Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a division of applicant&#39;s earlier application, Ser. No. 10/907,896, filed Apr. 20, 2005, which in turn is a division of applicant&#39;s earlier application, Ser. No. 10/064,207, filed Jun. 21, 2002. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method and a related apparatus for driving an LCD monitor, and more particularly, to a method and a related apparatus which can drive pixels located in a row of the LCD panel toward a target level so as to display a uniform gray level. 
         [0004]    2. Description of the Prior Art 
         [0005]    The advantages of the liquid crystal display (LCD) include lighter weight, less electrical consumption, and less radiation contamination. Thus, the LCD has been widely applied to several portable information products such as notebooks, and PDAs. The LCD gradually replaces the cathode ray tube (CRT) monitors of the conventional desktop computers. The incident light will produce different polarization or refraction effects when alignment of these liquid crystal molecules is different. The LCD utilizes the characteristics of the liquid crystal molecules to generate red, blue, and green lights with different intensities of gray level to produce gorgeous images. 
         [0006]    Please refer to  FIG. 1  of a schematic diagram of a conventional thin film transistor (TFT) liquid crystal display (LCD)  10 . The LCD  10  comprises an LCD panel  12 , a control circuit  14 , a first driving circuit  16 , a second driving circuit  18 , a first power supply  20 , and a second power supply  22 . The LCD panel  12  is composed of two substrates and an LCD layer interposed between the two substrates. A plurality of data lines  24 , a plurality of gate lines  26 , which are perpendicular to the data lines  24 , and a plurality of thin film transistors  28  are disposed on one of the two substrates. A common electrode is disposed on the other substrate for providing a constant voltage Vcom via the first power supply  20 . For easier description, only one thin film transistor  28  is illustrated in  FIG. 1 . However, a plurality of thin film transistors  28  are respectively disposed on intersections of the data lines  24  and the gate lines  26  in fact. Thus, the thin film transistors  28  are arranged on the LCD panel  12  in a matrix format. In another words, each of the data lines  24  corresponds to one column of the TFT LCD  10 , each of the gate lines  26  corresponds to one row of the TFT LCD  10 , and each of the thin film transistors  28  corresponds to one pixel. In addition, the two substrates of the LCD panel  12  can be regarded as an equivalent capacitor  30  according to their electrical performance. 
         [0007]    The driving method of the conventional TFT LCD  10  is described as follows. The control circuit  14  is used for controlling driving process of the TFT LCD  10 . When the control circuit  14  receives horizontal synchronization  32  and vertical synchronization  34 , the control circuit  14  inputs corresponding control signals to the first driving circuit  16  and the second driving circuit  18  respectively. Then, the first driving circuit  16  and the second driving circuit  18  generate input signals for each data line  24 , for instance DL 3 , and each gate line  26 , for instance GL 3 , according to the control signals so as to control conductance of the thin film transistors  28  and voltage differences between two ends of the equivalent capacitors  30  and to rearrange the alignment of the liquid crystal molecules and the corresponding light transmittance in advance. For example, the second driving circuit  18  inputs a pulse to the gate lines  26  so as to make the thin film transistors  28  conduct. Thus, the signals from the first driving circuit  16  to the data lines  24  can be input to the equivalent capacitors  30  via the thin film transistors  28  so as to control the gray levels of the corresponding pixels. In addition, different signals input to the data lines  24  from the first driving circuit  16  are generated by the second power supply  22 . The second power supply  22  is controlled according to the control circuit  14  and the display data  36  for providing adequate voltages. The second power supply  22  comprises a plurality of voltage dividing circuits (not shown) to produce different voltages V 0  to Vn for driving the thin film transistors  28 . Different voltages correspond to different gray levels. 
