JP2008198381A - Backlight module and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a desired NTSC ratio in a short time, with a low consumption current, and at a low cost in an FS system. <P>SOLUTION: The backlight module 10, in repetitively making a red-color LED 51, a green-color LED 52, and a blue-color LED 53 emit light in turn, makes a white-color LED 54 with a lower color purity than the red, green and blue colors emit light at a constant spectral intensity ratio. In doing so, an NTSC ratio is to be adjusted without carrying out matrix operation by making light sources of two colors of high purity and low purity in a color space emit light, without taking trouble to make light sources of three or more colors emit light. As a result, a desired NTSC ratio can be obtained in a short time, with a low consumption current, and at low cost. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a backlight module used in a field sequential type liquid crystal display device and a liquid crystal display device including the backlight module.

  Conventionally, a liquid crystal display device using a field sequential (hereinafter abbreviated as “FS”) driving method has been proposed (see, for example, Patent Document 1). The FS method is a method for obtaining a color display by displaying a red image, a green image, and a blue image in order in a short time and performing time mixing.

  In this method, red light is emitted from the backlight during a period (R field) in which an image corresponding to red is displayed on the liquid crystal display element, and an image corresponding to green is displayed on the liquid crystal display element. In the period (G field), green light is emitted from the backlight, and in the period (B field) in which an image corresponding to blue is displayed on the liquid crystal display element, blue light is emitted from the backlight. If these light irradiations are repeated within a short time, a human eye will recognize a color image obtained by combining a red image, a green image, and a blue image. Compared with a liquid crystal display device using a color filter, the FS mode liquid crystal display device has advantages such as a simplified manufacturing process and a significant increase in transmittance because it is not necessary to incorporate a color filter. Yes.

  In an FS liquid crystal display device, red, green, and blue light can be switched in a short time so that light can be emitted. As a backlight light source, a red light emitting diode (red LED), a green light emitting diode ( Green LEDs) and blue light emitting diodes (blue LEDs) are generally used. For this reason, in the FS liquid crystal display device, the ratio of the reproduction color gamut to the color system in NTSC (National Television System Committee), that is, the NTSC ratio is very high at about 110%.

  On the other hand, conventionally, there is an sRGB (standard RGB) standard as an international standard for a color space in a CRT. In the sRGB standard, the NTSC ratio is about 70%.

  Therefore, recently, even in the FS liquid crystal display device, the color purity of the display color is lowered, the NTSC ratio is set to about 70%, and the color display is performed without a sense of incongruity under the same color reproducibility as that of a cathode ray tube. There is a demand for it. In order to meet this requirement, conventionally, in the FS liquid crystal display device, the corresponding two colors of LEDs are turned on at the same time in the R field, the G field, and the B field. The ratio is reduced to about 70%.

  In each field, in order to make the NTSC ratio about 70% (that is, the NTSC ratio equivalent to the sRGB standard) in addition to the red LED, the green LED and the blue LED are simultaneously turned on. It is necessary to obtain the matrix operation by using an operation IC.

R ′ = K1 × R + K2 × G + K3 × B + K4
G ′ = K5 × R + K6 × G + K7 × B + K8
B ′ = K9 × R + K10 × G + K11 × B + K12
Here, R ′, G ′, and B ′ are total emission intensities of red, green, and blue that should be emitted from the backlight when displaying each color image, and R, G, and B are the total emission intensity. This is the light emission intensity of each color LED necessary for obtaining a typical light emission intensity. K1, K2, and K3 are the spectral intensity ratios of the red, green, and blue LEDs in the R field, and K5, K6, and K7 are the spectral intensity ratios of the red, green, and blue LEDs in the G field. Yes, K9, K10, and K11 are spectral intensity ratios of the red LED, green LED, and blue LED in the B field. K4, K8, and K12 are offsets in each field.
JP 2001-251642 A

  As described above, in the FS liquid crystal display device, in order to realize accurate color reproduction under a desired NTSC ratio, the emission intensity of the red LED, the green LED, and the blue LED is set using an arithmetic IC. It is necessary to obtain by matrix calculation. However, when an arithmetic IC is used, the calculation time is required, current consumption in the apparatus increases, and the apparatus cost increases.

  The present invention has been made in order to solve the above problems, and a backlight module used in an FS mode liquid crystal display device capable of obtaining a desired NTSC ratio in a short time, with low current consumption and at low cost, and An object of the present invention is to provide a liquid crystal display device including the backlight module.

