Patent Publication Number: US-8115718-B2

Title: Color passive matrix bistable liquid crystal display system and method for driving the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a passive matrix bistable liquid crystal display system, and more particularly to a color passive matrix bistable liquid crystal display system and a method for driving the same. 
     2. Description of the Related Art 
       FIG. 1  is a schematic block diagram of the conventional color passive matrix bistable liquid crystal display device, which includes a lower substrate  100 , a plurality of data electrodes  101  aligned in parallel, a plurality of scan electrodes  102  aligned in parallel, a data line driver  103 , a scan line driver  104 , a controller  102 , a voltage source  106 , a clock  107  and a plurality of blue light bistable liquid crystal cells (B)  108 B, a plurality of green light bistable liquid crystal cells (G)  108 G and a plurality of red light bistable liquid crystal cells (R)  108 R. The data electrodes  101  are disposed on one surface of the lower substrate  100 , and the scan electrodes  102  are perpendicularly stacked over the data electrodes  101 . An intersection area of each of the scan electrodes  102  and each of the data electrodes  101  defines a sub-pixel area  108 . For one respective scan electrode  102 , the blue light bistable liquid crystal cells  108 B, green light bistable liquid crystal cells  108 G and the red light bistable liquid crystal cells  108 R are sequentially sandwiched between one respective scan electrode  102  and the data electrodes  101  corresponding to the respective intersection areas thereof. In other words, for the conventional color passive matrix bistable liquid crystal display device, the liquid crystal cells of same color are aligned in a direction perpendicular to the scan electrodes  102 . The data line driver  103  electrically connects with each of the data electrodes  101  to provide addressing data voltages to the data electrodes  101 . The scan line driver  104  electrically connects with each of the scan electrodes  102  to provide scan driving voltages to the scan electrodes  102 . The controller  105  is used to control the transmissions of the addressing data voltages of the data electrodes  101  and the scan driving voltages of the scan electrodes  102 . The data voltages of the image signals are sequentially transmitted to the controller  105  through the voltage source  106  and the clock  107 . Then, the controller  105  controls the scan line driver  104  to sequentially scan the scan electrodes  102 . When the respective scan electrode  102  is scanned, the controller  105  controls the data line driver  103  to transmit the addressing data voltages to the data electrodes  101  to write the sub-pixel data into the corresponding sub-pixels. 
       FIG. 2  is an electro-optical graph of a known red light bistable liquid crystal, green light bistable liquid crystal and blue light bistable liquid crystal, and  FIG. 3  is an electro-optical graph of another known red light bistable liquid crystal, green light bistable liquid crystal and blue light bistable liquid crystal. In view of  FIG. 2  and  FIG. 3 , it can be seen that the scan driving voltages of the bistable liquid crystal cells of different illuminating colors are different, in which the scan driving voltage of the red light bistable liquid crystal cells is lowest, while the scan driving voltage of the blue light bistable liquid crystal cells is highest. In terms of the pixel arrangement of the conventional color passive matrix bistable liquid crystal display device, the respective scan electrode  102  corresponds to the liquid crystal cells of different illuminating colors. When the respective scan electrode  102  is scanned, the liquid crystal cells of different illuminating colors corresponding thereto are provided with the same scan driving voltage. As such, the pixel arrangement and driving method of the conventional color passive matrix bistable liquid crystal display device can not meet the demand that the liquid crystal cells of different illuminating colors have different scan driving voltages. 
     Taking  FIG. 3  as an example, the highest driving voltages of the data electrodes with respect to the red light, green light and blue light liquid crystals are different, i.e. the voltage levels of the data electrodes respectively corresponding thereto are different. As to the conventional driving method, the data electrodes  101  are divided to three groups, when the respective scan electrode  101  is scanned, three respective voltage levels are provided to the corresponding data electrodes  101  to satisfy the demand that the liquid crystals of three different illuminating colors have different voltage levels. It is necessary to develop additional addressing circuits to provide respective addressing voltages to the liquid crystals of different illuminating colors, and that makes the circuit design of the data line driver  103  become more complicated. The conventional color passive matrix bistable liquid crystal device needs to be improved to alleviate the above drawbacks. 