         [0008]    Please refer to  FIG. 1  and  FIG. 2 .  FIG. 2  is a schematic diagram of the driving method of the LCD  10  shown in  FIG. 1 . The second power supply  22  further comprises a voltage selection module  56  and an operational amplifier circuit  37  for driving the corresponding thin film transistors  28  respectively according to the different voltages V 0  to Vn generated by the second power supply  22 . The operational amplifier circuit  37  comprises a plurality of operational amplifiers  44 ,  45 ,  46 ,  47 ,  48  and  49 . Each of the operational amplifiers  44 ,  45 ,  46 ,  47 ,  48  and  49  is used to form an output buffer that has a unity gain. In addition, each operational amplifier  44 ,  45 ,  46 ,  47 ,  48 ,  49  in the operational amplifier circuit  37  is electrically connected to a corresponding multiplexer (MUX 3  to MUX 8  shown in  FIG. 2 ) positioned within the voltage selection module  56 . It is noteworthy that only six operational amplifiers and related multiplexers are shown in  FIG. 2  for simplicity. According to the control signals D 3  to D 8  outputted from the control circuit  14 , the corresponding multiplexers will select one specific voltage level from the different voltages (V 0  to Vn) generated by the second power supply  22 . The second power supply  22  further comprises a voltage divider for outputting the different voltages V 0 , V 1 , . . . , and Vn. It is noteworthy that each voltage level is individually transmitted via a power transmission line such as a metal wire  66  shown in  FIG. 2 . When the control circuit  14  receives the horizontal synchronization  32  and the vertical synchronization  34 , corresponding signals are then generated and are inputted to the first driving circuit  16 , the second driving circuit  18 , and the second power supply  22 . For example, when the second driving circuit  18  generates a pulse to make all thin film transistors located in one row conducted, that means thin film transistors  38 ,  39 ,  40 ,  41 ,  42  and  43  are conducted. The first driving circuit  16  determines that DL 3 , DL 4 , DL 5 , DL 6 , DL 7 , and DL 8  in the data lines  24  should be driven under the voltage V 1  according to the display data  36  so as to drive the thin film transistor  38 ,  39 ,  40 ,  41 ,  42  and  43  toward the target voltage V 1  via the operational amplifier circuit  37 . Therefore, the multiplexers MUX 3 , MUX 4 , MUX 5 , MUX 6 , MUX 7 , and MUX 8  related to the operational amplifiers  44 ,  45 ,  46 ,  47 ,  48 , and  49  are controlled to select the required voltage level V 1 . The operational amplifiers  44 ,  45 ,  46 ,  47 ,  48 , and  49  take the voltage level V 1  as an input voltage to drive the thin film transistor  38 ,  39 ,  40 ,  41 ,  42 , and  43  later. However, the operational amplifiers  44 ,  45 ,  46 ,  47 ,  48  and  49  have different offsets affecting the actual output voltages so that the voltage differences of the capacitors  50 ,  51 ,  52 ,  53 ,  54 , and  55  are different. According to the display data  36 , the pixels corresponding to DL 3 , DL 4 , DL 5 , DL 6 , DL 7 , and DL 8  in the data lines  25  should display the same gray level. However, the gray levels in the display screen are not uniform because different offsets of the output voltages are made by the operational amplifiers  44 ,  45 ,  46 ,  47 ,  48  and  49 , which therefore deteriorates the display quality. 
       SUMMARY OF THE INVENTION  
       [0009]    It is therefore a primary objective of the claimed invention to provide a driving device for a flat panel display apparatus for making pixels located in the same row of the display have the same target level so as to display a uniform gray level. 
         [0010]    The claimed invention provides a driving device for driving a flat panel display apparatus. The driving device comprises a first driving unit, a second driving unit, a third driving unit, wherein the second driving unit is deposited between the first driving unit and the third driving unit, and a fourth driving unit, wherein the third driving unit is deposited between the second driving unit and the fourth driving unit. The driving device also comprises a first switch circuit coupled between an output terminal of the first driving unit and an output terminal of the third driving unit, and a second switch circuit coupled between an output terminal of the second driving unit and an output terminal of the fourth driving unit. 
