JP2008020758A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device with which color breakup is alleviated and a peak current is reduced. <P>SOLUTION: In the liquid crystal display device, LEDs 5-7 of R, G and B are turned on in respective three field periods of each frame period, and W field periods are set, in which all of the LEDs 5-7 are turned on by sequentially turning on two LEDs one by one other than LEDs being turned on during each field period. Consequently the peak current is suppressed since turning on starting timing of the one LED and that of the other LED other than the LEDs being turned on are shifted from each other during the W field period. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a field sequential type liquid crystal display device including a liquid crystal panel and a backlight including a plurality of light emitting elements that emit light of different colors.

  In recent years, displays using liquid crystal instead of conventional CRT displays have become widespread as image displays used in computers and televisions.

  A liquid crystal is one of the states of a substance and has both the fluidity of a liquid and the optical properties of a solid (crystal). A liquid crystal display encloses a substance in a liquid crystal state between two glass plates, changes the direction of liquid crystal molecules in that portion by applying a voltage partially, and displays an image by increasing or decreasing the light transmittance. . Since the liquid crystal does not emit light by itself, a separate light source is required. In particular, in a transmissive liquid crystal display, a light source is disposed on the back surface of the liquid crystal screen. This light source is called a backlight. Liquid crystal displays are thinner and lighter than CRT displays and consume less power, so they have been used in portable devices and personal computers. Recently, however, they have also been used in large home TVs.

  As a light source of the backlight, a cold cathode tube is generally used, but recently, a backlight using an LED as a light source has been announced. When LED is used, the color reproduction range of the image is expanded by using three primary color LEDs of R (red), G (green), and B (blue), which are mercury-free and have a short rise stabilization time in the cold. LED backlights are expected to be widely used in the future because they have advantages such as long life, small size and thinning.

  FIGS. 13A to 13C are diagrams illustrating the configuration of a backlight using LEDs. The backlight has a plurality of tiles 52 arranged on a frame 51 as shown in FIG. As shown in FIG. 13B, a plurality of LEDs 53 are mounted on the surface of the tile 52. More specifically, the tile 52 is a substrate whose main material is metal or resin. In the tile 52 mainly made of metal, an insulating film is formed on a substrate, and a metal wiring for mounting the LED 53 is provided thereon. A plurality of tiles 52 are arranged and supported by a frame 51. In FIG. 13B, the plurality of LEDs 53 are arranged almost evenly on the tile 52. As the backlight, a light source that basically lights in white is desirable, and as a method therefor, a method using a white LED or a method of obtaining white by mixing the light of the three primary colors LEDs 54 to 56 of R, G, B There is. In FIG.3 (c), what uses LED54-56 of three primary colors of R, G, B as LED53 is shown. In the LED 53, a red LED 54, a green LED 55, and a blue LED 56 are collectively arranged.

  FIG. 14 is a diagram illustrating a configuration of a liquid crystal television using an LED backlight. FIG. 14 is a view of the frame 51 of FIG. 13 (a) from the back side. A tile 52 is disposed on the other side of the frame 51, and a liquid crystal panel 60 for video display on the television is further disposed on the other side. . With this arrangement, light emitted from the backlight is transmitted through the liquid crystal panel 60 and displayed as an image.

  In addition, on the surface of the frame 51 opposite to the side where the tile 52 is disposed, the tuner unit 61 that receives and decodes the broadcast radio wave, and the liquid crystal panel 60 displays on the basis of the output signal of the tuner unit 61. An image processing unit 62 for generating a video signal, an LCD control unit 63 for controlling the liquid crystal panel 60, an I / F unit 64 for exchanging signals with other devices, and a plurality of power supply voltages used in a television device from a commercial power source. Various functional units such as a power supply unit 65 to be generated, a fan 66 for cooling the inside of the device, and an LED drive unit 67 for turning on the LED backlight are mounted. These functional units are arranged, separated, omitted, etc. according to the TV specifications and the like.

  The liquid crystal panel 60 is mainly composed of a liquid crystal unit and three primary color filters, and color reproduction of the displayed image is controlled by turning on / off the backlight light for each pixel by the liquid crystal unit. It is obtained by doing. In this case, it is desirable that the backlight is basically lit so that white is obtained.

