Patent Publication Number: US-9842529-B2

Title: Display device having improved pixel pre-charging capability and driving method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to, and the benefit of, Korean Patent Application No. 10-2013-0092673 filed in the Korean Intellectual Property Office on Aug. 5, 2013, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     (a) Technical Field 
     Embodiments of the present invention relate generally to flat panel displays. More specifically, embodiments of the present invention relate to a display device and a driving method thereof. 
     (b) Description of the Related Art 
     A general display device includes two display panels including a pixel electrode and a common electrode, and a liquid crystal layer having dielectric anisotropy interposed therebetween. The pixel electrodes are arranged in a matrix form and connected to switching elements, such as thin film transistors (TFTs), to sequentially receive data voltages for every row. The common electrodes are formed over the entire surface of the display panel to receive common voltages. The pixel electrode, the common electrode, and the liquid crystal display therebetween form a liquid crystal capacitor when viewed from a circuit, and the liquid crystal capacitor becomes a basic unit which forms a pixel together with the switching element connected thereto. 
     In such a display device, an electric field is generated in the liquid crystal layer by applying voltages to the two electrodes, and transmittance of light passing through the liquid crystal layer is controlled by controlling an intensity of the electric field, thereby producing a desired image. In this case, in order to prevent a degradation phenomenon generated by applying the electric field in one direction to the liquid crystal layer for a long time, a voltage polarity of a data signal for the common voltage is inverted for each frame, for each row, or for each pixel. 
     Liquid crystal molecules may be aligned to some degree in advance by performing pre-charging for a predetermined time before a normal data voltage is applied to the liquid crystal capacitor. In this case, even though normal data voltages having the same magnitude are applied to a plurality of capacitors existing in the same pixel row, when pre-charging amounts are different from each other, a difference in luminance occurs due to different charging amounts charged in the liquid crystal capacitor, and as a result, an image quality defect in which a flicker is recognized occurs. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY 
     Embodiments of the present invention have been made in an effort to provide a display device and a driving method thereof having advantages of preventing an image quality defect due to an insufficient charging time of a liquid crystal capacitor. Further, embodiments of the present invention have been made in an effort to provide a display device and a driving method thereof having advantages of improving image quality of the display device occurring by pre-charging. Further, embodiments of the present invention have been made in an effort to provide a display device and a driving method thereof having advantages of reducing power consumption of the display device. 
     An exemplary embodiment of the present invention provides a display device, including: a current stage pixel, a previous stage pixel, and a before-previous stage pixel each including a liquid crystal layer; a data line connected to the before-previous stage pixel, the previous stage pixel, and the current stage pixel to transfer data voltages; a first gate line, a second gate line, and a third gate line connected to the before-previous stage pixel, the previous stage pixel, and the current stage pixel, respectively, so as to transfer gate-on voltages; a gate driver configured to apply the gate-on voltages to the first gate line, the second gate line, and the third gate line, respectively; a data driver configured to apply the data voltages to the data line; and a signal controller configured to control operations of the gate driver and the data driver. The gate-on voltage applied to the third gate line connected to the current stage pixel is configured to be applied during any one or more of a first pre-charge period, a second pre-charge period, and a main-charge period; the data voltages are configured to be applied, in order, to the before-previous stage pixel, the previous stage pixel, and the current stage pixel; and the signal controller is configured to control the gate driver to selectively apply the gate-on voltage to the gate line connected to the current stage pixel during at least one of the first pre-charge period while the before-previous stage pixel is being charged and the second pre-charge period while the previous stage pixel is charged, so as to at least partially pre-charge the current stage pixel. 
     In order to apply a first gray to the current stage pixel, the signal controller may be further configured to control the gate driver to apply the gate-on voltage to the gate line connected to the current stage pixel during the first pre-charge period, while a second gray is applied to the previous stage pixel. 
     The signal controller may be further configured to control the gate driver to apply a gate-off voltage to the gate line connected to the current stage pixel during the second pre-charge period. 
     The first gray may be a maximum gray, and the second gray may be a minimum gray. 
     In order to apply a first gray to the current stage pixel, the signal controller may be further configured to control the gate driver to apply the gate-on voltage to the gate line connected to the current stage pixel during the second pre-charge period, while the first gray is applied to the previous stage pixel. 
     The signal controller may be further configured to control the gate driver to apply the gate-on voltage to the gate line connected to the current stage pixel during the first pre-charge period, while the second gray is applied to the before-previous stage pixel. 
     The signal controller may be further configured to control the gate driver to apply a gate-off voltage to the gate line connected to the current stage pixel during the first pre-charge period, while the first gray is applied to the before-previous stage pixel. 
     In order to apply a second gray to the current stage pixel, 
     the signal controller may be further configured to control the gate driver so that the gate-on voltage is not applied to the gate line connected to the current stage pixel during either the second pre-charge period or the first pre-charge period. 
     The signal controller may be further configured to control the gate driver so that the gate-on voltage is not applied to the gate line connected to the current stage pixel while the first gray is applied to either the before-previous stage pixel or the previous stage pixel, during either the second pre-charge period or the first pre-charge period. 
