JP2010128445A - Image display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display which is inexpensive though being thin and has high contrast and low power consumption. <P>SOLUTION: The image display includes a plurality of light source units 2 disposed apart from each other, LED driving circuits 31, and a liquid crystal panel. Each light source unit 2 includes a light guide 21 and an LED 22, and the light guide 21 includes a light scattering part. Driving circuits 31 individually adjust luminous fluxes emitted from respective light source units 2 by controlling the light source units 2 in accordance with an image displayed on the liquid crystal panel, to change screen brightness of the liquid crystal panel. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image display device and a surface light source device using, for example, an LED (light emitting diode) as a light source.

  Video display devices using a transmissive liquid crystal display element are widely used in applications such as televisions and PC monitors. The transmissive liquid crystal display element requires a backlight as a light source on the back side when displaying an image. In recent years, an LED has been used as the backlight instead of CCFL (cold cathode tube) which has been the mainstream in the past. It has become like this.

  In a backlight using an LED as a light source (hereinafter referred to as an LED backlight), brightness control called “area active control” can be performed to reduce power consumption and improve contrast as a video display device. Are known. The area active control may be referred to by names such as local dimming and 2D dimming depending on the literature.

  Area active control is a technique in which the backlight is divided into a plurality of areas (regions) and driven, and the screen brightness for each area is controlled in accordance with the video signal. The area corresponding to the bright part of the video signal is brightened and the backlight area corresponding to the dark part is lit darkly. At the same time, image correction is performed to partially brighten the video signal by the amount that the backlight brightness is lowered, so that the displayed video does not change.

  When area active control is not performed, the backlight is always lit, so light leaks from the gap between the pixels even in the dark part of the image, that is, the part where the pixels of the liquid crystal display element are closed. Therefore, it does not become completely black and looks somewhat whitish. Due to this phenomenon called “whitening”, the contrast of the entire image was lowered. On the other hand, when area active control is performed, leakage light is reduced by weakening backlight light in an area corresponding to a dark portion of an image. Accordingly, it is possible to increase the contrast of the displayed image. In addition, since the amount of light from the backlight is partially reduced, it is possible to reduce power consumption compared to the case of conventional full lighting.

  In the conventional CCFL backlight, it is difficult to adjust the light at high speed according to the video signal due to the restriction of the response speed of the CCFL itself as the light source. On the other hand, since the LED can respond at a high speed of about several ns, it is possible to perform area active control by changing the brightness of each area in real time even for an HD image signal with a frame rate of 60 Hz to 120 Hz. It became possible.

  The structure of the LED backlight is roughly classified into a direct type and a side edge type, and in either of them, area active control has been attempted. The direct type has a structure in which a large number of LEDs, which are point light sources, are arranged in a two-dimensional plane to directly irradiate a liquid crystal element. The side edge type has a structure in which light from an LED disposed on a side surface of a flat light guide plate is incident on the light guide plate, and light is extracted from the upper surface of the light guide plate to obtain backlight light.

  For example, JP 2007-324047 A (Patent Document 1) discloses a mode in which area active control is realized by providing a partition between LEDs and individually driving each LED in a direct type LED backlight. Has been.

Japanese Patent Application Laid-Open No. 2007-293339 (Patent Document 2) shows an example in which a side-driven LED backlight performs partial driving by dividing a light guide plate to realize area active control. Yes.
JP 2007-324047 A JP 2007-293339 A

  However, when performing the area active control as described above, there is a problem that the price is very high compared to the case where the area active control is not performed. In the direct type LED backlight shown in Patent Document 1, since it is necessary to spread the LEDs in a two-dimensional plane, the number of LEDs tends to increase, and the member price tends to be expensive. In order to reduce the price, the number of LEDs may be reduced. However, in a direct type LED backlight, if the number of LEDs is small, the arrangement interval between the LEDs is widened. Before the light from the LED reaches the liquid crystal display element, a color mixing distance is required to mix the colors. Therefore, it is necessary to increase the distance between the liquid crystal display element and the backlight, and as a result, the thickness of the video display device increases. That is, in the direct type LED backlight, as shown in FIG. 13, the number of LEDs, that is, the price of the backlight device and the thickness of the device are in a trade-off relationship.

  On the other hand, in a side-edge type LED backlight using a light guide plate as shown in Patent Document 2, light is mixed in the light guide plate, so that the thickness is kept thin even when the number of LEDs is small. Is possible. However, in the side edge method, luminance unevenness due to luminance variation of the light source is likely to occur, so that sorting by the emission chromaticity rank of the LED is necessary, and the price of the LED tends to be expensive. In addition, since a light guide plate having the same size as the screen area is required, the price of the light guide plate becomes expensive particularly in a large video display device. Therefore, it is difficult to reduce the price of the LED backlight even in the side edge method.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an LED backlight as a surface light source device capable of area active control with a low price and a small number of LEDs. It is another object of the present invention to provide a video display device that is thin but inexpensive and has high contrast and low power consumption.

In order to solve the above problems, a video display device according to the present invention provides:
A plurality of light source units arranged at intervals from each other;
A drive circuit for individually supplying current to each light source unit to cause each light source unit to emit light;
A display screen for displaying an image using light from the light source unit,
The light source unit is disposed on the back surface of the display screen, and has at least one light guide, and at least one light source that is individually provided in each light guide and emits light to the light guide.
The light guide has a light scattering portion that emits light that is incident from the light source and guided inside the light guide by total reflection in the display screen direction,
The drive circuit changes the screen brightness of the display screen by controlling each light source unit and individually adjusting the luminous flux emitted from each light source unit according to the image displayed on the display screen. It is a feature.

  According to the video display device of the present invention, the light source unit includes the plurality of light source units, the drive circuit, and the display screen, and the light source unit includes the light guide and the light source. The display screen includes the light scattering unit, and the driving circuit controls the light source units and individually adjusts light beams emitted from the light source units according to an image displayed on the display screen. Since the screen brightness of each light source unit (light guide) is used, the brightness change of each light source unit is mitigated by the adjacent light source units, and even if the brightness variation of each light source is large, uneven brightness is caused. The light source can be made cheaper. Further, by independently driving each light source unit by the drive circuit, area active control can be performed, power consumption can be reduced, and contrast can be improved.

  Therefore, it is possible to perform practical area active control at a lower cost than both the conventional direct type and side edge type, and realize a low-cost, high-contrast, low-power video display device that is thin. can do.

  Moreover, in the video display apparatus of one Embodiment, the said light-scattering part is formed by printing the particle | grains which have light-scattering property on the surface of the said light guide.

  According to the video display device of this embodiment, the light scattering portion is formed by printing light-scattering particles on the surface of the light guide, so that light diffusion is performed on the surface of the light guide by printing. Since the structure can be easily formed, the light source is inexpensive, and a low-cost video display device can be realized.

Moreover, in the video display device of one embodiment,
At least one of the light sources is disposed on each of both end faces of the light guide,
The luminous flux emitted from each light source is individually controlled by the drive circuit.

