Backlight device, liquid crystal display device, and control method for backlight device

Abstract

This reduces flicker of light-emitting elements when using an asynchronous synchronization signal in response to the vertical synchronization signal used to drive the LCD panel to sequentially light up multiple light-emitting elements to reduce motion blur. [Solution] The backlight device is a backlight device disposed beneath a liquid crystal panel and comprises: a plurality of light-emitting units, each having one or more light sources; a backlight drive circuit that generates an asynchronous scan synchronization signal with respect to a vertical synchronization signal generated for each frame cycle of the liquid crystal panel, and sequentially lights up the plurality of light-emitting units in synchronization with the generated scan synchronization signal; and a lighting stop circuit that stops the lighting of the plurality of light-emitting units for one or more cycles of the scan synchronization signal.

Description

[Technical Field]

[0001] This disclosure relates to a backlight device, a liquid crystal display device, and a method for controlling a backlight device. [Background technology]

[0002] In liquid crystal display devices equipped with a backlight, a method is known to reduce motion blur by intermittently illuminating the backlight in synchronization with the drive signal that drives the liquid crystal panel. In this method, increasing the drive frequency of the backlight and keeping the ratio of the illumination period to the drive cycle constant reduces image flicker. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2013-222081 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] This disclosure aims to reduce flicker of light-emitting units when reducing motion blur in a backlight device and a liquid crystal display device having the backlight device by sequentially lighting up multiple light-emitting units using an asynchronous synchronization signal with respect to the vertical synchronization signal for driving the liquid crystal panel. [Means for solving the problem]

[0005] A backlight device according to one embodiment of the present disclosure is a backlight device disposed beneath a liquid crystal panel and comprises: a plurality of light-emitting units, each having one or more light sources; a backlight drive circuit that generates an asynchronous scan synchronization signal with respect to a vertical synchronization signal generated for each frame period of the liquid crystal panel, and sequentially lights up the plurality of light-emitting units in synchronization with the generated scan synchronization signal; and a lighting stop circuit that stops the lighting of the plurality of light-emitting units for one or more cycles of the scan synchronization signal. [Effects of the Invention]

[0006] According to one embodiment of the present disclosure, in a backlight device and a liquid crystal display device having the backlight device, when reducing motion blur by sequentially lighting up multiple light-emitting units using an asynchronous synchronization signal with respect to the vertical synchronization signal for driving the liquid crystal panel, flickering of the light-emitting units can be reduced. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic exploded perspective view showing an example of a backlight device and liquid crystal display device according to the first embodiment. [Figure 2] Figure 1 is a top view showing an example of a planar light source. [Figure 3] This is a cross-sectional view showing an example of a section along the line III-III in Figure 2. [Figure 4A] This is a top view showing a modified example of the planar light source shown in Figure 3. [Figure 4B] This is a cross-sectional view showing an example of a section along the XIB-XIB line in Figure 4A. [Figure 5] This figure shows an example of a rectangular region containing multiple light-emitting areas that emit light simultaneously in the backlight device shown in Figure 1. [Figure 6] A block diagram showing an example of a liquid crystal display device, as shown in Figure 1. [Figure 7] Figure 6 is a circuit block diagram showing an example of a backlight device. [Figure 8] Figure 7 is a circuit block diagram showing an example of a circuit breaker control unit. [Figure 9] Figure 1 is a timing diagram showing an example of the operation of a liquid crystal display device. [Figure 10] This timing diagram shows another example of the operation of the liquid crystal display device shown in Figure 1. [Figure 11] Figure 6 shows a waveform diagram illustrating an example of the current flowing through the light-emitting element when scanning each rectangular region of the planar light source. [Figure 12] This timing diagram shows an example of the operation of a liquid crystal display device that generates a scan synchronization signal asynchronously with the vertical synchronization signal and generates a cutoff signal synchronously with the vertical synchronization signal. [Figure 13] Block diagram showing an example of a liquid crystal display device according to the second embodiment. [Modes for carrying out the invention]

[0008] The following description will explain embodiments for carrying out the invention with reference to the drawings. In the following description, terms indicating specific directions or positions (for example, "up," "down," and other terms including these terms) will be used as needed. The use of these terms is for the purpose of facilitating the understanding of the invention with reference to the drawings, and the meaning of these terms does not limit the technical scope of the present invention. Also, parts with the same reference numerals appearing in multiple drawings indicate the same or equivalent parts or components.

[0009] Furthermore, the embodiments shown below are illustrative examples of liquid crystal display devices, backlight devices, etc., that embody the technical concept of the present invention, and do not limit the present invention to the following. Also, the dimensions, materials, shapes, relative arrangements, etc. of the components described below are intended to be illustrative, and not to limit the scope of the present invention unless otherwise specified. In addition, the content described in one embodiment is applicable to other embodiments and modifications. Furthermore, the size and positional relationships of the members shown in the drawings may be exaggerated in order to clarify the explanation. In addition, in order to avoid the drawings becoming excessively complex, schematic diagrams that omit the illustration of some elements may be used, or end view diagrams that show only the cut surface may be used as cross-sectional views.

[0010] In each drawing showing the structure, X-axis, Y-axis, and Z-axis orthogonal to each other are shown for reference. The direction parallel to the X-axis is also referred to as the X-direction, the direction parallel to the Y-axis is also referred to as the Y-direction, and the direction parallel to the Z-axis is also referred to as the Z-direction. In the X-direction, the direction in which the arrow points is also referred to as the +X direction, and the opposite direction of the +X direction is also referred to as the -X direction. In the Y-direction, the direction in which the arrow points is also referred to as the +Y direction, and the opposite direction of the +Y direction is also referred to as the -Y direction. In the Z-direction, the direction in which the arrow points is also referred to as the +Z direction, and the opposite direction of the +Z direction is also referred to as the -Z direction.

[0011] In addition, the symbol indicating a signal may be used as a symbol indicating a signal line, a signal terminal, or a signal node. The symbol indicating power / supply voltage may be used as a symbol indicating a power line / supply voltage line, a power terminal / supply voltage terminal, or a power node / supply voltage node.

[0012] <First Embodiment> (Backlight Device and Liquid Crystal Display Device) FIG. 1 is an exploded perspective view schematically showing an example of a backlight device and a liquid crystal display device according to the first embodiment. The liquid crystal display device 100 according to the present embodiment is, for example, a liquid crystal module (LCM: Liquid Crystal Module) used for a display of an external device (not shown) such as a television, a personal computer, or a game machine. The liquid crystal display device 100 includes a backlight device 110, a liquid crystal panel 120, a liquid crystal driving circuit 130, and a control circuit 140.

[0013] The backlight device 110 includes a planar light source 111, an optical member 112 disposed on the liquid crystal panel 120 side of the planar light source 111, and a backlight driving circuit 150. Note that the backlight driving circuit 150 may be provided outside the backlight device 110. <00001​The following describes the various parts of the liquid crystal display device 100. In Figure 1, for the sake of clarity, the electrical connections between components are shown by connecting them with solid lines. The solid lines connecting the components may include multiple signal lines and multiple power lines.

[0015] The control circuit 140 outputs video data and control signals to the liquid crystal drive circuit 130 for each frame in order to display the image on the liquid crystal panel 120, thereby displaying the image on the liquid crystal panel 120. The control circuit 140 may also output brightness control information to the backlight drive circuit 150, indicating how to illuminate the planar light source 111 based on the video data for each frame transferred to the liquid crystal panel 120.

[0016] In the backlight device 110, the planar light source 111 includes a rectangular substrate 113, a light guide member 115 arranged on the substrate 113, and two-dimensionally arranged light-emitting regions 111s. The light guide member 115 has a plurality of recesses formed in a matrix. The light-emitting regions 111s are provided corresponding to light sources (not shown) arranged in each recess. The backlight drive circuit 150 can irradiate light from one or more light-emitting regions 111s by driving the plurality of light sources arranged in a matrix in a two-dimensional manner.

[0017] For example, the backlight device 110 may perform local dimming control by adjusting the brightness every predetermined number of light-emitting areas 111s according to the image displayed on the liquid crystal panel 120. Local dimming control can improve the contrast ratio of the image and reduce the power consumption of the backlight device 110.

