Abstract:
A liquid crystal display device comprises a pixel matrix including a plurality of subpixels, wherein the voltage polarities of two horizontal adjacent subpixels are opposite to one another, and the voltage polarity of one subpixel in four serial subpixels along a diagonal direction is opposite to the voltage polarities of the other three subpixels.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device employing a polarity inversion driving method to improve the display quality thereof. 
         [0003]    2. Description of the Related Art 
         [0004]    Thin film transistor (TFT) liquid crystal displays (LCDs) generate images by applying voltages to field-generating subpixel electrodes to generate electrical fields, which align the liquid crystal molecules in a liquid crystal layer to produce the images. Generally, the TFTs are arranged as shown in  FIG. 1 . A TFT-LCD device  100  comprises a plurality of TFTs, a plurality of gate lines G 1 -Gm and a plurality of data lines D 1 -Dn disposed orthogonally to the gate lines G 1 -Gm. The TFTs T 11 -T mn  are disposed close to the cross-points of the gate lines G 1 -Gm and the data lines D 1 -Dn, and are connected correspondingly to subpixels P 11 -P mn . During the image display process, the liquid crystal molecules in the region of each of subpixels P 11 -P mn  are driven by a respective voltage polarity applied by the respective TFT T 11 -T mn  in each frame, and the voltage polarity of each subpixel is reversed between plus and minus from one frame to another. The methods used to drive the subpixels in every frame comprises a frame inversion driving method, a line inversion driving method, a column inversion driving method, a dot inversion driving method and a two-column inversion driving method. 
         [0005]    The frame inversion driving method applies the same voltage polarity to each subpixel in every frame, and the voltage polarity of each subpixel is reversed from one frame to another. However, asymmetry between the positive pixel voltage and the negative pixel voltage arises due to capacitive coupling between the gate and the source/drain of a TFT so that a flicker occurs on the entire picture screen of an LCD. 
         [0006]    When an LCD is driven by the line inversion driving method, the polarities of the voltage applied to the subpixels are reversed on a line-by-line basis. Because the polarities of the voltages of two adjacent lines are opposite, the flicker phenomenon can be eliminated. However, the subpixels along each line have the same polarity of voltage, and such a polarity arrangement causes serious crosstalk in the line direction. 
         [0007]    The dot inversion driving method provides the reversed polarity of voltage to two adjacent subpixels in both the row and column directions respectively so that the flicker phenomenon and the crosstalk can be suppressed. However, when the intensity of an LCD is reduced by alternately turning off a portion of the subpixels, the turned-on subpixels in every frame may have the same voltage polarity and then the flicker phenomenon occurs.  FIG. 2  shows an adjustment method of the luminous intensity of a prior art TFT-LCD. As shown in  FIG. 2 , the LCD  200   a  employs a dot inversion driving method. In order to reduce the intensity, a portion of the subpixels are turned off. Referring to the exemplary portion  202  of the three subpixels, the subpixel corresponding to red (R), having a positive polarity, and the subpixel corresponding to blue (B), also having a positive polarity, are both in the turned-on state, while the subpixel corresponding to green (G), having a negative polarity, is in the turned-off state. In the exemplary adjacent portion  204 , the subpixel corresponding to red (R), having a positive polarity, and the subpixel corresponding to blue (B), having a positive polarity, are both in the turned-off state, while the subpixel corresponding to green (G), having a negative polarity, is in the turned-on state. Such an on/off arrangement can reduce the intensity of the LCD by half and reduce electricity consumption, yet has no negative effect on the color balance of the LCD. However, the turned-on subpixels do have the same polarities in each frame, so screen flicker may still occur. 
         [0008]      FIG. 3  shows another adjustment method of the luminous intensity of a prior art TFT-LCD. The pixels of a TFT-LCD  200   b  are alternately turned off in a checkerboard pattern. The intensity of the TFT-LCD is cut in half and the electricity consumption thereof is reduced. As shown in  FIG. 3 , pixel  302  and pixel  304  of the TFT-LCD are in the turned-on state. The pixel  302  includes two subpixels having positive polarities and one subpixel having negative polarity, and the pixel  304  in the same row also includes two positive polarities and one negative polarity. Therefore, when the adjustment method is applied, the total number of subpixels having positive polarities is higher than the total number of subpixels having negative polarities, and such a situation can easily cause serious crosstalk in the row direction. 
