Abstract:
A liquid crystal display with multi-line inversion which reverses polarity of applied voltages every two or more rows for preventing the deterioration of liquid crystal. An LCD includes a data driver outputting analog gray voltages selected based on the image data to the data lines of the LC panel. The data driver includes a data line bias circuit biasing the data lines to an intermediate level voltage whenever displaying the pixels in one row. Accordingly, the amount of stored charges between the pixels in the rows with polarity inversion and the pixels in the rows without polarity inversion is reduced, and consequently, the luminance difference between the pixels in the rows with the polarity inversion. The application duration of the data signals for pixels in rows with polarity inversion is also extended, such that the difference in charge storage between the two rows is reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a national phase application of PCT/KR03/00512 filed on Mar. 17, 2003, and claims priority thereto under 35 USC 371. PCT/KR03/00512, in turn, claims priority from Korean Application No. 10-2002-0044157 filed on Jul. 26, 2002, the content of which is incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a liquid crystal display, and in particular, to a liquid crystal display with multi-line inversion which reverses polarity of applied voltages every two or more rows for preventing the deterioration of liquid crystal. The present invention relates to a liquid crystal display for improving uniformity of image quality of pixels in the rows having reversed polarity. 
     (b) Description of the Related Art 
     Recently, displays used for personal computers or TVs are required to be light and slim, and flat panel displays such as liquid crystal displays (LCD) instead of cathode ray tubes are developed and put to practical use for satisfying such a requirement. 
     The LCD includes a panel including a pixel matrix pattern and another panel opposite thereto. A liquid crystal (LC) having dielectric anisotropy is interposed between the panels. An electric field is generated between the panels. Desired images are displayed by adjusting the field strength to control the transmittance of light passing through the panels. 
     The LCD receives n-bit red, green, blue (RGB) data from an external graphics source. A timing controller of the LCD data-transforms the RGB data and a data driving integrated circuit (IC) selects gray voltages corresponding to the RGB data. The selected gray voltages are applied to the pixels of the panels to perform display. The gray voltages are DC components. Long-time application of gray voltages with a single polarity to the pixels on the panels deteriorates the liquid crystal in the pixels. This kind of the deterioration of the liquid crystal can be prevented by inversion which reverses the polarity every pixel, every pixel line (or row), or every frame. The present invention relates to an LCD in multi-line inversion, which reverses the polarity of the applied voltages every two or more lines. 
       FIG. 1  shows waveforms of a data signal and a load signal LOAD in an exemplary multi-line inversion, i.e., a double-line inversion reversing the polarity every two lines. 
     The data signal shown in  FIG. 1  represents display information by its voltage level and is outputted from a data driving IC to be applied to pixels of an LCD panel. The load signal LOAD controls a timing of data signal application from the data driving IC to the LC panels. A duration between two adjacent dotted lines is called a horizontal period (abbreviated as “1H”) and the character “N” means that the data signal is applied to the N-th pixel row in the LCD panel. For example, upon receipt of a pulse of the load signal LOAD, the data driving IC of the LCD outputs the data signal to a corresponding data line on the LC panel. 
     As shown in  FIG. 1 , the polarity of the data signal applied to the pixel on the LC panel is reversed every two pixel rows with respect to a common voltage Vcom. 
     The LCD in the multi-line inversion has a problem that the pixels in the rows with reversed polarity are not sufficiently charged. In the example shown in  FIG. 1 , the amount of charges stored in a pixel in the N-th row are different that stored in a pixels in the (N+1)-th row even if both the pixels represent equal gray level. Since a predetermined transition time for the voltage of the pixel in the N-th row to reach a target level due to the polarity inversion for the N-th row is required, the stored charges in the pixel in the N-th row and the pixel in the (N+1)-th row is different. The difference in the stored charges causes the difference in the luminance, thereby deteriorating display characteristics. For example, the pixel in the N-th row experiencing the polarity inversion is brighter than the pixel in the (N+1)-th row, which has an equal gray level, for a normally white mode LCD since the amount of the stored charges in the pixels of the N-th row is smaller than that the pixel of the (N+1)-th row. As a result, an LCD with the conventional multi-line inversion has a problem of luminance difference between the pixels in the rows experiencing the polarity inversion and the pixels in the other rows. 
     SUMMARY OF THE INVENTION 
     A motivation of the present invention is to solve the problem of the conventional art under the technical background and to provide a liquid crystal display and driving method thereof with multi-line inversion capable of reducing the luminance variation of the pixels between the rows with the polarity inversion and the other rows. 
     A liquid crystal display is provided, which includes: a liquid crystal panel including a plurality of gate lines, a plurality of data lines intersecting the gate lines, and a plurality of pixels provided near the intersections of the gate lines and the data lines; a timing controller receiving image data and synchronization signals from an external graphics source, performing format conversion for the image data and generating control signals required for driving the liquid crystal panel; a voltage generator generating gray voltages and gate voltages required for the liquid crystal panel; a gate driver sequentially scanning the gate lines of the liquid crystal panel by unit of one horizontal canning period based on the gate voltages; and a data driver arranges the image data from the timing controller corresponding to the data lines of the liquid crystal panel, selecting the gray voltages corresponding to the image data, and applying the select ed voltages the pixels connected to the scanned the gate lines through the data lines, wherein the data driver reverses the polarity of the gray voltages to be applied to the data lines of the liquid crystal panel by a predetermined number of rows, and biases the data lines to a voltage with a predetermined level before outputting the gray voltages to the pixels in each scanned row. 
     The data driver of the liquid crystal display biases the data lines to an intermediate level voltage whenever displaying the pixels in one row such that the amount of stored charges between the pixels in the rows with polarity inversion and the pixels in the rows without polarity inversion is reduced, and consequently, the luminance difference between the pixels in the rows with the polarity inversion. In addition, the present invention elongates the application duration of the data signals for the pixels in the rows with the polarity inversion compared with the application duration of the data signals for the pixels in the rows without the polarity inversion such that the difference in the charge storage between the two rows is reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages of the present invention will become more apparent by describing preferred embodiments thereof in detail with reference to the accompanying drawings in which: 
         FIG. 1  shows waveforms of a data signal and a load signal LOAD in a conventional double-line inversion; 
         FIG. 2  is a block diagram of an LCD according to an embodiment of the present invention; 
         FIG. 3  is an exemplary block diagram of a data driver shown in  FIG. 2 ; and 
         FIG. 4  illustrates waveforms of signals used for the data driver shown in  FIG. 3 . 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS INDICATING PRIMARY ELEMENTS IN THE DRAWINGS 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 10: LC panel 
                 20: gate driver 
               