     The signal controller may be further configured to control the gate driver to apply the gate-off voltage to the gate line connected to the current stage pixel during the second pre-charge period and the first pre-charge period. 
     Another exemplary embodiment of the present invention provides a method of driving a display device, including: sequentially applying data voltages to a before-previous stage pixel, a previous stage pixel, and a current stage pixel; for charging of the current stage pixel, determining, by a signal controller, whether a sufficient time to reach a target voltage exists; and controlling the gate driver, by the signal controller, to selectively apply a gate-on voltage to a gate line connected to the current stage pixel during a first pre-charge period during which the before-previous stage pixel is charged, or during a second pre-charge period during which the previous stage pixel is charged, based on the determining. 
     According to exemplary embodiments of the present invention, when a current pixel is charged up to a target voltage, it is possible to reduce unnecessary power consumption by selectively performing pre-charging 0 to 2 times, and to improve display quality by charging a voltage applied to the pixel up to the target voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a display device according to an exemplary embodiment of the present invention. 
         FIG. 2  is an equivalent circuit diagram for one pixel of the display device according to the exemplary embodiment of the present invention. 
         FIG. 3  is a diagram illustrating pixels in a matrix form according to the exemplary embodiment of the present invention. 
         FIG. 4  is a diagram illustrating a gate signal according to the exemplary embodiment of the present invention. 
         FIG. 5  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a first exemplary embodiment of the present invention. 
         FIG. 6  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a second exemplary embodiment of the present invention. 
         FIG. 7  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a third exemplary embodiment of the present invention. 
         FIG. 8  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a fourth exemplary embodiment of the present invention. 
         FIG. 9  is a diagram illustrating respective pixels in a matrix form for a display panel according to another exemplary embodiment of the present invention. 
         FIG. 10  is a diagram illustrating respective pixels in a matrix form for a display panel according to another exemplary embodiment of the present invention. 
         FIG. 11  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a first Comparative Example. 
         FIG. 12  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a second Comparative Example. 
         FIG. 13  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a third Comparative Example. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. The drawings are not to scale. 
     In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals designate like elements throughout the specification. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
     Hereinafter, a display device according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a block diagram of a display device according to an exemplary embodiment of the present invention, and  FIG. 2  is an equivalent circuit diagram for one pixel of the display device according to the exemplary embodiment of the present invention. 
     As illustrated in  FIGS. 1 and 2 , the display device according to the exemplary embodiment of the present invention includes a liquid crystal panel  300 , a gate driver  400  and a data driver  500  connected to the liquid crystal panel  300 , and a signal controller  600  controlling the liquid crystal panel  300 , the gate driver  400 , and the data driver  500 . 
     The display panel  300  includes a plurality of signal lines G 1 -G( 2   n ) and D 1 -Dm, and a plurality of pixels PX connected to the signal lines and arranged substantially in a matrix form, when viewed from an equivalent circuit. Meanwhile, the display panel  300  includes a lower panel  100  and an upper panel  200  facing each other, and a liquid crystal layer 3 interposed therebetween. 
     The signal lines G 1 -G( 2   n ) and D 1 -Dm include a plurality of gate lines G 1 -G( 2   n ) transferring gate signals (referred to as “scanning signals”), and a plurality of data lines D 1 -Dm transferring data voltages. The gate lines G 1 -G( 2   n ) extend substantially in a row direction and are substantially parallel to each other, and the data lines D 1 -Dm extend substantially in a column direction and are substantially parallel to each other. 
     In more detail, one of the data lines D 1 -Dm may be disposed for every two pixel columns. That is, one data line is present for each pair of pixel columns. The number of data lines may be a half of the number of pixel columns. 
     Further, a pair of gate lines G 1  and G 2 , G 3  and G 4 , . . . are positioned above and below each pixel row. Also, pixels R, G, and B in one pixel row are connected to any one of the pair of gate lines G 1  and G 2 , G 3  and G 4 , . . . above and below its row. That is, the number of gate lines may be twice the number of pixel rows. 
     A layout of the pixels R, G, and B of the display panel  300  according to the exemplary embodiment of the present invention will be described. In the display panel  300 , a column of blue pixels B expressing blue, a column of red pixels R expressing red, and a column of green pixels G expressing green are alternately arranged and disposed in a row direction. In this example, the display panel  300  may have columns of blue pixels B, columns of red pixels R, and columns of green pixels G sequentially and repetitively disposed, but embodiments of the invention are not necessarily limited thereto. Even though the order of the pixel columns may be changed, the present invention may still be applied. In addition, three primary colored pixels may be arranged in any manner, and other three primary colors other than blue, red, and green may also be used. Meanwhile, in order to implement color display, each pixel PX uniquely displays one of the primary colors (spatial division), or alternately displays primary colors with time (temporal division) so that a desired color may be recognized by the spatial and temporal sum of the primary colors. 
