Patent Publication Number: US-8970643-B2

Title: Display apparatus light emission control method and display unit

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display unit that employs light emitting elements arranged in a matrix, and a light emission control method for a display apparatus that employs the display units. 
     2. Description of the Related Art 
     Display units that employ light emitting diodes (LEDs) as light emitting elements, and display apparatuses that employ the display units have been manufactured. For example, a large display apparatus can be constructed of a plurality of display units that cooperate with each other. In the case where a display unit is constructed in a matrix with m rows and n columns for example, the anode terminals of LEDs that are arranged in each row are connected to corresponding one common line, while the cathode terminals of LEDs that are arranged in each column are connected to corresponding one driving line. The common lines of m rows are cyclically turned ON one by one at a predetermined sub-frame. When one of the common lines is turned ON, each of the driving lines can drive corresponding one of LEDs that are arranged on the one of the common lines, which is turned ON. 
     In this display unit control method, there is a problem that the brightness of light emitting elements that are first driven in each cycle may be smaller as compared with other light emitting elements. The reason is described with reference to  FIGS. 10 to 12 .  FIG. 10A  is a plan view schematically showing a display unit.  FIG. 10B  is a plan view schematically showing the display unit with the brightness of a row being smaller.  FIG. 11  is a timing chart showing the light emission timing of light emitting elements  1  in a conventional display unit. The following description describes the case where one cycle is divided into a plurality of frames for displaying an image. The frames are controlled so that an image can be displayed as a whole.  FIGS. 12A to 12H  are circuit diagrams showing the current flows in the display unit in sub-frames  11  to  23  in  FIG. 11 .  FIGS. 12A ,  12 B,  12 C,  12 D,  12 E, and  12 F show the sub-frames  11 ,  12 ,  13 ,  21 ,  22 , and  23 , respectively, in the cycle CL 1 .  FIG. 12G  shows the state where residual electric charge is stored.  FIG. 12H  shows the sub-frame  11  in the cycle CL 2  or later. In  FIGS. 12A to 12H , light emitting elements  1  shown in black are light emitting elements  1  that emit light at a desired amount of intensity. Current flows are shown by the arrows. Virtual equivalent capacitors C S0  to C S2  that are included as parasitic capacitances in the lines are shown on the driving lines S 0  to S 2  (hereinafter, S 0  to S 2  are occasionally referred to as simply lines “S”). 
     The display unit shown in  FIGS. 10A and 10B  includes a display portion in a matrix with three rows and three columns. Each dot includes an LED as light emitting element. This display unit will have the circuit construction states shown in  FIGS. 12A to 12H . The display unit includes the light emitting elements  1  that are arranged in the matrix with three rows and three columns (totally nine light emitting elements), three common lines C 0  to C 2  (hereinafter, C 0  to C 2  are occasionally referred to as simply lines “C”), the three driving lines S 0  to S 2 , a scanning portion  20 , and a driving portion  30 . Each of the common lines C 0  to C 2  is connected to the anode terminals of three light emitting elements  1 , which are arranged in corresponding one of the three rows. Each of the three driving lines S 0  to S 2  is connected to the cathode terminals of three light emitting elements  1  that are arranged in corresponding one of the three columns. The common lines C 0  to C 2  are scanned by the scanning portion  20 . The driving portion  30  can draw currents from the driving lines S 0  to S 2  so that the currents can flow through light emitting elements  1 . 
       FIG. 11  shows the light emission timing chart of the display unit. As shown in this chart, the first cycle CL is indicated by CL 1 . The first cycle CL is first provided to the display unit after power is supplied. The second and third cycles are indicated by CL 2  and CL 3 , respectively. Each of CL 1  to CL 3  is divided into a plurality of frames FM. In the frames, the scanning order of the common lines C is the same order of C 0 , C 1 , and C 2 . The assumed operation is that, in each cycle, all of the light emitting elements are driven at the minimum intensity (the minimum level) only in FM 1 , and all of the light emitting elements are turned OFF in other frames. That is, the assumed operation is that, in each of the cycles CL 1  to CL 3 , all the light emitting elements emit light at the minimum intensity. In  FIG. 11 , although it is shown as if the light emitting elements  1  connected to S 0 , S 1 , and S 2  are driven at the maximum intensity (maximum level) in the sub-frames  11 ,  12 , and  13  in each cycle for ease of illustration, the assumed operation is that the light emitting elements are driven at the minimum intensity (the minimum level) in FM 1 . 
     The operation in the cycle CL 1  is now described with reference to  FIG. 12A . In the sub-frame  11  where the common line C 0  to be first scanned is turned ON in the frame FM 1 , a voltage is applied to the common line C 0  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 . Accordingly, three light emitting elements  1  that are connected to C 0  are driven at a desired amount of intensity. Subsequently, in the sub-frame  12 , as shown by  FIG. 12B , the voltage is applied to the common line C 1  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 . Accordingly, three light emitting elements  1  that are connected to C 1  are driven at a desired amount of intensity. Similarly, in the sub-frame  13 , as shown in  FIG. 12C , three light emitting elements  1  that are connected to C 2  are driven at a desired amount of intensity. 
     After that, in the sub-frame  21  in the frame FM 2 , as shown in  FIG. 12D , although the voltage is applied to the common line C 0 , the driving lines are in the OFF state so that the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. Similarly, in the sub-frame  22 , as shown in  FIG. 12E , although the voltage is applied to the common line C 1 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be also charged. Similarly, in the sub-frame  23 , as shown in  FIG. 12F , the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be also charged. In this case, since the lines are similarly scanned in the frames, the parasitic capacitances of the lines will be fully charged and cannot be charged anymore as shown in  FIG. 12G . 
     The operation in the cycle CL 2  is now described. The light intensity of a light emitting element that is first driven will be smaller in the cycle CL 2  as compared with the cycle CL 1 . That is, as shown by  FIG. 12H , since, in the sub-frame  11  in the frame FM 1 , the voltage is applied to the common line C 0  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to C 0  are driven. 
     However, since the parasitic capacitances of the driving lines S 0  to S 2  are charged in the cycle CL 1 , the amounts of the currents that are drawn by the driving portion through the driving lines S 0  to S 2  include not only currents that flow in the light emitting elements  1  but also currents from the parasitic capacitances. That is, since the current that actually flows in the light emitting element  1  in the sub-frame  11  decreases by the amount of current that is discharged by the parasitic capacitance relative to the currents in other sub-frames  12  and  13 , the light emission amount of the light emitting element  1  that is connected to C 0  in the sub-frame of the cycle CL 2  will be smaller as compared with other light emitting elements  1  that are connected to C 1  and C 2 . As a result, a dark line may appear. 
     In  FIG. 11 , to show that light emitting elements  1  may be darker in the sub-frames  11  of the cycles CL 2  and CL 3 , the sub-frame blocks indicating that C 0  is in the ON state are hatched in the cycles CL 2  and CL 3 . Also, in  FIG. 12H , to show that the parasitic capacitances may reduce the amounts of light intensity of light emitting elements  1 , these light emitting elements  1  are hatched. 
     Subsequently, in the sub-frame  12 , as shown by  FIG. 12B , the voltage is applied to the common line C 1  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 . Since the currents corresponding to the parasitic capacitances have been drawn out by the driving portion  30  in the frame FM 1 , three light emitting elements  1  that are connected to C 1  can be driven at a desired amount of intensity. Similarly, in the sub-frame  13 , as shown in  FIG. 12C , three light emitting elements  1  that are connected to C 2  can be driven at a desired amount of intensity. Since the operation after the sub-frame  21  is similar to the cycle CL 1 , its description is omitted for the sake of brevity. In addition, after the cycle CL 3 , similarly, light emitting elements  1  may be darker in the sub-frame  11 . Since the reason is the same as CL 2 , its description is omitted for the sake of brevity. 
     As stated above, in conventional driving methods, the parasitic capacitances may reduce the amounts of light intensity of light emitting elements. For this reason, there is a problem that the darker light emitting elements may inversely affect the display quality. 
