KR20040051419A - Method of displaying picture and liquid crystal display apparatus using the same - Google Patents

Abstract

PURPOSE: An image displaying method and an LCD(Liquid Crystal Display) are provided to reduce power consumption and improve the quality of motion pictures. CONSTITUTION: The phase of light emitted from a light source is controlled to transmit or block the light along a screen scanning direction. An image is displayed using light incident on a partial region of a screen. The phase of light is controlled through a step of transmitting the light while maintaining polarized characteristic of the light without delaying the phase of light, and a step of delaying the phase of light to change the polarized characteristic to block the light. The light having the changed polarized characteristic is reflected using cholesteric liquid crystal. An LCD includes an LCD panel(1), a light source for irradiating light to the LCD panel, and a shutter(2) for controlling the phase of light traveling to the LCD panel to transmit or block the light along a scanning direction of the LCD panel.

Description

Image display method and liquid crystal display using the same {METHOD OF DISPLAYING PICTURE AND LIQUID CRYSTAL DISPLAY APPARATUS USING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat panel display device, and more particularly, to an image display method and a liquid crystal display device using the same to reduce power consumption and improve display quality of moving images.

The liquid crystal display displays an image by controlling an electric field applied to the liquid crystal layer in response to the video signal. The liquid crystal display is a flat panel display having advantages of small size, thinness, and low power consumption, and is used as a portable computer such as a notebook PC, an office automation device, an audio / video device, and the like.

However, the liquid crystal display device has not only a slow response characteristic of the liquid crystal but also a motion blurring phenomenon in which the screen is blurred or a tailing phenomenon in which the contour appears to be drawn when the moving image is realized by the liquid crystal holding characteristic. Such degradation in image quality cannot be completely eliminated even when the response speed of the liquid crystal is faster than one frame period (16,7 ms).

On the other hand, cathode ray tube (CRT) is an impulse type display device that displays an image instantaneously without retaining data, and almost no motion blur or tailing phenomenon occurs in moving images.

In other words, the cathode ray tube (CRT) emits phosphor only during a very short initial time of one frame period (16.7 ms) as shown in FIG. 1 to display data and does not emit phosphor for the rest of the time. Due to the impulse characteristics of the cathode ray tube CRT, the viewer can clearly see the moving image displayed on the cathode ray tube CRT. In contrast, the liquid crystal display maintains the data voltage supplied to the liquid crystal cell for one frame period as shown in FIG. 2. The maintenance characteristic of this liquid crystal display device allows viewers to feel motion blur or tailing in a moving picture.

In order to reduce image quality deterioration due to the retention characteristics of the liquid crystal display device, a so-called 'scanning back light blinking system' has been proposed.

In the scanning backlight blinking method, a backlight unit for irradiating light to the liquid crystal panel 1 includes a plurality of lamps 100a to 100e as shown in FIG. 3, and the lamps are sequentially turned on along the display area to which data is supplied. -Will be turned off. In FIG. 3, a portion of the center of the screen emits light according to the lighting of the third lamp 100c to display an image, whereas other regions of the screen display the first, second, fourth and fifth lamps 100a and 100b. Light is not emitted even if data is maintained in the liquid crystal cells of the corresponding area due to the lighting of 100d and 100e. When the scanning backlight blinking method is applied, the liquid crystal display emits light at the beginning of one frame period and blocks light in the remaining period as shown in FIG. 4 as the lamps 100a to 100e sequentially flash. Drive in a way. Therefore, the display quality of the moving image may be improved in the liquid crystal display by applying the scanning backlight blinking method. However, the scanning backlight blinking method requires a large number of lamps 100a to 100e and the lamps 100a to 100e need to be blinked at high speed.

Accordingly, an object of the present invention is to provide an image display method and a liquid crystal display device using the same to reduce power consumption and to improve display quality of a moving image.

1 is a graph showing the impulse characteristics of a cathode ray tube.

2 is a graph showing the retention characteristics of the liquid crystal display.

3 is a perspective view illustrating a conventional scanning backlight unit method.

