Patent Publication Number: US-2016231605-A1

Title: Rgbw tft lcd having reduced horizontal crosstalk

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application No. 201510065080.3 filed on Feb. 9, 2015, the contents of which are incorporated by reference herein. 
     FIELD 
     The subject matter herein generally relates to a TFT LCD (thin film transistor liquid crystal display), and particularly to a TFT LCD having an RGBW (red, green, blue, white) TFT array substrate with a reduced horizontal crosstalk. 
     BACKGROUND 
     TFT LCDs have become the most popular flat displays since they have advantages of compactness, low heat generation, long life and visual comfort. In general a TFT LCD includes a backlight module, a first polarizer, a TFT array substrate, a liquid crystal layer, a color filter and a second polarizer. The TFT array substrate forms a plurality of pixels thereon. The liquid crystal layer contains a plurality liquid crystals therein. Originally, each pixel includes three sub-pixels, i.e., a red sub-pixel, a green sub-pixel, and a blue sub-pixel. For such an RGB TFT LCD, the backlight module needs consuming more power in order to have sufficient light passing through the color filter. 
     To overcome the disadvantage of the RGB TFT LCD, an RGBW TFT LCD is developed, in which each pixel includes a red sub-pixel, a green sub-pixel, a blue sub-pixel, and a white sub-pixel. A transparent area corresponding to the white sub-pixel is defined in the color filter, whereby a light transmittance of the color filter is improved, and the power consumption required by the backlight module can be reduced. 
     However, for the RGBW TFT LCD, it confronts a problem of horizontal crosstalk which does not occur in the RGB TFT LCD. When the RGBW TFT LCD shows a one-colored segment (for example, an entirely green segment), every pixel in the segment has the same polarity, whereby Vcom couples cannot offset from each other, whereby a horizontal crosstalk happens which results in an uneven grey level beside the green segment. Here Vcom couple means a couple between data lines and an upper common electrode, i.e., CF (color filter) layer Vcom, for providing a bias across the liquid crystals in the liquid crystal layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is diagrammatic view of an RGBW TFT LCD in accordance with the present disclosure. 
         FIG. 2  is a diagrammatic view of a TFT array substrate of the RGBW TFT LCD in accordance with a first embodiment of the present disclosure. 
         FIG. 3  is a circuit diagram of a sub-pixel of the TFT array substrate of the RGBW TFT LCD of  FIG. 2 . 
         FIG. 4  is a diagrammatic view of a TFT array substrate of the RGBW TFT LCD in accordance with a second embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features. The description is not to be considered as limiting the scope of the embodiments described herein. 
     Several definitions that apply throughout this disclosure will now be presented. 
     The term “coupled” is defined as connected, whether directly or indirectly through intervening components, and is not necessarily limited to physical connections. The connection can be such that the objects are permanently connected or releasably connected. The term “substantially” is defined to be essentially conforming to the particular dimension, shape or other word that substantially modifies, such that the component need not be exact. For example, substantially cylindrical means that the object resembles a cylinder, but can have one or more deviations from a true cylinder. The term “comprising” means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in a so-described combination, group, series and the like. 
     The present disclosure is described in relation to an RGBW (red-green-blue-white) TFT (thin film transistor) LCD (liquid crystal display)  1 , which can be used in a screen of a mobile phone for example a smart phone, a monitor of a computer, a screen of a laptop, a screen of a television set, or a screen of a tablet computer. 
       FIG. 1  illustrates a diagrammatic view of the RGBW TFT LCD  1  having, along an upward direction, a backlight module  10 , a first polarizer  20 , a TFT array substrate  30 , a liquid crystal layer  40 , a color filter  50  and a second polarizer  60 . The TFT array substrate  30 , the liquid crystal layer  40 , the color filter  50  and a driver circuit assembly (not shown) in combination construct an LCD module  70 . The backlight module  10 , the first polarizer  20 , the TFT array substrate  30 , the liquid crystal layer  40 , the color filter  50  and the second polarizer  60  each have a substantially rectangular cross section. 
