KR100739758B1 - Back light unit for field sequential color LCD - Google Patents

Abstract

A backlight unit for a color sequential driving liquid crystal display device is disclosed.

The disclosed backlight unit is a backlight unit for a color sequential driving liquid crystal display device in which a liquid crystal panel is divided and driven into a plurality of panel regions, the backlight unit being disposed on a rear surface of the liquid crystal panel, A plurality of light sources provided to sequentially supply light; Disposed between the liquid crystal panel and the light source, and having a plurality of prisms formed in a light incidence plane facing the light source in a row parallel to the boundary between the divided backlight regions, the light supplied to one panel region is incident on the other panel region. It includes; diffusion plate to suppress that.

According to the above structure, color mixing of the liquid crystal display can be suppressed, and color reproducibility and color uniformity can be increased.

Description

Back light unit for field sequential color LCD

1 is a schematic cross-sectional view of a liquid crystal display device employing a backlight unit according to a preferred embodiment of the present invention.

FIG. 2 is a graph illustrating a division driving method employed in the liquid crystal display of FIG. 1.

3 is a schematic cross-sectional view of a liquid crystal display device employing a conventional backlight unit used in a comparative example showing that color mixing occurs.

4 is a schematic cross-sectional view of a backlight unit according to another exemplary embodiment of the present invention.

<Description of Symbols for Major Parts of Drawings>

10 ... Liquid crystal display device 11 ... LCD panel

20, 40 ... backlight unit 21 ... lamp

23,43 ... diffusion plate 23a, 43a ... transparent substrate

23b, 43b ... light transmissive surface 24,44 ... prism

25 ... Reflector 26 ... Home

27 ... optical sheet 29 ... chassis

P1, ..., P8 ... panel area B1, ..., B8 ... backlit area

R ... red G ... green

B ... blue

The present invention relates to a backlight unit for a color sequential driving liquid crystal display device, and more particularly, to a backlight unit for a color sequential driving liquid crystal display device in which generation of color mixing phenomenon is suppressed.

A liquid crystal display (LCD) displays an image by supplying a voltage to each pixel of a liquid crystal panel according to an input image signal and adjusting light transmittance of the pixels. The liquid crystal display (LCD) displays a laptop, a desktop computer, an LCD-TV, Used for mobile communication terminal.

In the liquid crystal display, a TFT-LCD using a thin film transistor as a switching element is mainly used. In the color implementation method, each pixel is, for example, red (R), green (G), and blue (B) to realize a color image. There is a spatial partitioning method for displaying any one of them, and a color sequential driving method in which all pixels display R, G, and B sequentially.

In the case of the color sequential driving method, the entire frame on the liquid crystal panel is divided into three subframes of R, G, and B, and the backlight unit includes the monochromatic light sources of R, G, and B, respectively. In other words, after scanning all the pixels according to the operation of the gate driver and the data driver, the R light source is turned on, and then the R light source is turned off, all the pixels are scanned again, the G light source is turned on, and finally the G light source is turned off. After scanning all the pixels once again, the G light source is turned on. When the colors are sequentially turned on as described above, the observer recognizes the synthesized color by integrating the displayed color for a predetermined time, so that the color can be expressed without the color filter.

On the other hand, in order to improve the brightness of the liquid crystal display and to implement a more accurate high-resolution video, a divided driving method for dividing the subframe into a plurality of panel regions and driving a light source for each panel region has been proposed. In the divided driving method, the liquid crystal panel is generally divided into N in the horizontal direction to drive the liquid crystal, and the light source corresponding to the panel region to which the liquid crystal reacts completely is driven.

In the case of the split driving method, since the liquid crystal panel and the light source are scanned with staggered times, the panel area before scanning maintains the color information of the previous subframe, and the light source also emits the previous color. That is, since the light sources may emit different colors at the same time zone by different panel areas, ideally, each light source should irradiate only the corresponding panel areas.

However, the backlight unit is designed so that the light emitted from the light source is spread over a wide angle for uniform brightness, so that the light of the light source that is turned on to display the color of the previous sub frame reaches the panel area where the image of the newly updated sub frame is formed. There is a problem that color mixing occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a backlight unit for a color sequential driving liquid crystal display device which makes the luminance uniform and suppresses color mixing.

In order to achieve the above object, a backlight unit for a color sequential driving liquid crystal display device according to the present invention is a backlight unit for a color sequential driving liquid crystal display device in which a liquid crystal panel is divided into a plurality of panel regions and sequentially driven.