         [0011]    It is an advantage of the claimed invention that the pixels located in a row have the same target voltage so as to display data in a uniform gray level. 
         [0012]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]      FIG. 1  is a schematic diagram of a conventional thin film transistor liquid crystal display monitor. 
           [0014]      FIG. 2  is a schematic diagram of the second power supply shown in  FIG. 1 . 
           [0015]      FIG. 3  is a schematic diagram of a first operational amplifier circuit according to the present invention. 
           [0016]      FIG. 4  is a schematic diagram of a second operational amplifier circuit according to the present invention. 
           [0017]      FIG. 5  is a schematic diagram of a third operational amplifier circuit according to the present invention. 
           [0018]      FIG. 6  is a simplified diagram of a connection between pixels and the third operational amplifier circuit shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION  
       [0019]    Please refer to  FIG. 1 ,  FIG. 2 , and  FIG. 3 .  FIG. 3  is a schematic diagram of a first operational amplifier circuit  60  according to the present invention. The operational amplifier circuit  60  in the present invention is used to replace the operational amplifier circuit  37  located in the second power supply  22  shown in  FIG. 2 . Please note that the detailed operation of the voltage selection module  56  has been described before in the prior art section, and the lengthy description is not repeated again for simplicity. The operational amplifier circuit  60  comprises a plurality of operational amplifiers  62  or operational transconductance amplifiers (OTA) to form output buffers with a unity gain and a plurality of switches  64  for controlling current routes. When the second driving circuit  18  inputs a pulse to the gate lines  26  according to the horizontal synchronization  32 , all thin film transistors  28  in the same gate line  26  conduct. Thus, the first driving circuit  16  must input the same voltage to DL 1 , DL 2 , DL 3 , . . . DLn in the data line  24  according to the display data  36  so as to display a corresponding gray level. At this time, the multiplexer related to the operational amplifier  62  is controlled to select a required voltage such as V 1 , and the switch  64  is switched to conduct two ends E 1  and E 2  so that the voltage V 1  can drive the capacitor  30  through the operational amplifier  62 . However, each operational amplifier  62  has a specific offset because of a semiconductor process mismatch, that is, each corresponding output voltage varies even the input voltage is the same for each operational amplifier  62 . Thus, DL 1 , DL 2 , DL 3 , . . . DLn in the data line  24  have different offsets due to above-mentioned effect of the operational amplifiers  62 . Therefore, different voltage levels are stored in each capacitors  30  corresponding to DL 1 , DL 2 , DL 3 , . . . DLn of the data lines  24 . Then, the switch  64  is switched to conduct the ends E 1  and E 3  to change current routes. Therefore, the voltage V 1  transmitted by the metal line  66  can not drive the capacitors  30  via the operational amplifier  62  owing to the status change of the switch  64 . However, each capacitor  30  is connected to the same metal line  66  due to conducting the ends E 1  and E 3 . Thus, all capacitors  30  are balanced quickly via the metal line  66  so as to have the same voltage level with an averaged offset. 
         [0020]    For example, the switch  64  is switched to connect the ends E 1  and E 2  at first. If the voltage V 1  is 5V, the voltages of DL 1 , DL 2 , DL 3 , . . . DLn in the data line  24  are driven toward 5V via the output buffers formed by the operational amplifiers  62 . However, the voltages of DL 1 , DL 2 , DL 3 , . . . DLn of the data line  24  vary differently because the offset related to each operational amplifiers  62  is different. For example, the voltages at DL 1 , DL 2 , DL 3 , . . . DLn of the data line  24  are 4.8V, 5.1V, 4.7V, . . . 4.9V respectively. At this time, the switch  64  is switched to connect the ends E 1  and E 3 . Since DL 1 , DL 2 , DL 3 , . . . DLn of the data line  24  are electrically connected to the same metal line  66  via the ends E 1  and E 3 , therefore, the voltages of DL 1 , DL 2 , DL 3 , . . . DLn of the data line  24  will generate an average voltage rapidly. In other words, each voltage of DL 1 , DL 2 , DL 3 , . . . DLn of the data line  24 , which are originally 4.8V, 5.1V, 4.7V, . . . 4.9V respectively, come to an average voltage via the metal line  66 . It is noteworthy that original different offsets are averaged to generate an identical offset for each data line  24  mentioned above, and the input voltage is then affected by the same averaged offset to generate the average voltage at each data line  24 . In addition, the pixels positioned in the same row will have the same gray level when the pixels are driven by the same voltage generated by the second power supply  22 . 