In the present invention, in order to solve the above problems, the following measures are taken.
(1) A first light source that emits red light, a second light source that emits green light, a third light source that emits blue light, and a fourth light that emits a fourth color having a lower color purity than red, green, and blue. A backlight module, wherein the first light source, the fourth light source, the second light source, the fourth light source, the third light source, and the fourth light source are made to repeatedly emit light in order. did.

(2) The fourth color is either white or yellow.

(3) Each of the light sources is a light emitting diode.

(4) A liquid crystal display device including the above backlight module was obtained.

  According to the backlight module and the liquid crystal display device, when the red light source, the green light source, and the blue light source are repeatedly emitted in order, the light sources are made to emit light, and at the same time, more colors than red, green, and blue. A light source that emits low purity light is emitted. In this way, the same spectrum is always obtained without performing matrix calculation by simultaneously emitting light sources of two colors of high and low purity in the color space without emitting light sources of three or more colors. With the intensity ratio, the NTSC ratio can be adjusted. Therefore, a desired NTSC ratio can be obtained in a short time, with low current consumption and low cost.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  The liquid crystal display device according to this embodiment is an FS liquid crystal display device. FIG. 1 shows a schematic configuration of a liquid crystal display device 1 including a backlight module according to the present embodiment. As shown in FIG. 1, the liquid crystal display device 1 according to this embodiment includes a liquid crystal controller 20, a liquid crystal panel LCD, a gate driver GD, a source driver SD, a backlight BL, a backlight driving unit 12, and the like. It has. The backlight module 10 is composed of the backlight BL and the backlight driving unit 12.

  The liquid crystal controller 20 performs overall control of the entire liquid crystal display device 1. The liquid crystal controller 20 drives the backlight BL via the backlight drive unit 12 and simultaneously drives the liquid crystal panel LCD via the gate driver GD and the source driver SD, so that the person viewing the liquid crystal panel LCD from the + Z side can be viewed. Recognize color images.

  The liquid crystal panel LCD is a so-called TFT active matrix driving type liquid crystal panel in which a thin film transistor (not shown) is formed for each pixel. The gate of the transistor corresponding to each pixel is connected to the gate driver GD, the source is connected to the source driver SD, and the drain is connected to the pixel electrode of the liquid crystal panel LCD. Further, the image electrode and the common electrode are disposed so as to sandwich the liquid crystal layer of the liquid crystal panel LCD. For this reason, if the thin film transistor is driven to control the voltage applied between the pixel electrode and the common electrode, the alignment state of the liquid crystal material of the liquid crystal layer changes, and the transmittance of light emitted from the backlight BL is changed. Can be changed for each pixel.

  Under the instruction of the liquid crystal controller 20, the gate driver GD applies a gate voltage to the transistors corresponding to the respective pixels of the liquid crystal panel LCD, and turns on those transistors. The source driver SD applies a source voltage to the transistor corresponding to each pixel under the instruction of the liquid crystal controller 20.

  The backlight BL is disposed on the back surface (−Z side) of the liquid crystal panel LCD. In FIG. 1, the backlight BL and the liquid crystal panel LCD are shown apart from each other in order to avoid complication of the drawing, but actually, the backlight BL is provided close to the liquid crystal panel LCD.

  The backlight BL includes a light emission source 50 and a light guide plate 60. The light emitting source 50 includes a red light emitting diode (hereinafter abbreviated as “red LED”) 51, a green light emitting diode (hereinafter abbreviated as “green LED”) 52, and a blue light emitting diode (hereinafter “blue LED”). ”53 and a white light emitting diode (hereinafter abbreviated as“ white LED ”) 54. The light of each color emitted from the light emitting source 50 is introduced into the light guide plate 60. The light guide plate 60 diffuses light of each color to illuminate substantially the entire back surface of the liquid crystal panel LCD.

  The backlight drive unit 12 drives the red LED 51, the green LED 52, the blue LED 53, and the white LED 54 to emit light in a predetermined sequence under the control of the liquid crystal controller 20. FIG. 2 shows a light emission sequence of each color LED. As shown in FIG. 2, the backlight drive unit 12 causes the red LED 51, the green LED 52, and the blue LED 53 to repeatedly emit light in this order at equal intervals (for example, 1/180 seconds). Thereby, the color of the light emitted from the light emission source 50 is switched in the order of red → green → blue → red → green → blue →..., And the light guide plate 60 is liquid crystal panel LCD in this order. Illuminate.

