Patent Publication Number: US-7719508-B2

Title: Scan driving apparatus, flat panel display having the same, and driving method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0038364, filed May 28, 2004, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flat panel display, and more particularly, to a flat panel display scan driving apparatus with decreased size and power consumption. 
     2. Discussion of the Background 
     Various flat panel displays have been recently developed as alternatives to heavier and bulkier cathode ray tubes (CRT). Such displays include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), and electroluminescent displays. 
     A conventional flat panel display may comprise a display region having a plurality of pixels formed at scan line and data line crossings, a scan driver to drive the scan lines, a data driver to drive the data lines, and a controller, which controls the scan driver and the data driver and transmits a data signal to the data driver. 
     Transmitting a scan signal to the scan line selects a pixel, and the pixel displays an image corresponding to the data signal transmitted to the data line. The pixel may be a liquid crystal cell of an LCD, a discharge cell of the FED or the PDP, or a light-emitting cell of the electroluminescent display. 
     The controller transmits a selection control signal to the scan driver to control its timing, transmits a data control signal to the data driver to control the data driver&#39;s timing, and transmits the external data signal to the data driver. 
     The scan driver may output the scan signals for sequentially driving the scan lines in response to the selection control signals, which may include a start pulse, a clock signal, and a control signal transmitted from the controller. Such a scan driver may comprise a plurality of registers to output the scan signals. 
     The data driver transmits the data signal from the controller to the pixel through the data lines in response to the controller&#39;s data control signals. The data driver may output the data signal to the data line corresponding to one horizontal line  1 H every one horizontal period. 
     As  FIG. 1  shows, in the conventional flat panel display, the data signal may be transmitted to the data line corresponding to one horizontal line  1 H based on the data driver&#39;s clock signal every one cycle T of the clock signal CLK transmitted to the scan driver. 
     Thus, the conventional flat panel display may consume a lot of power because of a scan driver register&#39;s operating frequency. Also, N registers may be needed to transmit the scan signal to N scan lines. In other words, the number of registers increases proportionally to the number of scan lines, thereby increasing the scan driver&#39;s size. 
     SUMMARY OF THE INVENTION 
     The present invention provides a smaller scan driving apparatus that may consume less power, a flat panel display having the same, and a driving method thereof. 
     Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. 
     The present invention discloses a scan driving apparatus comprising a shift register generating output signals shifted in sequence in response to a clock signal and a scan signal generator. The scan signal generator generates at least four scan signals in a cycle of a clock signal based on the output signals from the shift register and at least a first control signal and a second control signal. 
     The present invention also discloses a flat panel display comprising an image display part having a plurality of pixels defined by n scan lines and m data lines, a scan driver outputting at least four scan signals in sequence to the scan lines in a cycle of a clock signal, and a data driver transmitting a data signal to the data lines. 
     The present invention also discloses a method of driving a flat panel display comprising an image display part having a plurality of pixels defined by n scan lines and m data lines. The method comprises transmitting at least four scan signals in sequence to the scan lines in a cycle of a clock signal, and transmitting a data signal synchronized with the scan signals to the data lines. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
         FIG. 1  shows waveforms of a data signal and a clock signal of a conventional scan driver. 
         FIG. 2  is a schematic view showing a flat panel display according to an exemplary embodiment of the present invention. 
         FIG. 3  is a view showing the scan driver according to an exemplary embodiment of the present invention. 
         FIG. 4  shows driving signal and output signal waveforms of the scan driver according to an exemplary embodiment of the present invention. 
         FIG. 5  shows waveforms of a data signal transmitted and a clock signal according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to  FIG. 2 ,  FIG. 3 ,  FIG. 4  and  FIG. 5 . 
       FIG. 2  is a schematic view of a flat panel display comprising a scan driver according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , the flat panel display may comprise an image display portion  10  including a plurality of pixels  11  at intersections of a plurality of scan lines SL 1 ˜SLn and a plurality of data lines DL 1 ˜DLm, a scan driver  20  sequentially transmitting at least four scan signals SS every clock signal cycle, a data driver  30  to drive the data lines, and a controller  8  controlling the scan driver  20  and the data driver  30 . 
