WO2002099781A1

WO2002099781A1 - Liquid crystal display unit

Info

Publication number: WO2002099781A1
Application number: PCT/JP2002/005492
Authority: WO
Inventors: Kenji Nakao; Yoshinori Tanaka
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2001-06-04
Filing date: 2002-06-04
Publication date: 2002-12-12
Also published as: JP2005049362A

Abstract

A liquid crystal display unit (1) detects the color intensities of red, green and blue in each pixel on a liquid crystal display panel (10) based on one frame of pixel signal, and a maximum color intensity value for each color is detected based on the detected results. The liquid crystal display unit (1) displays the light emission intensities of light emitting diodes (23R, 23G, 23B) in images using a field sequential color system according to the maximum color intensity value of each color, with a light transmittance at each pixel on the panel (10) specified in response to the light emission intensities and an image signal.

Description

Detail

Liquid crystal display

〔Technical field〕

The present invention relates to a liquid crystal display device for displaying an image, and more particularly to a liquid crystal display device capable of realizing power saving.

[Technical background]

As a method for realizing a color display by a liquid crystal display device, color light of three primary colors (red, green, and blue) provided in each pixel is passed through white light emitted from a light source. The color filter system that performs one display is the most widespread. In such a color filter system, when light emitted from a light source passes through a color filter, only light of a specific wavelength is selectively transmitted, and light of other wavelengths is absorbed. Therefore, there was a problem that the light use efficiency was low and the power loss was large.

For this reason, a field-sequential color method has been proposed in which a plurality of light sources each emitting different color light are turned on in a time-division manner to perform color display. In the case of such a field sequential power system, light emitted from each color light source is used for image display without passing through a color filter. Therefore, high light use efficiency can be obtained, and power saving can be achieved.

FIG. 1 is a timing chart showing the operation of a conventional field-sequential color liquid crystal display device, in which (a) shows the light emission intensity and light emission time of the light source, and (b) shows the liquid crystal display panel. FIG. 6 is a diagram showing a change in light transmittance. As shown in Fig. 1 (a), one frame period of an image signal is composed of three sub-frame periods, and the green, blue, and red light sources emit light sequentially at a predetermined emission intensity for each sub-frame period. Emits light of each color. Here, the luminous intensity of the light source is not an instantaneous luminous intensity at a certain point in time, but an integrated value of the luminous intensity from the start to the end of light emission of the light source. It should be noted that the predetermined light emission intensity is usually set to the maximum light emission intensity of the light source. Therefore, FIG. 1 (a) shows an example in which light is emitted at the maximum emission intensity.

Also, as shown in FIG. 1 (b), the light transmittance of the liquid crystal display panel is changed according to the image signal. Here, reference numerals 1A and IB indicate transitions of the maximum value and the minimum value of the light transmittance of each pixel included in the liquid crystal display panel, respectively. Since the light transmittance of the liquid crystal display panel changes as described above, the color intensity of each color in the liquid crystal display panel is adjusted, and an image corresponding to the image signal is displayed.

[Disclosure of the Invention]

By the way, depending on an image to be displayed, there is a case where it is not necessary to emit light of a specific color with the above-mentioned emission intensity. For example, when displaying an image with a high yellow color intensity, the blue color intensity is low. In extreme cases, the blue color intensity may be zero.

However, as shown in FIG. 1 (a), in the case of the conventional field-sequential color liquid crystal display device as described above, each light source emits light of a predetermined luminous intensity no matter what image is displayed. Therefore, there is a problem that power required for light emission of the light source may be wasted.

In recent years, a liquid crystal display device is often used as a display device of a small electronic device such as a mobile phone. In such small electronic devices, much of the power consumption is consumed by liquid crystal display devices. That's why I mentioned earlier There is a strong demand to minimize wasteful power consumption and save power.

Generally, color display in a display device is realized by combining three colors of a color triangle on a chromaticity coordinate as shown in FIG. Therefore, an arbitrary color can be displayed by changing the color intensities of the three colors.

In the case of a liquid crystal display device, the following two methods can be considered for changing the color intensity of the liquid crystal display panel. That is, a means for changing the illumination intensity of an illumination device such as a backlight, and a means for changing the light transmittance of the liquid crystal display panel. From the standpoint of realizing power saving, the present inventors set the illumination intensity of the illumination device as low as possible, and optimized the light transmittance of the liquid crystal display panel correspondingly. I learned what I wanted.

The present invention has been made based on such knowledge, and an object of the present invention is to provide a liquid crystal display device capable of realizing power saving.

