Abstract:
A driving apparatus, a driving method and a liquid crystal display (LCD) using the same are provided, wherein the method includes the following steps of: setting a color display sequence, wherein the color display sequence is RGBG, RGRB or RBGB; alternately reading frame data from a first frame register and a second register according to a frame period having three field periods; and sequentially displaying four color data in a cycle period having four field periods according to the color display sequence and the read frame data. By utilizing the method in the present invention, color loss of a field sequential color display occurred in a lower temperature environment is improved.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 97130879, filed on Aug. 13, 2008. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a driving method of a liquid crystal display and more particularly, to a driving apparatus and driving method of a field sequential color liquid crystal display. 
     2. Description of Related Art 
     The liquid crystal display (LCD) has advantages such as low power consumption, thinness, light weight, and low driving voltages and thus is widely used in various electronic devices, for example, video recorders and players, notebook computers, desktop displays, mobile phones, and various projection devices. In terms of display devices, the thin film transistor liquid crystal display (TFT-LCD) has advantages such as highly effective space usage, low power consumption, and free of radiation so the TFT-LCD has become the main stream of the display market. 
     Display quality of an LCD is mainly influenced by reaction speed of liquid crystals. In a low temperature environment, reaction speed of liquid crystals becomes low, resulting in color loss in the display. Furthermore, in the field sequential color LCD (FSC-LCD), the order of switching color light of different colors (or a color display sequence of an RGB field period) may also affect the degree of color loss in addition to the reaction speed of liquid crystals. It can be known from simulation, when reaction speed of liquid crystals is low and the color display sequence of an RGB field period is from red (R) to green (G), from green (G) to blue (B), and from blue (B) to red (R), the degree of color loss is more serious as shown in  FIG. 1 , which is a chromaticity diagram according to prior art. 
       FIG. 1  illustrates a chromaticity curve range under different reaction speeds of liquid crystals. When the reaction speed of liquid crystals becomes lower, color saturation of the display becomes lower as well, the color that is originally red turns greenish, and the color that is originally green turns bluish. 
     SUMMARY OF THE INVENTION 
     The present invention provides a display method and an LCD using the same, in which the order of switching colors is changed to improve the problem of color loss and the display sequence of backlight is used to improve color vividness of still images and to improve LCD display quality in a low temperature environment. 
     The present invention provides a driving apparatus which uses a specific order of switching colors to drive an LCD. A color data is inserted in the original RGB color sequence to change the color display sequence and to improve the problem of color loss. 
     In light of the above, the present invention provides a display method suitable for a driving apparatus and a backlight module of an LCD. The driving apparatus sequentially updates a first frame data stored in a first frame register and a second frame data stored in a second frame register. Each of the frame data includes three color data of R, G and B. The backlight module is divided into a first sub region, a second sub region, and a third sub region according to a scan direction of the driving apparatus. The display method includes the following steps. 
     A color display sequence is set. The first frame data and the second frame data are alternately read according to a frame period. The frame period includes three field periods. Four color data are sequentially displayed according to the color display sequence and the read first frame data or second frame data in a cycle period. The cycle period includes four field periods. The four color data are respectively displayed during the field periods of the cycle period. The color display sequence is RGBG, RGRB or RBGB. 
     In one embodiment of the present invention, the step of sequentially displaying the four color data according to the color display sequence and the read first frame data and second frame data further includes the following steps. In a first field period of the cycle period, the displayed color lights in the first sub region, second sub region, and third sub region are sequentially updated according to a first color data corresponding to the first field period. When the first sub region is being updated, the second sub region is inserted with black. When the second sub region is being updated, the third sub region is inserted with black. When the third sub region is being updated, the first sub region is inserted with black. 
     In one embodiment of the present invention, the step of sequentially displaying the four color data according to the color display sequence and the read first frame data and second frame data further includes the following steps. In a second field period of the cycle period, the displayed color lights in the first sub region, second sub region, and third sub region are sequentially updated according to a second color data corresponding to the second field period. When the first sub region is being updated, the second sub region is inserted with black. When the second sub region is being updated, the third sub region is inserted with black. When the third sub region is being updated, the first sub region is inserted with black. 
