Abstract:
The present invention discloses an apparatus for driving a display in which each pixels of the display receives a driving voltage and a common voltage, and a luminance of each pixel is determined by a difference between the received driving voltage and the common voltage. The apparatus comprises a plurality of source driver chips, each of which receives a pixel value and generates the driving voltage corresponding to the pixel value according to a plurality of Gamma voltages, wherein at least one of the Gamma voltages is generated by one of the source driver chips.

Description:
FIELD OF THE INVENTION  
       [0001]    The present invention relates to a driving apparatus, and more particularly, to a LCD (Liquid Crystal Display) driving apparatus having gamma or common voltage generation circuits integrated into source drivers. 
       BACKGROUND OF THE INVENTION  
       [0002]    An LCD driving system must include circuits for generation of a common voltage and a group of gamma voltages. Each of the pixels of the LCD panel receives a driving voltage and the common voltage, and a voltage difference therebetween determines the orientation of liquid crystals and therefore the luminance of the pixel. The driving voltages are generated by source drivers. Each source driver receives a pixel value and selects one of the gamma voltages as the driving voltage corresponding to the received pixel value. 
         [0003]      FIG. 1  shows a conventional common voltage (denoted as Vcom voltage hereinafter) generation circuit. The conventional Vcom voltage generation circuit is set in a system PCB board. Strings of resistors and a changeable resistor divide the voltage difference between a high reference voltage (denoted as VrefH in  FIG. 1 ) and a low reference voltage (denoted as VrefL in  FIG. 1 ) to generate the Vcom voltage. Then, the Vcom voltage generated is sent out through an output buffer and further to a panel via a tape. 
         [0004]      FIG. 2  shows a conventional Gamma voltage generation circuit. The conventional Gamma voltage generation circuit is also set in the system PCB board. Strings of resistors divide the voltage difference between a high reference voltage (denoted as VrefH in  FIG. 2 ) and a low reference voltage (denoted as VrefL in  FIG. 2 ) to generate different Gamma voltages. Then, the Gamma voltages generated are sent out through output buffers and further sent to each source driver chips in a source driver circuit. 
         [0005]    Since the Vcom voltage generation circuit and the Gamma voltage generation circuit are set in the system PCB board, the layout of the system PCB board is complicated and is not cost effective. 
       SUMMARY OF THE INVENTION 
       [0006]    Therefore, one objective of the present invention is to provide an apparatus for driving a display to generate at least one Gamma voltage or a common voltage. 
         [0007]    Another objective of the present invention is to provide a Gamma voltage generation circuit, located in each source driver chips of a source driver circuit, generating at least one Gamma voltage to send to other source driver chips and to receive other Gamma voltages from other source driver chips. 
         [0008]    Still another objective of the present invention is to provide an apparatus for driving a display in which the Gamma voltage is generated according to a chip select control signal and signals sent from a timing controller. 
         [0009]    Still another objective of the present invention is to provide an apparatus for driving a display to simplify the layout of the system PCB board and to be cost effective. 
         [0010]    According to the aforementioned objectives, the present invention provides an apparatus for driving a display in which each pixels of the display receives a driving voltage and a common voltage, and a luminance of each pixel is determined by a difference between the received driving voltage and the common voltage. The apparatus comprises a plurality of source driver chips, each of which receives a pixel value and outputs the driving voltage corresponding to the pixel value according to a plurality of Gamma voltages, wherein at least one of the Gamma voltages is generated by one of the source driver chips. 
         [0011]    According to the preferred embodiment of the present invention, each of the source driver chips generates at least one of the Gamma voltages. Each of the source driver chips comprises a control module generating a selection code and at least one digital-to-analog converter outputting the Gamma voltage according to the selection code. Each of the source driver chips further comprises at least one output buffer receiving the Gamma voltage from the digital-to-analog converter and outputting the Gamma voltage. The control module generates the selection code according to a chip select control signal identifying a chip number of the source driver chip. The control module generates the selection code according to a voltage value output from a voltage selecting module. The voltage selecting module comprises a register and the voltage value is stored into the register according to a control signal sent from a timing controller. The voltage selecting module comprises a one-time-programming (OTP) memory which is programmed to generate the voltage value. The setting of the OTP memory can be programmed according to a register in the voltage selecting module and be fixed through a testing input signal. The voltage selecting module comprises a ROM storing the voltage value. The control module may be a multiplexer. The digital-to-analog converter receives a plurality of reference voltages to generate the Gamma voltage. The digital-to-analog converter has a R2R structure. 
