Abstract:
A liquid crystal display device and driving circuit thereof are provided. The liquid crystal display device includes a storage unit, an external gamma reference voltage generator and a source driver IC. The storage unit stores a plurality of digital gamma data each relating to at least one predetermined color. The source driver IC further comprises an internal gamma reference voltage generator and a digital to analog converter module. The internal gamma reference voltage generator generates a plurality of internal gamma reference voltage to the digital to analog converter module according to the digital gamma data supplied by the storage unit. The digital to analog converter module also receives a plurality of external gamma reference voltages supplied by the external gamma reference voltage generator.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to flat panel displays, and more particularly, to liquid crystal displays (LCDs) and driving circuits thereof. 
         [0003]    2. Description of Related Art 
         [0004]      FIG. 1  is a schematic diagram illustrating a source driver integrated circuit (IC)  1  for use in a conventional LCD display (not shown). The source driver IC  1  comprises a shift register  10 , a data register  11 , a data latch (also known as line latch)  12 , a level shifter  13 , a digital analog converter (DAC)  14 , and an output buffer  15 . The source driver IC  1  sequentially latches the RGB (Red, Green and Blue) data input thereto, converts the RGB data, and then outputs data voltages corresponding to the RGB data to the data lines on the display panel. According to the gamma reference voltage provided by a gamma reference voltage generator  2 , the DAC  14  converts the RGB data provided and level-shifted by the data latch  12  and the level shifter  13 , respectively. 
         [0005]    A plurality of transmission lines  21  exist between the gamma voltage generator  2  and the DAC  14 . Generally, the number of the transmission lines  21  used depends on the resolution of the source driver IC  1 . For instance, when the source driver IC  1  has a 6-bit resolution, ten transmission lines  21  are required; when source driver IC  1  has an 8-bit resolution, sixteen to twenty transmission lines  21  are required. 
         [0006]    In conventional LCDs, the differences in optical properties of the RGB pixels are not taken into account, and only a single gamma reference voltage related to the pixels is provided to the DAC  14 . However, in practical application, the optical properties of the RGB pixels are different, and the negligence of this consideration only results in the unbalance of gray levels of the colors displayed on the panel and visible color discrepancies on screen. 
         [0007]    To solve the aforementioned problems, three different sets of the gamma reference voltages characteristically related to the RGB pixels can be provided to the DAC  14 , accompanied by an increase in the number of the transmission lines  21 . For instance, when the source driver IC has a 6-bit resolution, the RGB pixels applied with a same gamma reference voltage would only require ten transmission lines; but instead if the RGB pixels are applied with three different sets of gamma reference voltages for the three respective RGB colors, then thirty transmission lines would be required, resulting in a steep increase in the printed circuit board (PCB) wiring area and manufacturing costs. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore an object of the present invention to provide an LCD device and the driving circuit thereof for reducing a wiring area of a PCB. 
         [0009]    It is therefore another object of the present invention to provide an LCD device and the driving circuit thereof for reducing manufacturing costs. 
         [0010]    According to one aspect of the invention, a driving circuit of an LCD device is provided. The driving circuit comprises a storage unit and a source driver integrated circuit (IC). The storage unit is for storing a plurality of digital gamma data, and the storage unit can be a non-volatile memory, such as an Electrically Erasable Programmable Read-Only Memory (EEPROM), an Erasable Programmable Read-Only Memory (EPROM), or a flash memory. 
         [0011]    The source driver IC is electrically connected to the storage unit through a serial transmission line, for example, through which the digital gamma data are transmitted from the storage unit to the source driver IC. The source driver IC further comprises a first gamma voltage generator and a DAC module. The first gamma voltage generator generates a plurality of sets of first gamma reference voltages according to the digital gamma data. The first gamma voltage generator outputs the first gamma reference voltages to the DAC module. The DAC module receives the first gamma reference voltages supplied by the first gamma voltage generator, and receives a plurality of second gamma reference voltages. The first gamma reference voltages are characteristically related to the gamma curve of a plurality of first predetermined colors. The second gamma reference voltages are characteristically related to the gamma curve of a second predetermined color. For instance, the first predetermined colors can be RGBW (Red, Green, Blue, and White), or RGBY (Red, Green, Blue and Yellow), or RGBC (Red, Green, Blue, and Cyan). The digital analog converter module converts video data according to the first gamma reference voltages or the second gamma reference voltages. 