     SUMMARY OF THE INVENTION 
     The present invention provides a color passive matrix bistable liquid crystal display system, in which sub-pixels of same color are arranged to correspond to one respective scan line and sub-pixels of different colors are arranged to correspond to neighboring scan lines, and the scan lines are grouped in accordance with the colors of the sub-pixels corresponding thereto such that different scan driving voltages can be switched when the scan lines are scanned, and thus providing the same scan driving voltage to the sub-pixels of same color and different scan driving voltages to the sub-pixels of different colors. 
     The color passive matrix bistable liquid crystal display system includes a plurality of data electrodes aligned in parallel, a plurality of scan electrodes aligned in parallel, a pixel scan line driver, a data line driver and a timing controller. The scan electrodes are perpendicular to the data electrodes and both overlap each other. An intersection area of each of the scan electrodes and each of the data electrodes defines a sub-pixel, and each of the scan electrodes corresponds to a plurality of the sub-pixels of same color, while the neighboring scan electrodes respectively correspond to the sub-pixels of different colors. The sub-pixels of different colors are constituted by bistable liquid crystals with different illuminating colors. The pixel scan line driver electrically connects with the scan electrodes and provides respective scan driving voltages to the scan electrodes in accordance with the illuminating colors of the sub-pixels corresponding thereto. The data line driver electrically connects with the data electrodes to provide data voltages to the data electrodes. The timing controller is used to control the pixel scan line driver and the data line driver to transmit the respective scan driving voltages and data voltages. 
     In one another aspect, the color passive matrix bistable liquid crystal display system of the present invention includes a line buffer for resorting the sub-pixels of the whole graphic display received by the timing controller prior to scanning the scan electrodes such that the data line driver can simultaneously transmit the data voltage for the sub-pixels of same color to the data electrodes corresponding to one respective scan electrode. 
     Additionally, the data electrodes of the present color passive matrix bistable liquid crystal display system can be switched to the respective voltage levels corresponding to the sub-pixels of different colors when the scan lines are scanned so as to satisfy the situation that the voltage levels of the data electrodes for the sub-pixels of different colors are different. And thus, it is not necessary to develop additional addressing data driving circuit for providing respective addressing voltages to the sub-pixels of different colors. 
     By way of the arrangement of the sub-pixels, the present color passive matrix bistable liquid crystal display system can satisfy the demand that the respective scan driving voltage levels and the respective data voltage levels corresponding to the sub-pixels of different colors are different without increasing the complexity of the circuit design of the driving system. The image quality is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic functional block diagram of a conventional color passive matrix bistable liquid crystal display device; 
         FIG. 2  is an electro-optical graph of a known red light bistable liquid crystal, green light bistable liquid crystal and blue light bistable liquid crystal; 
         FIG. 3  is an electro-optical graph of another known red light bistable liquid crystal, green light bistable liquid crystal and blue light bistable liquid crystal; 
         FIG. 4  is a schematic functional block diagram of a color passive matrix bistable liquid crystal display system of the present invention; and 
         FIG. 5  is a timing diagram of scan driving voltages of the color passive matrix bistable liquid crystal display system of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a color passive matrix bistable liquid crystal display system, which provides respective scan driving voltages to the scan electrodes in accordance with the illuminating colors of the sub-pixels corresponding thereto for driving the liquid crystals such that the demand that the sub-pixels of different colors require different scan driving voltages is satisfied. In other words, the present invention provides an appropriate arrangement of the liquid crystals of different illuminating colors to meet the need of the color passive matrix bistable liquid crystal display device and a driving system suitable for the same. In the present invention, the liquid crystals of different illuminating colors are aligned in the directions perpendicular to the scan electrodes and the liquid crystals of same illuminating colors are aligned in the directions parallel to the scan electrodes. Moreover, the present system provides a line buffer for resorting the pixel data transmitted in a standard way that the pixel data are transmitted by one red sub-pixel, one green sub-pixel and one blue sub-pixel as a transmission unit per time after the driving system receives the pixel data of different colors of the whole graphic display, and then transmitting the sub-pixel data of same color corresponding to one respective scan electrode to the data electrodes. 