     The backlight module  10  can include LEDs (light emitting diodes) or CCFLs (cold cathode fluorescent lamps) as a light source for generating white light radiating upwardly through the first polarizer  20 , the TFT array substrate  30 , the liquid crystal layer  40 , the color filter  50  and finally the second polarizer  60 . The first polarizer  20  polarizes the light, which means that only the orthogonal direction of light is allowed to pass through the first polarizer  20  to reach the TFT array substrate  30 . The liquid crystal layer  40  includes a plurality of liquid crystals therein. An direction of arrangement of the liquid crystals can be changed in accordance with a change of a bias across the liquid crystal layer  40 , thereby to adjust amount of light through the liquid crystal layer  40 . The color filter  50  in accordance with the present disclosure is an RGBW color filter and has a plurality of pixels each including a green sub-pixel, a red sub-pixel, a blue sub-pixel and a white sub-pixel. The white sub-pixels are transparent whereby a transmittance of the color filter  50  can be increased, in comparison with the RGB color filter, whereby the power needed by the backlight module  10  can be decreased. The function of the second polarizer  60 , similar to the first polarizer  20 , is used to allow only the orthogonal direction of light to pass therethrough. 
     Referring to  FIG. 2 , a circuit  31  of the TFT array substrate  30  of the RGBW TFT LCD  1  in accordance with a first embodiment of the present disclosure is shown. The circuit  31  is arranged in a manner than it is driven by column inversion and includes a plurality of pixels  311  arranged in a matrix. Each pixel  311  consists of a red sub-pixel  312 , a green sub-pixel  314 , a blue sub-pixel  316  and a white sub-pixel  318 . The four sub-pixels  312 ,  314 ,  316 ,  318  are arranged in a substantially square matrix (i.e., 2×2 matrix) with the red and green sub-pixels  312 ,  314  arranged in a same row and the blue and white sub-pixels  316 ,  318  arranged in a neighboring same row, while the red and white sub-pixels  312 ,  318  arranged in a same column and the green and blue sub-pixels  314 ,  316  arranged in a neighboring same column. In their respective same row, the red and green sub-pixels  312 ,  314  are alternated, and the blue and white sub-pixels  316 ,  318  are alternated. In their respective same column, the red and white sub-pixels  312 ,  318  are alternated, and the green and blue sub-pixels  314 ,  316  are alternated. 
     Along the column direction (horizontal direction), dummy data lines  330  and data lines  332  are parallel to each other and alternately arranged. Each of the dummy data and data lines  330 ,  332  is located between two columns of the sub-pixels. The dummy data line  330  is arranged between two adjacent pixels, and the data line  332  is arranged between two adjacent sub-pixels of each pixel. Two scan lines  320 ,  322  are located between two rows of the sub-pixels. The scan lines  320 ,  322  are orthogonal to and intersecting with the dummy data and data lines  330 ,  332 . The data lines  332  and the scan lines  320 ,  322  are electrically coupled to the sub-pixels via the thin film transistors, while the dummy data lines  330  are electrically coupled to the sub-pixels through a lower common electrode (Array Vcom) and storage capacitors (Csts). 
     Referring to  FIG. 3 , taking the green sub-pixel  314  of  FIG. 2  as an example, the dummy data line  330  in connection therewith electrically couples to a lower common electrode (i.e., Array Vcom)  400  in electrical coupling with a storage capacitor (i.e., Cst)  402  for the sub-pixel  314  whereby a resistance of the lower common electrode  400  can be lowered to shorten the charging time of the storage capacitor  402  thereby to improve the evenness of the display quality throughout the RGBW TFT LCD  1 . The storage capacitors  402  and the lower common electrode  400  therefor are well known by those skilled in the art; detailed descriptions thereof are omitted here. 
