Patent Publication Number: US-9412322-B2

Title: Liquid crystal display device and method for driving same

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to liquid crystal display (LCD) devices, and more particularly relates to a liquid crystal display device and a method for driving the liquid crystal display device. 
     BACKGROUND 
     At present, liquid crystal display devices are widely used in various electronic devices, such as computer monitors, TVs, notebooks, mobile phones and digital cameras, due to their advantages, such as slim shape, energy saving and low radiation. 
     Referring to  FIG. 1 , a circuit diagram of a typical liquid crystal display device  10  is shown. The liquid crystal display device  10  includes a liquid crystal panel  11 , a scanning voltage generator  12 , a scanning driver  13 , a data driver  14  and a common voltage generator  15 . The scanning driver  13  and the data driver  14  are configured for driving the liquid crystal panel  11 . The common voltage generator  15  is configured for providing a common voltage VCOM to the liquid crystal panel  11 . The scanning voltage generator  12  is configured for providing a first scanning voltage VGL and a second scanning voltage VGH to the scanning driver  13 . 
     The liquid crystal panel  11  includes a plurality of parallel scanning lines  131 , and a plurality of parallel data lines  141  orthogonal to and isolated from the scanning lines  131 . The scanning lines  131  and the data lines  141  are configured for defining a plurality of pixel regions  102 . Each pixel region  102  includes a thin-film transistor (TFT)  103  arranged in a vicinity of an intersecting point of the scanning lines  131  and the data lines  141 , a liquid crystal capacitor  104  and a storage capacitor  105 . 
     The liquid crystal capacitor  104  includes a pixel electrode  1041 , a common electrode  1042  and a liquid crystal layer (not shown) sandwiched between the pixel electrode  1041  and the common electrode  1042 . The storage capacitor  105  includes the pixel electrode  1041 , a storage electrode  1051  and an insulating layer (not shown) sandwiched between the pixel electrode  1041  and the storage electrode  1051 . 
     The thin-film transistor  103  includes a gate electrode (not labeled) connected to one of the scanning lines  131 , a source electrode (not labeled) connected to one of the data lines  141  and a drain electrode (not labeled) connected to the pixel electrode  1041 . 
     The scanning voltage generator  12  is configured for providing the first scanning voltage VGL and the second scanning voltage VGH to the scanning driver  13 . The scanning driver  13  is configured for providing a plurality of scanning signals to each scanning line  131  successively according to the first scanning voltage VGL and the second scanning voltage VGH. When the scanning driver  13  provides the scanning signal to one of the scanning lines  131  connected to the thin-film transistor  103  according to the second scanning voltage VGH, the thin-film transistor  103  is conducted. The data driver  14  is configured for providing a plurality of grayscale voltages to the plurality of data lines  141  so that one of the grayscale voltages may be provided to the pixel electrode  1041  via the source electrode and the drain electrode of the conducted thin-film transistor  103 . 
     The common voltage VCOM generated by the common voltage generator  15  is provided to the common electrode  1042  and the storage electrode  1051 , respectively. When one of the grayscale voltages is provided to the pixel electrode  1041  via the source electrode and the drain electrode of the conducted thin-film transistor  103 , a voltage difference is generated by the common voltage VCOM and the grayscale voltage between the pixel electrode  1041  and the common electrode  1042  of the liquid crystal capacitor  104 . Liquid crystal molecules in the liquid crystal layer sandwiched between the pixel electrode  1041  and the common electrode  1042  may be induced to a predetermined angle in order to achieve a predetermined gray-level according to the angle of the liquid crystal molecules. The storage capacitor  105  is configured for maintaining the grayscale voltage on the pixel electrode  1041 , so that the grayscale voltage on the pixel electrode  1041  may be maintained until a successive grayscale voltage is provided to the pixel electrode  1041 . 
     In general, there is a parasitic capacitor  106  between the gate electrode and the drain electrode of the thin-film transistor  103 . When the voltage on the gate electrode of the thin-film transistor  103  changes, for example from the second scanning voltage VGH to the first scanning voltage VGL, the voltage on the pixel electrode  1041  changes correspondingly, because the voltage difference on the parasitic capacitor  106  cannot change instantly. Furthermore, the common voltages VCOM on the storage electrode  1051  and the common electrode  1042  changes correspondingly, because the voltage differences on the storage capacitor  105  and the liquid crystal capacitor  104  cannot change instantly. Therefore, a picture displayed on the liquid crystal panel  11  may flicker due to the changes of the common voltages VCOM on the storage electrode  1051  and the common electrode  1042 . 
     What is needed, therefore, is a liquid crystal display device and a method for driving the liquid crystal display device which may overcome above problems. 