         [0021]    Please refer to  FIG. 4 , which is a schematic diagram of a second operational amplifier circuit  70  according to the present invention. The second operational amplifier circuit  70  has a plurality of operational amplifiers  72 ,  73 ,  74 , and  75  to function as output buffers, and a plurality of switches S 1 , S 2  related to the operational amplifiers  72 ,  73 ,  74 , and  75 . Please note that only four operational amplifiers are drawn in  FIG. 4  for simplicity, and the operational amplifiers  72 ,  73 ,  74 , and  75  and switches S 1 , and S 2  are used for driving corresponding pixels through data lines DL 1 , DL 2 , DL 3 , and DL 4 . The operation of the second operational amplifier circuit  70  is described as follows. In the beginning, each switch S 1  is first turned on to make the operational amplifiers  72 ,  73 ,  74 , and  75  electrically connected to corresponding data lines DL 1 , DL 2 , DL 3 , and DL 4 . As mentioned before, each operational amplifier  72 ,  73 ,  74 , and  75  has a unique offset respectively affecting the output voltage to deviate from the input voltage. In other words, if the pixels with regard to the operational amplifiers  72 , and  73  are prepared to be driven by the same input voltage level, that is, V 1  is equal to V 2 , the voltage levels of the data lines DL 1 , and DL 2  are different owing to the respective offsets corresponding to the operational amplifiers  72 , and  73 . Then, all the switches S 1  related to the operational amplifiers  72 ,  73 ,  74 , and  75  are turned off simultaneously. Next, if the operational amplifiers  72 , and  73  prepare to drive corresponding pixels toward the same gray level through data lines DL 1 , and DL 2 , the switch S 2  related to the operational amplifiers  72 , and  73  is then turned on. Therefore, the voltage levels of the data lines DL 1 , and DL 2  will quickly approach an average voltage from these two voltage levels. That is, the original offsets are averaged to generate the average voltage for the data lines DL 1 , and DL 2 . Similarly, if the operational amplifiers  73 , and  74  prepare to drive corresponding pixels toward the same gray level through data lines DL 2 , and DL 3 , the switch S 2  related to the operational amplifiers  73 , and  74  is then turned on as well. Therefore, any adjacent pixels driven by the same input voltage will finally have the same gray level with the help of switch S 2 . To sum up, voltage at each data line DL 1 , DL 2 , DL 3 , or DL 4  is first driven by a corresponding operational amplifier  72 ,  73 ,  74 , or  75  after the switch S 1  related to each operational amplifier  72 ,  73 ,  74 , or  75  is turned on. Then, each switch S 1  is turned off. In addition, the switch S 2  is turned on when related adjacent pixels related to the switch S 2  are prepared to have the same gray level. Finally, the voltage deviation between the adjacent data lines is eliminated by averaging the offsets generated by the corresponding operational amplifiers through the switch S 2 . In the preferred embodiment, the second operational amplifier circuit  70  is applied on a LCD panel driven according to a line inversion method. Because the pixels positioned in the same row will have the same polarity according to the line inversion method, the switch S 2  is capable of averaging voltages with the same polarity at adjacent data lines such as data lines DL 1 , and DL 2 . In addition, the different offsets are not averaged through the voltage selection module  56  shown in  FIG. 3  but are averaged through the related switch S 2 . Therefore, any voltage divider circuit that can provide the operational amplifier circuit  70  with different voltage levels is suitable for the second power supply  22  in the preferred embodiment. 
