Patent Publication Number: US-7724225-B2

Title: Display panel for liquid crystal display

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a liquid crystal display, and in particular, to a liquid crystal display circuit design. 
     2. Description of the Related Art 
       FIG. 1  shows a conventional display panel. The display panel comprises a timing controller (TCON)  102  for receiving differential signals like LVDS/TMDS/DVI, and two buses each coupled to a plurality of source drivers  104 . For example, all of the odd source drivers  104  may couple to the one bus, while all the even source drivers  104  may couple to the other bus. Given a 6-bits gray level, a total of 18 transmission lines is required to deliver red, blue and green information from the TCON  102  to each source driver  104 . Thus two buses utilize 36 transmission lines in total. If the gray level is 8 bits, 48 transmission lines are required. After the TCON  102  receives the LVDS/TMDS/DVI signals, the corresponding image information is transmitted to the source drivers  104  via the transmission lines. Signals on the transmission lines electrically conform to the TTL logic standard, and have a voltage of 3.3 V or 5V. The display panel also comprises a reference voltage generator  106 , providing voltages based on gamma correction parameters. 
       FIG. 2  shows a conventional advanced display panel. The TCON  202  comprises a bus, both ends of which are equipped with terminators  208 . All source drivers  204  simultaneously couple to the bus, thus the number of required transmission lines is reduced by half that of  FIG. 1 . Given a 6-bits gray level, the TCON  202  only requires 18 transmission lines to couple all source drivers  204 . After the TCON  202  receives the LVDS/TMDS/DVI signals, image information is delivered to the source drivers  204  via the transmission lines, and signals on the transmission lines electrically conform to the reduced swing differential signal standard (RSDS). Similarly, the display panel also comprises a reference voltage generator  206 , providing voltages based on gamma correction parameters. 
       FIG. 3  shows a conventional point-to-point display panel. The TCON  302  connects to each source driver  304  with individual transmission lines, and signals on the transmission lines conform to the point-to-point differential signal (PPDS) standard. The transmission lines are exclusive for each individual source driver  304 , therefore the bus clock need not be shared, and the transmission rate can be significantly increased. Moreover, only a few transmission lines are required to deliver red, green, blue, and additional data. Similarly, the display panel also comprises a reference voltage generator  306 , providing voltages based on gamma correction parameters. 
     Although PPDS reduces the number of transmission lines and the cost of PCBs, additional DC biased current is still required, thus, the power provided is inadequate for portable products. Additionally, with the progress of current technology, logic voltage requirement have been reduced from 5V to 1.8V/1.5V, making the implementation of differential signal will be more difficult. 
     BRIEF SUMMARY OF INVENTION 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     An exemplary embodiment of a display panel for a liquid crystal display circuit comprises a timing controller and a plurality of source drivers. The timing controller receives a LVDS/TMDS/DVI signal to generate a plurality of TTL signals and a sync signal. Each source driver comprises at least one bus directly connected to the timing controller for receiving a corresponding TTL signal. The timing controller comprises a clock line, coupled to the source drivers for transmission of the sync signal. Each TTL signal carries corresponding image information. The TTL signals, sequentially transmitted on the bus, conform to transistor-to-transistor logic (TTL) standard. 
     Each bus comprises three transmission lines that transmit a first TTL signal, a second TTL signal and a third TTL signal conforming to the TTL standard respectively. The first TTL signal, sequentially transmitted in one of the transmission lines, may carry red information. The second TTL signal, sequentially transmitted in another of the transmission lines, may carry green information. The third TTL signal, sequentially transmitted in the other of the transmission lines, may carry blue information. 
     A gamma reference table, coupled to the source drivers for providing gamma correction parameters, may be provided in the display panel. DC voltages of the first, second and third TTL signals are zero biased. The frequency of the first, second and third TTL signals is determined by the equation:
 
Frequency=(the clock of the timing controller×the number of the bit of the gray level)/(the number of the source drivers×2)
 
     Each source driver may comprise two buses directly connected to the timing controller. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The following detailed description, given by way of example and not intended to limit the invention solely to the embodiments described herein, will best be understood in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a conventional display panel; 
         FIG. 2  shows a conventional advanced display panel; 
         FIG. 3  shows a conventional point-to-point display panel; 
         FIG. 4   a  shows an embodiment of the display panel according to the invention; 
         FIG. 4   b  shows another embodiment of the display panel according to the invention; and 
         FIG. 5  is a transmitted rate table respective to display resolution. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     A detailed description of the present invention is provided in the following. 
       FIG. 4   a  shows an embodiment of the display panel according to the invention. Each source driver  404  is individually connected a TCON  402  via exclusive transmission lines, such as R 1 , G 1 , and B 1  to R 8 , G 8 , and B 8 . Each transmission line exclusively delivers the information of red, green or blue. The TCON  402  also comprises a clock line CLK coupled to each source driver  404 , providing a sync signal for sync control. The display panel also comprises a reference voltage generator  406  coupled to each source driver  404 , providing gamma correction parameters. In this case, the TCON  402  utilizes a total of 24 transmission lines. The number of the transmission lines of the embodiment is more than the number of the transmission lines of the  FIG. 2 , however, the number of the bits of the gray level is not limited to 6 bits. The transmission lines Rx, Gx and Rx are not limited to delivering red, green and blue information. Specifically in this architecture, the reference voltage generator  406  can be eliminated, and the corresponding gamma correction parameters can be generated from the TCON  402  and delivered to the source drivers  404  via the transmission lines. 
       FIG. 4   b  shows another embodiment of the display panel according to the invention. The display panel comprises four source drivers  408 , each comprises two set of RGB transmission lines coupled to the TCON  402 . The source driver  408  is a merged version of the source driver  404  in  FIG. 4   a , therefore a total number of required source drivers is reduced. 
       FIG. 5  is a transmitted rate table of display resolution. Since the number of transmission lines each source driver replies on is fixed, the transmission rate is proportional to the data quantity. Typically, the clock rate of a TCON varies from screen resolution. For example, the TCON clock rate is 65 MHz under a 60Hz XGA mode, where 6 bits of gray level of red, green, or blue is given, and the source driver number is 8. Consider that both a rising edge and a falling edge of the TCON clock are effective triggers, therefore the transmission rate for each transmission line can be derived by the following equation to obtain 24.375 MHz:
 Transmission rate=(the clock of the timing controller×the number of the bits of the gray level)/(the number of the Source drivers×2) 
     In summery, additional DC biased voltage is not required to utilize TTL logic signal, thus providing a significant advantage when implementing low voltage products such as a 1.8V system. The transmission lines are reduced while providing unlimited bits of gray level, and the power consumption is reduced. 
     While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.