  According to the video display device of this embodiment, at least one of the light sources is disposed on each of both end faces of the light guide, and light beams emitted from the light sources are individually controlled by the drive circuit. Therefore, the number of control areas can be doubled by arranging light sources on both end faces of the light guide and independently driving, and the contrast improvement and power consumption reduction effects of area active control can be further enhanced.

  In one embodiment, the drive circuit is a step-down switching converter circuit.

  According to the video display device of this embodiment, since the drive circuit is a step-down switching converter circuit, the area of the drive circuit itself is reduced, and the price of the drive circuit is suppressed even when a large number of light sources are independently driven. Can do.

  In one embodiment, the light source and the drive circuit are mounted on the same substrate.

  According to the video display device of this embodiment, since the light source and the drive circuit are mounted on the same substrate, the board area and connection can be achieved by mounting a small drive circuit on the same substrate as the light source. Members can be reduced. In addition, since the wiring distance between the drive circuit and the light source is shortened, generation of noise due to on / off of the drive current can be suppressed.

Moreover, in the video display device of one embodiment,
The light guide body extends in one direction, and the plurality of light source units are arranged in another direction orthogonal to the one direction,
The luminance distribution on the display screen in a state where one light source unit emits light has a substantially Gaussian distribution in the other direction (short direction of the light guide).

  According to the video display device of this embodiment, the light guide extends in one direction, the plurality of light source units are arranged in the other direction, and the display in a state where one light source unit emits light. Since the luminance distribution on the screen is almost Gaussian in the other direction, changing the luminance distribution of the light source unit alone to a Gaussian distribution causes variations in the luminance of the light source and displacement of the light source unit. Even the brightness unevenness on the screen becomes inconspicuous. Therefore, it is not necessary to select the light source based on the brightness rank, and the ease of assembly can be improved.

  Further, in the video display device according to an embodiment, information on the shape of the luminance distribution is held in a video circuit that processes a signal for displaying a video on the display screen.

  According to the video display device of this embodiment, the information on the shape of the luminance distribution is held in the video circuit that processes the signal for displaying the video on the display screen. By possessing it on the video circuit side, it is possible to calculate the backlight luminance distribution necessary for area active control and generate a corrected image at high speed with high accuracy.

  In the video display device of one embodiment, the luminance distribution on the display screen in a state in which the luminous flux emitted from all the light source units is maximized is a central portion in either or both of the vertical and horizontal directions of the display screen. The distribution shape is such that the maximum value is set and the value decreases toward the end.

  According to the video display device of this embodiment, the luminance distribution on the display screen in a state in which the luminous flux emitted from all the light source units is maximized is the central portion in either one or both of the vertical and horizontal directions of the display screen. Since the distribution shape is such that the maximum is reduced toward the edge, the brightness at the edge is lowered while maintaining the peak brightness at the center of the screen, further reducing the power consumption of the video display device and making the area active The power consumption reduction effect by control can be further strengthened.

Moreover, in the video display device of one embodiment,
A plurality of the light scattering portions are arranged at intervals in the longitudinal direction of the light guide,
The arrangement pattern of the light scattering portions in the light guide disposed in the center portion of the display screen is different from the arrangement pattern of the light scattering portions in the light guide disposed in the end portion of the display screen.

  According to the video display device of this embodiment, a plurality of the light scattering portions are arranged at intervals in the longitudinal direction of the light guide, and the light guide in the central portion of the display screen is arranged. Since the arrangement pattern of the light scattering portion is different from the arrangement pattern of the light scattering portion in the light guide disposed at the end of the display screen, the light diffusing particles of the light guide at the screen center and the screen end. By changing the pattern, it is possible to control the screen luminance distribution in the short direction as well as the longitudinal direction of the light guide. Thereby, power consumption can be reduced without wasting light that can be extracted from the light source.

The surface light source device of the present invention is
A plurality of light source units arranged at intervals from each other;
A drive circuit that individually supplies current to each light source unit to cause each light source unit to emit light, and
The light source unit has at least one light guide, and at least one light source that is individually provided in each light guide and emits light to the light guide,
The light guide has a light scattering portion that emits light that is incident from the light source and guided inside the light guide by total reflection in one direction,
The drive circuit controls each light source unit and individually adjusts a light beam emitted from each light source unit.

  According to the surface light source device of the present invention, the light source unit includes the plurality of light source units and the drive circuit, the light source unit includes the light guide and the light source, and the light guide includes the light scattering unit. The drive circuit controls each light source unit and individually adjusts the light beam emitted from each light source unit. Therefore, by using a plurality of light source units (light guides), adjacent light source units As a result, the luminance change of each light source unit is alleviated, and even when the luminance variation of each light source is large, the luminance unevenness can be alleviated and the light source can be made inexpensive. Further, by independently driving each light source unit by the drive circuit, area active control can be performed, power consumption can be reduced, and contrast can be improved.

  According to the video display device of the present invention, the light source unit includes the plurality of light source units, the drive circuit, and the display screen, and the light source unit includes the light guide and the light source. The display screen includes the light scattering unit, and the driving circuit controls the light source units and individually adjusts light beams emitted from the light source units according to an image displayed on the display screen. Therefore, it is possible to realize a low-priced, high-contrast, low-power-consumption video display device that is thin.

  According to the surface light source device of the present invention, the light source unit includes the plurality of light source units and the drive circuit, the light source unit includes the light guide and the light source, and the light guide includes the light scattering unit. The drive circuit controls each light source unit and individually adjusts the light beam emitted from each light source unit, so that uneven brightness can be reduced, the light source can be made inexpensive, and area active control is possible. Thus, power consumption can be reduced and contrast can be improved.

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

(First embodiment)
FIG. 1 is an exploded perspective view showing a first embodiment of a video display apparatus according to the present invention. FIG. 2 is a block diagram showing the configuration of the main part. As shown in FIGS. 1 and 2, the video display device 1 includes an LED backlight 11 (as a surface light source device), a diffusion plate 12, a transmissive liquid crystal panel 13 (as a display screen), a front cabinet 14, and a chassis 15. , A stand 16 and a video circuit board 17. An actual video display device has many other parts, but illustration and description of parts that do not affect the gist of the present invention are omitted below.

  The LED backlight 11 includes a plurality of light source units 2, and an LED substrate 3 and a control circuit substrate 4 for driving the light source units 2. These detailed structures and operations will be described later. In the present embodiment, the screen size of the liquid crystal panel 13 is 930 mm × 530 mm (42 type), and on the back side of the liquid crystal panel 13, that is, on the side opposite to the display surface, 32 LED backlight constituent units are provided. The light source units 2 are arranged at equal intervals. In the present embodiment, the light guides are arranged so that the longitudinal direction is directed to the short side of the display screen, but an embodiment is also possible in which the longitudinal direction is directed to the long side of the screen.

