Abstract:
A source driver and a liquid crystal display are provided. The source driver includes a plurality of pads, a first conducting wire, a second conducting wire, a plurality of first digital-to-analog converters (DACs), and a plurality of second DACs. The first conducting wire is coupled to a first voltage and the first DACs. The second conducting wire is coupled to a second voltage and the second DACs. The first DACs are disposed in a first layer. Output terminals of the first DACs are respectively coupled to a plurality of first pads included in the said pads. The second DACs are disposed in a second layer above the first layer. Output terminals of the second DACs are respectively coupled to a plurality of second pads included in the said pads. Thereby, the transmission quality of the conducting wires for transmitting signals is increased.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority benefit of Taiwan application serial no. 97123184, filed Jun. 20, 2008. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a liquid crystal display. More particularly, the present invention relates to a source driver. 
         [0004]    2. Description of Related Art 
         [0005]    Source driver is an important component within a thin film transistor liquid crystal display (TFT LCD), which can convert a digital signal required for displaying images into an analog signal, and transmits the analog signal to each sub-pixel (or referred to as dot) of the TFT LCD. 
         [0006]    Generally, buffer amplifiers of the source driver are disposed between digital-to-analog converters (DAC) and output pads, though such method requires a plenty of buffer amplifiers. To reduce the quantity of the buffer amplifiers within the source driver, the DACs are disposed between the buffer amplifiers and the output pads according to the conventional technique, detailed description thereof is as follows. 
         [0007]      FIG. 1  is a schematic diagram illustrating a conventional LCD. Referring to  FIG. 1 , only a display panel  20  and a source driver  30  are illustrated in the LCD  10 . The DACs DR 1 -DR 100 , DG 1 -DG 100  and DB 1 -DB 100  of the source driver  30  are disposed between buffer amplifiers  41  and  42  and pads R 1 -R 100 , G 1 -G 100  and B 1 -B 100 . The pads R 1 -R 100 , G 1 -G 100  and B 1 -B 100  are respectively coupled to data lines DL of the display panel  20 . 
         [0008]    The buffer amplifiers  41  and  42  are used for providing a gamma voltage to the DACs DR 1 -DR 100 , DG 1 -DG 100  and DB 1 -DB 100 . It should be noted that since conducting wires  51  and  52  have line impedance, when the gamma voltage is transmitted by the conducting wires  51  and  52 , it may be gradually attenuated, so that the DACs may receive different gamma voltages. As the impedance of the conducting wires  51  and  52  becomes greater, the gamma voltages received by the DACs are increasingly different. 
         [0009]    Moreover, a charging time T of a capacitor C of the display panel  20  is 5*r*n*Cload, wherein 5 times r*Cload is a time constant for the capacitor C being charged to 99%, r is an average impedance between the buffer amplifiers and each channel, n is a number of channels driven by a single buffer amplifier. Since the impedance of the conducting wires  51  and  52  directly influences the r value, and the greater the impedance of the conducting wires  51  and  52  is, the longer the charging time T of the capacitor C is. If the charging time T is excessive long, it may influence the display quality of the display panel  20 . 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is directed to a source driver, which may decrease an impedance of internal wiring. 
         [0011]    The present invention is directed to an LCD, which may apply the aforementioned source driver to improve a display quality thereof. 
         [0012]    The present invention provides a source driver including a plurality of pads, a first conducting wire, a second conducting wire, a plurality of first digital-to-analog converters (DACs), and a plurality of second DACs. The first conducting wire is coupled to a first voltage and the first DACs. The second conducting wire is coupled to a second voltage and the second DACs. The first DACs are disposed in a first layer, and output terminals of the first DACs are respectively coupled to a plurality of first pads included in the said pads. The second DACs are disposed in a second layer above the first layer, and output terminals of the second DACs are respectively coupled to a plurality of second pads included in the said pads. 
         [0013]    In an embodiment of the present invention, the source driver further includes a buffer amplifier. An output terminal of the buffer amplifier is coupled to the first conducting wire and the second conducting wire for providing the first voltage and the second voltage. The buffer amplifier can be disposed in the first layer or the second layer. 