     The color passive matrix bistable liquid crystal display system of the present invention and a method for driving the same will be described in detail in accordance with preferred embodiments with reference to accompanying drawings. 
       FIG. 4  is a schematic functional block diagram of the color passive matrix bistable liquid crystal display system according to one preferred embodiment of the present invention. In this preferred embodiment, the present color passive matrix bistable liquid crystal display system includes a lower substrate  400 , a plurality of data electrodes  401 , a plurality of scan electrodes  402 , a plurality of blue light bistable liquid crystal cells  403 B, a plurality of green light bistable liquid crystal cells  403 G, a plurality of red light bistable liquid crystal cells  403 R, a pixel scan line driver  404 , a data line driver  405 , a timing controller  406  and a line buffer  407 . The data electrodes  401  are aligned in parallel and disposed on a surface of the lower substrate  400 . The scan electrodes  402  are aligned in parallel and disposed over the data electrodes  401  and perpendicular to the data electrodes  401 . An intersection area of each of the data electrodes  401  and each of the scan electrodes  402  defines a sub-pixel area  403 . The blue light bistable liquid crystal cells  403 B, green light bistable liquid crystal cells  403 G and the red light bistable liquid crystal cells  403 R are sandwiched between the data electrodes  401  and the scan electrodes  402  corresponding to the respective intersection areas thereof. The bistable liquid crystal cells of same color are sandwiched between one respective scan electrode  402  and each of the data electrodes  401  corresponding to the respective intersection areas thereof. The bistable liquid crystal cells of different colors are sandwiched between one respective data electrode  401  and each of the neighboring scan electrodes  402  corresponding to the respective intersection areas thereof. In other words, the liquid crystal cells of same color are aligned in parallel to the scan electrodes  402  and the liquid crystal cells of different colors are aligned perpendicular to the scan electrodes  402 . In this preferred embodiment, more specifically, the blue light bistable liquid crystal cell  403 B, the green light bistable liquid crystal cell  403 G and the red light bistable liquid crystal cell  403 R are sequentially sandwiched between the scan electrodes  402  and the data electrodes  401  corresponding to the respective intersection areas along the direction perpendicular to the scan electrodes  402 . The scan electrodes  402  are electrically coupled to the pixel scan line driver  404 . The scan electrodes  402  are grouped in accordance with the different illuminating colors of the sub-pixels  403  such that the pixel scan line driver  404  provides respective scan driving voltages to the scan electrodes  402  in accordance with the illuminating colors of the sub-pixels  403  corresponding thereto. The data line driver  405  is electrically coupled to the data electrodes  401  to provide addressing data voltages to the data electrodes  401 . The timing controller  406  is electrically coupled to the data line driver  405  and the pixel scan line driver  404  to control the transmission of the addressing data voltages and the scan driving voltages. The line buffer  407  is connected to the timing controller  406  such that after the timing controller  406  receives image signals of the whole graphic display, i.e. after receiving the blue light sub-pixel data  403 B, the green light sub-pixel data  403 G and the red light sub-pixel data  403 R of the whole graphic display, the line buffer  407  resorts the sub-pixel data of the whole graphic display, and then transmitting to the data line driver  405  through the timing controller  406  so that the data line driver  405  can simultaneously transmit the data voltages of the sub-pixels of same color to the data electrodes  401  corresponding to one respective scan electrode  402 . As such, the present display system can be compatible with the standard pixel data transmission method that the red light sub-pixel data, the green light sub-pixel data and the blue light sub-pixel data are as a transmission unit per time. 