In order to achieve this object, a liquid crystal display device according to the present invention includes a first substrate, a second substrate, and a liquid crystal sandwiched between the first substrate and the second substrate. A liquid crystal layer comprising: a plurality of pixel electrodes arranged in a matrix on the first substrate so as to correspond to each of the pixels, and the first substrate or the second A liquid crystal display panel having a counter electrode provided on one of the substrates, a light source having a light source for emitting light of a plurality of colors, and illuminating the liquid crystal display panel with the light of the plurality of colors; A driving unit that adjusts, for each pixel, transmittance of light emitted from the lighting device in the liquid crystal layer by generating a potential difference between each pixel electrode and the counter electrode; Lighting that adjusts the light intensity for each color A degree adjusting means, one image signal corresponding to an image to be displayed in a frame period is input, the input image signal Contact Detecting means for detecting, for each color, the maximum color intensity from among the color intensities of the respective pixels, and controlling the lighting device so as to sequentially emit light of each color in the one frame period; and Controlling the illumination intensity adjusting means to adjust the intensity of light emitted from the illumination device for each color in the frame period, and controlling the driving means to emit light from the illumination device. Control means for adjusting the transmittance of light in the liquid crystal layer for each pixel.

Further, in the liquid crystal display device according to the present invention, the one frame period includes a plurality of sub-frame periods, and in the sub-frame period, one of the light sources emitting the plurality of colors emits light. It is preferred that

In the liquid crystal display device according to the present invention, it is preferable that the light sources emit red, green, and blue light, respectively.

Further, in the liquid crystal display device according to the present invention, it is preferable that the light sources emit red, green, blue, and white light, respectively.

Further, in the liquid crystal display device according to the present invention, it is preferable that the liquid crystal is a 〇CB mode liquid crystal.

Further, in the liquid crystal display device according to the present invention, it is preferable that the light source is a light emitting diode.

Further, a liquid crystal display device according to the present invention includes a first substrate, a second substrate, and a liquid crystal layer including a liquid crystal sandwiched between the first substrate and the second substrate. A plurality of pixel electrodes arranged in a matrix on the first substrate so as to correspond to each pixel, respectively, and a counter electrode is provided on either the first substrate or the second substrate. A liquid crystal display panel, a light source that emits light of a plurality of colors, respectively, and an illumination device that irradiates the light of the plurality of colors toward the liquid crystal display panel; and Irradiation from the lighting device by generating a potential difference between Driving means for adjusting the transmittance of the emitted light in the liquid crystal layer for each pixel; illumination intensity adjusting means for adjusting the emission time of the light emitted from the illumination device for each color; and displaying during one frame period. An image signal corresponding to an image to be input is input; a detection unit for detecting a maximum color intensity for each color from among the color intensities of the pixels in the input image signal; and a light source for each color sequentially in the one frame period The illumination device is controlled so as to emit light, and the illumination intensity adjusting means is controlled based on the maximum color intensity, and the emission time of light emitted from the illumination device in the frame period is set for each color. And control means for controlling the driving means to adjust the transmittance of light emitted from the lighting device in the liquid crystal layer for each pixel. .

In the liquid crystal display device according to the invention, it is preferable that the light source emits red, green, blue, and white light, respectively.

In the liquid crystal display device according to the present invention, it is preferable that the liquid crystal is an OCB (Optically self-Compensated Birefringence) mode liquid crystal.

The above objects, other objects, features, and advantages of the present invention will be apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings.

[Brief description of drawings] FIG. 1 is a timing chart showing the operation of a conventional field-sequential color liquid crystal display device, in which (a) shows the emission intensity and emission time of each color of red, blue, and green; () Is a diagram showing the transition of the light transmittance of the liquid crystal display panel.

FIG. 2 is a diagram illustrating a color triangle on chromaticity coordinates.

FIG. 3 is a perspective view showing a configuration of the liquid crystal display device of the present invention according to Embodiment 1.

FIG. 4 is a cross-sectional view schematically showing the alignment state of the liquid crystal.

FIG. 5 is a block diagram showing a configuration of the liquid crystal display device of the present invention according to Embodiment 1.

FIG. 6 is a conceptual diagram showing a case where an image of an apple is displayed on a liquid crystal display panel.

FIG. 7 is an evening timing chart showing the operation of the liquid crystal display device of the present invention according to Embodiment 1, wherein (a) shows the light emission intensity and light emission time of the red, blue and green light emitting diodes. (B) is a diagram showing a change in light transmittance of the liquid crystal display panel.

FIG. 8 is a diagram showing the correspondence between the light emission intensity of the light source, the light transmittance of a certain pixel, and the color intensity of a certain color in the pixel. FIG. 7 is a diagram showing the correspondence in the case of the liquid crystal display device of the invention, and FIG. 7 (b) is a diagram showing the correspondence in the case of the conventional liquid crystal display device.

FIG. 9 is a perspective view showing a configuration of a liquid crystal display device of the present invention according to Embodiment 2.

FIG. 10 is a diagram illustrating a color triangle on chromaticity coordinates.

FIG. 11 is a timing chart showing the operation of the liquid crystal display device according to the second embodiment of the present invention, wherein (a) shows the light emission intensity and light emission of red, green, blue and white light emitting diodes. Figure showing time, (b) is the LCD panel It is a figure showing transition of light transmittance.

FIG. 12 is a timing chart showing the operation of the liquid crystal display device according to the third embodiment of the present invention, wherein (a) shows the emission intensity and emission time of the red, green and blue light emitting diodes. And (b) is a diagram showing the transition of the light transmittance of the liquid crystal display panel.