  However, recently, a field sequential method that performs color reproduction without using a color filter has been attempted. In this method, each of the R, G, and B light sources is made to emit light one by one sequentially, and the color is perceived using the afterglow of human eyes. There are three advantages of this method: cost reduction by eliminating the need for expensive color filters, improvement in light utilization efficiency by eliminating light absorption by the color filters, reduction in power consumption, and R, G, and B. The display resolution can be improved by eliminating the need to configure one pixel, and desirable characteristics can be obtained as a display.

  FIG. 15 is a time chart showing the field sequential method. Generally, when a moving image is displayed, the display is performed in units of frames, and therefore, the three colors R, G, and B are caused to emit light independently and sequentially within one frame. Therefore, the R drive signal is set to “H” level, the R field period for causing the red LED 54 to emit light, the G drive signal is set to “H” level, the G field period for causing the green LED 55 to emit light, and the B drive signal is set to “H” level. A B field period in which the blue LED 56 emits light is provided. At the same time, the liquid crystal unit needs to perform liquid crystal control synchronized with each field. That is, the red component of the display image is displayed during the R field period, the green component of the display image is displayed during the G field period, and the blue component of the display image is displayed during the B field period.

  However, in the field sequential method, since the lighting of R, G, and B is not temporally the same, there is a problem that “color breakup” occurs when a display image is viewed. Here, “color breakup” will be described. Assume that an object A is displayed on the display screen as shown in FIG. When viewing this display screen, it is assumed that the line of sight is moved in the direction of the arrow in FIG. If the viewpoint positions at times t1, t2, and t3 are Pt1, Pt2, and Pt3, respectively, the object A in the display screen relatively moves in the field of view as A1, A2, and A3 in the drawing.

  Here, when time t1 is an R field period, time t2 is a G field period, and time t3 is a B field period, A1 is displayed in red, A2 is displayed in green, and A3 is displayed in blue. As a result, R, G, and B monochromatic portions are generated around the contour of the object A. This is a phenomenon called “color breakup” in which the object A is recognized by being separated into each color. In order to reduce the color breakup, it is necessary to reduce the degree of occurrence of R, G, B monochromatic portions around the contour of the object on the display image. The fundamental cause of the color breakup is that the R, G, and B single color fields are visually recognized.

  As one method for solving this, it is conceivable to quickly switch the fields so that the single color fields of R, G, and B cannot be visually recognized. However, as described above, the liquid crystal unit also needs to perform liquid crystal control synchronized with the field, but the current liquid crystal on / off state transition speed is as fast as about 4 mS, but only about 3 times in one frame. Transition is not possible, and in the field, only one transition can be realized per frame.

  As another method, if not only a single color but also a mixed color field is added in the frame, it is considered that the ratio of the single color is reduced and color breakup can be reduced. However, if other colors are mixed, the color balance will be lost and accurate color reproduction will not be possible. From this, it is thought that it is better to use an achromatic color as the color to be mixed. Achromatic colors are black, white and gray. Here, a field in which the mixed color is an achromatic color is referred to as a W field.

For example, in Patent Document 1, as shown in FIG. 17, an achromatic W field is added in one frame in order to reduce color breakup. Here, the R, G, B LEDs 54 to 56 are simultaneously turned on to obtain an achromatic color. In Patent Document 2, a W field is inserted into each of R, G, and B fields.
Japanese Patent Application Laid-Open No. 2002-229531 JP 2000-352701 A

  However, in Patent Document 1, the period occupied by each single color of R, G, B in one frame is only shortened from 1/3 frame to 1/4 frame, and each single color of R, G, B The reduction effect of visually recognizing the field is poor.

  In Patent Document 2, the W field is inserted in each of the R, G, and B fields, and the other two colors are turned on at the same time. Current will flow, causing problems such as generation of electromagnetic noise, unstable GND level, and high peak power source performance. Further, for example, in the case of an image having a pixel or a region having no or almost no component other than red (green and blue), a pixel or region having no or almost no component other than red (green and blue) is inserted by inserting a W field. The color saturation of the area is reduced. Similarly, green and blue also cause a decrease in color saturation.

  Therefore, a main object of the present invention is to provide a liquid crystal display device capable of reducing color breakup and peak current.