4 is a graph showing quasi-impulse characteristics of the liquid crystal display device shown by a conventional scanning backlight unit method.

5 is a block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

6 is a perspective view illustrating in detail the liquid crystal panel illustrated in FIG. 5.

7 and 8 are exploded perspective views showing the liquid crystal shutter shown in FIG. 5 in detail.

9 is a graph illustrating a voltage applied to a liquid crystal shutter and a phase delay amount accordingly.

10 is a cross-sectional view for describing a liquid crystal shutter according to a first exemplary embodiment of the present invention.

FIG. 11 is a cross-sectional view illustrating an optical path incident on the liquid crystal shutter and the liquid crystal panel shown in FIG. 5.

12 is a perspective view showing luminance of a display image in the liquid crystal display according to the exemplary embodiment of the present invention.

13 is a cross-sectional view for describing a liquid crystal shutter according to a second exemplary embodiment of the present invention.

14 is a plan view illustrating an electrode pattern formed on a liquid crystal shutter.

FIG. 15 is a waveform diagram illustrating voltages applied to the electrode patterns illustrated in FIG. 14.

<Description of Symbols for Main Parts of Drawings>

1: liquid crystal panel 2: liquid crystal shutter

3: backlight unit 4: controller

5 liquid crystal panel driving circuit 6 liquid crystal shutter driving circuit

7 Inverter driving circuit 35 Color filter substrate of liquid crystal panel

36: TFT substrate of liquid crystal panel 41,46: CLC 'polarizing plate or DBEF

42; Lower transparent substrate of liquid crystal shutter 43,55: Common electrode of liquid crystal shutter

44: upper transparent substrate of the liquid crystal shutter 45,53: electrode pattern of the liquid crystal shutter

47: liquid crystal layer 101,102 of the liquid crystal shutter: CLC polarizing plate

100a to 100e: Lamp 121,122: DBEF

In order to achieve the above object, the image display method according to an embodiment of the present invention by controlling the phase of the light incident from the light source to transmit and block the light along the scanning direction of the screen, and the light incident on a portion of the screen And displaying an image using.

The controlling the phase of the light may include transmitting the light by maintaining the polarization characteristic of the light as it is without delaying the phase of the light, and converting the polarization characteristic of the light by delaying the phase of the light to block the light.

The image display method according to an exemplary embodiment of the present invention further includes reflecting light converted into polarization characteristics by using the cholesteric liquid crystal.

According to an exemplary embodiment of the present invention, a liquid crystal display device includes a liquid crystal panel, a light source for irradiating light to the liquid crystal panel, and a shutter for transmitting and blocking light along the scanning direction of the liquid crystal panel by controlling a phase of light traveling toward the liquid crystal panel. It is provided.

The shutter is incident through a liquid crystal layer for controlling the phase of incident light according to an electric field, an incident side polarizer for transmitting the light of the first polarization to the liquid crystal layer and reflecting the light of the second polarization, and the liquid crystal layer. And an emission-side polarizing plate for transmitting the light of the first polarized light to be reflected and reflecting the light of the second polarized light incident through the liquid crystal layer.

The liquid crystal layer is characterized in that the polarization characteristic of the incident light is maintained without delaying the phase of the incident light in response to the first voltage.

The liquid crystal layer may convert the first polarized light into the second polarized light by delaying the phase of the incident light by one-half wavelength of the incident light in response to the second voltage.

The first polarized light may be any one of right circularly polarized light and left circularly polarized light.

The second polarized light is characterized by being circularly polarized light different from the first polarized light.

The first polarized light may be any one of vertical linearly polarized light and horizontal linearly polarized light.

The second polarized light is characterized by being linearly polarized light different from the first polarized light.

The light source includes a lamp for generating light, a light guide plate for converting a line light source from the lamp into a surface light source, and at least one optical sheet mounted on the light guide plate for controlling light incident from the light guide plate.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 5 to 15.

Referring to FIG. 5, the liquid crystal display according to the exemplary embodiment of the present invention includes a liquid crystal shutter 2 disposed between the liquid crystal panel 1 and the backlight unit 3.