         [0014]    In an embodiment of the present invention, the source driver further includes a first buffer amplifier and a second buffer amplifier. An output terminal of the first buffer amplifier is coupled to the first conducting wire for providing the first voltage. An output terminal of the second buffer amplifier is coupled to the second conducting wire for providing the second voltage. 
         [0015]    In another embodiment of the present invention, the source driver further includes a third conducting wire, a fourth conducting wire, a third buffer amplifier and a fourth buffer amplifier. The third conducting wire is coupled to a third voltage and the first DACs. The fourth conducting wire is coupled to a fourth voltage and the second DACs. An output terminal of the third buffer amplifier is coupled to the third conducting wire for providing the third voltage. An output terminal of the fourth buffer amplifier is coupled to the fourth conducting wire for providing the fourth voltage. 
         [0016]    In an embodiment of the present invention, the source driver further includes a third conducting wire and a plurality of third DACs. The third conducting wire is coupled to the third voltage and the third DACs. The third DACs are disposed in a third layer above the second layer, and output terminals thereof are correspondingly coupled to a plurality of third pads included in the said pads. In another embodiment, the first pads, the second pads and the third pads can be arranged in interleaving. 
         [0017]    The present invention provides an LCD including a display panel and the aforementioned source driver. The display panel includes a pixel array coupled to a plurality of data lines. The data lines are correspondingly coupled to the pads of the source driver. 
         [0018]    In the source driver of the present invention, the first conducting wire is coupled to the first voltage and a plurality of the first DACs, and the second conducting wire is coupled to the second voltage and a plurality of the second DACs. The first DACs are disposed in the first layer, and the second DACs are disposed in the second layer above the first layer. Therefore, signal transmission quality of the conducting wires can be improved. 
         [0019]    In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    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. 
           [0021]      FIG. 1  is a schematic diagram illustrating a conventional LCD. 
           [0022]      FIG. 2  is a schematic diagram illustrating an LCD according to a first embodiment of the present invention. 
           [0023]      FIG. 3  is a schematic diagram illustrating an LCD according to a second embodiment of the present invention. 
           [0024]      FIG. 4  is a schematic diagram illustrating an LCD according to a third embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    In the conventional technique, the DACs of the source driver are all disposed in a same layer. Such method may lead to excessive impedance between the DACs and the buffer amplifiers within the source driver, so that display quality of the LCD is decreased. Accordingly, in embodiments of the present invention, a plurality of first DACs are disposed in a first layer, and a plurality of second DACs are disposed in a second layer, so as to resolve the problem of excessive impedance between the DACs and the buffer amplifiers within the source driver. Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements or steps throughout. 
       First Embodiment 
       [0026]      FIG. 2  is a schematic diagram illustrating an LCD according to a first embodiment of the present invention. Referring to  FIG. 2 , the LCD  11  includes a display panel  21  and a source driver  31 . The display panel  21  may include a pixel array (not shown), a plurality of scan lines (not shown) and a plurality of data lines DL, wherein the pixel array is coupled to the scan lines and the data lines DL. The source driver  31  may include buffer amplifiers  43  and  44 , conducting wires  53 - 58 , DACs DR 1 -DR 100 , DG 1 -DG 100  and DB 1 -DB 100 , and pads R 1 -R 100 , G 1 -G 100  and B 1 -B 100 . 
         [0027]    The buffer amplifier  43  is coupled to the conducting wires  53 ,  55  and  57 . The buffer amplifier  44  is coupled to the conducting wires  54 ,  56  and  58 . The conducting wires  53  and  54  are respectively coupled to the DACs DR 1 -DR 100 . The conducting wires  55  and  56  are respectively coupled to the DACs DG 1 -DG 100 . The conducting wires  57  and  58  are respectively coupled to the DACs DB 1 -DB 100 . The DACs DR 1 -DR 100  are respectively coupled to the pads R 1 -R 100 . The DACs DG 1 -DG 100  are respectively coupled to the pads G 1 -G 100 . The DACs DB 1 -DB 100  are respectively coupled to the pads B 1 -B 100 . The pads R 1 -R 100 , G 1 -G 100  and B 1 -B 100  are correspondingly coupled to the data lines DL of the display panel  21 . In  FIG. 2 , quantities of the buffer amplifiers, the conducting wires, the DACs and the pads and coupling method thereof are only an example, and the present invention is not limited thereto. 