[Best mode for carrying out the invention]

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

(Embodiment 1)

FIG. 3 is a perspective view showing a configuration of the liquid crystal display device of the present invention according to Embodiment 1. As shown in FIG. 3, the liquid crystal display device 1 includes a liquid crystal display panel 10. As shown in FIG. 4, the liquid crystal display panel 10 includes two substrates, that is, an upper substrate 11 and a lower substrate 12. The upper substrate 11 and the lower substrate 12 are opposed to each other via a spacer (not shown). The liquid crystal layer 13 is formed by injecting the liquid crystal 14 into a gap formed between the upper substrate 11 and the lower substrate 12.

The upper substrate 11 is formed by laminating a counter electrode 6 and an alignment film 4 on the lower surface of a glass substrate 2 and a phase difference compensator 7 and a polarizing plate 8 on the upper surface. Further, the lower substrate 12 is configured such that a pixel electrode 40 and an alignment film 5 described later are laminated on the upper surface of the glass substrate 3 and a polarizing plate 9 is laminated on the lower surface similarly.

Needless to say, if necessary, the lower substrate 12 may be provided with a phase difference compensator. Further, as described above, the counter electrode 6 may not be formed on the upper substrate 11 side, but may be formed on the lower substrate 12 side. Therefore, for example, even if the configuration is the same as that of the liquid crystal display device in the IPS (I-P lane-Switch) mode, Good.

The liquid crystal display panel 10 configured as described above is configured such that a predetermined voltage is applied between the counter electrode 6 provided on the upper substrate 11 and the pixel electrode 40 provided on the lower substrate 12, and the liquid crystal 14 is provided. Is changed from the splay alignment (FIG. 4 (a)) to the bend alignment (FIG. 4 (b)), and an image is displayed according to the bend alignment state. That is, the liquid crystal display panel 10 is a liquid crystal display panel provided with a so-called CB mode liquid crystal. In the case of the field sequential color system, one frame period of an image signal is composed of a plurality of subframe periods, and it is necessary for the liquid crystal to complete a response in each of the subframe periods. Therefore, if the response of the liquid crystal is slow, good image display cannot be realized. Therefore, it is desirable that the liquid crystal display panel included in the liquid crystal display device of the present invention be a liquid crystal display panel including a 0 CB mode liquid crystal capable of high-speed response of the liquid crystal. A backlight 20 as an illumination device is arranged below the liquid crystal display panel 10 described above. The backlight 20 includes a light guide plate 21 made of a transparent rectangular synthetic resin plate, and a light source 23 (a light source plate 23) disposed near the one end surface 22 of the light guide plate 21 and facing the end surface 22. 23 R, 23 G, and 23 B). The light sources 23 R, 23 G, and 23 B are light emitting diodes (LEDs) that emit red, green, and blue light, respectively. Light emitting diodes are characterized by excellent responsiveness (rapid rise and fall of light emission) and little afterglow. Therefore, it is a light source suitable for field sequential driving as described later. However, the light source included in the liquid crystal display device of the present embodiment is not limited to the light emitting diode, and may be, for example, a cold cathode tube. Further, in the present embodiment, an explanation has been given by taking an example of an edge-light type backlight in which the light source is arranged near one end face 22 of the light guide plate 21. The backlight may be a direct-type backlight in which are arranged and configured. In the backlight 20 configured as described above, the light emitted from the light emitting diodes 23 R, 23 G, and 23 B of the respective colors enters the light guide plate 21 from the end face 22. The incident light is scattered inside the light guide plate 21 and emitted from the front surface of the upper surface. As a result, the entire liquid crystal display panel 10 is irradiated with red, green, or blue light.

Note that, in the present embodiment, as described above, one set of light sources provided with one red, green, and blue light emitting diode is provided, but a plurality of light emitting diodes of each color are provided. A plurality of sets of light sources may be provided. When a plurality of light sources are provided, light-emitting diodes of the same color may emit light at the same time. Further, for example, the screen may be divided into three regions, and one set of light sources may be arranged in each region. In this case, for example, the first light source emits a red light emitting diode, the second light source emits a green light emitting diode, and the third light source emits a blue light emitting diode for a predetermined time. After that, the first set of light sources emits a blue light emitting diode, the second set of light sources emits a red light emitting diode, and the third set of light sources emits a green light emitting diode for a predetermined time. The second light source emits a blue light emitting diode, the third light source emits a red light emitting diode for a predetermined time, and thereafter, this operation may be repeated. .

FIG. 5 is a block diagram showing a configuration of the liquid crystal display device 1 according to the first embodiment of the present invention. Referring also to FIGS. 3 and 4, the liquid crystal display panel 10 is a well-known TFT (Thin Film Transistor) type liquid crystal display element, and a counter electrode 6 is formed on the inner surface. The upper substrate (opposite substrate) 11 and the lower substrate (array substrate) 12 on which the pixel electrode 40, the gate line 31, the source line 32 and the switching element 33 are formed on the inner surface are liquid crystal. They are arranged so as to face each other with the layer 13 interposed therebetween. Further, in the array substrate 12, the gate lines 31 and the source lines 32 are alternately crossed. The pixel electrode 40 and the switching element 33 are formed so as to correspond to the pixel partitioned by the gate line 31 and the source line 32 <the gate line 31 and the source line 32 Are driven by a gate driver 34 and a source driver 35, respectively.