     See Laid-Open Patent Publication No. JP 2006-147,933 A 
     The present invention is devised to solve the above problems. It is a main object of the present invention to provide a display apparatus light emission control method and a display unit that can prevent that the amount of light intensity of a light emitting element that is first driven in each cycle is smaller than other light emitting elements, and can improve the display quality. 
     SUMMARY OF THE INVENTION 
     To achieve the above object, a light emission control method according to a first aspect of the present invention controls a display apparatus that includes a display portion  10 , a scanning portion  20 , and a driving portion  30 . The display portion  10  includes a plurality of light emitting elements  1  that are arranged in a matrix form. The scanning portion  20  is connected to a plurality of common lines C. Each of plurality of common lines C is connected to the anode terminals of corresponding elements of the plurality of light emitting elements  1  that are arranged in corresponding one of the rows of the display portion  10  so that the common lines C are scanned. The scanning portion  20  applies a voltage to selected one of the common lines C. The driving portion  30  is connected to a plurality of driving lines S. Each of the driving lines S is connected to the cathodes terminals of corresponding elements of the plurality of light emitting elements  1  that are arranged in corresponding one of the columns of the display portion  10 . The driving portion  30  can drive selected elements of the plurality of light emitting elements  1  when one of the common lines corresponding to the selected elements is scanned by the scanning portion. The display apparatus displays an image in each cycle that includes a plurality of frames. All of the common lines C are scanned by the scanning portion  20  in each of the plurality of frames. One(s) of the rows in one frame in one cycle is/are driven. Other one(s) or the other rows are driven in a frame after the one frame in the one cycle. According to this construction, since different rows are driven in different frames in one cycle, it is possible to suppress the phenomenon where the parasitic capacitance of the driving line reduces the amount of light intensity of a particular row (dark line). 
     In a light emission control method according to a second aspect of the present invention, a non-light-emission period can be provided between a driving sub-frame in which a predetermined row(s) is/are driven and the next driving sub-frame in which other row(s) is/are driven. In the non-light-emission period, one or more common lines are scanned by the scanning portion and the driving portion prevents current flows in the light emitting elements. According to this construction, the periods for activation of the driving lines can be distributed. As a result, it is possible to reduce the duration of a non-light-emission period where the driving lines are deactivated so that the light emitting elements do not emit light. Therefore, it is possible to suppress the appearance of dark line. 
     In a light emission control method according to a third aspect of the present invention, the duration of a non-light-emission period can be constant. According to this construction, since the duration of a time period where electric charge is charged as the parasitic capacitances of the driving lines can be constant, the light emission amounts of the light emitting elements in the rows can be constant. Therefore, it is possible to prevent the phenomenon where light emitting elements in a particular row become darker. 
     In a light emission control method according to a fourth aspect of the present invention, the same image can be displayed in continuous cycles. According to this construction, in still pictures, it is possible to suppress the appearance of dark line where a particular row becomes darker. 
     A light emission control method according to a fifth aspect of the present invention controls a display apparatus that includes a display portion  10 , a scanning portion  20 , and a driving portion  30 . The display portion  10  includes a plurality of light emitting elements  1  that are arranged in a matrix form. The scanning portion  20  is connected to a plurality of common lines C. Each of plurality of common lines C is connected to the anode terminals of corresponding elements of the plurality of light emitting elements  1  that are arranged in corresponding one of the rows of the display portion  10  so that the common lines C are scanned. The scanning portion  20  applies a voltage to selected one of the common lines C. The driving portion  30  is connected to a plurality of driving lines S. Each of the driving lines S is connected to the cathodes terminals of corresponding elements of the plurality of light emitting elements  1  that are arranged in corresponding one of the columns of the display portion  10 . The driving portion  30  can drive selected elements of the plurality of light emitting elements  1  when one of the common lines corresponding to the selected elements is scanned by the scanning portion. The display apparatus displays an image in each cycle that includes a plurality of frames. All of the common lines C are scanned by the scanning portion  20  in each of the plurality of frames. The rows of the display portion  10  are driven in a first light emission order so that the image is displayed in a first cycle. The rows of the display portion  10  are driven in a second cycle next to the first cycle in a second light emission order so that the image same as the first cycle is displayed. The row that is first driven in the second light emission order is different from the row that is first driven in the first light emission order. According to this construction, since the driving orders are different between frames in one cycle, it is possible to distribute the reduction amounts of light emission caused by the parasitic capacitances of the driving lines to the rows. Therefore, it is possible to suppress the appearance of dark line where a particular row becomes darker. 
     In a light emission control method according to a sixth aspect of the present invention, a non-light-emission period can be provided between a driving sub-frame in which a predetermined row(s) is/are driven and the next driving sub-frame in which other row(s) is/are driven. In the non-light-emission period, one or more common lines are scanned by the scanning portion and the driving portion prevents current flows in the light emitting elements. According to this construction, although the common line scanning order is not changed, since the periods for activation of the driving lines are distributed, it is possible to reduce the duration of a non-light-emission period where the driving lines are deactivated so that the light emitting elements do not emit light. Therefore, it is possible to suppress the appearance of dark line. 
     In a light emission control method according to a seventh aspect of the present invention, the orders in which the common lines are scanned in the frames by the scanning portion can be different between successive cycles. According to this construction, although activation timing of the driving lines is not changed, since the scanning order of the common lines is set different between cycles, it is possible to distribute light emitting elements the light emission amounts of which are reduced caused by the parasitic capacitances of the driving lines. Therefore, it is possible to suppress the phenomenon where particular light emitting elements become darker, that is, to make the phenomenon inconspicuous. 
     A display unit according to an eighth aspect of the present invention includes a display portion  10 , a scanning portion  20 , and a driving portion  30 . The display portion  10  includes a plurality of light emitting elements  1  that are arranged in a matrix form. The scanning portion  20  is connected to a plurality of common lines C. Each of plurality of common lines C is connected to the anode terminals of corresponding elements of the plurality of light emitting elements  1  that are arranged in corresponding one of the rows of the display portion  10  so that the common lines C are scanned. The scanning portion  20  applies a voltage to selected one of the common lines C. The driving portion  30  is connected to a plurality of driving lines S. Each of the driving lines S is connected to the cathodes terminals of corresponding elements of the plurality of light emitting elements  1  that are arranged in corresponding one of the columns of the display portion  10 . The driving portion  30  can drive selected elements of the plurality of light emitting elements  1  when one of the common lines corresponding to the selected elements is scanned by the scanning portion. The display unit is constructed to display an image in each cycle that includes a plurality of frames. All of the common lines are scanned by the scanning portion  20  in each of the plurality of frames. The display unit further includes a light emission control portion  2  that drives one(s) of the rows in one frame in one cycle, and drives other one(s) or the other rows in another frame in the one cycle. According to this construction, since different rows are driven in different frames in one cycle, it is possible to suppress the phenomenon where the parasitic capacitance of the driving line reduces the amount of light intensity of a particular row (dark line). 
     In a display unit according to a ninth aspect of the present invention, the light emission control portion  2  can have a non-light-emission period is provided between a driving sub-frame of a predetermined row and the next driving sub-frame of another row. In the non-light-emission period, one or more common lines are scanned by the scanning portion and the driving portion prevents current flows in the light emitting elements. According to this construction, the periods for activation of the driving lines can be distributed. As a result, it is possible to reduce the duration of a non-light-emission period where the driving lines are deactivated so that the light emitting elements do not emit light. Therefore, it is possible to suppress flicker. 
     In a display unit according to a tenth aspect of the present invention, the non-light emission period of the light emission control portion  2  can be constant. According to this construction, since the periods where electric charge is charged as the parasitic capacitances of the driving lines can be constant, the light emission amounts of the light emitting elements in the rows can be constant. Therefore, it is possible to prevent the phenomenon where light emitting elements in a particular row become darker. 
     In a display unit according to an eleventh aspect of the present invention, the display unit can display the same image on the display portion  10  in continuous cycles. According to this construction, in still pictures, it is possible to suppress the appearance of dark line where a particular row becomes darker. 