     A pixel  11  may be selected by the scan signal SS transmitted to the scan line SL, and the pixel displays an image corresponding to the data signal transmitted to the corresponding data line DL. The scan driver  20  may be used to select a liquid crystal cell of an LCD, a discharge cell of an FED or a PDP, or a light-emitting cell of an electroluminescent display. 
     The controller  8  transmits a selection control signal to the scan driver  20  to control the driver&#39;s timing, transmits a data control signal to the data driver  30  to control the data driver&#39;s timing, and transmits a data signal to the data driver  30 . 
       FIG. 3  shows the scan driver according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , the scan driver  20  may generate scan signals SS in response to the controller&#39;s selection control signals, which may include a start pulse SP, a clock signal CLK, and two control signals Enb 1 , Enb 2 , and sequentially transmit the scan signals SS to the scan lines SL. 
     The scan driver  20  may comprise a shift register  22 , which may include a plurality of registers SR, and a scan signal generator  24 , which may comprise a plurality of NAND gates N. 
     The shift register  22  may comprise (n/2)+1 registers SR 1 ˜SRn/2+1 to transmit the scan signals SS to n scan lines SL 1 ˜SLn. A register may shift the start pulse SP from the controller  8  in accordance with the clock signals CLK in sequence and transmit the shifted start pulse SP to the scan signal generator  24 . 
     More specifically, the 1 st  register SR 1  transmits output signals to the 1 st  and 2 nd  NAND gates N 1 , N 2 . The (n/2+1) th  register SRn/2+1 transmits output signals to the n−1 th  and n th  NAND gates Nn−1, Nn. Also, a register SRj (where, j=2, 3, 4, . . . , n/2), among the 2 nd ˜(n/2) th  registers SR 2 ˜SRn/2, transmits an output signal to four NAND gates Nk−3, Nk−2, Nk−1, Nk (where k=2×j). Accordingly, two adjacent registers SR among the 2 nd ˜(n/2) th  registers SR 2 ˜SRn/2 transmit the output signals to two adjacent NAND gates N. 
     For example, the 2 nd  register SR 2  transmits output signals to the 1 st ˜4 th  NAND gates N 1 , N 2 , N 3 , N 4 , respectively. Further, the 3 rd  register SR 3  transmits output signals to the 3 rd ˜6 th  NAND gates N 3 , N 4 , N 5 , N 6 , respectively. Likewise, each of the 4 th ˜(n/2) th  registers SR 4 ˜SRn/2 transmits output signals to four NAND gates Nk−3, Nk−2, Nk−1, Nk (where k=2×j), respectively. 
     Each NAND gate N 1 ˜Nn receives the output signals from the i th  register SRi and the (i+1) th  register SRi+1 (where i is a positive integer of 1 or more), respectively, and receives the first or second control signal Enb 1 , Enb 2 , which may have the same cycle and be transmitted leaving a predetermined time difference. The first control signal Enb 1  may be transmitted to odd NAND gates N 1 , N 3 , . . . Nn- 1 , and the second control signal Enb 2  may be transmitted to even NAND gates N 2 , N 4 , . . . Nn. Here, each cycle of the first and second control signals Enb 1 , Enb 2  may be half that that of the clock signal CLK transmitted to the shift register  22 . According to an exemplary embodiment of the present invention, the cycle of the clock signal CLK transmitted to the shift register  22  may be four times longer than that of the conventional clock signal CLK. 
       FIG. 4  shows waveforms of driving signals and output signals in the scan driver according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 3  and  FIG. 4 , the NAND gates N 1 ˜Nn operate as follows. 