  The basic operation of the video display device 1 using the transmissive liquid crystal panel 13 will be described. A current is supplied from the outside, and the LED driving circuit 31 mounted on the LED substrate 3 is operated. The LED drive circuit 31 turns on the white LED light source included in the light source unit 2. The light emitted from the light source unit 2 toward the front liquid crystal panel 13 passes through the diffusion plate 12 and is irradiated on the back surface of the liquid crystal panel 13 as backlight light.

  On the other hand, a video signal is input to the video circuit board 17 from a tuner or other device (not shown). This signal is processed by an image processing circuit mounted on the video circuit board 17 and input to a gate driver and a source driver (not shown) mounted inside the liquid crystal panel 13.

  The liquid crystal panel 13 has a number of vertical and horizontal pixel structures, and each pixel is provided with a transistor switch. The gate driver and the source driver turn on and off the transistor switch at an appropriate timing according to the video signal. In one pixel in the liquid crystal panel 13, when the transistor switch is on, the backlight light applied to the liquid crystal element passes through to display white, and when the transistor switch is off, the light is blocked and black is displayed.

  Thus, by performing an operation for switching between passing and blocking of the backlight light incident on each pixel of the liquid crystal panel on all the pixels in the screen, an image corresponding to the video signal is displayed on the screen of the liquid crystal panel 13. Will be. By rewriting this image display every 1/60 seconds that is one frame of the input video signal, the video can be displayed on the liquid crystal screen as a moving image.

  In FIG. 1, a reflective sheet is attached to the inner surface of the chassis 15. The reflection sheet is a white sheet made of a resin material such as PET (polyethylene terephthalate) or PC (polycarbonate), and diffusely reflects the component of the light emitted from the LED backlight 11 that has not entered the front liquid crystal panel direction. The direction of the light source is changed to enter the liquid crystal panel 13 to improve the brightness of the LED light source.

  The diffusing plate 12 is a diffusing plate made of a material such as PC or PMMA (polymethyl methacrylate), and has a function of diffusing and reflecting light incident from one surface and then emitting it from the opposite surface. Have. In the present video display device, backlight lights emitted from different LED light sources are mixed with each other to provide uniform screen brightness. For the purpose of improving the screen brightness and viewing angle characteristics of the video display device, another optical sheet may be added to the diffusion plate 12 and used.

  The front cabinet 14, the chassis 15, and the stand 16 are mechanical parts for holding the liquid crystal panel 13, the LED backlight 11, and other parts.

  The structure of the light source unit 2 that is a component of the LED backlight 11 will be described. 3A shows a side view of the light source unit 2, and FIG. 3B shows a state in which the light source unit 2 is disassembled. One light source unit 2 includes a rod-shaped light guide 21, a white LED 22 as a light source, and an aperture 23. The light guide has an elongated prismatic shape made of PMMA resin, and a light diffusion pattern 211 is provided on the surface. As a material for the light guide, any transparent material that satisfies optical requirements such as PC and glass can be used in addition to PMMA. Further, the shape of the light guide is not limited to the quadrangular prism shape as described in the present embodiment, and any other shape may be used as long as it can guide the inside by total reflection.

  In the present embodiment, the size of the light guide 21 is 10 mm wide × 6 mm high × 530 mm long, the arrangement interval between the light guides 21 in the video display device 1 is about 27 mm, and the liquid crystal panel from the lower surface of the light guide 21 The distance to 13 is about 18 mm. In this embodiment, since the width (10 mm) of the light guide is wider than the arrangement interval (27 mm) between the light guides, there is a gap of about 17 mm between the light guides. That is, it differs from the side-edge type backlight described in the prior art in that adjacent light guides are separated from each other. These numerical values are an example of design, and can be changed as needed. In order to exhibit the superiority of the present invention over the side-edge type backlight, it is desirable that the arrangement interval between the light guides is 1.5 times or more the width of the light guide.

  White LEDs 22 that are light sources are arranged on both end faces of the light guide 21 via apertures 23, respectively. The light emission centers of the LEDs 22 are arranged at positions shifted in opposite directions with respect to the longitudinal central axis of the light guide 21. Thereby, the loss by the emitted light from LED22 entering into LED22 which opposes can be reduced.

  The light diffusion pattern 211 of the light guide 21 is optimized to have a desired luminance distribution when both LEDs 22 are turned on. The light diffusion pattern 211 of the light guide 21 is formed by linearly patterning the surface of the light guide 21 with a mixture of light-scattering diffusion fine particles in a transparent resin by a screen printing method. A line that forms the pattern 211 is a light scattering portion that emits light incident from the LED 22 and guided through the light guide 21 by total reflection in the direction of the liquid crystal panel 13. A plurality of the light scattering portions are arranged at intervals in the longitudinal direction of the light guide 21. In the distribution of the light scattering portions (lines forming the pattern 211), the central portion in the longitudinal direction of the light guide 21 is dense, and the longitudinal ends of the light guide 21 are rough.

  Note that the same effect can be obtained even if the light scattering portion is not linear but dot-shaped. Furthermore, in addition to the light diffusion pattern obtained by printing, the same effect can be obtained by means such as a microprism, a V-shaped groove, a microlens structure, etc., which has the effect of scattering and reflecting light. Is not to be done.

  The light diffusion pattern 211 is printed on the surface corresponding to the upper surface and both side surfaces when the light guide 21 is disposed on the chassis 15 of the video display device 1. The lower surface of the light guide 21 is in contact with a reflection sheet disposed on the chassis 15. The upper surface of the light guide 21 is a surface facing the liquid crystal panel 13 side of the light guide 21, and the lower surface of the light guide 21 is a surface facing the chassis 15 side of the light guide 21.

  A white LED 22 as a light source is disposed at one end of the light guide 21. The white LED 22 has a structure in which a phosphor is disposed above a blue LED chip. White light is obtained by mixing the yellow fluorescence emitted from the phosphor that has absorbed part of the blue light of the LED chip and the original blue light. The structure of the LED is not limited to the above. For example, a method using two types of phosphors of red and green instead of a yellow phosphor, and a method of obtaining white light by mixing RGB LED chips of three colors. I do not care. The white LED 22 is mounted on the LED substrate 3 and is electrically connected to an LED drive circuit 31 described later.

  An aperture 23 is provided between the white LED 22 and the light guide 21. It has a through hole 231 that takes in light from the LED, and the side surface of the through hole 231 has a reflector shape that is inclined to reflect light. In addition, a groove 232 for positioning the light guide 21 is provided in a portion coupled with the light guide 21. The light distribution characteristic of the emitted light of the white LED 22 is normally a Lambert distribution with a full width at half maximum of 120 degrees or a distribution close thereto. Therefore, if the aperture 23 is not provided, a large amount of light does not enter the light guide 21 and is a leaked light. turn into. By providing the aperture 23, most of the light can be incident on the light guide 21 and the light coupling efficiency between the white LED 22 and the light guide 21 can be improved. As the material of the aperture 23, a highly diffuse reflective resin mixed with a white pigment, a film using a dielectric multilayer film, or a metal such as aluminum is used. However, when a metal material is used, consideration for preventing a short circuit with the electrode or the LED substrate pattern is necessary.