         [0022]    Please refer to  FIG. 5 , which is a schematic diagram of a third operational amplifier circuit  80  according to the present invention. The third operational amplifier circuit  80  is similar to the second operational amplifier circuit  70 . Only the arrangement of the switches S 1 , and S 2  is different. As shown in  FIG. 5 , there is a switch S 2  electrically connected to the operational amplifiers  72 ,  74 , and another switch S 2  is electrically connected to the operational amplifiers  73 ,  75 . That is, the adjacent data lines such as DL 1 , and DL 2  are not connected through the switch S 2 . When pixels are driven by a dot inversion method, a two dot line inversion method, or a column inversion method, adjacent pixels in the same row are driven by voltages with opposite polarities. That is, pixels connected to lines DL 1 , DL 2 , DL 3 , DL 4  respectively have polarities such as “+””−“”+””−“ or “−“”+””−“”+”. Therefore, the third operational amplifier circuit  80  uses switches S 2  connected to adjacent operational amplifiers that have the same polarity for averaging above-mentioned offsets when corresponding pixels with the same polarity are driven to the identical gray level. For example, if the pixels connected to the data lines DL 1 , and DL 3  are going to have the same gray level, the switches S 1  corresponding to operational amplifiers  72 , and  74  are first turned on in the beginning. Because the offsets related to the operational amplifiers  72 , and  74  are different, the voltages at the data lines DL 1 , and DL 3  are different as well. Then, the switch S 2  related to the lines DL 1 , and DL 3  is turned on. Therefore, the voltage deviation between the lines DL 1 , and DL 3  is eliminated by averaging the offsets generated by the corresponding operational amplifiers  72 , and  74 . It is noteworthy that the offsets generated from the operational amplifiers  72 , and  74  are averaged to generate an average voltage at both lines DL 1 , and DL 3 . In other words, the lines DL 1 , and DL 3  still have an averaged offset according to the present invention. But, the voltages at data lines DL 1 , and DL 3  are equal after all. In addition, if two adjacent pixels are not going to have the same gray level, the switch S 2  related to the corresponding pixels is kept off without affecting the gray levels of the adjacent pixels. In the preferred embodiment, the switch S 2  is connected to two data lines driven according to the same polarity, and these two data lines is spaced by another data line driven according to an opposite polarity. That is, the third operational amplifier circuit  80  is applied on an LCD panel driven by a column inversion method, a dot inversion method, or a two dot line inversion. In addition, the different offsets are not averaged through the voltage selection module  56  shown in  FIG. 3  but are averaged through the related switch S 2 . Therefore, any voltage divider circuit that can provide the operational amplifier circuit  70  with different voltage levels is suitable for the second power supply  22  in the preferred embodiment. 
         [0023]    Please refer to  FIG. 6 , which is a simplified diagram of a connection between pixels  82  and the third operational amplifier circuit  80  shown in  FIG. 5 . A specific color is generated by mixing three monochromatic lights such as a red light, a green light, and a blue light respectively having different intensities. Therefore, pixels  82  located at the same row are individually responsible for providing a gray level with regard to the red light, the green light, or the blue light. As shown in  FIG. 6 , there are pixels  82  used for representing a color sequence “RGBRGBRGBRGB”. When the pixels  82  are driven according to a dot inversion method, a two dot line inversion method, or a column inversion method, adjacent pixels  82  will have opposite polarities. For example, the pixels  82  are driven according to a polarity sequence ”+−+−+−+−+−+−”. Concerning the red light, the pixels  82   a  and  82   c  have the same polarity “+”, and the pixels  82   b  and  82   d  have the same polarity “−“. For the pixels  82   a,    82   b,    82   c,  and  82   d  with regard to the red light, one switch S 2  is connected between the pixels  82   a  and  82   c  driven by the same polarity “+”. In addition, another switch S 2  is connected between the pixels  82   b  and  82   d.  Therefore, when the third operational amplifier circuit  80  is used for driving pixels with regard to one specific monochromatic light, a switch S 2  is responsible for equaling voltages inputted into two adjacent pixels driven by the same polarity and driven to the same gray level. It is noteworthy that the above-mentioned driving method is also applied on driving pixels with regard to green light and blue light, and the repeated description is skipped for simplicity. 