A plurality of light sources disposed on a rear surface of the liquid crystal panel and provided in a plurality of backlight regions divided by the divided panel regions to sequentially supply light; The light supplied to another panel is disposed between the liquid crystal panel and the light source and includes a plurality of prisms formed on a light incident surface facing the light source in a row parallel to the boundary between the divided backlight regions. It characterized in that it comprises a; diffusion plate for suppressing incident to the area.

Hereinafter, a backlight unit for a color sequential driving liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 illustrates a liquid crystal display device 10 employing a backlight unit 20 according to an exemplary embodiment of the present invention.

Referring to the drawings, the liquid crystal display device 10 includes a liquid crystal panel 11 divided into N panel regions P1, P2, ..., PN, and respective panel regions P1, P2, ..., And a backlight unit 20 divided to correspond to the PN to supply light. Hereinafter, the case where N = 8 will be described as an example.

The liquid crystal panel 11 displays an image by determining an arrangement direction of liquid crystals according to whether voltage is applied and adjusting the amount of emitted light with respect to incident light in each pixel unit.

The backlight unit 20 includes a plurality of light sources 21 for supplying light to the liquid crystal panel 11, a diffuser sheet 23 for evenly diffusing the light emitted from the light source 21, and a light source 21. Reflecting plate 25 for reflecting the light emitted from the light into the diffuser plate (23). In addition, the backlight unit 20 further includes an optical sheet 27 made of a prism sheet or the like to improve brightness and viewing angle. The optical sheet 27, the diffusion plate 23, the light source 21, and the reflecting plate 25 are sequentially disposed on the rear surface of the liquid crystal panel 11. Reference numeral 29 denotes a chassis in which the light source 21 and the reflector 25 are provided.

The light source 21 is a monochromatic light source, and each monochromatic light source displays one of R, G, and B colors. For example, the light source 21 may be a light emitting diode. In the backlight unit 20 of the present invention, the light source 21 is disposed on the rear side of the liquid crystal panel 11 in a direct manner.

The backlight unit 20 is divided into first to eighth backlight areas B1, B2,..., And B8 facing the divided first to eighth panel areas P1, P2,..., And P8. Divided. Accordingly, the light source 21 includes first to eighth sub light sources 21a, 21b, ..., 21h respectively positioned in the first to eighth backlight areas B1, B2, ..., B8. The first to eighth sub light sources 21a, 21b, ..., 21h are sequentially driven in accordance with the driving of the first to eighth panel areas P1, P2, ..., P8.

The diffusion plate 23, which is one feature of the present invention, is disposed between the liquid crystal panel 11 and the light source 21, and spreads the light emitted from the light source 21 evenly therein, thereby providing brightness of the liquid crystal panel 11. It is made uniform and suppresses that light supplied to one panel area is incident to another panel area as will be described later.

Referring to an enlarged view in which a part of the diffusion plate 23 of FIG. 1 is enlarged, the diffusion plate 23 is a light incident surface formed by forming a plate-shaped transparent substrate 23a and a plurality of prisms 24 in a row ( 23b). The light incident surface 23b means a surface facing the light source 21 of the diffusion plate 23.

As the light transmissive substrate 23a, for example, a synthetic resin such as acrylic or polycarbonate (PC) can be used. The diffusion plate 23 can cause light diffusion by forming a diffusion layer for uniformly diffusing light on the light exit surface of the light transmissive substrate 23a or by including a diffuser or air bubbles in the light transmissive substrate 23a.

The prisms 24 are formed on the light incident surface 23b in a row in parallel with the boundary D between the backlight regions B1, B2, ..., B8. For example, when the panel areas P1, P2, ..., P8 are divided in the horizontal direction when viewed from the front of the liquid crystal panel 11, the backlight areas B1, B2, ..., B8 also correspond to this. Split in the horizontal direction. Accordingly, when viewed from the front of the liquid crystal panel 11, the boundary D also becomes a virtual line in the horizontal direction, and the prism 24 is also formed long in the horizontal direction parallel to the boundary D. FIG.

Prism 24 prevents light emitted from a light source in a particular backlight region from entering a panel region other than the panel region opposite the particular backlight region. For example, the prism 24 may have a panel other than the eighth panel region P8 in which light emitted from the eighth sub light source 21h in the eighth backlight region B8 is opposite to the eighth backlight region B8. To prevent it from entering the area. To this end, the peaks and valleys of the prism 24 must be sufficiently inclined. For example, the angle θ between the peak and the valley of the prism 24 is preferably about 90 to 110 degrees. In addition, the pitch interval w of the prism 24 is preferably larger than the wavelength of the incident light so that light can be sufficiently incident into the diffuser plate 23, for example, may be about 50 μm. In this case, the height h of the prism 24 is about 15 μm to 25 μm. Since the prism 24 serves to prevent the light reflected from the light incident surface 23b from spreading far away, the tip 24a of the peak of the prism 24 and the tip 24b of the valley are as shown in the cross section. It may be angular or round. In addition, the shape of the prism 24 in the present embodiment is shown as a cross-sectional shape of an isosceles triangle, but is not limited thereto. A shape of a right triangle may be employed.

