Abstract:
A driving method of an LCD device adapted to improve the quality of pictures is disclosed. The driving method includes: deriving a frame detection signal from a data enable signal and a data clock signal; simultaneously deriving a start signal and a first gate clock signal from the frame detection signal and the data clock signal; and deriving a second gate clock signal from the first gate clock signal and the data clock signal. The first gate clock signal is identical with the start signal in a start time point of enable interval.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2007-0135840, filed on Dec. 21, 2007, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     1. Field of the Disclosure 
     This disclosure relates to a liquid crystal display device, and more particularly, to a liquid crystal display device adapted to improve picture quality and a driving method thereof. 
     2. Description of the Related Art 
     As the information society spreads, flat display devices capable of displaying information have been widely developed. These flat display devices include liquid crystal display (LCD) devices, organic electro-luminescence display devices, plasma display devices, and field emission display devices. Among the above devices, LCD devices have advantages in that they can be light and small and can implement a low power consumption and a full color scheme. Accordingly, LCD devices have been widely used for mobile phones, navigation systems, portable computers, televisions and so on. 
       FIG. 1  is a block diagram showing an LCD device of related art,  FIG. 2  is a detailed block diagram showing a gate driver in  FIG. 1 , and  FIG. 3  is a circuitry diagram showing a first shift register in  FIG. 2 . 
     As shown in  FIG. 1 , the related art LCD device includes a liquid crystal panel  130 , a gate driver  110 , a data driver  120 , and a timing controller  100 . The liquid crystal panel  130  displays the pictures. The gate driver  110  drives the liquid crystal panel  130  by lines. The data driver  120  applies data voltages to the liquid crystal panel  130  by lines. The timing controller  100  controls the gate driver  110  and the data driver  120 . 
     In order to control the gate driver  110  and the data driver  120 , the timing controller  100  generates control signals. For example, the timing controller  100  generates a start signal Vst and first to fourth gate clock signals GCLK 1  to GCLK 4  to control the gate driver  110 . The timing controller  100  also generates a source start pulse SSP, a source shift clock SSC, a source output enable signal SOE, a polarity control signal POL, and so on. 
     The gate driver  110  is directly formed on the liquid crystal panel  130 . Such a structure panel is called a Gate-in-Panel. Also, the gate driver  110  includes a plurality of stages ST 1  to STn, as shown in  FIG. 2 . The stages ST 1  to STn are connected to one another to form a cascade configuration. Each of the stages ST 1  to STn receives an output signal from a previous stage and the three gate clock signals among the first to fourth gate clock signals GCLK 1  to GCLK 4  which are sequentially applied. The first stage ST 1  independently inputs the start signal Vst instead of the previous stage&#39;s output signal, because the previous stage did not exist. 
     Each of the stage ST 1  to STn uses the previous stage&#39;s output signal and the three gate clock signals of the first to fourth gate clock signals GCLK 1  to GCLK 4  and generates an output signal Vg 1  to Vgn. The output signals Vg 1  to Vgn generated in the stages ST 1  to STn are applied to gate lines GL 1  to GLn on the liquid crystal panel  130 , respectively. Such stages ST 1  to STn are identical with one another in their internal circuit configuration. Accordingly, for convenience of explanation, the circuit configuration of first stage ST 1  will be now described. 
     Referring to  FIG. 3 , the fourth gate clock signal GCLK 4  and the start signal Vst are applied to the first stage ST 1 . The first stage ST 1  includes a first control portion  112  responsive to the start signal Vst and the fourth gate clock signal GCLK 4 , controlling a first node Q; a second control portion  114  responsive to the third gate clock signal GCLK 3  and the start signal Vst, controlling a second node QB; and an output portion  116  responsive to voltages on the first and second nodes Q and QB, selectively outputting the first gate clock signal GCLK 1  and a first supply voltage VSS. 
     The fourth gate clock signal GCLK 4  turns on a second transistor T 2  so that the start signal Vst is charged into the first node Q through a first transistor T 1  and the second transistor T 2 , during a first interval. Then, a sixth transistor T 6  is slowly turned on by the voltage on the first node Q. A fifth transistor T 5  is also turned on so that the first supply voltage VSS is charged to the second node QB. The voltage VSS on the second node QB turns off third and seventh transistors T 3  and T 7 . Accordingly, although the sixth transistor T 6  is slowly turned on, the first gate line GL 1  maintains a low level state due to the first gate clock signal GCLK 1  of low level, during the first interval. 
