Patent Publication Number: US-7710385-B2

Title: Apparatus and method for driving liquid crystal display device

Description:
This application claims the benefit of Korean Patent Application No. P2006-56859, filed on Jun. 23, 2006, which is hereby incorporated by reference as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an apparatus and method for driving an LCD device. 
     2. Discussion of the Related Art 
     Liquid Crystal Display (LCD) devices have been used in many different types of electronic equipment. The LCD devices display images by adjusting the light transmittance of liquid crystal cells according to a video signal. Active matrix type LCD devices have a switching element formed for every liquid crystal cell and are well suited for displaying moving images. Thin film transistors (TFTs) are the devices primarily used as the switching element in the active matrix type LCD device. 
     However, LCD devices generally have a relatively slow response speed attributable to the inherent viscosity and elasticity of a liquid crystal, as can be seen from the following Equations 1 and 2: 
     
       
         
           
             
               
                 
                   
                     τ 
                     r 
                   
                   ∝ 
                   
                     
                       γ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         d 
                         2 
                       
                     
                     
                       Δɛ 
                       ⁢ 
                       
                          
                         
                           
                             V 
                             a 
                             2 
                           
                           - 
                           
                             V 
                             F 
                             2 
                           
                         
                          
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
           
         
       
         
         
           
             where τ r  is a rise time for response to a voltage is applied to the liquid crystal, Va is the applied voltage, V F  is a Frederick transition voltage at which liquid crystal molecules start to be inclined, d is a liquid crystal cell gap, and γ is the rotational viscosity of the liquid crystal molecules; and 
           
         
       
    
     
       
         
           
             
               
                 
                   
                     τ 
                     F 
                   
                   ∝ 
                   
                     
                       γ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         d 
                         2 
                       
                     
                     K 
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
             
           
         
       
         
         
           
             where τ F  is a falling time for returning the liquid crystal molecules to their original positions by an elastic restoration force after the voltage applied to the liquid crystal is turned off, and K is the inherent elastic modulus of the liquid crystal. 
           
         
       