  The angle of light incident on the inside of the light guide 21 changes due to the difference in refractive index between the air and the light guide 21, so that almost all of them are the boundary surface between the side surface of the light guide 21 and the air at an angle larger than the critical angle. Is incident on. For this reason, total reflection occurs at the boundary surface and propagates through the light guide 21 without going outside. However, the light hitting the diffusing fine particles in the light diffusing pattern 211 is changed in angle by diffuse reflection and the total reflection condition is broken, and a part of the light is emitted to the outside of the light guide 21.

  Since the two opposing surfaces of the light guide 21 are formed in parallel, the incident light propagates through the inside while repeating total reflection unless it collides with the diffusing fine particles in the light diffusion pattern 211. However, if there are fine irregularities such as processing marks on the surface of the light guide 21, the total reflection condition is broken and a part of the light that should be propagated is emitted out of the light guide 21 and is lost. Therefore, the surface of the light guide 21 is preferably manufactured with a surface roughness of the order of several μm.

  Note that the LED 22 may be disposed only on one end of the light guide 21. In this case, the other end of the light guide 21 is provided with a reflector made of a film using a highly diffuse reflective resin or a dielectric multilayer film so that total reflection is repeated without colliding with the diffusing fine particles. The light propagated to the end portion is repeatedly propagated by changing the direction by the reflecting plate.

  The light that collides with the diffusing fine particles in the light diffusion pattern 211 in the course of propagation enters the back surface of the liquid crystal panel 13 via the diffusion plate 12 and becomes backlight light. A portion where the light diffusion pattern 211 is dense has a high probability of propagating light colliding to become backlight light, and a portion where the light diffusion pattern 211 is sparse has a low probability. Therefore, the local luminance distribution of the emitted light can be arbitrarily changed depending on the density of the light diffusion pattern 211 to be printed.

  In order to use this light as backlight light, it is necessary to obtain uniform brightness at a position that has passed through the diffusion plate 12 in a state where area active control described later is not performed, that is, in a state where all LEDs are lit. By performing ray tracing using an optical simulation software for a certain light diffusion pattern 211, a luminance distribution in a state of being transmitted through the diffusion plate 12 can be obtained, and this result is fed back to the light diffusion pattern 211 and the simulation is repeated. Thus, the optimum light diffusion pattern 211 of the light guide 21 for obtaining a desired luminance distribution on the diffusion plate 12 can be determined.

  FIG. 4A, FIG. 4B, and FIG. 4C show the luminance distribution on the diffusion plate 12 in a state where the light source unit 2 is turned on in the present embodiment. 4B represents the luminance distribution in the section A-A ′ of FIG. 4A, and FIG. 4C represents the luminance distribution in the section B-B ′ of FIG. 4A. The luminance distribution shape on the diffusion plate 12 matches the luminance distribution shape on the screen when the liquid crystal panel 13 is displayed in white, that is, when all the pixels are opened.

  In the present embodiment, the luminance distribution when one light source unit 2 is turned on is a Gaussian distribution (Gaussian) as shown by a curve 52 in the short direction of the light guide 21, and in the longitudinal direction. A mountain-shaped distribution as shown by the curve 51, that is, a distribution that uniformly decreases toward the both ends with the central portion as a peak. The longitudinal luminance distribution when only one side of one light source unit 2 is lit has an asymmetric distribution shape as shown by the curves 51a and 51b. Yamagata distribution is realized as a sum.

  In the present embodiment, 32 light source units 2 are arranged at equal intervals in the lateral direction of the light guide 21. Since the luminance distribution of the entire LED backlight 11 in a state where all the light source units 2 emit light with the maximum luminous flux is the sum of the luminance distributions of all the light source units 2, a mountain-shaped distribution indicated by a curve 51 in the longitudinal direction, In the short direction, a uniform distribution indicated by a straight line 53 is obtained.

  In the side edge type LED backlight described in the prior art, as shown in FIG. 5A, the cross section of the luminance distribution on the diffusion plate 112 in a region corresponding to one area has a shape close to a rectangle. However, in that case, when luminance variations occur in the individual light sources 102, the luminance on the diffusion plate 112 when the plurality of light sources 102 are turned on rapidly changes. Therefore, it becomes easy to perceive luminance unevenness on the screen. On the other hand, in the case of the Gaussian distribution as in the present embodiment, as shown in FIG. 5B, there is a feature that the luminance unevenness is gently perceived and the variation in brightness is less likely to be perceived because the change is reduced by the adjacent area. . Therefore, even when the luminance variation of the single LED is large, the luminance unevenness can be reduced and the LED backlight can be made inexpensive.

On the other hand, the cross section in the longitudinal direction of the luminance distribution of the light source unit 2 has a mountain distribution, and the cross section in the short side direction of the luminance distribution obtained by arranging a plurality of light source units 2 is higher as the center of the screen is higher and toward both upper and lower ends. Distribution. Screen brightness required for conventional image display apparatus such as a liquid crystal TV or PC monitor is the order of 450~500cd / ^{m 2,} the peripheral area brightness while maintaining the luminance of 450~500cd / ^{m 2} at the center of the frame Even if it drops to about half, the viewer's eyes do not perceive any discomfort. Therefore, with such a distribution shape, it is possible to reduce the luminous flux necessary to obtain a desired screen luminance and to reduce power consumption.

  Furthermore, the LEDs 22 at both ends of one light guide 21 in the present embodiment are connected to different LED drive circuits 31, respectively. By independently driving each LED 22, one LED 22 of the light guide 21 is displayed on the screen. Area active control in which the area is divided in the vertical direction of the screen is possible with the LED 22 disposed above and the other LED 22 of the light guide 21 disposed below the screen. As a result, the number of control areas is twice the number of light guides 21, further reducing power consumption and improving contrast.

  Next, the configuration of the LED drive circuit 31 will be described. As shown in FIG. 6, the LED drive circuit 31 is disposed on the same surface as the LED 22 on the LED substrate 3 on which the LED 22 is mounted. The LED board 3 is a double-sided board, and a plurality of LEDs 22 and LED drive circuits 31 are arranged on one LED board 3. On the back surface of the LED substrate 3, a heat conductive sheet and a heat sink for dissipating the LEDs 22 are disposed.

  As shown in FIG. 7, the LED drive circuit 31 is a step-down switching converter circuit including a control IC 311, an inductor 312, a commutation diode 313, etc., and steps down a voltage input from the outside by a switching operation and supplies the voltage to the LED 22. is doing. The switching FET 314 is built in the control IC 311. By monitoring the voltage across the sense resistor RSEN connected in series with the LED 22 with the control IC 311 and performing feedback to the step-down switching operation, the current supplied to the LED 22 is kept constant.