  Here, the red light emission period is called the R field, the green light emission period is called the G field, and the blue light emission period is called the B field. The liquid crystal controller 20 divides an original image signal input from a host device (not shown) into an image corresponding to red, an image corresponding to green, and an image corresponding to blue. Then, the liquid crystal controller 20 drives the liquid crystal panel LCD so that an image corresponding to red is displayed in the R field via the gate driver GD and the source driver SD, and an image corresponding to green in the G field. The liquid crystal panel LCD is driven so that is displayed, and in the B field, the liquid crystal panel LCD is driven so that an image corresponding to green is displayed. As a result, the human eye recognizes a color image obtained by combining the red image, the green image, and the blue image.

  As shown in FIG. 2, the backlight drive unit 12 causes the red LED 51, the green LED 52, and the blue LED 53 to emit light, and at the same time, causes the white LED 54 to emit light. As will be described later, the emission intensity of the white LED 54 in each field is determined for each color that emits light together (for each field).

  FIG. 3 shows the emission spectrum of the white LED 54. In FIG. 3, the horizontal axis indicates the wavelength of light (unit: nm), and the vertical axis indicates the emission intensity at that wavelength (unit: au). As shown in FIG. 3, the emission spectrum of the white LED 54 has two peaks, but has a very wide band as a whole.

  Further, FIG. 4 shows an emission spectrum when the red LED 51, the green LED 52, and the blue LED 53 emit light alone. In FIG. 4, the horizontal axis indicates the wavelength of light (unit: nm), and the vertical axis indicates the emission intensity at that wavelength (unit: au). As shown in FIG. 4, the emission spectrum of the red LED 51 has a peak wavelength of about 650 nm, the peak wavelength of the emission spectrum of the green LED 52 is about 535 nm, and the peak of the emission spectrum of the blue LED 52. The wavelength is about 430 nm. The width of the emission spectrum of each color is very narrow.

  In the backlight module 10 according to the present embodiment, the white LED 54 emits light simultaneously with the red LED 51, the green LED 52, and the blue LED 53. In this way, the red, green, and blue emission spectra of the backlight BL have a wider frequency band than the emission spectra of the individual color LEDs shown in FIG. It begins to decline.

  FIG. 5 shows a CIE (Commission International del Eclairage) chromaticity diagram showing a color reproduction region in the liquid crystal display device 1. In FIG. 5, the color reproduction region when the red LED 51, the green LED 52, and the blue LED 53 are emitted alone without causing the white LED 54 to emit light is indicated by a dotted triangle, and together with the white LED 54, the red LED 51 and green The color reproduction region when the white LED 54 is caused to emit light simultaneously with the LED 52 and the blue LED 53 is indicated by a solid triangle. As can be easily seen from FIG. 5, when the white LED 54 is caused to emit light simultaneously with the red, green, and blue LEDs 51, 52, and 53, the color reproduction region on the CIE chromaticity diagram is small.

  Here, the NTSC ratio of the color reproduction region indicated by the dotted line is 115%. In the color reproduction region surrounded by the solid line, the spectral intensity ratio between the red LED 51 and the white LED 54 is 1.085: 0.028, and the spectral intensity ratio between the green LED and the white LED in the G field is 1.031: 0.033, and the spectral intensity ratio between the blue LED and the white LED in the B field is 1.000: 0.023. In this case, the NTSC ratio is 70%. In the liquid crystal display device 1 according to the present embodiment, if the spectral intensity ratio of each of the color LEDs 51, 52, 53 and the white LED 54 is set to the above numerical value, the NTSC ratio is 70% without breaking the white balance. It can be.

  Spectral intensity ratio of R field red LED and white LED to make NTSC ratio 70%, G field green LED and white LED spectral intensity ratio, B field blue LED and white LED spectral intensity ratio The ratio can be obtained in advance by a simulation calculation using a computer. These spectral intensity ratios are stored in the memory of the backlight driving unit 12, and the backlight driving unit 12 causes the red LED 51 and the white LED 54 to emit light in the R field according to the spectral intensity ratio stored in the memory. In the G field, the green LED 52 and the white LED 54 are caused to emit light, and in the B field, the blue LED 52 and the white LED 54 are caused to emit light.