    
     For a twisted nematic (TN) mode LCD device, although the response speed of the liquid crystal may vary with the physical properties and cell gap of the liquid crystal, rise times of 20 to 80 ms and the falling times of 20 to 30 ms are typical. Because these typical liquid crystal response times are longer than a moving image frame period (for example 16.67 ms for moving images according to the National Television Standards Committee (NTSC) standard), the voltage charged on the liquid crystal may not reach the desired level before the next frame data is presented, as shown in  FIG. 1 . The slow response results in motion blurring in which an afterimage is left on the LCD display panel. 
     As illustrated in  FIG. 1 , a related art LCD device may fail to display a desired color and brightness for a moving image because, when data VD is changed from one level to another level, the corresponding display brightness level BL is unable to reach the desired value due to the slow response of the LCD device. As a result, motion blurring occurs in moving images, causing degradation in contrast ratio and display quality. 
     As one method for overcoming the low response speed of the LCD device, U.S. Pat. No. 5,495,265 and PCT International Publication No. WO 99/09967 propose a method for modulating data using a look-up table (referred to hereinafter as an ‘over-driving method’). The principle of this over-driving method of the related art is illustrated in  FIG. 2 . 
     As may be appreciated with reference to  FIG. 2 , the related art over-driving method includes modulating input data VD to produce modulated data MVD, and applying the modulated data to a liquid crystal cell to obtain a desired brightness level MBL. By this method, the response speed of a liquid crystal is rapidly accelerated by increasing |V a   2 −V F   2 | in the Equation 1 for a variation in the input data from that of a previous frame period in order to obtain the desired brightness level corresponding to the luminance of the input data in one frame period. 
     Accordingly, a related art LCD device using the over-driving method is able to compensate for a slow response of a liquid crystal by modulation of a data value to reduce or eliminate motion blurring in a moving image to display a picture having the desired color and brightness. 
     In order to reduce the memory storage used in implementing over-driving, the related art over-driving method performs modulation by comparing only respective most significant bits (MSB) of a previous frame (Fn−1) and current frame (Fn) with each other, as shown in  FIG. 3 . In other words, the related art over-driving method compares respective most significant bit data (MSB) of the previous frame (Fn−1) and current frame (Fn) with each other to determine whether there is a variation between the two most significant bit data (MSB). If there is a variation between the two most significant bit data (MSB), the corresponding modulated data (MRGB) is selected from a look-up table as most significant bit data (MSB) of the current frame (Fn). 
       FIG. 4  illustrates a related art over-driving apparatus implementing the above-described over-driving method. 
     As illustrated in  FIG. 4 , the related art over-driving apparatus includes a frame memory  43  connected to a most significant bit bus line  42 , and a look-up table  44  connected in common with the output terminals of the most significant bit bus line  42  and frame memory  43 . 
     The frame memory  43  stores most significant bit data (MSB) for one frame period and supplies the stored data to the look-up table  44 . In the related art over-driving apparatus of  FIG. 4 , the most significant bit data (MSB) includes the four most significant bits of 8-bit source data (RGB). 
     The look-up table  44  compares most significant bit data (MSB) of a current frame (Fn) supplied from the most significant bit bus line  42  with most significant bit data (MSB) of a previous frame (Fn−1) inputted from the frame memory  43 , as in Table 1 below, and selects modulated data (MRGB) corresponding to the comparison result. The modulated data (MRGB) is combined with least significant bit data (LSB) from a least significant bit bus line  41  and then supplied to an LCD device. 
     Where the most significant bit data (MSB) is limited to four bits, the modulated data (MRGB) registered in the look-up table  44  of the over-driving apparatus and method is as follows: 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Current Frame 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
                 10 
                 11 
                 12 
                 13 
                 14 
                 15 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Previous 
                 0 
                 0 
                 1 
                 3 
                 4 
                 6 
                 7 
                 9 
                 10 
                 11 
                 12 
                 14 
                 15 
                 15 
                 15 
                 15 
                 15 
               
               
                 Frame 
                 1 
                 0 
                 1 
                 2 
                 4 
                 5 
                 7 
                 9 
                 10 
                 11 
                 12 
                 13 
                 14 
                 15 
                 15 
                 15 
                 15 
               
               
                   
                 2 
                 0 
                 1 
                 2 
                 3 
                 5 
                 7 
                 8 
                 9 
                 10 
                 12 
                 13 
                 14 
                 15 
                 15 
                 15 
                 15 
               
               
                   
                 3 
                 0 
                 1 
                 2 
                 3 
                 5 
                 6 
                 8 
                 9 
                 10 
                 11 
                 12 
                 14 
                 14 
                 15 
                 15 
                 15 
               
               
                   
                 4 
                 0 
                 0 
                 1 
                 2 
                 4 
                 6 
                 7 
                 9 
                 10 
                 11 
                 12 
                 13 
                 14 
                 15 
                 15 
                 15 
               
               
                   
                 5 
                 0 
                 0 
                 0 
                 2 
                 3 
                 5 
                 7 
                 8 
                 9 
                 11 
                 12 
                 13 
                 14 
                 15 
                 15 
                 15 
               
               
                   
                 6 
                 0 
                 0 
                 0 
                 1 
                 3 
                 4 
                 6 
                 8 
                 9 
                 10 
                 11 
                 13 
                 14 
                 15 
                 15 
                 15 
               
               
                   
                 7 
                 0 
                 0 
                 0 
                 1 
                 2 
                 4 
                 5 
                 7 
                 8 
                 10 
                 11 
                 12 
                 14 
                 14 
                 15 
                 15 
               
               
                   
                 8 
                 0 
                 0 
                 0 
                 1 
                 2 
                 3 
                 5 
                 6 
                 8 
                 9 
                 11 
                 12 
                 13 
                 14 
                 15 
                 15 
               
               
                   
                 9 
                 0 
                 0 
                 0 
                 1 
                 2 
                 3 
                 4 
                 6 
                 7 
                 9 
                 10 
                 12 
                 13 
                 14 
                 15 
                 15 
               