     In one embodiment of the present invention, the second sub region is between the first sub region and the third sub region. 
     In one embodiment of the present invention, the first color data is R, G, or B. 
     The present invention further provides an LCD including a liquid crystal panel, a driving apparatus, and a backlight module. The driving apparatus is used to drive the liquid crystal panel and to sequentially update a first frame data stored in a first frame register as well as a second frame data stored in a second frame register. Each frame data includes three color data R, G, and B. The driving apparatus is used to further perform the following steps. A color display sequence is set. The first frame data and the second frame data are alternately read according to a frame period. The frame period includes three field periods. Four color data are sequentially displayed according to the color display sequence and the read first frame data or second frame data in a cycle period. The cycle period includes four field periods. The four color data are displayed respectively during the field periods of the cycle period. 
     The backlight module provides backlight required by the liquid crystal panel and is divided into a first sub region, a second sub region, and a third sub region according to a scan direction of the driving apparatus. In a first field period of the cycle period, displayed color lights in the first sub region, second sub region, and third sub region are sequentially updated according to a first color data corresponding to the first field period. When the first sub region is being updated, the second sub region is inserted with black. When the second sub region is being updated, the third sub region is inserted with black. When the third sub region is being updated, the first sub region is inserted with black. The color display sequence is RGBG, RGRB or RBGB. 
     The present invention further provides a driving apparatus used in an LCD. The driving apparatus includes a line buffer, a frame register, and a timing controller. The line buffer is used to temporarily store a plurality of scan line data output from an image processor. The frame register is electrically connected to the line buffer and reads the scan line data through the line buffer to update a frame data stored in the frame register. The frame data includes three color data R, G, and B. The timing controller is electrically connected to the line buffer and the frame register to read the frame data in the frame register and to control the timing of the frame register updating the frame data. 
     The timing controller is further used to perform the following steps. A color display sequence is set to be RGBG, RGRB or RBGB. In a cycle period, four color data are sequentially displayed according to the color display sequence and the read frame data. The cycle period includes four field periods. The color data are displayed respectively during the field periods. In a first field period of the cycle period, a plurality of scan line pixels in a liquid crystal panel are sequentially scanned according to the frame data in the frame register. If the frame register has not updated the stored frame data with the scan line data, the timing controller continues scanning the scan line pixels in the liquid crystal panel according to the frame data. 
     The present invention further provides an LCD including a liquid crystal panel, a driving apparatus, and a backlight module. The driving apparatus is used to drive the liquid crystal panel and includes a line buffer, a frame register, and a timing controller. The line buffer is used to temporarily store a plurality of scan line data output from an image processor. The frame register is electrically connected to the line buffer and reads the scan line data through the line buffer to update a frame data stored in the frame register. The frame data includes three color data R, G, and B. The timing controller is electrically connected to the line buffer and the frame register to read the frame data in the frame register and to control the timing of the frame register updating the frame data. 
     The timing controller is further used to perform the following steps. A color display sequence is set to be RGBG, RGRB or RBGB. In a cycle period, four color data are sequentially displayed according to the color display sequence and the read frame data. The cycle period includes four field periods. The color data are displayed respectively during the field periods. In a first field period of the cycle period, a plurality of scan line pixels in a liquid crystal panel are sequentially scanned according to the frame data in the frame register. If the frame register has not updated the stored frame data with the scan line data, the timing controller continues scanning the scan line pixels in the liquid crystal panel according to the frame data. 
     The backlight module is used to provide backlight to the liquid crystal panel and is divided into a first sub region, a second sub region, and a third sub region according to a scan direction of the timing controller. In the first field period of the cycle period, displayed color lights in the first sub region, second sub region, and third sub region are sequentially updated according to a first color data corresponding to the first field period. When the first sub region is being updated, the second sub region is inserted with black. When the second sub region is being updated, the third sub region is inserted with black. When the third sub region is being updated, the first sub region is inserted with black. 
