Abstract:
A liquid crystal display panel includes at least one pixel units. Each pixel unit includes a first storage capacitor electrically connected to a first transistor, a second storage capacitor electrically connected to a second transistor, and a charge-sharing capacitor having two ends electrically connected to the second storage capacitor and to an inverter. The electric potential of the charge-sharing capacitor changes because of an inverted scanning signal output by the inverter and further alters the stored voltage applied on the second storage capacitor after the scan line finishes transmitting the scanning signal, so that the first storage capacitor and the second storage capacitor have different voltages. Therefore, the color washout phenomenon is improved.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a liquid crystal display (LCD) panel and a driving method thereof and more particularly, to an LCD panel which helps improve color washout and a driving method thereof. 
         [0003]    2. Description of Prior Art 
         [0004]    TFT-LCDs, having properties of high image quality, high space utilization efficiency, low consumption power, and no radiation, have gradually become the mainstream of the market. In order to meet current market requirements, TFT-LCDs tend to have the characteristics like high contrast ratios, high-speed response, and wide viewing angles. Technologies which can provide wide viewing angles nowadays include multi-domain vertically alignment (MVA), multi-domain horizontal alignment (MHA), twisted nematic plus wide viewing film (TN+film), and in-plane switching (IPS). 
         [0005]    Although TFT-LCDs adopting MVA feature wide viewing angles, this kind of TFT-LCD has a well-known disadvantage—color washout. When users try to see display images at different watching angles, they will, however, find that images have different colors, which is called color washout. For instance, users will see whiter images when seeing images with a more slanted angle. 
         [0006]    Ways to solve the above-mentioned color washout problem include adopting retardation films which are a combination of A-plate and C-plate, reducing cell gaps, and forming two LC capacitors inside a single pixel. However, the effect of compensation of retardation films formed by a combination of A-plate and C-plate is not obvious, and a reduction in cell gaps decreases yield rates and brightness. As for formation of two LC capacitors inside a single pixel, an additional dielectric layer is required, which usually causes some problems such as mura and residual images. 
       SUMMARY OF THE INVENTION 
       [0007]    The object of the present invention is to propose an LCD which utilizes charge-sharing capacitors to change pixel voltage in order to reduce the color washout phenomenon. 
         [0008]    In one aspect of the present invention, a liquid crystal display panel comprises a plurality of data lines, a plurality of scan lines, and a plurality of pixel units, characterized in that the liquid crystal display panel further comprising: at least one inverter electrically connected to a corresponding scan line for inverting the scanning signal; each of the inverters corresponding to at least one of the pixel units; each of the pixel units further comprising: a first transistor and a second transistor electrically connected to a corresponding scan line for conducting the data signal when receiving the scanning signal; a first storage capacitor electrically connected to the first transistor; a second storage capacitor electrically connected to the second transistor; and a charge-sharing capacitor having two ends electrically connected to the second storage capacitor and to the inverter. After the scan line finishes transmitting the scanning signal, a change of an electric potential on the charge-sharing capacitor, resulting from an inverted scanning signal output by the inverter, alters the stored voltage applied on the second storage capacitor, so that the first storage capacitor and the second storage capacitor have different voltagesIn another aspect of the present invention, a liquid crystal display panel comprises a plurality of data lines, a plurality of scan lines, and a plurality of pixel units, characterized in that each of the pixel units further comprising: a first transistor and a second transistor electrically connected to a first scan line; a first storage capacitor electrically connected to the first transistor; a second storage capacitor electrically connected to the second transistor; and a charge-sharing capacitor having two ends electrically connected to the second storage capacitor and to a second scan line in the following row. The first transistor and the second transistor conduct the data signal to the first storage capacitor, the second storage capacitor, and the charge-sharing capacitor after the first scan line finishes transmitting a first scanning signal and the second scan line finishes transmitting a second scanning signal; when the first scan line does not transmit the first scanning signal and the second scan line finishes transmitting the second scanning signal, a change of an electric potential of the charge-sharing capacitor resulting from the second scanning signal alters the stored voltage applied on the second storage capacitor, so that the first storage capacitor and the second storage capacitor have different voltages. 