[0018] The optical element 112 has, for example, a sheet shape or plate shape and has a light adjustment function such as diffusing the backlight light irradiated from the light-emitting area 111s toward the liquid crystal panel 120. In this embodiment, the number of optical elements 112 used in the backlight device 110 is one. However, the number of optical elements used in the backlight device 110 may be two or more.

[0019] The liquid crystal panel 120 is positioned above the backlight device 110 (in the +Z direction) and has a rectangular shape. The liquid crystal panel 120 has a plurality of pixels 120p arranged in a matrix. Although not particularly limited, each pixel 120p includes a subpixel that can transmit blue light, a subpixel that can transmit green light, and a subpixel that can transmit red light from the white light emitted from the backlight device 110. The light transmittance of each subpixel can be individually controlled by the liquid crystal driving circuit 130. As a result, the liquid crystal panel 120 can display a color image by individually controlling the gradation of each subpixel.

[0020] (Example of a surface light source) Figure 2 is a top view showing an example of the planar light source 111 shown in Figure 1. Figure 3 is a cross-sectional view showing an example of a cross-section along line III-III in Figure 2. The planar light source 111 includes a light-reflective sheet 114 formed on the substrate 113 shown in Figure 1, a light guide member 115, a plurality of light sources 116, a light-transmitting member 117, a first light-adjusting member 118, and a light-reflecting member 119.

[0021] The substrate 113 is a wiring board having an insulating member and a plurality of wirings arranged on the insulating member. The upper and lower surfaces of the substrate 113 are flat and are generally parallel to the X and Y directions (XY plane).

[0022] As shown in Figure 3, the light-reflective sheet 114 is placed on the substrate 113. The light-reflective sheet 114 has, for example, a first adhesive layer 114a, a light-reflective layer 114b placed on the first adhesive layer 114a, and a second adhesive layer 114c placed on the light-reflective layer 114b. The light-reflective sheet 114 is attached to the substrate 113 by the first adhesive layer 114a. For example, a resin containing a large number of air bubbles may be used for the light-reflective layer 114b.

[0023] Furthermore, the first adhesive layer 114a and the second adhesive layer 114c may contain, for example, a light diffusing agent. In this case, it is preferable that the concentration of the light diffusing agent contained in the second adhesive layer 114c is lower than the concentration of the light diffusing agent contained in the first adhesive layer 114a, thereby reducing brightness unevenness in the light-emitting region 111s, which will be described later. The light diffusing agent used in the first adhesive layer 114a and the second adhesive layer 114c can be appropriately selected from, for example, the light diffusing agents used in the second light adjusting member 116c and the third light adjusting member 116d, which will be described later.

[0024] The light guide member 115 is placed on the light-reflective sheet 114. The light guide member 115 is attached to the light-reflective sheet 114 by a second adhesive layer 114c. For example, the shape of the light guide member 115 is plate-like, but is not limited to a plate shape. The thickness of the light guide member 115 is preferably 200 μm or more and 800 μm or less. The light guide member 115 may be composed of a single layer or a laminate of multiple layers.

[0025] The material used for the light guide member 115 is, for example, a thermoplastic resin such as acrylic, polycarbonate, cyclic polyolefin, polyethylene terephthalate, or polyester, a thermosetting resin such as epoxy or silicone, or glass.

[0026] The light guide member 115 is provided with a plurality of light source placement sections 115a. The plurality of light source placement sections 115a are arranged in a matrix in a top view, as shown in Figure 2. Each light source placement section 115a is formed by a through hole that penetrates the light guide member 115 in the Z direction, as shown in Figure 3. However, the light source placement sections 115a may also be formed by recesses provided on the lower surface of the light guide member 115.

[0027] Each light source 116 is located within its respective light source arrangement section 115a. Therefore, multiple light sources 116 are also arranged in a matrix in a two-dimensional manner, as shown in Figure 2. However, if the light sources 116 are embedded in the light guide member 115, the light source arrangement section 115a does not need to be provided in the light guide member 115. Furthermore, a planar light source 111 does not necessarily need to have a light guide member 115. For example, a planar light source 111 may simply consist of multiple light sources 116 arranged in a matrix in a two-dimensional manner on a substrate, without the presence of a light guide member 115.

[0028] Each light source 116 is a light-emitting device that combines a light-emitting element 116a with a wavelength conversion member 116b, as shown in Figure 3. Each light source 116 further includes a second light-adjusting member 116c and a third light-adjusting member 116d. However, each light source 116 may be a light-emitting element alone rather than a light-emitting device.

[0029] The light-emitting element 116a is, for example, an LED (Light Emitting Diode). The light-emitting element 116a includes a semiconductor laminate 116e and a pair of electrodes 116f and 116g that electrically connect the semiconductor laminate 116e to the wiring of the substrate 113. Through holes are provided in the light-reflective sheet 114 in the portions located directly beneath each electrode 116f and 116g. Conductive members 113m are arranged within these through holes to electrically connect each electrode 116f and 116g to the wiring of the substrate 113.

[0030] The wavelength conversion member 116b includes a light-transmitting member 116h that covers the top and side surfaces of the semiconductor laminate 116e, and a wavelength conversion material 116i disposed within the light-transmitting member 116h that converts the wavelength of light emitted by the semiconductor laminate 116e to a different wavelength. The wavelength conversion material 116i is, for example, a phosphor.

[0031] For example, the light-emitting element 116a emits blue light. In this case, the wavelength conversion member 116b may include a phosphor that emits red light and a phosphor that emits green light. Hereinafter, the phosphor that emits red light will be referred to as the "red phosphor," and the phosphor that emits green light will be referred to as the "green phosphor."

[0032] The red phosphor is, for example, a CASN-based phosphor (e.g., CaAlSiN3:Eu), a KSF-based phosphor (e.g., K2SiF6:Mn), a KSAF-based phosphor (e.g., K2[Si p Al q Mn r F s (0.9 ≦ p + q + r ≦ 1.1, 0 < q ≦ 0.1, 0 < r ≦ 0.2, 5.9 ≦ s ≦ 6.1)), or a quantum dot phosphor (e.g., Ag p Cu 1-p In q Ga[[ID=十七]] 1-q S2(0 < p ≦ 1, 0 < q ≦ 1)).

[0033] Also, the green phosphor is, for example, a phosphor having a perovskite structure (e.g., CsPb(F,Cl,Br,I)3), a β - sialon - based phosphor (e.g., (Si,Al)3(O,N)4:Eu), a LAG - based phosphor (e.g., Lu3(Al,Ga)_{5}O 12 :Ce), or a quantum dot phosphor (e.g., AgIn p Ga 1-p S2(0 < p ≦ 1)). The backlight device 110 can emit white light, which is a mixed color light of the blue light emitted by the light - emitting element 116a and the red light and green light emitted by the wavelength - conversion member 116b.

[0034] However, the wavelength - conversion member 116b may be replaced with a light - transmissive member that does not contain a phosphor. In this case, or when the light source 116 is the light - emitting element 116a alone as described above, for example, a phosphor sheet containing a red phosphor and a green phosphor may be disposed on the planar light source 111, or a phosphor sheet containing a red phosphor and a phosphor sheet containing a green phosphor may be disposed on the planar light source 111. Thereby, the backlight device 110 can emit the same white light as in the case of using the wavelength - conversion member 116b.[[ID=三十三]]

[0035] The second light - adjusting member 116c is provided to cover the upper surface of the wavelength - conversion member 116b. The second light - adjusting member 116c can control the amount and emission direction of the light emitted from the upper surface of the wavelength - conversion member 116b.

[0036] The third light adjusting member 116d is provided so as to cover the lower surface of the light-emitting element 116a and the lower surface of the wavelength conversion member 116b, such that the lower surfaces of the electrodes 116f and 116g are exposed. The third light adjusting member 116d can be controlled to reflect light directed toward the lower surface of the wavelength conversion member 116b and emit it from the upper and side surfaces of the wavelength conversion member 116b.

[0037] The second light-adjusting member 116c and the third light-adjusting member 116d can each be composed of a translucent resin and a light-diffusing agent contained in the translucent resin. The translucent resin is, for example, a silicone resin, epoxy resin, or acrylic resin. The light-diffusing agent is, for example, particles of titania, silica, alumina, zinc oxide, magnesium oxide, zirconia, yttria, calcium fluoride, magnesium fluoride, niobium pentoxide, barium titanate, tantalum pentoxide, barium sulfate, or glass. In addition, the second light-adjusting member 116c may be made of a metal material such as aluminum or silver to prevent the brightness directly above the light source 116 from becoming too high.