         [0028]    In the present embodiment, the buffer amplifier can be used for providing a gamma voltage. Particularly, the buffer amplifier  43  can provide a positive polarity gamma voltage to the conducting wires  53 ,  55  and  57 . The buffer amplifier  44  can provide a negative polarity gamma voltage to the conducting wires  54 ,  56  and  58 . The DACs DR 1 -DR 100 , DG 1 -DG 100 , and DB 1 -DB 100  can convert digital signals into analog signals. To be specific, the DACs DR 1 -DR 100  can convert the digital signals with red gray level into the analog signals, the DACs DG 1 -DG 100  can convert the digital signals with green gray level into the analog signals, and the DACs DB 1 -DB 100  can convert the digital signals with blue gray level into the analog signals. The pads R 1 -R 100 , G 1 -G 100 , and B 1 -B 100  can function as signal output terminals of the source driver  31 . To be more specific, the pads R 1 -R 100  can function as output terminals of red analog signals, the pads G 1 -G 100  can function as output terminals of green analog signals, and the pads B 1 -B 100  can function as output terminals of blue analog signals. In the present embodiment, though the pads R 1 -R 100 , G 1 -G 100  and B 1 -B 100  are arranged in interleaving, the present invention is not limited thereto. 
         [0029]    It should be noted that in the present embodiment, the DACs DB 1 -DB 100  are disposed in a first layer, the DACs DG 1 -DG 100  are disposed in a second layer, and the DACs DR 1 -DR 100  are disposed in a third layer. Since the DACs are averagely disposed in the first to the third layers, an area of each layer can be effectively reduced. In the present embodiment, the buffer amplifiers  43  and  44  are disposed in the third layer, though the present invention is not limited thereto, and in other embodiments, the buffer amplifiers  43  and  44  can also be disposed at other positions such as the first layer or the second layer. 
         [0030]    According to another aspect, in the present embodiment, since the DACs are averagely disposed in the first to the third layers, the area of each layer can be effectively reduced, and lengths of the conducting wires  53 - 58  are shortened accordingly. It is known by those skilled in the art that the impedance of the leading wire is proportion to the length thereof. Therefore, averagely disposing the DACs in the first to the third layers can effectively reduce the impedances of the conducting wires  53 - 58 , so as to improve signal transmission qualities of the conducting wires  53 - 58 . Besides, a charging time of a capacitor C of the display panel  21  can also be effectively shortened, so as to improve a displaying quality of the LCD  11 . 
         [0031]    In the present embodiment, only one source driver  31  is illustrated in  FIG. 2 , though the present invention is not limited thereto. It is known by those skilled in the art that different number of the source drivers can be disposed in the LCD  11  according to a size of the display panel  21 , and implementing of the source drivers can be the same to that of the aforementioned source driver  31 , and detailed description thereof will not be repeated. 
         [0032]    Moreover, though the DACs are averagely disposed in the first layer, the second layer and the third layer, the present invention is not limited thereto. In other embodiments, the DACs of the source drivers  31  can also be dispatched in M layers, wherein M is a positive integer that is greater than or equal to 2. By such means, a similar function as the aforementioned embodiment can be achieved. 
         [0033]    It should be noted that though in the aforementioned embodiment, a possible pattern of the LCD and the source driver has been described in the above embodiment, it should be understood by those skilled in the art that the design of the LCD and the source driver varies with manufacturers, thus, application of the present invention should not be limited to such possible pattern. In other words, the spirit of the present invention is still met as long as a plurality of the first DACs of the source driver is disposed in the first layer and a plurality of the second DACs of the source driver is disposed in the second layer. To fully convey the concept of the present invention to those skilled in the art, embodiments are provided below for describing the present invention in detail. 
