KR101613727B1 - Liquid crystal display - Google Patents

Abstract

The present invention relates to an edge type backlight unit capable of local dimming, comprising: a liquid crystal display panel including liquid crystal cells in which data lines and gate lines are crossed and arranged in a matrix; A source driver for converting the digital video data into a data voltage and outputting the data voltage to the data lines; A gate driver sequentially supplying gate pulses to the gate lines; A light guide plate disposed below the liquid crystal display panel and having a lenticular lens array in a first direction; A plurality of point light sources arranged along a second direction orthogonal to the first direction so as to face the side surfaces of the light guide plate and for emitting light in the first direction; A light source driving unit for individually driving the point light sources; And a timing controller for supplying the digital video data to the source driver and controlling the drivers.

Description

[0001] LIQUID CRYSTAL DISPLAY [0002]

The present invention relates to a liquid crystal display capable of local dimming.

BACKGROUND ART [0002] Liquid crystal display devices are becoming increasingly widespread due to features such as light weight, thinness, and low power consumption driving. This liquid crystal display device is used as a portable computer such as a notebook PC, an office automation device, an audio / video device, and an indoor / outdoor advertisement display device. A transmissive liquid crystal display device that occupies most of the liquid crystal display device controls an electric field applied to the liquid crystal layer to modulate light incident from the backlight unit to display an image.

The image quality of the liquid crystal display device depends on the contrast characteristics. The method of modulating the light transmittance of the liquid crystal layer by controlling the data voltage applied to the liquid crystal layer of the liquid crystal display panel has a limitation in improving the contrast characteristic. In order to improve the contrast characteristic, a backlight dimming control method for adjusting the luminance of the backlight unit according to an image has been developed, which dramatically improves the contrast characteristic. The backlight dimming control method may reduce the power consumption by adaptively adjusting the brightness of the backlight unit according to the input image. The backlight dimming method includes a global dimming method for adjusting the brightness of the entire display surface and a local dimming method for locally adjusting the brightness of the display surface. The global dimming method can improve the dynamic contrast measured between the previous frame and the next frame. The local dimming method can improve the static contrast which is difficult to improve by the global dimming method by locally controlling the brightness of the display surface within one frame period.

The backlight unit is roughly divided into a direct type and an edge type. The edge type backlight unit has a structure in which a light source is disposed so as to face the side face of the light guide plate and a plurality of optical sheets are disposed between the liquid crystal display panel and the light guide plate. The edge type backlight unit may be realized to be thinner than the direct-type backlight unit due to the structural difference, but the light source irradiates light to one side of the light guide plate, and the light guide plate converts the linear light source or the point light source into the surface light source. Therefore, in the conventional structure of the edge type backlight unit, it is impossible to implement the local dimming because the light is diffused in the light guide plate and it is difficult to control the luminance locally.

On the other hand, the direct-type backlight unit has a structure in which a plurality of optical sheets and a diffusion plate are stacked under the liquid crystal display panel and a plurality of light sources are disposed under the diffusion plate. In the direct type backlight unit, a plurality of light sources are disposed under the diffusion plate, and the light sources are individually controlled to implement the local dimming. However, it is difficult to reduce the thickness of the direct light type backlight unit, thereby making it difficult to design the slim design of the liquid crystal display device. The reason why it is difficult to reduce the thickness of the direct-type backlight unit is due to the distance that must be secured between the diffusion plate and the light sources. The diffusion plate of the direct type backlight unit is used for the purpose of diffusing the light incident from the light sources to make the brightness of the display surface uniform. The distance between the light sources and the diffuser plate must be sufficiently long for the diffusion plate of the direct-type backlight unit to sufficiently diffuse the light. Due to the trend of thinning of the liquid crystal display device, although the distance between the diffusion plate and the light sources is narrowed, the light from the light sources is not sufficiently diffused, The luminance uniformity of the image may be lowered. In order to solve the problem of the luminance uniformity of such a display image, a method of increasing the number and arrangement density of the light sources, a method of enhancing the diffusion function in the optical sheet such as forming a fine prism pattern or a lens pattern on the diffusion plate facing the liquid crystal display panel , And a method of reinforcing a diffusion sheet. However, these methods also have limitations in raising the light diffusibility and cause an increase in cost.

