Patent Publication Number: US-8125437-B2

Title: Over-driving device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an over-driving device, and more particularly to an over-driving device applied in a display panel. 
     2. Description of the Related Art 
       FIGS. 1A and 1B  respectively show the variations of gray values and brightness of a pixel when a response time of a liquid crystal display panel is excessively long. Referring  FIGS. 1A and 1B , in an ideal situation, when the desired gray value of a pixel is changed from G 0  to G 1  at time point T 0 , the brightness thereof is changed from L 0  to L 1 . However, since the rotational speed of liquid crystal molecules of a pixel is slow, the response time during which the brightness is changed from L 0  to L 1  is excessively long, and the brightness reaches L 1  at time point T 2 . Thus, the brightness of the pixel can not reach the desired degree L 1  in a frame. 
     Since large-sized liquid crystal display panels are continuously being developed, it is important to shorten response time of a liquid crystal display panel. In order to solve the problem of a long response time, an over-driving method is used.  FIGS. 2A and 2B  respectively show the variations of gray values and brightness of a pixel utilizing an over-driving method. Referring to  FIG. 2A , to shorten response time, the desired gray value of a pixel is changed from G 0  to G 1 ′ (G 1 ′&gt;G 1 ) at time point T 0  and then changed from G 1 ′ to G 1  at time point T 1 . As shown in  FIG. 2B , brightness of the pixel reaches L 1  at time point T 1 , wherein the duration between time points T 0  and T 1  is shorter than the duration between time points T 0  and T 2 . Thus, by using an over-driving method, response time required for brightness change of a liquid crystal display panel from one frame to the next frame is shortened. 
     Taiwan Patent No. I269254 discloses an over-driving device and a method thereof. Referring to  FIG. 3 , an over-driving device  300  comprises a compression circuit  310 , a buffer  312 , two decompression circuits  314 - 1  and  314 - 2 , a comparison circuit  316 , a multiplexer  318 , and an over-driving module  320 . The compression circuit  310  receives and compresses a source signal to generate a compression data signal  311 . The buffer  312  receives the compression data signal  311  to temporarily store compression data of gray values in a frame and generate a buffering data signal which is output in a next frame. The decompression circuits  314 - 1  and  314 - 2  decompress the buffing data signal  313  and the compression data signal  311  to generate decompression data signals  315 - 1  and  315 - 2 , respectively. The comparison circuit  316  compares the decompression data signals  315 - 1  and  315 - 2 . In other words, the comparison circuit  316  compares gray values of the pixel (not shown) in the current and previous frames and then drives the over-driving module  320  to perform following operations according to the comparison result. 
     BRIEF SUMMARY OF THE INVENTION 
     An exemplary embodiment of an over-driving device is applied in a display device which comprises a plurality of pixels and displays images in successive frames. The over-driving device comprises a compression circuit, a buffer, a comparison circuit, a decompression circuit, and an over-driving unit. The compression circuit receives and compresses a first image signal to generate a first compression image signal in a first frame, and receives and compresses a second image signal to generate a second compression image signal in a second frame following the first frame. The buffer is coupled to the compression circuit. The buffer receives and temporarily stores the first compression image signal in the first frame and outputs the stored first compression image signal to serve as a first buffering image signal in the second frame. The comparison circuit is coupled to the compression circuit and the buffer. The comparison circuit receives and compares the second compression image signal and the first buffering image signal and generates an enable signal according to the comparison result in the second frame. The decompression circuit is coupled to the buffer. The decompression circuit receives and decompresses the first buffering image signal to generate a previous image signal in the second frame. The over-driving unit receives the second image signal to serve as a current image signal, receives the previous image signal and the enable signal, and determines to over drive the display device or not according to the enable signal in the second frame. 
     In some embodiments, the over-driving device further comprises a delay circuit coupled to the compression circuit and the comparison circuit. The delay circuit delays the second compression image signal for a predetermined period. 