     SUMMARY 
     Accordingly, the present disclosure provides a liquid crystal display device and a method for driving the liquid crystal display device which may reduce or even eliminate the picture flickering caused by the change of the common voltage. 
     The present disclosure provides an liquid crystal display device which includes a liquid crystal panel, a common voltage generator, a scanning voltage regenerator and a scanning driver. The liquid crystal panel includes a plurality of scanning lines, a plurality of data lines orthogonal to and isolated from the plurality of data lines, and a plurality of pixel regions defined by the scanning lines and the data lines. Each pixel region includes a storage capacitor and a thin-film transistor. The storage capacitor includes a pixel electrode and a storage electrode facing the pixel electrode. The thin-film transistor includes a gate electrode connected to one of the plurality of scanning lines, a source electrode connected to one of the plurality of data lines and a drain electrode connected to the pixel electrode. The common voltage generator is configured for providing a common voltage to the storage electrode. The scanning voltage regenerator includes a capacitor and an adder. The adder includes a first voltage input terminal, a second voltage input terminal and a voltage output terminal. The first voltage input terminal is configured for receiving a feedback common voltage via the capacitor from the storage electrode. The second voltage input terminal is configured for receiving a first scanning voltage for cutting-off the thin-film transistor. The voltage output terminal is configured for outputting a regenerated scanning voltage generated by adding an alternating current component of the feedback common voltage to the first scanning voltage. The scanning driver is configured for receiving the regenerated scanning voltage and a second scanning voltage for conducting the thin-film transistor, and outputting a plurality of scanning signals to each scanning line successively according to the regenerated scanning voltage and the second scanning voltage. 
     The present disclosure provides an liquid crystal display device which includes a liquid crystal panel, a common voltage generator and a scanning voltage regenerator. The liquid crystal panel includes a plurality of pixel regions formed in a matrix form. Each pixel region includes a thin-film transistor and a storage capacitor. The storage capacitor includes a pixel electrode and a storage electrode facing the pixel electrode. The common voltage generator is configured for providing a common voltage to the storage electrode. The scanning voltage regenerator is configured for receiving a feedback common voltage from the storage electrode and generating a regenerated scanning voltage for driving the thin-film transistor according to the feedback common voltage. 
     According to an exemplary embodiment of the present disclosure, the liquid crystal panel includes a plurality of scanning lines and a plurality of data lines. The plurality of scanning lines is orthogonal to and isolated from the plurality of data lines to define the plurality of pixel regions. The thin-film transistor includes a gate electrode connected to one of the plurality of scanning lines, a source electrode connected to one of the plurality of data lines and a drain electrode connected to the pixel electrode. 
     According to an exemplary embodiment of the present disclosure, the scanning voltage regenerator includes a blocking element and an adder. The adder includes a first voltage input terminal, a second voltage input terminal and a voltage output terminal. The first voltage input terminal is configured for receiving the feedback common voltage via the blocking element. The second voltage input terminal is configured for receiving a first scanning voltage for cutting-off the thin-film transistor. The voltage output terminal is configured for outputting the regenerated scanning voltage generated by adding an alternating current component of the feedback common voltage to the first scanning voltage. 
     According to an exemplary embodiment of the present disclosure, the blocking element is a capacitor. 
     According to an exemplary embodiment of the present disclosure, the liquid crystal display device further includes a scanning driver. The scanning driver is configured for receiving the regenerated scanning voltage and a second scanning voltage for conducting the thin-film transistor, and outputting a plurality of scanning signals to each scanning line successively according to the regenerated scanning voltage and the second scanning voltage. 
     According to an exemplary embodiment of the present disclosure, the liquid crystal display device further includes a scanning voltage generator configured for providing the first scanning voltage and the second scanning voltage. 
     According to an exemplary embodiment of the present disclosure, the liquid crystal display device further includes a data driver configured for providing a plurality of grayscale voltages to the data lines when the thin-film transistor is conducted. 
     The present disclosure provides a method for driving a liquid crystal display device. The liquid crystal display device includes a liquid crystal panel and a common voltage generator. The liquid crystal panel includes a plurality of pixel regions formed in a matrix form. Each pixel region includes a thin-film transistor and a storage capacitor. The storage capacitor includes a pixel electrode and a storage electrode facing the pixel electrode. The common voltage generator is configured for providing a common voltage to the storage electrode. The method includes receiving a feedback common voltage from the storage electrode; generating a regenerated scanning voltage according to the feedback common voltage; and driving the thin-film transistor with the regenerated scanning voltage. 