  The liquid crystal display device according to the present invention is a field sequential type liquid crystal display device including a liquid crystal panel and a backlight including a plurality of light emitting elements that emit light of different colors, and each of the plurality of field periods in each frame period. A plurality of light emitting elements of a color corresponding to the field are turned on, and a plurality of light emitting elements corresponding to colors other than the light emitting element being lit are sequentially turned on in at least one field period of the plurality of field periods. The subfield period is provided at least once.

Preferably, the subfield period is provided at least once in each field period.
Preferably, the length of the subfield period is changed for each frame.

  Preferably, the length of the subfield period is set based on image information of one frame.

  Preferably, the length of the subfield period is set based on image information of a plurality of frames.

Preferably, the image information is an average luminance of the image.
Preferably, each color component of the display image is compared with a threshold value, and when each color component other than a certain color component is equal to or smaller than the threshold value, a subfield period is set in a field period in which a light emitting element emitting a certain color is turned on. Not provided.

  Preferably, the number of light emitting elements is three, and the three light emitting elements emit light in red, green and blue, respectively.

  In the liquid crystal display device according to the present invention, the plurality of light emitting elements are turned on in each of the plurality of field periods of each frame period, and the light emitting elements other than the light emitting elements being turned on are within at least one field period of the plurality of field periods. A subfield period in which the plurality of light emitting elements are sequentially turned on is provided at least once. Therefore, since the subfield period in which all the light emitting elements are turned on in the field period is provided, color breakup can be reduced. In addition, in the subfield period, a plurality of light emitting elements other than the light emitting elements that are turned on are sequentially turned on, so that peak current can be suppressed.

[Embodiment 1]
1 is a block diagram showing a main part of a liquid crystal display according to Embodiment 1 of the present invention. In FIG. 1, this liquid crystal display includes an image display control unit 1, a liquid crystal panel 2, a timing control unit 3, an LED drive unit 4, a red LED 5, a green LED 6, and a blue LED 7, and adopts a field sequential method. A plurality of sets of LEDs 5 to 7 are provided to constitute a backlight as shown in FIGS.

  The image display control unit 1 receives an input image signal and performs image processing and liquid crystal panel control for displaying an image on the liquid crystal panel 2. The liquid crystal panel 2 is controlled by the image display control unit 1 to display an input image. The input image signal includes a frame synchronization signal that is a signal synchronized with each normal frame. The image display control unit 1 detects a frame synchronization signal from the input image signal and outputs it to the timing control unit 3. The LED driving unit 4 drives each of the red LED 5, the green LED 6, and the blue LED 7 independently.

  As shown in FIG. 2, the LED drive unit 4 includes OR gates 11 to 13, an R driver 14, a G driver 15, a B driver 16, and an LED power source 17. The anodes of the LEDs 5 to 7 both receive the output voltage of the LED power source 17. The cathodes of LEDs 5-7 are connected to drivers 14-16, respectively. Each of drivers 14 to 16 is constituted by a constant current drive circuit, for example. Each of the drivers 14 to 16 includes an input terminal for externally controlling on / off.

  An R drive signal, a G drive signal, a B drive signal, a Wr drive signal, a Wg drive signal, and a Wb drive signal are introduced as signals for controlling on / off of the drivers 14 to 16. The R drive signal and the Wr drive signal are signals for turning on / off the red LED 5 and are input to the OR gate 11. The G drive signal and the Wg drive signal are signals for turning on / off the green LED 6 and are input to the OR gate 12. The B drive signal and the Wb drive signal are signals for turning on / off the blue LED 7 and are input to the OR gate 13. The output signals of the OR gates 11 to 13 are input to the input terminals of the drivers 14 to 16, respectively.

  Thus, for example, when the red LED 5 is turned on, the R drive signal or the Wr drive signal may be set to the “H” level of the activation level. This is because it is easier to control the W field if the Wr drive signal is separated from the R drive signal. These R, G, B, Wr, Wg, and Wb drive signals are output from the timing control unit 3. The timing control unit 3 controls the lighting timing of the LEDs 5 to 7 while synchronizing with the input image signal.

  Here, a method for reducing color breakup will be described. As described above, in order to make it difficult to perceive color breakup, it is considered that the time for continuously lighting only the single colors of R, G, B in one frame may be shortened. If the lighting time of the field is shortened, the display brightness is lowered, resulting in a dark image. Therefore, a reduction in luminance is prevented by adding an achromatic (white / gray) field (referred to as a W field). The W field is obtained by lighting each LED of R, G, and B with a predetermined amount of light.