     The odd NAND gates N 1 , N 3 , . . . , Nn−1 apply the NAND operation to the first control signal Enb 1  and the output signals transmitted from the i th  register SRi and the (i+1) th  register SRi+1, thereby generating the scan signal SS for the odd scan lines. Further, the even NAND gates N 2 , N 4 , . . . , Nn apply the NAND operation to the second control signal Enb 2  and the output signals transmitted from the i th  register SRi and the (i+1) th  register SRi+1, thereby generating the scan signal SS for the even scan lines. 
     For example, in the case of the 1 st ˜4 th  NAND gates N 1 ˜N 4 , the 1 st  NAND gate N 1  applies the NAND operation to the output signal from the 1 st  register SR 1 , the output signal from the 2 nd  register SR 2 , and the first control signal Enb 1 , thereby outputting the scan signal SS to the first scan line SL  1 . The 2 nd  NAND gate N 2  applies the NAND operation to the output signal from the 1 st  register SR 1 , the output signal from the 2 nd  register SR 2 , and the second control signal Enb 2 , thereby outputting the scan signal SS to the second scan line SL 2 . The 3 rd  NAND gate N 3  applies the NAND operation to the output signal from the 2 nd  register SR 2 , the output signal from the 3 rd  register SR 3 , and the first control signal Enb 1 , thereby outputting the scan signal SS to the third scan line SL 3 . The 4 th  NAND gate N 4  applies the NAND operation to the output signal from the 2 nd  register SR 2 , the output signal from the 3 rd  register SR 3 , and the second control signal Enb 2 , thereby outputting the scan signal SS to the fourth scan line SL 4 . 
     Thus, in the scan driver  20 , as shown in  FIG. 4 , n/2+1 registers SR 1 ˜SRn/2+1 sequentially output the start pulses SP according to the clock signals CLK, and n NAND gates N 1 ˜Nn apply the NAND operation to the output signals from the registers according to the first and second control signals Enb 1 , Enb 2 , thereby sequentially outputting the scan signals SS to the scan lines. The scan driver  20  may sequentially output four scan signals SS to four scan lines, respectively, for every cycle of the clock signal CLK. 
     The data driver  30  may transmit the data signal from the controller  8  to the pixel  11  through the data line DL in response to the controller&#39;s data control signals. The data driver  30  may transmit the data signal corresponding to one horizontal line every one horizontal period for which the scan driver  20  transmits the scan signal SS to the scan line SL. 
       FIG. 5  shows waveforms of a data signal and a clock signal transmitted to the scan driver of the flat panel display according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 2  and  FIG. 5 , the data driver  30  may transmit the data signals corresponding to four horizontal lines  1 H,  2 H,  3 H,  4 H to the data line DL every cycle T of the clock signal CLK transmitted to the scan driver  20 . 
     Thus, the operation frequency of the register SR may be decreased by half. Since the operation frequency of the register SR may decrease, the switching time of the register SR decreases, thereby reducing the scan driver&#39;s power consumption. Further, in the flat panel display according to an exemplary embodiment of the present invention, third through j th  control signals Enb 3  through Enbj (where j is a positive integer of 3 or more), together with the first and second control signals Enb 1 , Enb 2 , may be transmitted to the scan signal generator  24  in consideration of gate-on time, provided the gate-on time does not affect the image displayed on the image display portion  10 . Thus, the scan driver  20  may sequentially generate at least four scan signals SS for every cycle T of the clock signal CLK. 
     The data driver  30  and the scan driver  20  may be directly mounted on an organic panel including the image display portion  10 . 
     As described above, exemplary embodiments of the present invention provide a smaller scan driving apparatus using less power, a flat panel display having the same, and a driving method thereof, in which a scan signal is generated with a control signal and output signals of two registers. According to an exemplary embodiment of the present invention, four scan signals may be generated every cycle of the clock signal transmitted to the scan driver. Thus, the frequency of the clock signal decreases, thereby decreasing power consumption due to register switching. Further, fewer registers may be used, thereby decreasing the scan driver&#39;s size. 
     It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.