[0038] Within the light source arrangement section 115a, a light-transmitting member 117 is arranged to cover the light source 116. A first light adjustment member 118 is arranged on the light-transmitting member 117. The first light adjustment member 118 reflects a portion of the light incident from the light-transmitting member 117 and transmits the other portion, so that the brightness directly above the light source 116 does not become too high. Furthermore, it is preferable that the first light adjustment member 118 is arranged to cover the interface between the light-transmitting member 117 and the light guide member 115 when viewed from above. This makes it possible to suppress the scattering of light from the light source 116 at the interface between the light-transmitting member 117 and the light guide member 115, which would cause the brightness to become partially high. The first light adjustment member 118 can be made of the same material as the second light adjustment member 116c or the third light adjustment member 116d.

[0039] Furthermore, the light guide member 115 is provided with partition grooves 115b that surround each light source arrangement section 115a when viewed from above. The partition grooves 115b extend in a grid pattern in the X and Y directions. The partition grooves 115b penetrate the light guide member 115 in the Z direction. The partition grooves 115b may also be recesses provided on the upper or lower surface of the light guide member 115. In addition, the partition grooves 115b may not be provided on the light guide member 115.

[0040] A light-reflecting member 119 is placed within the partition groove 115b. The light-reflecting member 119 can be, for example, the same type of member as the second light-adjusting member 116c or the third light-adjusting member 116d. The light-reflecting member 119 covers a portion of the side surface of the partition groove 115b in a layered manner. The light-reflecting member 119 may extend to further cover the upper surface of the light-reflective sheet 114, particularly the second adhesive layer 114c, exposed within the partition groove 115b, so that the light from the light source 116 can be partitioned into light-emitting regions 111s, which will be described later. The light-reflecting member 119 may be placed so as to fill the entire partition groove 115b. Alternatively, the light-reflecting member 119 may not be placed within the partition groove 115b.

[0041] The outputs of the multiple light sources 116 can be individually controlled by the backlight drive circuit 150 (Figure 1). Here, "controllable output" means that it is possible to switch between on and off, and that the brightness in the on state can be adjusted. The light-emitting region 111s represents each region when the planar light source 111 is divided into regions, each containing a light source 116 whose light output is individually controlled, as seen in the top view of Figure 2. The light-emitting region 111s corresponds to the smallest region in the planar light source 111 where the brightness is adjusted by local dimming control.

[0042] Each light-emitting region 111s corresponds to a region when the planar light source 111 is divided into a grid, similar to the partition groove 115b in this embodiment. Therefore, the shape of each light-emitting region 111s is rectangular, as shown in Figure 2. One light source 116 is arranged within each light-emitting region 111s. However, the planar light source 111 may have multiple light source groups, each containing multiple light sources 116, arranged in a matrix in two dimensions, and the output may be controlled for each light source group. In this case, one light source group, i.e., multiple light sources 116, is arranged within one light-emitting region 111s.

[0043] The multiple light-emitting regions 111s are arranged in a matrix in a two-dimensional manner when viewed from above. In the following, in a matrix structure such as multiple light-emitting regions 111s, groups of elements such as light-emitting regions 111s arranged in the X direction will be referred to as "rows," and groups of elements such as light-emitting regions 111s arranged in the Y direction will be referred to as "columns." The row located furthest to the +Y side (above the liquid crystal display device 100 in Figure 1) will be referred to as the "first row," and the row located furthest to the -Y side (below the liquid crystal display device 100 in Figure 1) will be referred to as the "last row." Similarly, the column located furthest to the -X side (below the liquid crystal display device 100 in Figure 1) will be referred to as the "first column," and the column located furthest to the +X side (to the right of the liquid crystal display device 100 in Figure 1) will be referred to as the "last column." The multiple light-emitting regions 111s are arranged in N rows and M columns. Here, N and M are arbitrary integers, and in the example shown in Figure 2, "N" is 9 and "M" is 16.

[0044] (Variation of a planar light source) Figure 4A is a top view showing a modified example of the planar light source 111 shown in Figure 3. Figure 4B is a cross-sectional view showing an example of a cross-section along the line XIB-XIB in Figure 4A. The following explanation will mainly focus on the differences from the explanation above. Content not explained is the same as described above.

[0045] The planar light source 211 shown in Figures 4A and 4B comprises a substrate 113, an adhesive member 215, a light-reflective sheet 214, and a plurality of light sources 216. For example, the planar light source 211 is mounted on a backlight device 110 instead of the planar light source 111 shown in Figures 1 and 2.

[0046] The light-reflective sheet 214 is attached to the substrate 113 by an adhesive member 215. The light-reflective sheet 214 is provided with a plurality of through holes 214a. The plurality of through holes 214a are arranged in a matrix in the X and Y directions. A light source 216 is placed inside each through hole 214a. The light source 216 corresponds to the light source 116 in Figures 2 and 3, and is arranged in a matrix in two dimensions within the planar light source 211.

[0047] Furthermore, the light-reflective sheet 214 is provided with bent portions 214b that surround each through-hole 214a, i.e., each light source 216. The bent portions 214b are formed by folding the light-reflective sheet 214 so that it protrudes in the Z direction. In the planar light source 211, one region enclosed by the Z-direction peaks of the bent portions 214b corresponds to one light-emitting region 211s. The light-emitting region 211s corresponds to the light-emitting region 111s in Figure 2.

[0048] The light-reflective sheet 214 is formed using a resin sheet containing numerous air bubbles (e.g., a foamed resin sheet) or a resin sheet containing a light-diffusing material. The resins used in the light-reflective sheet 214 are thermoplastic resins such as acrylic resin, polycarbonate resin, cyclic polyolefin resin, polyethylene terephthalate resin, or polyester resin, or thermosetting resins such as epoxy resin or silicone resin. The light-diffusing material used in the light-reflective sheet 214 is titanium dioxide, silica, alumina, zinc oxide, or glass.

[0049] Each light source 216 includes a light-emitting element 216a and a wavelength conversion member 216b. The light-emitting element 216a is electrically connected to the substrate 113. The wavelength conversion member 216b is provided covering the side and top surfaces of the light-emitting element 216a. Note that the planar light sources 111 and 211 are not limited to the structures shown in Figures 3, 4A, and 4B, as long as the light-emitting regions are arranged in a matrix in a two-dimensional structure.

[0050] (Light-emitting area of ​​backlight device) Figure 5 shows an example of a rectangular region in the backlight device 110 of Figure 1, each containing multiple light-emitting regions 111s that emit light simultaneously. For example, the backlight device 110 can be divided into three rectangular regions 110z0, 110z1, and 110z2 arranged in the Y direction. In the following description, when the rectangular regions 110z0, 110z1, and 110z2 are described without distinction, they will also be referred to as rectangular region 110z. The backlight drive circuit 150 in Figure 1 controls the emission of light from the light source 116 for each rectangular region 110z. Each rectangular region 110z is an example of a light-emitting section.

[0051] Each rectangular region 110z contains at least one row of light-emitting regions 111s. In the example shown in Figure 5, the backlight device 110 is divided into three rectangular regions 110z, each rectangular region 110z containing three rows of light-emitting regions 111s arranged in a planar manner. Hereinafter, the rectangular region 110z located furthest to the +Y side of the three rectangular regions 110z will also be referred to as the "upper region 110z0". The rectangular region 110z located on the -Y side of the upper region 110z0 will also be referred to as the "middle region 110z1". The rectangular region 110z located on the -Y side of the middle region 110z1 will also be referred to as the "lower region 110z2".

[0052] In Figure 5, an example is shown where each rectangular region 110z includes multiple light-emitting regions 111s of the planar light source 111 shown in Figure 2. However, a light guide plate may be placed in each of the three rectangular regions 110z, and an edge-lit LED module may be placed as a light source at one end of each light guide plate in the X direction. In this case, the backlight drive circuit 150 performs a scan drive to sequentially light up the three LED modules. The three light guide plates, each corresponding to one of the three LED modules, function as light-emitting units that direct light from the LED modules toward the liquid crystal panel 120.

