Abstract:
A method of driving a liquid crystal display panel that is adaptive for providing the entire panel with a brightness uniformity. In the method, the scanning direction of the panel is inverted at a desired period, for example, every frame, or within a frame. Accordingly, the average turn-on interval of all of the pixels within the panel becomes equal, so that the brightness of the entire panel can be uniform.

Description:
This application claims the benefit of Korean Patent Application No. 1999-40985, filed on Sep. 22, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of driving a liquid crystal display panel, and more particularly to a method of driving a liquid crystal display panel that is adaptive for providing the entire panel with a uniform brightness. 
     2. Discussion of the Related Art 
     Generally, in a liquid crystal display panel, a liquid crystal layer controls a transmissivity of a light generated from a backlight in accordance with a voltage level of a data signal applied to the liquid crystal layer to display a picture. Such a liquid crystal display panel has a structure in which pixels provided with a liquid crystal layer and pixel electrodes and a reference electrode for applying a driving voltage to the liquid crystal layer and a reference electrode are arranged in a matrix type. 
     FIG. 1 is a schematic view of a liquid crystal display and a driving apparatus therefor. In FIG. 1, each pixel  22  is provided at each of intersections between m data lines D 1  to Dm and n gate lines G 1  to Gn within the liquid crystal panel  20 . The pixels  22  arranged along each gate line form scanning lines and are connected, via the gate lines G 1  to Gn, to a gate driver  24 . Also, the pixels  22  are connected, via the data lines D 1  to Dm, to the data driver  26 . An equivalent circuit of the pixel  22  as a unit picture element is illustrated within an exploded view within the “circle” of FIG.  1 . Herein, a liquid crystal layer driven by a voltage difference between the pixel electrode and the reference electrode within a single pixel  22  is equivalent to a liquid crystal capacitor Clc. The pixel electrode is connected to a drain electrode of a thin film transistor (TFT) as a switching device, whereas the reference electrode is connected to a common voltage source Vcom. A gate electrode and a source electrode of the TFT are connected to a gate line and a data line, respectively. 
     The gate driver  24  sequentially applies a gate driving voltage to each gate line G 1  to Gn to drive each scanning line of the panel sequentially. If a voltage is applied, via the gate lines G 1  to Gn, to the gate electrodes of the TFT, then a channel is formed between the source electrode and the drain electrode of the TFT. At this time, a data voltage applied from the data driver  24 , via the data lines D 1  to Dn, to the source electrode of the TFT is applied to the drain electrode of the TFT. A difference voltage between a voltage applied to the drain electrode and a common voltage source Vcom is charged in the liquid crystal capacitor Clc to drive a liquid crystal layer of each pixel  22 . Then, the liquid crystal layer controls a transmissivity of a light generated from the backlight in accordance with a difference voltage between the common voltage source Vcom and the data voltage. 
     In a general color display panel, a mixed ratio of colors three red (R), green (G) and blue (B), is controlled to realize various colors. In the liquid crystal display panel, red (R), green (G) and blue (B) color filers are mounted at each pixel  22  for transmitting a white light, or a color filer is replaced by three backlight lamps for generating red (R), green (G) and blue (B) lights. A driving method of a liquid crystal display panel without color filters is different from that of a liquid crystal display panel with color filters. In a liquid crystal display panel including three color backlight lamps instead of color filters, one frame making a picture is trisected to apply red (R), green (G) and blue (B) color data to the panel sequentially during each frame interval. 
     FIG. 2 is a timing chart showing an operation process made during one frame interval in a liquid crystal display panel with no conventional color filter. Referring to FIG. 2, in the case of the liquid crystal display panel with no color filter, a data voltage for each of the red (R), green (G) and blue (B) colors applied from the data driver  26  is time-divided during one frame interval to be sequentially charged in the pixels  22  of the panel  20 . A backlight lamp having the corresponding color is turned on from a certain time when a data voltage for one color is being charged sequentially for one scanning line within the panel  20 , until a time when a data voltage for another color begins to be charged in each ⅓ frame interval. 
     Herein, to turn on the backlight lamp having the corresponding color before a charge of a data voltage for any one color has been completed aims at lengthening a lamp turn-on time sufficiently to improve the brightness of a picture. If the backlight lamp is turned on before a data voltage for any one color was charged in all of the pixels  22  within the panel  20  as mentioned above, however, there exists a problem in that color purity of a picture displayed on the lower part of the panel  20  is deteriorated. As described earlier, during a time interval when a data voltage is charged in the panel  20 , the gate driver  24  drives each gate line G 1  to Gn in sequence from the first gate line G 1  to the n gate line Gn. In other words, a scanning direction of the panel  20  is set to a direction going from the upper end of the panel to lower end thereof. In the pixels within the scanning line to which a gate voltage is applied, a conductive channel is provided between the source electrode and the drain electrode of the TFT to charge a data voltage applied, via the data driver  24 , from the data lines D 1  to Dm. Accordingly, if the backlight lamp is turned on before the scanning lines provided at the lower part of the panel  20  have been charged, then color purity of a picture displayed on the pixels at the lower part of the panel  20  is deteriorated because they is in a state of maintaining a data voltage for the preceding color. In order to solve this problem, the liquid crystal display panel with no color filter takes advantages of a scheme of simultaneously resetting all the pixels  22  within the panel  20  before applying a data voltage for any one color, to erase the entire previous data having been charged into each pixel  22  as shown in FIG.  2 . If such a scheme is used, then, even though the backlight lamp having the corresponding color is turned on before charging of a data voltage for any one color has been completed, the pixels in which charging of the data voltage for the color has not been made go into a state of erasing the data for the preceding color, so that it is possible to prevent a problem of the color purity deterioration caused by residual data. 