     A first pixel and a second pixel of a second row are connected to a first data line D 1 . In this case, the first pixel in the second row is connected to an upper gate line, and the second pixel in the second row is connected to a lower gate line. 
     The first pixel and second pixel of a first row are connected to a second data line D 2 . In this case, the first pixel in the first row is connected to an upper gate line, and the second pixel in the first row is connected to a lower gate line. Further, a third pixel and a fourth pixel in the second row are connected to the second data line D 2 . The third pixel in the second row is connected to the upper gate line, and the fourth pixel in the second row is connected to the lower gate line. 
     A third pixel and a fourth pixel in the first row are connected to a third data line D 3 . In this case, the third pixel in the first row is connected to an upper gate line, and the fourth pixel in the first row is connected to a lower gate line. Further, a fifth pixel and a sixth pixel in the second row are connected to the third data line D 3 . In this case, the fifth pixel in the second row is connected to a lower gate line, and the sixth pixel in the second row is connected to an upper gate line. 
     A fifth pixel and a sixth pixel in the first row are connected to a fourth data line D 4 . In this case, the fifth pixel in the first row is connected to a lower gate line, and the sixth pixel in the first row is connected to an upper gate line. 
     According to this exemplary embodiment of the present invention, in each pixel structure of the display panel  300 , the pixel structure described above is repeated. That is, when respective pixels R, G, and B of the display panel  300  are represented in a matrix form, the pixels R, G, and B have a structure in which pixel units (hereinafter, referred to as inversion driving units) of 6×2 size are repeated. 
     According to the exemplary embodiment of the present invention, each pixel has a first polarity or a second polarity. Further, the polarity of each pixel may be inverted by frame unit. According to the exemplary embodiment of the present invention, the first polarity and the second polarity have opposite polarities. That is, when the first polarity is a positive (+) polarity, the second polarity is a negative (−) polarity, and further, when the first polarity is a negative (−) polarity, the second polarity is a positive (+) polarity. 
     Each of the pixels R, G, and B includes a pixel electrode  191  receiving a data signal through a switching element Q, such as a thin film transistor, connected to the gate lines G 1 -G( 2   n ) and the data lines D 1 -Dm, and a common electrode  270  facing the pixel electrode  191  and receiving a common voltage Vcom. 
     The liquid crystal capacitor Clc includes the pixel electrode  191  of the lower panel  100  and the common electrode  270  of the upper panel  200  as two terminals, and the liquid crystal layer 3 between the two electrodes  191  and  270  serves as a dielectric material. The pixel electrode  191  is connected to the switching element Q, and the common electrode  270  is formed on substantially the entire surface of the upper panel  200  to receive a common voltage Vcom. Unlike  FIG. 2 , the common electrode  270  can be provided on the lower panel  100 , and in this case, at least one of the two electrodes  191  and  270  may be formed in a linear shape or a rod shape. 
     A storage capacitor Cst providing a storage capacitance for the liquid crystal capacitor Clc is formed when a separate signal line (not illustrated) provided on the lower panel  100  and the pixel electrode  191  overlap each other with an insulator therebetween, and a predetermined voltage such as a common voltage Vcom is applied to the separate signal line. However, the storage capacitor Cst may also be formed when the pixel electrode  191  overlaps the gate line of a different pixel. 
       FIG. 2  illustrates that each pixel PX may include a color filter  230  expressing one of the primary colors and positioned in a region of the upper panel  200  corresponding to the pixel electrode  191 , as an example of spatial division. That is, three pixels PX expressing red, green, and blue form one dot expressing one color. The color filter  230  may be disposed above or below the pixel electrode  191  of the lower panel  100 . 
     At least a pair of polarizers can polarize light, and be attached onto an outer surface of the display panel  300 . 
     Referring back to  FIG. 1 , the gate driver  400  is connected to the gate lines G 1 -G( 2   n ) of the display panel  300  to apply gate signals, configured by a combination of a gate-on voltage Von turning on the switching elements and a gate-off voltage Voff turning off the switching elements, to the gate lines G 1 -G( 2   n ). 
     In more detail, the gate driver  400  receives a control signal from the signal controller  600  to apply the gate-on voltage Von to the gate lines G 1 -G( 2   n ) during a main-charging period. Further, the gate driver  400  receives a control signal from the signal controller  600  to selectively apply the gate-on voltage Von or the gate-off voltage Voff to the gate lines G 1 -G( 2   n ) during a first or second pre-charging period. A process will be described below in detail, in which the gate driver  400  receives a control signal from the signal controller  600  to selectively apply the gate-on voltage Von or the gate-off voltage Voff to the gate lines G 1 -G( 2   n ) during the first or second pre-charging period. 
     The gate driver  400  applies the gate-on voltage Von to the gate lines G 1 -G( 2   n ) according to a gate control signal CONT 1  from the signal controller  600  to turn on the switching elements Q connected to the gate lines G 1 -G( 2   n ). Then, the data voltages applied to the data lines D 1 -Dm are applied to the corresponding pixels PX through the turned-on switching elements Q. 