         [0009]    The two-column inversion driving method may avoid the flicker and crosstalk issues that the dot inversion driving method suffers from. However, the two-column inversion driving method introduces a color imbalance issue.  FIG. 4  shows an adjustment method of the luminous intensity of a prior art TFT-LCD  400  driven by a two-column inversion driving method. The total numbers of positive polarities and negative polarities of the row that includes the turned-on pixel  402  and the turned-on pixel  404  are the same so that the polarities of the row are in balance and there is no cross talk in the row direction. However, due to the parasitic capacitance coupling effect to common electrode signals and the interference of the electrical field from data lines D 1 -Dn to subpixels, the two-column inversion driving method results in color imbalance. For example, in the turned-on pixel  402 , the subpixel corresponding to R has positive polarity, and because the adjacent subpixel corresponding to G also has positive polarity, the luminous intensity of the subpixel corresponding to R will be lower; on the other hand, because the subpixel corresponding to B and next to the subpixel corresponding to G has negative polarity, the luminous intensity of the subpixel corresponding to G will be higher. As a result, the color of the pixel  402  will shift toward green. In the turned-on pixel  408 , the subpixel corresponding to G has a negative polarity and the next subpixel corresponding to B also has a negative polarity so that the luminous intensity of the subpixel corresponding to G is lower and the color of the pixel  408  shifts toward purple. Consequently, the color of the image provided by the LCD  400  will alternate between green and purple along the row direction. 
         [0010]    According to the above description, there is no driving method that can make TFT-LCDs provide images with good quality under different driving situations such as intensity adjustment by turning off a portion of the pixels. Therefore, a new driving method that can be used in different driving situations without any shortcomings is required by the LCD industry. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention proposes a liquid crystal display device, which employs a polarity inversion driving method. Under a particular display mode, two adjacent pixels will have different color subpixels that have higher luminous intensity. As such, the liquid crystal display will not display images with green and purple alternating colors across the images. 
         [0012]    The present invention proposes a liquid crystal display device, which comprises a pixel matrix. The pixel matrix comprises a plurality of subpixels, wherein the voltage polarities of any two row-wise adjacent subpixels are opposite to one another and the voltage polarity of one subpixel in any four serial subpixels along any diagonal direction is opposite to the voltage polarities of the other three subpixels. 
         [0013]    The present invention proposes a liquid crystal display device, which comprises a first pixel row, a second pixel row, a third pixel row, and a fourth pixel row. The first pixel row comprises a plurality of first subpixels along a horizontal direction, wherein the voltage polarities of the first subpixels are repetitiously applied in an order of a first polarity, the first polarity, a second polarity, and the second polarity from left to right. The second pixel row comprises a plurality of second subpixels along a horizontal direction, wherein the voltage polarities of the second subpixels are repetitiously applied in an order of the second polarity, the second polarity, the first polarity, and the first polarity from left to right. The third pixel row comprises a plurality of third subpixels along a horizontal direction, wherein the voltage polarities of the third subpixels are repetitiously applied in an order of the second polarity, the first polarity, the first polarity, and the second polarity from left to right. The fourth pixel row comprises a plurality of fourth subpixels along a horizontal direction, wherein the voltage polarities of the fourth subpixels are repetitiously applied in an order of the first polarity, the second polarity, the second polarity, and the first polarity from left to right; wherein the first polarity and the second polarity are opposite, and a first one of the first subpixels, a first one of the second subpixels, a first one of the third subpixels, and a first one of the fourth subpixels are aligned along a vertical direction. 
