Abstract:
The present invention relates to a driving system of a liquid crystal display and a driving method thereof. A storage capacitor voltage (V CS ) is applied to an auxiliary shielding storage capacitor electrode and a common electrode voltage (V com ) is applied to a common electrode in a liquid crystal display panel comprising of an upper substrate, a lower substrate, and a liquid crystal layer. Besides, a specific voltage is applied to a storage capacitor electrode and makes a predetermined voltage difference between the auxiliary shielding storage capacitor electrode and the common electrode, thereby improving the side light leakage of the liquid crystal display, enhancing the process when assembling the upper substrate and the lower substrate, and reducing the width of a black matrix shielding layer of the upper substrate to increase the aperture ratio.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an LCD driving system and a driving method thereof, especially to a driving system and its driving method for using in a thin film transistor LCD. 
         [0003]    2. Description of Related Art 
         [0004]    The structure of a conventional thin film transistor LCD generally includes a liquid crystal display panel comprising an upper substrate, a lower substrate and a liquid crystal layer, wherein the liquid crystal layer is sealed between the upper substrate and the lower substrate. Further, the lower substrate has a plurality of pixel electrodes, and the upper substrate has a plurality of black matrix (BM) shielding patterns and a common electrode made of an Indium Tin Oxide (ITO) transparent thin film. 
         [0005]    However, with regard to the region around boundary edge of pixel electrodes, the arrangement of liquid crystal molecules within this region cannot be controlled by means of controlling the voltage between the pixel electrodes and the common electrode. Therefore, light would leak out of this region thereby causing orthographic light leakage and side light leakage. 
         [0006]    Further,  FIG. 5A  illustrates a top view of a conventional thin film transistor LCD, and  FIG. 5B  illustrates a cross-sectional view corresponding to the arrowhead mark of  FIG. 5A , so as to learn more about the structure of a conventional Cs-on-Common H-type auxiliary shielding storage capacitor frame designed in response to the above light leakage problem. 
         [0007]    As shown in  FIGS. 5A and 5B , the lower substrate  1  includes a storage capacitor line  12 , a metal layer  121  formed as an H pattern with the storage capacitor line  12 , a gate insulator (GI) layer  16 , a source line  11 , a passivation layer  17 , a pixel electrode  14  made of ITO, and an alignment film  18  formed thereon. Further, the upper substrate  2  includes a black matrix shielding pattern  100  of a color filter, a common electrode  13 , and a common alignment film  20 . The gate insulator  16  and the passivation layer  17  could be composed of Silicon Oxide, Silicon Nitride, and its similar compound. 
         [0008]    The conventional LCD display principle is to control the voltages of the pixel electrode  14  and the common electrode  13 , such that liquid crystal molecules  15  between the pixel electrode  14  and the common electrode  13  would be influenced by the voltage difference between the pixel electrode  14  and the common electrode  13 , thereby changing the arrangement of the liquid crystal molecules  15 , so as to control the light direction within the liquid crystal molecules  15  and form a variety of gray scales in combination with a polarizing sheet. 
         [0009]    Therefore, the way that the Cs-on-Common H-patterned auxiliary shielding storage capacitor frame improves the above light leakage problem is to utilize the auxiliary storage capacitor line  12  to form an H-patterned metal layer  121  around the boundary edge of the pixel electrode  14 , so as to shield the light leakage from the edge of the pixel electrode  14 . Further, regarding the design of the color filter, a black matrix shielding pattern  100  is disposed above a gap between two neighbor pixel electrodes  14 , for blocking the orthographic light leakage and side light leakage between the source line  11  and the H-patterned metal layer  121  of the auxiliary storage capacitor. 
         [0010]    On the other hand, as to electricity, please refer to  FIG. 6  showing the electronic signal of the conventional LCD panel. Conventionally, the voltage difference between an auxiliary shielding storage capacitor voltage (V CS ) of the H-patterned metal layer  121  of the auxiliary storage capacitor at two sides of the source line  11  and a common electrode voltage (V com ) of the common electrode  13  is down to zero, which means, the voltages of the H patterned metal layer  121  and the common electrode  13  are identical, V CS =V com . Therefore, with regard to the liquid crystal molecules  15  between the H patterned metal layer  121  and the common electrode  13 , the light transmittance of the molecule arrangement direction is high. 
         [0011]    However, if the lower substrate  1  and the upper substrate  2  are not properly sealed during the sealing process, or if the overlap between the black matrix shielding layer  100  and the H-patterned metal layer  121  changes, the liquid crystal molecules  15  under such arrangement status still tend to generate side light leakage (shown as the directions indicated by arrows in  FIG. 5B ). 