               
                   
                 10 
                 0 
                 0 
                 0 
                 0 
                 1 
                 2 
                 4 
                 5 
                 7 
                 8 
                 10 
                 11 
                 13 
                 14 
                 15 
                 15 
               
               
                   
                 11 
                 0 
                 0 
                 0 
                 0 
                 0 
                 2 
                 3 
                 5 
                 6 
                 7 
                 9 
                 11 
                 12 
                 14 
                 15 
                 15 
               
               
                   
                 12 
                 0 
                 0 
                 0 
                 0 
                 0 
                 1 
                 3 
                 4 
                 5 
                 7 
                 8 
                 10 
                 12 
                 13 
                 15 
                 15 
               
               
                   
                 13 
                 0 
                 0 
                 0 
                 0 
                 0 
                 1 
                 2 
                 3 
                 4 
                 6 
                 8 
                 10 
                 11 
                 13 
                 14 
                 15 
               
               
                   
                 14 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 1 
                 2 
                 3 
                 5 
                 7 
                 9 
                 11 
                 13 
                 14 
                 15 
               
               
                   
                 15 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 1 
                 2 
                 4 
                 6 
                 9 
                 11 
                 13 
                 14 
                 15 
               
               
                   
               
            
           
         
       
     
     In the above Table 1, the leftmost column represents the data voltage (VDn−1) of the previous frame (Fn−1) and the uppermost row represents the data voltage (VDn) of the current frame (Fn). The contents of Table 1 are look-up table information obtained by expressing four most significant bits in decimal form. 
     The related art apparatus and method for driving the LCD device is used to provide a high response speed of liquid crystal during a gray-to-gray change between previous frame and current frames. In comparison to the variation associated with a black-to-white change, the gray-to-gray change involves a relatively small voltage difference between frames, so that the liquid crystal response for each gray-to-gray change without overdriving would be slow or non-linear, resulting in poor color change in a moving image or degradation in picture quality. 
     In the above-described over-driving apparatus a digital memory, such as the look-up table  44 , is used in the generation of modulated data (MRGB) in the comparison of the data of the previous frame (Fn−1) with that of the current frame (Fn). The use of the digital memory increases chip size as well as manufacturing costs for the LCD device. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an apparatus and method for driving an LCD device, which substantially obviates one or more problems due to limitations and disadvantages of the related art. 
     An advantage of the present invention is to provide an apparatus and method for driving an LCD device wherein a response speed of liquid crystal can be increased even without using a memory, thereby preventing degradation in picture quality. 
     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. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a data driver for driving a liquid crystal display device having a plurality of data lines includes a modulator that generates modulated data from input data; and a control circuit to selects between converting the modulated data to first analog data of a driving output and converting the input data to second analog data of the driving output, and to supply the driving output to the plurality of data lines, wherein the driving output may provide a gray-to-gray response time of the liquid crystal display device substantially the same as one of a black-to-white and a white-to-black response time of the liquid crystal display device by reducing actual liquid crystal response time of the liquid crystal display device. 
     In another aspect of the present invention, a method for driving an LCD device having an image display unit including a plurality of liquid crystal cells formed in areas defined by a plurality of gate and data lines includes generating modifying data from at least one most significant bit of input data; generating modulated data by combining input data with the modifying data; selecting between converting the input data into an analog video signal and converting the modulated data into the analog video signal; and supplying the analog video signal to the data lines, wherein a gray-to-gray response time of the LCD device is made substantially the same as one of a black-to-white and a white-to-black response time of the LCD device by reducing actual liquid crystal response time of the LCD device. 
     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 waveform diagram illustrating a data-dependent brightness variation in a related art LCD device; 