The reflecting plate 25 is disposed between the light source 21 and the chassis 29, and the surface of the light source 21 side is preferably a mirror reflection surface for reflecting light as it is or a diffuse reflection surface for diffusing and reflecting light. The reflective plate 25 may have a structure in which a plurality of grooves 26 are formed in the flat plate. The groove 26 has a bottom surface 26a and an inclined surface 26a, and the bottom surface 26a and the inclined surface 26a form part of the reflecting plate 25. The groove 26 is formed in parallel with the boundary D between the backlight regions B1, B2, ..., B8 whose longitudinal direction is divided. In addition, at least one groove 26 is formed for each backlight area B1, B2, ..., B8, and each of the corresponding sub light sources 21a, 21b, ..., 21h is formed in the groove 26. Are arranged in rows on the bottom surface 26a of the substrate. The irradiation area of the light source 21 arranged in the groove 26 varies depending on the depth of the bottom surface 26a of the groove 26 and the inclination of the inclined surface 26b. Therefore, the groove 26 has a depth of the bottom surface 26a such that the irradiation area of the light emitted from each of the sub light sources 21a, 21b, ..., 21h is limited to the corresponding backlight area or the backlight area adjacent thereto. And the inclination of the inclined surface 26b. For example, the groove 26 may irradiate all of the first backlight area B1 corresponding to the first sub light source 21a from the back of the diffuser plate from the light emitted from the first sub light source 21a. It is preferable to have a depth of the bottom surface 26a and an inclination of the inclined surface 26b to the extent that the seventh or eighth backlight regions B7 and B8 far from the first backlight region B1 cannot be irradiated. Depending on the way of division driving, the irradiation area of the light source 21 may be wider. For example, the structure in which the groove 26 is formed is an example of the reflective plate 25, but is not limited thereto.

Hereinafter, the principle of preventing color mixing in the diffusion plate 23 according to the preferred embodiment of the present invention having the above-described structure will be described.

2 is a graph showing a division driving method employed in the above-described liquid crystal display device. The vertical axis of FIG. 2 (a) corresponds to the eight divided panel regions P1, P2, ..., P8, and the vertical axis of FIG. 2 (b) corresponds to the eight divided backlight regions B1, B2, .. Corresponds to .B8). 2A and 2B, the horizontal axis is the time axis t. The time interval T on the time axis is a time from immediately after the scanning of the image data in one panel region starts to just before the scanning of the image data in the next panel region begins.

The subframe divided into R, G, and B is divided into eight panel areas P1, P2, ..., P8. For example, R, G, and B images are sequentially formed in the first to eighth panel areas P1, P2, ..., P8, and the first to eighth panel areas P1, P2, ... In the first to eighth backlight areas B1, B2, ..., B8 opposite to P8, the first to eighth sub light sources 21a, 21b of R, G, and B corresponding to the pre-formed image. .., 21h) lights up sequentially.

For example, an R image is sequentially formed in the first to eighth panel areas P1, P2, ..., P8 during the time from time 0T to 8T. For example, at time 5T, the liquid crystal from the first panel region to the fifth panel region P1,..., P5 is driven according to the R image, and although not shown in the drawing, the reaction time of the liquid crystal is considered. At this time, the driving is completed from the liquid crystal of the first panel region P1. Accordingly, the first sub light source 21a of R lights up from the first backlight region B1 facing the first panel region P1 in which the image is completely formed. However, during the time period between 5T and 8T, the R image of the first panel P1 is formed, and the first sub light source 21a of R of the first backlight region B1 is turned on. And the seventh and eighth sub-light sources 21g and 21h of B in the eighth backlight regions B7 and B8 are turned on, so that the B light emitted from the seventh and eighth sub-light sources 21g and 21h of B is turned on. Color mixing of R and B may occur in the R image of the first panel region P1. This color mixing phenomenon will be more prominent in the case of employing a conventional diffuser plate that is faithful only to spread the light evenly and will cause a deterioration in image quality.

