Patent Publication Number: US-8115724-B2

Title: Driving circuit for display panel

Description:
FIELD OF THE INVENTION 
     The present invention relates to a driving circuit, and particularly to a driving circuit for a display panel. 
     BACKGROUND OF THE INVENTION 
     Modern technologies develop prosperously. Information products are introduced continuously to satisfy varied demands of numerous people. Most of early displays are cathode ray tubes (CRTs). However, their size is huge and their power consumption is great. In addition, the radiation they produced may endanger the health of long-term users. Thereby, current displays in the market are gradually replaced by liquid crystal displays (LCDs). LCDs have the characteristics of lightness, thinness, shortness, and smallness. Besides, they also have the advantages of low radiation and power consumption. Hence, they have become the mainstream of the market. 
     LCDs display images by controlling the light transmittance of liquid-crystal cells according to data signals. Because active-matrix LCDs adopt active control switches, the LCDs of this sort own advantages in displaying motion pictures. Thin-film transistors (TFTs) are switches mainly used in active-matrix LCDs. 
       FIG. 1  shows a schematic diagram of the driving system for an LCD according to the prior art. As shown in the figure, the driving system comprises a display panel  10 ′, a scan driving circuit  12 ′, a data driving circuit  14 ′, a timing control circuit  16 ′, and a circuit for producing reference voltages  18 ′. The display panel  10 ′ is used for displaying images. The scan driving circuit  12 ′ is used for producing and transmitting a scan signal to the display panel  10 ′ for driving a thin-film transistor (TFT) of the display panel  10 ′. The data driving circuit  14 ′ is used for producing and transmitting a data signal to the display panel  10 ′ for displaying the images. The timing control circuit  16 ′ produces a timing control signal, and transmitting the timing control signal to the scan driving circuit  12 ′ and the data driving circuit  14 ′, respectively, for controlling the scan driving circuit  12 ′ and the data driving circuit  14 ′ to transmit the scan signal and data signal to the display panel  10 ′, respectively, and for displaying the images. In addition, the circuit for producing reference voltages  18 ′ produces a reference voltage and transmits the reference voltage to the data driving circuit  14 ′ for making the data driving circuit  14 ′ to produce the data signal according to the timing control signal and the reference voltage. 
       FIG. 2  shows a schematic diagram of a circuit for producing reference voltages according to the prior art. If the digital display data corresponding to RGB is comprised by, for example, 6 bits, the circuit for producing reference voltages  18 ′ can output  64  analog voltages V 0 ˜V 63  corresponding to 2 6 =64 grayscales. The circuit for producing reference voltage  18 ′ is comprised by resistive voltage division circuit including resistors R 0 ˜R 7  connected in series. Each of the resistors R 0 ˜R 7  is further comprised by 8 resistors connected in series. As shown in  FIG. 3 , the 8 resistors R 01 ˜R 08  are connected in series to form the resistor R 0 . Other resistors R 1 ˜R 7  are formed similarly. Thereby, the circuit for producing reference voltages  18 ′ is comprised by 64 resistors and produces voltages V 0 ˜V 63 . 
     However, because 64 resistors are needed to produce 64 different voltage levels, the area of the circuit for producing reference voltages  18 ′ is increased, and hence increasing the area of the display. Besides, in order to reduce the area of the circuit for producing reference voltages  18 ′, resistors with larger resistance have to be used, which will affect the driving capability of the data driving circuit  14 ′. Moreover, when the data driving circuit  14 ′ drives the display panel  10 ′ via the resistors, a large amount of power will be consumed on the resistors, and thus wasting power of the display. 
     Accordingly, the present invention provides a novel driving circuit for a display panel, which can reduce the amount of resistors used without sacrificing the driving capability of the data driving circuit  14 ′. Thereby, the area of the display can be reduced, and the power of the display can be saved. 
     SUMMARY 
     An objective of the present invention is to provide a driving circuit for a display panel, which uses a switching module to switch a first power supply or a second power supply to a buffer circuit for saving power of the driving circuit, and hence saving power of the display. 