       FIG. 5  is a timing diagram of the scan driving voltages of the present color passive matrix bistable liquid crystal display system. After the timing controller  406  receives the pixel data of the whole graphic display, the line buffer  407  resorts the pixel data to become one respective pixel line is formed of the sub-pixel data of the same color, and then transmitting the respective resorted line pixel data formed of the same color sub-pixel data to the timing controller  406 . Next, the timing controller  406  controls the pixel scan line driver  404  to sequentially transmit the respective scan driving voltages V B , V G  and V R  to the respective scan electrodes  402  corresponding thereto so as to drive the corresponding bistable liquid crystal cells. After one of the scan electrodes  402  is applied with the respective scan driving voltage, the data line driver  405  transmits the addressing data voltages from the timing controller  406  to the data electrodes  401  to write the sub-pixel data into the corresponding bistable liquid crystal cells. The present invention proposes a sub-pixel arrangement design and a concept that grouping the sub-pixels in accordance with their illuminating colors, and thereby the pixel scan line driver provides the respective scan driving voltages to the corresponding scan electrodes in accordance with the illuminating colors of the sub-pixels corresponding thereto. As shown in  FIG. 2  and  FIG. 3 , the scan driving voltage of the red light bistable liquid crystal cells is lowest, but the scan driving voltage of the blue light bistable liquid crystal cells is highest. As a consequence, the present invention can provide the respective scan driving voltages to the scan electrodes  402  in accordance with the illuminating colors of the sub-pixels corresponding thereto when sequentially scanning the scan electrodes  402 . The efficiency for driving the liquid crystal cells is improved. 
       FIG. 3  is an electro-optical graph of the known red light bistable liquid crystal cells, green light bistable liquid crystal cells and blue light bistable liquid crystal cells, showing that the slopes of the right-side curves of the electro-optical graph corresponding to the crystal liquid cells of different illuminating colors are different. As such, the data voltages of the data electrodes  401  corresponding to the sub-pixels  403  of different colors are different. In other words, the voltages of the data electrodes  401  of the blue light liquid crystal cells, the green light liquid crystal cells and the red light liquid crystal cells are different. Under this circumstance, when the respective scan line (the scan electrode  402 ) is scanned, the data addressing positions in the direction perpendicular to the scanned scan line correspond to the liquid crystal cells of same color. As such, the data addressing voltage levels are the same when the respective scan line is changed. Only the scan line is changed, the data addressing voltage levels are changed. By way of the inventive concept of the present invention that the liquid crystal cells of same color are aligned in parallel and the liquid crystal cells are grouped in accordance with the illuminating colors thereof, the data addressing voltage levels are changed only as the scan line is changed. It is not necessary to develop respective data addressing driving circuits for the liquid crystal cells of different illuminating colors to meet the demand that the liquid crystal cells of different illuminating colors have different data addressing voltage levels. Therefore, the circuit design of the driving system of the present invention can cost down. In addition, the present invention can base on the electro-optical characteristics of the liquid crystal cells to keep the data addressing voltage levels in the direction perpendicular to the scan lines being the same when changing the respective scan lines. Hence, it does not need to change the data addressing voltage levels when scanning the respective scan lines. 
     By way of the arrangement of the sub-pixels, the present color passive matrix bistable liquid crystal display system can satisfy the demand that the respective scan driving voltage levels and the respective data voltage levels corresponding to the sub-pixels of different colors are different without increasing the complexity of the circuit design of the driving system. The image quality is improved. 
     While the invention has been described by way of examples and in terms of preferred embodiments, it is to be understood that those who are familiar with the subject art can carry out various modifications and similar arrangements and procedures described in the present invention and also achieve the effectiveness of the present invention. Hence, it is to be understood that the description of the present invention should be accorded with the broadest interpretation to those who are familiar with the subject art, and the invention is not limited thereto.