         [0012]    Therefore, according to the above description, in the conventional Cs-on-Common H-type auxiliary shielding storage capacitor frame, the light would still leak from the directions indicated by arrows shown in  FIG. 5B . That is, the physical shielding effect of the conventional Cs-on-Common H-type auxiliary shielding storage capacitor frame cannot completely shield the side light leakage of the edge region of the pixel electrode  14 . 
         [0013]    Further, in conventional designs, there are two ways applied to prevent the side light leakage problem: 1. reducing the width between the source line  11  and the H-patterned metal layer  121  of the auxiliary storage capacitor at two sides of the source line  11 , 2. increasing the width of the black matrix shielding layer  100 . 
         [0014]    However, the former is subject to the influence of the process stability thereby causing the source line  11  to be coupled to the auxiliary storage capacitor line  12  and resulting in a bad driving problem; while the latter increases the width of the black matrix shielding layer thereby reducing the aperture ratio. 
         [0015]    Therefore, it is desirable to provide a better LCD driving system and driving method thereof in a more convenient and accurate way so as to mitigate and/or obviate the aforementioned problems. 
       SUMMARY OF THE INVENTION 
       [0016]    An object of the present invention is to provide an LCD driving method for improving the side light leakage. 
         [0017]    Another object of the present invention is to provide an LCD driving method adapted to a design of reducing the width of the black matrix shielding layer and increasing the aperture ratio. 
         [0018]    Another object of the present invention is to provide an LCD driving method for reducing the limitation of the assembly process of the upper substrate and the lower substrate to increase the yield. 
         [0019]    Another object of the present invention is to provide an LCD driving method for reducing the cost of the printed wire board. 
         [0020]    Another object of the present invention is to provide a voltage difference between the H-patterned auxiliary shielding storage capacitor and the common electrode. 
         [0021]    To achieve the above objects, the present invention provides an LCD driving method. The LCD comprises an LCD panel comprising an upper substrate, a lower substrate and a liquid crystal layer, wherein the liquid crystal layer is sealed between the upper substrate and the lower substrate. The lower substrate further includes a plurality of pixel electrodes and an auxiliary shielding storage capacitor electrode, and the upper substrate includes a black matrix shielding layer and a common electrode. The common electrode is disposed on a surface of the upper substrate or the black matrix shielding layer, and the auxiliary shielding storage capacitor electrode is disposed under the pixel electrodes and arranged along edges of the pixel electrodes. The black matrix shielding layer is arranged corresponding to a gap between each two adjacent pixel electrodes. The driving method comprises the following steps of: applying a storage capacitor voltage to the auxiliary shielding storage capacitor electrode; and applying a common electrode voltage to the common electrode, and controlling the difference between the storage capacitor voltage and the common electrode voltage to form a predetermined voltage difference. 
         [0022]    To achieve the above objects, the present invention provides an LCD driving system, which comprises: an LCD panel, comprising an upper substrate, a lower substrate and a liquid crystal layer, wherein the liquid crystal layer is sealed between the upper substrate and the lower substrate, the lower substrate further comprising a plurality of pixel electrodes and an auxiliary shielding storage capacitor electrode, the upper substrate comprising a black matrix shielding layer and a common electrode, the common electrode disposed on a surface of the upper substrate or the black matrix shielding layer, the auxiliary shielding storage capacitor electrode disposed under the pixel electrodes and arranged along edges of the pixel electrodes, the black matrix shielding layer arranged corresponding to a gap between each two adjacent pixel electrodes; a voltage converter for receiving an operating voltage input and providing a storage capacitor voltage and a common electrode voltage, wherein a predetermined voltage difference exists between the storage capacitor voltage and the common electrode voltage; at least one source driver, electronically connected to the voltage converters and the LCD panel, for providing a plurality of data signals to the LCD panel; and at least one gate driver, electronically connected to the voltage converters and the LCD panel, for providing a plurality of scan signals to the LCD panel; wherein the storage capacitor voltage is applied to the auxiliary shielding storage capacitor electrode, and the common electrode voltage is applied to the common electrode, so as to keep the predetermined voltage difference between the auxiliary shielding storage capacitor electrode and the common electrode. 
         [0023]    Accordingly, liquid crystal material placed between the auxiliary shielding storage capacitor electrode and the common electrode with the predetermined voltage difference would be driven to influence the light transmittance between the auxiliary shielding storage capacitor electrode and the common electrode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1A  illustrates a block diagram of an LCD driving system of one preferred embodiment according to the present invention. 
           [0025]      FIG. 1B  illustrates a schematic drawing of a voltage converter of the LCD driving system of one preferred embodiment according to the present invention. 
           [0026]      FIGS. 2A˜2D  illustrate top views of a pixel of one preferred embodiment according to the present invention. 
