Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a liquid crystal display, and more particularly to a liquid crystal display and a driving method wherein an application sequence of a data is changed so as to improve a picture quality.  
           [0003]    2. Description of the Related Art  
           [0004]    Generally, a liquid crystal display (LCD) uses a pixel matrix arranged in each intersection between gate lines and data lines to thereby display a picture corresponding to video signals. Each pixel consists of a liquid crystal cell controlling a transmitted light quantity in accordance with a video signal, and a thin film transistor (TFT) for switching the video signal to be applied from the data line to the liquid crystal cell.  
           [0005]    The LCD is provided with gate and data driving integrated circuits, hereinafter referred to as “D-IC&#39;s”, for driving the gate lines and the data lines. In this case, a demultiplexor (DEMUX) is connected between the data D-IC so as to simplify a circuit configuration of the LCD.  
           [0006]    The DEMUX reduces the required number of data D-IC by connecting any one output line of the data D-IC to a plurality of data lines. For instance, when the number of data lines is n and the number of data lines connected to one DEMUX, the output line number k of data D-IC becomes ‘n/m’. In other words, the required number of the data D-IC is reduced to ‘1/m’. The DEMUX is formed on the same substrate as the pixels upon manufacturing of the LCD.  
           [0007]    The data D-IC outputs a data m times for one horizontal period 1H. The data outputted from the data D-IC is applied, via the DEMUX, to the data lines. The DEMUX receives control signals corresponding to the number of data lines allowable to itself so as to sequentially connect a plurality of data lines to one output line of the data D-IC.  
           [0008]    Hereinafter, a conventional LCD driving method will be described with reference to FIG. 1 and FIG. 2.  
           [0009]    Referring to FIG. 1, there is shown a conventional LCD device including first to kth demultiplexors DEMUX 1  to DEMUXk connected to n data lines DL 1  to DLn between a data D-IC  12  and a liquid crystal display panel  10 . The data D-IC includes k output lines corresponding to the first to kth demultiplexors DEMUX 1  to DEMUXk. Each of the k demultiplexors DEMUX 1  to DEMUXk is connected to four data lines DL 1  to DLn. To this end, each of the demultiplexors DEMUX 1  to DEMUXk includes four MOS transistors MN 1  to MN 4 .  
           [0010]    The four MOS transistors MN 1  to MN 4  receive first to fourth control signals CS 1  to CS 4  from the exterior thereof. The first to fourth control signals CS 1  to CS 4  are sequentially enabled every horizontal synchronous interval as shown in FIG. 2.  
           [0011]    The conventional LCD device further includes a gate D-IC  14  for driving m gate lines GL 1  to GLm on the liquid crystal display panel  10 . The gate D-IC  14  sequentially applies a gate scanning signal GSS to m gate lines GL 1  to GLm for one frame.  
           [0012]    The gate scanning signal GSS maintains a high state for one horizontal synchronous interval at a certain gate line GL as shown in FIG. 2. When the gate line GL maintains a high state, the data D-IC  12  sequentially applies four data to each of the demultiplexors DEMUX 1  to DEMUXK. At this time, each of the demultiplexors DEMUX 1  to DEMUXk responds to the first to fourth control signals CS 1  to CS 4  supplies four data inputted from the output line of the data D-IC  12  to four data lines.  
           [0013]    More specifically, the first demultiplexor DEMUX 1  receives four data R 1 , G 1 , B 1  and R 2  from the data D-IC  12  as shown in FIG. 2 and sequentially delivers them to the first and fourth data lines DL 1  to DL 4 . Similarly, the second demultiplexor DEMUX 2  receives four data G 2 , B 2 , R 3  and G 3  from the data D-IC  12  and sequentially delivers the same to the fifth to eighth data lines DL 5  to DL 8 .  
           [0014]    Such a conventional LCD driving method causes a phenomenon in which a data is distorted due to a coupling capacitor Cs between the data lines. More specifically, as shown in FIG. 3, the fifth data line DL 5  receives a green data signal G 2  from the first MOS transistor MN 1  of the second demultiplexor DEMUX 2  in a time interval when the first control signal CS 1  has a high state. On the other hand, the fifth data line DL 5  becomes a floating state when the first control signal CS 1  has a low state. Then, the sixth data line DL 6  receives a blue data signal B 2  from the second MOS transistor MN 2  of the second demultiplexor DEMUX 2  in a time interval when the second control signal CS 2  has a high state. At this time, a green data signal G 2  charged in the fifth data line DL 5  is changed due to the coupling capacitor Cc between the fifth and sixth data lines DL 5  and DL 6 .  
           [0015]    After the blue data signal B 2  was charged in the second data line DL 6 , the seventh data line DL 7  receives a red data signal R 3  from the third MOS transistor MN 3  of the second demultiplexor DEMUX 2  in a time interval when the third control signal CS 3  has a high state. At this time, the blue data signal B 2  charged in the sixth data line DL 6  is changed due to the coupling capacitor Cc between the sixth and seventh data lines DL 6  and DL 7 .  