  In the present embodiment, the configuration of the LED drive circuit 31 is a simple step-down switching converter format. The number of parts can be reduced and the circuit can be reduced in size as compared with other drive systems such as a boost converter and a SEPIC converter. The largest component in the drive circuit 31 is the inductor 312, but when the output power is equal, the inductance value of the step-down drive circuit can be reduced as the switching frequency is increased. It is necessary to make the switching frequency as high as possible. If the output power is 1 to 2 W, the switching frequency is preferably 500 kHz or more. In the present embodiment, the step-down operation is performed at a switching frequency of 1.4 MHz. The mounting area of the drive circuit is as small as 20 mm × 7 mm × 2 mm, and can be mounted on the same substrate 3 as the LED 22 by using the space on the side surface of the video display device 1.

  The control IC 311 has an enable terminal ENA, and the operation / stop of the switching operation can be instantaneously switched by applying a digital signal to the terminal from the outside. The enable terminal of each LED drive circuit 31 is connected to an external control board, and the dimming of each light source unit 2 is performed by transmitting a PWM signal with an arbitrary duty from 0% to 100% from the FPGA of the control board. It can be performed. If the frequency of this PWM signal is too low, it will be perceived as flickering during dimming, and if it is too high, the difference from the switching frequency will be small and the PWM resolution will be reduced. A desirable frequency range is considered to be about 200 Hz to 1 kHz.

  When performing area active control, it is necessary to provide independent LED drive circuits 31 for individually driving the LEDs 22 as light sources. Therefore, there is a tendency that the number of wires connecting the LED drive circuit 31 and the LED 22 increases and becomes complicated. Further, when the LED 22 is driven by PWM, a large current flowing through the LED 22 frequently repeats on / off, which may cause electromagnetic noise. In the present embodiment, by arranging the small LED drive circuit 31 on the same substrate as the LED 22, the wiring between the LED drive circuit 31 and the LED 22 can be formed on the LED substrate 3 with the shortest distance. Therefore, connection of a large number of wirings becomes complicated, and generation of electromagnetic noise can be minimized. However, the PWM signal lines that connect the control board and the enable terminals of the LED drive circuits 31 need to be transmitted independently by the number of LED drive circuits 31.

  Next, the area active control operation in the present embodiment will be described with reference to FIG. 2 again. In FIG. 2, RGB 10-bit digital signals obtained by decoding signals input from a tuner or other devices are sent to a video signal processing circuit 171 in the video circuit board 17. The video signal processing circuit 171 converts this signal into a signal suitable for display on the liquid crystal panel 13 and transmits it to the area active control circuit 41 in the control circuit board 4. In order to maintain signal quality at the time of transmission, signal transmission between both circuits is performed in the LVDS (Low Voltage Differential Signaling) format, and an LVDS transmitter and an LVDS receiver are used for the transmission unit and the reception unit, respectively.

  A memory 42 for storing various parameters of the light source unit 2 is provided in the control circuit board 4. The area active control circuit 41 analyzes the input RGB 10-bit digital signals and generates 32 PWM signals and RGB 10-bit corrected video signals according to a procedure described later with reference to the memory 42. The PWM signal is transmitted to the LED substrate 3 and input to the enable terminal of each LED drive circuit 31. The enable terminal is configured to switch the operation / stop of the LED drive circuit 31 as a switching converter. Therefore, by changing the duty of the PWM signal from 0% to 100%, the LED can be arbitrarily dimmed from all-off to all-on.

  The corrected video signal is transmitted to the liquid crystal controller 18, and then transmitted to a source driver and a gate driver (not shown) on the liquid crystal panel 13 at an appropriate timing, and displayed as an image on the liquid crystal panel. Although a signal delay occurs during computation in the video signal processing circuit 171 and the area active control circuit 41, a time difference does not occur between the luminance change of the LED backlight 11 and the video display of the liquid crystal panel 13. In addition, the delay amount of each signal is controlled in each circuit.

  Since the video signal processing circuit 171 and the area active control circuit 41 require real-time high-speed calculation and a large number of input / output terminals in accordance with the transmission speed of the video signal, an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated) is required. It is suitable to realize by Circuit).

  A specific procedure for generating the PWM signal and the corrected video signal in the area active control will be described. As a basic algorithm, a calculation method disclosed in a conventional patent document can be used. However, in the present embodiment, since the luminance distribution on the diffusion plate 12 of the light source unit 2 is designed to be a Gaussian distribution, some modification is required due to the influence. An example of the calculation procedure is shown below, but the calculation procedure is not limited to this, and various changes can be made according to the configuration of the backlight and the like.

  The center of the screen is the origin, and the x axis is in the horizontal direction of the screen, that is, the short direction of the light guide 21, and the y axis is in the vertical direction of the screen, that is, the longitudinal direction of the light guide 21. In the present embodiment, the luminance distribution in the y-axis direction is a mountain-shaped distribution and is divided into two upper and lower areas. However, for simplicity in the following calculation, the luminance distribution in the y-axis direction is assumed to be uniform.

The luminance distribution on the screen when the light source unit existing at the position of x = _xn is turned on is a Gauss distribution of the following equation.
_{G n (x) = K n} · exp (- (x-x n) 2 / (2σ 2))
However, (sigma) represents the standard deviation of Gauss distribution, ie, the breadth of a light source. K _n is a Gaussian distribution peak value given by G _n (x _n ), and is constant regardless of x _n if the light diffusion patterns of the light source and the light guide are the same.

Here, in a region where _xxn is large (away from the light source), the value of G (x) is extremely small, and thus may be ignored in the calculation. The negligible range is determined from the resolution of PWM used for dimming the LED. For example, when the PWM resolution is 8 bits, that is, 1/256, the numerical value that is less than half of 1/512 is very small, and even if it is regarded as 0, the calculation can be terminated without affecting the whole. This determines the area on the screen where calculation is performed for one light source. This is called a calculation area for the light source.

The luminance distribution of the entire LED backlight is the sum of the luminance distributions of all the light source units.

When an original image is given as RGB m-bit signals P _0R (x, y), P _0G (x, y), P _0B (x, y), first, the maximum value of RGB of each pixel And normalize with the maximum value (2 ^m −1) as 1. This is called the brightness value P ₀ (x, y) of each pixel.

A luminance reduction coefficient is obtained for each light source. If the brightness P ₀ (x, y) of the first pixel is 0.5, assuming that the brightness of this pixel is 1 by correction, there is room for the backlight to be reduced to at least 0.5 times the initial value. There will be. Therefore, the luminance reduction coefficient of all the light sources including the pixel in the calculation area is set to 0.5. The brightness of the next pixel is obtained, and the luminance increase coefficients of all the light sources including that pixel in the calculation area are rewritten. If the luminance reduction coefficient is larger than the previous value, the luminance reduction coefficient is rewritten. If the luminance reduction coefficient is equal or smaller, the previous value is maintained.

  This is sequentially calculated for all the pixels on the screen, and the luminance reduction coefficient of the light source is sequentially rewritten.