The operation of the backlight 20 is controlled by the illumination intensity adjusting means 37. As a result, the illumination intensity of the backlight 20 is adjusted as described later.

Further, the liquid crystal display device 1 includes a storage unit 39 for storing an image signal input from an external device, and a detection unit for executing a detection process described later based on the image signal stored in the storage unit 39. Means 3 8. Here, this image signal is a signal relating to a color image.

In the liquid crystal display device 1 configured as described above, the control means 36 controls the light emission intensity of the light emitting diodes 23 R, 23 G, and 23 B of each color based on the result of the detection processing by the detection means 25. Is calculated.

Further, the control means 36 outputs a control signal to the illumination intensity adjusting means 37 in order to cause the light emitting diodes 23 R, 23 G, and 23 B to emit light sequentially in each subframe period. The control signal includes information indicating the calculated light emission intensity. Therefore, the illumination intensity adjusting means 37 causes the light emitting diodes 23 R, 23 G, and 23 B to sequentially emit light at the calculated emission intensity for each subframe period.

Further, the control means 36 outputs an image signal to the source driver 35 in order to display an image related to each color in synchronization with the light emission of the light emitting diodes 23 R, 23 G, and 23 B. At the same time, a control signal is output to the gate driver 34 and the source driver 35. As a result, the gate driver 34 outputs a scanning signal corresponding to a voltage for turning on the switching element 33 to the gate line 31 so that the switching element 33 of each pixel is sequentially turned on. On the other hand, the source driver 35 The image signal is sequentially written to the pixel electrode 44 of each pixel through the source line 32. More specifically, the gate driver 34 outputs the above-described scanning signal to the gate line 31 of the first row, so that the switching element 33 connected to the gate line 31 of the first row is output. Turn on. Then, when the switching element 33 is turned on, the image signal output from the source driver 35 to each source line 32 is written to the pixel electrode 4 of the pixel in the first row.

Next, the gate driver 34 outputs a signal corresponding to the voltage for turning off the switching element 33 to the gate line 31 of the first row, and connects the gate driver 31 to the gate line 31 of the first row. At the same time, the switching element 33 is turned off, and the gate driver 34 outputs the scanning signal to the gate line 31 of the second row at the same time. Turn on the switching element 33 connected to 1. Then, similarly to the case of the first row, the image signal output from the source driver 35 to each source line 32 is written to the pixel electrode 40 of the pixel of the second row.

By performing the same operation thereafter, the image signal is sequentially written to the pixel electrodes 40 of the pixels in each row. As a result, a potential difference is generated between the counter electrode and the pixel electrode 40 to drive the liquid crystal 14, and the transmittance of light emitted from the backlight 20 in the liquid crystal display panel 10 changes. As a result, an image corresponding to the image signal appears in the eyes of the observer.

Next, the details of the adjustment of the illumination intensity of the backlight 20 and the light transmittance of the liquid crystal display panel will be specifically described using an image of a red apple with green leaves shown in FIG. Note that, for ease of explanation, the liquid crystal display panel 10 has 64 × 480 pixels (= 3702 pixels), and has a resolution of VGA standard (640 pixels). It is assumed that an image corresponding to X480) can be displayed. It is also assumed that the color intensities of red, green, and blue are each divided into 16 levels. In this case, the LCD panel 10 16 ³ colors = 4 0 9 6 colors can be displayed.

The detection means 38 reads out the image signal for one frame from the storage means 39 at a predetermined timing, and from the read out image signal, the color of each of red, green and blue in each of the three hundred seventy-nine pixels. The intensity is detected individually. Next, the detecting means 38 detects the maximum value of the color intensity of each color in the image represented by the image signal. Then, the detection means 38 outputs a signal indicating the maximum value of the detected color intensity of each color to the control means 36.

The control means 36, based on the maximum value of the color intensity of each color indicated in the signal output from the detection means 38, performs light emitting diode 23R, 23G, 23B as follows. Are respectively calculated.

For example, it is assumed that the red color intensity at pixel 50 in FIG. 6 is 14 out of 16 levels, and is larger than the red color intensity at any other pixel. In this case, the light emission intensity of the red light emitting diode 23 R during the red subframe period is 0.875 times (= 14/16 times) the maximum light emission intensity of the light emitting diode 23 R. I do.

It is also assumed that the green color intensity at pixel 51 in FIG. 6 is 13 out of 16 levels, which is larger than the green color intensity at any other pixel. In this case, the light emission intensity of the green light-emitting diode 23 G during the green subframe period is 0.8 1 25 times (= 13 16 times) the maximum light emission intensity of the light-emitting diode 23 G. I do.

Further, it is assumed that the blue color intensity at pixel 52 in FIG. 6 is 5 out of 16 levels, and is a value larger than the blue color intensity at any other pixel. In this case, the light emission intensity of the blue light emitting diode 23 B during the blue subframe period is set to 0.31 25 times (= 5 16 times) the maximum light emission intensity of the light emitting diode 23 B. .

