WO2012165369A1

WO2012165369A1 - Liquid crystal display device

Info

Publication number: WO2012165369A1
Application number: PCT/JP2012/063608
Authority: WO
Inventors: 亮山川
Original assignee: シャープ株式会社
Priority date: 2011-06-02
Filing date: 2012-05-28
Publication date: 2012-12-06

Abstract

The purpose of the present invention is to provide a liquid crystal display device capable of decreasing power consumption without lowering the image display quality. This liquid crystal display device is provided with a liquid crystal panel (12) having a pixel electrode arranged oppositely of each pixel, a liquid crystal controller (5) driving the liquid crystal panel, and a backlight (2) arranged on the back surface of the liquid crystal panel and having LEDs (23) as the light source. The liquid crystal controller (5) includes a drive voltage determination circuit (51) which, on the basis of the image information to be displayed, determines the drive voltage necessary to drive the pixel electrodes of the liquid crystal panel, an overshoot voltage determination circuit (52) which determines, on the basis of the aforementioned drive voltage and the temperature of the aforementioned pixel electrodes, the overshoot voltage to be added to the drive voltage, and an overshoot voltage determination LUT (531) having multiple overshoot parameters for determining the overshoot voltage.

Description

Liquid crystal display

The present invention relates to a liquid crystal display device used for a flat-screen television receiver or the like.

The liquid crystal display device includes a backlight unit that emits planar light, and a liquid crystal panel unit that adjusts a transmission amount (transmittance) of the planar light emitted from the backlight unit and forms an image. . Since the backlight unit has the advantages of downsizing (thinning), power saving, and long life, the use of LEDs as a light source is increasing. There are mainly two types of backlight units. One is an edge light system in which light from a light source is incident on a light receiving surface on a side surface of a light-transmitting plate-shaped light guide plate, and planar light is emitted from a light output surface which is one of main surfaces. The other is a direct type system in which a light source is arranged on a planar substrate.

In the direct type backlight unit, the image display area of the liquid crystal panel unit is divided into a plurality of areas, and the liquid crystal panel unit is irradiated with light having a luminance according to the image displayed in the area. There is a backlight unit. The area active type backlight unit can increase the contrast of the image and reduce the power consumption of the backlight unit compared to the backlight unit that emits planar light with the same brightness on the entire surface. It is.

On the other hand, the liquid crystal panel unit has a structure in which two transparent substrates on which electrodes are formed are arranged in parallel, and a liquid crystal layer containing a liquid crystal material is arranged between the two transparent substrates. Since the liquid crystal material (liquid crystal molecules) has a dielectric anisotropy, applying a voltage to the liquid crystal layer changes the major axis direction of the liquid crystal molecules in the liquid crystal layer, and transmits polarized light. The direction is changing. Furthermore, polarizing plates are attached to both sides of the surface of the transparent substrate through which light is transmitted, so that the amount of light transmitted through the liquid crystal layer is changed according to the voltage. In the liquid crystal panel unit, by applying a voltage to each pixel, the light transmission degree (luminance) for each pixel is adjusted, and an image is displayed in the image display area of the liquid crystal panel unit.

In the liquid crystal panel unit, it takes a certain amount of time (hereinafter referred to as response time) from when a voltage is applied to the liquid crystal layer until the liquid crystal layer has a transmittance corresponding to the voltage. This response time is affected by the temperature of the liquid crystal layer. When the temperature of the liquid crystal layer is high, the response time is short (response is good), and when the temperature of the liquid crystal layer is low, the response time is long (response Is worse). This response time greatly affects the switching of the image of the liquid crystal display device.

For example, when a moving image (moving image) is displayed on the liquid crystal display device, the display image is switched in time series to express the motion. When such an image switching is performed, if the response is poor, the light transmission of each pixel is not sufficiently switched before and after the image switching, and the remaining (afterimage) of the previous image is displayed, and the display quality of the moving image is deteriorated.

In order to suppress such an afterimage, in the liquid crystal panel unit, when a voltage is applied to the liquid crystal layer, a voltage (overvoltage) that is higher than a voltage to be applied (in other words, a voltage necessary for displaying an image) is to be applied. An “overshoot control” is applied to apply a shoot voltage).

Also, in each pixel of the liquid crystal display device, if the change in gradation between the pre-display and the post-display is large, the light transmittance of the liquid crystal layer is not sufficiently changed, and an afterimage may occur. In view of this, a liquid crystal display device has been proposed in which the amount of overshoot is adjusted according to the amount of gradation change between the front display and the rear display, and the light transmittance of the liquid crystal layer in each pixel is quickly changed. (For example, JP 2007-233301 A).