     Another objective of the present invention is to provide a driving circuit for a display panel, which uses a digital-to-analog converter for reducing the amount of resistive devices used, and hence saving area of the display. 
     The driving circuit for a display panel according to the present invention comprises a switching module, a buffer circuit, and a plurality of resistive devices. The switching module is coupled to a first power supply and a second power supply. The voltage of the first power supply is smaller than that of the second power supply. The buffer circuit is coupled to the switching module, and is used for buffering a data signal and producing a buffer signal. The plurality of resistive devices is connected in series, and is coupled to the buffer circuit. A plurality of driving signal is produce between the plurality of resistive devices according to the buffer signal. The driving circuit switches between the first power supply and second power supply sequentially to supply power to the buffer circuit. Thereby, one of the plurality of driving signals charges a capacitor of the display panel for saving power of the driving circuit. Accordingly, the power of the display can be saved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of the driving system for an LCD according to the prior art; 
         FIG. 2  shows a schematic diagram of a circuit for producing reference voltages according to the prior art; 
         FIG. 3  shows a schematic diagram of a detailed circuit for producing reference voltages according to the prior art; 
         FIG. 4  shows a schematic diagram of the driving system for an LCD according to a preferred embodiment of the present invention; 
         FIG. 5  shows a block diagram according to a preferred embodiment of the present invention; and 
         FIG. 6  shows a timing diagram of driving according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In order to make the structure and characteristics as well as the effectiveness of the present invention to be further understood and recognized, the detailed description of the present invention is provided as follows along with preferred embodiments and accompanying figures. 
       FIG. 4  shows a schematic diagram of the driving system for an LCD according to a preferred embodiment of the present invention. As shown in the figure, the driving system comprises a display panel  10 , a scan driving circuit  12 , a data driving circuit  14 , a timing control circuit  16 , and a Gamma circuit  18 . The display panel  10  is used for display images. The scan driving circuit  12  is used for producing and transmitting a scan signal to the display panel  10  to drive a thin-film transistor (TFT) of the display panel  10 . The data driving circuit  14  is used for producing and transmitting a data signal to the display panel  10  to display the images according to the data signal. The timing control circuit  16  produces a timing control signal and transmits the timing control signal to the scan driving circuit  12  and the data driving circuit  14  for controlling the scan driving circuit  12  and the data driving circuit  14  to transmit the scan signal and data signal to the display panel  10 , respectively. Thereby, the images can be displayed. In addition, the Gamma circuit  18  produces a reference voltage and transmits the reference voltage to the data driving circuit  14 . Hence, the data driving circuit  14  can produce the data signal according to the timing control signal and the reference voltage. 
       FIG. 5  shows a block diagram according to a preferred embodiment of the present invention. As shown in the figure, the driving circuit for a display panel according to the present invention is applied to the data driving circuit  14  for receiving 64 voltage levels produced by the Gamma circuit  18 . Because the driving circuit according to the present invention can receive 8-bit signals, the data driving circuit  14  needs to use 8 driving circuits for receiving and processing said 64 voltage levels. According to the present preferred embodiment, only one driving circuit is used for description. The driving circuit according to the present invention comprises a switching module, a buffer circuit  142 , and a plurality of resistive devices  143 ,  144 ,  146 ,  148 . The switching module is coupled to a first power supply and a second power supply. The voltage of the first power supply is smaller than that of the second power supply. According to a preferred embodiment, the voltage of the second power supply is twice the voltage of the first power supply. The buffer circuit  142  is coupled to the switching module, and is used for buffering a data signal and producing a buffer signal. The plurality of resistive devices  143 ,  144 ,  146 ,  148  is connected in series and is coupled to the buffer circuit  142 . Namely, one end of the resistive device  143  is coupled to the buffer circuit  142 , and the other end thereof is connected with the resistive device  144  in series; one end of the resistive device  148  is coupled to the buffer circuit  142 , and the other end thereof is connected with the resistive device  146  in series. The plurality of resistive devices  143 ,  144 ,  146 ,  148  produces a plurality of driving signal therebetween according to the buffer signal. The driving circuit switches between the first power supply and second power supply sequentially to supply power to the buffer circuit  142 . Thereby, one of the plurality of driving signals charges a capacitor  100  of the display panel. Accordingly, the power of the driving circuit can be saved, and hence the power of the display can be saved. 