     In a driving method including the step of sequentially charging a data voltage and the step of simultaneously resetting the pixels  22 , however, a brightness non-uniformity phenomenon, differentiating the brightness of a picture displayed on the upper part of the panel  20  from the brightness of a picture displayed on the lower part thereof, is generated. Such a problem will be described in conjunction with FIG.  3  and FIG.  4 . In the conventional panel driving method, each gate line G 1  to Gn provided within the panel  20  is driven in sequence from the first gate line G 1  positioned at the top of the panel, to the nth gate line Gn positioned at the bottom thereof. As shown in FIG. 3, the scanning direction of the panel  20  is always constant for each frame interval. As mentioned above, when all the pixels  22  are simultaneously reset prior to charging the next data, a data sustaining interval until a pixel  22  is to be reset becomes different in accordance with whether the pixel  22  is located at any part of the panel. In other words, since all the pixels  22  are not charged simultaneously, the data-sustaining intervals of the pixels  22  become different for each scanning line at the reset time. For instance, data sustaining intervals between A pixels positioned at the first scanning line of the panel  20 , B pixels positioned at the middle scanning line of the panel  20  and C pixels positioned at the nth scanning line at the bottom of the panel  20  as shown in FIG. 1 become different as shown in FIG. 4. A data sustaining interval of the A pixels in which a data voltage is first charged is longest, whereas a data sustaining interval of the C pixels in which a data voltage is last charged is shortest. As described above, the backlight lamp is turned on after a data charge for all the pixels  22  has been completed, but it is turned off after being turned on in the course of a scanning interval of the panel  20  prior to a reset interval of the next pixels  22  so as to improve the brightness. Accordingly, turn-on intervals of the A pixels, the B pixels and the C pixels become different, and a difference in turn-on interval is always generated every frame when a scanning direction of the panel  20  is always constant every frame to cause a brightness difference between the upper part and the lower part of the panel  20 . 
     Such a problem also is generated in the case of driving a liquid crystal display panel with color filters. In a liquid crystal display panel mounted with a color filter for each pixel and including a single backlight lamp, red (R), green (G) and blue (B) data are simultaneously applied every frame as shown in FIG.  5 . Also, a scanning direction of the panel  30  is always constant from the upper end of the panel  30  until the lower end thereof. The liquid crystal display panel  30  with color filers provides a data reset interval for each frame so as to prevent a phenomenon of leaving an image from the previous frame onto a residual image when a picture is changed frame by frame to exhibit a slow response speed. The problem related with the residual image is solved by eliminating during the reset interval data which was charged into each pixel in the previous frame. In such a case, the sustaining interval of a data voltage charged into the pixel becomes different in accordance with a position of the pixel within the panel  30  as shown in FIG.  4 . Accordingly, since a difference in a data turn-on interval according to a position of the pixel is always generated every frame when a scanning direction of the panel  30  is always constant for each frame, a brightness non-uniformity phenomenon according to a position of the pixel is generated at the panel  30 . 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to method of driving liquid crystal display that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a method of driving a liquid crystal display panel that is capable of providing the panel with an entirely uniform brightness. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
     In the drawings: 
     FIG. 1 is a schematic view showing the configuration of a liquid crystal display panel and a driving apparatus thereof; 
     FIG. 2 is a timing chart representing an operation process during one frame interval in a liquid crystal display panel with no color filter; 
     FIG. 3 is a timing chart for explaining a conventional driving method for driving the liquid crystal display panel with no color filter; 
     FIG. 4 is a timing chart representing a difference between data sustaining intervals and turn-on intervals among A, B and C pixel cells shown in FIG. 1 when the liquid crystal display panel is driven as shown in FIG. 3; 
     FIG. 5 is a view for explaining the conventional driving method for driving a liquid crystal display panel with color filters; 
     FIG. 6 is a view for explaining a driving method of a liquid crystal display panel with no color filter according to a first embodiment; 
     FIG. 7 is a timing chart representing a change in a data sustaining interval and a turn-on interval for each of the A, B and C pixel cells shown in FIG. 1 when the liquid crystal display panel is driven as shown in FIG. 6; and 
     FIG. 8 is a view for explaining a driving method of a liquid crystal display panel with color filters according to a first embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIG. 6 represents a method of driving a liquid crystal display panel according to a first embodiment, which is related to a driving method of a liquid crystal display panel driven by a color sequential driving system without color filters. In the case of driving a liquid crystal display panel with no color filter, one frame is time-divided to sequentially charge each data voltage corresponding to each of red (R), green (G) and blue (B) colors. A backlight lamp having the corresponding color is turned on from any one time in a time interval when a data voltage related to any one color is charged in each pixel within the panel  20  until a time when a data voltage related to the next color begins to be charged as shown in FIG. 2 in order to improve the brightness. Also, in order to improve the color purity, all the pixels within the panel  20  are simultaneously reset prior to charging of the next data to erase the entire previous data having been maintained in each pixel. 