           [0016]    After a red data signal R 3  was charged in the seventh data line DL 7 , the eighth data line DL 8  receives the red data signal G 3  from the fourth MOS transistor MN 4  of the second demultiplexor DEMUX 2  in a time interval when the fourth control signal CS 4  has a high state. At this time, a red data signal R 3  charged in the seventh data line DL 7  is changed due to the coupling capacitor Cc between the seventh and eighth data lines DL 7  and DL 8 .  
           [0017]    Further, the green data signal G 2  charged in a pixel on the fifth data line DL 7  is changed when the red data signal R 2  is applied to the fourth data line D 4 . In other words, a data signal received from the first MOS transistor MN 1  is changed twice by the coupling capacitor while data signals received from the second and third MOS transistors MN 2  and MN 3  are changed once by the coupling capacitor. On the other hand, a data signal received from the fourth MOS transistor MN 4  is not changed. As a result, a conversion frequency of the data signal is differentiated, so that a stripe-shaped distortion is generated at a picture displayed on the liquid crystal display panel  10 .  
           [0018]    In the conventional LCD driving method, a different leakage current is generated depending on an application sequence of data signals applied to the data lines DL 1  to DLn. Such a different leakage current from the data lines DL 1  to DLn is caused by a fact that a holding interval is different in accordance with an application sequence of the data signals. In other words, as shown in FIG. 4, a data having the same voltage value is sampled in a state changed into a different absolute voltage value from each pixel. More specifically, the first data line DL 1  receives the first red data signal R 1  from the first MOS transistor MN 1  of the first demultiplexor DEMUX 1  in a time interval when the first control signal CS 1  has a high state. The first data line DL 1  maintains a voltage charged until the falling edge of the gate scanning signal GSS. In other words, a voltage charged in the first data line DL 1  is leaked for a long time from the falling edge of the first control signal CS 1  until the falling edge of the gate scanning signal GSS. As a result, the first data line DL 1  applies a voltage signal lower than the initially received red data signal R 1  to the pixel. In other words, a voltage applied to the first data line DL 1  is leaked by a voltage ΔV1.  
           [0019]    The fourth data line DL 4  receives the second red data signal R 2  from the fourth MOS transistor MN 4  of the first demultiplexor DEMUX 1  in a time interval when the fourth control signal CS 4  has a high state. The fourth data line DL 4  maintains the charged voltage until the falling edge of the gate scanning signal GSS. The voltage charged in the fourth data line DL 4  is leaked for a short time from the falling edge of the fourth control signal CS 4  until the falling edge of the gate scanning signal GSS. As a result, a voltage applied to the fourth data line DL 4  is leaked by a voltage ΔV2. Accordingly, the voltage applied to the fourth data line DL 4  becomes higher than the voltage applied to the first data line DL 1 . For this reason, a picture displayed on the liquid crystal display panel  10  is more distorted to thereby deteriorate a picture quality.  
           [0020]    As a result, in the conventional LCD driving method, the same data is supplied to each pixel at a different voltage level to thereby distort a picture displayed on the liquid crystal display panel. Also, since a color data supplied to each data line is changed by the coupling capacitor, a picture distortion phenomenon becomes serious.  
         SUMMARY OF THE INVENTION  
         [0021]    Accordingly, it is an object of the present invention to provide a liquid crystal display and a driving method thereof that allow each data line to have an averagely uniform change frequency of a data signal and a uniform leakage current.  
           [0022]    In order to achieve these and other objects of the invention, a method of driving a liquid crystal display according to one aspect of the present invention includes the steps of supplying a data to a desired number of data lines on a basis of first sequence in a first horizontal period; and supplying said data to the desired number of data lines on a basis of second sequence in a second horizontal period following the first horizontal period.  
           [0023]    A method of driving a liquid crystal display according to another aspect of the present invention includes the steps of supplying a data to a desired number of data lines on a basis of first sequence in the (4i+1)th and (4i+4)th frames (wherein i is an integer); and supplying said data to the desired number of data lines on a basis of second sequence in the (4i+2)th and (4i+3)th frames.  
           [0024]    A liquid crystal display device according to still another aspect of the present invention includes switching devices a desired number of which are included in each demultiplexor and each of which is connected to one data line; and control means for controlling the switching devices such that a data is sequentially distributed to the desired number of data lines in a first horizontal period and such that said data is reverse-sequentially distributed to the desired number of data lines in a second horizontal period following the first horizontal period.  