[0053] The number of rectangular regions 110z in the backlight device 110, and the number and number of rows of light-emitting regions 111s included in each rectangular region 110z, are not limited to the above numbers. For example, the number of rectangular regions 110z in the backlight device 110 may be four or more, and the number of rows of light-emitting regions 111s included in each rectangular region 110z may be one or more. Furthermore, the multiple rows of light-emitting regions 111s included in each rectangular region 110z may not only be arranged together as shown in Figure 5, but may also be distributed in the Y direction. For example, if the row at the end in the +Y direction is the 1st row and the row at the end in the -Y direction is the 9th row, then rectangular region 110z0 may be arranged in the 1st, 4th, and 7th rows, rectangular region 110z1 may be arranged in the 2nd, 5th, and 8th rows, and rectangular region 110z2 may be arranged in the 3rd, 6th, and 9th rows. Furthermore, each rectangular region 110z0-110z2 may be distributed in the Y direction in one row, or it may be distributed in the Y direction in multiple rows.

[0054] Furthermore, for example, it is possible to make each of the light-emitting regions 111s a rectangular region and control the illumination of each light-emitting region 111s independently. However, the more rectangular regions there are, the more wiring is required, and the circuit size of the backlight drive circuit 150 and its peripheral circuits increases with the increase in the number of wires.

[0055] (Block diagram of a liquid crystal display device) Figure 6 is a block diagram showing an example of the liquid crystal display device 100 shown in Figure 1. In Figure 6 and subsequent figures, data lines that transmit video data for displaying images on the liquid crystal panel 120 are omitted, and signal lines that transmit various control signals and power lines that supply various voltages are shown as solid lines. The direction of the arrows on the signal lines indicates the direction of signal transmission, and the direction of the arrows on the power lines indicates the direction of current flow.

[0056] As shown in Figure 1, the liquid crystal display device 100 includes a backlight device 110, a liquid crystal panel 120, a liquid crystal driving circuit 130, and a control circuit 140. The backlight device 110 includes a planar light source 111, a backlight driving circuit 150, an illumination stop circuit 161, and an illumination circuit 162. The illumination stop circuit 161 and the illumination circuit 162 are peripheral circuits of the backlight driving circuit 150 and are mounted, for example, on the substrate 113 in Figure 3. Note that the illumination stop circuit 161 may be included in the backlight driving circuit 150, or both the illumination stop circuit 161 and the illumination circuit 162 may be included in the backlight driving circuit 150.

[0057] Figure 6 shows an example in which, for the sake of simplicity, each of the upper region 110z0, middle region 110z1, and lower region 110z2 of the planar light source 111 has three light-emitting regions 111s arranged in the lateral direction. That is, each of the upper region 110z0, middle region 110z1, and lower region 110z2 has three light sources 116 arranged in the lateral direction. In Figure 6, the optical member 112 placed between the planar light source 111 and the liquid crystal panel 120 is omitted from the description.

[0058] When operating the liquid crystal panel 120, the control circuit 140 outputs a vertical synchronization signal Vsync, which is a synchronization signal that determines the duration of one frame of the liquid crystal panel 120, at each frame period. The vertical synchronization signal Vsync is also supplied to the backlight drive circuit 150. Although not shown in the figures, the control circuit 140 may also output control signals other than the vertical synchronization signal Vsync to the liquid crystal drive circuit 130 or the backlight device 110. In this case, the control circuit 140 and the liquid crystal drive circuit 130 or the backlight device 110 may be connected via a serial interface such as SPI (Serial Peripheral Interface) that transmits multiple control signals.

[0059] The backlight drive circuit 150 generates a scan synchronization signal Sync_VS asynchronously with respect to the vertical synchronization signal Vsync. The backlight drive circuit 150 generates a scan signal Sync_VS0 in synchronization with the scan synchronization signal Sync_VS to control the lighting of the light source 116 in the upper region 110z0, and outputs the generated scan signal Sync_VS0 to the lighting circuit 162. Thus, the scan synchronization signal Sync_VS is generated asynchronously with respect to the vertical synchronization signal Vsync and is a synchronization signal used to control the lighting and extinguishing of the light source 116 of the planar light source 111.

[0060] The backlight drive circuit 150 generates a scan signal Sync_VS1 that controls the illumination of the light source 116 in the middle region 110z1 in synchronization with the scan synchronization signal Sync_VS, and outputs the generated scan signal Sync_VS1 to the illumination circuit 162. The backlight drive circuit 150 also generates a scan signal Sync_VS2 that controls the illumination of the light source 116 in the lower region 110z2 in synchronization with the scan synchronization signal Sync_VS, and outputs the generated scan signal Sync_VS2 to the illumination circuit 162. In the following, when the scan signals Sync_VS0, Sync_VS1, and Sync_VS2 are described without distinction, they will also be referred to as scan signal Sync_VSi.

[0061] Furthermore, the backlight drive circuit 150 outputs a cutoff signal OFF to the light-off circuit 161, which stops the illumination of the light source 116 in all rectangular regions 110z of the planar light source 111. The backlight drive circuit 150 holds a value indicating the period P for which the cutoff signal OFF is output and a value indicating the period T for which the cutoff signal OFF is output. Then, the backlight drive circuit 150 generates a cutoff signal OFF having an output period indicated by period P and an output period indicated by period T, in synchronization with the scan synchronization signal Sync_VS.

[0062] Furthermore, the backlight drive circuit 150 controls the voltage of source line S0 connected to the light source 116 of the first column (leftmost column) of the planar light source 111. The backlight drive circuit 150 controls the voltage of source line S1 connected to the light source 116 of the second column (center column) of the planar light source 111. The backlight drive circuit 150 controls the voltage of source line S2 connected to the light source 116 of the last column (rightmost column) of the planar light source 111. Source lines S1, S2, and S3 function as power lines connected to a low-level line set to a low level via the backlight drive circuit 150. The voltage of the low-level line may be 0V or a voltage slightly higher than 0V (for example, 0.1V to 0.5V).

[0063] The backlight drive circuit 150 may receive a vertical synchronization signal Vsync generated for each frame of the liquid crystal panel 120, and brightness information (not shown) indicating the brightness distribution of the image displayed on the liquid crystal panel 120. The backlight drive circuit 150 may also have a brightness adjustment unit that adjusts the brightness in synchronization with the vertical synchronization signal Vsync at predetermined intervals of light-emitting areas 111s or rectangular areas 110z, according to the image displayed on the liquid crystal panel 120 for each frame.

[0064] As a result, the backlight drive circuit 150 can perform local dimming control even when the light sources 116 in the upper region 110z0, middle region 110z1, and lower region 110z2 are lit without synchronization with the vertical synchronization signal Vsync. The vertical synchronization signal Vsync is a synchronization signal used for controlling the output of video data to the liquid crystal panel 120 every frame, and for controlling the brightness of the light sources 116 of the planar light source 111 in accordance with the video data every frame.

[0065] The lighting stop circuit 161 disconnects the connection between power line VLED, which is a current source, and power line VLED1 while it receives an active level (e.g., low level) OFF cutoff signal from the cutoff control unit 153. The lighting stop circuit 161 connects power line VLED to power line VLED1 while it receives an inactive level (e.g., high level) OFF cutoff signal from the cutoff control unit 153. Power line VLED is a current source for the planar light source 111.

[0066] The illumination stop circuit 161 then stops the illumination of all rectangular regions 110z of the planar light source 111 for one or more cycles of the scan synchronization signal Sync_VS each time a predetermined number of scan synchronization signals Sync_VS are generated. Here, the number of cycles for which the illumination of all rectangular regions 110z is stopped is less than the predetermined number of cycles of the scan synchronization signal Sync_VS. Therefore, each time a predetermined number of scan synchronization signals Sync_VS are generated, the rectangular region 110z is turned off for one or more cycles and turned on for the remaining predetermined number of cycles. The operation of stopping the illumination of all rectangular regions 110z by the cutoff signal OFF is explained in Figures 9 and 10.

[0067] The lighting circuit 162 connects power line VLED1 to power line VLED20 while receiving an active-level scan signal Sync_VS0, and disconnects power line VLED1 and power line VLED20 while receiving an inactive-level scan signal Sync_VS0. Power line VLED20 is connected to the light source 116 in the upper region 110z0.

[0068] The lighting circuit 162 connects power line VLED1 to power line VLED21 while receiving an active-level scan signal Sync_VS1, and disconnects power line VLED1 and power line VLED21 while receiving an inactive-level scan signal Sync_VS1. Power line VLED21 is connected to the light source 116 in the central region 110z1.