JP 2007-233301 A

The backlight unit using an LED as a light source generates less heat than a backlight unit using a fluorescent tube that has been conventionally used. For this reason, the temperature distribution of the light guide plate in the edge light type backlight unit has a high temperature near the light source, and the temperature tends to decrease as the distance increases. Since the temperature of the light guide plate is transmitted to the liquid crystal panel unit, a similar temperature distribution occurs in the liquid crystal panel unit. Accordingly, in the liquid crystal panel unit, the temperature of the liquid crystal material is high in the region close to the light source, and the response speed is increased. Further, in the region away from the light source, the temperature of the liquid crystal material is difficult to increase, and the response speed is slow.

Further, when the LED is used as the light source in the area active type backlight unit, the brightness of the incident light is different for each region. That is, in a region where the brightness of the display image of the liquid crystal panel unit is high, high brightness light is incident and the temperature is high. Further, in a region where the luminance of the display image of the liquid crystal panel unit is low, light with low luminance is incident and the temperature is lowered. As described above, a temperature difference (temperature distribution) is generated in the liquid crystal material between the region where the luminance of the display image is high and the region where the luminance is low. As a result, as in the case of the edge light type backlight unit, the response speed varies depending on the area, such that the response speed of the liquid crystal material is high in the high temperature area and the response speed is low in the low temperature area.

Also, in the conventional liquid crystal display device, the amount of overshoot of the voltage applied to the liquid crystal material is determined by the gradation of the image, and the same overshoot amount according to the change of the gradation regardless of the response speed of the liquid crystal material. Overshoot control is performed. As a result, the response speed of the liquid crystal material cannot be sufficiently increased in the low temperature part, and the image quality is deteriorated. In the high temperature part, excessive power consumption is applied by applying an excessive overshoot amount. It will become.

Therefore, an object of the present invention is to provide a liquid crystal display device capable of reducing power consumption without deteriorating the display quality of an image.

In order to achieve the above object, the present invention provides a liquid crystal panel having pixel electrodes opposed to each pixel, a liquid crystal panel driving means for driving the liquid crystal panel, and a rear surface of the liquid crystal panel. A liquid crystal display device including a backlight, wherein the liquid crystal panel driving means applies a voltage higher than a voltage required for driving when applying a voltage to the pixel electrode, and displays Voltage determining means for determining a driving voltage necessary for driving the pixel electrode of the liquid crystal panel based on image information, and an overshoot voltage to be added to the driving voltage based on the temperature of the pixel electrode and the driving voltage. Overshoot voltage determining means for determining.

According to this configuration, the variation in the response speed of the liquid crystal material in each pixel can be reduced regardless of the temperature of the liquid crystal panel by changing the voltage value of the LED based on the driving of the LED in the backlight. . Thereby, power consumption can be reduced without degrading the display quality of the image.

In the above configuration, the liquid crystal panel driving unit further includes an overshoot voltage determining table having a plurality of overshoot parameters for determining the overshoot voltage, and the overshoot voltage determining unit includes the overshoot voltage determining unit. The overshoot voltage may be determined based on the shoot parameter.

In the above configuration, the liquid crystal panel driving means includes time measuring means for measuring a predetermined time from the moment when the frame is switched, and the liquid crystal panel driving means is a predetermined time from the moment when the frame is switched. A voltage obtained by adding the drive voltage and the overshoot voltage may be applied to the pixel electrode during the interval, and then the drive voltage may be applied to the pixel electrode.

In the above configuration, the time measuring means is included in the overshoot voltage determining means, and the overshoot voltage determining means outputs a voltage obtained by adding the overshoot voltage to the drive voltage immediately after the frame is switched, The drive voltage may be output as it is after a predetermined time has elapsed.

In the above configuration, the backlight may be one in which the LEDs are two-dimensionally arranged on the back surface of the liquid crystal panel.

In the above configuration, the backlight may be one in which LEDs are arranged so that the density is high in the central part and the density is low in the edge part.

In the above-described configuration, the backlight may include a light guide plate having a light incident surface on which light from the LED is incident on a side surface.

In the above configuration, the overshoot voltage determination table may include the overshoot parameter in accordance with the temperature distribution of the liquid crystal panel.

In the above configuration, the overshoot voltage determination table may divide the liquid crystal panel into a plurality of regions for each temperature level, and may include an overshoot parameter for each region.

In the above configuration, the backlight is divided into a plurality of areas, and includes a backlight controller that can independently adjust the luminance of the LEDs included in the area, and obtains luminance information for each frame of the LEDs in each area. And a synchronization means for sending to the overshoot voltage determination means, wherein the overshoot voltage determination means is based on the luminance information of the LED that emits light incident on the pixel in the previous frame, and May be determined.

According to the present invention, the variation of the response speed of the liquid crystal material in each pixel can be achieved regardless of the temperature of the liquid crystal panel by changing the voltage value when performing the overshoot control based on the driving of the light source in the backlight. It is possible to provide a liquid crystal display device that can reduce power consumption without reducing the image display quality.