         [0012]    According to another aspect of the present invention, an LCD device is provided. The LCD device comprises a display panel, a storage unit, and at least one source driver IC. The storage unit is for storing a plurality of digital gamma data. The source driver IC is electrically connected to the display panel, and electrically connected to the storage unit through serial transmission lines, for example, through which the digital gamma data are transmitted from the storage unit to the at least one source drive IC. The source driver IC further comprises a first gamma voltage generator and a DAC module. The first gamma voltage generator generates a plurality of sets of first gamma reference voltages according to the digital gamma data, and outputting the generated first gamma reference voltages to the DAC module. The DAC module receives the first gamma reference voltages from the first gamma voltage generator and receives a plurality of second gamma reference voltages. The first gamma reference voltages are characteristically related to the gamma curve of a plurality of the first predetermined colors. The second gamma reference voltages are characteristically related to the gamma curve of a plurality of the second predetermined colors. The DAC module therefore converts the video data according to the first gamma reference voltages or the second gamma reference voltages. 
         [0013]    The first gamma voltage generator comprises a deserializer, a positive gamma reference voltage generator, and a negative gamma reference voltage generator. The deserializer is electrically connected to the positive gamma reference voltage generator and the negative gamma reference voltage generator. 
         [0014]    The deserializer receives the serial digital gamma data supplied by the storage unit and divides the serial digital gamma data into a first digital data and a second digital data for outputting to the positive gamma reference voltage generator and the negative gamma reference voltage generator, respectively. 
         [0015]    The positive reference voltage generator generates a plurality of sets of positive gamma reference voltages according to the first digital data for outputting to the DAC module. The negative reference voltage generator generates a plurality of sets of negative gamma reference voltages according to the second digital data for outputting to the DAC module. 
         [0016]    The positive gamma reference voltage generator comprises a first DAC, a first sample-and-hold circuit, and a plurality of first unity-gain buffers. The first DAC is electrically connected to the deserializer and the first sample-and-hold circuit. The first sample-and-hold circuit is electrically connected to the first unity-gain buffers. 
         [0017]    The first DAC receives the first digital data and converts the same into one of the first gamma reference voltages to be transmitted to one of the first unity-gain buffers and output to the DAC module. 
         [0018]    The negative gamma reference voltage generator=comprises a second DAC, a second sample-and-hold circuit, and a plurality of second unity-gain buffers. The second DAC is electrically connected to the deserializer and the second sample-and-hold circuit. The second sample-and-hold circuit is electrically connected to the second unity-gain buffers. 
         [0019]    The digital gamma data reference table is stored in the storage unit in the form of reference tables, and the source driver IC determines the reference table for use therefrom according to an environmental parameter (e.g., temperature). 
         [0020]    Other objects, advantages, and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic diagram illustrating the source driver IC of a conventional LCD. 
           [0022]      FIG. 2  is a functional block diagram illustrating a preferred embodiment of the invention. 
           [0023]      FIG. 3  is a functional block diagram illustrating a gamma voltage generator according to a preferred embodiment of the invention. 
           [0024]      FIG. 4  is a schematic diagram illustrating a preferred embodiment of the invention. 
           [0025]      FIG. 5  is a plot illustrating the gamma curve of a source driver IC according to a preferred embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]      FIG. 2  is a functional block diagram illustrating a preferred embodiment of a driving circuit, according to the present invention. The driving circuit  20  comprises a storage unit  3 , an external (second) gamma voltage generator  4 , and a source driver IC  5 . The source driver IC  5  comprises an internal (first) gamma voltage generator  51 , a data register  52 , a shift register  53 , a data latch  54 , a level shifter  55 , a DAC module  56 , and an output buffer  57 . 