     A display unit according to a twelfth aspect of the present invention includes a display portion  10 , a scanning portion  20 , and a driving portion  30 . The display portion  10  includes a plurality of light emitting elements  1  that are arranged in a matrix form. The scanning portion  20  is connected to a plurality of common lines C. Each of plurality of common lines C is connected to the anode terminals of corresponding elements of the plurality of light emitting elements  1  that are arranged in corresponding one of the rows of the display portion  10  so that the common lines C are scanned. The scanning portion  20  applies a voltage to selected one of the common lines C. The driving portion  30  is connected to a plurality of driving lines S. Each of the driving lines S is connected to the cathodes terminals of corresponding elements of the plurality of light emitting elements  1  that are arranged in corresponding one of the columns of the display portion  10 . The driving portion  30  can drive selected elements of the plurality of light emitting elements  1  when one of the common lines corresponding to the selected elements is scanned by the scanning portion. The display unit is constructed to display an image in each cycle that includes a plurality of frames. All of the common lines are scanned by the scanning portion  20  in one of the plurality of frames. The display unit further includes a light emission control portion  2  that, when displaying the same image in successive first and second cycles, controls the driving orders so that the row that is first driven in the second cycle is different from the row that is first driven in the first cycle. According to this construction, since the driving orders are different between frames in one cycle, it is possible to distribute the reduction amounts of light emission caused by the parasitic capacitances of the driving lines to the rows. Therefore, it is possible to suppress the appearance of dark line where a particular row becomes darker. 
     In a display unit according to a thirteenth aspect of the present invention, the light emission control portion  2  can have a non-light-emission period is provided between a driving sub-frame of a predetermined row and the next driving sub-frame of another row. In the non-light-emission period, one or more common lines are scanned by the scanning portion and the driving portion prevents current flows in the light emitting elements. According to this construction, although the common line scanning order is not changed, since the periods for activation of the driving lines are distributed, it is possible to reduce the duration of a non-light-emission period where the driving lines are deactivated so that the light emitting elements do not emit light. Therefore, it is possible to suppress the appearance of dark line. 
     In a display unit according to a fourteenth aspect of the present invention, the light emission control portion  2  can control the driving orders so that the orders in which the common lines C are scanned in the frames by the scanning portion are different between successive cycles. According to this construction, although activation timing of the driving lines is not changed, since the scanning order of the common lines is set different between cycles, it is possible to distribute light emitting elements the light emission amounts of which are reduced caused by the parasitic capacitances of the driving lines. Therefore, it is possible to suppress the phenomenon where a particular row becomes darker, that is, to make the phenomenon inconspicuous. 
     The above and further objects of the present invention as well as the features thereof will become more apparent from the following detailed description to be made in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a display unit according to a first embodiment of the present invention; 
         FIG. 2  is a timing chart showing a light emission control method according to the first embodiment of the present invention; 
         FIGS. 3A to 3J  are circuit diagrams showing current flows in the display unit in sub-frames  11  to  23  shown in  FIG. 2 ; 
         FIG. 4  is a timing chart showing a light emission control method according to a second embodiment of the present invention; 
         FIG. 5  is a timing chart showing a light emission control method according to a third embodiment of the present invention; 
         FIG. 6  is a timing chart showing a light emission control method according to a fourth embodiment of the present invention; 
         FIG. 7  is a block diagram for illustrating a display apparatus according to a fifth embodiment of the present invention; 
         FIG. 8  is a block diagram for illustrating a display unit to be used for a display apparatus according to a sixth embodiment of the present invention; 
         FIG. 9  is a timing chart showing the display unit according to the first embodiment of the present invention; 
         FIG. 10A  is a plan view schematically showing a display unit; 
         FIG. 10B  is a plan view schematically showing the display unit shown in  FIG. 10A  with one row being darker in light emission; 
         FIG. 11  is a timing chart of a conventional light emission control method for driving the display unit shown in  FIG. 10 ; and 
         FIGS. 12A to 12H  are circuit diagrams showing current flows in the display unit in sub-frames  11  to  23  shown in  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT(S) 
     The following description will describe embodiments according to the present invention with reference to the drawings. It should be appreciated, however, that the embodiments described below are illustrations of a light emission control method and a display unit used therein to give a concrete form to technical ideas of the invention, and a light emission control method and a display unit of the invention are not specifically limited to description below. Furthermore, it should be appreciated that the members shown in claims attached hereto are not specifically limited to members in the embodiments. Unless otherwise specified, any dimensions, materials, shapes and relative arrangements of the parts described in the embodiments are given as an example and not as a limitation. Additionally, the sizes and the positional relationships of the members in each of drawings are occasionally shown larger exaggeratingly for ease of explanation. Members same as or similar to those of this invention are attached with the same designation and the same reference signs, and their description is omitted. In addition, a plurality of structural elements of the present invention may be configured as a single part that serves the purpose of a plurality of elements, on the other hand, a single structural element may be configured as a plurality of parts that serve the purpose of a single element. Also, the description of some of examples or embodiments may be applied to other examples, embodiments or the like. 
     In this specification, the term “parasitic capacitance” mainly refers to the parasitic capacitance of a driving line S. However, the “parasitic capacitance” is not limited to this. The “parasitic capacitance” can include the capacitive component of other part such as the capacitance of an electronic part that is connected to the driving line. 
     First Embodiment 
       FIG. 1  is a block diagram showing a display unit  100  according to a first embodiment of the present invention.  FIG. 2  is a timing chart showing a light emission control method for driving the display unit  100 .  FIGS. 3A to 3J  are circuit diagrams showing current flows indicated by the arrows in the display unit in sub-frames shown in  FIG. 2 . 
     (Display Portion) 
     The display unit  100  includes a display portion  10  and a light emission control portion  2 , as shown in  FIG. 1 . The display portion  10  includes a plurality of light emitting elements  1 , a plurality of common lines C 0  to C 2 , and a plurality of driving lines S 0  to S 2 . The light emitting elements  1  are arranged in a matrix. Each of the common lines C 0  to C 2  is connected to the anode terminals of the light emitting elements  1  that are arranged in corresponding one of rows. Each of the common lines S 0  to S 2  are connected to the cathode terminals of the light emitting elements  1  that are arranged in corresponding one of columns. 
     (Light Emission Control Portion  2 ) 
     The light emission control portion  2  includes a frame dividing portion  40 , a scanning portion  20 , a driving portion  30 , and a scanning order control portion  50 . The frame dividing portion  40  divides one cycle for displaying an image into a plurality of frames. The scanning portion  20  is connected to the common lines C. The common lines C are scanned in each frame by the scanning portion  20 . The scanning portion  20  can apply a voltage to the common lines C. The driving portion  30  is connected to the driving lines S, and can drive selected light emitting elements  1  in corresponding one of the frames in one cycle based on control data provided from the outside. The scanning order control portion  50  is connected to the scanning portion  20 , and controls the scanning orders so that the scanning orders in which the common lines are scanned are different between the frame in a cycle and the frame in another cycle. 
     The light emission control portion  2  controls the display portion  10  in the light emission control method of light emission timing shown in  FIG. 2 . As a result, it is possible to prevent the phenomenon where the amount of light emission of a conventional display portion  10  partially decreases as shown in  FIG. 10B , that is, to prevent the appearance of dark line. Therefore, it is possible to provide uniform and quality image as shown in  FIG. 10A . The following description will describe the light emission control method. 
     In conventional light emission control methods, the scanning order of the common lines C is set in ascending numeric order as shown in  FIG. 11  in every cycle, which may cause the phenomenon where the parasitic capacitance reduces the amounts of light intensity of the emitting elements  1  that are arranged in a row and are first driven in each cycle as compared with other light emitting elements  1 . The common line C that will be the dark line when turned ON is indicated as hatched blocks in  FIG. 11 . Although the dark line is inconspicuous in motion video or at high brightness, the dark line will be conspicuous in still image particularly at low brightness, which in turn causes poor image quality. To address this, in this embodiment, the scanning order is set different between cycles, that is, the dark line is changed depending on cycles in order to suppress that a particular row is conspicuous as the dark line. 
     Specifically, in the display unit  100  according to the first embodiment, the scanning order control portion  50  controls the scanning order so that the dark line will appear in C 0 , C 1 , and C 2  in each frame FM 1  in cycle  4 , cycle  5 , and cycle  6 , respectively as shown in  FIG. 2 . According to this light emission control method, the dark line will cyclically appear on the three common lines C in a cycle of three cycles. Dissimilar to the conventional case of  FIG. 10B , the dark line does not appear only in the first row. Since the row where the dark line will appear can be changed depending on cycles, the light intensity difference can be distributed. Accordingly, it is possible to prevent that the dark line will appear in a particular row. As a result, it is possible to display a more uniform image as a whole. In this embodiment, the scanning order is cyclically changed in a cycle of three cycles. For this reason,  FIG. 2  illustrates the cycles CL 4  to CL 6 . 
     The display unit  100  includes the light emitting elements  1 , three common lines C 0  to C 2 , and three driving lines S 0  to S 2 , as discussed above. The light emitting elements  1  are arranged in the matrix with three rows and three columns (totally nine light emitting elements). Each of the three common lines C 0  to C 2  is connected to the anode terminals of three of the light emitting elements  1  that are arranged in corresponding one of rows. Each of the three driving lines S 0  to S 2  is connected to the cathode terminals of three of the light emitting elements  1  that are arranged in corresponding one of columns. In the light emission control method shown in  FIG. 2 , each of the cycles CL 4  to CL 6  is divided into a plurality of frames (FM 1 , FM 2 , . . . ) for driving the display portion. The assumed operation is that, in each cycle, all of light emitting elements are driven at the minimum intensity (the minimum level) only in FM 1 , and all of light emitting elements are turned OFF in other frames, for sake of brevity. That is, in each cycle, all of the light emitting elements are driven at the minimum intensity. In  FIG. 2 , although it is shown as if the light emitting elements  1  connected to the driving lines S 0 , S 1 , and S 2  are driven at the maximum intensity (maximum level) in the sub-frames  11 ,  12 , and  13  in the frame FM 1  in each cycle for ease of illustration, the assumed operation is that the light emitting elements are driven at the minimum intensity (the minimum level). 
     The operation of the cycle CL 4  is now described. In the cycle CL 4 , the scanning order of the common lines C is set to the order of the common lines C 0 , C 1 , and C 2  in each frame. That is, this scanning order of the common lines C is ascending numeric order. In other words, the scanning order of the common lines C in this cycle is same as conventional light emission control method shown in  FIG. 11 . Specifically, in the sub-frame  11  in the frame FM 1  shown in  FIG. 2 , the voltage is applied to the common line C 0  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , as shown in  FIG. 3H . As discussed above in the case of  FIG. 11 , the parasitic capacitance charged in the previous cycle CL 3  (not shown) reduces the light intensity of the light emitting elements  1  that are connected to the common line C 0 , which is first selected in the cycle CL 4 , to a light intensity amount lower than a desired light intensity amount. In  FIG. 3H , the hatched light emitting elements  1  are indicated as the light emitting elements  1  that emit light at a light intensity amount lower than a desired light intensity amount (same goes for other circuit diagrams). Current flows are shown by the arrows in  FIGS. 3A to 3J . In addition, in  FIGS. 3A to 3J , virtual equivalent capacitors C S0  to C S2  that are included as parasitic capacitances in the lines are shown on the driving lines S. 
     Subsequently, in the sub-frame  12 , the voltage is applied to the common line C 1  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 . Since the parasitic capacitances have been drawn out in the previous frame FM 1 , three light emitting elements  1  that are connected to the common line C 1  can be driven at a desired amount of intensity as shown in  FIG. 3B . Similarly, in the sub-frame  13 , as shown in  FIG. 3C , three light emitting elements  1  that are connected to the common line C 2  are driven at a desired amount of intensity. Subsequently, in the sub-frame  21  in the frame FM 2 , as shown in  FIG. 3D , although the voltage is applied to the common line C 0 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. Also, in the sub-frame  22 , as shown in  FIG. 3E , although the voltage is applied to the common line C 1 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines will be charged. Similarly, in the sub-frame  23 , as shown in  FIG. 3F , although the voltage is applied to the common line C 2 , the parasitic capacitances of the lines will be charged. Thus, the parasitic capacitances of the lines will be fully charged, and cannot be charged anymore as shown in  FIG. 3G . 
     The operation in the cycle CL 5  is now described. Dissimilar to the aforementioned cycle CL 4 , in the cycle CL 5 , the scanning order of the common lines C is set to the order of the common lines C 1 , C 2 , and C 0  in each frame. Since, in the sub-frame  11  in the frame FM 1 , the voltage is first applied to the common line C 1  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to the common line C 1  are driven. The parasitic capacitance charged in the cycle CL 4  reduces the light intensity of the light emitting elements  1  that are connected to the common line C 1 , which is first selected in the cycle CL 5 , to a light intensity amount lower than a desired light intensity amount as shown in  FIG. 3I . Subsequently, in the sub-frame  12 , the voltage is applied to the common line C 2  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 . Since the parasitic capacitances have been drawn out in the sub-frame  11 , three light emitting elements  1  that are connected to the common line C 2  can be driven at a desired amount of intensity as shown in  FIG. 3C . Similarly, in the sub-frame  13 , as shown in  FIG. 3A , three light emitting elements  1  that are connected to C 0  are driven at a desired amount of intensity. Thus, the parasitic capacitances of the lines will be also charged after the sub-frame  21 . 
     The operation in the cycle CL 6  is now described. In the cycle CL 6 , the scanning order of the common lines C is set to the order of C 2 , C 0 , and C 1  in each frame. Since, in the sub-frame  11  in the frame FM 1 , the voltage is first applied to the common line C 2  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to C 2  are driven. The parasitic capacitance reduces the light intensity of the light emitting elements  1  that are connected to the common line C 2 , which is first selected, to a light intensity amount lower than a desired light intensity amount as shown in  FIG. 3J . Subsequently, in the sub-frame  12 , the voltage is applied to the common line C 0  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 . Since the parasitic capacitances have been drawn out in the sub-frame  11 , three light emitting elements  1  that are connected to the common line C 0  can be driven at a desired amount of intensity as shown in  FIG. 3A . Similarly, in the sub-frame  13 , as shown in  FIG. 3B , three light emitting elements  1  that are connected to C 1  are driven at a desired amount of intensity. Thus, the parasitic capacitances of the lines will be also charged after the sub-frame  21 . Since the operation after the cycle CL 7  is similar to the cycles CL 4  to CL 6 , their description is omitted for the sake of brevity. 
     As discussed above, the orders in which the common lines C are scanned by the scanning portion in the frames are different between successive cycles. Accordingly, although activation timing of the driving lines is not changed, since the scanning order of the common lines is set different between cycles, it is possible to distribute the dark line to the rows. Therefore, it is possible to make the dark line inconspicuous. As a result, it is possible to provide a quality display unit that can display the image without light emission unevenness caused by the dark line even in the case where a still image is displayed at low light intensity. In particular, in the case where the same image is displayed in successive cycles as still image, if only a particular row becomes dark, the particular row will be very conspicuous. According to the aforementioned control method, even in the case of a still image where a dark line is likely to be conspicuous, since the dark line does not appear only in a particular row, the dark line can be inconspicuous. 
     Second Embodiment 
     The method according to the foregoing embodiment has been described to change the row that is first driven depending on cycles so that the dark line cyclically appears in different rows depending on cycles. In this method, the rows of the display portion  10  are driven in a first light emission order in a first cycle, while the rows of the display portion  10  are driven next to the first cycle in a second light emission order so that the row that is first driven in the second light emission order is different from the row that is first driven in the first light emission order. However, the present invention is not limited to this method. One(s) of the rows can be driven in one frame in one cycle, and other one(s) or the other rows can be driven in the one frame or a frame following the one frame in the one cycle. According to this method, the row that is first driven in each cycle can be also changed depending on cycles. As a result, it is also possible to suppress the dark line. 
     An exemplary method according to a second embodiment is now described with reference to a timing chart of  FIG. 4 . In the second embodiment, although the scanning order of the common lines is fixed, the activation timing of the driving lines is controlled. In this embodiment, although the scanning portion controls the common lines C 0  to C 2  similarly to the method shown in  FIG. 11  or the like, the driving portion can shift an activation timing period (a series of activation timing sub-frames) of the driving lines corresponding to one frame so that the activation timing sub-frames in this one frame overlaps the next frame. In the light emission control method shown in  FIG. 4 , each of the cycles CL 7  to CL 9  is divided into a plurality of frames FM 1  to FM 3 . In addition, each of the frames is divided into three sub-frames as the minimum timing period for ON/OFF operation by the scanning portion and the driving portion. 
     The operation of the cycle CL 7  is similar to the cycle CL 4  in  FIG. 2 . That is, the scanning order of the common lines C is set to the order of the common lines C 0 , C 1 , and C 2  in each frame. As a result, in the sub-frame  11  in the frame FM 1 , the voltage is applied to the common line C 0  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , as shown in  FIG. 3H . The parasitic capacitance charged in the previous cycle CL 6  (not shown) reduces the light intensity of the light emitting elements  1  that are connected to the common line C 0  to a light intensity amount lower than a desired light intensity amount. That is, the dark line will appear in the common line C 0  in the cycle CL 7 . In the next sub-frame  12 , the voltage is applied to the common line C 1  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 . As a result, three light emitting elements  1  that are connected to the common line C 1  are driven at a desired light intensity amount as shown in  FIG. 3B . Similarly, in the sub-frame  13 , as shown in  FIG. 3C , three light emitting elements  1  that are connected to the common line C 2  are driven at a desired amount of intensity. Subsequently, in the sub-frame  21  in the frame FM 2 , as shown in  FIG. 3D , although the voltage is applied to the common line C 0 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. Also, in the sub-frame  22 , as shown in  FIG. 3E , although the voltage is applied to the common line C 1 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines will be charged. Similarly, in the sub-frame  23 , as shown in  FIG. 3F , although the voltage is applied to the common line C 2 , the parasitic capacitances of the lines will be charged. Thus, the parasitic capacitances of the lines will be fully charged, and cannot be charged anymore as shown in  FIG. 3G . 
     The operation in the cycle CL 8  is now described. In the cycle CL 8 , the scanning order of the common lines C in each frame is fixed, in other words, the scanning order in the cycle CL 8  is same as the cycle CL 7 . Although an activation timing period (a series of the activation timing sub-frames) of the driving lines corresponding to one frame extends only in the one frame in the cycle CL 7 , an activation timing period (a series of the activation timing sub-frames) of the driving lines corresponding to one frame extends over two successive frames in the cycle CL 8 . 
     In the sub-frame  11 , as shown in  FIG. 3D , although the voltage is applied to the common line C 0 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. 
     Subsequently, in the sub-frame  12 , as shown in  FIG. 3I , the voltage is applied to the common line C 1  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to the common line C 1  are driven. The parasitic capacitance charged in the cycle CL 7  and the sub-frame  11  of CL 8  reduces the light intensity of the light emitting elements  1  that are connected to the common line C 1 , which is first driven in the cycle CL 8 , to a light intensity amount lower than a desired light intensity amount. That is, the dark line will appear in the common line C 1  in the cycle CL 8 . 
     Subsequently, in the sub-frame  13 , the voltage is applied to the common line C 2  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 . Since the parasitic capacitances have been drawn out in the sub-frame  12 , three light emitting elements  1  that are connected to the common line C 2  can be driven at a desired amount of intensity as shown in  FIG. 3C . 
     Similarly, in the sub-frame  21  in the frame FM 2 , as shown in  FIG. 3A , three light emitting elements  1  that are connected to C 0  are driven at a desired amount of intensity. After that, the parasitic capacitances of the lines will be also charged in the sub-frame  22  or later. 
     The operation of the cycle CL 9  is now described. In the cycle CL 9 , the scanning order of the common lines C in each frame is fixed, in other words, the scanning order in the cycle CL 9  is same as the cycles CL 7  and CL 8 . Similar to the cycle CL 8 , an activation timing period (a series of the activation timing sub-frames) of the driving lines corresponding to one frame extends over two successive frames in the cycle CL 9 . In the cycle CL 8 , two of the three sub-frames are allocated to the frame FM 1 , and one of the three sub-frames is allocated to the frame FM 2 . In cycle CL 9 , one of the three sub-frames is allocated to the frame FM 1 , and two of the three sub-frames are allocated to the frame FM 2 . 
     In the sub-frame  11  in the frame FM 1 , as shown in  FIG. 3D , although the voltage is applied to the common line C 0 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. Subsequently, also in the sub-frame  12 , as shown in  FIG. 3E , although the voltage is applied to the common line C 1 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. 
     Subsequently, in the sub-frame  13 , as shown in  FIG. 3J , the voltage is applied to the common line C 2  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to the common line C 2  are driven. In this case, since the parasitic capacitance is charged in the previous sub-frames, the parasitic capacitance reduces the light intensity of the light emitting elements  1  that are connected to the common line C 2 , which is first driven in the cycle CL 9 , to a light intensity amount lower than a light intensity amount driven by an originally-specified current. That is, the dark line will appear in the common line C 2  in the cycle CL 9 . 
     Subsequently, in the sub-frame  21  in the frame FM 2 , as shown in  FIG. 3A , three light emitting elements  1  that are connected to C 0  are driven at a desired amount of intensity. Subsequently, in the sub-frame  22 , as shown in  FIG. 3B , three light emitting elements  1  that are connected to C 1  are driven at a desired amount of intensity. After that, in the sub-frame  23 , as shown in  FIG. 3F , the driving lines are deactivated so that the parasitic capacitances of the lines will be charged. Subsequently, also in the frame FM 3 , the driving lines are deactivated so that the parasitic capacitances of the lines will be charged. 
     As discussed above, in the light emission control method shown in  FIG. 4 , the three activation timing sub-frames of the driving lines are allocated to the frame FM 1  in the cycle CL 7 , to the frame FM 1  (sub-frames  12  and  13 ) and the frame FM 2  (only sub-frame  21 ) in the cycle CL 8 , and to the frame FM 1  (only sub-frame  13 ) and the frame FM 2  (sub-frames  21  and  22 ) in the cycle CL 9 . Thus, an activation timing period of the three activation timing sub-frames can extend over frames adjacent to each other. Accordingly, the dark line can cyclically appear depending on cycles in the order of the common lines C 0 , C 1 , and C 2 . As a result, the average values of the current amounts can be even so that the amounts of light intensity can be uniform. Therefore, it is possible to provide effects similar to the first embodiment. 
     In the case of  FIG. 4 , the duration of a non-light emission period (a series of non-light emission sub-frames) is seven sub-frames and constant. The number of seven sub-frames is greater by one sub-frame than the two frames (six sub-frames). Thus, the non-light emission period consists of a number of periods that is not an integral multiple of the number of sub-framed of one frame, and is shifted. Accordingly, the number of the non-light emission period can be fixed, while the activation timing period can extend over frames. Needless to say, in the case where the number of the non-light emission period is not fixed but variable, the activation timing period can be set to extend over frames. 
     Third Embodiment 
     The foregoing second embodiment mentioned has been described to control the driving portion so that the activation timing period (a series of activation timing sub-frames) for activating the driving lines extends over frames, and the sub-frames for activating the driving lines continuously extend correspondingly to one frame. However, it is not necessary to control the driving line so that the sub-frames for activating the driving lines continuously extend correspondingly to one frame. The sub-frames for activating the driving lines can be distributed.  FIG. 5  shows this type of control method according to a third embodiment. In this illustrated light emission control method, between the sub-frames where one row and the next rows are driven, the common lines are scanned, while the driving lines are deactivated (a non-light emission period are provided). That is, dissimilar to the foregoing first and second embodiments, a series of contiguous activation timing sub-frames for activating the driving lines is not provided, but discontiguous driving line activation timing periods each of which has a length of one sub-frame are distributed so that non-light emission periods where the light emitting elements are not driven are provided between the discontiguous driving line activation timing sub-frames. According to this construction, the activation sub-frames for activating the driving lines are distributed without changing the scanning control where the scanning portion activates the common lines so that the dark line can be suppressed. In particular, according to this method, it is possible to reduce the duration of a series of non-light emission sub-frames where the driving lines are deactivated, in other words, where the light emitting elements are not driven. Accordingly, it is possible to reduce the period of time where the parasitic capacitances are charged. Correspondingly, it is possible to suppress the reduction of light intensity. 
     The light emission control method according to the third embodiment is now described with reference to  FIG. 5 . Also in this embodiment, the common lines C 0  to C 2  are controlled in the order of the common lines C 0 , C 1 , and C 2  by the scanning portion similar to the case of  FIG. 11  or the like, while the driving line activation timing is controlled so that the dark line is suppressed. In the light emission control method shown in  FIG. 5 , each of the cycles CL 10  to CL 12  is divided into a plurality of frames FM 1  to FM 3 . In addition, each of the frames is divided into three sub-frames as the minimum timing period for ON/OFF operation by the scanning portion and the driving portion. 
     In the cycle CL 10 , the driving lines are activated in the sub-frame  11  in the frame FM 1 , in the sub-frame  22  in the frame FM 2 , and in the sub-frame  33  in the frame FM 3 . That is, the driving line activation timing periods are distributed to the three frames so that each of the frames includes one driving line activation timing sub-frame. Specifically, in the sub-frame  11  in the frame FM 1 , the voltage is applied to the common line C 0  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , as shown in  FIG. 3H . The parasitic capacitance charged in the previous cycle CL 9  (not shown) reduces the intensity of the light emitting elements  1  that are connected to the common line C 0  to a light intensity amount lower than a desired light intensity amount. That is, a first dark line will first appear in the common line C 0  in the sub-frame  11  in the cycle CL 10 . Subsequently, in the sub-frame  12 , as shown in  FIG. 3E , although the voltage is applied to the common line C 1  by the scanning portion  20 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. Also, in the sub-frame  13 , as shown in  FIG. 3F , although the voltage is applied to the common line C 2 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines will be charged. 
     Subsequently, in the sub-frame  21  in the frame FM 2 , as shown in  FIG. 3D , although the voltage is also applied to the common line C 0 , the parasitic capacitances of the lines will be charged. After that, in the sub-frame  22 , as shown in  FIG. 3I , the voltage is applied to the common line C 1  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to the common line C 1  are driven. The parasitic capacitance charged in the sub-frames  12 ,  13 , and  21  reduces the light intensity of the light emitting elements  1  that are connected to the common line C 1  to a light intensity amount lower than a desired light intensity amount. That is, a second dark line will appear in the common line C 1  in the cycle CL 10 . Also, in the sub-frame  23 , as shown in  FIG. 3F , although the voltage is applied to the common line C 2 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines will be charged. 
     Similarly, in the sub-frame  31  in the frame FM 3 , as shown in  FIG. 3D , although the voltage is applied to the common line C 0 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. Also, in the sub-frame  32 , as shown in  FIG. 3E , although the voltage is applied to the common line C 1 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines will be charged. Subsequently, in the sub-frame  33 , as shown in  FIG. 3J , the voltage is applied to the common line C 2  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to the common line C 2  are driven. In this case, since the parasitic capacitance is charged in the previous sub-frames, the parasitic capacitance reduces the light intensity of the light emitting elements  1  that are connected to the common line C 2  to a light intensity amount lower than a light intensity amount driven by an originally-specified current. That is, a third dark line will appear in the common line C 2  in the cycle CL 10 . 
     Thus, in the cycle CL 10 , the dark line will appear in each frame. In addition, all driven rows will be dark lines. However, the non-light emission period (a series of the non-light emission sub-frames) in the embodiment has a length of three sub-frames, which is shorter as compared with the first and second embodiments. Correspondingly, the parasitic capacitances will be charged for a shorter time period so that the amount of charged capacity of the parasitic capacitance will be smaller. Accordingly, it is possible to reduce the amount of reduction current corresponding to the amount of charged capacity of the parasitic capacitance. In other words, it can be said that the light intensity reduction of the dark line in the cycle CL 10  is smaller as compared with the first and second embodiments. 
     The operation in the cycle CL 11  is now described. In the sub-frame  11  in the frame FM 11 , as shown in  FIG. 3D , although the voltage is applied to the common line C 0 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. Subsequently, in the sub-frame  12 , as shown in  FIG. 3I , the voltage is applied to the common line C 1  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to the common line C 1  are driven. The parasitic capacitance reduces the light intensity of the light emitting elements  1  that are connected to the common line C 1  to a light intensity amount lower than a desired light intensity amount. Subsequently, in the sub-frame  13 , as shown in  FIG. 3F , although the voltage is applied to the common line C 2 , the parasitic capacitances of the lines will be charged. 
     After that, in the sub-frame  21  in the frame FM 2 , the voltage is applied to the common line C 0  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , as shown in  FIG. 3H . The parasitic capacitance reduces the light intensity of the light emitting elements  1  that are connected to the common line C 0  to a light intensity amount lower than a desired light intensity amount. Subsequently, in the sub-frame  22 , as shown in  FIG. 3E , although the voltage is applied to the common line C 1  by the scanning portion  20 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. Subsequently, in the sub-frame  23 , as shown in  FIG. 3J , the voltage is applied to the common line C 2  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to the common line C 2  are driven. In this case, the light intensity of the light emitting elements  1  that are connected to the common line C 2  is reduced by a light intensity amount corresponding to the parasitic capacitance. 
     In the frame FM 3 , the driving lines are deactivated so that the parasitic capacitances of the lines will be charged in the sub-frame  31  as shown in  FIG. 3D , in the sub-frame  32  as shown in  FIG. 3E , and in the sub-frame  33  as shown in  FIG. 3F . Thus, the dark lines will appear in all of three light emission sub-frames in the cycle CL 11 . Specifically, the dark lines will appear in one sub-frame in the frame FM 1  and two sub-frames in the frame FM 2 . In this cycle, since the non-light emission period has a length of one sub-frame, which is the minimum period, the reduction of current amount is minimized. For this reason, the reduction of light intensity can be very small as compared with the first and second embodiments. 
     The operation in the cycle CL 12  is now described. In the cycle CL 12 , the scanning order of the common lines C in each frame is fixed, in other words, the scanning order in the cycle CL 12  is same as the cycles CL 10  and CL 11 . In the sub-frame  11  in the frame FM 1 , as shown in  FIG. 3D , although the voltage is applied to the common line C 0 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. Also, in the sub-frame  12 , as shown in  FIG. 3E , although the voltage is applied to the common line C 1 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines will be charged. Subsequently, in the sub-frame  13 , as shown in  FIG. 3J , the voltage is applied to the common line C 2  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to the common line C 2  are driven. In this case, the light intensity of the light emitting elements  1  that are connected to the common line C 2  is reduced by a light intensity amount corresponding to the parasitic capacitance. 
     In addition, in the sub-frame  21  in the frame FM 2 , as shown in  FIG. 3D , although the voltage is applied to the common line C 0 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. Subsequently, in the sub-frame  22 , as shown in  FIG. 3I , the voltage is applied to the common line C 1  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to the common line C 1  are driven. In this case, the light intensity of the light emitting elements  1  that are connected to the common line C 1  is reduced by a light intensity amount corresponding to the parasitic capacitance. Also, in the sub-frame  23 , as shown in  FIG. 3F , although the voltage is applied to the common line C 2 , the parasitic capacitances of the lines will be charged. 
     In the sub-frame  31  in the frame FM 3 , the voltage is applied to the common line C 0  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , as shown in  FIG. 3H . In this case, the light intensity of the light emitting elements  1  that are connected to the common line C 0  is reduced by the parasitic capacitances to a light intensity amount lower than a desired light intensity amount. Also, in the sub-frame  32 , as shown in  FIG. 3E , although the voltage is applied to the common line C 1 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines will be charged. Similarly, in the sub-frame  33 , as shown in  FIG. 3F , although the voltage is applied to the common line C 2 , the parasitic capacitances of the lines will be charged. 
     As discussed above, according to the third embodiment, since the duration of activation time period is minimized, a number of activation timing periods can be provided. Correspondingly, it is possible to reduce the duration of the non-light emission period (a series of non-light emission sub-frames), that is, the duration of the charge time period where the parasitic capacitance will be charged. As a result, the charged amount of parasitic capacitance can be reduced. Therefore, it is possible to suppress the amount of current that flows in the light emitting element. In this method, since the duration of the non-light emission period (a series of non-light emission sub-frames) is changed depending on cycles, the amounts of light intensity of the dark lines are not constant. In the case of  FIG. 5 , although the light emission timing pattern is changed depending on cycles of CL 10  to CL 12 , the present invention is not limited to this. For example, the light emission timing pattern in the cycle CL 10  may be repeated. 
     Fourth Embodiment 
     It has been described the foregoing embodiments that one of the scanning order of the common lines and the activation timing of the driving lines is changed so that the dark line will appear in different rows depending on frames. As a result, it can make the dark line inconspicuous in a particular row on the display portion in light emission. However, the present invention is not limited to this. Both the scanning order of the common lines and the activation timing of the driving lines can be changed.  FIG. 6  shows this type of control method according to a fourth embodiment. In this illustrated light emission control method, since the duration of the non-light emission period (a series of the non-light emission sub-frames) is constant in each cycle, the light intensity of the dark line can be constant. That is, since the light intensity of dark lines can be constant, it is possible to prevent that a dark line with a darker light intensity appears. Specifically, the light emission control method is now described with reference to  FIG. 6 . In this embodiment, the light emitting elements are driven in the first sub-frame in each frame in each cycle. Accordingly, the duration of the non-light emission period (a series of non-light emission sub-frames) is two sub-frames. The driving portion controls the driving timing so that the driving line is activated only in the first sub-frame, and the other sub-frames are non-light emission sub-frames. On the other hand, the scanning order of the common lines is changed depending on frames in one cycle by the control of the scanning portion so that the common line that is first driven in the first sub-frame in each frame is changed depending on frames in the one cycle. According to this construction, it is possible to drive the light emitting elements only in the first sub-frame in each frame, and to change the common line scanning order depending on frames in one cycle. 
     In the control of the cycle CL 13 , in the sub-frame  11  in frame FM 1 , the voltage is applied to the common line C 0  by the scanning portion  20 , while predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , as shown in  FIG. 3H . The light intensity of the light emitting elements  1  that are connected to the common line C 0  is reduced correspondingly to the parasitic capacitance charged in the previous cycle CL 12  (not shown). Subsequently, in the sub-frame  12 , as shown in  FIG. 3E , although the voltage is applied to the common line C 1  by the scanning portion  20 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines (S 0 , S 1 , and S 2 ) will be charged. Also, in the sub-frame  13 , as shown in  FIG. 3F , although the voltage is applied to the common line C 2 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines will be charged. 
     Subsequently, in the sub-frame  21  in the frame FM 2 , as shown in  FIG. 3I , the voltage is applied to the common line C 1  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to the common line C 1  are driven. In this case, the light intensity of the light emitting elements  1  that are connected to the common line C 1  is reduced correspondingly to the parasitic capacitances. Subsequently, in the sub-frame  22 , as shown in  FIG. 3F , although the voltage is applied to the common line C 2 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines will be charged. Also, in the sub-frame  23 , as shown in  FIG. 3D , although the voltage is applied to the common line C 0 , the parasitic capacitances of the lines will be charged. 
     In the sub-frame  31  in the frame FM 3 , as shown in  FIG. 3J , the voltage is applied to the common line C 2  by the scanning portion  20 , and predetermined currents are drawn by the driving portion  30  through the driving lines S 0  to S 2 , three light emitting elements  1  that are connected to the common line C 2  are driven. In this case, the light intensity of the light emitting elements  1  that are connected to the common line C 2  is reduced correspondingly to the parasitic capacitances. Subsequently, in the sub-frame  32 , as shown in  FIG. 3D , although the voltage is applied to the common line C 0 , the driving portion  30  does not draw currents. Accordingly, the parasitic capacitances of the lines will be charged. Also, in the sub-frame  33 , as shown in  FIG. 3E , although the voltage is applied to the common line C 1 , the parasitic capacitances of the lines will be charged. The same procedure is repeated also in the subsequent cycles CL 14  and CL 15 . As a result, the duration of the non-light emission period (a series of the non-light emission sub-frames) can be constant in the cycles. 
     As discussed above, since the light emitting elements are driven in the first sub-frame in each frame, and the duration of the non-light emission period can be constant, the light intensity of dark lines can be constant. That is, since the duration of the non-light emission period is two sub-frames and constant, the periods where electric charge is charged as the parasitic capacitances of the driving lines S 0  to S 2  can be constant. Accordingly, the light emission amounts of the light emitting elements in the rows can be constant. Therefore, it is possible to eliminate the dark line. In addition, since the scanning order pattern of the common lines and the activation timing pattern of the driving lines are fixed for cycles, the scanning portion and the driving portion can simply control the common lines and the driving lines. 
     The foregoing embodiments have been described that one cycle includes three frames, and one frame includes three sub-frames. However, needless to say, one cycle can include any number of frames, while one frame can includes any number of sub-frames. 
     (Display Portion  10 ) 
     The following description describes main components of the light emission display apparatus  100  that can emit light based on any of the light emission control methods according to the foregoing first to fourth embodiments. The display portion  10  includes the plurality of common lines C, which are arranged in the rows in parallel to each other, and the plurality of driving lines S, which are arranged in the columns perpendicular to the row in parallel to each other. The plurality of light emitting elements  1  are connected between the common lines C and the driving lines S. Thus, the light emitting elements  1  are arranged in a matrix. Specifically, the common lines C corresponds to the rows, while the driving lines S corresponds to the columns in  FIG. 1 . Thus, the light emitting elements  1  are arranged in a matrix with m rows and n columns. The cathode terminals of the light emitting elements  1  of each column is connected to corresponding one of the driving lines S, while the anode terminals of the light emitting elements  1  of each row is connected to corresponding one of the common lines C. 
     Although the display portion  10  is described to include the light emitting elements  1  that are arranged in a matrix with three rows and three columns, needless to say, the display portion can include light emitting elements that are arranged in a matrix with any number of rows and any number of columns. In this specification, the “row” and “column” refer to the horizontal and vertical directions, respectively, for ease of explanation. However, the “row” and “column” are not limited to the horizontal and vertical directions. That is, the “row” and “column” can have a directional relationship relative to each other. For example, the “row” and “column” may refer to the vertical and horizontal directions, respectively, in other words, the display unit  100  may be turned by 90 degrees in the clockwise or counterclockwise direction in  FIG. 1 . 
     (Light Emitting Element  1 ) 
     The light emitting elements  1  are semiconductor light emitting elements. Typically, light emitting diodes (LEDs) can be used as the semiconductor light emitting elements. In this embodiment, LEDs are used as the light emitting elements  1 . 
     (Scanning Portion  20 ) 
     The scanning portion  20  is connected to the common lines C. Any of the common lines C can be scanned by the scanning portion  20  so that a voltage (e.g., 5 V) is applied to the selected one of the common lines C one after another. The scanning portion  20  includes switches (not shown) corresponding to the common lines C, and controls ON/OFF of the common lines C based on the instructions from the scanning order control portion  50 . 
     (Driving Portion  30 ) 
     The driving portion  30  includes the driving elements (not shown) that are connected to the driving lines S, and can drive the light emitting elements  1  based on the instructions from a PWM controller  90 . An image can be displayed in each cycle by combination of frame level control based on display data read from a RAM  70  and PWM level control controlled by a PWM controller  90  in each frame. 
     (Frame Division Portion  40 ) 
     The frame dividing portion  40  divides one cycle CL into a plurality of frames FM. One cycle CL corresponds to an image to be displayed that is generated by a timing controller  80  as discussed later. 
     In this embodiment, the display unit  100  includes the frame dividing portion  40 . However, the display unit may be constructed without the frame dividing portion  40 . The reason is that, even in the case where the display unit does not include the frame dividing portion, the parasitic capacitance on the driving line S will be charged if there is a time period where the driving portion  30  does not draw the current when the common line C is selected by the scanning portion  20 . Also, in this case, the dark line may appear. 
     (Scanning Order Control Portion  50 ) 
     The scanning order control portion  50  can change the scanning order of the common lines C depending on cycles. The scanning order control portion  50  can autonomously control the scanning order of the common lines C. Alternatively, the scanning order control portion  50  may be constructed to control the scanning order of the common lines C based on the instructions from the outside. The common lines C are scanned by the scanning portion  20  based on the instructions from the scanning order control portion  50 . 
     In  FIG. 1 , three common lines C are provided (C 0 , C 1 , and C 2 ). In this embodiment, the common line C that is first scanned in each cycle is changed from C 0  to C 2  in successively ascending numeric order. In the case where the five or more common lines C are provided, the common line C that is first scanned in each cycle can be changed in discrete numeric order. That is, the scanning order control portion can control the scanning order so that the line numbers of the common lines that are first scanned in a predetermined cycle and the next cycle are discrete numbers. For example, in the case where the display unit includes the common lines C of C 0  to C 4 , which are arranged in this order, the common line that is first selected in the first cycle is C 0 , the common line that is first selected in the subsequent cycle is set as C 2 , the common line that is first selected in the subsequent cycle is C 4 , the common line that is first selected in the subsequent cycle is C 1 , and the common line that is first selected in the subsequent cycle is C 3 , so that the common lines C are cyclically and repeatedly scanned in this order. In the case where the line numbers of the common lines that are first scanned in adjacent cycles are discrete numbers, it is possible to suppress the phenomenon where movement of the dark line moves in the scanning direction is perceived. 
     (Shift Register  60 ) 
     A shift register  60  provides display data DAT A_IN corresponding to an image from the outside in accordance with the shift clock CLK_IN. The shift register  60  can retain the display data, which includes frame level data and PWM level data for all of the light emitting elements  1  of the display portion  10 . 
     (RAM  70 ) 
     A RAM  70  retains data in the shift register  60  in accordance with LATCH_IN. Although not illustrated, in order to control the display operation in the display portion  10 , two or more independent RAMs are provided to read data from the frame dividing portion  40  and the PWM controller  90 , and to write the display data from the outside, i.e., the data in the shift register  60 . 
     (Timing Controller  80 ) 
     The timing controller  80  generates the cycle in accordance with VSYNC_IN, and controls the timing of the control portions. 
     (PWM Controller  90 ) 
     The PWM controller  90  controls the PWM level based on the display data read from the RAM  70  in the frame, which generated by the frame dividing portion  40 . 
     Fifth Embodiment 
     Although the foregoing embodiments have been described to use the display unit alone, the present invention is not limited to this. A plurality of display units can be connected to each other so that a large display apparatus is constructed of the a plurality of display units.  FIG. 7  shows this type of display system according to a fifth embodiment. In this illustrated display system, the plurality of display units  100  are connected to each other, while an external control portion  500  is connected to the end of a series of the plurality of display units  100 . The external control portion  500  provides control data including display data and the like to the display units  100 . Thus, the display system is constructed. Therefore, it is possible to provide a display system capable of suppressing the dark line. 
     Sixth Embodiment 
     In the display apparatus of the fifth embodiment, the scanning order in the cycle is controlled by the scanning order control portion  50 , which is included in the display unit. However, even in the case where the display unit does not include the scanning order control portion  50 , the scanning order can be changed depending on cycles by the control data from the external control portion. That is, the control data from the external control portion contains scanning order control data for setting the different scanning orders of the common lines, which are different between one cycle and the next cycle. According to this construction, it is possible to provide a display apparatus having effects similar to the fifth embodiment.  FIG. 8  is a block diagram showing this type of display apparatus according to a sixth embodiment. 
     In the display apparatus according to this embodiment, the external control portion generates the frames, and controls the levels in each frame. The frames are combined so that an image is displayed in one cycle. The levels are controlled in each frame by controlling the PWM controller  90  based on PWMCLK_IN, which is a control signal from the external control portion, and BLANK_IN, which is a reset signal for a PWM counter. 
     The scanning portion  20  is controlled in each frame not by the scanning order control portion  50  but by scanning order control data ADR_IN [1:0] from the external control portion. In this embodiment, 2-bit data is enough to select one of C 0  to C 2 . In the case where the scanning order is changed depending on cycles as shown in  FIG. 2 , it is possible to provide effects similar to the first embodiment. 
     Example 1 
     The following description describes a display unit according to an example 1 of the present invention that includes LEDs arranged in 32 rows×32 columns. Although not illustrated, the display portion includes four sets of common lines, and four sets of driving lines. Each set of common lines includes eight common lines C 0  to C 7 . Each set of driving lines includes eight driving lines S 0  to S 7 . 1024 LEDs are connected to the common and driving lines correspondingly at the intersection between the common and driving lines. More specifically, each of the LEDs includes three light emitting elements of red, green, and blue. The main components such as the scanning portion  20  and the driving portion  30  are similar to the first embodiment ( FIG. 1 ), and their description is omitted for sake of brevity. 
     The display unit according to this example is driven in a ⅛-duty dynamic driving manner. As shown in a timing chart of  FIG. 9 , one cycle of 16.384 ms includes 16 frames, and the scanning order of the common lines C is changed depending on cycles. Specifically, in the cycle CL 1 , the common lines are scanned in the order of C 0 , C 1 , . . . , C 6 , and C 7  in each frame. In CL 2 , the common lines are scanned in the order of C 1 , C 2 , . . . , C 7 , and C 0  in each frame. In CL 3 , the common lines are scanned in the order of C 2 , C 3 , . . . , C 0 , and C 1  in each FM. Thus, the scanning order is cyclically changed so that, after eight cycles, the scanning order returns to the first scanning order. 
     In this display unit, all of the LEDs are driven in FM 1  in every cycle for 50 ns, which is the minimum time unit where the dark line is likely to be conspicuous. Even in the case where all of the LEDs are driven at the minimum light intensity, the dark line can be inconspicuous in this example as compared with a comparative example 1. According to this example, a quality display unit can be provided. 
     Comparative Example 1 
     The same display unit as the example 1 is produced as a comparative example 1 except that the scanning order is set to the order of C 0 , C 1 , . . . , C 6 , and C 7  in each frame for every cycles. In the comparative example 1, when all of the LEDs are driven in FM 1  in every cycle for 50 ns, which is the minimum time unit, the dark line appears in the LEDs that are arranged in C 0 . 
     INDUSTRIAL APPLICABILITY 
     A display apparatus light emission control method and display unit according to the present invention can be used for a large television and traffic information, for example. 
     It should be apparent to those with an ordinary skill in the art that while various preferred embodiments of the invention have been shown and described, it is contemplated that the invention is not limited to the particular embodiments disclosed, which are deemed to be merely illustrative of the inventive concepts and should not be interpreted as limiting the scope of the invention, and which are suitable for all modifications and changes falling within the scope of the invention as defined in the appended claims. The present application is based on Application No. 2011-250,182 filed in Japan on Nov. 15, 2011, the content of which is incorporated herein by reference.