[0069] The lighting circuit 162 connects power line VLED1 to power line VLED22 while receiving an active-level scan signal Sync_VS2, and disconnects power line VLED1 and power line VLED22 while receiving an inactive-level scan signal Sync_VS2. Power line VLED22 is connected to the light source 116 included in the lower region 110z2. For example, the active level of the scan signal Sync_VSi is a low level, and the inactive level of the scan signal Sync_VSi is a high level.

[0070] The liquid crystal drive circuit 130 outputs various control signals CNTL to the liquid crystal panel 120 each time it receives a vertical synchronization signal Vsync from the control circuit 140, and displays one frame of image on the liquid crystal panel 120 in synchronization with the vertical synchronization signal Vsync.

[0071] (Circuit block diagram of the backlight device) Figure 7 is a circuit block diagram showing an example of the backlight device 110 in Figure 6. In the following explanation, we will assume that the light-emitting elements 116a included in each light source 116 of the planar light source 111 in Figure 6 are LEDs.

[0072] In the planar light source 111, the three light-emitting elements 116a in the upper region 110z0 have their anodes connected to the power line VLED20 and their cathodes connected to one of the source lines S0, S1, or S2, respectively. The three light-emitting elements 116a in the middle region 110z1 have their anodes connected to the power line VLED21 and their cathodes connected to one of the source lines S0, S1, or S2, respectively. The three light-emitting elements 116a in the lower region 110z2 have their anodes connected to the power line VLED22 and their cathodes connected to one of the source lines S0, S1, or S2, respectively.

[0073] The lighting stop circuit 161 includes a resistor R20 and a switch SW21 arranged in series between the power line VLED and the ground line VSS, and a switch SW22 arranged between the power line VLED and VLED1. Switch SW22 is an example of a second switch. For example, switch SW21 is an n-channel MOS (Metal Oxide Semiconductor) transistor, and switch SW22 is a p-channel MOS transistor.

[0074] Switch SW21 turns on when it receives a high-level cutoff signal OFF at its gate, supplying a low level to the gate of switch SW22 and turning on switch SW22. When switch SW22 is on, power line VLED is connected to power line VLED1. Switch SW21 turns off when it receives a low-level cutoff signal OFF at its gate. While switch SW21 is off, a high level is supplied to the gate of switch SW22 from power line VLED via resistor R20, and switch SW22 is turned off. When switch SW22 is off, power line VLED1 becomes floating.

[0075] The lighting circuit 162 includes resistors R100, R101, R110, R111, R120, and R121, and switches SW10, SW11, and SW12 that supply current to the planar light source 111, respectively. Switches SW10, SW11, and SW12 are examples of first switches.

[0076] For example, switches SW10, SW11, and SW12 are p-channel MOS transistors. Switch SW10 is placed between power lines VLED1 and VLED20. Switch SW11 is placed between power lines VLED1 and VLED21. Switch SW12 is placed between power lines VLED1 and VLED22.

[0077] Resistors R100 and R101 are placed in series between the power line VLED1 and the scan signal line Sync_VS0. Resistors R110 and R111 are placed in series between the power line VLED1 and the scan signal line Sync_VS1. Resistors R120 and R121 are placed in series between the power line VLED1 and the scan signal line Sync_VS2.

[0078] The gate of switch SW10 is connected to the connection nodes of resistors R100 and R101, connected to the power line VLED1 via resistor R100, and connected to the scan signal line Sync_VS0 via resistor R101. The gate of switch SW11 is connected to the connection nodes of resistors R110 and R111, connected to the power line VLED1 via resistor R110, and connected to the scan signal line Sync_VS1 via resistor R111. The gate of switch SW12 is connected to the connection nodes of resistors R120 and R121, connected to the power line VLED1 via resistor R120, and connected to the scan signal line Sync_VS2 via resistor R121.

[0079] Switch SW10 turns on when the cutoff signal OFF is set to a high level and the scan signal Sync_VS0 is set to a low level, connecting the anodes of the three light-emitting elements 116a in the upper region 110z0 to the power line VLED. Switch SW11 turns on when the cutoff signal OFF is set to a high level and the scan signal Sync_VS1 is set to a low level, connecting the anodes of the three light-emitting elements 116a in the middle region 110z1 to the power line VLED. Switch SW12 turns on when the cutoff signal OFF is set to a high level and the scan signal Sync_VS2 is set to a low level, connecting the anodes of the three light-emitting elements 116a in the lower region 110z2 to the power line VLED.

[0080] A light-emitting element 116a, whose anode is connected to the power line VLED, lights up when a current flows from the anode to the cathode when the source line S0, S1, or S2 connected to the cathode is set to a low level (for example, the ground voltage VSS). For example, in this embodiment, each of the light-emitting elements 116a in the upper region 110z0, the middle region 110z1, and the lower region 110z2 is lit exclusively when all source lines S0-S2 are set to a low level by the drive signal generation unit 151 and one of the scan signals Sync_VSi is set to a low level.

[0081] On the other hand, when the scan signal Sync_VS0 is set to a high level, switch SW10 turns off regardless of the level of the cutoff signal OFF, stopping the supply of current to the three light-emitting elements 116a in the upper region 110z0. When the scan signal Sync_VS1 is set to a high level, switch SW11 turns off regardless of the level of the cutoff signal OFF, stopping the supply of current to the three light-emitting elements 116a in the middle region 110z1. When the scan signal Sync_VS2 is set to a high level, switch SW12 turns off regardless of the level of the cutoff signal OFF, stopping the supply of current to the three light-emitting elements 116a in the lower region 110z2.

[0082] Furthermore, when the cutoff signal OFF is set to a low level, the power line VLED1 connected to the source of switches SW10, SW11, and SW12 becomes floating. As a result, power lines VLED20, VLED21, and VLED22 also become floating, and the supply of current to all light-emitting elements 116a of the planar light source 111 is stopped. Therefore, when the cutoff signal OFF is set to a low level, the light-emitting elements 116a in the upper region 110z0, the middle region 110z1, and the lower region 110z2 all turn off simultaneously, regardless of the levels of the scan signals Sync_VS0, Sync_VS1, and Sync_VS2.

[0083] The backlight drive circuit 150 includes a drive signal generation unit 151, a storage unit 152, and a cutoff control unit 153. The drive signal generation unit 151 asynchronously generates a scan synchronization signal Sync_VS, which is a reference signal for operating the backlight device 110, relative to the vertical synchronization signal Vsync used for the operation of the liquid crystal panel 120.

[0084] The drive signal generation unit 151 performs scan driving in synchronization with the scan synchronization signal Sync_VS, and within one cycle of the scan synchronization signal Sync_VS, it exclusively sets the scan signals Sync_VS0, Sync_VS1, and Sync_VS2 to low levels in sequence. As a result, when the cutoff signal OFF is set to a high level and the power line VLED1 is set to the power supply voltage VLED, the switches SW10, SW11, and SW12 of the lighting circuit 162 are sequentially turned on within one cycle of the scan synchronization signal Sync_VS.

[0085] Furthermore, the drive signal generation unit 151 performs control to connect source lines S0-S2, which are connected to the cathodes of the light-emitting elements 116a of the planar light source 111, to the low-level line, and control to disconnect the source lines S0-S2 from the low-level line. The drive signal generation unit 151 sequentially generates scan signals Sync_VS0, Sync_VS1, and Sync_VS2 in synchronization with the scan synchronization signal Sync_VS, and can control the lighting and extinguishing of each light-emitting element 116a by connecting or disconnecting the source lines S0-S2 from the low-level line. As described above, the voltage of the low-level line may be 0V or a voltage slightly higher than 0V.

[0086] For example, the brightness of the light-emitting region 111s due to the illumination of the light-emitting element 116a can be adjusted by changing the time (duty cycle) for setting the corresponding source lines S0-S2 to a low level for each ON period of each scan signal Sync_VS0, Sync_VS1, and Sync_VS2, thereby changing the amount of current flowing to the light-emitting element 116a per unit time. For example, the drive signal generation unit 151 may change the low-level period per unit time of each source line S0-S2 by PWM (Pulse Width Modulation) control. This makes it possible to perform local dimming control, which controls the illumination period (i.e., brightness) for each predetermined number of light-emitting elements 116a in accordance with the image displayed on the liquid crystal panel 120.