           [0025]    A liquid crystal display device according to still another aspect of the present invention includes switching devices a desired number of which are included in each demultiplexor and each of which is connected to one data line; and control means for controlling the switching devices such that a data is sequentially distributed to the desired number of data lines on a basis of first sequence in the (4i+1)th and (4i+4)th frames (wherein i is an integer) and said data is reverse-sequentially distributed to the desired number of data lines on a basis of second sequence in the (4i+2)th and (4i+3)th frames. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    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:  
         [0027]    [0027]FIG. 1 is a schematic block circuit diagram showing a configuration of a liquid crystal display driven by a conventional liquid crystal display driving method;  
         [0028]    [0028]FIG. 2 is a waveform diagram of control signals applied to the demultiplexors shown in FIG. 1;  
         [0029]    [0029]FIG. 3 is a block circuit diagram of the coupling capacitor formed between data lines as shown in FIG. 1;  
         [0030]    [0030]FIG. 4 is a waveform diagram for showing a leakage current difference generated from the data lines on the liquid crystal display panel when the data lines are sequentially driven;  
         [0031]    [0031]FIG. 5 is a waveform diagram for showing a method of driving a liquid crystal display according to a first embodiment of the present invention;  
         [0032]    [0032]FIG. 6A and FIG. 6B are waveform diagrams for representing a leakage current generated from the data line upon driving according to the driving method shown in FIG. 5; and  
         [0033]    [0033]FIG. 7A and FIG. 7B are waveform diagrams for showing a method of driving a liquid crystal display according to a first embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0034]    [0034]FIG. 5 shows a driving method for a liquid crystal display according to a first embodiment of the present invention. Such a driving method will be described in conjunction with the liquid crystal display shown in FIG. 1.  
         [0035]    Referring to FIG. 5, in the driving method according to the first embodiment of the present invention, a sequence of control signals Cs is converted every horizontal period. In other words, when a gate scanning signal GSS is applied to a second gate line GL 2 , demultiplexors DEMUX 1  to DEMUXk  
         [0036]    reverse-sequentially supply four data to data lines DL 1  to DLn. To the contrary, when the gate scanning signal GSS is applied to a third gate line GL 3 , the demultiplexors DEMUX 1  to DEMUXk sequentially supply four data to the data lines DL 1  to DLn. In other words, in the first embodiment of the present invention, if a data is sequentially sent in a certain horizontal period, then the data is reverse-sequentially sent in the next horizontal period. To this end, a sequence of the control signals CS 1  to CS 4  inputted to each of the demultiplexors DEMUX 1  to DEMUXk is converted every horizontal period.  
         [0037]    More specifically, when the gate scanning signal GSS is inputted to the second gate line GL 2 , the first to fourth control signals CS 1  to CS 4  are reverse-sequentially applied to the demultiplexors DEMUX 1  to DEMUXk. First, the fourth MOS transistor MN 4  is turned on in a time interval when the fourth control signal CS 4  has a high state, to thereby apply a green data signal G 3  from the data D-IC  12  to the eighth data line DL 8 . Thereafter, the third demultiplexor DEMUX 3  is supplied with the third control signal CS 3 . The third MOS transistor MN 3  is turned on in a time interval when the third control signal CS 3  has a high state, to thereby a red data signal R 3  from the D-IC  12  to the seventh data line DL 7 . At this time, the green data signal G 3  charged in the eighth data line DL 8  by the coupling capacitor between the seventh and eighth data lines DL 8  and DL 7  is changed by the red data signal R 3  applied to the seventh data line DL 7 .  
         [0038]    After the red data signal R 3  was applied to the seventh data line DL 7 , the second demultiplexor DEMUX 2  is supplied with the second control signal CS 2 . In a time interval when the second control signal CS 2  has a high state, the second MOS transistor MN 2  is turned on, to thereby apply a blue data signal B 2  from the data D-IC to the sixth data line DL 6 . At this time, the red data signal R 3  charged in the seventh data line DL 7  by the coupling capacitor Cc between the seventh and sixth data lines DL 7  and DL 6  is changed by the blue data signal B 2  applied to the sixth data line DL 6 .  
         [0039]    After the blue data signal B 2  was applied to the sixth data line DL 6 , the first demultiplexor DEMUX 1  is supplied with the first control signal CS 1 . In a time interval when the first control signal CS 1  has a high state, the first MOS control signal is turned on, to thereby apply a green data signal from the data D-IC  12  to the fifth data line DL 5 . At this time, the blue data signal B 2  charged in the sixth data line DL 6  by the coupling capacitor Cc between the sixth and fifth data lines DL 6  and DL 5  is changed by the green data signal G 2  applied to the fifth data line DL 5 .  
         [0040]    Similarly, the green data signal G 3  charged in the eighth data line DL 8  also is changed by a blue data signal B 3  applied to the ninth data line DL 9 . In other words, when the control signals CS 1  to CS 4  are reverse-sequentially applied, the data signal applied to the eighth data line DL 8  is changed twice while the data signals applied to the seventh and sixth data lines DL 7  and DL 6  are changed once. On the other hand, the data signal applied to the fifth data line DL 5  is not changed.  