     For a second interval, the start signal Vst and the first to fourth gate clock signal GCLK 1  to GCLK 4  are not applied. The status of the first stage ST 1  in the first interval continues even-in spite of for the second interval. 
     The first gate clock signal GCLK 1  is applied to a source terminal of the sixth transistor T 6  during a third interval. Then, a bootstrapping phenomenon is caused by an internal capacitor (or a parasitic capacitor) Cgs between the source and gate terminals of the sixth transistor T 6 , thereby increasing the voltage on the first node Q connected with the gate terminal of the sixth transistor T 6 . As a result, the sixth transistor T 6  is fully or completely turned on so that the first gate clock signal GCLK 1  of high level is charged on the first gate line GL 1  of the liquid crystal panel  130  via the sixth transistor T 6 . 
     For a fourth interval, a second supply voltage VDD is charged to the second node QB through a fourth transistor T 4  which is turned on by the third gate clock signal GCLK 3 . At this time, since the first gate clock signal GCLK 1  has the low level, the bootstrapping phenomenon ceases so that the first node Q maintains the previous voltage, i.e., the voltage of the start signal Vst. The voltage on the second node QB turns on the third and seventh transistors T 3  and T 7 , thereby charging the first supply voltage VSS to both of the first node Q and the first gate line GL 1  of the liquid crystal panel  130  through each of the third and seventh transistors T 3  and T 7 . 
     In this manner, the start signal Vst and the first to fourth gate clock signals GCLK 1  to GCLK 4  should be applied from the timing controller  100  in order to drive the gate driver  110 . 
     However, when the first gate clock signal GCLK 1  is compared with the second to fourth gate clock signals GCLK 1  to GCLK 4  in the high level interval, the first gate clock signal GCLK 1  has a relatively short high level interval, as shown in  FIG. 4 . Accordingly, thin film transistors on the first gate line GL 1  each have a relatively short turning-on interval in comparison with those on the other gate lines GL 2  to GLn of the liquid crystal panel  130 , thereby allowing pixels on the first gate line GL 1  to be brighter than those on the other gate lines GL 2  to GLn. 
     As a result, a brightness difference between the pixels of the first gate line GL 1  and the pixels of the other gate lines GL 2  to GLn is generated, thereby deteriorating the quality of picture. 
     BRIEF SUMMARY 
     Accordingly, the present embodiments are directed to an LCD device that substantially obviates one or more of problems due to the limitations and disadvantages of the related art. 
     An object of the present embodiment is to provide an LCD device that enables the rising edge of a first gate clock signal GCLK 1  to be identical with that of a start signal so as to improve the quality of picture, and a driving method thereof. 
     Additional features and advantages of the embodiments 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 embodiments. The advantages of the embodiments will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     According to one general aspect of the present embodiment, a driving method of liquid crystal display device includes: deriving a frame detection signal from a data enable signal and a data clock signal; simultaneously deriving a start signal and a first gate clock signal from the frame detection signal and the data clock signal; and deriving a second gate clock signal from the first gate clock signal and the data clock signal. The first gate clock signal is identical with the start signal in a start time point of high level interval. 
     An LCD device according to another aspect of the present embodiment includes: a frame detector deriving a frame detection signal from a data enable signal and a data clock signal by detecting a blank interval between frames; a start and first gate clock signal generator simultaneously deriving a start signal and a first gate clock signal from the frame detection signal and the data clock signal; and a second gate clock signal generator deriving a second gate signal from the first gate clock signal and the data clock signal, wherein the first gate clock signal is identical with that of the start signal in a start time point of high level interval. 