     A difference between the data voltage applied to the pixel PX and the common voltage Vcom is represented as a charging voltage of the liquid crystal capacitor Clc, that is, a pixel voltage. The arrangement of the liquid crystal molecules varies according to a magnitude of the pixel voltage, and as a result, polarization of light passing through the liquid crystal layer 3 is changed. The change in the polarization is represented as a change in transmittance of light by a polarizer attached onto the display panel  300 , and as a result, the pixel PX displays luminance represented by a gray of an image signal DAT. 
     The process is repeated for each horizontal period (referred to as “1H”, and being the same as one period of a horizontal synchronizing signal Hsync and a data enable signal DE), and as a result, the gate-on voltages Von are sequentially applied to all the gate lines G 1 -G( 2   n ), and the data voltages are applied to all the pixels PX, thereby displaying an image for one frame. 
     Meanwhile, when voltages are applied to both ends of the liquid crystal capacitor Clc, the liquid crystal molecules of the liquid crystal layer 3 are rearranged to a stable state corresponding to the voltage, but since a response speed of the liquid crystal molecules is slow, some time is required until the liquid crystal molecules reach this stable state. When the voltage applied to the liquid crystal capacitor Clc is maintained at a particular level, the liquid crystal molecules continuously move until the liquid crystal molecules reach the stable state, and light transmittance varies during that time. When the liquid crystal molecules reach the stable state and then do not move any more, the light transmittance further becomes uniform. 
     As such, when the pixel voltage in the stable state is referred to as a target voltage and light transmittance is referred to as a target light transmittance, the target voltage and the target light transmittance have one to one correspondence. Further, when reaching the target voltage, a charging amount of the liquid crystal capacitor Clc of the pixel is referred to as a target charging amount. 
     The data driver  500  is connected to the data lines D 1 -Dm of the display panel  300  to apply a data voltage to the data lines D 1 -Dm. 
     The signal controller  600  receives input image signals R, G and B, and an input control signal controlling display of the input image signals R, G and B, from an external graphic controller (not illustrated). The input image signals R, G and B store luminance information for each pixel PX, and luminance has a predetermined number of grays, for example, 1024 (=2^10), 256 (=2^8), or 64 (=2^6) grays. The input control signal includes a vertical synchronizing signal Vsync, a horizontal synchronizing signal Hsync, a main clock MCLK, a data enable signal DE, and the like. 
     The signal controller  600  generates and properly processes input image signals R, G, and B and an input image signal DAT based on an input control signal, and generates a gate control signal CONT 1 , a data control signal CONT 2 , and the like. Thereafter, the signal controller  600  transmits the gate control signal CONT 1  to the gate driver  400 , and transmits the data control signal CONT 2  and the processed image signal DAT to the data driver  500 . 
     The gate control signal CONT 1  includes a scanning start signal STV instructing scanning start, and at least one clock signal controlling an output period of the gate-on voltage Von. The gate control signal CONT 1  may further include an output enable signal OE limiting a duration time of the gate-on voltage Von. 
     The data control signal CONT 2  includes a horizontal synchronization start signal STH notifying transmission start of the output image signals DAT for one set of pixels PX, a load signal LOAD instructing a data voltage to be applied to the display panel  300 , and a data clock signal HCLK. The data control signal CONT 2  may further include an inversion signal RVS inverting a voltage polarity of the data voltage for the common voltage Vcom (hereinafter, referred to as a “polarity of the data signal” which is shorthand for a “voltage polarity of the data signal for the common voltage”). 
     According to the data control signal CONT 2  from the signal controller  600 , the data driver  500  receives the digital output image signal DAT for one set of pixels PX and selects a gray voltage corresponding to each digital output image signal DAT, converts the gray voltage into an analog data voltage, and then applies the converted analog data voltage to the corresponding data lines D 1 -Dm. 
     Hereinafter, a selective pre-charging according to the exemplary embodiment of the present invention will be described. The gate driver  400  according to the exemplary embodiment of the present invention receives control signals from the signal controller  600  to apply the gate-on voltage Von to the gate line. When the gate-on voltage Von is applied to the gate line, the data voltage is applied to the pixel connected to the gate line to which the gate-on voltage Von is applied, and the liquid crystal capacitor Clc of the pixel is charged according to the applied data voltage. 
     According to exemplary embodiments of the present invention, there are three periods in which the liquid crystal capacitor Clc of the pixel is charged according to the gate-on voltage. The three periods according to the exemplary embodiment of the present invention include a first pre-charge period Pre1 in which the liquid crystal capacitor Clc of a before-last (or before-previous) pixel is charged, a second pre-charge period Pre2 in which the liquid crystal capacitor Clc of a previous pixel is charged, and a main-charge period Main in which the liquid crystal capacitor Clc of a current pixel is charged. 
     Further, the signal controller  600  may control the gate driver  400  to apply the gate-on voltage Von or the gate-off voltage Voff to the gate line connected to the current pixel during the first pre-charge period, the second pre-charge period, or the main-charge period. 