         [0041]    After the gate scanning signal GSS was inputted to the second gate line GL 2 , the gate scanning signal GSS is applied to the third gate line GL 3 . When the gate scanning signal GSS is inputted to the third gate line GL 3 , the first to fourth control signals CS 1  to CS 4  are sequentially applied to the demultiplexors DEMUX 1  to DEMUXk. If the control signals CS 1  to CS 4  are sequentially applied, then the data signal applied to the fifth data line DL 5  is changed twice as mentioned above. The data signals applied to the sixth and seventh data lines DL 6  and DL 7  are changed once. On the other hand, the data signal applied to the eighth data line DL 8  is not changed.  
         [0042]    In the driving method according to the first embodiment of the present invention, although a change frequency of the data supplied to the data lines DL 1  to DLn is not uniform in each horizontal period, the data is averaged on a time basis. Accordingly, the liquid crystal display according to the first embodiment of the present invention can obtain a visually uniform picture.  
         [0043]    [0043]FIG. 6A shows a leakage current generated at the data line when a control signal is sequentially applied.  
         [0044]    Referring to FIG. 6A, the first data line DL 1  receives a first red data signal R 1  from the first MOS transistor MN 1  of the first demultiplexor DEMUX 1  in a time interval when the first control signal CS 1  has a high state. The first data line DL 1  maintains the charged voltage until the falling edge of the gate scanning signal GSS. In other words, a voltage charged in the first data line DL 1  is leaked for a long time from the falling edge of the first control signal CS 1  until the falling edge of the gate scanning signal GSS. As a result, the first data line DL 1  applies a voltage signal lower than the initially received red data signal R 1  to the pixel. In other words, a voltage applied to the first data line DL 1  is leaked by a voltage ΔV1.  
         [0045]    The fourth data line DL 4  receives the second red data signal R 2  from the fourth MOS transistor MN 4  of the first demultiplexor DEMUX 1  in a time interval when the fourth control signal CS 4  has a high state. The fourth data line DL 4  maintains the charged voltage until the falling edge of the gate scanning signal GSS. The voltage charged in the fourth data line DL 4  is leaked for a short time from the falling edge of the fourth control signal CS 4  until the falling edge of the gate scanning signal GSS. As a result, a voltage applied to the fourth data line DL 4  is leaked by a voltage ΔV2.  
         [0046]    However, as shown in FIG. 6B, when the control signal is reverse-sequentially applied, the first data line DL 1  is leaked by ΔV2 while the fourth data line DL 4  is leaked by ΔV1. Accordingly, the present liquid crystal display has an averagely uniform leakage voltage, so that it can obtain a visually uniform picture.  
         [0047]    [0047]FIG. 7A and FIG. 7B are waveform diagrams for showing a driving method according to a second embodiment of the present invention.  
         [0048]    Referring to FIG. 7A and FIG. 7B, in the driving method according to the second embodiment of the present invention, a sequence of the control signals CS 1  to CS 4  is changed every frame. In other words, the control signals CS 1  to CS 4  are sequentially applied in the first and fourth frames while being reverse-sequentially applied in the third and fourth frames. Accordingly, a change frequency of the data signal applied to the data lines DL 1  to DLn and a leakage current becomes uniform averagely, thereby obtaining a visually uniform picture. The setting of a conversion frequency of the control signals CS 1  to CS 4  to four frames in the second embodiment of the present invention aims to prevent a generation of a direct current offset voltage from each pixel. In other words, when the liquid crystal display panel  10  is driven in a dot inversion, each data line DL 1  to DLn is alternately supplied with a data signal having positive and negative voltage levels.  
         [0049]    More specifically, if a positive red data signal +R is applied to the first data line DL 1  in a certain horizontal period, then a negative green data signal −G is applied to the second data line DL 2 . In the next horizontal period, a negative red data signal −R is applied to the first data line DL 1  while a positive green data signal +G is applied to the second data line DL 2 . Accordingly, when the control signals CS 1  to CS 4  are applied in a four-frame period like the second embodiment of the present invention, a sum of direct current voltages becomes zero. Thus, a direct current offset voltage is not generated.  
         [0050]    Alternatively, in the second embodiment of the present invention, the control signals CS 1  to CS 4  may be reverse-sequentially applied in the first and fourth frames while being sequentially applied in the third and fourth frames.  
         [0051]    As described above, according to the present invention, the control signals are sequentially and reverse-sequentially applied to the demultiplexors alternately every frame or every horizontal period. Accordingly, a voltage level of the data line and a conversion frequency of the data signal become averagely uniform, to thereby obtain a uniform picture.  
         [0052]    Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.

Technology Category: 3