         [0027]    The storage unit  3  is electrically connected to the source driver IC  5 . For instance, the storage unit  3  is electrically connected to the internal gamma voltage generator  51  of the source driver IC  5  through a serial transmission line  30 , for example. The external gamma voltage generator  4  and the internal gamma voltage generator  51  are both electrically connected to the DAC module  56 . The DAC module  56  is electrically connected to the output buffer  57  and the level shifter  55 . The Data latch  54  is electrically connected to the level shifter  55 , the data register  52 , and the shift register  53 . 
         [0028]    In this embodiment, the storage unit  3  is an EEPROM, for example. In other embodiments, the storage unit  3  can also be other types of non-volatile memory, such as a flash memory, or an EPROM. The storage unit  3  is stored with a plurality of digital gamma data. The digital gamma data are characteristically related to the gamma curve of the predetermined colors respectively. For instance, the predetermined colors can be red (R), green (G), blue (B), white (W), yellow (Y), or cyan (C). That is, the digital gamma data can be characteristically related to RGBW, RGBY or RGBC, achieving better color performance through a multi-color calibration system. Besides, during the manufacturing process, the digital gamma data can be stored in the storage unit  3  in the form of reference tables such that the source drive IC  5  can select the reference table to use therefrom according to environmental parameters such as temperature or the like. 
         [0029]      FIG. 3  depicts the functional block diagram of the internal gamma voltage generator, according to the present invention, and reference is also made to  FIG. 2  for illustration. The internal gamma voltage generator  51  comprises a deserializer  511 , a positive gamma reference voltage generator  512 , and a negative gamma reference voltage generator  513 . The positive gamma reference voltage generator  512  comprises a first internal DAC  5121 , a first sample-and-hold circuit  5122 , and a plurality of first unity-gain buffers  5123 . The negative gamma reference voltage generator  513  comprises a second internal DAC  5131 , a second sample-and-hold circuit  5132 , and a plurality of second unity-gain buffer  5133 . 
         [0030]    The deserializer  511  is electrically connected to the positive gamma reference voltage generator  512  and the negative gamma reference voltage generator  513 . Specifically, the deserializer  511  is electrically connected to both the first internal the DAC  5121  of the positive gamma reference voltage generator  512  and the second internal DAC  5131  of the negative gamma reference voltage generator  513 . The first internal DAC  5121  is also electrically connected to the first sample-and-hold circuit  5122 , and the first sample-and-hold circuit  5122  is electrically connected to the first unity-gain buffers  5123 . The second internal DAC  5131  is also electrically connected to the second sample-and-hold circuit  5132 , and the second sample-and-hold circuit  5132  is electrically connected to the second unity-gain buffers  5133 . 
         [0031]    Referring to  FIGS. 2 and 3 , the internal gamma voltage generator  51  receives the serial digital gamma data supplied by the storage unit  3 , and according to the digital gamma data, generates a plurality of sets of internal gamma reference voltages for outputting to the DAC module  56 . For instance, if the source driver IC  5  makes use of the RGBW gamma reference voltages, then the storage unit  3  supplies digital gamma data characteristically related to the RGBW colors (i.e. the digital gamma data is characteristically related to the gamma curve of each of the colors respectively) to the internal gamma voltage generator  51  of the source driver IC  5 . Then; after the internal gamma voltage generator  51  receives the digital gamma data, the deserializer  511  divides the serial digital gamma data into a first digital data and a second digital data, wherein the first digital data is transmitted to the positive gamma reference voltage generator  512 , and the second digital data is transmitted to the negative gamma reference voltage generator  513 . 
         [0032]    Further referring to  FIGS. 2 and 3 , the positive gamma reference voltage generator  512  generates a plurality of sets of internal positive gamma reference voltages according to the first digital data for outputting to the DAC module  56 . That is, after receiving the first digital data, the first internal DAC  5121  of the positive gamma reference voltage generator  512  converts the first digital data into a positive internal gamma reference voltage, and through the sample-and-hold circuit  5122 , the positive internal gamma reference voltage is output to one set of the first unity gain buffers  5123  for voltage stabilization. The stabilized positive internal gamma reference voltage is then output to the positive-voltage-portion-of-DAC  561  of the DAC module  56 , as shown in  FIG. 3 . 