     According to an exemplary embodiment of the present disclosure, the step of generating the regenerated scanning voltage according to the feedback common voltage includes adding an alternating current component of the feedback common voltage to a first scanning voltage for cutting-off the thin-film transistor. 
     According to an exemplary embodiment of the present disclosure, the step of driving the thin-film transistor with the regenerated scanning voltage includes receiving the regenerated scanning voltage and a second scanning voltage for conducting the thin-film transistor, and outputting a plurality of scanning signals to each scanning line in the liquid crystal panel successively according to the regenerated scanning voltage and the second scanning voltage to drive the thin-film transistor. 
     The liquid crystal display device and the method for driving the liquid crystal display device provided in the present disclosure may generate a regenerated scanning voltage according to a feedback common voltage, and drive thin-film transistors with the regenerated scanning voltage. Thus, the change of the common voltage may be compensated, and the flickering of picture caused by the change of the common voltage may be reduced or even eliminated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of at least one embodiment of the present disclosure. In the drawings, like reference numerals designate corresponding parts throughout various views, and all the views are schematic. 
         FIG. 1  shows a circuit diagram of a conventional liquid crystal display device. 
         FIG. 2  shows a circuit diagram of a liquid crystal display device according to an exemplary embodiment of the present disclosure. 
         FIG. 3  shows a circuit diagram of a scanning voltage regenerator of the liquid crystal display device shown in  FIG. 2  according to an exemplary embodiment of the present disclosure. 
         FIG. 4  shows a flow diagram of a method for driving the liquid crystal display device shown in  FIG. 2  according to an exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Reference will now be made to the drawings to describe preferred and exemplary embodiments of the present disclosure in detail. 
     Referring to  FIG. 2 , a circuit diagram of a liquid crystal display device  20  according to an exemplary embodiment of the present disclosure is shown. The liquid crystal display device  20  includes a liquid crystal panel  21 , a scanning voltage generator  22 , a scanning driver  23 , a data driver  24 , a common voltage generator  25  and a scanning voltage regenerator  26 . 
     The liquid crystal panel  21  includes a plurality of scanning lines  231  and a plurality of data lines  241 . The scanning lines  231  are orthogonal to and isolated from the data lines  241 , so that a plurality of pixel regions  202  may be defined in a matrix form. Each pixel region  202  includes a thin-film transistor  203 , a liquid crystal capacitor  204  and a storage capacitor  205 . 
     The liquid crystal capacitor  204  includes a pixel electrode  2041 , a common electrode  2042  facing the pixel electrode  2041  and a liquid crystal layer (not shown) sandwiched between the pixel electrode  2041  and the common electrode  2042 . The storage capacitor  205  includes the pixel electrode  2041 , a storage electrode  2051  facing the pixel electrode  2041  and an insulating layer (not shown) sandwiched between the pixel electrode  2041  and the storage electrode  2051 . 
     The thin-film transistor  203  includes a gate electrode (not labeled), a source electrode (not labeled) and a drain electrode (not labeled). The gate electrode is connected to one of the scanning lines  231 . The source electrode is connected to one of the data lines  241 . The drain electrode is connected to the pixel electrode  2041 . There is a parasitic capacitor  206  cooperatively formed by the source electrode and the drain electrode of the thin-film transistor  203 . 
     The scanning voltage generator  22  is configured for providing a first scanning voltage VGL for cutting-off the thin-film transistor  203  and a second scanning voltage VGH for conducting the thin-film transistor  203 . The common voltage generator  25  is configured for providing a common voltage VCOM to the common electrode  2042  and the storage electrode  2051 , respectively. 
     The scanning voltage regenerator  26  is connected to the storage electrode  2051  in each pixel region  202  via a feedback line  261 , and is configured for receiving a feedback common voltage VCOM′ from the storage electrode  2051 . The scanning voltage regenerator  26  is further configured for generating a regenerated scanning voltage VGL′ for driving the thin-film transistor  203  according to the feedback common voltage VCOM′. The scanning driver  13  is configured for receiving the regenerated scanning voltage VGL′ and the second scanning voltage VGH, and outputting a plurality of scanning signals to each scanning line  231  successively according to the regenerated scanning voltage VGL′ and the second scanning voltage VGH. 
     Referring to  FIG. 3 , a circuit diagram of the scanning voltage regenerator  26  of the liquid crystal display device  20  according to an exemplary embodiment of the present disclosure is shown. The scanning voltage regenerator  26  includes an adder  262  and a blocking element  263 . The adder  262  includes a first voltage input terminal  2621 , a second voltage input terminal  2622  and a voltage output terminal  2623 . 