         [0012]    According to another objective, the present invention provides a Gamma voltage generation circuit, embedded in a source driver chip. The Gamma voltage generation circuit generates at least one Gamma voltage and comprises a voltage selecting module determining a voltage value, a control module generating a selection code according to the voltage value, and at least one digital-to-analog converter outputting the Gamma voltage according to the selection code. 
         [0013]    According to the preferred embodiment of the present invention, the Gamma voltage generation circuit further comprises at least one output buffer receiving the Gamma voltage from the digital-to-analog converter and outputting the Gamma voltage. The control module generates the selection code according to a chip select control signal identifying a chip number of the source driver chip. The voltage selecting module comprises a register and the voltage value is stored into the register according to a control signal. The control signal is sent from a timing controller. The voltage selecting module comprises a one-time-programming (OTP) memory which is programmed to generate the voltage value. The setting of the OTP memory can be programmed according to a register in the voltage selecting module and be fixed through a testing input signal. The voltage selecting module comprises a ROM storing the voltage value. The control module may be a multiplexer. The digital-to-analog converter receives a plurality of reference voltages to generate the Gamma voltage. The digital-to-analog converter has a R2R structure. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0015]      FIG. 1  illustrates a conventional Vcom voltage generation circuit; 
           [0016]      FIG. 2  illustrates a conventional Gamma voltage generation circuit; 
           [0017]      FIG. 3  illustrates a diagram of driving system according to the source driver circuit/chip of the preferred embodiment of the present invention; 
           [0018]      FIG. 4  illustrates the block diagram of the Gamma voltage generation circuit according to the preferred embodiment of the present invention; and 
           [0019]      FIG. 5  illustrates the block diagram of the Vcom voltage generation circuit according to the preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    In order to make the illustration of the present invention more explicit and complete, the following description is stated with reference to  FIGS. 3 through 5 . 
         [0021]    Reference is made to  FIG. 3  illustrating a diagram of driving system according to the source driver circuit/chip of the preferred embodiment of the present invention. Each source driver chip receives pixel values (not shown) and outputs driving voltages corresponding to the pixel values according to a plurality of Gamma voltages. As shown in  FIG. 3 , a Vcom voltage generation circuit  314  and a Gamma voltage generation circuit  316  are both located in a source driver chip  306  in the preferred embodiment of the present invention. The Vcom voltage generation circuit  314  and the Gamma voltage generation circuit  316  generate a Vcom voltage and a Gamma voltage, respectively. Furthermore, the source driver chips ( 306 ,  308 ,  310 ,  312 ) also generate and send out at least one Gamma voltage, respectively, and receive other Gamma voltages provided by other source driver chips. In other words, at least one of the Gamma voltages (Gamma  1 ˜ 4 ) is generated by one of the source driver chips ( 306 ˜ 312 ). Besides, each of the source driver chips also send out a Vcom voltage and the Vcom voltage can be sent to a panel via a tape (not shown in the drawing). The detail of how the Gamma voltage generation circuit  316  and the Vcom voltage generation circuit  314  in the source driver chip function will be describe as follows. 
         [0022]    Reference is made to  FIG. 4  illustrating the block diagram of the Gamma voltage generation circuit according to the preferred embodiment of the present invention. The Gamma voltage generation circuit is located in the source driver chip. As shown in  FIG. 4 , the Gamma voltage generation circuit comprises a voltage selecting module  402 , a control module  404 , a digital-to-analog converter  408  and an output buffer  410 . The voltage selecting module  402  selects one of voltage values corresponding to the Gamma voltages according to a control signal  412 . The control signal  412  may be a serial control bus signal sent from the timing controller. A register  422 , a one-time-programming (OTP) memory  424  and a ROM  426  are set in the voltage selecting module  402 . The voltage values corresponding to the Gamma voltages are stored into the register  422  according to the control signal  412  during development, testing or normal operation stage. It is also the one-time-programming (OTP) memory  424  or the ROM  426  that can be used to generate the voltage values. The setting of the OTP memory  424  can be programmed according to the data from the register  422  and be fixed through a testing input signal  414 . 
