Patent Publication Number: US-6335719-B1

Title: Method and apparatus for driving liquid crystal panel in dot inversion

Description:
This application claims the benefit of Korean Patent Application No. P98-27035, filed on Jul. 4, 1998, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a technique for driving a liquid crystal panel in a liquid crystal display device, and more particularly to a liquid crystal panel driving method for driving a liquid crystal panel in a dot inversion system and an apparatus thereof. 
     2. Description of the Related Art 
     Generally, a liquid crystal display device controls the light transmissivity of liquid crystal cells in a liquid crystal panel to display a picture corresponding to a video signal. Such a liquid crystal display device uses three driving methods, such as a frame inversion system, a line inversion system and a dot inversion system, so as to drive the liquid crystal cells in the liquid crystal panel. 
     In a liquid crystal panel driving method of the frame inversion system, polarities of data signals applied to the liquid crystal cells are inverted whenever the frame is changed. In a liquid crystal panel driving method of the line inversion system, polarities of data signals applied to the liquid crystal cells are inverted in accordance with lines on the liquid crystal panel, that is, gate lines. In a liquid crystal panel driving method of the dot inversion system, data signals having polarities contrary to the adjacent liquid crystal cells on the gate lines and to the adjacent liquid crystal cells on the data lines are applied to each liquid crystal cell in the liquid crystal panel, and the polarities of data signals applied to all liquid crystal cells in the liquid crystal panel are inverted every frame. In other words, in the dot inversion system, data signals are applied to the liquid crystal cells in the liquid crystal panel in such a manner that the positive (+) polarity and the negative (−) polarity appear alternately, as shown in FIG. 1, as the data signals go from the liquid crystal cell at the left upper end into the liquid crystal cells at the right side and into the liquid crystal cells at the lower side when a video signal in the odd-numbered frame is displayed; while data signals are applied to the liquid crystal cells in the liquid crystal panel in such a manner that the positive (+) polarity and the negative (−) polarity appear alternately, as shown in FIG. 2, as the data signals go from the liquid crystal cell at the left upper end into the liquid crystal cells at the right side and into the liquid crystal cells at the lower side when a video signal in the even-numbered frame is displayed. 
     The dot inversion system in the above three liquid crystal panel driving methods allows data signals having polarities contrary to data signals applied to the liquid crystal cells adjacent in the vertical and horizontal direction to be applied to certain liquid crystal cells, and thus provides a better quality of picture compared with the frame and line inversion systems. Due to this advantage, a liquid crystal driving method of the dot inversion system has been mainly used in the industry. 
     However, a specific pattern, for example, a check pattern, a subpixel pattern or a windows shut-down mode pattern, may be displayed when the liquid crystal panel driving method of the dot inversion system is used. In this case, a frame inversion effect appears in the liquid crystal panel driving method of dot inversion. Depending on the images being displayed, a flicker may be generated and the picture quality is deteriorated in a picture displayed by the liquid crystal panel driving method of the dot inversion system. For example, when a potential difference between data signals applied to liquid crystal cells indicated with the oblique lines and the remaining cells in the liquid crystal cells in the liquid crystal panel as shown in FIG. 3 is large, only liquid crystal cells indicated with the oblique lines are assumed to be driven in a pattern having the polarities inverted every frame. In other words, only liquid crystal cells indicated with the oblique lines in FIG. 3 seem to be driven with the frame inversion system. Due to this, in the liquid crystal panel driving method of the dot inversion system, a flicker noise emerging on the screen is dictated by a picture pattern. As a result, the picture quality displayed by the liquid crystal panel driving method of the dot inversion system is inconsistent. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a liquid crystal panel driving method and apparatus that is adaptive for stably keeping picture quality independently of a picture pattern as well as improving picture quality. 
     In order to achieve these and other objects of the invention, a liquid crystal panel driving method according to one aspect of the present invention includes the steps of dividing a liquid crystal panel into a plurality of blocks; responding liquid crystal cells included in each block to data signals having polarities contrary to the adjacent liquid crystal cells; responding to each of the liquid crystal cells included in each block are data signals having polarities contrary to data signals applied to the liquid crystal cells included in the adjacent blocks; and responding in all liquid crystal cells in the liquid crystal panel are data signals having opposite polarities every predetermined interval. 