           [0027]      FIG. 2E  illustrates a cross-sectional view of an LCD pixel of one preferred embodiment according to the present invention. 
           [0028]      FIG. 3  illustrates an electronic signal schematic drawing of a storage capacitor voltage (V CS ) and a common electrode voltage (V com ) within a pixel of one preferred embodiment according to the present invention. 
           [0029]      FIG. 4  illustrates an electronic signal schematic drawing of a storage capacitor voltage (V CS ) and a common electrode voltage (V com ) within a pixel of another preferred embodiment according to the present invention. 
           [0030]      FIG. 5A  illustrates a top view of a conventional thin film transistor LCD pixel. 
           [0031]      FIG. 5B  illustrates a cross-sectional view of a conventional thin film transistor LCD pixel. 
           [0032]      FIG. 6  illustrates an electronic signal schematic drawing of a conventional pixel. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0033]    Please refer to  FIGS. 1A and 1B .  FIG. 1A  illustrates a block diagram of an LCD driving system of one preferred embodiment according to the present invention, and  FIG. 1B  illustrates a schematic drawing of a voltage converter of the LCD driving system of one preferred embodiment according to the present invention. 
         [0034]    The LCD driving system as shown in  FIGS. 1A and 1B  is electronically connected to a plurality of pixel electrodes  24  (shown in  FIGS. 2A and 2B ), and comprises a low voltage differential signal connector  9 , a voltage converter  8 , a timing controller  3 , a gamma circuit  4 , a gate connector  5 , a source driver  6  and a gate driver  7 . 
         [0035]    The low voltage differential signal connector  9  is electronically connected to the timing controller  3 , the voltage converter  8  is electronically connected to the gamma circuit  4 , the gate connector  5  and the source driver  6 , the timing controller  3  is electronically connected to the gate connector  5  and the source driver  6 , the gamma circuit  4  is electronically connected to the source driver  6 , the source driver  6  is electronically connected to the gate connector  5 , and the gate connector  5  is electronically connected to the gate driver  7 . Further, the source driver  6  and the gate driver  7  are electronically connected to an LCD panel  300  (shown in  FIG. 2E ) via source lines  21  (shown in  FIG. 2B ) and gate lines  29  (shown in  FIG. 2B ), respectively. 
         [0036]    Moreover, the gamma circuit  4  provides a gamma reference voltage to the source driver  6 , the timing controller  3  outputs electronic signals to the source driver  6  and the gate driver  7  to control the operation of the source driver  6  and the gate driver  7 , such that the source driver  6  could output display data to the source lines  21 , and the gate driver  7  could output scan signals to the gate lines  29 , so as to transmit the display data and the scan signals to the LCD panel  300  via the source lines  21  and the gate lines  29 . 
         [0037]    As to the system operation, first, an operating voltage V is inputted to the low voltage differential signal connector  9 , the voltage converter  8 , the gamma circuit  4  and the source driver  6 . The low voltage differential signal connector  9  provides the operating voltage V to the timing controller  3 , and the voltage converter  8  performs a voltage increasing or a voltage decreasing process to the operating voltage V for providing various kinds of voltages, such as a highest gate voltage (V GH ), a lowest gate voltage (V GL ), a storage capacitor voltage (V CS ) and a common electrode voltage (V com ), to supply the voltage required by the LCD panel during operation. Then, the printed wire board (PWB) (not shown in figures) or the circuit (not shown in figures) on the side of the lower substrate  1  transmits the voltage outputted by the voltage converter  8  to the gate driver  7 . The electronic signals of V GH  and V GL  are converted by the gate driver  7  connected to the gate connector  5 , so as to drive the gate lines  29  of the LCD panel. 
         [0038]    Please refer to  FIGS. 2A˜2E .  FIGS. 2A˜2D  illustrate top views of a pixel of one preferred embodiment according to the present invention by showing the layer relation of each layer according to the order during the manufacturing process.  FIG. 2E  illustrates a cross-sectional view corresponding to the arrow mark region of  FIG. 2D . Please note that  FIGS. 2A˜2E  illustrate a similar structure in appearance as shown in  FIGS. 5A and 5B  for an easier description. 