     The signal controller  600  according to the exemplary embodiment of the present invention determines whether a time required for the liquid crystal capacitor Clc of each pixel to reach a target charging amount exists, based on input image signals R, G, and B. That is, the signal controller  600  according to the exemplary embodiment of the present invention determines whether the first pre-charge or the second pre-charge is required for the charging amount of the liquid crystal capacitor Clc of each pixel to reach a target charging amount. This determination is made according to a relationship with the data voltage applied to the data line connected to each pixel based on input image signals R, G, and B. More specifically, the signal controller  600  selects a pre-charging method from among various pre-charging methods, according to the pattern of the data voltage applied to the data line. Since the signal controller  600  makes this determination simply based on the specific pattern used, data throughput is reduced. 
     According to the exemplary embodiment of the present invention, the gate driver  400  receives a control signal from the signal controller  600  to apply the gate-on voltage Von or the gate-off voltage Voff to the pixel to which the gate line is connected during the first pre-charge period or the second pre-charge period. Hereinafter, it will be described that the gate-on voltage Von has a high level, and the gate-off voltage Voff has a low level. However, the present invention is not limited thereto, and may also be applied to a gate-on voltage Von having a low level and a gate-off voltage Voff having a high level. 
     The driving devices  400 ,  500 , and  600  may be integrated into the display panel  300  together with the signal lines G 1 -G( 2   n ) and D 1 -Dm, and the switching elements Q. Alternatively, the driving devices  400 ,  500 , and  600  may be directly installed on the display panel  300  in at least one IC chip form, installed on a flexible printed circuit film (not illustrated) to be attached to the display panel  300  in a tape carrier package (TCP) form, or installed on a separate printed circuit board (not illustrated). Further, the driving devices  400 ,  500 , and  600  may be integrated into a single chip, or at least one of the driving devices or at least one circuit element configuring the driving devices may be positioned outside of the single chip. 
     Next, an operating method of the present invention will be described with reference to  FIGS. 3 to 8 . 
       FIG. 3  is a diagram illustrating pixels in a matrix form according to the exemplary embodiment of the present invention. 
     In  FIG. 3 , a blue pixel B and a red pixel R may be first grays, and a green pixel G may be a second gray. Further, in this specification, the first gray may be a maximum gray, and the second gray may be a minimum gray. This means that a change of the data voltage is large from the maximum gray to the minimum gray, and a gray value equivalent to the maximum gray and a gray value equivalent to the minimum gray may have similar characteristics. 
     In step S 1  of  FIG. 3 , two adjacent pixels in the same row are connected to the same data line. In step S 2 , the two adjacent pixels in the same row are connected to different data lines, respectively. Further, in step S 2 , previous pixels from these two pixels in the same row may be pixels having the second gray, respectively. 
     In step S 1 , thereafter, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the main-charge period, the liquid crystal capacitor Clc of the current pixel is charged up to the target charging amount. As a result, during the main-charge period, the gray of the current pixel reaches the target gray. 
     During the main-charge period, since the charging amount of the liquid crystal capacitor Clc of the current pixel starts from a sufficiently high voltage, that is, the target voltage or less, the charging amount may reach up to the sufficient target charging amount. The reason is that in step S 1 , during the second pre-charge period, the gate-on voltage Von is applied to the gate line connected to the current pixel, and further, the gray of the previous pixel of the current pixel is the first gray. As a result, since during the second pre-charge period, the liquid crystal capacitor Clc of the current pixel is charged to the target amount or less, thereafter, during the main-charge period, sufficient time exists for the capacitor Clc to be charged up to the target charging amount. 
     In step S 2 , when the gate-on voltage Von is applied to the gate line connected to the current pixel during the second pre-charge period, the liquid crystal capacitor Clc of the current pixel is charged to 5 V or less, that is, the common voltage or less. 
     Thereafter, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the main-charge period, the liquid crystal capacitor Clc of the current pixel is charged. However, in step S 2 , since the charging amount of the liquid crystal capacitor Clc of the current pixel during the main-charge period starts from a very low voltage, only one pre-charging does not reach up to the target charging amount. Accordingly, the gate driver  400  according to the present invention may perform pre-charging by applying the gate-on voltage Von to the gate line connected to the current pixel even during the first pre-charge period. According to the present invention, if the charging amount of the liquid crystal capacitor Clc of the current pixel charged by the pre-charging corresponding to the gate-on voltage Von of the first pre-charge period is sufficient so that the liquid crystal capacitor Clc of the current pixel is charged to its target charging amount during the main-charge period, the gate driver  400  need not perform pre-charging during the second pre-charge period. 
     Further, referring to  FIG. 3 , the liquid crystal capacitor Clc of each pixel according to the present invention is charged in an order connected to the data line. 
     For example, the liquid crystal capacitor Clc of the first pixel of the first row (connected to D 2 ), the liquid crystal capacitor Clc of the second pixel of the first row, the liquid crystal capacitor Clc of the third pixel of the second row, and the liquid crystal capacitor Clc of the fourth pixel of the second row are charged in sequence. 