     A liquid crystal panel driving apparatus according to another aspect of the present invention includes signal coupling means for applying data signals to the liquid crystal panel in such a manner that the liquid crystal cells are driven by one line unit; and polarity control means for controlling the data signals applied to the liquid crystal panel in such a manner that the liquid crystal panel is divided into a plurality of blocks and that each block responds to data signals having polarities contrary to the data signals applied to the adjacent blocks. 
     A liquid crystal display device according to still another aspect of the present invention includes a liquid crystal panel having picture elements and transistors connected to each of the picture elements, said picture elements being positioned at intersections in which a plurality of gate lines cross a plurality of source lines; a gate driver, connected to the plurality of gate lines, for sequentially applying a scanning signal to the gate lines; and a source driver for supplying data voltages to the plurality of source lines in such a manner that the liquid crystal panel is divided into a plurality of blocks, that the polarities of data voltages applied to the picture elements adjacent to each other in the horizontal and vertical direction within each block are contrary to each other, and that a polarity arrangement of the data voltages applied between the blocks adjacent in the horizontal and vertical direction is contrary to each other. 
     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. 
     These and other objects of the invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings, in which: 
     FIGS. 1 to  3  illustrate polarity patterns of data signals applied to liquid crystal cells in the liquid crystal panel by a liquid crystal panel driving method of a dot inversion system; 
     FIGS. 4 and 5 illustrate polarity patterns of data signals applied to liquid crystal cells in the liquid crystal panel by a liquid crystal panel driving method according to an embodiment of the present invention; 
     FIG. 6 is a schematic block diagram showing the configuration of a liquid crystal panel driving apparatus according to an embodiment of the present invention; and 
     FIG. 7 is an operational timing diagram in each part of the liquid crystal panel driving apparatus shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 4 and 5 are views for explaining a liquid crystal panel driving method according to an embodiment of the present invention. In FIGS. 4 and 5, a liquid crystal panel  10  having liquid crystal cells arranged in a matrix pattern is divided into a number of blocks. Each block preferably includes the same number of liquid crystal cells. The liquid crystal cells included in each block are driven with data signals having polarities contrary to the liquid crystal cells adjacent in the up, down, left and right directions. 
     The liquid crystal cells included in each block are driven with data signals having opposite polarities to data signals applied to the liquid crystal cells included in the blocks adjacent in the up, down, left and right directions. Accordingly, the liquid crystal cells positioned at the edges of each block are coupled with data signals having the same polarities as the liquid crystal cells positioned at the edges of the blocks located diagonally therefrom. For example, a data signal applied to the first liquid crystal cell in the first block  12 A in FIG. 4 has the same polarity as a data signal applied to the first liquid crystal cell in the fourth block  12 D, but has the opposite polarity compared to the first liquid cell in the second and third blocks  12 B and  12 C. The first liquid crystal cell in the second block  12 B has the same polarity as a data signal applied to the first liquid crystal cell in the third block  12 C but has the opposite polarity compared to the first liquid cell in the first and fourth blocks  12 A and  12 D. In addition, the second liquid crystal cell positioned at the second line in the first block  12 A receives a data signal having the polarity (e.g., positive polarity (+)) contrary to those (e.g., negative polarity (−)) of data signals applied to four liquid crystal cells adjacent in the up, down, left and right directions. Data signals applied to the liquid crystal cells included in the first to fourth blocks  12 A to  12 D in FIG. 4 have the inverted polarities as shown in FIG. 5 as the frame is changed. As a result, in the liquid crystal panel driving method according to the present invention, the polarities of data signals applied to the liquid crystal cells in the liquid crystal panel are inverted every frame, every block and every dot. 
     As described above, in the liquid crystal panel driving method according to the present invention, the polarities of data signals are inverted every frame, every block and every dot so that the liquid crystal panel is not driven by the frame inversion system. Accordingly, even when a specific pattern, such as a check pattern, subpixel pattern and windows shut-down mode pattern, is displayed, a flicker noise is reduced and, further, picture quality can be stably maintained independently of a pattern of a picture. 