     The preset invention uses a specific color display sequence in connection with a specific backlight driving method to display images so color loss resulting from the display color turning from red to green, from green to blue, or from blue to red may be reduced, especially when displaying a still image or in a low temperature environment. In addition, in the present invention, images are displayed according to the color display sequence and the frame data stored in the frame buffer without care of whether the frame data has been updated (i.e. ignoring whether the original image data has been completely displayed on screen). Therefore, the technical means of the present invention may be integrated with the conventional FSC-LCD and only the driving timing of the timing controller needs to be adjusted. 
     In order to make the aforementioned features and advantages of the present invention more comprehensible, several embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  illustrates a chromaticity curve range under different reaction speeds of liquid crystals. 
         FIG. 2  illustrates an FSC-LCD device according to the first embodiment of the present invention. 
         FIG. 3A  is a circuit diagram of a driving apparatus  230  according to the first embodiment of the present invention. 
         FIG. 3B  is a display timing schematic diagram according to the first embodiment of the present invention. 
         FIG. 4  is a schematic diagram illustrating regions of a backlight module  220  according to the first embodiment of the present invention. 
         FIG. 5  is a schematic diagram illustrating update of color light of the backlight module  220  according to the first embodiment of the present invention. 
         FIG. 6  is a flow chart illustrating a display method according to the second embodiment of the present invention. 
         FIG. 7  is a circuit diagram of a driving apparatus according to the third embodiment of the present invention. 
         FIG. 8  illustrates a chromaticity curve range according to the embodiments of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The First Embodiment 
       FIG. 2  illustrates an FSC-LCD device according to the first embodiment of the present invention. An LCD  200  includes a liquid crystal panel  210 , a backlight module  220 , and a driving apparatus  230 . The backlight module  220  is disposed behind the liquid crystal panel  210  and is used to provide backlight required by the backlight module  220 . The driving apparatus  230  is used to drive pixels in the liquid crystal panel  210  to display images. The backlight module  220  emits, in association with the driving timing of the driving apparatus  230 , a color light corresponding to the color display sequence. 
     In the present embodiment, the color display sequence of the liquid crystal panel  210  and the backlight module  220  is RGBG, wherein R, G and B represent the three primary colors of light (red, green and blue). Compared with color display sequence RGB of conventional technology, a field of G is inserted each time after three fields of RGB have been displayed in the present embodiment. The frame data stored in the frame register of the driving apparatus  230  is directly used for the color data of the G field without care of whether the frame data of the original image has been completely displayed on screen. In other words, the main concern of the frame display method in the present embodiment lies in the display sequence of the fields and ignores whether the frame data is valid. Therefore, it matters not whether the current read frame data is the current frame data to be displayed as long as the corresponding color data is the same. With the RGBG color display sequence, color loss resulted from the switching process of turning from red to green, from green to blue, and from blue to red may be reduced. 
     Next, the driving apparatus  230  is further illustrated in the following. Referring to  FIG. 3A ,  FIG. 3A  is a circuit diagram of the driving apparatus  230  according to the first embodiment of the present invention. The driving apparatus  230  at least includes frame registers  320  and  330  and a timing controller  340 . The driving apparatus  230  alternately stores, in the frame registers  320  and  330 , image data, including a plurality of frame data each of which comprises a plurality of scan line data  9 , and may be divided into three color data RGB, output from an image processor  310  so as to update the frame data in the frame registers  320  and  330 . It should be noted that the frame registers  320  and  330  may respectively consist of two registers or may be two memory magnetic sectors in a same memory device as long as the frame registers  320  and  330  may respectively support read or write functions. Read or Write path of the frame registers  320  and  330  may be switched through switches  312  and  314 . When the frame register  320  is storing the image data output from the image processor  310 , the timing controller  340  reads the frame data in the frame register  330  through the switch  314  for display. Correspondingly, when the frame register  330  is storing the image data output from the image processor  310 , the timing controller  340  reads the frame data in the frame register  320  through the switch  314  for display. 