[0087] As shown in Figure 2, if the planar light source 111 has N rows and M columns of light-emitting regions 111s, and as shown in Figure 5, each of the three rectangular regions 110z of the planar light source 111 has three rows of light-emitting regions 111s, then 16 source lines S0-S15 (not shown) corresponding to the M columns are connected between the planar light source 111 and the backlight drive circuit 150. In addition, each power line VLED20, VLED21, and VLED22 are connected to the anodes of the 48 light-emitting elements 116a in the corresponding rectangular region 110z.

[0088] The memory unit 152 has a ROM (Read Only Memory) or fuse, etc., that holds the period P and the period T. For example, the period P and the period T are written to the memory unit 152 when the backlight device 110 is manufactured or before the backlight device 110 is shipped.

[0089] The cutoff control unit 153 generates a cutoff signal OFF in synchronization with the scan synchronization signal Sync_VS, having an output period indicated by a period P held in the storage unit 152 and an output period indicated by a period T held in the storage unit 152. An example of the circuit block of the cutoff control unit 153 is shown in Figure 8, and examples of the waveform of the cutoff signal OFF are shown in Figures 9 and 10.

[0090] By generating the OFF cutoff signal within the backlight device 110, even when different types of backlight devices 110 are mounted on the liquid crystal display device 100, the flicker reduction operation of the planar light source 111, as described in Figure 9, can be appropriately performed for each backlight device 110. In other words, flicker reduction can be achieved for each backlight device 110 without having to incorporate a function to reduce the flicker of the planar light source 111 into the control circuit 140.

[0091] Figure 8 is a circuit block diagram showing an example of the cutoff control unit 153 in Figure 7. The cutoff control unit 153 includes a counter 154 and a cutoff signal output unit 155. The counter 154 counts in synchronization with the scan synchronization signal Sync_VS and outputs the number of pulses of the scan synchronization signal Sync_VS as the counter value CNT. The counter 154 is reset when the rising edge of the cutoff signal OFF is received at the reset terminal RST, and the counter value CNT is initialized to, for example, "0". The counter 154 is also initialized when the liquid crystal display device 100 or the backlight device 110 is started up.

[0092] The cutoff signal output unit 155 sets the cutoff signal OFF to the active level (low level) for a period T when the counter value CNT from the counter 154 becomes the value obtained by subtracting the period T from the period P. Here, the period T is indicated by the period of the scan synchronization signal Sync_VS.

[0093] For example, when the period T is "1", the cutoff signal output unit 155 sets the cutoff signal OFF to a low level, which is the active level, for the duration of one cycle of the scan synchronization signal Sync_VS. When the period T is "2", the cutoff signal OFF is set to a low level, which is the duration of two cycles of the scan synchronization signal Sync_VS. When the period T has elapsed, the cutoff signal output unit 155 returns the cutoff signal OFF to a high level, which is the inactive level.

[0094] (Operating timing of liquid crystal display) Figure 9 is a timing diagram showing an example of the operation of the liquid crystal display device 100 in Figure 1. For example, the operation shown in Figure 9 is realized by implementing a control method for the backlight device 110. Figure 9 shows an example in which motion blur countermeasures are implemented and the period P is set to "3" and the period T is set to "1" in order to prevent flickering.

[0095] The liquid crystal drive circuit 130 shown in Figure 6 displays an image on the liquid crystal panel 120 at one-frame intervals corresponding to the period of the vertical synchronization signal Vsync, which is a positive pulse signal. For example, an image is displayed on the liquid crystal panel 120 in each of frames 1 through 6. The drive signal generation unit 151 connects the source lines S0-S2 in Figure 7 to the low-level lines for at least the period during which an image is displayed on the liquid crystal panel 120 (at least 6 frames in Figure 9).

[0096] In the power lines VLED1, VLED20, VLED21, and VLED22 shown in Figure 9, solid lines indicate that power voltage is being supplied, and dashed lines indicate that the LEDs are floating. In the upper region 110z0, middle region 110z1, and lower region 110z2 shown in Figure 9, rectangles indicate that the light-emitting element 116a is lit, and areas without rectangles indicate that the light-emitting element 116a is off.

[0097] The drive signal generation unit 151 in Figure 7 repeatedly generates a scan synchronization signal Sync_VS, which is a positive pulse signal, asynchronously with respect to the vertical synchronization signal Vsync. In the example shown in Figure 9, the drive signal generation unit 151 generates the scan synchronization signal Sync_VS at a period shorter than the period of the vertical synchronization signal Vsync. Within one period of the scan synchronization signal Sync_VS, the drive signal generation unit 151 sequentially generates scan signals Sync_VS0, Sync_VS1, and Sync_VS2, each having a negative pulse, without overlapping negative pulses.

[0098] The cutoff control unit 153 outputs a high-level cutoff signal OFF while the counter value CNT is less than "period P - period T" ("0" or "1"). When the counter value CNT becomes "period P - period T" (i.e., "2"), the cutoff control unit 153 sets the cutoff signal OFF to a low level. The cutoff control unit 153 maintains the cutoff signal OFF at a low level for the number of cycles of the scan synchronization signal Sync_VS indicated by period T ("1"), and then returns the cutoff signal OFF to a high level. The counter 154 resets the counter value CNT to "0" in response to the change in the cutoff signal OFF to a high level.

[0099] The lighting stop circuit 161 turns on switch SW22 and supplies power voltage VLED to power line VLED1 when the cutoff signal OFF is at a high level. The lighting stop circuit 161 turns off switch SW22 and sets power line VLED1 to a floating state when the cutoff signal OFF is at a low level.

[0100] The lighting circuit 162 sequentially connects power line VLED1 to power lines VLED20, VLED21, and VLED22 during the low-level periods of scan signals Sync_VS0, Sync_VS1, and Sync_VS2 while power line VLED1 is connected to power line VLED. As a result, power lines VLED20, VLED21, and VLED22 are sequentially connected to power line VLED via power supply voltage VLED1, and the corresponding light-emitting elements 116a in the upper region 110z0, middle region 110z1, and lower region 110z2 are sequentially lit.

[0101] The lighting circuit 162 sets power lines VLED20, VLED21, and VLED22 to a floating state, regardless of the levels of scan signals Sync_VS0, Sync_VS1, and Sync_VS2, while the cutoff signal OFF is set to a low level and power line VLED1 is in a floating state. Therefore, while the cutoff signal OFF is at a low level, all light-emitting elements 116a of the planar light source 111 are turned off, regardless of the levels of scan signals Sync_VS0, Sync_VS1, and Sync_VS2.

[0102] The cutoff signal OFF and the scan signals Sync_VS0, Sync_VS1, and Sync_VS2 are generated in synchronization with the scan synchronization signal Sync_VS. The low-level period of the cutoff signal OFF coincides with the period of one cycle of the scan synchronization signal Sync_VS, indicated by period T. Therefore, the falling and rising edges of the cutoff signal OFF do not appear during the low-level period (active period) of the scan signals Sync_VS0, Sync_VS1, and Sync_VS2.

[0103] Therefore, the illumination period of each light-emitting element 116a can be prevented from being shortened by the low level of the cutoff signal OFF, and the illumination period of all light-emitting elements 116a can be kept constant. In other words, it is possible to prevent the illumination period of the light-emitting elements 116a from being shorter than the low-level period of the scan signals Sync_VS0, Sync_VS1, and Sync_VS2. Since variations in the illumination period of the light-emitting elements 116a can be prevented, flickering in each rectangular region 110z can be reduced.

[0104] When the cutoff signal OFF is fixed at a high level, for example, one or both of the period P and duration T are set to "0". When the cutoff signal OFF is fixed at a high level, the scan signals Sync_VS0, Sync_VS1, and Sync_VS2 are set to low levels exclusively in sequence, and the light-emitting elements 116a in the corresponding upper region 110z0, middle region 110z1, and lower region 110z2 are lit exclusively in sequence without being turned off simultaneously.

[0105] Figure 10 is a timing diagram showing another example of the operation of the liquid crystal display device 100 in Figure 1. Detailed explanations of the same operation as in Figure 9 are omitted. For example, the operation shown in Figure 10 is achieved by implementing a control method for the backlight device 110. Figure 10 shows an example in which motion blur countermeasures are implemented and the period P is set to "5" and the duration T is set to "2" in order to prevent flickering. The waveforms of the number of frames, vertical sync signal Vsync, scan sync signal Sync_VS and scan signals Sync_VS0, Sync_VS1, and Sync_VS2 are the same as in Figure 9.