     Other systems, methods, features and advantages will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims. Nothing in this section should be taken as a limitation on those claims. Further aspects and advantages are discussed below in conjunction with the embodiments. It is to be understood that both the foregoing general description and the following detailed description of the present disclosure are exemplary and explanatory and are intended to provide further explanation of the disclosure as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the disclosure. In the drawings: 
         FIG. 1  is a block diagram showing an LCD device of related art; 
         FIG. 2  is a detailed block diagram showing a gate driver in  FIG. 1 ; 
         FIG. 3  is a circuitry diagram showing in detail a first stage in  FIG. 2 ; 
         FIG. 4  is a waveform diagram showing control signals generated in a timing controller of  FIG. 1 ; 
         FIG. 5  is a block diagram showing a timing controller of an LCD device according to an embodiment of the present disclosure; 
         FIG. 6  is a circuitry diagram showing a first stage of a gate driver according to an embodiment of the present disclosure; and 
         FIG. 7  is a waveform diagram explaining control signals generated in a timing controller of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. These embodiments introduced hereinafter are provided as examples in order to convey their spirits to the ordinary skilled person in the art. Therefore, these embodiments might be embodied in a different shape, so are not limited to these embodiments described here. Also, the size and thickness of the device might be expressed to be exaggerated for the sake of convenience in the drawings. Wherever possible, the same reference numbers will be used throughout this disclosure including the drawings to refer to the same or like parts. 
       FIG. 5  is a block diagram showing a timing controller of an LCD device according to an embodiment of the present disclosure. Referring to  FIG. 5 , the timing controller includes a frame detector  300 , a start &amp; first gate clock signal generator  300   a , and second to fourth gate clock signal generators  300   b  to  300   d.    
     The frame detector  300  receives a data enable signal DE and a data clock signal DCLK, counts clocks included in the data clock signal DCLK, and detects a blank interval of the data enable signal DE on the basis of the counted clock value. The data enable signal DE includes the blank interval (i.e., a vertical blank interval) between frame intervals. Also, the data enable signal DE further includes horizontal intervals of high level periodically arranged within one frame interval. In accordance therewith, the frame detector  300  counts the clocks included in the data clock signal DCLK and determines an arbitrary interval in which the data enable signal DE continuously maintains the low level until the counted clock value reaches to a constant value, as the blank interval. The frame detector  300  also detects a rising edge of the data enable signal DE, which is changed from the low level to the high level and corresponds to the end position of the determined blank interval, on the basis of the determined blank interval. Furthermore, the frame detector  300  generates the frame detection signal Vf which is synchronized with the detected rising edge and is equal to the clock of the data clock signal DCLK in width. Herein, the width of the frame detection signal Vf can be larger or smaller than one clock of the data clock signal DCLK. 
     The start &amp; first gate clock signal generator  300   a  receives the frame detection signal Vf from the frame detector  300  and the data clock signal DCLK. This start &amp; first gate clock signal generator  300   a  derives a start signal Vst and a first gate clock signal GCLK 1  from the frame detection signal Vf and the data clock signal DCLK. The start signal Vst and the first gate clock signal GCLK 1  are equal to each other in a start time point of high level, but are different from each other in an end time point of high level. The high level intervals of the start and first gate clock signals Vst and GCLK 1  may be established by the data clock signal DCLK in lengths different from each other. These start and first gate clock signals Vst and GCLK 1  are applied to the second gate clock signal generator  300   b.    
     The second gate clock signal generator  300   b  derives a second gate clock signal GCLK 2  from the data clock signal DCLK and the first gate clock signal GCLK 1 . The second gate clock signal GCLK 2  has a high level interval (i.e., an enable interval) equal to the one of the first gate clock signal GCLK 1 , but that can be delayed from the first gate clock signal GCLK 1  by a fixed period. The fixed shift period can be changed in accordance with the specifications of a display device. Such a second gate clock signal GCLK 2  is applied to the third gate clock signal generator  300   c.    
     The third gate clock signal generator  300   c  also derives a third gate clock signal GCLK 3  from the second gate clock signal GCLK 2  and the data clock signal DCLK. The third gate clock signal GCLK 3  has a high level interval equal to the one of the second gate clock signal GCLK 2 , but that can be delayed from the second gate clock signal GCLK 2  by the fixed period. The fixed shift period can be changed in accordance with the specifications of a display device. Such a third gate clock signal GCLK 3  is applied to the fourth gate clock signal generator  300   d.    