It is therefore an object of the present invention to provide a liquid crystal display device which realizes local dimming by using an edge type backlight unit as a solution to the problems of the prior art.

According to an aspect of the present invention, there is provided a liquid crystal display device including: a liquid crystal display panel including liquid crystal cells arranged in a matrix, the data lines and gate lines intersecting with each other; A source driver for converting the digital video data into a data voltage and outputting the data voltage to the data lines; A gate driver sequentially supplying gate pulses to the gate lines; A light guide plate disposed below the liquid crystal display panel and having a lenticular lens array in a first direction; A plurality of point light sources arranged along a second direction orthogonal to the first direction so as to face the side surfaces of the light guide plate and for emitting light in the first direction; A light source driving unit for individually driving the point light sources; And a timing controller for supplying the digital video data to the source driver and controlling the drivers.

The present invention can implement local dimming using an edge type backlight including a light guide plate in which a uniaxial lenticular lens array is formed and further can realize scanning backlight driving using the edge type backlight unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Like reference numerals throughout the specification denote substantially identical components. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 1 to 14. FIG.

1 to 3, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 10, a source driver 12 for driving data lines 14 of the liquid crystal display panel 10, A gate driver 13 for driving the gate lines 15 of the liquid crystal display panel 10, a timing controller 11 for controlling the source driver 12 and the gate driver 13, A backlight unit for irradiating light, and a light source driver 17.

In the liquid crystal display panel 10, a liquid crystal layer is formed between two glass substrates. A plurality of data lines 14 and a plurality of gate lines 15 are intersected with each other on a lower glass substrate of the liquid crystal display panel 10. The liquid crystal cells Clc are arranged in a matrix form in the liquid crystal display panel 10 by the intersection structure of the data lines 14 and the gate lines 15. [ The pixel electrodes of the liquid crystal cells Clc connected to the data lines 14, the gate lines 15, the thin film transistors TFT, and the thin film transistors TFT are connected to the lower glass substrate of the liquid crystal display panel 10, A capacitor Cst and the like are formed.

On the upper glass substrate of the liquid crystal display panel 10, a black matrix, a color filter, and a common electrode are formed. The common electrode is formed on the upper glass substrate in a vertical electric field driving method such as a TN (Twisted Nematic) mode and a VA (Vertical Alignment) mode, and a horizontal electric field such as IPS (In Plane Switching) mode and FFS (Fringe Field Switching) Is formed on the lower glass substrate together with the pixel electrode in the driving method. On the upper glass substrate and the lower glass substrate of the liquid crystal display panel 10, a polarizing plate is attached and an alignment film for forming a pre-tilt angle of the liquid crystal is formed on the inner surface in contact with the liquid crystal.

The source driver 12 includes a plurality of source drive ICs. The source driver 12 latches the digital video data (RGB) under the control of the timing controller 11. The source driver 12 converts the digital video data RGB to positive / negative polarity analog data voltages using the positive / negative gamma compensation voltages and supplies them to the data lines 14.

The gate driver 13 includes a plurality of gate driver ICs. The gate driver 13 includes a shift register, a level shifter for converting an output signal of the shift register into a swing width suitable for driving the TFT of the liquid crystal cell, and an output buffer. The gate driver 13 sequentially outputs gate pulses (or scan pulses) having a pulse width of about one horizontal period, which are composed of a plurality of gate drive integrated circuits, and supplies the gate pulses to the gate lines 15.

The timing controller 11 receives digital video data (RGB) and timing signals (Vsync, Hsync, DE, DCLK) input from a system board on which an external video source is mounted. The timing signals Vsync, Hsync, DE and DCLK include a vertical synchronizing signal Vsync, a horizontal synchronizing signal Hsync, a data enable signal DE and a dot clock signal DCLK. The timing controller 11 generates timing control signals DDC and DDC for controlling the operation timings of the source driver 12 and the gate driver 13 based on the timing signals Vsync, Hsync, DE, and DCLK from the system board. GDC). The timing controller 11 inserts an interpolation frame between the frames of the input video signal input at a frame frequency of 60 Hz and multiplies the source timing control signal DDC and the gate timing control signal GDC to obtain 60 × N It is possible to control the operation of the source driver 12 and the gate driver 13 at a frame frequency of Hz. The timing controller 11 outputs the dimming signal DIM in the y-axis direction according to the input image at the time of local dimming, modulates the data in the x-axis direction and supplies the modulated data RGB 'to the source driver 12 do.