       FIG. 4  is a diagram illustrating a gate signal according to the exemplary embodiment of the present invention. 
     According to the exemplary embodiment of the present invention, as illustrated in  FIG. 4 , respective gate signals having different forms may be applied to the respective gate lines G 1 -G( 2   n ) in different situations. 
     According to the exemplary embodiment of the present invention, the gate driver  400  may apply the gate-off voltage Voff to the gate lines G 1 -G( 2   n ) during the first pre-charge period in the case where the pre-charging for the first pre-charge period is not required. 
     The signal controller  600  determines a target charging amount for the liquid crystal capacitor Clc of the current pixel, and calculates forms of the gate signals to be applied to the respective gate lines G 1 -G( 2   n ) in response to the target charging amount. Further, the signal controller  600  controls the gate driver  400  so as to output the calculated gate signal. 
     Hereinafter are examples of the application of gate signals having different forms. 
       FIG. 5  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a first exemplary embodiment of the present invention. 
     The signal controller  600  applies the gate signal for the gate line connected to the current pixel of the gate driver  400 , so that the current pixel (also referred to as a current stage pixel) achieves a target gray during the main-charge period. For the pixel of  FIG. 5 , when the second gray is applied to the previous stage pixel before the first gray applied during the main-charge period and pre-charging is performed by the second gray, the current stage pixel may not reach the target voltage, and as a result, the first gray voltage of a before-last pixel (also referred to as a before-last stage pixel) of the current pixel is used as the pre-charging voltage. 
     Hereinafter, the target gray means the gray of the current pixel when the amount of charge of the liquid crystal capacitor Clc of the current pixel is at the target charging amount. 
     There are three periods in which the liquid crystal capacitor Clc of the pixel is charged according to the gate-on voltage, in the exemplary embodiment. The three periods according to the exemplary embodiment of the present invention include a first pre-charge period Pre in which the liquid crystal capacitor Clc of a before-last pixel is charged, a second pre-charge period Pre in which the liquid crystal capacitor Clc of a previous pixel is charged, and a main-charge period Main in which the liquid crystal capacitor Clc of a current pixel is charged. 
     According to  FIG. 5 , when the target gray of the current pixel (also referred to as a current stage pixel) is the first gray, and the gray of the before-last pixel (referred to as a before-last stage pixel) during the first pre-charge period and the gray of the previous pixel (referred to as a current stage pixel) during the second pre-charge period are the second gray, the signal controller  600  controls the gate driver  400  to apply the gate-on voltage Von during the first pre-charge period and to apply the gate-off voltage Voff during the second pre-charge period. When describing  FIG. 3  as an example, the fourth pixel in the first row may be a before-last stage pixel, the sixth pixel in the second row may be the previous stage pixel, and the fifth pixel in the second row may be the current stage pixel. 
     According to  FIG. 5 , when the gate-on voltage Von during the first pre-charge period is applied to the gate line connected to the current pixel, the liquid crystal capacitor Clc of the current pixel is charged with 5 V or more, that is, a common voltage or more. Hereinafter, an example in which the common voltage is 5 V is described, but the present invention is not limited thereto. The present invention may be applied to common voltages having any magnitudes. 
     Thereafter, when the gate-off voltage Voff is applied to the gate line connected to the current pixel during the second pre-charge period, the charging voltage of the liquid crystal capacitor Clc of the current pixel is substantially maintained. 
     According to the first exemplary embodiment of the present invention, the gate driver  400  applies the gate-on voltage Von of the second pre-charge period to the gate line connected to the current pixel to charge the liquid crystal capacitor Clc of the current pixel to 10 V or less, that is, the target charging amount or less. 
     Thereafter, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the main-charge period, the liquid crystal capacitor Clc of the current pixel is charged up to the target charging amount. As a result, during the main-charge period, the gray of the current pixel reaches the target gray. 
     According to the first exemplary embodiment of the present invention, when the target gray of the current pixel is the first gray, the gate driver  400  may apply the gate-on voltage Von to the gate line connected to the current pixel during the first pre-charge period. 
       FIG. 6  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a second exemplary embodiment of the present invention. 
     The signal controller  600  applies the gate signal for the gate line connected to the current pixel of the gate driver  400  so that the current pixel (also referred to as a current stage pixel) has a target gray during the main-charge period. In the pixel of  FIG. 6 , the first gray is applied to the previous stage pixel before the first gray applied during the pre-charging period, and the current stage pixel is pre-charged by the first gray to reach the target voltage. Accordingly, in this case, the pre-charging may be performed or not during the first pre-charge period. However, in this case, when the pre-charging is performed during the first pre-charge period, the current stage pixel may more rapidly reach the target voltage. 
