common voltage will be counteracted due to the opposite polarities of the odd pixel data and the even pixel data.
When the difference of the amount of the odd pixel data in the gray scale value range and the amount of the even pixel data of the horizontal line signal in the gray scale value range is greater than M and more than N times, the whole horizontal data line will influence the common voltage. For example, if the odd pixel data have negative polarities and the even pixel data have positive polarities, a reduced common voltage 504 will be generated when the polarity POL is a positive polarity 501 and is at the falling edge 503 of the latch pulse signal; and then an increased common voltage 505 will be generated when the polarity POL is a negative polarity 502 and is at the falling edge 503 of the latch pulse signal. Therefore, the compensation circuit 305 determines the size of the output common voltage compensation signal according to the value control signal output from the data analyzer 311, and determines the polarity of the output common voltage compensation signal according to the polarity control signal output from the polarity selector 315, so as to generate a proper common voltage compensation signal to compensate the common voltage.
For example, if the amount of the odd pixel data in the gray scale value range is 1000 and the amount of the even pixel data in the gray scale value range is 600, the difference thereof is 400 (=1000−600) and the former is 1.67 (=1000/600) times the latter. If it is assumed that the M and N are respectively adjusted to 300 and 2 according to, for example, the horizontal resolution of the display panel or the size of the display panel, there is no need to perform the common voltage compensation as the above difference is 400 (>M) and the times thereof is 1.67 (<N).
To sum up, the present invention can compensate the common voltage of a display panel influenced by the coupling effect of the parasitic capacitance without modifying the process because of adopting a common voltage compensation device to analyze the gray scale distribution of each horizontal line signal of the received image signal, thereby improving the display quality.
Although the present invention is disclosed as above by preferred embodiments, they are not intended to limit the present invention. Various variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention, and the scope of the present invention shall be defined by the appended claims.