The backlight unit includes a light guide plate 201 on which a lenticular lens array 201a is formed and a light source array 202 for irradiating light on a side surface of the light guide plate 201. [ The backlight unit includes a plurality of optical sheets stacked between the light guide plate 201 and the liquid crystal display panel 10. [ The optical sheets 205 include at least one prism sheet and at least one diffusing sheet to diffuse the light incident from the diffuser plate and to guide the light path of the light at an angle substantially perpendicular to the light incident surface of the liquid crystal display panel Refract. The optical sheets 205 may comprise a dual brightness enhancement film (DBEF).

The light guide plate 201 may be made of a flat plate or a wedge plate. On the upper surface of the light guide plate 201, a lenticular lens array 201a as shown in Figs. 3 and 4 is formed. The lenticular lens array 201a formed on the upper surface of the light guide plate 201 has mountains and valleys. A plurality of fine patterns 201b are formed on the lower surface of the light guide plate 201. [ The fine patterns 201b reflect light incident on the fine patterns 201b toward the liquid crystal display panel 10 side. The lenticular lens array 201a includes lenticular lenses arranged in parallel in the x-axis direction. Each of the lenticular lenses is elongated in the y-axis direction and has a hemispherical or semi-elliptical cross-sectional structure. Each of the lenticular lenses of the lenticular lens array 201a increases the straightness of the light incident in the y-axis direction from the light source array 202. [

The light source array 202 includes point light sources such as a light emitting diode (LED). The point light sources are arranged along the x-axis direction and irradiate light in a direction parallel to the mountain / valley direction of the lenticular lens array 201a. The light source array 202 is disposed so as to face at least one of the upper side surface and the lower side surface of the light guide plate 201.

The light source driving unit 17 adjusts a current applied to each of the point light sources in response to the dimming signal DIM from the timing controller 11. [

The inventors of the present invention have derived a light guide structure most suitable for local dimming and scanning backlight driving through experiments. This will be described in detail with reference to FIGS. 4 to 8. FIG.

The upper surface of a general light guide plate is flat. When a light source is disposed on a side surface of a general light guide plate and light is irradiated to the upper surface of the light guide plate through a side surface of the light guide plate at an angle larger than a total reflection critical angle, the light is transmitted through the upper surface of the light guide plate. When light is irradiated onto the upper surface of a general light guide plate at an angle smaller than the total reflection critical angle, the light is reflected on the upper surface of the light guide plate and diffused and propagated at a wide angle in the light guide plate medium. Lambertian scattering occurs due to the fine patterns 201b when light is irradiated to the lower side of a general light guide plate.

When a light source is disposed on the side surface of the light guide plate 201 having the lenticular lens array 201a as shown in FIGS. 3 and 4 and the light is irradiated to the upper surface of the light guide plate through the side surface of the light guide plate at an angle larger than the total reflection critical angle, And condenses the light. When the light is irradiated to the upper surface of the light guide plate having the lenticular lens array 201a at an angle smaller than the total reflection critical angle, the light is reflected at the upper surface of the light guide plate and propagates at a narrow angle in the light guide plate medium due to the light- condensing effect due to the lenticular lens surface. When light is irradiated to the lower surface of the light guide plate 201 having the lenticular lens array 201a formed therein, the light is scattered by the lambs cyan due to the fine patterns 201b. Accordingly, the light guide plate 201 having the lenticular lens array 201a formed thereon compared to the general light guide plate has the advantage that the directivity of the light propagating in the light guide plate medium and the light converging property of the light traveling toward the liquid crystal display panel 10 through the upper surface of the light guide plate, great.