         FIG. 2  is a waveform diagram illustrating a data modulation-dependent brightness variation in a related art over-driving method of an LCD device; 
         FIG. 3  is a view illustrating most significant bit data modulation in a related art over-driving apparatus of an LCD device; 
         FIG. 4  is a block diagram of the related art over-driving apparatus of an LCD device; 
         FIG. 5  is a schematic view illustrating a driving apparatus of an LCD device according to an embodiment of the present invention; 
         FIG. 6  is a block diagram schematically illustrating a data driver according to an embodiment of the present invention; 
         FIG. 7  is a block diagram schematically illustrating a data output signal generator according to an embodiment of the present invention; 
         FIG. 8  is a driving timing view of a data output signal generator shown in  FIG. 7 ; 
         FIG. 9  is a block diagram schematically illustrating a modulator according to an embodiment of the present invention; and 
         FIG. 10  is a waveform diagram illustrating an analog video signal according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     Hereinafter, an apparatus and method for driving an LCD device according to the present invention will be explained with reference to the accompanying drawings. 
       FIG. 5  is a schematic view illustrating a driving apparatus of an LCD device according to an embodiment of the present invention. 
     As shown in  FIG. 5 , the driving apparatus is provided with an image display unit  2  that includes a plurality of liquid crystal cells respectively formed in areas defined by n gate lines (GL 1  to GLn) and m data lines (DL 1  to DLm); a gate driver  4  that sequentially supplies a scan pulse to the gate lines (GL 1  to GLn); a data driver  6  that converts i-bit input data (Data) to i-bit modulated data to enable rapid response speed of liquid crystal based on at least two most significant bit data of i-bit input data, converts the i-bit modulated data or i-bit input data to an analog video signal, and supplies the analog video signal to the data lines (DL 1  to DLm) in synchronization with the scan pulse; and a timing controller  8  that arranges source data (RGB) supplied from the external, supplies the arranged source data (RGB) to the data driver  6 , and controls the gate driver  4  and the data driver  6 . 
     The image display unit  2  includes a transistor array substrate and a color filter array substrate that are bonded together; spacers to maintain a uniform cell gap between the bonded substrates; and a liquid crystal layer formed in the gap provided between the two bonded substrates and maintained by the spacers. 
     The image display unit  2  further includes a plurality of thin film transistors (TFT) formed at the liquid cells defined by n gate lines (GL 1  to GLn) and m data lines (DL 1  to DLm). The liquid crystal cells are each connected to a respective TFT. The TFTs supply the analog video signals provided from the data lines (DL 1  to DLm) to the liquid crystal cells in response to the scan pulse provided from the gate lines (GL 1  to GLn). 
     Each liquid crystal cell can be equivalently represented as a liquid crystal capacitor Clc because each liquid crystal cell is provided with a common electrode facing a pixel electrode connected to the TFT with liquid crystal between the common electrode and the pixel electrode. Each liquid crystal cell includes a storage capacitor Cst for maintaining the analog video signal charged on the liquid crystal capacitor Clc until the next analog video signal is charged thereon. 
     The timing controller  8  arranges source data (RGB) supplied from a source external to the LCD device to a form appropriate for driving the image display unit  2 , and supplies the arranged source data (RGB) to the data driver  6 . The timing controller  8  generates a data control signal (DCS) and a gate control signal (GCS) using a dot clock signal (DCLK), a data enable signal (DE), and horizontal and vertical synchronous signals (Hsync and Vsync) supplied from an external source, and applies the generated data control signal (DCS) and gate control signal (GCS) respectively to the data and gate drivers  6  and  4 , to thereby control the driving timing thereof. 
     The gate driver  4  includes a shift register that generates a scan pulse (gate high signal) in response to the gate control signal (GCS) of the timing controller  8 . The gate driver  4  sequentially supplies the gate high signal to the gate lines (GL) of the image display unit  2 , to thereby turn on the TFTs connected with each gate line (GL). 
     The data driver  6  converts i-bit input data (Data) to i-bit modulated data to provide a rapid response speed of liquid crystal based on at least two most significant bits of i-bit input data supplied from the timing controller  8  in response to the data control signal (DCS) supplied from the timing controller  8 , converts the i-bit modulated data or i-bit input data to the analog video signal, and supplies the analog video signal for one horizontal line to the data lines (DL 1  to DLm) by one horizontal period supplied with the scan pulse. The data driver  6  inverts the polarity of the analog video signal supplied to the data lines (DL) in response to a polarity control signal (POL). 
     As shown in  FIG. 6 , for the purpose of supplying the analog video signal, the data driver  6  includes a control block  110 , a gamma voltage generator  115 , a shift register  120 , a latch  130 , a modulator  140 , a digital-analog converter (DAC)  150 , and an output buffer  160 . 