この調光後バックライト輝度と補正後画像との合成画像が原画像と等しくなる必要から、補正後のＲＧＢ画像データのうちＲについては下式で求められる。
Ｐ_１Ｒ（ｘ，ｙ）＝Ｐ_０Ｒ（ｘ，ｙ）／Ｌ_１（ｘ）
また、Ｐ_１Ｇ（ｘ，ｙ），Ｐ_１Ｂ（ｘ，ｙ）も同様である。 The value R _n of the luminance increase coefficient of each light source when scanning of all pixels is completed is the luminance reduction rate allowed for the light source. When PWM dimming of each light source is performed based on this luminance reduction rate, the luminance distribution of the entire backlight is expressed by the following equation.

Since the composite image of the backlight brightness after dimming and the corrected image needs to be equal to the original image, R of the corrected RGB image data is obtained by the following equation.
P _1R (x, y) = P _0R (x, y) / L ₁ (x)
The same applies to P _1G (x, y) and P _1B (x, y).

で求められる。 When the power consumption of each light source is all equal, the power consumption reduction rate when applying the result obtained by this calculation is

Is required.

In an actual video display device, if the Gauss distribution of each light source is calculated each time, the amount of calculation becomes very large, and real-time processing according to the video signal becomes difficult. In order to reduce the amount of calculation, it is desirable to store information on the luminance distribution of the light source unit in a memory and refer to it appropriately at the time of calculation. For example, parameters corresponding to the position x _{n of} each light source, the σ value of the Gauss distribution, the calculation area, and the like are stored, and a LUT (Look Up Table) corresponding to a Gauss distribution with x = 0 is created in the memory. , X can be referred to as appropriate while shifting the value of x.

  Further, in this embodiment, the luminance distribution in the y-axis direction is not uniform and has an asymmetric distribution shape in the vertical direction. The distribution shape is also digitized in the same manner as in the horizontal direction and stored in a memory as an LUT. Additional measures such as leaving are required.

  Note that the above procedure for calculating the luminance reduction coefficient does not give the smallest possible value, so there is room for further reduction of the value by devising the calculation procedure. For example, an even lower power consumption reduction value D can be obtained by returning the calculation result to the initial value and performing the calculation repeatedly. Whether or not to perform such more advanced calculation can be adjusted in consideration of the relationship between the signal frequency of the video signal and the calculation capability of the area active control circuit to be used.

  The luminance distribution after area active control is shown in FIG. FIG. 8 shows the luminance distribution of the A-A ′ cross section of FIG. 4A. The luminance distribution indicated by a curve 61 when each light source unit 2 is maximized is changed as indicated by a curve 62 by area active control. As a result, the luminance distribution of the entire LED backlight is indicated by a curve 63. become.

  In order to grasp the effect quantitatively, the power consumption reduction rate when the area active control is performed and when it is not performed is calculated. The above calculation was performed by changing the number of divisions using 25 test images consisting of 19 natural images and 6 artificial images, and the average value of the power consumption reduction rate was obtained. The results are shown in FIG.

  In a range where the number of divisions is relatively small, increasing the number of divisions increases the power consumption reduction effect. However, when the number of divisions is further increased, it gradually reaches its peak. Under the present conditions, the power consumption reduction rate increased by 3.2 points when the number of divisions was increased from 14 to 28, but even when the number was further increased to 64, the reduction rate was only increased by 2.0 points. Considering that the number of light sources increases and the cost increases as the number of divisions increases, it is considered that about 16 to 64 divisions are preferable in terms of cost performance when assuming a one-dimensional Gaussian distribution as in this embodiment. It is done.

  Note that the one-dimensional Gaussian distribution as in the present embodiment is more effective in reducing power consumption than a case where a Gaussian distribution is used in both the vertical and horizontal directions (so-called two-dimensional Gaussian distribution) when compared with the same number of area divisions. For example, the one-dimensional Gaussian distribution of 1 × 28 horizontal areas can consume less power than the two-dimensional Gaussian distribution of 4 × 7 vertical areas. This is considered to be due to the fact that the overlapping portions of the areas are simple.

  On the other hand, the one-dimensional Gauss distribution is less effective in reducing power consumption than the pseudo-rectangular distribution that divides the areas more clearly. However, as described above, the one-dimensional Gauss distribution is more advantageous in terms of lowering the price of the video display device because it has a higher tolerance for variations in the luminance of the LEDs and assembly errors of the light source unit.

  In the above description, it is assumed that the area active control calculation is processed by a separate FPGA or ASIC from the video signal processing circuit. However, this calculation is incorporated into the video signal processing circuit in the previous stage and 1 It is also possible to make a chip. In the video signal processing circuit, various image processing such as gamma correction and double speed driving are performed. Although description of these is omitted, even when area active control is performed inside the video signal processing circuit, it is possible to perform these image processings in the same manner as a conventional video display device.

According to the video display device having the above configuration,
A plurality of light source units 2 arranged at intervals from each other;
A drive circuit 31 for individually supplying current to each light source unit 2 to cause each light source unit 2 to emit light;
A display screen (liquid crystal panel 13) for displaying an image using light from the light source unit 2;
The light source unit 2 is disposed on the back surface of the display screen, and is provided with at least one light guide 21 and at least one light source (white) that is individually provided in each light guide 21 and emits light to the light guide 21. LED 22),
The light guide 21 has a light scattering portion (light diffusion pattern 211) that emits light incident from the light source and guided through the light guide 21 by total reflection in the display screen direction.
The drive circuit 31 controls the light source units 2 and individually adjusts the light beams emitted from the light source units 2 according to the image displayed on the display screen, thereby changing the screen brightness of the display screen. Let

  Therefore, by using a plurality of light source units 2 (light guides 21), the luminance change of each light source unit 2 is mitigated by the adjacent light source units 2, and the luminance unevenness can be mitigated even when the luminance variation of each light source is large. The light source can be made inexpensive. Further, by independently driving each light source unit 2 by the drive circuit 31, area active control is possible, power consumption can be reduced, and contrast can be improved.

  In this way, it is possible to perform practical area active control at a lower cost than both the conventional direct type and the side edge type, and it is a thin, low-cost, high-contrast, low-power video display device. Can be realized.

  Moreover, since the light scattering portion is formed by printing light scattering particles on the surface of the light guide 21, a light diffusion structure can be easily formed on the surface of the light guide 21 by printing. Therefore, the light source is inexpensive and a low-priced video display device can be realized.

  In addition, at least one of the light sources is disposed on each of both end faces of the light guide 21, and light beams emitted from the light sources are individually controlled by the drive circuit 31. By arranging light sources on both end faces of 21 and driving them independently, the number of control areas can be doubled, and the contrast improvement and power consumption reduction effects of area active control can be further enhanced.

  Further, since the drive circuit 31 is a step-down switching converter circuit, the area of the drive circuit 31 itself can be reduced, and the price of the drive circuit 31 can be suppressed even when a large number of light sources are independently driven.

  Since the light source and the drive circuit 31 are mounted on the same substrate 3, mounting the small drive circuit 31 on the same substrate as the light source can reduce the board area and connection members. it can. In addition, since the wiring distance between the drive circuit 31 and the light source is shortened, generation of noise due to on / off of the drive current can be suppressed.