         [0024]    The voltage selection module  56  shown in  FIG. 3  is used for providing the operational amplifier circuit  60  with appropriate voltage levels. In addition, the metal lines  66  within the voltage selection module  56  not only transmit electric power but also average voltage levels at different data lines  24 . That is, the pixels located at different positions in the same row will have the same gray level when driven by the same voltage provided by the voltage selection module  56 . The metal line  66  performs a global voltage average operation. The operational amplifier circuits  70 , and  80  shown in  FIG. 4  and  FIG. 5  use switches S 2  to perform the local voltage average operation. That is, the switch S 2  is turned on only when two adjacent pixels related to the switch S 2  are prepared to be driven by an identical voltage level. Users are only sensitive to gray level difference between adjacent pixels, but are not sensitive to the gray level of each pixel. Therefore, the objective of the operational amplifier circuits  70 , and  80  is to eliminate the gray level difference between adjacent pixels when the adjacent pixels are driven by the same voltage level. That is, switches S 2  of the operational amplifier circuits  70 , and  80  take place of the metal lines  66  located in the voltage selection module  56  for eliminating voltage deviations between two adjacent pixels only to achieve a uniform gray level. 
         [0025]    As mentioned above, the second operational amplifier circuit  70  is applied on an LCD monitor driven by a line inversion method, and the third operational amplifier circuit  80  is applied on an LCD monitor driven by a column inversion method, a dot inversion method, or a two dot line inversion. Therefore, the operational amplifier circuit according to the present invention can be applied on an LCD monitor, which is driven according to a predetermined method, to solve the offset deviation problem. In addition, the TFT LCD according to the present invention further comprises a XOR logic circuit or a comparator to determine whether the switch S 2  is turned on or not. That is, the XOR logic circuit is used for comparing digital input driving data related two pixels to check whether the pixels are going to have the same gray level, and the comparator is used for comparing analog input driving data related to two pixels to check whether the pixels are going to have the same gray level. When the XOR logic circuit or the comparator acknowledges that two pixels are prepared to be driven toward the same gray level, the switch S 2  related to the pixels will be turned on to eliminate the offset deviation. In other words, the TFT LCD has a detecting circuit such as a XOR logic circuit for digital driving data or a comparator for analog driving data to compare driving data with regard to two pixels. When these two pixels are going to have the same gray level, the switch S 2  related to these two pixels is turned on according to a comparison result generated from the XOR logic circuit or the comparator. Furthermore, the present invention is capable of using operational transconductance amplifiers instead of the operational amplifiers to drive the pixels. 
         [0026]    In contrast to the prior art, the driving method according to the present invention uses a switch to connect the output terminals of the output buffers. Therefore, the power supply generates a target level to drive the pixels located in a row of the LCD panel toward the same target level. There are different offsets between the output levels of the driving units for driving the pixels and the target level. When the output terminals of the output buffers are connected together via the switches, the original different output levels of driving units of each pixels are changed towards an average voltage generated from averaging voltages at output terminals of the driving units of the pixel. Although the average voltage may be not exactly equal to the target level, the pixels, which are located in the same row and are predetermined to be driven toward the same target level, are driven to the same level by using the method of the present invention. Thus, the uniformity problem in the prior art caused by level offsets can be solved. 
         [0027]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Technology Category: 3