The control means 36 generates a signal indicating the light emission intensity of each of the light emitting diodes 23 R, 23 G, and 23 B determined in this manner, and generates the signal. Output to the illumination intensity adjusting means 37.

On the other hand, the control means 36 calculates the light transmittance of each pixel of the liquid crystal display panel 10 in each subframe period as follows.

First, in the red sub-frame period, the transmittance of the pixel 50 having the maximum red color intensity is maximized. For the pixels other than the pixel 50, the transmittance is determined according to a value obtained by dividing the color intensity of the pixel by the color intensity of the pixel 50. Specifically, for example, when the red color intensity of the pixel 53 is 13 out of 16 levels, the transmittance of the pixel 53 is set to 13/14 times the maximum transmittance. By calculating the transmittance for the other pixels in the same manner, the transmittance of all the pixels of the liquid crystal display panel 10 is calculated.

The control means 36 executes the same processing also in the sub-frame period for displaying the blue and green images, thereby reducing the light transmittance of each pixel of the liquid crystal display panel 10 in each sub-frame period. calculate. Then, the control means 36 generates an image signal to be written to each pixel in order to realize the transmittance calculated as described above, and outputs the image signal to the source driver 35.

As a result of the above processing, the gate dryno '34, the source driver 35, and the illumination intensity adjusting means 37 operate synchronously as described above, so that one frame of image is displayed on the liquid crystal display panel 10. Will be displayed.

FIG. 7 is a timing chart showing the operation of the liquid crystal display device 1 according to the first embodiment of the present invention, wherein (a) shows the light emission intensity and light emission of the light emitting diodes 23 R, 23 G, and 23 B. FIG. 6B is a diagram showing time, and FIG. 7B is a diagram showing transition of light transmittance of the liquid crystal display panel 10. In FIG. 7 (b), reference numerals 2A and 2B indicate transitions of the maximum value and the minimum value of the light transmittance of each pixel of the liquid crystal display panel 10, respectively.

As shown in Fig. 7 (a), the light emitting diode The modes 23R, 23G, and 23B emit light sequentially at the emission intensity calculated as described above. Therefore, unlike the conventional case, the light emitting diodes 23 R, 23 G, and 23 B do not always emit light with the maximum light emission intensity.

When the light transmittance of the liquid crystal display panel 10 changes in accordance with the image signal generated as described above, the transmittance of at least one of the pixels of the liquid crystal display panel 10 is changed. Will be the largest. Therefore, as shown in Fig. 7 (b), the maximum value of the light transmittance of the liquid crystal display panel 10 in the screen always changes at the same value as the maximum transmittance of the liquid crystal display panel 10 .

FIG. 8 is a diagram showing the correspondence between the light emission intensity of the light source, the light transmittance of a certain pixel, and the color intensity of a certain color in the pixel. FIG. 7 is a diagram showing the above-mentioned correspondence in the case of the liquid crystal display device 1 of the invention, and FIG. 7 (b) is a diagram showing the above-mentioned correspondence in the case of a conventional liquid crystal display device. FIG. 8 (a) shows the above-described correspondence when the maximum value of the color intensity is 14 out of 16 levels, such as the red color intensity in the above-described example. The values shown in Fig. 8 (a) and (b) are standardized so that the maximum value is 1. Therefore, for example, when the light emission intensity of the light source is 14 16, the value indicates that the value is 14 16 which is the maximum value of the light emission intensity of the light source.

As shown in FIG. 8 (b), in the case of the conventional liquid crystal display device, the light emission intensity of the light source is 1 regardless of the color intensity. This is because, as described above, in the conventional liquid crystal display device, while the light source always emits light with the maximum light emission intensity, the color intensity is changed by adjusting the light transmittance of the liquid crystal display panel. . Therefore, even when the color intensity is set to 14 Z 16, the light emission intensity of the light source is 1.

On the other hand, in the case of the liquid crystal display device 1 of the present embodiment, as shown in FIG. 4 Z 16 and the transmittance is 1. As described above, in the liquid crystal display device of the present embodiment, the light emission intensity of the light source may be smaller than in the conventional case. Therefore, the power required for light emission of the light source can be reduced, and accordingly, power saving can be achieved.

In the case of the liquid crystal display device of the present embodiment, when a white pixel is present in the screen, each color must be displayed with the maximum color intensity. I can't do it. However, since images generally tend to be biased toward one of the colors, sufficient power savings can be expected. In particular, since the tendency is remarkable in the case of a natural image, the liquid crystal display device of the present embodiment is considered to be suitable for a television receiver or the like that often displays a natural image.

(Embodiment 2)

The liquid crystal display device of the first embodiment has three light emitting diodes of red, green, and blue as light sources. In this case, as described above, when there are many white displays, power saving cannot be expected so much. Therefore, the liquid crystal display device according to the second embodiment includes a white light emitting diode in addition to the three color light emitting diodes as described later.