     In some embodiments, the over-driving device further comprises a delay circuit coupled to the buffer circuit and the comparison circuit. The delay unit delays the first buffering image signal for a predetermined period. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIGS. 1A and 1B  respectively show the variations of gray values and brightness of a pixel when a response time of a liquid crystal display panel is excessively long; 
         FIGS. 2A and 2B  respectively show the variations of gray values and brightness of a pixel in an over-driving method; 
         FIG. 3  shows an over-driving device disclosed by Taiwan Patent No. I269254; 
         FIG. 4  shows an exemplary embodiment of an over-driving device and the transmission of signals in a frame F M−1 ; 
         FIG. 5  shows the transmission of signals in the over-driving device in a frame F M ; 
         FIG. 6  shows the transmission of signals in the over-driving device in a frame F M+1 ; 
         FIG. 7  shows an exemplary embodiment of an over-driving device with a delay circuit coupled between a compression circuit and a comparison circuit; and 
         FIG. 8  shows an exemplary embodiment of an over-driving device with a delay circuit coupled between the buffer and the comparison circuit. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
     Over-driving devices are provided. In an exemplary embodiment of an over-driving device in  FIG. 4 , an over-driving device  4  is applied in a display device, such as a liquid crystal display device. The display device comprises a plurality of pixels and displays images in successive frames. As shown in  FIG. 4 , the over-driving device  4  comprises compression circuit  40 , a buffer  41 , a comparison circuit  42 , a decompression circuit  43 , and an over-driving unit  44 . In following description, three successive frames F M−1 , F M , and F M+1  in which the over-driving device  4  operates are given as an example. 
     Referring to  FIG. 4 , in the frame F M−1 , the compression circuit  40  receives an image signal S M−1 . The compression circuit  40  compresses the image signal S M−1  to generate a compression signal SC M−1 . The buffer  41  is coupled to the compression circuit  40 . The buffer  41  receives the compression signal SC M−1  and stores it temporarily for outputting in the next frame F M . 
     Referring to  FIG. 5 , in the frame F M , the compression circuit  40  receives an image signal S M . The compression circuit  40  compresses the image signal S M  to generate a compression signal SC M . After the compression circuit  40  generates the compression signal SC M , the buffer  41  receives and temporarily stores the compression signal SC M  for outputting in the next frame F M+1  to serve as a buffering image signal SB M , and, at the same time, the buffer  41  outputs the compression signal SC M−1  to serve as a buffering image signal SB M−1 . The decompression circuit  43  is coupled to the buffer  41 . In the frame F M , the decompression circuit  43  receives and decompresses the buffering image signal SB M−1  from the buffer  41  to generate a previous image signal SD M−1  for the frame F M . 
     The comparison circuit  42  is coupled to the compression circuit  40  and the buffer  41 . In the frame F M , the comparison circuit  42  receives and compares the compression image signal SC M  and the buffering image signal SB M−1 . The comparison circuit  42  generates an enable signal SE M  according to the comparison result. The over-driving unit  44  receives the image signal S M  to serve as a current image signal SD M  for the frame F M . The over-driving unit  44  also receives the previous image signal SD M−1  and the enable signal SE M . The over-driving unit  44  determines to over drive the display device or not in the frame F M  according to the enable signal SE M . 
     In some embodiments, in the frame F M , when the current image signal SD M  and the buffering image signal SB M−1  are the same, the comparison circuit  42  outputs a de-asserted enable signal SE M  for driving the over-driving unit  44  to stop over driving the display device. When the current image signal SD M  and the buffering image signal SB M−1  are different, the comparison circuit  42  outputs an asserted enable signal SE M  for driving the over-driving to over drive the display device. 
     In some other embodiments, the comparison circuit  42  has a reference value. When the difference between the compression image signal SC M  and the buffering image signal SB M−1  is less than or equal to the reference value, the comparison circuit  42  outputs a de-asserted enable signal SE M  for driving the over-driving unit  44  to stop over driving the display device. When the difference between the compression image signal SC M  and the buffering image signal SB M−1  is greater than the reference value, the comparison circuit  42  outputs an asserted enable signal SE M  for driving the over-driving unit  44  to over drive the display device. 
     The over-driving unit  44  comprises a table  440 . The table  440  comprises a plurality of over-driving parameters. When the over-driving unit  44  determines to over drive the display device according to the enable signal SE M , the over-driving unit  44  checks the table  440  to select one over-driving parameter corresponding to the combination of the current image signal SD M  and the previous image signal SD M−1 . The over-driving unit  44  over drives the display device according to the selected over-driving parameter. When the over-driving unit  44  determines to stop driving the display device according to the enable signal SE M , the over-driving unit  44  stops checking the table  440 . 