     In a preferred embodiment driving method as disclosed herein, a scanning direction of the panel  20  is inverted every frame in an interval when a data voltage is charged in each pixel. More specifically, a sequential scanning beginning with the first scanning line of the panel  20  and going toward the lower end of the panel  20  is made during the odd-numbered frames, whereas a sequential scanning beginning with the nth scanning line of the panel  20  and going toward the upper end of the panel  20  is made during the even-numbered frames. To this end, in a liquid crystal display device shown in FIG. 1, when the gate driver  24  applies a gate line “ON” signal to each gate line G 1  to Gn of the liquid crystal display panel  20 , an application of the gate line “ON” signal begins with the first gate line G 1  and terminates with the nth gate line Gn during the odd-numbered frames. On the other hand, an application of the gate line “ON” signal begins with the nth gate line Gn and terminates with the first gate line G 1  during the even-numbered frames. 
     As shown in FIG. 7, if the panel  20  is driven in this manner, then data sustaining intervals and turn-on intervals of the A pixels, the B pixels and the C pixels within the liquid crystal display panel  20  shown in FIG. 1 become different every frame. FIG. 7 is a timing chart illustrating a change in the data sustaining interval and the turn-on interval for each of the A, B and C pixels shown in FIG. 1 when a scanning direction of the panel  20  is inverted every frame. Referring to FIG. 7, in a frame interval when the scanning direction of the panel  20  is set to go from the upper end of the panel  20  to the lower end thereof, the data sustaining interval and the turn-on interval of the A pixels provided at the first scanning line are longest, while the data sustaining interval and the turn-on interval of the C pixels provided at the nth scanning line are shortest. On the other hand, in the next frame interval when the scanning direction of the panel  20  is set to go from the lower end of the panel  20  to the upper end thereof, the data sustaining interval and the turn-on interval of the C pixels are longest, while those of the A pixels are shortest. Accordingly, a difference in the data sustaining interval and the turn-on interval among the A, B and C pixels generated during any one frame interval is compensated in the next frame interval. As a result, the average turn-on intervals of the A, B and C pixels provided at different positions on the panel  20  are equalized by the process of inverting the scanning direction of the panel  20  for each frame, so that the brightness of the entire panel  20  can be uniform. 
     FIG. 8 represents a method of driving a liquid crystal display panel according to a second embodiment, which has been applied to a liquid crystal display panel with color filters. Referring now to FIG. 8, in a driving method of a liquid crystal panel with color filters, red (R), green (G) and blue (B) data voltage are simultaneously charged during one frame interval as mentioned above. Also, all the data stored in each pixel within the panel  30  at the earlier frames are erased in the reset interval just prior to the beginning of a new frame so as to eliminate the residual image effect. In the driving method according to the second embodiment for driving the liquid crystal display panel  30  with color filters, the scanning direction of the panel  30  is inverted every frame in similarity to the driving method according to the first embodiment. More specifically, during the odd-numbered frames, a sequential scanning beginning with the first scanning line at the upper end of the panel  30  and going toward the lower end of the panel  30  is made to simultaneously charge the red (R), green (G) and blue (B) data voltages in one frame interval. On the other hand, during the even-numbered frames, a sequential scanning beginning with the nth scanning line at the lower end of the panel  30  and going toward the upper end of the panel  30  is made to simultaneously charge each of the red (R), green (G) and blue (B) data voltages. In a frame interval when the scanning direction of the panel  30  is set to go from the upper end of the panel  30  to the lower end thereof, the data sustaining interval and the turn-on interval of the A pixels provided at the first scanning line of the liquid crystal display panel  30  in FIG. 1 are longest while the data sustaining interval and the turn-on interval of the C pixels provided at the nth scanning line are shortest. On the other hand, in the next frame interval when the scanning direction of the panel  30  is set to go from the lower end of the panel  30  into the upper end thereof, the data sustaining interval and the turn-on interval of the C pixels are longest while those of the A pixels are shortest. Accordingly, a difference in the data sustaining interval and the turn-on interval among the A, B and C pixels generated during any one frame interval is compensated for in the next frame interval. As a result, the average turn-on intervals of the A, B and C pixels provided at a different position on the panel  30  are equalized by the process of inverting the scanning direction of the panel  30  for each frame, so that the brightness of the entire panel  30  can be uniform. 
     As described above, the scanning direction is inverted every frame. Thus, a turn-on interval difference generated between the upper part and the lower part of the panel in any one frame interval is compensated in the next frame interval. Accordingly, an average turn-on interval of all the pixels is equalized, so that the brightness of the entire panel can be uniform. 
     It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention within the scope of the appended claims and their equivalents.