         [0033]    Referring to  FIG. 3 , the sample-and-hold circuit  5122  comprises a plurality of sample-and-hold units, with each of which sampling the positive internal gamma reference voltage characteristically related to one of the colors. For instance, one of the sample-and-hold units can sample a plurality of sets of the positive internal gamma reference voltages characteristically related to the color red (R). That sample-and-hold unit then can transmit the sampled voltages to the corresponding part of the first unity-gain buffers  5123 . 
         [0034]    Similarly, the negative gamma reference voltage generators  513  generate a plurality of sets of the internal negative gamma reference voltages according to the second digital data for outputting to the DAC module  56 . That is, after receiving the second digital data, the second internal DAC  5131  of the negative gamma reference voltage generator  513  converts the second digital data into a negative internal gamma reference voltage, and through the sample-and-hold circuit  5132  the negative internal gamma reference voltage is output to one set of the second unity gain buffers  5133  for voltage stabilization. The stabilized negative internal gamma reference voltage is then output to the negative-voltage-portion-of-DAC  562  of the DAC module  56 . 
         [0035]    Although the source driver IC  5  makes use of more than one gamma reference voltages characteristically related to the colors, only one transmission line is sufficient for operation since in this embodiment the digital gamma data characteristically related to the colors is already stored in the storage unit  3  and transmitted via the serial transmission line  30 , for example. Through such configuration, the wiring area on the PCB and manufacturing costs can therefore be greatly reduced. 
         [0036]      FIG. 4  is a schematic diagram illustrating a preferred embodiment of an LCD module  40 , according to the present invention. The LCD module  40  comprises a storage unit  3 , an external (second) gamma voltage generator  4 , a plurality of source driver ICs  5 ,  6 , and  7 , a plurality of gate driver ICs  81 ,  82 , and  83 , and a display panel  9 . The source driver ICs  5 ,  6 , and  7  and the gate driver ICs  81 ,  82 , and  83  are all electrically connected to the display panel  9 . The storage unit  3  is electrically connected to the source driver ICs  5 ,  6 , and  7 . The external gamma voltage generator  4  is electrically connected to the source driver ICs  5 ,  6 , and  7 . The operation of the source driver ICs  5 ,  6 , and  7  is as previously described. 
         [0037]      FIG. 5  is a plot illustrating the gamma curve of a source driver IC, according to the present invention, which is divided into four parts, i.e., A, B, C, and D. The parts A, B, and D on the plot experience greater changes (i.e., greater change in gray levels), and the part C experiences less changes (i.e., smaller change in gray levels). Therefore, when the video data received by the source drive IC fall within the predetermined section of the gamma curve (part C of the curve), the DAC module receives the plurality of sets of externally input gamma reference voltages (characteristically related to the gamma curve of one of the colors) supplied by the external gamma voltage generator. The externally input gamma reference voltage comprises a plurality of sets of external positive gamma reference voltages and external negative gamma reference voltages. The DAC module then converts the received video data according to the externally input gamma reference voltages. Alternatively, when the video data received by the source driver IC do not fall within the predetermined section of the gamma curve (i.e., fall within A, B, D parts of the curve), the DAC module converts the received video data according to the internal gamma reference voltages. 
         [0038]    Thus, with the hybrid analog/digital gamma voltage generation supplied by the embodiment of the present invention, when the source driver IC displays part of a picture, the internal gamma reference voltage is generated according to the digital gamma data, which are characteristically related to at least one color. Also, the present invention achieves better color performance without the use of the excessive wiring area that increases size and manufacturing costs. Additionally, when certain pictures are displayed, the source driver IC can still employ conventional methods to supply gamma reference voltages, and hence without the use of the excessive internal gamma reference voltages (which are characteristically related to at least a color) but rather merely one set of the external gamma reference voltage characteristically related to certain colors is sufficient to achieve the required color performance, thus reducing power consumption. 
         [0039]    Although the present invention has been explained in relation to its preferred embodiments, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.