     Referring now to FIG. 6, there is shown a liquid crystal panel driving apparatus according to an embodiment of the present invention. The liquid crystal panel driving apparatus includes gate driving integrated circuits (ICs)  20  for divisionally driving n gate lines GL 1  to GLn on a liquid crystal panel  10 , and j data driving ICs  22  for divisionally driving m data lines DL 1  to DLm on the liquid crystal panel  10 . Each data driving IC  22  drives k data lines. The liquid crystal panel  10  is provided with a number of liquid crystal cells and thin film transistors (TFTs) for switching data signals applied to each liquid crystal cell. The number of liquid crystal cells is installed at the intersections in which the data lines DL 1  to DLm cross the gate lines GL 1  to GLn, and the TFTs also are positioned at the intersections. The gate driving ICs  20  apply a gate drive pulse to n gate lines GL 1  to GLn on the liquid crystal panel  10  sequentially to drive the n gate lines GL 1  to GLn sequentially. Then, the TFTs in the liquid crystal panel  10  are sequentially driven for one gate line to apply data signals to liquid crystal cells for one gate line sequentially. Each of the j data driving ICs  22  applies k data signals to the k data lines DL 1  to DLk whenever the gate drive pulse is generated. The k data signals generated at each data driving IC  22  have polarities alternated in accordance with an arrangement sequence of the adjacent data lines. Also, the k data signals generated at each data driving IC  22  have polarities that change alternately as the frame progresses. 
     The liquid crystal driving apparatus further includes a counter  24 , a first toggle flip-flop  26  and a second toggle flip-flop  28  for commonly receiving a vertical synchronizing signal Vsync. The counter  24  is initialized in a blanking interval of the vertical synchronizing signal Vsync as shown in FIG. 7, and performs a count operation with a horizontal synchronizing signal Hsync applied to its clock terminal CLK in a vertical scanning interval of the vertical synchronizing signal Vsync. At the time of a count operation, with the aid of the horizontal synchronizing signal Hsync to generate a carry signal Cs having a waveform in which the horizontal synchronizing signal Hsync is frequency-divided into a certain integer, the counter  24  repeatedly counts until a certain integer is reached (e.g., α=4). In a similar manner, the first toggle flip-flop  26  is initialized in the blanking interval of the vertical synchronizing signal Vsync while performing a toggle operation in the scanning interval of the vertical synchronizing signal Vsync. During the scanning interval of the vertical synchronizing signal Vsync, the first toggle flip-flop  26  inverts a logic state of an output signal whenever the horizontal synchronizing signal Hsync is inputted to its clock terminal CLK. Accordingly, the first toggle flip-flop  26  generates a two-frequency-divided horizontal synchronizing signal DHsync, as shown in FIG. 7, inverted every horizontal synchronous period during the vertical scanning interval. The two-frequency-divided horizontal synchronizing signal DHsync generated at the first toggle flip-flop  26  is applied to a first exclusive OR gate  30 . 
     The second toggle flip-flop  28  generates a two-frequency-divided vertical synchronizing signal DVsync, as shown in FIG. 7, having a logic state inverted every period of the vertical synchronizing signal Vsync. The two-frequency-divided vertical synchronizing signal DVsync generated at the second toggle flip-flop  28  is applied to a second exclusive OR gate  32 . 
     The first exclusive OR gate  30  selectively inverts the two-frequency-divided horizontal synchronizing signal DHsync from the second toggle flip-flop  26  in accordance with a logic state of the carry signal Cs from the counter  24 . In other words, the first exclusive OR gate  30  inverts the two-frequency-divided horizontal synchronizing signal DHsync only during a time interval when the carry signal Cs remains at a high logic state. Accordingly, the first exclusive OR gate  30  generates a pulse signal PS maintaining a high logic state or a low logic state in each interval corresponding to a certain time at the horizontal synchronous interval. 
     In a similar manner, the second exclusive OR gate  32  selectively inverts the pulse signal PS from the first exclusive OR gate  30  in accordance with a logic value of the two-frequency-divided vertical synchronizing signal DVsync from the second toggle flip-flop  28 . In other words, the second exclusive OR gate  32  inverts the pulse signal PS only during a time interval when the two-frequency-divided vertical synchronizing signal DVsync remains at a high logic state. Accordingly, the second exclusive OR gate  32  generates an inversion control signal ICS, as shown in FIG. 7, in which the pulse signal PS is inverted at every vertical synchronous interval. 
     The inversion control signal ICS is commonly applied to the even-numbered data driving ICs in the k data driving ICs  22 , and simultaneously applied to an inverter  34 . The inverter  34  inverts the inversion control signal ICS from the second exclusive OR gate  32  as shown in FIG. 7, and applies the inverted inversion control signal /ICS to the odd-numbered data driving ICs  22  in the j data driving ICs  22 . As a result, the counter  24 , the first and second toggle flip-flops  26  and  28 , the first and second exclusive OR gates  30  and  32  and the inverter  34  serve as inversion control means that generate the inversion control signal ICS and the inverted inversion control signal /ICS making use of the vertical and horizontal synchronizing signals Vsync and Hsync. 