  The light guide 21 extends in one direction, the plurality of light source units 2 are arranged in another direction orthogonal to one direction, and the display screen in a state where one light source unit 2 emits light. Since the upper luminance distribution is substantially Gaussian in the other direction, the luminance distribution of the light source unit 2 alone is changed to the Gaussian distribution. However, uneven brightness is not noticeable on the screen. Therefore, it is not necessary to select the light source based on the brightness rank, and the ease of assembly can be improved.

  Further, since the information on the shape of the luminance distribution is held in the video circuit (video signal processing circuit 171) that processes the signal for displaying the video on the display screen, the information on the luminance distribution of the light source unit 2 is displayed as video. By storing the circuit on the circuit side, it is possible to calculate the backlight luminance distribution necessary for area active control and generate a corrected image with high accuracy and high speed.

  In addition, the luminance distribution on the display screen in a state where the luminous flux emitted from all the light source units 2 is maximized has a central portion at the maximum and an end portion (peripheral portion) in either or both of the vertical and horizontal directions of the display screen. ), The power consumption of the video display device is further reduced by reducing the luminance at the edge while maintaining the peak luminance at the center of the screen, and the power consumption by area active control. The reduction effect can be further enhanced.

  Further, the surface light source device (LED backlight 11) having the above configuration includes the plurality of light source units 2 and the drive circuit 31, and the light source unit 2 includes the light guide 21 and the light source. The light guide 21 has the light scattering portion, and the drive circuit 31 controls the light source units 2 and individually adjusts the light beams emitted from the light source units 2. By using the light source unit 2 (light guide 21), the luminance change of each light source unit 2 is mitigated by the adjacent light source unit 2, and even when the luminance variation of each light source is large, the luminance unevenness can be mitigated, and the light source is inexpensive. Can be. Further, by independently driving each light source unit 2 by the drive circuit 31, area active control is possible, power consumption can be reduced, and contrast can be improved.

(Second Embodiment)
FIG. 10 shows a second embodiment of the video display apparatus of the present invention. The difference from the first embodiment will be described. The second embodiment is different in that one light source unit is configured by using two light guides. Constituent elements that are the same as those in the first embodiment are given the same reference numerals in the drawings, and descriptions thereof are omitted.

  As shown in FIG. 10, in the light source unit 2 </ b> A, the two light guides 21 are arranged in parallel to each other, and an aperture 23 is attached to each end face of the two light guides 21. One aperture 23 fixes the end face of one light guide 21 and the end face of the other light guide 21 at the same time.

  White LEDs 22 as light sources are arranged on both end faces of each light guide 21 via apertures 23 respectively. The light emission centers of the LEDs 22 are arranged at positions shifted in opposite directions with respect to the longitudinal central axis of the light guide 21. Thereby, the loss by the emitted light from LED22 entering into LED22 which opposes can be reduced.

  The LEDs 22 at both ends of each light guide 21 are connected to different LED drive circuits 31, and by independently driving each, an area active control in which the area is divided in the vertical direction becomes possible.

  The light diffusion pattern 211 of one light guide 21 and the light diffusion pattern 211 of the other light guide 21 are different from each other. A total of four LEDs 22 arranged at both ends of both light guides 21 can be independently driven.

  FIG. 11A, FIG. 11B, and FIG. 11C show the luminance distribution on the diffusion plate 12 in a state where the light source unit 2A is turned on in the present embodiment. FIG. 11B represents the luminance distribution in the A-A ′ section in FIG. 11A, and FIG. 11C represents the luminance distribution in the B-B ′ section in FIG. 11A. The luminance distribution shape on the diffusion plate 12 matches the luminance distribution shape on the screen when the liquid crystal panel 13 is displayed in white, that is, when all the pixels are opened.

  The luminance distribution on the diffusion plate 12 in a state where the four LEDs 22 in one light source unit 2A are lit alone is as shown by curves 81a, 81b, 81c, 81d. It is designed to have a desired mountain-shaped luminance distribution shown by a curve 81 in a state where these four LEDs 22 are turned on. With this configuration, four independent control areas can be provided in the vertical direction.

  The luminance distribution when one light source unit 2A is turned on is a Gaussian distribution (Gaussian) as shown by a curve 82 in the short direction of the light guide 21, and when all the light source units 2A are turned on. The luminance distribution is a uniform distribution indicated by a straight line 83 in the short direction.

  The arithmetic processing procedure of area active control is basically the same as that described in the first embodiment. However, while the first embodiment is divided into two in the vertical direction, this embodiment is divided into four in the vertical direction. Therefore, the area active control further reduces the power consumption and improves the contrast. Can be made.

(Third embodiment)
FIG. 12 shows a third embodiment of the video display apparatus of the present invention. The difference from the first embodiment will be described. The third embodiment is different in that the print pattern (light diffusion pattern) of the light guide is changed between the screen center and the screen periphery. Constituent elements that are the same as those in the first embodiment are given the same reference numerals in the drawings, and descriptions thereof are omitted.

  FIG. 12 is a horizontal direction (screen left-right direction) cross-sectional view of the luminance distribution on the diffusion plate 12 of the LED backlight 11. The light source units 2 (light guides 21) are arranged so that the arrangement interval gradually increases from the center of the screen toward the periphery of the screen. The light diffusion patterns 211 of the light guide 21 are also different patterns, and are designed such that the σ value of the Gauss distribution increases from the center of the screen toward the periphery of the screen. When all the light fluxes of the individual LEDs 22 are the same and are lit at the same current value / PWM value, the peak of the Gauss distribution with a large σ value becomes low. Accordingly, when all the luminance distributions indicated by the curve 91 of each light source unit 2 are added to obtain the luminance distribution of the entire LED backlight 11, a mountain-shaped distribution as indicated by the curve 92 is obtained.

In the present embodiment, unlike the previous embodiment, the mountain distribution can be made not only in the vertical direction of the screen but also in the horizontal direction. While maintaining the brightness of the center of the screen at 450 to 500 cd / m ² , the brightness of the top, bottom, left, and right of the screen can be lowered within a range that does not cause a sense of incongruity, so it is possible to further reduce the power consumption as an LED backlight Become.

  Area active control is performed by controlling the luminous flux of each light source unit 2. The area active calculation procedure is basically the same as in the first embodiment. However, since the luminance distributions of the individual light source units 2 are different, it is necessary to separately store parameters or LUTs related to the luminance distributions in the memory.

  That is, the arrangement pattern of the light scattering portions in the light guide 21 arranged in the central portion of the display screen is different from the arrangement pattern of the light scattering portions in the light guide 21 arranged in the end portion (peripheral portion) of the display screen. Therefore, by changing the pattern of the light diffusing particles of the light guide 21 between the screen center and the screen end, the screen luminance distribution in the short direction as well as the longitudinal direction of the light guide 21 can be controlled. Thereby, power consumption can be reduced without wasting light that can be extracted from the light source.