     Returning to  FIG. 2 , the red sub-pixel  312  is electrically connected with one of the scan lines  322  immediately thereabove and one of the data lines  332  adjacent thereto by a thin film transistor  313 . The thin film transistor  313  has a source electrode (not labeled) in electrical coupling with the data line  332 , a gate electrode (not labeled) in electrical coupling with the scan line  322  and a drain electrode (not labeled) in electrical coupling with a pixel electrode (not labeled) of the red sub-pixel  312 . 
     The green sub-pixel  314  is electrically connected with one of the scan lines  320  immediately therebelow and one of the data lines  332  adjacent thereto by a thin film transistor  315 , wherein the connected data line  332  is commonly connected with the red sub-pixel  312 . The thin film transistor  315  has a source electrode (not labeled) in electrical coupling with the data line  332 , a gate electrode (not labeled) in electrical coupling with the scan line  320  and a drain electrode (not labeled) in electrical coupling with a pixel electrode (not labeled) of the green sub-pixel  314 . 
     The blue sub-pixel  316  is electrically connected with one of the scan lines  320  immediately therebelow and one of the data lines  332  adjacent thereto by a thin film transistor  317 , wherein the connected data line  332  is commonly connected with the red and green sub-pixels  312 ,  314 . The thin film transistor  317  has a source electrode (not labeled) in electrical coupling with the data line  332 , a gate electrode (not labeled) in electrical coupling with the scan line  320  and a drain electrode (not labeled) in electrical coupling with a pixel electrode of the blue sub-pixel  316 . 
     The white sub-pixel  318  is electrically connected with one of the scan lines  322  immediately thereabove and one of the data lines  332  adjacent thereto by a thin film transistor  319 , wherein the connected data line  332  is commonly connected with the red, green and blue sub-pixels  312 ,  314 ,  316 . The thin film transistor  319  has a source electrode (not labeled) in electrical coupling with the data line  332 , a gate electrode (not labeled) in electrical coupling with the scan line  322  and a drain electrode (not labeled) in electrical coupling with a pixel electrode of the white sub-pixel  318 . Since in this embodiment, the sub-pixels are driven by column inversion, along each of the data lines  332 , the sub-pixels in electrical connection therewith have the same polarity. 
     In operation, the data lines  332  are alternately supplied with positive voltage and negative voltage, whereby the red (green, blue, white) sub-pixel  312  ( 314 ,  316 ,  318 ) and a neighboring red (green, blue, white) sub-pixel in the same row have opposite polarities. Accordingly when the RGBW TFT LCD  1  is required to show a single color of one of the red, green blue and white colors, the pixels  311  in two neighboring columns have opposite polarities, i.e., one being positive and the other being negative. By such arrangement, the coupling effects caused by capacitors (i.e., Cscs)  404  ( FIG. 3 ) of each two neighboring columns of the pixels  311  on the waveform of an upper common electrode (i.e., CF (color filter) layer Vcom, not shown) can offset from each other to obviate the horizontal crosstalk, wherein the capacitor  404  ( FIG. 3 ) is a capacitor interconnecting a corresponding data line  332  and the upper common electrode for supplying a bias across the liquid crystal layer  40 . The upper common electrode and the capacitors  404  (FG  3 ) for connecting the upper common electrode and the data lines  332  are well known by those skilled in the art; detailed descriptions thereof are omitted here. 
     Referring to  FIG. 4 , a circuit  34  of the TFT array substrate  30  of the RGBW TFT LCD  1  in accordance with a second embodiment of the present disclosure is shown. The circuit  34  is arranged in a manner that it is driven by dot inversion and includes a plurality of pixels  341  arranged in a matrix. Each pixel  341  consists of a red sub-pixel  342 , a green sub-pixel  344 , a blue sub-pixel  346  and a white sub-pixel  348 . The four sub-pixels  342 ,  344 ,  346 ,  348  are arranged in a substantially square matrix (i.e., 2×2 matrix) with the red and green sub-pixels  342 ,  344  arranged in a same row and the blue and white sub-pixels  346 ,  348  arranged in a neighboring same row, while the red and white sub-pixels  342 ,  348  arranged in a same column and the green and blue sub-pixels  344 ,  346  arranged in a neighboring same column. 