       FIG. 6  shows a timing diagram of driving according to a preferred embodiment of the present invention. As shown in the figure, the dashed line represents that the driving circuit charges the capacitor  100  directly by a doubled unit voltage and drives the display panel  10 . On the other hand, the solid line represents that the driving circuit first switches to the first power supply by means of the switching module for supplying power to the buffer circuit  142 , where the first power supply has a unit voltage. After a period of time, the switching module switches to the second power supply for supplying power to the buffer circuit  142 , where the second power supply has a doubled unit voltage. From the figure, it is known that the power consumption of the driving circuit supplying power to the buffer circuit by two-step voltages according to the present invention is less than that by merely a doubled unit voltage. That is to say, during the time T 1 , the driving circuit supplies power to the buffer circuit  142  by a unit voltage provided by the first power supply. Then, during the time T 2 , the driving circuit supplies power to the buffer circuit  142  by a doubled unit voltage provided by the second power supply. Thereby, the power of the driving circuit according to the present invention can be truly saved, and accordingly the power of the display can be saved. 
     In addition, the driving circuit according to the present invention further comprises an analog-to-digital converter  15  used for converting an input signal and producing the data signal. The analog-to-digital converter  15  is coupled to the Gamma circuit  18  for receiving correction data produced by the Gamma circuit  18  as the input signal. The Gamma signal  18  produces the correction data according to a Gamma curve. Besides, the analog-to-digital converter  15  is further coupled to a memory unit  20 , which is used for storing a plurality of pixel data. The analog-to-digital converter  15  receives the plurality of pixel data and the correction data as the input signal and produces the data signal. The memory unit  20  is a random access memory (RAM). 
     Referring back to  FIG. 5 , a first switch  150 , a second switch  152 , and a third switch  154  are set between the plurality of resistive devices  143 ,  144 ,  146 ,  148 . The analog-to-digital converter can produce a control signal according to the pixel data stored in the memory unit  20  for closing/opening the first switch  150 , the second switch  152 , or the third switch  154 . Furthermore, the buffer circuit  142  includes a first buffer  1420  and a second buffer  1421 . The first buffer  1420  is used for buffering the data signal and producing a first buffer signal; the second buffer  1421  is used for buffering the data signal and producing a second buffer signal. The plurality of resistive devices  143 ,  144 ,  146 ,  148  produces the driving signal according to the voltage difference between the first buffer signal produced by the first buffer  1420  and the second buffer signal produced by the second buffer  1421 . The first buffer  1420  and the second buffer  1421  are operational amplifiers. In addition, the switching module includes a first switching mechanism  140  and a second switching mechanism  142 . The first switching mechanism  140  is used for switching between the first power supply and the second power supply and then power can be supplied to the first buffer  1420 . Likewise, the second switching mechanism  142  is used for switching between the first power supply and the second power supply and then power can be supplied to the second buffer  1421 . 
     To sum up, the driving circuit for a display panel according to the present invention comprises a switching module, a buffer circuit, and a plurality of resistive devices. The switching module is coupled to a first power supply and a second power supply. The voltage of the first power supply is smaller than that of the second power supply. The buffer circuit is coupled to the switching module, and is used for buffering a data signal and producing a buffer signal. The plurality of resistive devices is connected in series and coupled to the buffer circuit, and produces a plurality of driving signals between the plurality of resistive devices according to the buffer signal. The driving circuit switches between the first power supply and second power supply sequentially to supply power to the buffer circuit. Thereby, one of the plurality of driving signals charges a capacitor of the display panel for saving power of the driving circuit. Accordingly, the power of the display can be saved. 
     Accordingly, the present invention conforms to the legal requirements owing to its novelty, non-obviousness, and utility. However, the foregoing description is only a preferred embodiment of the present invention, not used to limit the scope and range of the present invention. Those equivalent changes or modifications made according to the shape, structure, feature, or spirit described in the claims of the present invention are included in the appended claims of the present invention.