[0106] Similar to Figure 9, the drive signal generation unit 151 sequentially generates scan signals Sync_VS0, Sync_VS1, and Sync_VS2 within one cycle of the scan synchronization signal Sync_VS, without overlapping negative pulses. In addition, the drive signal generation unit 151 connects the source lines S0-S2 in Figure 7 to the low-level lines for at least the period during which an image is displayed on the liquid crystal panel 120.

[0107] The cutoff control unit 153 outputs a high-level cutoff signal OFF while the counter value CNT is less than the period P minus the period T ("0", "1", or "2"). When the counter value CNT reaches the period P minus the period T (i.e., "3"), the cutoff control unit 153 sets the cutoff signal OFF to a low level. The cutoff control unit 153 maintains the cutoff signal OFF at a low level for the number of cycles of the scan synchronization signal Sync_VS indicated by the period T ("2"), and then returns the cutoff signal OFF to a high level. The counter 154 resets the counter value CNT to "0" in response to the change in the cutoff signal OFF to a high level.

[0108] The lighting stop circuit 161 turns on switch SW22 and supplies power voltage VLED to power line VLED1 when the cutoff signal OFF is at a high level. The lighting stop circuit 161 turns off switch SW22 and sets power line VLED1 to a floating state when the cutoff signal OFF is at a low level.

[0109] As described above, similar to Figure 9, during the period when the cutoff signal OFF is at a high level, the scan signals Sync_VS0, Sync_VS1, and Sync_VS2 are sequentially set to low levels. Then, current flows sequentially to the light-emitting elements 116a in the upper region 110z0, middle region 110z1, and lower region 110z2 corresponding to the scan signals Sync_VS0, Sync_VS1, and Sync_VS2, causing the light-emitting elements 116a to light up sequentially. Also, during the period when the cutoff signal OFF is at a low level, regardless of the levels of the scan signals Sync_VS0, Sync_VS1, and Sync_VS2, all light-emitting elements 116a of the planar light source 111 are turned off.

[0110] In Figure 10, the falling and rising edges of the OFF cutoff signal do not appear during the low-level period (active period) of the scan signals Sync_VS0, Sync_VS1, and Sync_VS2. Therefore, the illumination period of the light-emitting element 116a is prevented from being shortened by the low level of the OFF cutoff signal, and the illumination period of all light-emitting elements 116a can be kept constant. Since variations in the illumination period are prevented, flickering in each rectangular region 110z can be reduced.

[0111] (Current flowing through the light-emitting element during scanning) Figure 11 is a waveform diagram showing an example of the current flowing through the light-emitting element 116a when scanning and driving each rectangular region 110z0, 110z1, and 110z2 of the planar light source 111 in Figure 6. During scanning, the light-emitting element 116a to be lit is selected by the combination of the anode connected to the power line VLED and the cathode connected to the low-level line. Then, the light-emitting element 116a whose anode is connected to the power line VLED and whose cathode is connected to the low-level line is lit.

[0112] In the scan drive shown in Figures 9 and 10, the light-emitting elements 116a in multiple rectangular regions 110z of the planar light source 111 are sequentially selected by the corresponding scan signal Sync_VSi, and current flows to the light-emitting elements 116a. As a result, the lighting and extinguishing of the light-emitting elements 116a in the rectangular regions 110z are periodically repeated without overlapping lighting periods. The number of rectangular regions 110z is also referred to as the number of scans.

[0113] Here, because the light-emitting element 116a blinks at a high speed (e.g., 480Hz or higher), the human eye perceives the light-emitting element 116a in the rectangular region 110z as being constantly lit. In reality, the illumination period of the light-emitting element 116a in the rectangular region 110z is 1 / 3 of the period of the scan synchronization signal Sync_VS.

[0114] Therefore, the average brightness of the light emitted from the light-emitting region 111s is 1 / 3 of the brightness in the case of DC (Direct Current) drive, where a constant DC current is passed through all light-emitting elements 116a to keep them constantly lit. In other words, the average brightness is "1 / (number of scans)". In order to make the brightness during scan drive the same as the brightness during DC drive, it is necessary to pass a current approximately the number of scans through the light-emitting elements 116a. For example, if the current during DC drive is "i" and the planar light source 111 is divided into three rectangular regions 110z (number of scans = 3), then it is necessary to pass a current of "3i" through each light-emitting element 116a.

[0115] (Example of flickering timing of a surface light source) Figure 12 is a timing diagram showing an example of the operation of a liquid crystal display device in which the scan synchronization signal Sync_VS is generated asynchronously with the vertical synchronization signal Vsync, and the cutoff signal OFF is generated synchronously with the vertical synchronization signal Vsync. Detailed explanations of the same operation as in Figure 9 are omitted. In the upper region 110z0, the middle region 110z1, and the lower region 110z2, the dashed rectangles indicate that even though the scan signals Sync_VS0, Sync_VS1, or Sync_VS2 are at a low level, the supply of current to the light-emitting element 116a is cut off by the low-level cutoff signal OFF, causing the light-emitting element 116a to turn off.

[0116] If the cutoff signal OFF is not synchronized with the scan synchronization signal Sync_VS, the falling and rising edges of the cutoff signal OFF will appear during the low-level period (active period) of the scan signals Sync_VS0, Sync_VS1, and Sync_VS2. This causes variations in the on-time and off-time of each rectangular region 110z of the planar light source 111, resulting in the planar light source 111 of the backlight device 110 appearing to flicker.

[0117] <Second Embodiment> (Block diagram of a liquid crystal display device) Figure 13 is a block diagram showing an example of a liquid crystal display device according to the second embodiment. Elements identical to those in Figure 6 are denoted by the same reference numerals, and detailed explanations are omitted. The general structure of the liquid crystal display device 100A shown in Figure 13 is the same as that in Figure 1. The structure of the planar light source 111 is the same as that in Figures 2 and 3, or the same as that in Figures 4A and 4B. The allocation of the rectangular region 110z of the planar light source 111 is the same as that in Figure 5.

[0118] The liquid crystal display device 100A includes a backlight device 110A, a liquid crystal panel 120, a liquid crystal driving circuit 130, and a control circuit 140A. The backlight device 110A includes a planar light source 111, a lighting stop circuit 161, a lighting circuit 162, and a backlight driving circuit 150A.

[0119] The backlight drive circuit 150A has a drive signal generation unit 151 that generates a scan synchronization signal Sync_VS, but does not have the storage unit 152 and cutoff control unit 153 shown in Figure 7. The backlight drive circuit 150A has the same functions as the backlight drive circuit 150 in Figure 7, except that it does not have the storage unit 152 and the cutoff control unit 153 that outputs the cutoff signal OFF.

[0120] The control circuit 140A includes a register 142 and a cutoff control unit 143. The register 142 holds a changeable period P and duration T. For example, the setting of period P and duration T to the cutoff control unit 143 is performed during the initialization process when the liquid crystal display device 100A is started up. This allows the period P and duration T to be reset, and the waveform of the cutoff signal OFF to be changed, for example, by changing the firmware of the liquid crystal display device 100A after the control circuit 140A has been designed or after the liquid crystal display device 100A has been shipped.

[0121] The period P and duration T may be set according to the electrical specifications, such as the voltage conditions, of the backlight device 110A mounted on the liquid crystal display device 100A, and the frequency of the scan signal Sync_VSi. This allows the light-emitting element 116a to be properly lit in accordance with the backlight device 110A mounted on the liquid crystal display device 100A.

[0122] The period P and duration T may be set in the storage unit 152 by the control circuit 140 according to the operating mode of the liquid crystal display device 100 set by the user or the like. Alternatively, the period P and duration T may be set in the storage unit 152 by instruction from the user viewing the screen of the liquid crystal display device 100. Furthermore, fixed values ​​may be set for each liquid crystal display device 100 for the period P and duration T.

[0123] The configuration of the cutoff control unit 143 is the same as that of the cutoff control unit 153 in Figure 8. The cutoff control unit 143 receives the scan synchronization signal Sync_VS from the drive signal generation unit 151 of the backlight drive circuit 150A and generates a cutoff signal OFF based on the period P and duration T held in the register 142. The cutoff control unit 143 outputs the generated cutoff signal OFF to the lighting stop circuit 161. The operation of the liquid crystal display device 100A is the same as the operation shown in Figures 9 to 11, except that the cutoff signal OFF is generated by the control circuit 140A.