         [0009]    According to the present invention, when the first scan line delivers first scanning signal and the second scan line does not deliver the second scanning signal, the first and second transistors pre-charge. In addition, a transmission of the first scanning signal from the first scan line is prior to that of the second scanning signal from the second scan line is enabled to transmit. 
         [0010]    In yet another aspect of the present invention, a pixel unit comprises a first transistor and a second transistor electrically connected to a scan line, for conducting a data signal in response to a scanning signal, a first storage capacitor electrically connected to the first transistor, a second storage capacitor electrically connected to the second transistor, and a charge-sharing capacitor having two ends electrically connected to the second storage capacitor and to a driving signal. After the scan line transmits a scanning signal, a change of an electric potential of the charge-sharing capacitor, resulting from a change of the driving signal, alters the stored voltage applied on the second storage capacitor, so that voltages across the first storage capacitor and the second storage capacitor are different. 
         [0011]    According to the present invention, the driving signal is a scanning signal from the next scan line. 
         [0012]    According to the present invention, the driving signal is an inversion of the scanning signal. 
         [0013]    According to the present invention, the first storage capacitor is electrically connected to the first transistor and a first sharing voltage end. The second storage capacitor is electrically connected to the second transistor and a second sharing voltage end. The first and the second sharing voltage end are used for supplying constant voltages, respectively. The constant voltages from the first sharing voltage end from the second sharing voltage end are identical. 
         [0014]    As compared with the prior art, the pixel unit of the LCD panel of the present invention has a first storage capacitor, a second storage capacitor, and a charge-sharing capacitor. The two storage capacitors are electrically connected to two transistors, respectively. Two ends of the charge-sharing capacitor are electrically connected to the second storage capacitor and to a signal end with a different electric potential, respectively. When the pixel unit is activated, the charge-sharing capacitor causes the voltage of the first storage capacitor to be different from that of the second storage capacitor by means of the level of the signal end. Thus, LC molecules on the pixel unit can generate different inclination angles to solve the color washout problem of LCD screens. 
         [0015]    These and other objects of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is an equivalent circuit diagram illustrating a pixel unit according to a first embodiment of the present invention. 
           [0017]      FIG. 2  is a waveform diagram illustrating a scanning signal transmitted by the scan line and voltage applied on the charge-sharing capacitor. 
           [0018]      FIG. 3  is an equivalent circuit diagram illustrating a pixel unit according to a second embodiment of the present invention. 
           [0019]      FIG. 4  is a waveform diagram illustrating a scanning signal transmitted by the scan lines and voltage applied on the charge-sharing capacitor. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Referring to  FIG. 1 ,  FIG. 1  is an equivalent circuit diagram illustrating a pixel unit  100  according to a first embodiment of the present invention. An LCD panel  10  comprises a plurality of scan lines, a plurality of data lines, and a plurality of pixel units  100 . To facilitate illustration and explanation,  FIG. 1  simply illustrates a pixel unit  100 , a scan line G 1 , and a data line S 1 . Both of the scan line G 1  and the data line S 1  are electrically connected to the pixel unit  100 . The pixel unit  100  comprises a first thin film transistor T 1 , a second thin film transistor T 2 , a first pixel electrode  108   a , a second pixel electrode  108   b , a charge-sharing capacitor Cs, a first storage capacitor C st1 , and a second storage capacitor C st2 . The first thin film transistor T 1  and the second thin film transistor T 2  are electrically connected to the data line S 1  and the scan line G 1 . And, the first pixel electrode  108   a  and the second pixel electrode  108   b  are electrically connected to the first thin film transistor T 1  and the second thin film transistor T 2 , respectively. The first storage capacitor C st1  acts as a holding capacitor of the pixel unit  100  on one side, and the second storage capacitor C st2  acts as a holding capacitor of the pixel unit  100  on the other side. Two ends of the first storage capacitor C st1  are electrically connected to the first thin film transistor T 1  and a first sharing voltage end V com1 . Two ends of the second storage capacitor C st2  are electrically connected to the second thin film transistor T 2  and a second sharing voltage end V com2 . The two sharing voltage ends V com1 , V com2  are for supplying constant voltage. Preferably, the voltages from the two sharing voltage ends V com1 , V com2  are identical. The charge-sharing capacitor Cs is connected to the drain of the second thin film transistor T 2  with the top electrode plate and to voltage of the scan line  104  inverted by an inverter INV, with the bottom electrode plate. 