     The timing controller  340  alternately reads the frame data in the frame registers  320  and  330  according to a frame period and displays the frame data on the liquid crystal panel  210 , wherein each of the frame periods includes three field periods. The timing controller  340  sequentially displays four color data in a cycle period according to the RGBG color display sequence and the read frame data, wherein the cycle period includes four field periods. The color data are displayed respectively during the field periods. In other words, in the present embodiment, the frame data are alternately read by the duration of the frame period, but the color display sequence corresponding to the field period would be cycled by the sequence RGBG. 
     Referring to  FIG. 3B ,  FIG. 3B  is a display timing schematic diagram according to the present embodiment. The timing controller  340  alternately reads the frame data in the frame registers  320  and  330  according to the frame periods FP 1 ˜FP 4 . Each of the frame periods FP 1 ˜FP 4  includes three field periods SP. Each of the cycle periods CP 1 ˜CP 3  includes four field periods SP to sequentially display the four color data RGBG. Therefore, the length of each cycle periods CP 1 ˜CP 3  and the length of each frame periods FP 1 ˜FP 4  are not consistent. The timing controller  340  reads from the frame register  330  during the frame period FP 1  so the color data R 330 , G 330 , and B 330  from the frame register  330  are displayed in the first three field periods of the cycle period CP 1 . In the fourth field period of the cycle period CP 1 , the color data G 330  from the frame register  320  is displayed. 
     Afterward, when entering the next cycle period CP 2 , images are also displayed according to the color display sequence RGBG. However, the color data are respectively read from the frame register  320  (the color data R 320  and G 320 ) and the frame register  330  (the color data B 330  and G 330 ). Although the color data B 320  corresponding to B in the frame register  320  is not displayed during the frame period FP 2 , the read and write path is still switched to the frame register  330  when entering the frame period FP 3 . Display is performed according to the frame data in the frame register  330  and the color data B 320  that is not displayed in the previous frame period FP 2  is ignored. Following procedures may be deduced similarly and are not to be iterated hereby. 
     From the above illustration, data update in the frame registers  320  and  330  and the read timing may be performed according to timing in conventional technology. The timing controller  340  uses the color display sequence RGBG to display images. The timing controller  340  only considers about the color display sequence and not about whether the color data correspond to a same frame period or come from a same frame register  320  or  330 . The color data that is not displayed is directly ignored. 
     In addition, it should be noted that the color display sequence set by the timing controller  340  is not limited to RGBG and may also be RGRB or RBGB. In the case of RGBG, R and B are both surrounded by G to avoid a situation of turning from B to R. In the case of RGRB, G and B are both surrounded by R to avoid a situation of turning from G to B. In the case of RBGB, R and G are both surrounded by B to avoid a situation of turning from R to G. Hence, the aforementioned color switching sequences all have the effect of reducing color loss. Persons of ordinary skill in the art should be able to deduce implementation details in the cases of RGRB and RBGB from the above illustrated embodiment, which will not be further described herein. 
     The driving method of the backlight module  220  of the present embodiment is further illustrated in the following section. Referring to  FIG. 4 ,  FIG. 4  is a schematic diagram illustrating regions of the backlight module  220  according to the present embodiment. The backlight module  220  is divided into a first sub region  410 , a second sub region  420 , and a third sub region  430  according to a scan direction (e.g. from top to bottom) of the driving apparatus  230 . The backlight module  220  sequentially updates the first sub region  410 , the second sub region  420 , and the third sub region  430  according to the corresponding color data in each field period. 
     Take the first field period SP in the cycle period CP 1  as an example, the corresponding color data is R 320  (i.e. red). Thus, red color light is sequentially displayed in the first sub region  410 , the second sub region  420 , and the third sub region  430  in association with the timing and region of the timing controller  340  scanning the liquid crystal panel  210 . In addition, to avoid the problem of light intermixing between adjacent sub regions, black insertion (turning off backlight) is performed in the next sub region of the sub region being updated. Thus, when the color light of the first sub region  410  is being updated, the second sub region  420  is inserted with black. When the color light of the second sub region  420  is being updated, the third sub region  430  is inserted with black. When the color light of the third sub region  430  is being updated, the first sub region  410  is inserted with black. The backlight module  220  completes three update processes in each field period SP, i.e. sequentially updating the color lights of the first sub region  410 , the second sub region  420 , and the third sub region  430 . 