         [0023]    A chip select control signal  406  is inputted to the control module  404  to determine each source driver chip generates the corresponding Gamma voltage, respectively, since the Gamma voltage generation circuits are all the same in each source driver chip. That is, although the source driver chips are the same, just by controlling the chip select control signal  406  can make different Gamma voltage generation circuits generate different Gamma voltages as shown in  FIG. 3 . The chip select control signal  406  may be an address with at least one bit, and the bit number is based on the amount of the source driver chips. For example, if there are eight source driver chips, the address will be 3 bit. 
         [0024]    The control module  404  generates a selection code according to the voltage value outputted from the voltage selecting module  402  and according to the chip select control signal  406  identifying a chip number of the source driver chip. The control module  404  may be a multiplexer. The digital-to-analog converter  408  generates the Gamma voltage of the current Gamma voltage generation circuit according to the selection code. Then, the Gamma voltage is outputted via the output buffer  410 . The digital-to-analog converter  408  receives a plurality of reference voltages  416  that are filtered out the noise to generate the Gamma voltage. The digital-to-analog converter  408  may have a R2R structure. 
         [0025]    It is noted that the Gamma voltage generation circuit of the present invention may also generate more than one Gamma voltage. It can be embodied by adding more sets of digital-to-analog converters and output buffers coupled to the control module. 
         [0026]    Hence, a feature of the present invention is that the Gamma voltage generation circuit and the output buffer are set in each of the source driver chips. 
         [0027]    Another feature of the present invention is that the Gamma voltage generation circuit generates at least one Gamma voltage to send to other source driver chips and receives other Gamma voltages from other source driver chips. 
         [0028]    Still another feature of the present invention is that the control module in the Gamma voltage generation circuit generates a selection code according to the voltage value outputted from the voltage selecting module and according to the chip select control signal identifying a chip number of the source driver chip. 
         [0029]    Similarly, reference is made to  FIG. 5  illustrating the block diagram of the Vcom voltage generation circuit according to the preferred embodiment of the present invention. The Vcom voltage generation circuit is also located in the source driver chip. As shown in  FIG. 5 , the Vcom voltage generation circuit comprises a voltage selecting module  502 , a control module  504 , a digital-to-analog converter  506  and an output buffer  508 . The voltage selecting module  502  selects one of the voltage values corresponding to the Vcom voltages according to a control signal  512 . The control signal  512  may be a serial control bus signal sent from the timing controller. A register  522 , a one-time-programming (OTP) memory  524  and a ROM  526  are set in the voltage selecting module  502 . The voltage values corresponding to the Vcom voltages are stored into the register  522  according to the control signal  512  during development, testing or normal operation stage. It is also the one-time-programming (OTP) memory  524  or the ROM  526  that can be used to generate the voltage value. The setting of the OTP memory  524  can be programmed according to the data from the register  522  and be fixed through a testing input signal  514 . 
         [0030]    The control module  504  generates a selection code according to the voltage value outputted from the voltage selecting module  502 . The control module  504  may be a multiplexer. The digital-to-analog converter  506  generates the Vcom voltage of the current Vcom voltage generation circuit according to the selection code. Then, the Vcom voltage is outputted via the output buffer  508 . The digital-to-analog converter  506  receives a plurality of reference voltages  516  that are filtered out the noise to generate the Vcom voltage. The digital-to-analog converter  506  may have a R2R structure. 
         [0031]    It is noted that there is no need to input the chip select control signal into the Vcom voltage generation circuit of the present invention since the Vcom voltage are the same in each source driver chip, so no certain Vcom voltage generation circuit need to be assigned to generate the Vcom voltage. 
         [0032]    In the other alternative, one source driver chip generates the Vcom voltage for uses of the other source driver chips. 
         [0033]    According to the aforementioned description, one advantage of the present invention is that the voltage generation circuit is set in each source driver chip to generate at least one Gamma voltage or a Vcom voltage. 
         [0034]    According to the aforementioned description, yet another advantage of the present invention is that the Gamma voltage generation circuit in one source driver chip generates at least one Gamma voltage to send to other source driver chips and to receive other Gamma voltages from other source driver chips. 
         [0035]    According to the aforementioned description, yet another advantage of the present invention is that the voltage generation circuit is cost effective and can simplify the layout of the system PCB board. 
         [0036]    According to the aforementioned description, yet another advantage of the present invention is that the Gamma voltage is generated according to an address in a chip select control signal and according to signals sent from a timing controller. 
         [0037]    As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrative of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.