It is a disassembled perspective view of an example of the liquid crystal display device concerning this invention. It is a block diagram which shows schematic structure of the liquid crystal display device shown in FIG. It is a figure which shows the relationship between the brightness | luminance at the time of overshoot drive at the time of low temperature, and the voltage applied to a pixel electrode, and time. FIG. 4 is a diagram illustrating the relationship between the brightness of overshoot drive when the temperature is high in the same pixel as in FIG. 3 and the voltage applied to the pixel electrode and time. It is a disassembled perspective view of the other example of the liquid crystal display device concerning this invention. It is the schematic which shows the temperature distribution of a liquid crystal panel. 7 is an overshoot voltage determination LUT showing overshoot parameters in each region shown in FIG. 6. It is a disassembled perspective view of the liquid crystal display device concerning this invention. It is a temperature distribution of the liquid crystal panel of the liquid crystal display device shown in FIG. It is a table | surface which shows an example of LUT for overshoot voltage determination.

(First embodiment)
FIG. 1 is an exploded perspective view of an example of a liquid crystal display device according to the present invention, and FIG. 2 is a block diagram showing a schematic configuration of the liquid crystal display device shown in FIG. As shown in FIG. 1, the liquid crystal display device A includes a liquid crystal panel unit 1 and a backlight unit 2 (backlight). The liquid crystal display device A has a horizontally long rectangular shape as a whole, and is integrally held by a frame-like bezel (not shown) or the like. In addition to the liquid crystal panel unit 1 and the backlight unit 2, the liquid crystal display device A includes an image data acquisition unit 3, an image signal processing unit 4, a liquid crystal controller 5 (liquid crystal panel driving means), A synchronization circuit 6 and the like are provided.

As shown in FIG. 1, the liquid crystal panel unit 1 has a rectangular shape in plan view, and a pair of glass substrates are bonded together with a predetermined gap therebetween, and liquid crystal is sealed between the glass substrates. A liquid crystal panel 12 is provided.

One glass substrate is provided with a switching element (for example, TFT (thin film transistor)) connected to a source wiring and a gate wiring orthogonal to each other, a pixel electrode connected to the switching element, an alignment film, and the like. The other glass substrate is provided with a color filter in which colored portions such as R (red), G (green, and B (blue)) are arranged in a predetermined arrangement, a common electrode, and an alignment film. Further, a polarizing plate is disposed on the outside of both substrates.

With such a configuration, the liquid crystal panel unit 1 is provided with color pixels of 1920 × 1080 dots, for example, for high vision. Each pixel is divided into subcells that emit red (R), green (G), and blue (B) light. By adjusting the transmittance of each subcell, the color and brightness of each pixel are divided. It is the composition which adjusts.

As shown in FIG. 2, the liquid crystal panel unit 1 includes a liquid crystal driver 11 and a liquid crystal panel 12. Then, the liquid crystal driver 11 applies a voltage to the pixel electrode using the switching element of each pixel of the liquid crystal panel 12 based on the signal received from the liquid crystal controller 5. Thereby, the liquid crystal panel 12 adjusts the voltage of each pixel electrode in accordance with the image data, drives the liquid crystal arranged in each pixel (subcell), and adjusts the light transmission degree (luminance) of each pixel (subcell). Is done. In the liquid crystal display device A, when the planar light from the backlight unit 2 is incident from the back surface of the liquid crystal panel unit 1, the subcell of the liquid crystal panel 12 emits RGB light of a predetermined gradation, and each pixel has Light of a predetermined color and brightness is emitted. Thereby, an image corresponding to the image data is displayed in the image display area of the liquid crystal panel unit 1.

The backlight unit 2 is an illuminating device that is driven by an LED control signal generated by an LED controller 21 described later and irradiates the liquid crystal panel unit 1 with planar light. The backlight unit 2 includes an LED panel (LED mounting board) 20, an LED controller 21 (backlight controller), an LED driver 22, an LED (Light Emitting Diode) 23, an optical member 24 such as a diffusion plate or an optical sheet, and the like. It has. In the backlight unit 2, the LED panel 20 has the LED 23 mounted on the mounting surface facing the liquid crystal panel unit 1.

As shown in FIG. 1, the LED panel 20 has a configuration in which a plurality of areas 200 are arranged vertically and horizontally. The area 200 is set so as to include at least one LED 23. In the backlight unit 2, the LED panel 20 includes 16 areas × 9 areas (144 in total). The LED driver 22 drives the LED 23 for each area 200 (light emission driving). Note that the LED data signal and the luminance data generated based on the LED data signal (details will be described later) are data provided for each area 200.