The liquid crystal panel 1 displays an image by controlling the amount of light from the liquid crystal shutter 2 in accordance with the control of the electric field applied to the liquid crystal layer in response to the video signal. In this liquid crystal panel 1, a color filter substrate 35 and a thin film transistor substrate (hereinafter referred to as a "TFT substrate") 36 are bonded to each other with the liquid crystal layer 15 interposed therebetween as shown in FIG. The color filter substrate 35 and the common electrode 14 are formed on the rear surface of the upper glass substrate 12, and the polarizing plate 11 is attached to the front surface of the upper glass substrate 12. In the color filter 13, color filter layers of red (R), green (G), and blue (B) colors are disposed to transmit light of a specific wavelength band, thereby enabling color display. A black matrix (not shown) is formed between the color filters 13 of adjacent colors. The TFT substrate 36 faces the backlight unit 3. In the TFT substrate 36, the data lines 19 and the gate lines 18 are formed to cross each other on the front surface of the lower glass substrate 16, and the TFTs 20 are formed at the intersections thereof. In addition, the pixel electrode 21 is formed in a matrix form on the front surface of the lower glass substrate 16 in the cell region between the data line 19 and the gate line 18. The TFT 20 drives the pixel electrode 21 by switching the data transfer path between the data line 19 and the pixel electrode 21 in response to the scanning signal from the gate line 18. The polarizing plate 17 is attached to the back surface of the TFT substrate 36. The liquid crystal layer 15 adjusts the amount of light transmitted through the TFT substrate 36 in response to the electric field applied thereto. The polarizers 11 and 17 attached to the color filter substrate 35 and the TFT substrate 36 transmit light polarized in either direction, and their polarization directions when the liquid crystal 15 is in the 90 ° TN mode. Are orthogonal to each other. An alignment film (not shown) is formed on the liquid crystal facing surfaces of the color filter substrate 35 and the TFT substrate 36. The liquid crystal panel 1 is not limited to that shown in FIG. 6 but may be implemented as a liquid crystal panel having a different structure, for example, a transverse electric field.

The backlight unit 3 serves to irradiate the liquid crystal shutter 2 by converting the line light source into a surface light source. The backlight unit 3 includes a lamp, a light guide plate, a reflecting plate, and a plurality of optical sheets such as a prism sheet and a diffusion sheet.

The liquid crystal shutter 2 serves to control the light irradiated from the backlight unit 3 toward the liquid crystal panel 1 along a partial region where an image is displayed on the liquid crystal panel 1. Here, the partial region includes tens to hundreds of horizontal display lines. By this liquid crystal shutter 2, light is irradiated to some areas where an image is displayed on the liquid crystal panel 1, and light is not irradiated to other areas. That is, the liquid crystal shutter 2 controls the distribution of light irradiated to the liquid crystal panel 2. This liquid crystal shutter 2 will be described in detail with reference to FIGS. 7 to 15.

In addition, the liquid crystal display device according to the embodiment of the present invention includes a liquid crystal panel driving circuit 5 for driving the liquid crystal panel 5, a liquid crystal shutter driving circuit 6 for driving the liquid crystal shutter 6, and a backlight. An inverter circuit 7 for driving the unit 7, a controller 4 for controlling the respective driving circuits 5, 6, 7, and a controller 4 are provided.

The liquid crystal panel driver circuit 5 converts data input from the controller 4 into an analog voltage to supply data to the data lines 19 of the liquid crystal panel 5 and the controller 4 of the controller 4. And a gate driving circuit for supplying scan pulses to the gate lines 18 of the liquid crystal panel 5 under control.

The liquid crystal shutter driving circuit 6 generates a voltage required for one electrode and the other electrode of the liquid crystal shutter 2 under the control of the controller 4 and supplies the voltage to the liquid crystal shutter 2. Light on some areas where the current image is displayed

The inverter circuit 7 generates a power supply voltage necessary for the lamp of the backlight unit 3 under the control of the controller 4.

7 and 8 show the liquid crystal shutter 2 in detail.