     Referring to  FIG. 5 ,  FIG. 5  is a schematic diagram illustrating update of color light of the backlight module  220  according to the present embodiment. Taking the first field period SP of the cycle period CP 1  as an example, the color light of the first sub region  410  is updated during the first duration T 1  which is the former ⅓ of the field period SP. The first sub region  410  displays the corresponding red color light and the second sub region  420  is inserted with black. The color light of the second sub region  420  is updated during the second duration T 2  which is the middle ⅓ of the field period SP. The second sub region  420  displays the corresponding red color light and the third sub region  430  is inserted with black. The color light of the third sub region  430  is updated during the third duration T 3  which is the latter ⅓ of the field period SP. The third sub region  430  displays the corresponding red color light and the first sub region  410  is inserted with black. 
     When entering the second field period of the cycle period CP 1 , the green color light is used to update the first sub region  410 , the second sub region  420 , and the third sub region  430  sequentially. In different field periods, the main difference is the color light used to update the sub regions. The remaining flow of operation is similar to the abovementioned, which will not be further described herein. 
     The Second Embodiment 
     From the above illustration of the first embodiment, a display method of an LCD is summarized. Referring to both  FIG. 5  and  FIG. 6 ,  FIG. 6  is a flow chart illustrating a display method according to the second embodiment of the present invention. The present display method is suitable for the driving apparatus  230  and the backlight module  220  of the LCD in  FIG. 2 . The driving apparatus  230  sequentially updates the frame data stored in the frame registers  320  and  330  (respectively referred to as a first frame data and a second frame data). Each frame data includes three color data R, G, and B. The backlight module  220  is divided into a first sub region, a second sub region, and a third sub region according to a scan direction of the driving apparatus  230 . 
     First, a color display sequence is set (step S 610 ). Then, the frame data in the frame registers  320  ad  330  are alternately read according to a frame period. The frame period similarly includes three field periods to correspondingly display three color data (step S 620 ). Next, in a cycle period, four color data are sequentially displayed according to the color display sequence and the read first frame data or second frame data. The cycle period includes four field periods. The color data are displayed respectively during the field periods (step S 630 ). The color display sequence is RGBG, RGRB or RBGB. 
     It should be noted that in the step S 630 , whether the read data is the first frame data or the second frame data depends on the frame period. Namely, the first frame data and the second frame data are alternately switched to be read out every time a frame period passes. The color data required for display comes from the currently read frame register  320  or  330  and is not limited to the first frame data or the second frame data. In other words, in the present embodiment, when reading the frame data, a switch is made according to the frame period. Color switches are made according to the cycle period during display. Each cycle period does not necessarily correspond to a complete image. During display, the frame data that can be currently read is used directly for display. What matters is the color display sequence and not whether the frame corresponding to the color data is the same. 
     In addition, the step S 630  further includes backlight control. In the first field period of the cycle period, the color light of the first sub region, second sub region, and third sub region is sequentially updated according to the corresponding color data in the first field period. When the first sub region is being updated, the second sub region is inserted with black. When the second sub region is being updated, the third sub region is inserted with black. When the third sub region is being updated, the first sub region is inserted with black. Please refer to the above illustrations of  FIG. 4  and  FIG. 5  for implementation details of backlight control. Please refer to the illustration of the first embodiment for remaining operation details of the present embodiment, which will not be further described herein. 
     Third Embodiment 
     In combination with the abovementioned display method, the present invention further provides a driving apparatus, wherein the number of frame registers may be reduced. Referring to  FIG. 7 ,  FIG. 7  is a circuit diagram of a driving apparatus according to the third embodiment of the present invention. A driving apparatus  730  is electrically connected between an image processor  310  and a liquid crystal panel  210 . The driving apparatus  730  includes a line buffer  732 , a frame register  734 , and a timing controller  736 . The frame register  734  is electrically connected between the line buffer  732  and the timing controller  736 . The timing controller  736  is further electrically connected to the line buffer  732  to control the frame register  734  through the timing that the line buffer  732  updates the frame data. 