     The control block  110  supplies the i-bit input data (Data) provided from the timing controller  8  to the latch  130 , and supplies the data control signal (DCS) provided from the timing controller  8  to the shift register  120 , the latch  130 , and the DAC  150 . The control block  110  supplies a first enable signal (EN 1 ) corresponding to a source start pulse (SSP) and a clock signal (CLK) corresponding to a source shift clock (SSC) to the shift register  120 , and outputs a second enable signal (EN 2 ) corresponding to a carry signal (Car) outputted from the shift register  120 . The control block  110  supplies a source output enable (SOE) to the latch  130 , and supplies the polarity control signal (POL) to the DAC  150 . 
     The control block  110  includes a data output signal generator that generates first and second data output signals (DOS 1  and DOS 2 ) to selectively convert the i-bit modulated data or the i-bit input data to an analog video signal by using the source output enable (SOE) provided from the timing controller  8 , and supplies the generated first and second data output signals (DOS 1  and DOS 2 ) to the modulator  140 . 
       FIG. 7  is a block diagram schematically illustrating a data output signal generator according to an embodiment of the present invention, and  FIG. 8  is a driving timing view of a data output signal generator shown in  FIG. 7 . Referring to  FIG. 7  in association with  FIG. 8 , the data output signal generator  112  includes a source output enable multiply unit  200 , a delay unit  210 , and first and second data output signal generating units  220  and  230 . 
     The source output enable multiply unit  200  multiplies the source output enable (SOE) by two, providing two DSOE signals for every single SOE signal, and supplies the multiplied source output enable (DSOE) to the delay unit  210  and the second data output signal generating unit  220 , respectively. 
     The delay unit  210  delays the source output enable (SOE) according to an output signal (DSOE) from the source output enable multiply unit  200 , and supplies the delayed signal to the second data output signal generating unit  220 . That is, the delay unit  210  delays the source output enable (SOE) according to a rising edge of the multiplied source output enable (DSOE). 
     The second data output signal generating unit  220  logically operates on the output signal (DSOE) of the source output enable multiply unit  200 , and the output signal (DS) of the delay unit  210  to thereby generate the second data output signal (DOS 2 ). For example, the second data output signal generating unit  220  may include a NOR-operation gate that generates the second data output signal (DOS 2 ) with a high state only when both of the input signals (DSOE and DS) to the NOR-operation gate are in the low state. 
     The first data output signal generating unit  230  logically operates on the source output enable (SOE) and the second data output signal (DOS 2 ) to thereby generate the first data output signal (DOS 1 ). For example, the first data output signal generating unit  230  may include a second NOR-operation gate that generates the first data output signal (DOS 1 ) having the high state only when both of the input signals (SOE and DOS 2 ) to the second NOR-operation gate are in the low state. 
     The data output signal generator  112  supplies the first data output signal (DOS 1 ) having the high state to the modulator  140  during an initial time period (T 1 ) of the data output of source output enable (SOE) supplied by one horizontal period ( 1 H), and supplies the second data output signal (DOS 2 ) of the high state to the modulator  140  during the remaining time period (T 2 ) excluding the initial time period (T 1 ) on the data output of source output enable (SOE). In the illustrated embodiment, the initial time period (T 1 ) is substantially equal in duration to the remaining time period (T 2 ). 
     In  FIG. 6 , the gamma voltage generator  115  generates 2 i  gamma voltages (GV), each gamma voltage distinct from one another and then supplies the generated 2 i  gamma voltages to the DAC  150 . For example, the distinct gamma voltages may be generated by dividing a gamma reference voltage (GMA) supplied from a gamma reference voltage generator by each of the i-bit gray scale numbers. 
     The shift register  120  generates a sampling signal (Sam) by sequentially shifting the first enable signal (EN 1 ) supplied from the control block  110  in response to the clock signal (CLK) of the control block  110 , and supplies the sampling signal (Sam) to the latch  130 . 
     The latch  130  latches i-bit input data (Data), provided from the control block  110 , for one horizontal line based on the sampling signal provided from the shift register  120 . The latch  130  supplies i-bit data (RData) latched for one horizontal line in response to the source output enable (SOE) to the modulator  140 . 
     As shown in  FIG. 9 , the modulator  140  includes a gray-scale analyzing unit  310 , an addition bit generating unit  320 , adding unit  330 , and first and second output units  340  and  350 . 
     The gray-scale analyzing unit  310  analyzes at least two most significant bit data (j) of i-bit latch data (RData) supplied from the latch  130 , and supplies a gray-scale analyzing signal (GAS) to the addition bit generating unit  330 . For example, the gray-scale analyzing unit  310  may generate the gray-scale analyzing signal (GAS) as shown in the following table 2, according to the two most significant bit data of i-bit latch data (RData) supplied from the latch  130 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Two most significant bits 
                 Gray-scale analyzing signal (GAS) 
               