       Second Embodiment 
       [0034]      FIG. 3  is a schematic diagram illustrating an LCD according to a second embodiment of the present invention. Referring to  FIG. 2  and  FIG. 3 , in the first embodiment, the buffer amplifiers  43  and  44  of the source driver  31  are respectively used for providing a gamma voltage to the three hundred DACs. Though, in other embodiments, different number of the buffer amplifiers can be disposed in the source driver to provide the gamma voltage to the DACs. For example, in a source driver  32  of the present embodiment, four buffer amplifiers  45 ,  46 ,  45 ′ and  46 ′ are applied. To be more specific, the buffer amplifiers  45  and  46  respectively provide the gamma voltage to the DACs DR 1 -DR 50 , DG 1 -DG 50  and DB 1 -DB 50 , and the buffer amplifiers  45 ′ and  46 ′ respectively provide the gamma voltage to the DACs DR 51 -DR 100 , DG 51 -DG 100  and DB 51 -DB 100 . 
         [0035]    The buffer amplifiers  45 ,  46 ,  45 ′ and  46 ′ respectively provide the gamma voltage to the one hundred and fifty DACs, while the buffer amplifiers  43  and  44  respectively provide the gamma voltage to the three hundred DACs. Therefore, a length of the conducting wires  53 ′- 58 ′ is only a half of the length of the conducting wires  53 - 58 . As described in the first embodiment, the impedance of the conducting wire is proportion to the length thereof. Therefore, compared to the first embodiment, the signal transmission quality of the conducting wires  53 - 58  can be further improved, the charging time of the capacitor C of the display panel  21  can be shortened, and the display quality of the LCD  12  can be improved. In the following content, another embodiment is provided for further description. 
       Third Embodiment 
       [0036]      FIG. 4  is a schematic diagram illustrating an LCD according to a third embodiment of the present invention. Referring to  FIG. 2  and  FIG. 4 , a source driver  33  of the LCD  13  applies six buffer amplifiers  47 ,  48 ,  47 ′,  48 ′,  47 ″ and  48 ″. The buffer amplifiers  47 ″ and  48 ″ are disposed in the first layer for respectively providing the gamma voltage to the DACs DB 1 -DB 100 . The buffer amplifiers  47 ′ and  48 ′ are disposed in the second layer for respectively providing the gamma voltage to the DACs DG 1 -DG 100 . The buffer amplifiers  47  and  48  are disposed in the third layer for respectively providing the gamma voltage to the DACs DR 1 -DR 100 . In the present embodiment, the buffer amplifiers  47 ,  48 ,  47 ′,  48 ′,  47 ″ and  48 ″ of the source driver  33  respectively provide the gamma voltage to the one hundred DACs, and the buffer amplifier  43  and  44  of the source driver  31  of the first embodiment respectively provide the gamma voltage to the three hundred DACs. Compared to  FIG. 2 , the source driver  33  of  FIG. 4  not only has similar functions as the source driver  31  of  FIG. 2 , but may also improve a driving capability of the buffer amplifiers thereof. 
         [0037]    In summary, in the source driver of the present invention, a plurality of the DACs is dispatched in multi layer. Therefore, the area of each layer can be reduced. Moreover, the embodiments of the present invention have at least the following advantages:
       1. Since the area of each layer is reduced, the lengths of the conducting wires between the buffer amplifiers and the DACs are shortened accordingly, and since the length of the conducting wire is proportion to the impedance, as the lengths of the conducting wires are shortened, the signal transmission quality of the conducting wires can be improved.   2. Since the charging time of the capacitor of the display panel is proportion to the impedance of the conducting wire (the impedance of the conducting wire between the buffer amplifier and the DAC), as the length of the conducting wire is shortened, the charging time of the capacitor of the display panel is shortened accordingly, so that the display quality of the LCD is improved.       
 
         [0040]    3. The DACs are divided into a plurality of regions, and suitable number of buffer amplifiers is disposed in each region for providing the gamma voltage to the DACs of each region. By such means, the length of the conducting wire between the buffer amplifier and the DAC can be further reduced.
       4. Increasing the number of the buffer amplifiers of the source driver can enhance the driving capability of the buffer amplifiers.       
 
         [0042]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure or 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 cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.