Normally, information indicating a color image is represented by information on three colors, red, green, and blue. This is because a point on chromaticity coordinates can be represented by a combination of at least three colors. In order to extend the range that can be represented by combining the three colors, it is desirable to use colors that are far apart on the chromaticity coordinates, such as red, green, and blue.

However, the use of a point on a chromaticity coordinate to represent a point is not limited to the above three colors. Three colors different from the three colors may be used, or four or more colors may be used.

Therefore, the liquid crystal display device of the present embodiment emits white light in order to save power in electronic devices in which white display is frequently performed, such as a mobile phone. Light emitting diode.

FIG. 9 is a perspective view showing a configuration of a liquid crystal display device of the present invention according to Embodiment 2. As shown in FIG. 9, in the vicinity of one end face 22 of the light guide plate 21 provided in the knock light 20, a light source 23 (23R, 23G, 23) facing the end face 22 is provided. B, 23 W). The light sources 23 R, 23 G, 23 B, and 23 W are light-emitting diodes that emit red, green, blue, and white light, respectively. The other configuration of the liquid crystal display device according to the second embodiment is the same as that of the first embodiment, and a description thereof will not be repeated.

In the case of the liquid crystal display device 1 according to the second embodiment configured as described above, one frame period of an image signal is divided into four sub-frame periods for displaying images of red, green, blue, and white, respectively. Constitute.

In the case of the liquid crystal display device of the present embodiment, in order to represent a certain point on the chromaticity coordinates, three colors close to the point may be selected and expressed using the three colors. Therefore, for example, in order to display light yellow, it is only necessary to combine white, red, and green colors (see FIG. 10). Therefore, when light yellow is displayed on all the pixels of the liquid crystal display panel 10, blue display is unnecessary, and it is necessary to emit the blue light emitting diode 23B during the sub-frame period for displaying the blue image. Is gone. However, even in such a case, it goes without saying that the blue light emitting diode 23B may be made to emit light supplementarily.

As described above, in the liquid crystal display device 1 of the present embodiment, a point on the chromaticity coordinates is represented using three colors of red, green, blue, and white. Therefore, the liquid crystal display device 1 of the present embodiment determines which of the three colors of red, green, blue, and white should be combined for the display on each pixel of the liquid crystal display panel 10 according to the image signal. select. Then, in the same manner as in the first embodiment, the light emission intensities of the light emitting diodes 23 R, 23 G, 23 B, and 23 W and the light transmittance of the liquid crystal display panel 10 are adjusted, and Is displayed. More specifically, this implementation The liquid crystal display device 1 according to the first embodiment detects the color intensity of each color of red, green, blue, and white in each pixel, and then detects the maximum value of the color intensity of each color. Next, based on the maximum value of the color intensity, the emission intensity of each of the light emitting diodes 23 R, 23 G, 23 B, and 23 W is determined as described above. In addition, the light transmittance of each pixel is determined based on the color intensity of each pixel as described above. Then, the light emitting diodes 23 R, 23 G, 23 B, and 23 W emit light sequentially at the emission intensity determined in this manner, and in synchronization with the timing, the transmission determined as described above is performed. The liquid crystal is driven so as to obtain the ratio.

In the case of the liquid crystal display device 1 of the present embodiment, the light emitting diode 23W emits light and the light transmittance of the liquid crystal display panel 10 is maximized in the subframe period in which a white image is displayed. When higher luminance is required, the red, green, and blue light emitting diodes 23 R, 23 G, and 23 B may be made to emit auxiliary light. Further, the light transmittance of the liquid crystal display panel 10 may be increased in each sub-frame period in which images of red, green, and blue are displayed.

FIG. 11 is a timing chart showing the operation of the liquid crystal display device 1 according to the second embodiment of the present invention, in which (a) shows light emitting diodes 23 R, 23 G, 23 B, and 23 FIG. 2 is a diagram showing the light emission intensity and light emission time of W, and FIG. 2 (b) is a diagram showing a change in light transmittance of the liquid crystal display panel 10; In FIG. 11 (b), reference numerals 3A and 3B represent transitions of the maximum value and the minimum value of the light transmittance of each pixel of the liquid crystal display panel 10, respectively. As shown in Fig. 11 (a), the emission diodes 23R, 23G, 23B, and 23W in each subframe period were calculated in the same manner as in the first embodiment. Light is emitted sequentially with intensity. Therefore, the light emitting diodes 23R, 23G, 23B, and 23W do not always emit light with the maximum light emission intensity unlike the conventional case. Therefore, in the liquid crystal display device of the present embodiment, the light emission intensity of the light source may be smaller than in the conventional case. Therefore, As in the case of Embodiment 1, the power required for light emission of the light source can be reduced, and power can be saved.

(Embodiment 3)

In the case of the liquid crystal display device of Embodiment 1, the illumination intensity of the backlight is changed by changing the emission intensity of the light emitting diode of the backlight. On the other hand, the liquid crystal display device of the third embodiment changes the illumination intensity of the backlight by changing the light emission time of the light emitting diode. The configuration of the liquid crystal display device of the third embodiment is the same as that of the first embodiment. Therefore, a description will be given below with reference to FIGS. 3 and 5.