               
                   
                   
               
             
            
               
                   
                 00 
                 0 
               
               
                   
                 01 
                 1 
               
               
                   
                 10 
                 2 
               
               
                   
                 11 
                 3 
               
               
                   
                   
               
            
           
         
       
     
     The addition bit generating unit  320  generates addition bit (ABit) of at least two bits in accordance with the gray-scale analyzing signal (GAS) supplied from the gray-scale analyzing unit  310 . For example, as shown in the following table 3, if the gray-scale analyzing signal (GAS) corresponds to ‘0’ or ‘3’, the addition bit generating unit  320  generates the addition bit (ABit) of ‘001’. If the gray-scale analyzing signal (GAS) corresponds to ‘1’ or ‘2’, the addition bit generating unit  320  generates the addition bit (ABit) of ‘010’. The following table 3 shows one example of a correspondence between analyzing signal and the generated addition bit (ABit), but the invention may be practicing using correspondences other than that illustrated in table 3. For example, the generation of the addition bit (ABit) may be varied to accommodate different resolutions and liquid crystal operating modes of the LCD panel. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Gray-scale 
                   
               
               
                   
                 analyzing signal (GAS) 
                 Addition bit (ABit) 
               
               
                   
                   
               
             
            
               
                   
                 0 
                 001 
               
               
                   
                 1 
                 010 
               
               
                   
                 2 
                 010 
               
               
                   
                 3 
                 001 
               
               
                   
                   
               
            
           
         
       