     In the embodiments in  FIGS. 4 and 5 , the image signal S M−1  comprises a gray value of a target pixel in the frame F M−1 , and the image signal S M  comprises a gray value of the target pixel in the frame F M . However, the invention is not limited to the disclosed embodiments. 
     In some embodiments, the image signal S M−1  can comprise gray values of a predetermined number of pixels in the frame F M−1 , and the image signal S M  can comprise gray values of the predetermined number of pixels in the frame F M . In these examples, the comparison circuit  42  compares gray values corresponding to the predetermined number of pixels in the compression image signal SC M  and gray values corresponding to the predetermined number of pixels in the buffering image signal SB M−1  in a predetermined order. When determining to over drive the display device according to the enable signal SE M , the over-driving unit  44  over drives the predetermined number of pixels in the predetermined order. 
     Referring to  FIG. 6 , in the frame F M+1 , the compression circuit  40  receives an image signal S M+1 . The compression circuit  40  compresses the image signal S M+1  to generate a compression signal SC M+1 . After the compression circuit  40  generates the compression signal SC M+1 , the buffer  41  receives and temporarily stores the compression signal SC M+1  for outputting in a next frame, and, at the same time, the buffer  41  outputs the compression signal SC M  to serve as a buffering image signal SB M . In the frame F M+1 , the decompression circuit  43  receives and decompresses the buffering image signal SB M  from the buffer  41  to generate a previous image signal SD M  for the frame F M+1 . 
     In the frame F M+1 , the comparison circuit  42  receives and compares the compression image signal SC M+1  and the buffering image signal SB M . The comparison circuit  42  generates an enable signal SE M+1  according to the comparison result. The over-driving unit  44  receives the image signal S M+1  to serve as a current image signal SD M+1  for the frame F M+1 . The over-driving unit  44  also receives the previous image signal SD M  and the enable signal SE M+1 . The over-driving unit  44  determines to over drive the display device or not in the frame F M+1  according to the enable signal SE M+1 . 
     In the embodiments of  FIGS. 4-6 , the buffer  41  with a reading-writing synchronization mode is given as an example. In some embodiments, the buffer  41  can be in a writing prior to reading mode or a reading prior to writing mode. 
     Referring to  FIG. 7 , when the buffer  41  is in a writing prior to reading mode, the over-driving device  4  further comprises a delay circuit  70  coupled between the compression circuit  40  and the comparison circuit  42 . In the frame F M , since the compression image signal SC M  is written into the buffer  41  first and then the buffering image signal SB M−1  is read from the buffer  41 , there is a predetermined period between the time point the compression circuit  40  generates the compression image signal SC M  and the time point the buffer  41  outputs the buffering image signal SB M−1 . In other words, the time point the compression circuit  40  generates the compression image signal SC M  is earlier than the time point the buffer  41  outputs the buffering image signal SB M−1 . The delay circuit  70  receives the compression image signal SC M  and delays the compression image signal SC M  for the predetermined period, so that the compression image signal SC M  and the buffering image signal SB M−1  can reach the comparison circuit  42  at the same time. 
     Referring to  FIG. 8 , when the buffer  41  is in a reading prior to writing mode, the over-driving device  4  further comprises a delay circuit  80  coupled between the buffer  41  and the comparison circuit  42 . In the frame F M , since the buffering image signal SB M−1  is read from the buffer  41  first and then the compression image signal SC M  is written into the buffer  41 , there is a predetermined period between the time point the compression circuit  40  generates the compression image signal SC M  and the time point the buffer  41  outputs the buffering image signal SB M−1 . In other words, the time point the buffer  41  outputs the buffering image signal SB M−1  is earlier than the time point the compression circuit  40  generates the compression image signal SC M . The delay circuit  80  receives the buffering image signal SB M−1  and delays the buffering image signal SB M−1  for the predetermined period, so that the compression image signal SC M  and the buffering image signal SB M−1  can reach the comparison circuit  42  at the same time. 
     According above embodiments, by comparing the compression image signal SC M−1  corresponding to the current frame and the buffering image signal SB M  corresponding to the previous frame, the over-driving unit  44  determines to over drive the display device in the current frame. 
     Moreover, the over-driving device  4  comprises only one decompression circuit, saving circuit space. Since the comparison circuit  42  compares decompressed signals, the band width of data buses for the comparison circuit  42  is decreased. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.