     Similarly, the fourth gate clock signal generator  300   d  derives a fourth gate clock signal GCLK 4  from the third gate clock signal GCLK 3  and the data clock signal DCLK. The fourth gate clock signal GCLK 4  has a high level interval equal to the one of the third gate clock signal GCLK 3 , but that can be delayed from the third gate clock signal GCLK 3  by the fixed period. The fixed shift period can be changed in accordance with the specifications of a display device. 
     This fourth gate clock signal GCLK 4  is applied to the start and first gate clock signal generator  300   a  so that it derives the start and first gate clock signals Vst and GCLK 1  from the fourth gate clock signal GCLK 4  and the data clock signal DCLK and applies to the first gate clock signal GCLK 1  to the second gate clock signal generator  300   b.    
       FIG. 6  is a circuitry diagram showing a first stage which is included in a gate driver according to an embodiment of the present disclosure.  FIG. 7  is a waveform diagram explaining control signals generated in the timing controller of  FIG. 5 . The gate driver according to the embodiment of the present invention includes a plurality of stages which each have a configuration as shown in  FIG. 6 . As the plural stages are identical with one another in their internal circuit configuration, the circuit configuration of first stage ST 1  will be now described by way of example, for convenience of explanation. 
     Referring to  FIG. 6 , the first stage ST 1  includes: a first control portion  212 , responsive to the start signal Vst and the fourth gate clock signal GCLK 4 , controlling a first node Q; a second control portion  214 , responsive to the third gate clock signal GCLK 3  and the start signal Vst, controlling a second node QB; and an output portion  216 , responsive to voltages on the first and second nodes Q and QB, selectively outputting the first gate clock signal GCLK 1  and a first supply voltage VSS. 
     The fourth gate clock signal GCLK 4  turns on a second transistor T 2  so that the start signal Vst is charged into the first node Q through a first transistor T 1  and the second transistor T 2 , during a first interval. Then, a sixth transistor T 6  is turned on by the voltage on the first node Q. A fifth transistor T 5  is also turned on by the start signal Vst so that the first supply voltage VSS is charged to the second node QB through the fifth transistor T 5 . The voltage VSS on the second node QB turns off third and seventh transistors T 3  and T 7 . Accordingly, the sixth transistor T 6  is turned on, thus the first gate line GL 1  charges the first gate clock signal GCLK 1  of a high level. As a result, an output signal of high level develops on the first gate line GL 1  of the liquid crystal display panel (not shown). 
     The first gate clock signal GCLK 1  continuously maintains the high level during a second interval. In accordance therewith, the status of the first stage T 1  in the first interval continues for the second interval. 
     For a third interval, a second supply voltage VDD is charged to the second node QB through a fourth transistor T 4  which is turned on by the third gate clock signal GCLK 3 . At this time, since the first gate clock signal GCLK 1  has the low level, the first node Q maintains the previous voltage, i.e., the voltage of the start signal Vst. The voltage on the second node QB turns on the third and seventh transistors T 3  and T 7 , thereby charging the first supply voltage VSS to both the first node Q and the first gate line GL 1  of the liquid crystal display panel  130  through the third and seventh transistors T 3  and T 7 . 
     Referring to  FIG. 7 , the timing controller in the present invention enables the first gate clock signal GCLK 1  to simultaneously change into a high level together with the start signal Vst. In other words, the first gate clock signal GCLK has the same rising edge as the start signal Vst. Accordingly, the first gate clock signal GCLK 1  has the high level interval equal to those of the second to fourth gate clock signals GCLK 2  to GCLK 4 , and the first to fourth gate clock signals GCLK 1  to GCLK 4  are shifted from one another by a fixed period. 
     As described above, the liquid crystal display device, according to the embodiment of the present disclosure, makes the start signal Vst and the first gate clock signal GCLK 1  equal to each other in the start time of high level interval, i.e., in the rising edge, thereby setting up the high level interval of the first gate clock signal GCLK 1  to correspond to a period of two horizontal synchronous intervals. Accordingly, a pre-charging period of the first gate line GL 1  is equal to those of the other gate lines GL 2  to GLn, so that the brightness difference between the first gate line GL 1  and the other gate lines GL 2  to GLn can be improved. As a result, the liquid crystal display device can improve the quality of picture. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure. Thus, it is intended that the present disclosure cover the modifications and variations of this embodiment provided they come within the scope of the appended claims and their equivalents.