[0124] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims.

[0125] In addition to the embodiments described above, the following further notes are disclosed. (Note 1) A backlight device located beneath the liquid crystal panel, Multiple light-emitting units, each having one or more light sources, A backlight drive circuit generates an asynchronous scan synchronization signal in response to the vertical synchronization signal generated for each frame period of the liquid crystal panel, and sequentially lights up the plurality of light-emitting units in synchronization with the generated scan synchronization signal. A backlight device having a lighting stop circuit that stops the lighting of the plurality of light-emitting units for one or more cycles of the scan synchronization signal. (Note 2) The system includes a first switch positioned between the light source and current source of each of the plurality of light-emitting units, which connects the corresponding light source to the current source during the active period of the scan signal generated by the backlight drive circuit for each of the plurality of light-emitting units in synchronization with the scan synchronization signal, The active periods of the scan signals corresponding to each of the plurality of light-emitting units do not overlap with each other. The backlight device according to Appendix 1, wherein the lighting stop circuit comprises a second switch positioned between the first switch corresponding to each of the plurality of light-emitting parts and the current source, and which is interrupted during one cycle or the plurality of cycles. (Note 3) The backlight device according to Appendix 1 or 2, further comprising a brightness adjustment unit that adjusts the brightness of each of the plurality of light-emitting units in synchronization with the vertical synchronization signal. (Note 4) Each of the plurality of light-emitting units has a plurality of the light sources, The backlight device according to any one of the appendices 1 to 3, wherein the multiple light sources of the multiple light-emitting units are arranged in two dimensions. (Note 5) A counter that counts the pulses of the scan synchronization signal, The system includes a cutoff signal output unit that outputs a cutoff signal to the lighting stop circuit for one or more cycles each time the counter counts a predetermined number, The lighting stop circuit stops the lighting of the plurality of light-emitting units while it is receiving the cutoff signal from the cutoff signal output unit, as described in any one of the appendices 1 to 4. (Note 6) A backlight device as described in any one of the appendices 1 to 5, A liquid crystal display device having a liquid crystal panel disposed on top of the backlight device. (Note 7) A backlight device as described in any one of the appendices 1 to 4, A liquid crystal panel placed on the backlight device, A liquid crystal driver circuit that drives the liquid crystal panel, The system includes a control circuit that generates the vertical synchronization signal to be output to the liquid crystal drive circuit and the backlight drive circuit, and receives the scan synchronization signal from the backlight drive circuit, The aforementioned control circuit is A counter that counts the pulses of the scan synchronization signal, The system includes a cutoff signal output unit that outputs a cutoff signal to the lighting stop circuit for one or more cycles each time the counter counts a predetermined number, The aforementioned illumination stop circuit stops the illumination of the plurality of light-emitting units while it is receiving the shut-off signal from the shut-off signal output unit, and is a liquid crystal display device. (Note 8) The liquid crystal display device according to Appendix 7, wherein the control circuit can change the predetermined number counted by the counter and the number of cycles, which is the output period of the cutoff signal, based on an external input. (Note 9) A control method for a backlight device having a plurality of light-emitting units, each having one or more light sources, which are positioned beneath a liquid crystal panel, The backlight drive circuit of the backlight device generates an asynchronous scan synchronization signal in response to the vertical synchronization signal generated for each frame period of the liquid crystal panel, and sequentially lights up the plurality of light-emitting units in synchronization with the generated scan synchronization signal. A control method for a backlight device, wherein the backlight device's illumination stop circuit stops the illumination of the plurality of light-emitting units for one or more cycles of the scan synchronization signal. [Explanation of symbols]

[0126] 100, 100A Liquid Crystal Display 110, 110A backlight device 110z0 Upper area (rectangular area) 110z1 Middle area (rectangular area) 110z2 Lower area (rectangular area) 111 Planar light source 111s Emitting Region 112 Optical components 113 circuit boards 115 Light guide member 116 Light source 116a Light-emitting element 120 LCD panel 120p pixels 130 LCD driving circuit 140, 140A control circuit 142 registers 143 Interruption Control Unit 150, 150A backlight driver circuit 151 Drive signal generation unit 152 Storage section 153 Interruption control unit 154 counter 155 Cutoff signal output section 161 Light-off circuit 162 Lighting Circuit 211 Planar light source 211s Emitting Region 216 Light source 216a Light-emitting element CNT counter value CNTL control signal OFF cutoff signal P period R20 Resistor R100, R101, R110, R111, R120, R121 Resistors RST Reset terminal S0, S1, S2 source lines SW10, SW11, SW12 switches SW21, SW22 switches Sync_VS scan synchronization signal Sync_VS0, Sync_VS1, Sync_VS2 scan signals T period VLED, VLED1 power supply wire VLED20, VLED21, VLED22 power line VSS ground wire Vsync Vertical synchronization signal

Claims

1. A backlight device located beneath the liquid crystal panel, A plurality of light-emitting units, each having one or more light sources, A backlight drive circuit generates an asynchronous scan synchronization signal in response to the vertical synchronization signal generated for each frame period of the liquid crystal panel, and sequentially lights up the plurality of light-emitting units in synchronization with the generated scan synchronization signal. A backlight device having a lighting stop circuit that stops the lighting of the plurality of light-emitting units for one or more cycles of the scan synchronization signal.

2. The system includes a first switch positioned between the light source and current source of each of the plurality of light-emitting units, which connects the corresponding light source to the current source during the active period of the scan signal generated by the backlight drive circuit for each of the plurality of light-emitting units in synchronization with the scan synchronization signal, The active periods of the scan signals corresponding to each of the plurality of light-emitting units do not overlap with each other. The backlight device according to claim 1, wherein the lighting stop circuit comprises a second switch positioned between the first switch corresponding to each of the plurality of light-emitting units and the current source, and which is interrupted during one cycle or the plurality of cycles.

3. The backlight device according to claim 1, further comprising a brightness adjustment unit that adjusts the brightness of each of the plurality of light-emitting units in synchronization with the vertical synchronization signal.

4. Each of the plurality of light-emitting units has a plurality of the light sources, The backlight device according to claim 1, wherein the multiple light sources of the multiple light-emitting units are arranged in a two-dimensional manner.

5. A counter that counts the pulses of the scan synchronization signal, The system includes a cutoff signal output unit that outputs a cutoff signal to the lighting stop circuit for one or more cycles each time the counter counts a predetermined number, The backlight device according to claim 1, wherein the lighting stop circuit stops the lighting of the plurality of light-emitting units while it is receiving the cutoff signal from the cutoff signal output unit.

6. A backlight device according to any one of claims 1 to 5, A liquid crystal display device having a liquid crystal panel disposed on top of the backlight device.

7. A backlight device according to any one of claims 1 to 4, A liquid crystal panel placed on the backlight device, A liquid crystal driver circuit that drives the liquid crystal panel, The system includes a control circuit that generates the vertical synchronization signal to be output to the liquid crystal drive circuit and the backlight drive circuit, and receives the scan synchronization signal from the backlight drive circuit, The aforementioned control circuit is A counter that counts the pulses of the scan synchronization signal, The system includes a cutoff signal output unit that outputs a cutoff signal to the lighting stop circuit for one or more cycles each time the counter counts a predetermined number, The aforementioned illumination stop circuit stops the illumination of the plurality of light-emitting units while it is receiving the shut-off signal from the shut-off signal output unit, and is a liquid crystal display device.

8. The liquid crystal display device according to claim 7, wherein the control circuit can change the predetermined number counted by the counter and the number of cycles, which is the output period of the cutoff signal, based on an external input.

9. A control method for a backlight device having a plurality of light-emitting units, each having one or more light sources, which are positioned beneath a liquid crystal panel, The backlight drive circuit of the backlight device generates an asynchronous scan synchronization signal in response to the vertical synchronization signal generated for each frame period of the liquid crystal panel, and sequentially lights up the plurality of light-emitting units in synchronization with the generated scan synchronization signal. A control method for a backlight device, wherein the backlight device's illumination stop circuit stops the illumination of the plurality of light-emitting units for one or more cycles of the scan synchronization signal.

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