         [0021]    Referring to  FIG. 1  and  FIG. 2 ,  FIG. 2  is a waveform diagram illustrating a scanning signal transmitted by the scan line G 1  and voltage applied on the charge-sharing capacitor Cs. During the t 0 -t 1  period, the scanning signal transmitted by the scan line G 1  turns on the first thin film transistor T 1  and the second thin film transistor T 2 . Afterwards, a data signal transmitted by the data line S 1 , passing through the first thin film transistor T 1  and the second thin film transistor T 2 , is conducted to the first storage capacitor C st1 , the second storage capacitor C st2 , the charge-sharing capacitor Cs, the first pixel electrode  108   a , and the second pixel electrode  108   b . The first pixel electrode  108   a  and the second pixel electrode  108   b  adjust the moving direction of LC modules based on voltage applied on the data signal. Meanwhile, the first storage capacitor C st1 , the second storage capacitor C st2 , and the charge-sharing capacitor Cs store the voltage applied on the data signal, so that the voltage V st1  applied on the first storage capacitor C st1  and the voltage V st2  applied on the second storage capacitor C st2  are roughly the same. But the other one end of the charge-sharing capacitor Cs is electrically connected to the inverter INV, which outputs an inverted scanning signal, so the voltage across the charge-sharing capacitor Cs is different from that across the second storage capacitor C st2 . During the t 1 -t 2  period, the electrically connected charge-sharing capacitor Cs and second storage capacitor C st2  share the charge, which causes the voltage V st2  applied on the second storage capacitor C st2  to be altered. Accordingly, the voltage V st2  is different from the voltage V st1  applied on the first storage capacitor C st1 . The first pixel electrode  108   a  and the second pixel electrode  108   b  determine angles of rotation of LC molecules based on voltages V st1  and V st2 , so the color washout problem can be solved effectively based on different angles of rotation of the LC molecules. If the pixel unit  100  is decided to be applied to an MVA LCD, the pixel unit  100  can be designed to let the first and second storage capacitors C st1  and C st2  have two different voltages V st1  and V st2  by adjusting the capacity value of the charge-sharing capacitor Cs. Thus, the color washout problem can be solved. 
         [0022]    Referring to  FIG. 3 ,  FIG. 3  is an equivalent circuit diagram illustrating a pixel unit  200  according to a second embodiment of the present invention. An LCD panel  20  comprises a plurality of scan lines, a plurality of data lines, and a plurality of pixel units  200 . To facilitate illustration and explanation,  FIG. 3  simply illustrates two pixel units  200 , scan lines G 1 , G 2 , and G 3 , and a data line S 1 . Both of the scan lines G 1 , G 2 , and G 3 , and the data line S 1  are electrically connected to the pixel units  200 . Each of the pixel units  200  comprises a first thin film transistor T 1 , a second thin film transistor T 2 , a first pixel electrode  208   a , a second pixel electrode  208   b , a charge-sharing capacitor Cs, a first storage capacitor C st1 , and a second storage capacitor C st2 . The first thin film transistor T 1  and the second thin film transistor T 2  are electrically connected to the data line S 1  and the scan line G 1 . Besides, the first pixel electrode  208   a  and the second pixel electrode  208   b  are electrically connected to the first thin film transistor T 1  and the second thin film transistor T 2 , respectively. The first storage capacitor C st1  acts as a holding capacitor on one side of the pixel unit  200 , and the second storage capacitor C st2  acts as a holding capacitor on the other side. Two ends of the first storage capacitor C st1  are electrically connected to the first thin film transistor T 1  and a first sharing voltage end V com1 ; two ends of the second storage capacitor C st2  are electrically connected to the second thin film transistor T 2  and a second sharing voltage end V com2 . The two sharing voltage ends V com1 , V com2  are for supplying constant voltage. Preferably, the voltages from the two sharing voltage ends V com1 , V com2  are identical. Two ends of the charge-sharing capacitor Cs are electrically connected to the scan line G 2  and the second storage capacitor C st2 , respectively. 