The liquid crystal display device 1 of the present embodiment calculates the maximum value of the color intensity of each color in each pixel in the same manner as in the first embodiment, and based on the result, the light emitting diode 23 R in each subframe period. , 23G, and 23B emission times are determined. Hereinafter, a more specific description will be given using the example of the apple image (see FIG. 6) described in the first embodiment.

Assume that the red color intensity at pixel 50 in FIG. 6 is 14 out of 16 levels and is greater than the red color intensity at any other pixel. In this case, the light emitting time of the red light emitting diode 23R during the red subframe period is set to be 14/16 times the normal light emitting time of the light emitting diode 23R.

It is also assumed that the green color intensity of the pixel 51 in FIG. 6 is 13 out of 16 levels, and is larger than the green color intensity of any other pixel. In this case, the light emitting time of the green light emitting diode 23 G during the green subframe period is set to be 13/16 times the normal light emitting time of the light emitting diode 23 G.

Further, it is assumed that the blue color intensity at pixel 52 in FIG. 6 is 5 out of 16 levels and is larger than the blue color intensity at any other pixel. This In the case of, the light emitting time of the blue light emitting diode 23 B during the blue sub-frame period is 5 13 times the normal light emitting time of the light emitting diode 23 B.

The control means 36 included in the liquid crystal display device 1 of the present embodiment generates a signal indicating the light emission time of each of the light emitting diodes 23 R, 23 G, and 23 B determined as described above. Then, the signal is output to the illumination intensity adjusting means 37.

The control unit 36 calculates the light transmittance of each pixel of the liquid crystal display panel 10 in each sub-frame period in the same manner as in the first embodiment. Then, the control means 36 generates an image signal to be written to each pixel in order to realize the transmittance calculated as described above, and outputs the image signal to the source driver 35.

As a result of the above processing, the gate driver 34, the source driver 35, and the illumination intensity adjusting means 37 operate in synchronization, whereby an image for one frame is displayed on the liquid crystal display panel 10.

FIG. 12 is a timing chart showing the operation of the liquid crystal display device of the present invention according to Embodiment 3, wherein (a) shows the light emission intensity and light emission of the light emitting diodes 23 R, 23 G, and 23 G. FIG. 5B is a diagram showing time, and FIG. 6B is a diagram showing a change in light transmittance of the liquid crystal display panel 10. In FIG. 12 (b), reference numerals 4A and 4B indicate transitions of the maximum value and the minimum value of the light transmittance of each pixel included in the liquid crystal display panel 10, respectively.

As shown in FIG. 12 (a), the light emitting diodes 23R, 23G and 23B emit light sequentially in the light emission time calculated as described above in each subframe period. During these light-emitting times, the light-emitting diodes 23R, 23G, and 23B emit light at the maximum light-emitting intensity of the light-emitting diodes.

It is clear from the comparison between Fig. 12 (a) and Fig. 1 (a). In addition, in the case of the liquid crystal display device 1 of the present embodiment, the light emission time of the light emitting diode in each subframe period is shorter than that of the conventional liquid crystal display device. Therefore, in the case of the liquid crystal display device 1 of the present embodiment, the power required for light emission of the light emitting diode can be reduced as compared with the related art. Even when the light emission time is shortened in this manner, an image display with a desired color intensity can be realized by adjusting the light transmittance of each pixel of the liquid crystal display panel 10. Is the same as in the first embodiment.

In the liquid crystal display device 1 of the present embodiment, the correspondence between the light emission time of the light source, the light transmittance of one pixel, and the color intensity of one color in the pixel is the same as in FIG. That is, if “light emission intensity of light source” is replaced with “light emission time of light source”, FIG. 8 can be applied to this embodiment as it is.

Note that, similarly to the case of the second embodiment, the liquid crystal display device 1 of the present embodiment may have a configuration in which a white light emitting diode is provided in addition to the three color light emitting diodes. Good. In this case, sufficient power saving can be achieved even when there are many white displays.

(Reference)

In the liquid crystal display devices according to the first to third embodiments, the light emission of the light source is controlled according to the displayed image. In addition to the image displayed in this way, it is also possible to save power by controlling the light emission of the light source, for example, according to the state of use.

For example, in the case of a mobile phone, it is only necessary to be able to display the minimum necessary display when waiting. Therefore, color display is often unnecessary. Therefore, when a light source that emits four colors of light is provided as in Embodiment 2, only the light source that emits white light may be emitted during standby. In addition, when a light source that emits three colors of light is provided as in Embodiment 1, If this is the case, only a light source that emits green light with high visibility may be emitted during standby.

It is also conceivable to control the light emission of the light source according to the brightness of the surroundings. <For example, only white light is emitted when it is bright, and three or four colors of light are time-divided in order to display a full color when it is dark. You may make it emit. Specifically, the liquid crystal display device of the present invention may include a sensor such as a photodiode for detecting ambient brightness, and perform white display or color display based on information output from the sensor. Good.

It is also conceivable to control the light emission of the light source according to the type of image. <For example, color display may be performed only when displaying a natural image, and white display may be performed in other cases. . In this case, it can be easily realized by including an identification signal indicating whether or not to perform the color display in the image signal in advance.