Referring to FIG. 7, the liquid crystal shutter 2 according to the exemplary embodiment of the present invention may include an electrode pattern 45 formed on the upper transparent substrate 44, a common electrode 43 formed on the lower transparent substrate 42, A cholesteric liquid crystal polarizing plate (hereinafter referred to as a 'CLC polarizing plate') or a dual brightness enhancement film (DBEF) attached to each of the upper transparent substrate 44 and the lower transparent substrate 42. 41 and 46).

The upper transparent substrate 44 and the lower transparent substrate 42 are made of a transparent glass substrate or a transparent plastic substrate. A liquid crystal 47 is injected between the upper transparent substrate 44 and the lower transparent substrate 42 to delay the phase of light by 0 to λ / 2 according to the voltage as shown in FIG. 9. Is the wavelength of light.

The liquid crystal 47 may be selected from any one of a vertical aligned mode (VA), an electrically controlled labile fringefringence (ECB), and a ferro-electric liquid crystal (FLC).

The electrode pattern 45 is formed in a number and size corresponding to each of a plurality of regions including tens to hundreds of horizontal display lines of the liquid crystal panel 1.

The common electrode 43 is supplied with a constant DC voltage, for example, a ground voltage GND.

The common electrode 43 and the electrode pattern 45 are formed of a transparent conductive material, for example, Indum-Tin-Oxide (ITO), Indum-Zine-Oxide (IZO), Indum-Tin-Zine-Oxide (ITZO), or the like. To transmit light.

The positions of the common electrode 43 and the electrode pattern 45 may be changed as shown in FIG. 8. That is, as shown in FIG. 8, the common electrode 55 may be formed on the upper plate of the liquid crystal shutter 2, and the electrode pattern 53 may be formed on the lower plate of the liquid crystal shutter 2.

Each of the CLC polarizers or DBEFs 41 and 46 utilizes the selective reflection characteristics of the CLC or DBEF. The selective reflection characteristic of the CLC means that the CLC arranged so that the liquid crystal molecules are twisted along the spiral axis reflects the circularly polarized light in the same spiral direction as its spiral axis and transmits the circularly polarized light in a direction different from the spiral direction. DBEF was developed by '3M'. This DBEF has the property of transmitting the linear flat light of a specific optical axis and reflecting the linear polarization of the optical axis orthogonal thereto. Thus, the CLC polarizers or DBEFs 41 and 46 transmit circularly polarized light (or linearly polarized light) in a specific direction and block other circularly polarized light (or linearly polarized light).

10 shows a liquid crystal shutter 2 according to the first embodiment of the present invention. An operation of the liquid crystal shutter 2 according to the first embodiment of the present invention will be described with reference to FIGS. 9, 11, and 12.

The operation principle according to the first embodiment of the liquid crystal shutter 2 will be described in detail with reference to FIGS. 9 and 10.

9 and 10, CLC polarizers 101 and 102 are respectively attached to upper and lower plates of the liquid crystal shutter 2 according to the first exemplary embodiment of the present invention to reflect left circularly polarized light and transmit right circularly polarized light. The liquid crystal layer 47 is formed between the upper plate and the lower plate of the liquid crystal shutter 2 so that the arrangement of liquid crystal molecules is changed in response to an electric field applied to the liquid crystal shutter 2 so as not to delay the phase of incident light or to delay by? / 2.

Assuming that a voltage below Vth is applied to the electrode patterns 45 and 53 formed in the A region of the liquid crystal layer 47, and a VR voltage is applied to the electrode patterns 45 and 53 of the B region of the liquid crystal layer 47. The right circularly polarized light incident on the A region passes through the liquid crystal layer 47 without phase delay, while the right circularly polarized light incident on the B region is delayed by λ / 2 and converted into left circularly polarized light.