         [0039]    Similarly, the lower substrate  1  includes a gate line  29  and a storage capacitor line  22  made of the same layer of metal as the lowest layer structure shown in  FIG. 2A . An auxiliary shielding storage capacitor electrode  221  connected to the storage capacitor line  22  is formed as well. Next, a gate insulator  26  is formed, then, as shown in  FIG. 2B , a source line  21  and a storage capacitor area  222  made of the same layer of the source line  21  are formed. Then, a passivation layer  27 , a pixel electrode  24  as shown in  FIG. 2C , are formed. Finally, an alignment film  28  is formed. Referring to  FIG. 2E , the upper substrate  2  includes a black matrix shielding layer  200  of a color filter (not shown), in which the black matrix shielding layer  200  is arranged on a position corresponding to a gap between the adjacent pixel electrodes  24  as shown in  FIG. 2D . Next, a layer of a common electrode  23  is formed as shown in  FIG. 2E , in which the common electrode  23  is disposed on a surface of the black matrix shielding layer  200 . Alternatively, the common electrode  23  is disposed on a surface of the substrate  2 . Finally, a layer of a common alignment film  30  is formed. The passivation layer  27  could be formed as the structure of single-layer or multi-layer by inorganic material of silicon oxide, silicon nitride and its similar compound, or organic material. 
         [0040]    On the lower substrate  1 , the auxiliary shielding storage capacitor electrode  221  is arranged along the boundary edge of the pixel electrodes  24 . Further, in the embodiment, the auxiliary shielding storage capacitor electrode  221  and the storage capacitor line  22  are formed as an H-patterned metal layer, in which the auxiliary shielding storage capacitor electrode  221  is formed corresponding to the edges of the abovementioned pixel electrode  24 . 
         [0041]    In this embodiment, a storage capacitor voltage (V CS ) provided by the voltage converter  8  is applied to the auxiliary shielding storage capacitor electrode  221 , i.e. the H-patterned metal layer of the storage capacitor line  22 , a common electrode voltage (V com ) provided by the voltage converter  8  is applied to the common electrode  23 , and the difference between the storage capacitor voltage (V CS ) and the common electrode voltage (V com ) is controlled to form a predetermined voltage difference. In this embodiment, the storage capacitor voltage (V CS ) is less than about −2V, the common electrode voltage (V com ) is about 3˜5V. Therefore, the predetermined voltage difference formed between the auxiliary shielding storage capacitor electrode  221  and the common electrode  23  is greater than about 5˜7V, thereby influencing the arrangement direction of liquid crystal molecules  25  between the auxiliary shielding storage capacitor electrode  221  and the common electrode  23 , further influencing the light transmittance between auxiliary shielding storage capacitor electrode  221  and the common electrode  23 , so as to eliminate light leaked out of the edge of the black matrix shielding layer  200  to avoid the side light leakage problem. Accordingly, the width of the black matrix shielding layer could be narrowed to increase the aperture ratio as well as improve the assembly process of the LCD panel. 
         [0042]    Please refer to  FIG. 3  illustrating an electronic signal schematic drawing of the storage capacitor voltage (V CS ) and the common electrode voltage (V com ) within a pixel of one preferred embodiment according to the present invention. Shown as the arrow, the predetermined voltage between the storage capacitor voltage (V CS ) and a common electrode voltage (V com ) is 5V. 
         [0043]    In another preferred embodiment of the present invention, a voltage output source equivalent to a lowest gate voltage (V GL ) is directly pulled out from the voltage converter  8  for being connected to the auxiliary shielding storage capacitor electrode  221 , for applying the storage capacitor voltage (V CS ) with the voltage identical to the lowest gate voltage (V GL ) to the auxiliary shielding storage capacitor electrode  221 . That is, V GL =V CS . In this embodiment, the lowest gate voltage (V GL ) is −6V, the common electrode voltage (V com ) is 3˜5V. Therefore, comparing to the previous embodiment, there is a larger predetermined voltage difference formed between the auxiliary shielding storage capacitor electrode  221  and the common electrode  23 , i.e. 9˜11V, thereby much more influencing the light transmittance of the liquid crystal molecules  25  between the auxiliary shielding storage capacitor electrode  221  and the common electrode  23 , so as to more efficiently avoid the side light leakage problem. Therefore, the manufacturing cost of the printed wire board is reduced by saving the circuit design for providing the storage capacitor voltage (V CS ) of the voltage converter  8 . 
         [0044]    Please refer to  FIG. 4  illustrating an electronic signal schematic drawing of the storage capacitor voltage (V CS ) and the common electrode voltage (V com ) within a pixel of another preferred embodiment according to the present invention. Shown as the arrow, the predetermined voltage difference between the storage capacitor voltage (V CS ) and a common electrode voltage (V com ) is 9V. 
         [0045]    According to the above description, an auxiliary shielding storage capacitor electrode is formed on a position of the lower substrate corresponding to the edge of pixel electrode, a storage capacitor voltage is applied to the auxiliary shielding storage capacitor electrode, a common electrode voltage is applied to the common electrode, and the difference between the storage capacitor voltage and the common electrode voltage is a predetermined voltage difference, such that the liquid crystal material between the auxiliary shielding storage capacitor electrode and the common electrode would be influenced by the predetermined voltage difference to change its optics nature, so as to improve the side light leakage problem of the LCD. 
         [0046]    Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.