               
                   
                 30: data driver 
                 40: voltage generator 
               
               
                   
                 50: timing controller 
                 31: shift register 
               
               
                   
                 32: D/A converter 
                 33: latch 
               
               
                   
                 34: data line bias circuit 
               
               
                   
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the inventions are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
     Now, LCDs and driving methods thereof according to an embodiment of the present invention are described in detail with reference to the accompanying drawings. 
       FIG. 2  is a block diagram of an LCD according to an embodiment of the present invention and  FIG. 3  is an exemplary block diagram of a data driver shown in  FIG. 2 . 
     Referring to  FIG. 2 , an LCD according to an embodiment of the present invention includes an LC panel  10 , a gate driver  20 , a data driver  30 , a voltage generator  40 , and a timing controller  50 . 
     The LC panel  10  includes, although it is not shown in the figure, a plurality of gate lines, a plurality of gate lines, a plurality of data lines crossing the gate lines, and a plurality of pixels provided near intersections of the data lines and the data lines and arranged in matrix. Each pixel includes a thin film transistor (TFT) having a gate electrode connected to one of the gate lines, a source electrode connected to one of the data lines, and a drain electrode, and a pixel capacitor and a storage capacitor connected to the drain electrode of the TFT. The TFTs turns on in response to a gate signal for selecting relevant one of the gate lines from the gate driver  20 . The data driver  30  applies data voltages representing display information to the data lines. The data voltages are applied to the pixel capacitors and the storage capacitors of the pixels through the TFTs to driver the capacitors, thereby performing display operations. 
     The timing controller  50  receives RGB data (RGB DATA), synchronization signals SYNC, a data enable signal DE, and a clock signal CLK from an external graphics source (not shown). The timing controller  50  converts format of the RGB data RGB DATA suitable for a standard required for the data driver  30  and generates and outputs control signals CONT 1  and CONT 2  to be used by the gate driver  20              the data driver  30  for driving the LC panel  10  based on the synchronization signals (SYNC), the data enable signal DE and the dock signal CLK. In addition, the timing controller  50  generates a pair of load signals TP 1  and TP 2  for controlling a timing of the application of the data voltages from the data driver  30  to the pixels on the LC panel  10  and outputs the load signals TP 1  and TP 2  to the data driver  30 .
     The voltage generator  40  generates and outputs gray voltages Vgray to be applied to the data lines of the LC panel  10  and a pair of gate voltages Vgate to be applied to the gate lines of the LC panel  10 . The gray voltages Vgray have a plurality of voltage levels and are transmitted to the data driver  30 . The gate voltages Vgate includes a gate-on voltage and a gate-off voltage and are transmitted to the gate driver  20 . 
     The gate driver  20  includes a plurality of the gate driving ICs respectively taking charge of a predetermined number of the gate lines of the LC panel  10 . The gate driver  20  sequentially scans the gate lines of the LCD panel  10  by unit of a horizontal scanning period based on the control signals CONT 1  from timing controller  50  and the gate voltages Vgate from the voltage generator  40 . For example, the gate driver  20  applied the gate-on voltage to a gate line to be scanned for one horizontal scanning period and applied the gate-off voltage to the remaining gate lines. The above-described scanning is sequentially performed to all gate lines. 
     The data driver  30  includes a plurality of data driving IC respectively taking charge of a predetermined number of the data lines of the LC panel  10 . An exemplary configuration of each data driving IC is illustrated in  FIG. 3 , which will be described later in detail. The data driver  30  shifts the serially inputted RGB data (RGB DATA) supplied from the timing controller  50  to be arranged corresponding to the respective data lines, and thereafter, it selects appropriate gray voltages Vgray for the RGB data and applied the selected gray voltages the data lines of the LC panel  10  as the data signals. The data arrangement, the gray voltage selection, and the voltage application to the LC panel are repeated to all row of the LC panel. 
     In the meantime, the present invention suggests two solutions for insufficient charging of the pixels in the rows experiencing the polarity inversion when the gray voltages are applied to the data lines. 