Right circularly polarized light incident from the backlight unit 3 into the area A of the liquid crystal shutter 2 passes through the lower CLC polarizer 102, the liquid crystal layer 47, and the upper CLC polarizer 101 as it is and enters the liquid crystal panel 1. do. The left circularly polarized light irradiated to the A region of the liquid crystal shutter 2 is reflected by the lower CLC polarizing plate 102. The amount of light transmitted through the A region of the liquid crystal shutter 2 is the sum of the right circularly polarized light incident from the backlight unit 3 and the right circularly polarized light incident from the B region to the A region through the reflection process in the B region as shown in FIG. 11. to be. Therefore, the luminance of the A region of the liquid crystal shutter 2 is higher than that of displaying an image in the corresponding region only by light incident directly from the backlight unit 3 as shown in FIG. 12.

The right circularly polarized light incident from the backlight unit 3 into the B region of the liquid crystal shutter 2 passes through the lower CLC polarizing plate 102 as it is, and then passes through the liquid crystal layer 47 and is delayed in phase by λ / 2 to become left circularly polarized light. It is converted and reflected by the upper CLC polarizer 101. Further, the left circularly polarized light incident from the B region of the liquid crystal shutter 2 from the backlight unit 3 or the left circularly polarized light incident from the A region to the B region is reflected by the lower CLC polarizing plate 102. Therefore, the left circularly polarized light or the right circularly polarized light incident on the region B cannot be transmitted toward the liquid crystal panel 1.

By the liquid crystal shutter 2, the light incident on the liquid crystal panel 1 is concentrated on the liquid crystal panel 1, and thus the luminance is higher in the corresponding region than in the conventional scanning backlight blinking method.

On the other hand, when the CLC polarizing plate 121 is formed on the upper plate of the liquid crystal shutter 2 as shown in FIG. 10, the light penetrating the CLC polarizing plate 121 and incident on the liquid crystal panel 1 is circularly polarized light. The lower plate of the phase difference plate for converting circularly polarized light into linearly polarized light, for example, λ / 4 plate may be formed.

13 shows a liquid crystal shutter 2 according to a second embodiment of the present invention. The operation of the liquid crystal shutter 2 according to the second embodiment of the present invention will be described with reference to FIGS. 9 and 11.

9 and 13, DBEFs 121 and 122 are respectively attached to upper and lower plates of the liquid crystal shutter 2 according to the second exemplary embodiment of the present invention to reflect horizontal linear polarization and transmit vertical linear polarization. The liquid crystal layer 47 is formed between the upper plate and the lower plate of the liquid crystal shutter 2 so that the arrangement of liquid crystal molecules is changed in response to an electric field applied to the liquid crystal shutter 2 so as not to delay the phase of incident light or to delay by? / 2.

Assuming that a voltage below Vth is applied to the electrode patterns 45 and 53 formed in the A region of the liquid crystal layer 47, and a VR voltage is applied to the electrode patterns 45 and 53 in the B region of the liquid crystal layer 47. The vertical linearly polarized light incident on the A region passes through the liquid crystal layer 47 without phase delay, while the vertical linearly polarized light incident on the B region is delayed in phase by λ / 2 and converted into horizontal linearly polarized light.

The vertical linearly polarized light incident from the backlight unit 3 into the area A of the liquid crystal shutter 2 passes through the lower DBEF 122, the liquid crystal layer 47, and the upper DBEF 121 as it is and enters the liquid crystal panel 1. The horizontal linearly polarized light radiated to the area A of the liquid crystal shutter 2 is reflected by the lower DBEF 122. The amount of light transmitted through the A region of the liquid crystal shutter 2 is the sum of the vertical linear polarization incident from the backlight unit 3 and the vertical linear polarization incident from the B region to the A region through the reflection process in the B region as shown in FIG. 11. to be. Therefore, the luminance of the area A of the liquid crystal shutter 2 is higher than that of the case where an image is displayed in the area only by light incident directly from the backlight unit 3.

The vertical linearly polarized light incident from the backlight unit 3 into the B region of the liquid crystal shutter 2 passes through the lower DBEF 202 as it is, and then passes through the liquid crystal layer 47 to be delayed in phase by λ / 2 and converted into horizontal linearly polarized light. And is reflected from the upper DBEF 121. In addition, horizontal linearly polarized light incident from the B region of the liquid crystal shutter 2 from the backlight unit 3 or horizontal linearly polarized light incident from the A region to the B region is reflected by the lower DBEF 122. Therefore, vertical linearly polarized light or horizontal linearly polarized light incident on the region B cannot be transmitted toward the liquid crystal panel 1.