  As a feature of the present invention, a plurality of the W fields are provided in one frame to enhance the effect of reducing color breakup. This is because the W field includes all the colors of R, G, and B. By adding the W field to each of the single color fields of R, G, and B, the time for continuously lighting only the single color can be separated and shortened. Because. In addition, by controlling the lighting timings of the R, G, and B LEDs 5 to 7 in the W field not simultaneously, the generation of electromagnetic noise is suppressed, the GND level is prevented from becoming unstable, and the peak of the power source for the light source Provide a backlight control method that does not require high performance.

  Next, LED lighting timing will be described with reference to FIG. When an input image signal is input, a frame synchronization signal is output from the image display control unit 1 to the timing control unit 3. In synchronism with the frame synchronization signal, an R drive signal, a G drive signal, and a B drive signal are output from the timing control unit 3 to the LED drive unit. Each drive signal is sequentially output in a period of approximately 1/3 of one frame. And the LED drive part 4 drives LED5-7 with the timing of this R drive signal, G drive signal, and B drive signal. Further, a W field is added to each of the R, G, and B fields.

  The W field is realized by a Wr drive signal, a Wg drive signal, and a Wb drive signal. Further, since the W field is achromatic, it is realized by turning on all the R, G, and B LEDs 5 to 7 by a predetermined amount of light. In this example, it is assumed that LEDs that can obtain an achromatic color by lighting the LEDs 5 to 7 for the same time are used. Further, although the achromatic colors can be obtained by lighting the LEDs 5 to 7 for the same time, it is not necessary to light them simultaneously as the lighting timing. This is because even if it is lit with a slight shift, it is perceived as an achromatic color from the afterglow of the eyes when viewed by humans.

  By shifting the lighting timing of the LEDs 5 to 7, the current timings flowing through the LEDs 5 to 7 do not overlap, so that the overall peak current can be kept low. That is, as shown in FIG. 4A, for example, when the G and B LEDs 6, 7 are driven by the G and B drive signals, the waveform of the current flowing through the LEDs 6, 7 has a peak at the time of rising. As shown in FIG. 4A, when these lighting timings are simultaneously performed, the peaks overlap, and a large current flows instantaneously. Therefore, a large electromagnetic noise is generated, the GND level becomes unstable, and a high capability is required as the current peak performance of the LED power source 7. On the other hand, as shown in FIG. 4B, by shifting the lighting timing, the current peaks do not overlap and the above-mentioned problem does not occur.

  Next, returning to FIG. 3, the insertion of the W field into the R field will be described. The Wr drive signal is raised to the “H” level after a predetermined time tdr from the start of the R field, and further lowered to the “L” level after the predetermined time tw has elapsed. In this case, since the R field is being used, the red LED 5 has already been driven by the R drive signal, so the drive state of the red LED 5 does not change with respect to the Wr drive signal.

  The Wg drive signal is raised to “H” level after elapse of a predetermined time tdg from the start of the G field, and is further lowered to “L” level after elapse of the predetermined time tw. The green LED 6 is driven while the Wg drive signal is at “H” level. The Wb drive signal is raised to “H” level after a lapse of a predetermined time tdb from the start of the B field, and is further lowered to “L” level after a lapse of the predetermined time tw. The blue LED 7 is driven while the Wb drive signal is at “H” level. In this way, the W field is inserted into the R field. Note that the delay times tdr, tdg, tdb, and tw may be values set in advance in the timing control unit 3 or may be set from the outside. Similarly, the W field is also inserted in the G field and the B field.

  The operation of the timing control unit 3 at this time will be described in detail with reference to FIG. The timing control unit 3 is configured by a processor such as a CPU, for example. When the main routine of this control is started, the timing control unit 3 sets delay times tdr, tdg, tdb and a lighting time tw in step S1. tdr ≠ tdg ≠ tdb, for example, tdr <tdg <tdb. The setting destination may be a memory such as a register. Next, in step S2, it waits for a frame synchronization signal to be input. When an image signal is input, a frame synchronization signal is input from the image display control unit 1. Therefore, in step S 3, the R drive signal is set to “H” level to start the R field, and at the same time, the R field period tr The timer count to know the elapsed time is started. Also, the Wr routine, Wg routine, and Wb routine, which are subroutines for inserting the W field, are started. In the main routine, in step S4, the process waits until tr has elapsed for 1/3 frame.