     Along the column direction (horizontal direction), dummy data lines  360  and data lines  362  are parallel to each other and alternately arranged. Each of the dummy data and data lines  360 ,  362  is located between two columns of the sub-pixels. The dummy data line  360  is arranged between two adjacent pixels, and the data line  362  is arranged between two adjacent sub-pixels of each pixel. Two scan lines  350 ,  352  are located between two rows of the sub-pixels. The scan lines  350 ,  352  are orthogonal to and intersecting with the dummy data and data lines  360 ,  362 . The data lines  362  and the scan lines  350 ,  352  are electrically coupled to the sub-pixels, while the dummy data lines  360  do not electrically couple with the sub-pixels. The dummy data lines  360  electrically couple to the lower common electrode (not shown) in electrically coupling with the storage capacitors (not shown) whereby a resistance of the lower common electrode can be lowered to shorten the charging time of the storage capacitors thereby to improve the evenness of the display quality throughout the RGBW TFT LCD  1 . 
     The red sub-pixel  342  is electrically connected with one of the scan lines  352  immediately thereabove and one of the data lines  362  adjacent thereto by a thin film transistor  343 . The thin film transistor  343  has a source electrode (not labeled) in electrical coupling with the data line  362 , a gate electrode (not labeled) in electrical coupling with the scan line  352  and a drain electrode (not labeled) in electrical coupling with a pixel electrode (not labeled) of the red sub-pixel  342 . 
     The green sub-pixel  344  is electrically connected with one of the scan lines  350  immediately therebelow and one of the data lines  362  adjacent thereto by a thin film transistor  345 , wherein the connected data line  363  is commonly connected with the red sub-pixel  342 . The thin film transistor  345  has a source electrode (not labeled) in electrical coupling with the data line  362 , a gate electrode (not labeled) in electrical coupling with the scan line  350  and a drain electrode (not labeled) in electrical coupling with a pixel electrode (not labeled) of the green sub-pixel  344 . 
     The blue sub-pixel  346  is electrically connected with one of the scan lines  350  immediately therebelow and one of the data lines  362  adjacent thereto by a thin film transistor  347 , wherein the connected data lines  362  commonly connected with the red and green sub-pixels  342 ,  344 . The thin film transistor  347  has a source electrode (not labeled) in electrical coupling with the data line  362 , a gate electrode (not labeled) in electrical coupling with the scan line  350  and a drain electrode (not labeled) in electrical coupling with a pixel electrode of the blue sub-pixel  346 . 
     The white sub-pixel  348  is electrically connected with one of the scan lines  352  immediately thereabove and one of the data lines  362  adjacent thereto by a thin film transistor  349 , wherein the connected data line  362  is commonly connected with the red, green and blue sub-pixels  342 ,  344 ,  346 . The thin film transistor  349  has a source electrode (not labeled) in electrical coupling with the data line  362 , a gate electrode (not labeled) in electrical coupling with the scan line  352  and a drain electrode (not labeled) in electrical coupling with a pixel electrode of the white sub-pixel  348 . Since in this embodiment, the sub-pixels are driven by dot inversion, along each of the data lines  332 , the sub-pixels in electrical connection therewith have alternately opposite polarities, while the alternating signals supplied to two neighboring data lines are shifted from each other by 180 degrees. 
     In operation, since the data lines  362  are driven by dot inversion, the red (green, blue, white) sub-pixel  342  ( 344 ,  346 ,  348 ) and a neighboring red (green, blue, white) sub-pixel in the same row have opposite polarities. Accordingly when the RGBW TFT LCD  1  is required to show a single color of one of the red, green blue and white colors, the pixels  341  in two neighboring columns have opposite polarities, i.e., one being positive and the other being negative. By such arrangement, the coupling effects caused by the liquid-crystal capacitors (Clcs, not shown) of each two neighboring columns of the pixels on the waveform of the upper common electrode (Com, not shown) can offset from each other to obviate the horizontal crosstalk. 
     The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, including in particular the matters of shape, size and arrangement of parts within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims.