Patent Publication Number: US-2010117942-A1

Title: Liquid crystal display

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display using a color filter (CF) to perform color display. 2. Description of the Related Art 
     In recent years, liquid crystal displays (LCDs) are commonly used as display monitors for liquid crystal televisions, notebook computers, car navigation systems and the like. A typical liquid crystal display uses a color filter to perform full-color display. 
       FIG. 17  illustrates an example of a color filter used for such full-color display. In this case, a red (R) color filter  103 R, a green (G) color filter  103 G or a blue (B) color filter  103 B corresponding to three primary colors of light is arranged on each of pixels  102 . Luminance in each of such pixels  102  is controlled by the color filter  103 R,  103 G or  103 B so as to allow full-color display. 
     However, light is spatially divided into three colors by the color filters  103 R,  103 G and  103 B, so light which is spatially effectively usable is only approximately 33% of incident light. Moreover, the transmittance of light having an optimum wavelength through each of the color filters  103 R,  103 G and  103 B is only approximately 70 to 80%, so with all things considered, only approximately 25% of the incident light is usable. In addition, the other 75% or over of the incident light is converted into heat in the color filters  103 R,  103 G and  103 B. 
     Therefore, as a technique for solving an issue of such low light use efficiency, a field-sequential (time-division) drive has been heretofore proposed as described in, for example, Japanese Unexamined Patent Application Publication No. 2003-280614 and Yi-Fu Chen, et al., “Mixed Color Sequential Technique for High Contrast LCD with Optimum Power Consumption”, SID′07, p. 134, 2007. In the field-sequential drive, light sources allowed to emit light of RGB colors, respectively, such as LEDs (Light Emitting Diodes) are used, and full-color display is performed by temporally switching among light of RGB colors. In such a field-sequential system, the above-described color filters are not necessary (refer to  FIG. 18 ), so it is considered that 4 or more times higher light use efficiency is obtained in the field-sequential system. 
     SUMMARY OF THE INVENTION 
       FIG. 18  illustrates an example of a pixel configuration in a field-sequential system in related art. Each of pixels  202  is a colorless pixel on which a color filter is not arranged as described above, and data of RGB colors are line-sequentially written to the pixels  202  in order of RGB, and a backlight emits light of RGB colors in order of RGB in synchronization with these data. 
     However, in such a field-sequential system, light use efficiency is high, but a temporally effective period is approximately ⅙ or less of one frame period, so to obtain a certain luminance, it is necessary for the backlight to have the maximum luminance which is higher than that in related art. For example, in the case where LEDs are used, a larger number of LEDs than that in related art are necessary, thereby it is disadvantageous in terms of costs. Moreover, the LEDs tend to reduce their light emission amounts relative to electric power according to a reduction in duty ratio when the LEDs light up, so even if light use efficiency is improved, power efficiency is reduced. 
     Moreover, a fundamental issue in the field-sequential system is a so-called color breakup phenomenon. In the color breakup phenomenon, when time-divided images are focused on the same position on a retina, colors are correctly superimposed, but depending on the movement of an object or an eye when watching motion pictures, the time-divided images are focused on different positions on the retina without intention, thereby RGB colors are separately seen. To suppress such a color breakup phenomenon, for example, in a DLP (Digital Light Processing) or the like as a projector using a DMD (Digital Micromirror Device), performing a sextuple-speed drive or the like which is a faster drive is considered, but it is difficult to take similar measures in a liquid crystal which is slow in response. 
     It is desirable to provide a liquid crystal display allowing an improvement in image quality in color display while enhancing light use efficiency and power efficiency. 
     According to an embodiment of the invention, there is provided a liquid crystal display including: a light source section allowed to separately emit first primary color light, second primary color light and third primary color light in different wavelength regions; a liquid crystal display panel including a plurality of pixels arranged in a matrix form as a whole, and modulating each of the first primary color light, the second primary color light and the third primary color light emitted from the light source section in response to a picture signal, each of the plurality of pixels including a first sub-pixel and a second sub-pixel; and a drive section driving the light source section and each sub-pixel in the liquid crystal display panel in response to the picture signal so as to include a first drive period and a second drive period in one vertical period time-dividedly. In this case, the above-described first sub-pixel allows at least the first primary color light and the second primary color light to pass therethrough, and the above-described second sub-pixel allows at least the second primary color light and the third primary color light to pass therethrough. Moreover, in the above-described first drive period, the above-described drive section drives the light source section to separately emit the first primary color light and the third primary color light, and the drive section drives the first sub-pixel and the second sub-pixel in response to a picture signal for the first primary color light and a picture signal for the third primary color light, respectively, and in the above-described second drive period, the drive section drives the light source section to emit the second primary color light, and the drive section drives the first and second sub-pixels in response to a picture signal for the second primary color light. 
     In the liquid crystal display according to the embodiment of the invention, in the first sub-pixel period, the first primary color light and the third primary color light are emitted from the light source section, and then the first primary color light is selectively modulated in the first sub-pixel in response to the picture signal for the first primary color light to display a picture by the first primary color light, and the third primary color light is selectively modulated in the second sub-pixel in response to the picture signal for the third primary color light to display a picture by the third primary color light. Moreover, in the second drive period, the second primary color light emitted from the light source section is selectively modulated in the first and second sub-pixels in response to the picture signal for the second primary color light to display a picture by the second primary color light. Then, such first and second drive periods are included in one vertical period time-dividedly, so full-color display corresponding to the picture signal for each primary color light is performed. At this time, in the first drive period, the first primary color light and the third primary color light are emitted from the light source section, and in the second drive period, the second primary color light is emitted from the light source section, thereby each primary color light emission period (a lighting-up period) in one vertical period is longer than that in a field-sequential system in related art. Moreover, in the second drive period, only the second primary color light is emitted, and is modulated in both of the first and second sub-pixels, so compared to a three-primary-color filter system in related art, an aperture ratio in full-color display is improved. Further, in the first drive period, both of the first primary color light and the third primary color light are emitted, so the occurrence of a color breakup phenomenon is prevented. 
     In the liquid crystal display according to the embodiment of the invention, in the first drive period, the first primary color light and the third primary color light are emitted from the light source section, and in the second drive period, the second primary color light is emitted from the light source section, so each primary color light emission period (a lighting-up period) in one vertical period is allowed to be longer than that in the field-sequential system in related art, and an improvement in duty ratio is allowed. Moreover, in the second drive period, only the second primary color light is emitted, and is modulated in both of the first and second sub-pixels, so compared to the three-primary-color filter system in related art, an improvement in aperture ratio in full-color display is allowed. Further, in the first drive period, both of the first primary color light and the third primary color light are emitted, so the occurrence of a color breakup phenomenon is preventable. Therefore, while light use efficiency and power efficiency are enhanced, an improvement in image quality in color display is allowed. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating the whole configuration of a liquid crystal display according to an embodiment of the invention. 
         FIG. 2  is a schematic plan view illustrating a specific configuration example of a backlight section illustrated in  FIG. 1 . 
         FIG. 3  is a circuit diagram illustrating a specific configuration example of a pixel illustrated in  FIG. 1 . 
         FIG. 4  is a plan view illustrated in a configuration example of a color filter arranged in each sub-pixel in the pixel illustrated in  FIG. 3 . 
         FIG. 5  is a timing chart for describing a method of displaying a picture by a field-sequential system in related art according to Comparative Example 1. 
         FIG. 6  is a timing chart for describing a method of displaying a picture by a field-sequential system in related art according to Comparative Example 2. 
         FIG. 7  is a timing chart for describing a method of displaying a picture in the liquid crystal display according to the embodiment. 
         FIGS. 8A and 8B  are schematic views for describing details of the method of displaying a picture illustrated in  FIG. 7 . 
         FIG. 9  is a timing chart for describing a method of displaying a picture according to Modification 1 of the invention. 
         FIG. 10  is a timing chart for describing a method of displaying a picture according to Modification 2 of the invention. 
         FIG. 11  is a timing chart for describing a method of displaying a picture according to Modification 3 of the invention. 
         FIGS. 12A and 12B  are schematic views for describing details of the method of displaying a picture illustrated in  FIGS. 10 and 11 . 
         FIG. 13  is a plan view illustrating a configuration example of a color filter according to Modification 4 of the invention. 
         FIGS. 14A and 14B  are schematic plan views for describing a vertical streak phenomenon when displaying a picture. 
         FIG. 15  is a circuit diagram illustrating a configuration of a pixel according to Modification 5 of the invention. 
         FIG. 16  is a timing waveform chart illustrating an example of a driving method in the configuration of the pixel illustrated in  FIG. 15 . 
         FIG. 17  is a plan view illustrating a configuration example of a color filter used in a liquid crystal display in related art. 
         FIG. 18  is a plan view illustrating a configuration example of a color filter used in a method of displaying an image by a field-sequential system in related art. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment will be described in detail below referring to the accompanying drawings. 
     The Whole Configuration Example of Liquid Crystal Display 
       FIG. 1  illustrates the whole configuration of a liquid crystal display (a liquid crystal display  1 ) according to an embodiment of the invention. The liquid crystal display  1  includes a liquid crystal display panel  2 , a backlight section  3 , an image processing section  41 , a data driver  51 , a gate driver  52 , a timing control section  61  and a backlight drive section  62 . 
     The backlight section  3  is a light source applying light to the liquid crystal display panel  2 , and includes, for example, LEDs or the like. The backlight section  3  is allowed to separately emit light of three primary colors in different wavelength regions (red light (first primary color light), green light (second primary color light) and blue light (third primary color light)). More specifically, for example, as illustrated in  FIG. 2 , the backlight section  3  includes red light sources  3 R, green light sources  3 G and blue light sources  3 B. 
     The liquid crystal display panel  2  modulates light emitted from the backlight section  3  based on a drive voltage supplied from the data driver  51  in response to a drive signal supplied from the gate driver  52  which will be described later to display a picture corresponding to a picture signal Din. The liquid crystal display panel  2  includes a plurality of pixels  20  arranged in a matrix form as a whole. 
     The image processing section  41  performs predetermined image processing on the picture signal Din from outside to produce a picture signal D 1  which is an RGB signal. 
     The gate driver  52  line-sequentially drives each pixel  20  in the liquid crystal display panel  2  along a scanning line (a gate line G which will be described later) according to timing control by the timing control section  61 . 
     The data driver  51  supplies a drive voltage corresponding to the picture signal D 1  supplied from the timing control section  61  to each pixel  20  of the liquid crystal display panel  2 . More specifically, the data driver  51  performs D/A conversion on the picture signal D 1  to produce a picture signal (the above-described drive voltage) as an analog signal and output the picture signal to each pixel  20 . In addition, the picture signal D 1  includes red data D 1 R, green data D 1 G and blue data D 1 B. 
     The backlight drive section  62  controls the lighting operation (light emission operation) of the backlight section  3 . The timing control section  61  controls driving timings of the gate driver  52  and the data driver  51 , and supplies the picture signal D 1  to the data driver  51 . 
     Specific Configuration Example of Pixel 
     Next, referring to  FIGS. 3 and 4 , a specific configuration of each pixel  20  will be described in detail below.  FIG. 3  illustrates a circuit configuration example of a pixel circuit in each pixel  20 . 
     Each pixel  20  includes two sub-pixels  20 A and  20 B. The sub-pixel  20 A includes a liquid crystal device  22 A and a thin film transistor (TFT) device  21 A. On the other hand, the sub-pixel  20 B includes a liquid crystal device  22 B and a TFT device  21 B. Moreover, one gate line G for line-sequentially select a pixel to be driven and two data lines DA and DB for supplying a drive voltage (the drive voltage supplied from the data driver  51 ) to the sub-pixels  20 A and  20 B in the pixel to be driven, respectively, are connected to each pixel  20 . 
     The liquid crystal device  22 A functions as a display element of performing an operation for display (emitting display light) in response to the drive voltage supplied from the data line DA to one end thereof through the TFT device  21 A. On the other hand, the liquid crystal device  22 B functions as a display element of performing an operation for display (emitting display light) in response to the drive voltage supplied from the data line DB to one end thereof through the TFT device  21 B. The liquid crystal devices  22 A and  22 B each include a liquid crystal layer (not illustrated) formed of, for example, a VA (Vertical Alignment) mode or TN (Twisted Nematic) mode liquid crystal, and a pair of electrodes (not illustrated) between which the liquid crystal layer is sandwiched. One of the pair of electrodes in the liquid crystal device  22 A (one end of the liquid crystal device  22 A) is connected to a drain of the TFT device  21 A, and the other electrode (the other end of the liquid crystal device  22 A) is connected to a ground. Moreover, one of the pair of electrodes in the liquid crystal device  22 B (one end of the liquid crystal device  22 B) is connected to a drain of the TFT device  21 B, and the other electrode (the other end of the liquid crystal device  22 B) is connected to a ground. 
     The TFT device  21 A includes a MOS-FET (Metal Oxide Semiconductor-Field Effect Transistor), and in the TFT device  12 A, a gate is connected to the gate line G, and a source is connected to the data line DA, and a drain is connected to the one end of the liquid crystal device  22 A. The TFT device  21 A functions as a switching device for supplying a drive voltage for the sub-pixel  20 A (a drive voltage corresponding to the picture signal D 1 ) to the one end of the liquid crystal device  22 A. More specifically, the TFT device  21 A selectively provides conduction between the data line DA and the one end of the liquid crystal device  22 A in response to a selection signal supplied from the gate driver  52  through the gate line G. 
     On the other hand, the TFT device  21 B also includes a MOS-FET, and in the TFT device  21 B, a gate is connected to the gate line G, a source is connected to the data line DB, and a drain is connected to the one end of the liquid crystal device  22 B. The TFT device  21 B functions as a switching device for supplying a drive voltage for the sub-pixel  20 B (a drive voltage corresponding to the picture signal D 1 ) to the one end of the liquid crystal device  22 B. More specifically, the TFT device  21 B selectively provides conduction between the data line DB and the one end of the liquid crystal device  22 B in response to a selection signal supplied from the gate driver  52  through the gate line G. 
     Moreover, as illustrated in  FIG. 4 , in the embodiment, the sub-pixel  20 A includes a yellow (Y) color filter  23 Y, and at least red light and green light are allowed to pass through the sub-pixel  20 A. On the other hand, the sub-pixel  20 B includes a cyan (C) color filter  23 C, and at least green light and blue light are allowed to pass through the sub-pixel  20 B. 
     The timing control section  61 , the backlight drive section  62 , the data driver  51  and the gate driver  52  correspond to specific examples of “a drive section” in the invention. The sub-pixel  20 A corresponds to a specific example of “a first sub-pixel” in the invention, and the sub-pixel  20 B corresponds to a specific example of “a second sub-pixel” in the invention. 
     Next, functions and effects of the liquid crystal display  1  according to the embodiment will be described below. 
     Basic Operation of Liquid Crystal Display 
     First, referring to  FIGS. 1 to 3 , the basic operation of the liquid crystal display  1  will be described below. 
     In the liquid crystal display  1 , as illustrated in  FIG. 1 , the image processing section  41  performs image processing on the picture signal Din supplied from outside to produce the picture signal D 1  for each pixel  20 . Then, the picture signal D 1  is supplied to the data driver  51  through the timing control section  61 . In the data driver  51 , D/A conversion is performed on the picture signal D 1  to produce a picture signal as an analog signal. Then, a display drive operation is line-sequentially performed on each pixel  20  in response to the picture signal by drive voltages outputted from the gate driver  52  and the data driver  51  to each pixel  20 . 
     More specifically, as illustrated in  FIG. 3 , switching between operating/nonoperating (ON/OFF) states of the TFT devices  21 A and  21 B is performed in response to a selection signal supplied from the gate driver  52  through the gate line G. Thereby, conduction between the data line DA and the liquid crystal device  22 A and conduction between the data line DB and the liquid crystal device  22 B are selectively provided. As a result, a drive voltage corresponding to the picture signal supplied from the data driver  51  is supplied to the liquid crystal devices  22 A and  22 B to perform the display drive operation. 
     Then, in the pixel  20  in which conduction between the data line DA and the liquid crystal device  22 A and conduction between the data line DB and the liquid crystal device  22 B are provided, illumination light from each of the light sources  3 R,  3 G and  3 B in the backlight section  3  illustrated in  FIG. 2  is modulated in the liquid crystal display panel  2  to be emitted as display light. Thereby, a picture corresponding to the picture signal Din is displayed on the liquid crystal display  1 . 
     Specific Example of Method of Displaying a Picture in Liquid Crystal Display 
     Next, referring to  FIG. 5  to  FIGS. 8A and 8B , a method of displaying a picture (a color display method) as one of characteristic points of the invention will be described in detail compared to comparative examples.  FIGS. 5 and 6  illustrate timing charts of methods of displaying a picture by a field-sequential system in related art according to Comparative Examples 1 and 2. Moreover,  FIG. 7  and  FIGS. 8A and 8B  illustrate a timing chart and schematic views of a method of displaying a picture in the liquid crystal display  1  according to the embodiment, respectively. In addition, in  FIGS. 5 to 7  and subsequent drawings, (A) illustrates a picture signal (each color data) writing operation state in the liquid crystal display panel, and (B) illustrates lighting-up/off states of each color light source in the backlight section. 
     First, in a color display method using color filters of three primary colors in related art illustrated in  FIG. 17 , light is spatially divided into three colors by color filters  103 R,  103 G and  103 B, so light which is spatially effectively usable is only approximately 33% of incident light. Moreover, the transmittance of light having an optimum wavelength through each of the color filters  103 R,  103 G and  103 B is only approximately 70 to 80%, so with all things considered, only approximately 25% of the incident light is usable. In addition, the other 75% or over of the incident light is converted into heat in the color filters  103 R,  103 G and  103 B. 
     On the other hand, in Comparative Example 1 illustrated in  FIG. 5 , as illustrated in  FIG. 18 , each pixel  202  is a colorless pixel on which the color filter is not arranged, and data of RGB colors are line-sequentially written to the pixels  202  in order of RGB, and a backlight emits light of RGB colors in order of RGB in synchronization with these data. In a backlight-on period ΔTon in the drawing, data for a single color is written on the whole screen, so the backlight is allowed to emit light of a color corresponding to the single color. On the other hand, a backlight-off period ΔToff is a transition period to the next single color, so in the period ΔToff, data of a different color is present on the screen at the same time. Therefore, to prevent the colors from being mixed, in the period ΔToff, the backlight is not allowed to emit light. In the case of a normal 60-Hz drive, one frame period (one vertical period) is 16.6 ms, but in the case where the period is divided into RGB by the field-sequential system, each sub-frame period is 5.56 ms. Therefore, even if writing to the liquid crystal and the response of the liquid crystal are completed within 2.78 ms which is ½ of the sub-frame period, a period in which the backlight is allowed to emit light is only 2.78 ms. In addition, in the case where writing to the liquid crystal or the response of the liquid crystal is slow, the lighting-up period is further reduced. 
     Thus, in Comparative Example 1, although light use efficiency is high, a temporally effective period is approximately ⅙ or less of the one frame period, so to obtain a certain luminance, it is necessary for the backlight to have the maximum luminance which is higher than that in related art. For example, in the case where LEDs are used, a larger number of LEDs than that in related art are necessary, thereby it is disadvantageous in terms of costs. Moreover, the LEDs tend to reduce their light emission amounts relative to electric power according to a reduction in duty ratio when the LEDs light up, so even if light use efficiency is improved, power efficiency is reduced. 
     Moreover, in Comparative Example 2 illustrated in  FIG. 6 , to prevent images prepared for the colors from being mixed when the backlight alternately emits light of RGB colors in succession, a black display time is provided when the color of light from the backlight is changed. In this case, it is necessary to drive each pixel  202  at sextuple speed, so power consumption for driving each pixel  202  is increased. Moreover, in the black display period, the light from the backlight is absorbed, so light use efficiency is ½ or less. In addition, light use efficiency or ½ or less is a value at a very high liquid crystal response speed of 2.78 ms, so in the case where the liquid crystal response speed is slower than 2.78 ms, the light use efficiency is further reduced. 
     Moreover, in Comparative Examples 1 and 2, as a fundamental issue in the field-sequential system, the above-described color breakup phenomenon occurs. To suppress such a color breakup phenomenon, for example, in a device such as a DMD, performing a sextuple-speed drive or the like which is a faster drive is considered, but it is difficult to take similar measures in a liquid crystal which is slow in response. 
     On the other hand, in the embodiment, for example, as illustrated in  FIG. 7 , the backlight section  3  and the sub-pixels  20 A and  20 B in the liquid crystal display panel  2  are driven so as to include backlight-on periods ΔTon 1  (a first drive period) and ΔTon 2  (a second drive period) which will be described later in one vertical period time-dividedly. First, in a backlight-off period ΔToff, a picture signal D 1 R for red light is written to the sub-pixel  20 A, and a picture signal D 1 B for blue light is written to the sub-pixel  20 B. After that, when the red light source  3 R and the blue light source  3 B emit light at the same time, magenta (M) light is emitted from the backlight section  3  in the backlight-on period ΔTon 1 . 
     More specifically, the backlight-on period ΔTon 1  is in a state as illustrated in  FIG. 8(A) . In other words, red light and blue light are emitted from the backlight section  3 , and the red light is selectively modulated in response to the picture signal D 1 R for red light in the sub-pixel  20 A to display a picture by the red light. On the other hand, the blue light is selectively modulated in response to the picture signal D 1 B for blue light in the sub-pixel  20 B to display a picture by the blue light. 
     Next, in the backlight-off period ΔToff, a picture signal D 1 G for green light is written to both of the sub-pixels  20 A and  20 B. After that, the green light source  3 G lights up, thereby green light is emitted from the backlight section  3  in the backlight-on period ΔTon 2 . 
     More specifically, the backlight-on period ΔTon 2  is in a state as illustrated in  FIG. 8(B) . In other words, green light emitted from the backlight section  3  is selectively modulated in response to the picture signal D 1 G for green light in both of the sub-pixels  20 A and  20 B to display a picture by the green light. 
     Then, such backlight-on periods ΔTon 1  and ΔTon 2  are included in one vertical period time-dividedly, thereby full-color display corresponding to the picture signals D 1 R, D 1 G and D 1 B for the three primary colors is performed. 
     At this time, in the backlight-on period ΔTon 1 , red light and blue light are emitted from the backlight section  3 , and in the backlight-on period ΔTon 2 , green light is emitted from the backlight section  3 . Thereby, each primary color light emission period (a lighting-up period) in one vertical period is longer than that in Comparative Examples 1 and 2 (in the field-sequential system in related art). More specifically, aperture ratios for the red light and the blue light are reduced to ½ by the color filters, so the light use efficiency of the red light and the light use efficiency of the blue light are reduced to ½. However, the lighting-up period is increased to 5.56 ms (the response of the liquid crystal is 2.78 ms which is equal to that in related art) to cause an increase in duty ratio. In addition, this effect is more remarkable in the case where the response of the liquid crystal is slow. 
     Moreover, in the backlight-on period ΔTon 2 , only green light is emitted, and then modulated in both of the sub-pixels  20 A and  20 B, so compared to a three-primary-color filter system in related art, the aperture ratio in full-color display is improved. More specifically, the aperture ratio for green light is unchanged, and the period is extended, so efficiency is increased twice or more as high as that in related art. At present, power luminous efficiency of the green LED is approximately ½ of that of each of other color LEDs, so a backlight including green LEDs which is twice as many as other color LEDs such as a backlight including RGGB LEDs is frequently used. Therefore, improving the light use efficiency of the green light is more effective in costs and power than LEDs of other colors. 
     Further, in the backlight-on period ΔTon 1 , both of red light and blue light are emitted, so the occurrence of the color breakup phenomenon is prevented. More specifically, when the red light and the blue light are allowed to be emitted at the same time, color breakup between the two colors does not occur. In related art, fluctuations specifically in luminance of G and B are large, but when the red light and the bleu light are emitted at the same time, fluctuations in luminance are prevented. Moreover, even if a frame frequency is unchanged, a period until the same color is displayed is reduced. For example, the period is reduced from 13.89 ms in Comparative Examples 1 and 2 to 11.11 ms. 
     As described above, in the embodiment, in the backlight-on period ΔTon 1 , red light and blue light are emitted from the backlight section  3 , and in the backlight-on period ΔTon 2 , green light is emitted from the backlight section  3 , so each primary color light emission period (a lighting-up period) in one vertical period is allowed to be longer than that in the field-sequential system in related art, and an increase in duty ratio is allowed. Moreover, in the backlight-on period ΔTon 2 , only green light is emitted, and the green light is modulated in both of the sub-pixels  20 A and  20 B, so compared to the three-primary-color filter system in related art, the aperture ratio in full-color display is allowed to be increased. Further, in the backlight-on period ΔTon 1 , both of red light and blue light are emitted, so the occurrence of the color breakup phenomenon is preventable. Therefore, while enhancing light use efficiency and power efficiency, an improvement in image quality in color display is allowed. 
     Moreover, in the backlight-on period ΔTon 2 , the sub-pixels  20 A and  20 B are collectively driven, so a reduction in a writing time is allowed. 
     Further, the gate line G is commonly connected to the sub-pixels  20 A and  20 B in each pixel  20 , and the data lines DA and DB are connected to the sub-pixels  20 A and  20 B, respectively, so even if the number of pixels is doubled, a writing period is prevented from being reduced. 
     Modifications 
     Next, some modifications of the invention will be described below. In the modifications, like components are denoted by like numerals as of the embodiment and will not be further described. 
     Modification 1 
       FIG. 9  illustrates a timing chart of a method of displaying a picture according to Modification 1. In the modification, in the backlight-on periods ΔTon 1  and ΔTon 2 , black display is performed in response to a picture signal for black display before driving the sub-pixels  20 A and  20 B in response to the picture signals D 1 R, D 1 G and D 1 B for the primary colors. 
     More specifically, first, in a state in which liquid crystal cells display black, red data and blue data are written to a sub-pixel including a yellow (Y) color filter and a sub-pixel including a cyan (C) color filter, respectively, and then red light and blue light are emitted at the same time, thereby light from a backlight has the color of magenta. Next, black is written to the liquid crystal cells again, and then the backlight selectively emits green light, and then green image data is written to the sub-pixel including the yellow (Y) color filter and the sub-pixel including the cyan (C) color filter. 
     Therefore, also in the modification, as in the case of the above-described embodiment, while light use efficiency and power efficiency are enhanced, an improvement in image quality in color display is allowed. 
     Moreover, the period in which the backlight lights up extends to a ½ frame period, that is, 8.33 ms, so a decline in efficiency due to the duty ratio is largely reduced. In a period in which the liquid crystal cells display black, light from the backlight is absorbed, but a period other than the period in which the liquid crystal cell display black is as long as 5.56 ms, so efficiency is not much reduced. As in the case of the embodiment, light use efficiency of green light is specifically improved. 
     Modifications 2 and 3 
       FIG. 10  illustrates a timing chart of a method of displaying a picture according to Modification 2.  FIG. 11  illustrates a timing chart of a method of displaying a picture according to Modification 3. In addition, the method of displaying a picture according to Modification 2 corresponds to a modification of the method of displaying a picture according to the above-described embodiment, and the method of displaying a picture according to Modification 3 corresponds to a modification of the method of displaying a picture according to Modification 1. 
     In the modifications, the first primary light is red (R) light, and the second primary light is blue (B) light, and the third primary light is green (G) light. Moreover, the sub-pixel  20 A includes a magenta (M) color filter  23 M, and allows at least red light and blue light to pass therethrough. On the other hand, the sub-pixel  20 B includes a cyan (C) color filter  23 C, and allows at least green light and blue light to pass therethrough. 
     More specifically, in the backlight-on period ΔTon 1 , as illustrated in  FIG. 12(A) , yellow (Y) light is emitted from the backlight section  3 . Then, red light and green light are emitted from the backlight section  3 , and the red light is selectively modulated in the sub-pixel  20 A in response to the picture signal D 1 R for red light to display a picture by the red light. On the other hand, the green light is selectively modulated in the sub-pixel  20 B in response to the picture signal D 1 G for green light to display a picture by the green light. 
     On the other hand, in the backlight-on period ΔTon 2 , as illustrated in  FIG. 12(B) , blue light emitted from the backlight section  3  is selectively modulated in both of the sub-pixels  20 A and  20 B in response to the picture signal D 1 B for blue light to display a picture by the blue light. 
     Thus, also in the modifications, as in the case of the above-described embodiment, while light use efficiency and power efficiency are enhanced, an improvement in image quality in color display is allowed. 
     Moreover, color breakup between green and red both of which have high visibility is suppressed, so an effect of suppressing color breakup is further improved. 
     Modification 4 
       FIG. 13  is a plan view of a configuration example of a color filter according to Modification 4. In the modification, in the liquid crystal display panel  2 , the sub-pixels  20 A and  20 B (the color filters  23 Y and  23 C) are arranged in a staggered fashion. 
     Thereby, in the modification, the occurrence of a vertical streak phenomenon which will be described below is preventable. In other words, the vertical streak phenomenon in which, for example, as illustrated in  FIG. 14A , vertical streaks are not observed in white light, but, for example, as illustrated in  FIG. 14B , vertical streaks are easily observed at the instant of emitting red light and blue light is preventable. In addition, in the invention, the width of the pixel is larger than a pixel in related art, so the effect is more remarkable. 
     Modification 5 
       FIG. 15  illustrates a circuit diagram of a configuration of a pixel (a pixel  20 - 1 ) according to Modification 5. 
     In the modification, the gate lines GA and GB are connected to the sub-pixels  20 A and  20 B in each pixel  20 , respectively, and the data line D is commonly connected to the sub-pixels  20 A and  20 B. 
     Thereby, in the modification, the cost of the gate driver  52  is approximately ⅓ of the cost of the data driver  51 , so the modification has an effect of reducing costs. 
     In addition, it is feared that a writing period is reduced, so, for example, as illustrated in  FIG. 16 , in the case of a period in which green is written, two gate lines GA and GB are preferably selected at the same time to gain the writing period. 
     Although the present invention is described referring to the embodiment and the like, the invention is not limited thereto, and variously modified. 
     For example, the color of the color filter arranged on each of the sub-pixels  20 A and  20 B, and the color of light emitted from the backlight section  3  in each of the backlight-on periods ΔTon 1  and ΔTon 2  are not limited to the colors described above, and a combination of any other colors may be used. 
     Moreover, the circuit configuration of each pixel is not limited to those described in the above-described embodiment and the like, and each pixel may have any other circuit configuration. For example, a gate line and a data line may be separately connected to each sub-pixel. 
     The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2008-285305 filed in the Japan Patent Office on Nov. 6, 2008, the entire content of which is hereby incorporated by references. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.