As described above, the liquid crystal display device of the present invention according to each embodiment can achieve power saving by controlling light emission of the light source in accordance with a displayed image.

Although the liquid crystal display device of the present invention uses liquid crystal of the 〇CB mode, the present invention is not limited to this. A liquid crystal having spontaneous polarization, such as a ferroelectric liquid crystal or an antiferroelectric liquid crystal, which can respond at high speed similarly to the OCB mode liquid crystal, may be used. Further, the liquid crystal may be a liquid crystal in a TN (Twisted-Nematic) mode or the like.

In each of the above-described embodiments, the maximum value of the color intensity of each pixel is detected for each color with one frame as one unit. However, similar processing is performed with multiple frames as one unit. Is also good.

■ Also, the image signal input from an external device such as a personal computer may be a signal in which the maximum value of the color intensity of each pixel is included in advance. Video provided The pod detects the maximum value of the color intensity of each pixel for each color, and generates an image signal including the detected maximum value of the color intensity. In this case, the liquid crystal display device of the present invention simplifies the processing for detecting the maximum value of the color intensity of each pixel, so that the display processing can be sped up.

From the above description, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Accordingly, the above description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and / or function may be substantially changed without departing from the spirit of the invention.

[Possibility of industrial use]

The liquid crystal display device according to the present invention is useful as a display device of a small electronic device such as a liquid crystal television, a liquid crystal monitor, or a portable telephone.

Claims

3 Range of request

1. A first substrate, a second substrate, and a liquid crystal layer including a liquid crystal sandwiched between the first substrate and the second substrate. Each pixel is provided on the first substrate. A plurality of pixel electrodes arranged in a matrix so as to correspond to each other, and a liquid crystal display panel provided with a counter electrode on either the first substrate or the second substrate;

An illuminating device having a light source that respectively emits light of a plurality of colors, and illuminating the liquid crystal display panel with the light of the plurality of colors;

A driving unit that adjusts, for each pixel, the transmittance of light emitted from the illumination device in the liquid crystal layer by generating a potential difference between each of the pixel electrodes and the counter electrode;

Illumination intensity adjustment means for adjusting the intensity of light emitted from the illumination device for each color;

Detecting means for receiving an image signal corresponding to an image to be displayed in one frame period, and detecting a maximum color intensity for each color from color intensity of each pixel in the input image signal;

The illumination device is controlled so as to sequentially emit light of each color in the one frame period, and the illumination intensity adjusting means is controlled based on the maximum color intensity to emit light from the illumination device in the frame period. Control means for adjusting the intensity of the emitted light for each color, and controlling the driving means for adjusting the transmittance of the liquid crystal layer for the light emitted from the illumination device for each pixel.

The liquid crystal display device provided with.

2. The one frame period includes a plurality of subframe periods, 2. The liquid crystal display device according to claim 1, wherein, in the sub-frame period, one of the light sources emitting the plurality of colors emits light.

3. The liquid crystal display device according to claim 1, wherein the light sources emit red, green, and blue light, respectively.

4. The liquid crystal display device according to claim 1, wherein the light sources emit red, green, blue, and white light, respectively.

5. The liquid crystal display device according to claim 1, wherein the liquid crystal is an OCB mode liquid crystal.

6. The liquid crystal display device according to claim 1, wherein the light source is a light emitting diode.

7. A first substrate, a second substrate, and a liquid crystal layer made of liquid crystal sandwiched between the first substrate and the second substrate, wherein each pixel is provided on the first substrate. A liquid crystal display panel comprising a plurality of pixel electrodes arranged in a matrix so as to correspond to each other, and a counter electrode provided on either the first substrate or the second substrate;

A driving unit that adjusts, for each pixel, a transmittance of light emitted from the lighting device in the liquid crystal layer by generating a potential difference between each of the pixel electrodes and the counter electrode;

Illumination intensity adjusting means for adjusting the emission time of light emitted from the illumination device for each color;

Detecting means for receiving an image signal corresponding to an image to be displayed in one frame period, detecting a maximum color intensity for each color from color intensity of each pixel in the input image signal,

The lighting device is controlled so as to sequentially emit light of each color during the one frame period, and the lighting intensity is controlled based on the maximum color intensity. Controlling the intensity adjustment means to adjust the light emission time of the light emitted from the lighting device in the frame period for each color, and controlling the driving means to control the light emitted from the lighting device in the liquid crystal layer. Control means for adjusting the transmittance for each pixel;

The liquid crystal display device provided with.

8. The one frame period according to claim 7, wherein the one frame period includes a plurality of sub-frame periods, and in the sub-frame period, one of the light sources emitting the plurality of colors emits light. Liquid crystal display device.

9. The liquid crystal display device according to claim 7, wherein the light sources emit red, green, and blue light, respectively.

10. The liquid crystal display device according to claim 7, wherein the light sources emit red, green, blue, and white light, respectively.

11. The liquid crystal display device according to claim 7, wherein the liquid crystal is an OCB mode liquid crystal.

12. The liquid crystal display device according to claim 7, wherein the light source is a light emitting diode.