     
     The adding unit  330  adds the addition bit (ABit) of at least two bits provided from the addition bit generating unit  320  to the most significant data of i-bit latch data (RData) provided from the latch  130  to thereby generate i-bit modulated data (MData). The adding unit  330  supplies i-bit modulated data (MData) to the first output unit  340 . Accordingly, the gray scale of i-bit modulated data (MData) is larger than the gray scale of i-bit latch data (RData). 
     In response to the first data output signal (DOS 1 ) of the high state, the first output unit  340  supplies the i-bit modulated data (MData) provided from the adding unit  330  to the DAC  150 . In response to the second data output signal (DOS 2 ) of the high state, the second output unit  350  supplies the i-bit latch data (RData) provided from the latch  130  to the DAC  150 . 
     The modulator  140  converts the i-bit latch data (RData) into the i-bit modulated data (MData) for the rapid response speed of liquid crystal in accordance with at least two most significant bit data of the i-bit latch data (RData) supplied from the latch  130 . After supplying the i-bit modulated data (MData) to the DAC  150  in response to the first data output signal (DOS 1 ) of the high state, the modulator  140  supplies the i-bit latch data (RData) to the DAC  150  in response to the second data output signal (DOS 2 ) of the high state. 
     For example, if the latch  130  supplies the latch data (RData) of ‘011000’ to the modulator  140 , the modulator  140  generates the addition bit (ABit) of ‘010’ according to the gray-scale analyzing signal (GAS) of ‘1’ corresponding to the two most significant bits of ‘01’ in the latch data (RData) of ‘011000’, and adds the addition data (ABit) of ‘010’ to the three most significant bits of the latch data (RData) of ‘011000’, thereby generating modulated data (MData) of ‘101000’. 
     The modulator  140  supplies the modulated data (MData) of ‘101000’ to the DAC  150  while the first data output signal (DOS 1 ) has a the high state during the initial time period (T 1 ) in the data output period of the source output enable (SOE). The modulator  140  supplies the latch data (RData) of ‘011000’ to the DAC  150  while the second data output signal (DOS 2 ) has a the high state during the remaining time period (T 2 ) of the data output period that excludes the initial time period (T 1 ) in the data output period of the source output enable (SOE). 
     Referring again to  FIG. 6 , the DAC  150  selects positive and negative polarity gamma voltages (GV) corresponding to the i-bit modulated data (MData) supplied from the modulator  140  among the 2 i  gamma voltages (GV) having the different values supplied from the gamma voltage generator  115 , selects one of the positive and negative polarity gamma voltages (GV) based on the polarity control signal (POL) as the analog video signal (Vmdata), and supplies the analog video signal to the output buffer  160 . 
     The DAC  150  selects positive and negative polarity gamma voltages (GV) corresponding to the i-bit latch data (RData) supplied from the modulator  140  from the 2 i  gamma voltages (GV) having the different values supplied from the gamma voltage generator  115 , selects one of the positive and negative polarity gamma voltages (GV) based on the polarity control signal (POL) as the analog video signal (Vdata), and supplies the selected voltage to the output buffer  160 . 
     The output buffer  160  buffers the analog video signal (Vmdata) corresponding to the i-bit modulated data (MData) supplied from the DAC  150 , and supplies the buffered signal to the data lines (DL) during the initial time period (T 1 ) in the data output period of the source output enable (SOE). The output buffer  160  buffers the analog video data (Vdata) corresponding to the i-bit latch data (RData) supplied from the DAC  150 , and supplies the buffered signal to the data lines (DL) during the remaining time period (T 2 ) that excludes the initial time period (T 1 ) in the data output period of the source output enable (SOE). The output buffer  160  amplifies and outputs the analog video signal (Vmdata or Vdata) at a suitable level in consideration of the loading on the data lines (DL). 
     As shown in  FIG. 10 , after the data driver  6  previously drives the liquid crystal cell with the analog video signal (Vmdata) corresponding to the i-bit modulated data (MData) during the initial time period (T 1 ) in the data output of the source output enable (SOE), the data driver  6  drives the liquid crystal cell with the analog video signal (Vdata) corresponding to the original i-bit input data (Data) during the remaining time period (T 2 ) that excludes the initial time period (T 1 ) in the data output of the source output enable (SOE). 
     Therefore, in the apparatus and method for driving the LCD device according to the present invention, the gray-to-gray response time of the LCD device substantially the same as one of a black-to-white and a white-to-black response time of the LCD device by reducing actual liquid crystal response time of the LCD device. 
     As described above, the apparatus and method for driving the LCD device according to the present invention may provide the following advantages. 
     In the apparatus and method for driving the LCD device according to the present invention, the liquid crystal cell is previously driven by modulating the input data in accordance with at least two bits of the input data, and then the liquid crystal cell is driven to the desired state in accordance with the original input data. 
     Accordingly, the response speed of liquid crystal for the intermediate gray scale may be increased without using the additional memory to prevent the color change or degradation in picture quality. Further, by allowing the omission of additional memory in an apparatus and method for driving the LCD device according to the present invention the fabrication cost of the LCD device can be decreased. 
     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 provided they come within the scope of the appended claims and their equivalents.