         [0014]    In one embodiment, the first electrode strips are disposed along a first direction and the touch panel circuitry further comprises a plurality of substantially parallel second electrode strips, which are configured for generating a touch signal, and are arrayed along a second direction, wherein the first direction and the second direction can be mutually orthogonal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention will be described according to the appended drawings in which: 
           [0016]      FIG. 1  is a diagram for illustrating a TFT pixel arrangement in a prior art TFT-LCD; 
           [0017]      FIG. 2  shows an adjustment method of the luminous intensity of a prior art TFT-LCD; 
           [0018]      FIG. 3  shows another adjustment method of the luminous intensity of a prior art TFT-LCD; 
           [0019]      FIG. 4  shows an adjustment method of the luminous intensity of a prior art TFT-LCD driven by a two-column inversion driving method; 
           [0020]      FIG. 5  is a diagram for illustrating an inversion driving method in a TFT-LCD device and an adjustment method of the luminous intensity of the TFT-LCD device according to one embodiment of the present invention; 
           [0021]      FIG. 6  is an adjustment method of the luminous intensity of the TFT-LCD device according to another embodiment of the present invention; and 
           [0022]      FIG. 7  is an adjustment method of the luminous intensity of the TFT-LCD device according to the other embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIG. 5  is a diagram for illustrating an inversion driving method in a TFT-LCD device  500   a  and an adjustment method of the luminous intensity of the TFT-LCD device  500   a  according to one embodiment of the present invention. The TFT-LCD device  500   a  is driven by the inversion driving method such that the polarity of voltage is repetitiously reversed in a unit of two subpixels in each row of subpixels. All rows of subpixels comprise four row pixel polarity patterns, and the four row pixel polarity patterns are repetitiously arranged through the TFT-LCD device  500   a . As shown in  FIG. 5 , the first two rows (Row  1  and Row  2 ) are respectively arranged according to two row pixel polarity patterns such that the polarity of voltage is repetitiously reversed in a unit of two subpixels in each row of subpixels and the polarities of voltage of two adjacent subpixels in the column direction are reversed. The next two rows (Row  3  and Row  4 ) are respectively arranged according to the other two row pixel polarity patterns such that the polarity of voltage is also repetitiously reversed in a unit of two subpixels in each row of subpixels and the polarities of voltage of two adjacent subpixels in the column direction are reversed, but each pixel (including R, G, and B subpixels) of the two rows is shifted by one pixel-position relative to the first two rows respectively in round-robin fashion. In the present embodiment, Row  3  and Row  4  are obtained by shifting each pixel (including R, G, and B subpixels) of Row  1  and Row  2  by one pixel-position to the left in round-robin fashion. 
         [0024]    Referring to  FIG. 5 , the polarity arrangement of Row  1  is “plus, plus, minus, minus, . . . (++−− . . . )”; the polarity arrangement of the first pixel (RGB) is “plus, plus, minus (++−)”; and the polarity arrangement of the second pixel (RGB) is “minus, minus, plus (−−+).” The polarity arrangement of Row  2  is “minus, minus, plus, plus, . . . (−−++ . . . )”; the polarity arrangement of the first pixel (RGB) is “minus, minus, plus (−−+)”; and the polarity arrangement of the second pixel (RGB) is “plus, minus, minus (+−−).” The polarities of the subpixels of Row  1  and Row  2  are correspondingly reversed. The polarity arrangement of Row  3  is “minus, plus, plus, minus, . . . (−++− . . . ).” The polarity arrangement begins with the first pixel (RGB), the polarity arrangement of which is “minus, plus, plus (−++).” The polarity arrangement of Row  3  is the same as the sequential pixels of Row  1  using the second pixel of Row  1  as the first pixel. The polarity arrangement of Row  4  is “plus, minus, minus, plus, . . . (−++− . . . ).” The polarity arrangement of the first pixel (RGB) is “plus, minus, minus (+−−).” The polarity arrangement of Row  4  is the same as the sequential pixels of Row  2  using the second pixel of Row  2  as the first pixel. The polarity arrangements of Row  1  to Row  4  are repeated for Row  5  to Row  8  respectively and for successive rows. In the present embodiment, in Rows  1 - 4 , the arrangement of colors corresponding to subpixels is in the sequence of red (R), green (G), and blue (B). In other embodiments, the color arrangement corresponding to subpixels can be a sequential repetition of any combination of R, G, and B. 
         [0025]    Moreover, referring to  FIG. 5 , the voltage polarity of one subpixel in any four serial subpixels along any diagonal direction ( 502   a  or  502   b ) is opposite to the voltage polarities of the other three subpixels, and in each diagonal direction, a certain polarity arrangement continues repetitiously. 