3 is a comparative example showing that color mixing occurs in a conventional LCD unit employing the backlight unit 30. The conventional backlight unit 30 includes a diffuser plate 33 whose incidence surface 33a is flat, and a reflector plate 35 whose reflecting surface is flat. The remaining components except for the diffuser plate 33 and the reflector plate 35 in the backlight unit 30 are the same as the backlight unit 20 of FIG. 1, and therefore, the same reference numerals will be used. . The drawing exemplarily shows that the light emitted from the eighth sub light source 21h is irradiated to the first panel region P1 by reflecting light repeatedly from the diffuser plate 33 and the reflector plate 35. As illustrated, color mixing occurs in the image of the first panel region P1 by the seventh and eighth sub light sources 21g and 21h. As such, since the conventional backlight unit 30 has a diffuser plate 33 having a flat light incident surface, light incident at an angle to the light incident surface obliquely causes reflection and causes color mixing.

In contrast, referring to FIG. 1, the liquid crystal display of the present invention reflects the light emitted from the eighth sub-light source 21h to the eighth backlight region B8 to the adjacent backlight region even when the light emitted from the diffuser plate 23 is reflected. Since the light is incident only to the panel region P8 corresponding to the eighth backlight B8 to the neighboring panel region, the light supply to one panel region is prevented from entering the other panel region to suppress color mixing.

4 illustrates a backlight unit according to another embodiment of the present invention.

In the backlight unit 40 of the present exemplary embodiment, the rest of the components except for the diffusion plate 43 are the same as those of the above-described embodiment, and the same components are denoted by the same reference numerals and detailed description thereof will be omitted.

Referring to the enlarged view of FIG. 4, the diffusion plate 43 has a plate-shaped light transmissive substrate 43a and a light incident surface 43b formed by forming a plurality of prisms 44 in a row. The prism 44 is formed symmetrically with respect to the center line of the backlight areas B1, B2, ..., B8 for each of the divided backlight areas B1, B2, ..., B8. The center line is a line parallel to the boundary D between the backlight areas B1, B2, ..., B8. For example, as shown, the cross section of the prism 44 is a right triangle with a slope 44a and each sub light source 21a, 21b, ..., 21h is a backlight area B1, B2, ..., B8. When arranged in a row at each center, the center line is a line connecting the centers of the light sources arranged at the center of the backlight regions B1, B2, ..., B8. In this case, the prisms 44 are arranged symmetrically with respect to the center line.

The prism 44 may be formed symmetrically with respect to each array line of the sub light sources 21a, 21b, ..., 21h disposed therein for each of the divided backlight regions B1, B2, ..., B8. . The sub light sources 21a, 21b, ..., 21h have at least one array for each of the backlight regions B1, B2, ..., B8, and the array line means a line connecting the light sources arranged.

As described above, when the shape of the prism 44 is symmetrically formed for each of the backlight regions B1, B2, ..., B8 or according to the arrangement position of the sub light sources 21a, 21b, ..., 21h, The light reflected from the incident surface 43a of 44 can be more effectively suppressed from spreading farther, and the color mixing phenomenon can be prevented more effectively.

As described above, the backlight unit for color sequential driving liquid crystal display according to the present invention includes a diffuser plate having a prism formed on a light incident surface to suppress color mixing, thereby improving color reproducibility and color uniformity. Can provide.

Such a back light unit for a color sequential driving liquid crystal display device according to the present invention has been described with reference to the embodiment shown in the drawings for clarity, but this is merely illustrative, and those skilled in the art can variously change and It will be appreciated that other equivalent embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

Claims (5)

In the backlight unit for a color sequential driving liquid crystal display device in which a liquid crystal panel is divided into a plurality of panel regions and sequentially driven, A plurality of light sources disposed on a rear surface of the liquid crystal panel and provided in a plurality of backlight regions divided by the divided panel regions to sequentially supply light; The light emitted from one backlight area of the light source includes a plurality of prisms disposed between the liquid crystal panel and the light source and arranged in parallel with a boundary between the divided backlight areas to form a light incident surface facing the light source. And a diffuser plate for suppressing incident to other panel regions other than the panel region corresponding to the one backlight region. The method of claim 1, And reflecting the light emitted from the light source to the diffuser plate, the reflector including a plurality of grooves formed in parallel with the boundary between the divided backlight regions, and the light sources arranged in rows for each of the grooves. A backlight unit for a color sequential driving liquid crystal display device. The method of claim 1, And the angle between the peak and the valley of the prism is 90 to 110 degrees. The method of claim 1, When the line parallel to the boundary between the divided backlight regions and passing through the central portion of each of the divided backlight regions is called a center line of the backlight region, And a cross-sectional shape of each of the plurality of prisms is formed to be symmetrical with respect to the center line of the backlight area for each of the backlight areas. The method according to claim 1 or 4, And the light source comprises red, green, and blue light sources.

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