  As shown in FIGS. 6A to 6C, when the Wr routine is started, the timing control unit 3 starts a timer count for detecting the elapse of tdr in step S21, and the elapse of tdr in step S22. wait. When tdr elapses, the Wr drive signal is set to the “H” level in step S23, a timer count for detecting the elapse of tw is started, and the elapse of tw is waited in step S24. When tw has elapsed, the W drive signal is lowered to the “L” level in step S25, and the Wr routine is terminated.

  When the Wg routine starts, the timing control unit 3 starts a timer count for detecting the elapse of tdg in step S31, and waits for the elapse of tdg in step S32. When tdg elapses, the Wg drive signal is set to the “H” level in step S33, and a timer count for detecting the elapse of tw is started, and the elapse of tw is waited in step S34. When tw has elapsed, the W drive signal is lowered to the “L” level in step S35 and the Wg routine is terminated.

  When the Wb routine is started, the timing control unit 3 starts a timer count for detecting the passage of tdb in step S41, and waits for the passage of tdb in step S42. When tdb elapses, the Wb drive signal is set to the “H” level in step S43, and a timer count for detecting the elapse of tw is started, and the elapse of tw is waited in step S44. When tw has elapsed, the W drive signal is lowered to the “L” level in step S45, and the Wb routine is terminated.

  Returning to FIG. 5, when tr of the main routine has elapsed by 1/3 frame time, the R drive signal is lowered to “L” level in step S 5, and shifts to G field control. In step S6, the timing controller 3 raises the G drive signal to the “H” level to start the G field, and at the same time starts a timer count for detecting the elapse of the G field time tg. Also, the Wr routine, Wg routine, and Wb routine, which are subroutines for inserting the W field, are started. In step S7, it waits for tg to elapse for 1/3 frame time. When tg has passed for 1/3 frame time, the G drive signal is lowered to “L” level in step S8 and the process proceeds to B field control.

  In step S9, the timing controller 3 raises the B drive signal to the “H” level to start the B field, and simultaneously starts a timer count for detecting the passage of the B field time tb. Also, the Wr routine, Wg routine, and Wb routine, which are subroutines for inserting the W field, are started. In step S10, it waits for tb to elapse for 1/3 frame time. When tb has elapsed by 1/3 frame time, in step S11, the B drive signal is lowered to the “L” level, the process returns to step S2, and the process waits until the next synchronization signal is received.

  Note that an effect of reducing flicker can be obtained by changing the delay times tdr, tdg, and tdb for each frame. That is, if the W field is inserted at a fixed timing in one frame, the W field and the R, G, B single color lighting timings are visually recognized in the same period in all fields. May be recognized. By changing the delay times tdr, tdg, and tdb for each frame, the single-color lighting timings for the W field and R, G, and B are changed for each frame, and the lighting periodicity is reduced, so that flicker is reduced. Giving randomness to the delay times tdr, tdg, and tdb is effective in reducing flicker.

  Further, the image display control unit 1 displays the red component image of the image during the R field period, the green component image during the G field period, and the blue image of the image during the B field period. Panel control to display component images. In order to synchronize the display on the liquid crystal panel and the lighting timing of the LEDs 5 to 7 with higher accuracy, the timing control unit 3 may give the image display control unit 1 signals corresponding to the R, G, and B field periods. Good.

[Embodiment 2]
As described in the first embodiment, in the W field, achromatic light is obtained by lighting the R, G, and B LEDs 5 to 7 for the same time. However, if the W field period is excessively long, the display image becomes whitish. On the other hand, if the W field period is excessively short, the luminance of the display image decreases. In order to avoid this, by adjusting the W field period optimally, the screen brightness can be maintained and the image can be prevented from becoming whitish. In order to realize this, a W period setting unit 20 is added between the image display control unit 1 and the timing control unit 3 as shown in FIG. The W period setting unit 20 receives image information from the image display control unit 1 and sets a W field period based on the image information.