4 and 5, the ratio of the thickness (A) of the light guide plate 201 to the peak height (C) of the lenticular lens is 1: It was confirmed that the linearity of the light propagating in the light guide plate 201 was the best when the light intensity was 0.01. Figs. 6 and 7 are top and side views of the light guide plate sample manufactured with the numerical values shown in Fig. 5, taken with an L300 optical microscope. According to the experimental results, as shown in FIG. 8, when the thickness of the light guide plate 201 is thin between 0.5 mm and 1.5 mm, the straightness of light is most excellent. The local dimming effect and the scanning backlight driving effect are better as the directivity of light is higher. Therefore, the light guide plate 201 of the present invention is required to have a lenticular lens array 201a formed on its upper surface so as to be suitable for local dimming and scanning backlight driving. The thickness A of the light guide plate 201: the height of the lenticular lens C ) Is 1: 0.01 and its thickness is 0.5 mm to 1.5 mm.

9 is a flowchart showing the local dimming control method of the timing controller 11 step by step.

9, the timing controller 11 maps input data (RGB) to virtual blocks divided into a matrix form on the display screen of the liquid crystal display panel 10, and derives a representative value of data for each block (S1 to S3) The representative value of the data for each block may be selected from a histogram of data in each block, that is, an accumulated value of the cumulative distribution function, and an average value and a mode value of the cumulative distribution function.

The timing controller 11 modulates the gray level of the data (RGB) of the block having a high representative value for each block as shown in FIG. 10, while the gray level of the data (RGB) (S4) Further, the timing controller 11 calculates the average value of the representative values of the blocks arranged in the y-axis direction (or the column direction and the data line direction) Lt; / RTI > The dimming values of neighboring blocks in the x-axis direction may vary depending on the input image.

The timing controller 11 secondarily compensates the modulation data and / or the dimming value to reduce the problem of excessive compensation of the luminance due to the block-by-block data modulation and the overlap of the dimming values in the y-axis direction, '). The final dimming value and the final data (RGB ') are proportional to the dimming value per block. The final dimming value is input to the backlight driver 17 as a pulse width modulation control signal PWM. The PWM duty ratio of the final dimming value increases as the average value of the representative values of the blocks arranged along the y axis direction increases, while the average value of the representative values of the blocks arranged along the y axis direction decreases.

The operations S3 to S7 may be implemented by a look-up table that outputs a compensation value and a dimming value of data with the representative value of each block as an input address.

11 is a diagram illustrating a local dimming method of the present invention.

Referring to FIG. 11, the point light sources of the backlight unit emit light with a current varying according to the dimming value in the y-axis direction (minor axis direction). At the same time, the block-by-block data of the liquid crystal display panel 10 is modulated on the basis of the block-by-block representative value in the same manner as in FIG. Accordingly, the local dimming is realized by the effect of dimming and data compensation in the y-axis direction of the point light sources determined according to the block-by-block analysis result of the input data.

The liquid crystal display device is a hold-type display device. As a result, the liquid crystal display device has a problem that a residual image due to motion blur remains. One technique that can solve this problem is scanning backlight technology. The scanning backlight technique can reduce the motion blur by sequentially turning off the point light sources of the backlight unit along the data scanning direction of the liquid crystal display panel, thereby significantly reducing the afterimage problem and further reducing the power consumption of the backlight unit.

12 to 14, the light guide plate 201 having the lenticular lens array 201a formed thereon can be used to enhance the straightness of the light propagated in the light guide plate 201, thereby further enhancing the scanning backlight effect.

12 is a view schematically showing a scanning backlight driving liquid crystal display device according to a first embodiment of the present invention.

Referring to FIG. 12, the scanning backlight driving liquid crystal display of the present invention includes a data driving circuit 12, a gate driving circuit 13, and a light source array 202. 12, the liquid crystal display panel 10, the timing controller 11, and the light source driver 17 are omitted.

The data lines and the gate lines of the liquid crystal display panel 10 are formed in the direction opposite to the data lines and gate lines shown in Fig. That is, the data lines are formed long along the x-axis direction, and the gate lines are formed long along the y-axis direction.

The source driver 12 is disposed on the left side and / or the right side of the liquid crystal display panel 10 so as to be connected to the input pads of the data lines. The gate driver 13 is disposed at the top and / or bottom of the liquid crystal display panel 10 so as to be connected to the input pads of the gate lines. The gate driver 13 shifts the gate pulse synchronized with the data voltage from the left side to the right side of the liquid crystal display panel.