     According to  FIG. 6 , when the target gray of the current pixel is the first gray, the gray of the before-last pixel during the first pre-charge period is the second gray, and the gray of the previous pixel during the second pre-charge period is the first gray, the signal controller  600  controls the gate driver  400  to apply the gate-on voltage Von to the gate line connected to the current pixel during the first pre-charge period, and to apply the gate-on voltage Von to the gate line connected to the current pixel during the second pre-charge period. When describing  FIG. 3  as an example, the sixth pixel in the first row may be the before-last stage pixel, the fifth pixel in the first row may be the previous stage pixel, and the seventh pixel in the second row may be the current stage pixel. 
     According to  FIG. 6 , when the gate-on voltage Von during the first pre-charge period is applied to the gate line connected to the current pixel, the liquid crystal capacitor Clc of the current pixel is charged with 5V or less, that is, a common voltage or less. 
     Thereafter, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the second pre-charge period, the liquid crystal capacitor Clc of the current pixel is charged up to 10 V or less, that is, the target charging amount or less. 
     Thereafter, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the main-charge period, the liquid crystal capacitor Clc of the current pixel is charged up to the target charging amount. As a result, during the main-charge period, the gray of the current pixel reaches the target gray. 
     According to the second exemplary embodiment of the present invention, when the target gray of the current pixel is the first gray, the gate driver  400  may apply the gate-on voltage Von to the gate line connected to the current pixel during the first pre-charge period or the second pre-charge period. 
       FIG. 7  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a third exemplary embodiment of the present invention. 
     The signal controller  600  applies the gate signal for the gate line connected to the current pixel of the gate driver  400  so that the current pixel (also referred to as a current stage pixel) has a target gray during the main-charge period. In the pixel of  FIG. 7 , the first gray is applied to the previous stage pixel before the first gray applied during the pre-charging period, and the current stage pixel is pre-charged by the first gray to reach the target voltage. Accordingly, in this case, pre-charging need not necessarily be performed during the first pre-charge period. However, in this case, when the pre-charging is performed during the first pre-charge period, the current stage pixel may more rapidly reach the target voltage. 
     According to  FIG. 7 , when the target gray of the current pixel is the first gray, the gray of the before-last pixel during the first pre-charge period is the first gray, and the gray of the previous pixel during the second pre-charge period is the first gray, the signal controller  600  controls the gate driver  400  to apply the gate-off voltage Voff to the gate line connected to the current pixel during the first pre-charge period, and to apply the gate-on voltage Von to the gate line connected to the current pixel during the second pre-charge period. When describing  FIG. 3  as an example, an eleventh pixel in the first row may be a before-last stage pixel, a thirteenth pixel in the second row may be a previous stage pixel, and a fourteenth pixel in the second row may be a current stage pixel. 
     According to the third exemplary embodiment of the present invention, the gate driver  400  may apply the gate-on voltage Von to the gate line connected to the current pixel during the second pre-charge period. 
     According to  FIG. 7 , when the gate-off voltage Voff is applied to the gate line connected to the current pixel during the first pre-charge period, the liquid crystal capacitor Clc of the current pixel is not charged. 
     Thereafter, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the second pre-charge period, the liquid crystal capacitor Clc of the current pixel may be charged to 10V or less, that is, the common voltage or less. 
     Thereafter, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the main-charge period, the liquid crystal capacitor Clc of the current pixel is charged up to the target charging amount. As a result, during the main-charge period, the gray of the current pixel reaches the target gray. 
       FIG. 8  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a fourth exemplary embodiment of the present invention. 
     The signal controller  600  performs the pre-charging during the first pre-charge period or the second pre-charge period. According to the embodiments, the signal controller  600  may not perform pre-charging during the first pre-charge period and the second pre-charge period in case the current pixel (also referred to as a current stage pixel) has a target gray during the main-charge period. 
     According to  FIG. 8 , when the target gray of the current pixel is the second gray, the gray of the before-last pixel during the first pre-charge period is the first gray, and the gray of the previous pixel during the second pre-charge period is the first gray, the signal controller  600  controls the gate driver  400  to apply the gate-off voltage Voff to the gate line connected to the current pixel during the first pre-charge period, and to apply the gate-on voltage Von to the gate line connected to the current pixel during the second pre-charge period. When describing  FIG. 3  as an example, the first pixel in the first row may be a before-last stage pixel, the second pixel in the first row may be the previous stage pixel, and the third pixel in the second row may be the current stage pixel. 
     According to  FIG. 8 , when the gate-off voltage Voff is applied to the gate line connected to the current pixel during the first pre-charge period, the liquid crystal capacitor Clc of the current pixel is not charged. 
     Thereafter, when the gate-off voltage Voff is applied to the gate line connected to the current pixel during the second pre-charge period, the liquid crystal capacitor Clc of the current pixel is not charged. 
     Thereafter, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the main-charge period, the liquid crystal capacitor Clc of the current pixel is charged up to the target charging amount. As a result, during the main-charge period, the gray of the current pixel reaches the target gray. 
     According to the fourth exemplary embodiment of the present invention, when the target gray of the current pixel is the second gray, the gate driver  400  may apply the gate-off voltage Voff to the gate line connected to the current pixel during the first pre-charge period and the second pre-charge period. 