     A solution biases the data signals for a pixel row of the LCD panel  10  to a voltage with a predetermined level when the data signals for the pixel row are outputted after the data signals for a previous pixel row is outputted from the data driver  30 . This solution equalizes the charges in all the data lines of the LC panel  10  and is called charge sharing. That is, after the pixels in a row experiencing the polarity inversion are supplied with the data signals, the voltages of all the data lines on the LC panel are converted into an intermediates level and then the data lines are supplied with the data signals when the pixels in a row without the polarity inversion are supplied with the data signals. Accordingly, the voltage of each pixel without the polarity inversion requires a transition time for the intermediate level to a target level, and hence the difference in charging voltage levels between the pixels in the rows with the polarity inversion and the pixels in the rows without the polarity inversion can be reduced. Although the present invention exemplifies a ground level as the predetermined intermediate level, the scope of the present invention is not limited hereto. It is apparent that an ordinary skill in the art differentiates the intermediates levels for different polarity, for example, a positive intermediate voltage and a negative intermediate voltage are used for biasing the data lines. 
     The other solution differentiates the application durations of the data signals for the rows with the polarity inversion and for the rows without the polarity inversion. In detail, the application duration of the data signals for the pixels in the rows with the polarity inversion are elongated since the pixels in the rows with the polarity inversion are less charged than the pixels in the rows without the polarity inversion. It is obtained by controlling the timing of the load signal used in the data driver  30 . In detail, the pulse intervals of the load signal are set so that the application duration of the data signals for the pixels in the rows with the polarity inversion (referred to as a first application duration hereinafter) are longer than the application duration of the data signals for the pixels in the rows without the polarity inversion (referred to as a first application duration hereinafter). 
     An LCD according to an embodiment of the present invention is described in more detail with reference to  FIGS. 3 and 4 . 
     A block diagram shown in  FIG. 3  shows an exemplary detailed configuration of a data driving IC of the data driver  30  shown in  FIG. 2 . 
     Each data driving IC of the data driver  30  includes a shift register  31 , a digital-to-analog (D/A) converter  32 , a latch  33 , and the data line bias circuit  34 . Each data driving IC is assigned to a predetermined number of the data lines of the LC panel  10 . 
     The shift register  31  shifts in bits the RGB data from the timing controller  50  and arranges the RGB data corresponding to the assigned data lines of the data driving IC. The D/A converter  32  digital-to-analog converts the RGB data by selecting analog gray voltages Vgray in accordance with the digital RGB data aligned with the data lines. The latch  33  outputs the gray voltages selected for the respective data lines to the LC panel  10  in response to the load signals TP 1  and TP 2 . Referring to  FIG. 4 , upon the generation of pulses of the load signals TP 1  and TP 2 , a row in the LC panel  10  to be displayed are selected by a gate signal and the data signals are outputted from the data driving IC to the LC panel  10  such that the pixels in the selected row are written with the data signals. The timing controller  50  controls the pulse generation timing of the load signals TP 1  and TP 2  such that a duration T 1  for the application of the data signals to the pixels in the rows with the polarity inversion is longer than a duration T 2  for the application of the data signals to the pixels in the rows without the polarity inversion. The data line bias circuit  34  biases the data lines assigned to the data driving IC into a ground potential upon every generation of the load signals TP 1  and TP 2 . In an example shown in  FIG. 4 , after the pixels in a row with the polarity inversion are supplied with positive data signals, and then the data signals are temporarily dropped down to an intermediate level and then start rising when the target is changed into the next row. On the contrary, the negative data signals are temporarily increased to the intermediate level and then fall again. In this way, the pixels in the rows with the polarity inversion have increased charging time while the pixels in the rows without the polarity inversion have decreased charging time. Accordingly, the difference in the charging time between the rows with the polarity inversion and the pixels in the rows without the polarity inversion is reduced to improve the luminance difference in the conventional art. 
     As described above, although the embodiments of the present invention illustrate the double-line inversion, the scope of the present invention includes any multi-line inversion. 
     As described above, a data driver of an LCD in multi-line inversion biases the data lines into an intermediate level whenever the pixels of every line are subject to display such that the difference in the charge storage between the pixels in the rows with the polarity inversion and the pixels in the rows without the polarity inversion, and accordingly, the luminance difference between the pixels in the rows with the polarity inversion. In addition, the LCD according to an embodiment of the present invention elongates the application duration of the data signals for the pixels in the rows with the polarity inversion compared with that for the pixels in the rows without the polarity inversion such that the difference in the charge storages between the two lines is reduced. 
     Although preferred embodiments of the present invention have been described in detail hereinabove, it should be dearly understood that many variations and/or modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.