     In the present embodiment, a frame rate of the timing controller  736  is not an integral multiple of an output frame data rate of the image processor  310 . Therefore, the timing controller  736  and the image processor  310  do not access the frame data in the frame register  734  in a synchronized manner. The timing controller  736  outputs the frame data to the liquid crystal panel  210  for display at a higher rate. While the timing controller  736  is reading from the frame register  734 , the frame data output from the image processor  310  is stored in the line buffer  732  (depending on the length of time, there may only be pixel data of a few scan lines, briefly referred to as scan line data). When the timing controller  736  stops reading from the frame register  734 , the frame register  734  then reads the scan line data in the line buffer  732  to update the frame data in the frame register  734 . 
     If the bandwidth of the frame register  734  is large enough, updating the required frame data may be finished within the interval when the timing controller  736  stops reading from the frame register  734 . If the bandwidth of the frame register  734  is not large enough or the updating time is inadequate, the timing controller  736  still display images according to old frame data and does not wait for the frame register  734  to finish updating. Similarly, the data in the line buffer  310  is updated at the output rate of the image processor  310  without consideration on whether the frame register  734  has been read. 
     In other words, in the present embodiment, the timing controller  736  drives the liquid crystal panel  210  at its own frame rate while the image processor  310  outputs frame data at its own data output rate, without interfering with each other. If the data in the frame register  734  has been updated, the timing controller  736  displays the new frame data. If the data in the frame register  734  has not been updated, the timing controller  736  displays old frame data. Therefore, in an entire image, the pixel data of part of the scan lines may be displayed according to the data of a previous image. The ratio of the image displayed according to old data depends on the bandwidth of the frame register  734  and the time that the frame register  734  may be updated. In addition, it should be noted that when the image is a still image, the display quality of the present invention is not affected. 
     The timing that the timing controller  736  drives the liquid crystal panel  210  and the color display sequence are as described in the above first embodiment and second embodiment and the color display sequence is RGBG, RGRB or RBGB, for example. The main differences between the present embodiment and the above first embodiment lie in the circuit structures of the frame register  734  and the line buffer  732  and the method of data access thereof. In addition, the operating frequency of the timing controller  736  is also different. For example, the frame rate is greater than 60 Hz (i.e. field period rate of 180 Hz). In terms of color display sequence, the timing controller  736  similarly uses the color display sequence RGBG, RGRB or RBGB to update the liquid crystal panel  210 . However, the displayed scan line data may be data of a current image or data of a previous image in an individual frame. 
     In other words, the present embodiment uses a line buffer  732  and a frame register  734  to replace the two frame registers  320  and  330  in  FIG. 3A  to save the number of frame registers. The remaining operating details of the timing controller  736  are as described in the illustration on the timing controller  340  in the first embodiment and in the display method in the second embodiment. The timing controller  736  in the present embodiment drives the liquid crystal panel  210  according to the display method in the second embodiment. The remaining operating details are not further described herein. Please refer to the illustration on  FIG. 5  for the remaining operation details of the backlight module  220 , which is not further described herein. 
       FIG. 8  illustrates a chromaticity curve range according to the above embodiments of the present invention. It can be found, by comparing  FIG. 1  and  FIG. 8 , that the chromaticity curve range of the above embodiments is more linear with a lower degree of color loss. 
     Furthermore, it should be noted that the above embodiments may be incorporated with conventional driving methods, wherein the driving methods of the above embodiments may be used when displaying a still image, while a conventional driving method may be switched to when displaying dynamic images so as to increase the display quality of dynamic images. 
     In summary, the present invention uses the color display sequence RGBG, RGRB or RBGB to update the liquid crystal panel and thus may improve the problem of color loss of the FSC-LCD due to a low transition speed of liquid crystals in a low temperature environment. At the same time, the present invention further provides a data access method particularly directed at displaying still images to reduce the required number of frame registers and thus save manufacturing costs. Furthermore, the present invention is especially suitable for improving display quality in a low temperature environment and reduces color loss of images due to a low transition speed of liquid crystals. 
     It will be apparent to those of ordinary skills in the technical field that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.