  Setting the W field period is synonymous with setting the value of tw. Hereinafter, a setting example of tw will be described with reference to FIG. For example, the average luminance of the screen is calculated from the received image information of one frame, and tw corresponding to the frame is set based on the obtained average luminance value. The average luminance of the screen is generally determined by the G component of R, G, and B of the image. Therefore, the G component of all the pixels of the received image information is stored in the image memory 21, and the average value Xg of the stored G components of all the pixels is calculated by the Xg calculation unit 22. When the maximum value of tw is twmax and the resolution of each pixel is 8 bits, the tw calculator 23 calculates the tw corresponding to the frame based on the formula tw = twmax * Xg / 256. The calculation result of tw is given to the timing control unit 3 by the output unit 24. The timing control unit 3 sets the W field period according to tw given from the W period setting unit 20. The maximum value twmax of tw may be a value set in advance in the W period setting unit 20 or may be set from the outside. The calculation for obtaining tw may be completed within tdr, tdg, tdb, which is the time for inserting the W field from the start of the R, G, B fields.

  As another example of setting the W field period, for example, calculating the average luminance of the screen of the received image information of a plurality of frames, and setting the W field period corresponding to the plurality of frames based on the obtained average luminance value Is also possible. The average value Xg1 for the G component of all the pixels of the received image information of a plurality of frames is calculated. By calculating tw1 corresponding to the plurality of frames based on the formula tw1 = twmax * Xg1 / 256, tw1 can be obtained. The number of frames may be a value set in advance in the W period setting unit 20 or may be set from the outside. In this way, it is not necessary to calculate tw for each frame, and it can be handled by a low-speed system.

[Embodiment 3]
In the first and second embodiments, the example in which the W field is inserted once in each of the R, G, and B fields has been described. However, in this third embodiment, as shown in FIG. Insert W field multiple times in each field. In FIG. 9, the W1 field is inserted after the elapse of a predetermined time tdr1 from the start of each field of R, G, B, and the W2 field is inserted after the elapse of a predetermined time tdr2 from the start of each field of R, G, B. . The delay times tdr1 and tdr2 may be values set in advance in the timing control unit 3 or may be set from the outside. In addition, the W1 field time tw1 and the W2 field time tw2 may be values set in advance in the timing control unit 3 or may be set from the outside.

  Further, as described in the second embodiment, when the W field is inserted while maintaining the screen luminance, tw is calculated, and for example, tw1 = tw / 2 and tw2 = tw / 2 may be set. In this way, the time for which each single color of R, G, B is continuously displayed is shortened separately from the first and second embodiments, so that the color breakup is further reduced.

[Embodiment 4]
For example, if there is a pixel or region that does not contain any components other than red (ie, green and blue components) in the display image, this pixel or region should be displayed in a single red color. In the first to third embodiments, the W field is inserted for each of the R, G, and B fields. In such a case, since the W field is mixed in the R field, the pixel or region is not related. Red saturation will decrease. Therefore, in the fourth embodiment, in order to avoid this, insertion of the W field into the R field is stopped in such a case. Similarly, if there is a pixel or region that does not contain any component other than green (that is, red and blue components) in the display image, the insertion of the W field in the G field is stopped, and the component other than blue in the display image If there is a pixel or region that does not contain any (ie, red and green components), the insertion of the W field into the B field is stopped. By doing so, the reduction in color breakup is lower than when the W field is inserted in all the R, G, and B fields, but it is possible to ensure color saturation in a single color pixel or region. I can do it.

  In addition, when there is a pixel or region that has a component other than red (that is, green and blue components) or less in the display image and there is a pixel or region that has a component other than green (that is, red and blue components) in the display image. Or if there is an area, if there is a pixel or area below the threshold that has a component other than blue (that is, red and green components) in the display image, and the threshold is very small, the same can be said. The W field insertion in the field to be performed may be stopped.

  In order to realize this, as shown in FIG. 10, a color information recognition unit 30 is provided between the image display control unit 1 and the timing control unit 3 in addition to the configuration of FIG. 7. Details of the color information recognition unit 30 are shown in FIG. Image information from the image display control unit 1 is stored in the image memory 31. The R component extraction unit 32, the G component extraction unit 33, and the B component extraction unit 34 extract R, G, and B components from the image information in the image memory 31, and an R threshold value setting unit 35, a G threshold value setting unit 36, and a B threshold value are extracted. The setting unit 37 sets R, G, and B thresholds, and the R comparing unit 38, the G comparing unit 39, and the B comparing unit 40 compare the extracted component and the threshold for each of R, G, and B. As a result of the comparison, the colors below the threshold are output to the timing control unit 3 via the output unit 41. When the two colors are equal to or less than the threshold value, the timing control unit 3 controls the W drive signal in FIG. 2 so as not to insert the W field into the field corresponding to the remaining colors. The threshold values for R, G, and B may be values set in advance in the color information recognition unit 30 or may be set from the outside.