The controller 4 controls the liquid crystal shutter 2 by supplying an on pulse set to the VR voltage to the electrode patterns 45 and 53. When the number of the electrode patterns 45 and 53 is n (where n is a positive integer of 2 or more), the display areas partitioned by the electrode patterns 45 and 53 under the control of the controller 4 are 1 / n × 1. The image is displayed with a time difference of the frame period, and emits light for one half of the frame period, and blocks the light for the remaining period. For example, if eight electrode patterns 45 and 53 are configured as illustrated in FIG. 14, the controller 4 may have a 1/8 × 1 frame period (eg, the first to eighth electrodes L1 to L8) as shown in FIG. 15. 1 / 60sec ≒ 16.7ms) is supplied in order to supply the on pulse sequentially. In this case, the high voltage of the on-pulse is maintained for 1/2 x 1 frame period ≒ 8.3 ms. Here, when the duration of the high voltage of the on-pulse is greater than 1/2 × 1 frame period, motion blurring may appear in the video. If the duration is less than 1/2 × 1 frame period, the motion blurring effect is large, but the luminance is high. Is lowered.

As described above, the image display method and the liquid crystal display device using the same according to the present invention maintain the polarization characteristics of incident light according to the electric field and transmit the light toward the liquid crystal panel or delay the phase of the incident light by λ / 2. By converting to block the light propagating toward the liquid crystal panel. Accordingly, the image display method and the liquid crystal display device using the same according to the present invention reduce the power consumption and minimize the motion blurring or tailing phenomenon in the video, compared to the conventional scanning backlight blinking method of flashing a plurality of lamps at high speed. The display device can improve the display quality of the video. Furthermore, the image display method and the liquid crystal display device using the same according to the present invention can increase the luminance of the display area by using light incident on the non-display area for the display area.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. For example, the image display method according to the present invention has been described as an example applied to the liquid crystal display device, but may be applied to other flat panel display devices as well as the liquid crystal display device. 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.

Claims (11)

Transmitting and blocking the light along the scanning direction of the screen by controlling the phase of the light incident from the light source; And displaying an image using the light incident on a portion of the screen. The method of claim 1, Controlling the phase of the light, Transmitting the light by maintaining the polarization characteristic of the light without phase retardation of the light; Retarding the phase of the light to convert the polarization characteristic of the light to block the light. The method of claim 1, And reflecting the light whose polarization characteristic is converted using a cholesteric liquid crystal. LCD panel, A light source for irradiating light onto the liquid crystal panel; And a shutter for transmitting and blocking the light along the scanning direction of the liquid crystal panel by controlling the phase of the light traveling toward the liquid crystal panel. The method of claim 4, wherein The shutter is a liquid crystal layer for controlling the phase of the incident light according to the electric field; An incident side polarizing plate for transmitting light of a first polarization to the liquid crystal layer and reflecting light of a second polarization; And an emission-side polarizing plate configured to transmit light of the first polarized light incident through the liquid crystal layer and to reflect light of the second polarized light incident through the liquid crystal layer. The method of claim 5, wherein The liquid crystal layer maintains the polarization characteristic of the incident light without delaying the phase of the incident light in response to the first voltage, while the phase of the incident light is changed to 1 / th of the incident light in response to the second voltage different from the first voltage. And converting the first polarized light into the second polarized light by delaying the wavelength by two wavelengths. The method of claim 5, wherein And the first polarized light is any one of right circularly polarized light and left circularly polarized light. The method of claim 7, wherein And the second polarized light is circular polarized light different from the first polarized light. The method of claim 5, wherein And the first polarized light is one of vertical linearly polarized light and horizontal linearly polarized light. The method of claim 9, And the second polarization is a linear polarization different from the first polarization. The method of claim 4, wherein The light source is a lamp for generating light, A light guide plate for converting the line light source from the lamp into a surface light source; And at least one optical sheet mounted on the light guide plate to control light incident from the light guide plate.