         [0026]    Referring to  FIG. 5 , under the operation mode with a checkerboard-like pattern such that subpixels treated in a unit are partially turned on and off (the subpixels with cross lines represent turned-off subpixels in  FIG. 5 ), the polarity arrangement of the turned-on subpixels separated by one turned-off subpixel is alternately reversed along both row and column directions so as to avoid a flickering screen. Moreover, each row has equal numbers of positive and negative polarity subpixels so that the crosstalk in the row direction is suppressed. 
         [0027]      FIG. 6  is an adjustment method of the luminous intensity of the TFT-LCD device  500   b  according to another embodiment of the present invention. Under the pixel operation mode with a checkerboard-like pattern, pixels treated in a unit are partially turned on and off. Each row has equal numbers of positive and negative polarity subpixels similar to the embodiment shown in  FIG. 5  so that the crosstalk in the row direction is suppressed. In the first column of pixels, for example, the subpixel in pixel  602 , corresponding to R, has positive polarity, the subpixel corresponding to G has positive polarity, and the subpixel corresponding to B has negative polarity. Due to such a polarity arrangement, the luminous intensity of the subpixel corresponding to R is comparatively lower and the luminous intensity of the subpixel corresponding to G is comparatively higher. The subpixel in pixel  604 , corresponding to R, has negative polarity, the subpixel corresponding to G has positive polarity, and the subpixel corresponding to B has positive polarity. Due to such a polarity arrangement, the luminous intensity of the subpixel corresponding to G is comparatively lower and the luminous intensity of the subpixel corresponding to R is comparatively higher. Such a result can minimize color imbalance of a screen image, which causes the color of the image to alternate between green and purple along a line direction. Consequently, the compensation for color imbalance between turned-on pixels (for example, the lower luminous intensity of the R subpixel in pixel  602  is compensated by the R subpixel in pixel  604  which has higher luminous intensity; the lower luminous intensity of the G subpixel in pixel  604  is compensated by the G subpixel in pixel  602  which has higher luminous intensity) can reduce asymmetry between the positive pixel voltage and the negative pixel voltage due to capacitive coupling between the gate and the source/drain of a TFT, and the interference of the electrical field from data lines D 1 -Dn to subpixels so that the color of the screen image can be uniformly provided without suffering from the issues of prior art driving methods. 
         [0028]      FIG. 7  is an adjustment method of the luminous intensity of the TFT-LCD device  500   c  according to the other embodiment of the present invention. Under the operation mode such that pixels treated in a unit are alternately turned on and off, each row has equal numbers of positive and negative polarity subpixels, just as with the embodiment shown in  FIG. 5 , so that the crosstalk in the row direction is suppressed. In the first column of pixels, for example, the subpixel in pixel  702 , corresponding to R, has positive polarity, the subpixel corresponding to G has positive polarity, and the subpixel corresponding to B has negative polarity. The subpixel in pixel  704 , corresponding to R, has negative polarity, the subpixel corresponding to G has negative polarity, and the subpixel corresponding to B has positive polarity. The subpixel in pixel  706 , corresponding to R, has negative polarity, the subpixel corresponding to G has positive polarity, and the subpixel corresponding to B has positive polarity. The subpixel in pixel  706 , corresponding to R, has negative polarity, the subpixel corresponding to G has positive polarity, and the subpixel corresponding to B has positive polarity. The subpixel in pixel  708 , corresponding to R, has positive polarity, the subpixel corresponding to G has negative polarity, and the subpixel corresponding to B has negative polarity. Such a polarity arrangement in pixels has a similar effect as the embodiment shown in  FIG. 6  and can minimize color imbalance of a screen image causing the color of the image to alternate between green and purple along a line direction. The color imbalance is varied in a unit of two rows and each unit is compensated by the next unit. For example, the lower luminous intensity of the R subpixels in pixel  702  and in pixel  704  is compensated by the R subpixels in pixel  706  and in pixel  708  which have higher luminous intensity; the lower luminous intensity of the G subpixels in pixel  706  and in pixel  708  is compensated by the G subpixels in pixel  702  and in pixel  704  which have higher luminous intensity. Such an effect of compensation can reduce asymmetry between the positive pixel voltage and the negative pixel voltage due to capacitive coupling between the gate and the source/drain of a TFT, and the interference of the electrical field from data lines D 1 -Dn to subpixels so that the color of the screen image can be uniformly provided without implying the issues of prior art driving methods. 
         [0029]    The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by persons skilled in the art without departing from the scope of the following claims.