  In other words, the backlight drive unit 12 emits the LEDs of each color according to a predetermined spectral intensity ratio (without changing the driving conditions of the conventional liquid crystal), and performs the NTSC ratio without performing a special matrix calculation. Can be made 70%.

  As described above in detail, according to the backlight module 10 and the liquid crystal display device 1 according to the present embodiment, when the red LED 51, the green LED 52, and the blue LED 53 are repeatedly emitted in order, simultaneously with the light emission of those LEDs. The white LED 54 having a lower color purity than red, green, and blue is caused to emit light. In this way, two or more light sources of high purity (red, green, blue) and low purity (white) in the color space are emitted without simultaneously emitting LEDs of three or more colors. By doing so, the NTSC ratio can be adjusted in accordance with the spectral intensity ratio of the two colors of light. As a result, NTSC ratio of 70% can be realized in a short time, with low current consumption and low cost.

  That is, in the present embodiment, it is not necessary to perform matrix calculation for calculating the light emission intensities of the three color light sources, and it is not necessary to provide a calculation IC for that purpose. Reduction of time, current consumption, and cost can be realized.

  Note that the white LED 54 has better light emission efficiency than the red LED 51, the green LED 52, and the blue LED 53. Therefore, when the white LED 54 emits light simultaneously with each color LED, the red LED 51 and the green LED 52 are subjected to the same current consumption. The brightness of the backlight BL is improved as compared with the case where the blue LED 53 is caused to emit light alone. Conversely, when the backlight BL only needs to emit light with the same luminance, the red LED and white LED, the green LED and white LED, and the blue LED are emitted rather than the red LED 51, green LED 52, and blue LED 53 emitting alone. The total current consumption can be reduced by causing the LED and the white LED to emit light simultaneously.

  In the present embodiment, the white LED 54 is used as the fourth light source in the light source of the backlight module 10, but the white LED may be a blue light emitting diode coated with a yellow phosphor. Absent. Even in this case, when the emission spectrum is equivalent to that shown in FIG. 3, the spectral intensity ratio between the red LED 51 and the white LED 54 is set to 1.085: 0.028. If the spectral intensity ratio between the green and white LEDs in the field is 1.031: 0.033 and the spectral intensity ratio between the blue and white LEDs in the B field is 1.000: 0.023, the NTSC ratio Is 70% as in the present embodiment.

  Further, a yellow light emitting diode may be used instead of the white LED 54. In addition, even for light emitting diodes having a color purity lower than that of red, green, blue, etc., if the NTSC ratio can be lowered with the white balance adjusted, light emitting diodes of other colors should be applied. Also good.

  Further, the adjusted NTSC ratio is not limited to 70%. If the NTSC ratio of the red, green, and blue LEDs alone is 115% or less, a desired NTSC ratio can be realized by changing the spectral intensity ratio of each color LED and white LED.

  In addition, a light source other than a light emitting diode may be used as long as the light source has a response high enough to be used as the backlight BL of the FS liquid crystal display device 1.

  Further, the liquid crystal display device according to the above embodiment is a TFT active matrix drive type liquid crystal display device, but other drive methods (for example, simple matrix method) may be FS type liquid crystal display devices. The present invention can be applied.

1 is a schematic configuration diagram of a liquid crystal display device according to an embodiment of the present invention. It is a timing chart which shows the light emission sequence of each color. It is a figure which shows the emission spectrum of white LED. It is a figure which shows the emission spectrum of red LED, green LED, and blue LED. It is a figure which shows NTSC ratio in the CIE chromaticity diagram of the color system of the liquid crystal display device of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 10 Backlight module 12 Backlight drive part 20 Liquid crystal controller 50 Light emission source 51 Red LED
52 Green LED
53 Blue LED
54 White LED
60 Light guide plate BL Backlight GD Gate driver LCD Liquid crystal panel SD Source driver

Claims (4)

A first light source that emits red, a second light source that emits green, a third light source that emits blue, a fourth light source that emits a fourth color having a color purity lower than red, green, and blue, With
The backlight module, wherein the first light source, the fourth light source, the second light source, the fourth light source, the third light source, and the fourth light source emit light repeatedly in order.   The backlight module according to claim 1, wherein the fourth color is one of white and yellow.   The backlight module according to claim 1, wherein each of the light sources is a light emitting diode.   A liquid crystal display device provided with the backlight module as described in any one of Claims 1-3.

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