  As another method of forming such a mountain-shaped luminance distribution shape, for example, in the direct type LED backlight 11, the value of the current passed through the LEDs 22 of the light source unit 2 arranged on the left and right of the screen and the duty value of PWM driving are changed. A method of reducing the luminance of the left and right parts is conceivable. In that case, however, the peripheral LED 22 always emits light with a low current value or PWM duty value, and this causes waste in terms of performance. On the other hand, in the method realized by the light diffusion pattern 211 as described above, the luminous flux saved by lowering the luminance of the peripheral portion contributes to the luminance improvement of the central portion, and therefore the LED backlight 11 as a whole. The luminous flux can be used effectively, and the necessary screen brightness can be obtained with the minimum number of LEDs. In other words, a cheaper configuration can be achieved while achieving the screen brightness required for the video display device.

  As described above, in the present embodiment, the light diffusion pattern 211 and the arrangement interval of the light guide 21 are individually changed, so that it is possible to further reduce power consumption while having an inexpensive configuration.

  In addition, this invention is not limited to the above-mentioned embodiment. For example, in the above embodiment, a white LED is used as the light source of the LED backlight, but it is also possible to perform area active control independently for each of the three colors using three RGB light sources corresponding to each color of the video signal. It is. In that case, a higher power consumption reduction effect than in area active control in white can be obtained.

  In these embodiments, since the light source unit luminance distribution can be controlled by a light diffusion pattern by printing, in addition to the Gauss distribution and the pseudo-rectangular distribution described above, an arbitrary luminance distribution shape can be set as necessary. For example, the light source unit placed at the edge of the screen is affected by the reflected light on the side of the chassis, resulting in a luminance distribution that differs from the central part. It is also possible to make the print pattern different from the central portion.

  In the present invention, the video display device mainly used as a liquid crystal television or a PC monitor has been described. However, the present invention can be applied to other devices. Application examples include, but are not limited to, sign boards, public display boards, traffic signs, and the like. In addition, the LED backlight described in the present embodiment is not only used in a form incorporated as a part of a video display device, but also for modules and components alone for use in replacement of an existing video display device. It is also possible to utilize it in the form.

It is a disassembled perspective view which shows 1st Embodiment of the video display apparatus of this invention. It is a block diagram of a video display device. It is a top view of the light source unit used for a video display apparatus. It is a disassembled perspective view of the light source unit used for a video display apparatus. It is a top view of a video display device. It is a figure which shows the luminance distribution on the screen at the time of lighting one light source unit and all the light source units in the A-A 'cross section of FIG. 4A. It is a figure which shows the luminance distribution on the screen at the time of lighting of one light source unit and all the light source units in the B-B 'cross section of FIG. 4A. It is a figure which shows the pseudo rectangle type luminance distribution in the conventional video display apparatus. It is a figure which shows the Gaussian type luminance distribution in a video display apparatus. It is a top view of the LED board used for a video display apparatus. It is a schematic circuit diagram of the LED drive circuit used for a video display apparatus. It is a figure which shows the luminance distribution at the time of applying area active control in a video display apparatus. It is a figure which shows the relationship between the area division | segmentation number of area active control, and power consumption in a video display apparatus. It is a top view which shows the structure of the light source unit used for 2nd Embodiment of the video display apparatus of this invention. It is a top view of a video display device. It is a figure which shows the luminance distribution on the screen at the time of lighting one light source unit and all the light source units in the A-A 'cross section of FIG. 11A. It is a figure which shows the luminance distribution on the screen at the time of lighting one light source unit and all the light source units in the B-B 'cross section of FIG. 11A. It is a figure which shows the luminance distribution on the screen in 3rd Embodiment of the video display apparatus of this invention. In a conventional video display device using a direct type LED backlight, it is a diagram showing a relationship between the number of LEDs used, the thickness of the device, and the price.

Explanation of symbols

1 Video display device 11 LED backlight (surface light source device)
12 Diffusion plate 13 LCD panel (display screen)
14 Front cabinet 15 Chassis 16 Stand 17 Video circuit board 171 Video signal processing circuit 2, 2A Light source unit 21 Light guide 211 Light diffusion pattern (light scattering part)
22 White LED (light source)
23 Aperture 3 LED board 31 LED drive circuit 4 Control circuit board 41 Area active control circuit

Claims (10)

A plurality of light source units arranged at intervals from each other;
A drive circuit for individually supplying current to each light source unit to cause each light source unit to emit light;
A display screen for displaying an image using light from the light source unit,
The light source unit is disposed on the back surface of the display screen, and has at least one light guide, and at least one light source that is individually provided in each light guide and emits light to the light guide.
The light guide has a light scattering portion that emits light that is incident from the light source and guided inside the light guide by total reflection in the display screen direction,
The drive circuit changes the screen brightness of the display screen by controlling each light source unit and individually adjusting the luminous flux emitted from each light source unit according to the image displayed on the display screen. A characteristic video display device. The video display device according to claim 1,
The image display device, wherein the light scattering portion is formed by printing light-scattering particles on the surface of the light guide. The video display device according to claim 1 or 2,
At least one of the light sources is disposed on each of both end faces of the light guide,
The image display apparatus characterized in that light beams emitted from the respective light sources are individually controlled by the drive circuit. In the video display device according to any one of claims 1 to 3,
The video display device, wherein the drive circuit is a step-down switching converter circuit. In the video display device according to any one of claims 1 to 4,
The video display device, wherein the light source and the driving circuit are mounted on the same substrate. In the video display device according to any one of claims 1 to 5,
The light guide body extends in one direction, and the plurality of light source units are arranged in another direction orthogonal to the one direction,
An image display device, wherein a luminance distribution on the display screen in a state where one light source unit emits light has a substantially Gaussian distribution in the other direction. The video display device according to claim 6,
The information on the shape of the luminance distribution is held in a video circuit that processes a signal for displaying a video on the display screen. The video display device according to any one of claims 1 to 7,
The luminance distribution on the display screen in a state where the luminous flux emitted from all the light source units is maximized so as to decrease toward the end with the center at the maximum in either or both of the vertical and horizontal directions of the display screen. Video display device characterized by having a distributed shape. In the video display device according to any one of claims 1 to 8,
A plurality of the light scattering portions are arranged at intervals in the longitudinal direction of the light guide,
The arrangement pattern of the light scattering portions in the light guide disposed in the central portion of the display screen is different from the arrangement pattern of the light scattering portions in the light guide disposed in the end portion of the display screen. A characteristic video display device. A plurality of light source units arranged at intervals from each other;
A drive circuit that individually supplies current to each light source unit to cause each light source unit to emit light, and
The light source unit has at least one light guide, and at least one light source that is individually provided in each light guide and emits light to the light guide,
The light guide has a light scattering portion that emits light that is incident from the light source and guided inside the light guide by total reflection in one direction,
The surface light source device, wherein the drive circuit controls each light source unit and individually adjusts a light beam emitted from each light source unit.

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