     Depending on a logic state of the inversion control signal ICS, the even-numbered data driving ICs  22  receiving the inversion control signal ICS from the second exclusive OR gate  32  have the polarities inverted alternately along the vertical axis (i.e., the data lines), and have the same polarities as the previous gate line every certain number of gate lines along the vertical axis (i.e., the gate lines) and have alternate polarities at the remaining gate lines. Also, the even-numbered data driving ICs  22  generate k data signals at the k data lines DL k+1  to DL 2k , DL 3k+1  to DL 4k , . . . , DL (j−1)k+1  to DL m  in such a manner that the polarities are inverted every frame interval along the time axis. In other words, each one of the even-numbered data driving ICs  22  inverts a polarity pattern of the data signals in such a manner to follow the blocks, in which the liquid crystal panel  10  is divided into a certain number of gate line units, along the vertical axis and to be alternated on a time basis. In a similar manner, depending on a logic state of the inverted inversion control signal /ICS, each of the odd-numbered data driving ICs  22  receiving the inverted inversion control signal /ICS from the inverter  34  has the polarities inverted alternately along the horizontal axis (i.e., the data lines), and has the same polarities as the previous gate line every certain number of gate lines along the vertical axis (i.e., the gate lines) and has alternate polarities at the remaining gate lines. Also, the odd-numbered data driving ICs  22  apply data signals to the k data lines DL k+1  to DL 2k , DL 3k+1  to DL 4k , . . . , DL (j−1)k+1  to DL m  in such a manner as to have the polarities inverted every frame interval along the time axis and to have the polarities contrary to the data lines DL driven with the adjacent even-numbered data driving ICs  22 . In other words, each of the odd-numbered data driving ICs  22  inverts a polarity pattern of the data signals in such a manner as to follow the blocks, in which the liquid crystal panel  10  is divided into a certain number of gate line units, along the vertical axis and to be alternated on a time basis, and, at the same time, in such a manner as to be opposite to the polarity patterns of data signals generated at the adjacent even-numbered data driving ICs  22 . As a result, by the inversion control signal ICS and the inverted inversion control signal /ICS, the j data driving ICs  22  divide the liquid crystal panel  10  into blocks including liquid crystal cells corresponding to a product of a certain integer α by k, and drive the blocks in the dot inversion system in such a manner as to have a polarity pattern contrary to the adjacent blocks. 
     Accordingly, in the liquid crystal panel driving apparatus according to an embodiment of the present invention, a phenomenon of driving the liquid crystal panel in the frame inversion system does not appear and a flicker noise is sufficiently reduced or not generated, even when a picture having a specific pattern, such as a check pattern, subpixel pattern and windows shutdown mode pattern, is displayed. As a result, the liquid crystal panel driving apparatus, according to an embodiment of the present invention, is capable of stably maintaining the quality of a picture displayed on the liquid crystal panel independently of a pattern of a picture. 
     Moreover, the liquid crystal panel driving apparatus includes a second inverter  36  for receiving a reset signal RST. The second inverter  36  inverts the reset signal RST as shown in FIG. 7, and commonly applies the inverted reset signal to the counter  24  and the reset terminals of the first and second toggle flip-flops  26  and  28 . The counter  24  and the first and second toggle flip-flops  26  and  28  responding to the inverted reset signal from the second inverter  26  are operated during a time interval when the reset signal RST remains at a high logic state. Also, the counter  24  and the first and second toggle flip-flops  26  and  28  initialize their outputs during a time interval when the reset signal RST remains at a low logic state. 
     The discrete components described in the embodiments of the present invention may be substituted with a programmable processor and a program code to operate the same. Alternatively, an application specific integrated circuit (ASIC) may also be used. 
     As described above, in the liquid crystal panel driving method and apparatus according to the present invention, a liquid crystal panel is driven in a different polarity pattern of data signals for each block in the dot inversion system, so that a phenomenon of driving the liquid crystal panel in the frame inversion system does not appear even though a picture having a specific pattern, such as a check pattern, subpixel pattern and windows shut-down mode pattern, etc., is displayed. Accordingly, the liquid crystal panel driving method and apparatus according to the present invention is capable of preventing the generation of a flicker noise independently of a pattern of a picture as well as providing a good quality of picture stably. 
     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 covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.