     Next, a pixel structure of the display panel  300  according to another exemplary embodiment of the present invention will be described with reference to  FIGS. 9 and 10 . 
       FIG. 9  is a diagram illustrating respective pixels in a matrix form for a display panel according to another exemplary embodiment of the present invention. 
     According to another exemplary embodiment of the present invention, the present invention may also be applied to a case where inversion driving units of 6×2 size described in  FIG. 1  are disposed. 
     According to  FIG. 9 , only some of the pixel units (hereinafter, referred to as inversion driving units) having 6×2 size described in  FIG. 1  are disposed, and the remaining pixels may be applied to a case of having the first gray. 
       FIG. 10  is a diagram illustrating respective pixels in a matrix form of a display panel according to another exemplary embodiment of the present invention. 
     According to another exemplary embodiment of the present invention, the present invention may also be applied to a case where inversion driving units of 6×2 size described in  FIG. 1  are disposed. 
     According to  FIG. 10 , only some of the pixel units (hereinafter, referred to as inversion driving units) having 6×2 size described in  FIG. 1  are disposed, and the remaining pixels may be applied to a case of having the second gray. 
     Next, an operation of a display device according to Comparative Examples will be described with reference to  FIGS. 11 to 13 . 
       FIG. 11  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a first Comparative Example. 
     According to the first Comparative Example, when the target gray of the current pixel is the first gray and the gray of the previous pixel during the second pre-charging period is the second gray, the signal controller  600  controls the gate driver  400  to apply the gate-on voltage Von to the gate line connected to the current pixel during the second pre-charge period. 
     According to  FIG. 11 , when the gate-on voltage Von is applied to the gate line connected to the current pixel during the second pre-charge period, the liquid crystal capacitor Clc of the current pixel is charged to 5 V or less, that is, the common voltage or less. 
     Thereafter, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the main-charge period, the liquid crystal capacitor Clc of the current pixel is charged. However, according to the first Comparative Example, since the charging amount of the liquid crystal capacitor Clc of the current pixel during the main-charge period starts from a very low voltage, the charging amount does not reach up to the target charging amount. That is, in the first Comparative Example, a charging shortage may occur. More specifically, the time required charging up to the target charging amount exceeds the main-charge period because the charging is performed from a very low voltage when charging starts during the second pre-charge period. 
       FIG. 12  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a second Comparative Example. 
     According to the second Comparative Example, when the target gray of the current pixel is the first gray and the gray of the previous pixel during the second pre-charging period is also the first gray, the signal controller  600  controls the gate driver  400  to apply the gate-on voltage Von to the gate line connected to the current pixel during the second pre-charge period. 
     According to  FIG. 12 , when the gate-on voltage Von is applied to the gate line connected to the current pixel during the second pre-charge period, the liquid crystal capacitor Clc of the current pixel is charged to 10V or less, that is, the common voltage or less. 
     Thereafter, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the main-charge period, the liquid crystal capacitor Clc of the current pixel is charged up to the target charging amount. As a result, during the main-charge period, the gray of the current pixel reaches the target gray. 
     According to the second Comparative Example, during the main-charge period, since the charging amount of the liquid crystal capacitor Clc of the current pixel starts from a sufficiently high voltage, that is, the target voltage or perhaps slightly less, the charging amount may reach up to the sufficient target charging amount. That is, according to the second Comparative Example, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the second pre-charge period, and further, the gray of the previous pixel of the current pixel is the first gray, the liquid crystal capacitor Clc of the current pixel is charged to sufficient amount that the target charging amount is reached during the main-charge period. 
       FIG. 13  is a diagram illustrating a charging amount of a liquid crystal capacitor according to a third Comparative Example. 
     According to the third Comparative Example, when the target gray of the current pixel is the second gray and the gray of the previous pixel during the second pre-charging period is the first gray, the signal controller  600  controls the gate driver  400  to apply the gate-on voltage Von to the gate line connected to the current pixel during the second pre-charge period. 
     According to  FIG. 13 , when the gate-on voltage Von is applied to the gate line connected to the current pixel during the second pre-charge period, the liquid crystal capacitor Clc of the current pixel is charged to 10V or less, that is, the common voltage or less. 
     Thereafter, when the gate-on voltage Von is applied to the gate line connected to the current pixel during the main-charge period, the liquid crystal capacitor Clc of the current pixel is charged. However, according to the third Comparative Example 3, since the charging amount of the liquid crystal capacitor Clc of the current pixel during the main-charge period starts from an excessively high voltage, the charging amount does not reach up to the target charging amount. 
     That is, according to the third Comparative Example, during the second pre-charge period, the charging amount of the liquid crystal capacitor Clc of the current pixel is charged to the target charging amount or more, and as a result, excessive power consumption occurs. Further, during the main-charge period, since the charging amount of the liquid crystal capacitor Clc of the current pixel starts from an excessively high voltage, the charging amount does not reach the target charging amount. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     DESCRIPTION OF SYMBOLS 
     
         
         
           
               300 : Display panel 
               400 : Gate driver 
               500 : Data driver 
               600 : Signal controller