         [0023]    Referring to  FIG. 3  and  FIG. 4 ,  FIG. 4  is a waveform diagram illustrating a scanning signal transmitted by the scan lines G 1  and G 2  and voltage applied on the charge-sharing capacitor Cs. At first, the scan line G 1  emits a scanning signal in advance during the t 0 -t 1  period to turn on the first thin film transistor T 1  and the second thin film transistor T 2 , so that the first thin film transistor T 1  and the second thin film transistor T 2  can achieve pre-charge before the data signal is conducted. 
         [0024]    Next, the scanning signal of the scan line G 1  continues activating the first thin film transistor T 1  and the second thin film transistor T 2  during the t 1 -t 2  period. The first and second thin film transistors T 1  and T 2  have been activated for a period of time, so they are completely activated during the t 1 -t 2  period. Thus, the data signal transmitted from the data line S 1  can be conducted to the first storage capacitor C st1 , the second storage capacitor C st2 , the charge-sharing capacitor Cs, the first pixel electrode  208   a , and a second pixel electrode  208   b  after passing through the first thin film transistor T 1  and the second thin film transistor T 2  completely. The first pixel electrode  208   a  and the second pixel electrode  208   b  adjust the moving direction of LC modules based on the voltage of the data signal. Meanwhile, the first storage capacitor C st1 , the second storage capacitor C st2 , and the charge-sharing capacitor Cs store the voltage of the data signal, so the voltage V st1  of the first storage capacitor C st1  and the voltage V st2  of the second storage capacitor C st2  are roughly the same. At this time, the scan line G 2  also emits the scanning signal to prompt the first thin film transistor T 1  and the second thin film transistor T 2  of the pixel unit  200  in the following row to enter a pre-charge status. 
         [0025]    During the t 2 -t 3  period, the other end of the charge-sharing capacitor Cs is electrically connected to the scan line G 2 . The scan line G 2  continues outputting a scanning signal while the scan line G 1  does not output any scanning signal at this period. At this time, the pixel electrodes  208   a  and  208   b  can remain the same for grayscale output based on the voltage stored by the first and second storage capacitors C st1  and C st2 . 
         [0026]    During the t 3 -t 4  period, the scan line G 2  does not transmit any pulse of the scanning signal. The scanning signal without any pulse is served as a driving signal fed to the charge-sharing capacitor Cs, so the voltage across the charge-sharing capacitor Cs is different from that across the second storage capacitor C st2 . During this period, the electrically connected charge-sharing capacitor Cs and second storage capacitor C st2  share the charge, which causes the voltage V st2  applied on the second storage capacitor C st2  to be altered. Accordingly, the voltage V st2  is different from the voltage V st1  applied on the first storage capacitor C st1  The first pixel electrode  208   a  and the second pixel electrode  208   b  determine angles of rotation of LC molecules based on voltages V st1  and V st2 , so the color washout problem can be effectively solved based on different angles of rotation of the LC molecules. If the pixel unit  200  is decided to be applied to an MVA LCD, the pixel unit  200  can be designed to let the first and second storage capacitors C st1  and C st2  have two different voltages V st1  and V st2  by adjusting the capacity value of the charge-sharing capacitor Cs. Thus, the color washout problem can be solved. 
         [0027]    Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.