     The first voltage input terminal  2621  is configured for receiving the feedback common voltage VCOM′ via the blocking element  263 . The blocking element  263  is configured for filtering a direct current (DC) component of the feedback common voltage VCOM′, and outputting an alternating current (AC) component VCOM″ of the feedback common voltage VCOM′ to the first voltage input terminal  2621 . In the present embodiment, the blocking element  263  is a capacitor. In alternative embodiments, the blocking element  263  may be any element or circuit that may filter the direct current component of the feedback common voltage VCOM′ and pass the alternating current component VCOM″ of the feedback common voltage VCOM′. The second voltage input terminal  2622  is configured for receiving the first scanning voltage VGL for cutting-off the thin-film transistor  203 . The voltage output terminal  2623  is configured for outputting the regenerated scanning voltage VGL′. The regenerated scanning voltage VGL′ is generated by adding the alternating current component VCOM″ of the feedback common voltage VCOM′ to the first scanning voltage VGL:
 
 VGL′=VCOM″+VGL   (1)
 
     The scanning driver  23  is configured for receiving the regenerated scanning voltage VGL′, and selectively providing the regenerated scanning voltage VGL′ to one of the scanning lines  231  connected to the thin-film transistor  203  in order to cut-off the thin-film transistor  203 . The scanning driver  23  is further configured for receiving the second scanning voltage VGH and selectively providing the second scanning voltage VGH to one of the scanning lines  231  connected to the thin-film transistor  203  in order to conduct the thin-film transistor  203 . 
     When the thin-film transistor  203  is conducted, the data driver  24  is configured for providing a plurality of grayscale voltages to the data lines  241 . One of the grayscale voltages is provided to the pixel electrode  2041  via the source electrode and the drain electrode of the conducted thin-film transistor  203 . In the present embodiment, the regenerated scanning voltage VGL′ and the second scanning voltage VGH may be provided to the scanning lines  231 , and the grayscale voltages may be provide to the data lines  241  by well-known means, which will be not described in detail. 
     While the voltage on the gate electrode of the thin-film transistor  203  changes, for example from the second scanning voltage VGH to the first scanning voltage VGL, the common voltages VCOM on the storage electrode  2051  and the common electrode  2042  change correspondingly, due to the existences of the parasitic capacitor  206 , the storage capacitor  205  and the liquid crystal capacitor  204 . The scanning voltage regenerator  26  may adjust the first scanning voltage VGL and generate the regenerated scanning voltage VGL′ correspondingly to the change of the feedback common voltage VCOM′ (i.e. the alternating current component VCOM″). The regenerated scanning voltage VGL′ provided to the gate electrode of the thin-film transistor  203  may change synchronously to the common voltages VCOM on the storage electrode  2051  and the common electrode  2042 . Thus, the flickering of the picture displayed on the liquid crystal panel  21  caused by the change of the common voltages VCOM may be reduced or even eliminated. 
     It should be noted that only one scanning voltage regenerator  26  is configured in the liquid crystal display device  20  and is connected to the storage electrode  2051  in each pixel region  202  in the liquid crystal panel  21 . Therefore, the scanning voltage regenerator  26  receives the feedback common voltage VCOM′ from all the storage electrodes  2051  in the liquid crystal panel  21 . However, a plurality of scanning voltage regenerators  26  may be configured in the liquid crystal display device  20 . For example, each scanning voltage regenerator  26  may correspond to one row of the pixel regions  202  or any predetermined amount of the pixel regions  202 . 
     Referring to  FIG. 4 , a flow diagram of a method for driving the liquid crystal display device  20  according to an exemplary embodiment of the present disclosure is shown. The method includes following steps. 
     In step  301 , the feedback common voltage VCOM′ is received from the storage electrode  2051 . 
     In step  302 , the regenerated scanning voltage VGL′ is generated according to the feedback common voltage VCOM′. In a preferred embodiment, the regenerated scanning voltage VGL′ is generated by adding the alternating current component VCOM″ of the feedback common voltage VCOM′ to the first scanning voltage VGL for cutting-off the thin-film transistor  203 . 
     In step  303 , the regenerated scanning voltage VGL′ may be configured for driving the thin-film transistor  203 . 
     In the method mentioned above, the steps  301  and  302  may be performed by the scanning voltage regenerator  26  shown in  FIG. 2 , and the step  303  may be performed by the scanning driver  23  shown in  FIG. 2 . The detailed performing process has been described above and will be omitted here. 
     As is mentioned above, the liquid crystal display device and the method for driving the liquid crystal display device provided in the present disclosure may generate a regenerated scanning voltage according to a feedback common voltage, and drive thin-film transistors with the regenerated scanning voltage. Thus, the change of the common voltage may be compensated, and the flickering of picture caused by the change of the common voltage may be reduced or even eliminated. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.