The display screen of the liquid crystal display panel 10 is virtually divided into N scan blocks (positive integers of 2 or more) in the x-axis direction, and the point light sources are dividedly driven into N backlight blocks. When gate pulses are sequentially applied to the gate lines in the scan block as shown by the dotted line in FIG. 13, the point light sources responsible for the two neighboring backlight blocks around the scan block are connected to the input current I). The backlight driver 17 simultaneously supplies a current synchronized with the gate pulse to the point light sources of neighboring N-1th and Nth backlight blocks under the control of the timing controller 11, Currents are simultaneously supplied to the point light sources of the first backlight blocks. Therefore, it is possible to reduce the phenomenon in which the boundary between the backlight blocks is visible in the scanning backlight driving.

In order to implement the scanning backlight driving in the liquid crystal display device as shown in FIGS. 1 and 2, in order to sequentially illuminate the backlight blocks along the scanning direction of the liquid crystal display panel 10 facing downward as shown in FIG. 14, The direction of the lenticular lens array 201a in the x-axis direction must be changed to the x-axis direction. The light source array 202 should be disposed on the left side and / or the right side of the light guide plate 201 so that light can be irradiated to the left and / or right of the light guide plate 201.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

1 is a block diagram showing a liquid crystal display device according to an embodiment of the present invention;

2 is a circuit diagram showing equivalently a part of a pixel array of the liquid crystal display panel shown in Fig.

3 is an exploded perspective view showing the structure of the liquid crystal display panel and the edge type backlight unit shown in FIG.

4 is a cross-sectional view showing the structure of the light guide plate shown in FIG.

5 is a graph showing the ratio of the light guide plate thickness to the peak height of the lenticular lens in the light guide plate of the present invention.

Figs. 6 and 7 are top and side views of the light guide plate sample manufactured with the numerical values shown in Fig. 5, taken with an L300 optical microscope.

8 is a graph showing the results of the straightness test of light according to the thickness of the light guide plate in the light guide plate having the lenticular lens array formed therein.

Fig. 9 is a flowchart showing the local dimming control method of the timing controller step by step.

10 is a diagram showing an example of data modulation.

11 is a diagram illustrating a local dimming implementation principle of the present invention.

12 is a view schematically showing a scanning backlight driving liquid crystal display device according to an embodiment of the present invention.

13 is a view showing current application timing of the point light source and synchronization of gate pulses in the scanning backlight driving liquid crystal display device shown in FIG.

FIG. 14 is a view schematically showing a scanning backlight driving liquid crystal display device according to another embodiment of the present invention.

Description of the Related Art

201: light guide plate 201a: lenticular lens array

202: Light source array

Claims (6)

A liquid crystal display panel including liquid crystal cells in which data lines and gate lines are crossed and arranged in a matrix form; A source driver for converting the digital video data into a data voltage and outputting the data voltage to the data lines; A gate driver sequentially supplying gate pulses to the gate lines; A light guide plate disposed below the liquid crystal display panel and having a lenticular lens array in a first direction; A plurality of point light sources arranged along a second direction orthogonal to the first direction so as to face the side surfaces of the light guide plate and for emitting light in the first direction; A light source driving unit for individually driving the point light sources; And And a timing controller that supplies the digital video data to the source driver and controls the drivers, The lenticular lens array includes: And a plurality of lenticular lenses formed along the first direction, Wherein the lenticular lenses are arranged side by side along the second direction, Wherein the ratio of the thickness of the light guide plate to the peak height of the lenticular lens is 1: 0.01, and the ratio of the thickness of the light guide plate to the pitch of the lenticular lens is 1: 0.026. delete The method according to claim 1, Wherein the thickness of the light guide plate is between 0.5 mm and 1.5 mm. The method according to claim 1, The timing controller includes: A method of driving a liquid crystal display (LCD) device, comprising: mapping a data of an input image to virtually divided blocks on a display screen of the liquid crystal display panel, deriving a representative value of data for each block, And outputs a dimming value at a PWM duty ratio proportional to a representative value of the block data. 5. The method of claim 4, Wherein the light source driving unit individually drives the point light sources in response to a dimming value. The method according to claim 1, The data lines are formed along the second direction and the gate lines are formed in the first direction so as to be parallel with the lenticular lens array, Wherein the light source driver sequentially turns on the point light sources in synchronization with the gate pulse sequentially applied to the gate lines.

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