  FIG. 12 is a timing chart when there are pixels or regions in which components other than red (that is, green and blue components) are equal to or less than a threshold value. In this case, the red saturation of the pixel or region is secured by not inserting the W field in the R field.

  Note that the image display control unit 1, the timing control unit 3, the W period setting unit 20, and the color information recognition unit 30 may be provided integrally in a CPU or DSP in the liquid crystal display device.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a block diagram which shows the principal part of the liquid crystal display by Embodiment 1 of this invention. It is a circuit block diagram which shows the structure of the LED drive part shown in FIG. It is a time chart which shows the lighting timing of LED shown in FIG. It is a wave form diagram which shows the electric current which flows into LED shown in FIG. It is a flowchart which shows operation | movement of the timing control part shown in FIG. 6 is another flowchart showing the operation of the timing control unit shown in FIG. 1. It is a block diagram which shows the principal part of the liquid crystal display by Embodiment 2 of this invention. FIG. 8 is a circuit block diagram illustrating a configuration of a W period setting unit illustrated in FIG. 7. It is a time chart which shows the lighting timing of LED in the liquid crystal display by Embodiment 3 of this invention. It is a block diagram which shows the principal part of the liquid crystal display by Embodiment 4 of this invention. It is a circuit block diagram which shows the structure of the color information recognition part shown in FIG. It is a time chart which shows the lighting timing of LED shown in FIG. It is a figure which shows the structure of the LED backlight of the conventional liquid crystal display. It is a figure which shows the structure of the liquid crystal television provided with the LED backlight shown in FIG. It is a time chart which shows a field sequential system. It is a figure for demonstrating the problem of the field sequential system demonstrated in FIG. 17 is a time chart illustrating a method for solving the problem described in FIG. 16.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Image display control part, 2 Liquid crystal panel, 3 Timing control part, 4 LED drive part, 5,54 Red LED, 6,55 Green LED, 7,56 Blue LED, 11-13 OR gate, 14 R driver, 15 G Driver, 16 B driver, 17 LED power supply, 20 W period setting unit, 21, 31 image memory, 22 Xg calculation unit, 23 tw calculation unit, 24, 41 output unit, 32 R component extraction unit, 33 G component extraction unit, 34 B component extraction unit, 35 R threshold value setting unit, 36 G threshold value setting unit, 37 B threshold value setting unit, 38 R comparison unit, 39 G comparison unit, 40 B comparison unit, 51 frame, 52 tile, 53 LED, 60 liquid crystal Panel, 61 Tuner unit, 62 Image processing unit, 63 LCD control unit, 64 I / F unit, 65 Power supply unit, 66 Fan, 6 LED drive unit.

Claims (8)

In a field sequential type liquid crystal display device comprising a liquid crystal panel and a backlight including a plurality of light emitting elements that emit light of different colors,
The plurality of light emitting elements having colors corresponding to the respective fields are turned on in a plurality of field periods of each frame period, and the light emitting elements other than the light emitting elements being turned on are included in at least one field period of the plurality of field periods. A liquid crystal display device, wherein a plurality of light-emitting elements corresponding to colors are sequentially turned on, and a subfield period is provided at least once.   The liquid crystal display device according to claim 1, wherein the subfield period is provided at least once in each field period.   The liquid crystal display device according to claim 1, wherein the length of the subfield period is changed for each frame.   4. The liquid crystal display device according to claim 3, wherein the length of the subfield period is set based on image information of one frame.   The liquid crystal display device according to claim 3, wherein the length of the subfield period is set based on image information of a plurality of frames.   The liquid crystal display device according to claim 4, wherein the image information is an average luminance of the image.   Each color component of the display image is compared with a threshold value, and when each color component other than a certain color component is equal to or less than the threshold value, the subfield period is provided in the field period in which the light emitting element emitting light with the certain color is turned on. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is not provided.   The liquid crystal display device according to claim 1, wherein the number of the light emitting elements is three, and the three light emitting elements emit light in red, green, and blue, respectively.

Images