The LED 23 forms, for example, an LED unit in which LED chips that emit light of wavelengths of red, green, and blue (R, G, B) are gathered. The LED unit becomes white light as a whole by emitting light of each wavelength. Moreover, about the structure (a kind, a color, a combination, etc.) of LED23, another aspect may be sufficient. For example, a white LED such as a pseudo white LED or a high color rendering white LED may be used instead of the LED unit described above, and an LED that emits light having a yellow (Y) wavelength in addition to the RGB described above. A concentrated LED unit may be used.

Also, the light emission time of the LED 23 is controlled by PWM (pulse width modulation) control. The brightness of the LED 23 is adjusted by adjusting the light emission time, and the LED 23 becomes brighter as the light emission time is longer. The rate at which the LED 23 is turned on (emits light) per unit time is referred to as a light emission duty ratio, and the light emission of the LED 23 is controlled by the light emission duty ratio. The LED controller 21 generates a light emission duty ratio (hereinafter referred to as luminance data) used for PWM control based on the LED data signal.

As described above, the backlight unit 2 can adjust the luminance of the LED 23 mounted on the LED panel 20 for each area 200. That is, the backlight unit 2 is a so-called area active type backlight unit that can irradiate the liquid crystal panel unit 1 with planar light (with a luminance distribution) adjusted in luminance for each area 200. In the area active type backlight unit 2, the LED 23 emits light in accordance with the luminance of the image displayed on the liquid crystal panel unit 1, that is, the luminance is high in a portion where the luminance of the image is high and low in a low portion. Thereby, power consumption can be reduced without reducing the contrast of the video.

The image data acquisition unit 3 is an interface for inputting an image signal from the outside. Here, a television broadcast signal is received, the received signal is converted into an image signal, and transmitted to the image processing unit 4.

The image processing unit 4 generates an LCD data signal for driving the liquid crystal panel unit 1 and an LED data signal for driving the backlight unit 2 based on the input image signal. The image processing unit 4 includes a Y / C separation circuit 41 that separates an image signal into a luminance signal Y and a color signal C, a signal adjustment circuit 42 that independently adjusts the luminance signal Y and the color signal C, and adjusted luminance. A color demodulation circuit 43 that demodulates the signal Y and the color signal C into an RGB signal, a contrast adjustment circuit 44 that performs contrast adjustment, a gamma correction circuit 45 that performs gamma correction, an LED data signal and an LCD from the gamma-corrected RGB signal And a signal generation circuit 46 for generating a data signal.

Then, the LED data signal generated by the signal generation circuit 46 is transmitted to the LED controller 21, and the LCD data signal is transmitted to the liquid crystal controller 5. Further, the signal generation circuit 46 inputs the gradation information contained in the video signal to the LED controller 21 as a gradation signal.

The liquid crystal controller 5 is a control circuit that generates a signal for driving the liquid crystal panel 12 based on the LCD data signal and transmits the signal to the liquid crystal driver 11. The liquid crystal controller 5 includes a drive voltage determination circuit 51 (voltage determination means), an overshoot voltage determination circuit 52 (overshoot voltage determination means), and a memory 53.

The LCD data signal includes RGB gradation data for each pixel of the liquid crystal panel 12. Based on the LCD data signal, the drive voltage determination circuit 51 determines the light transmittance in the RGB subcell of each pixel, and calculates the voltage applied to the switching element to obtain the light transmittance.

In the liquid crystal display device A, the luminance of the pixel is a combination of the light transmittance of the liquid crystal panel 12 and the luminance of the LED 23, and the light transmittance of the liquid crystal panel 12 needs to be synchronized with the luminance of the LED 23. Therefore, the synchronizing circuit 6 is used to synchronize the luminance of the LED 23 and the light transmittance of the liquid crystal panel 12 and control each pixel to have a luminance corresponding to the image data. Specifically, the synchronization circuit 6 receives the light emission luminance data of the LED 23 for each area 200 for each frame, and sends the light emission luminance data to the drive voltage determination circuit 51.

The drive voltage determination circuit 51 includes drive voltage data including the drive voltage of the switching element of each pixel (subcell) based on the LCD data signal and the light emission luminance data of the LED 23 so that each pixel (subcell) has a desired luminance. It is generated and sent to the overshoot voltage determination circuit 52.

Here, in order to facilitate the description of the overshoot voltage determination circuit 52, the temperature characteristics of the response speed of the liquid crystal will be described. In the liquid crystal panel 12, each pixel has a desired luminance by applying a voltage between the pixel electrodes of each pixel. In the liquid crystal panel 12, when a voltage is applied, a certain time is required until the luminance of the pixel is switched to a desired luminance. Further, the liquid crystal panel 12 has a characteristic that the luminance is switched faster as the difference in applied voltage is larger. Therefore, in the liquid crystal panel unit 1, a voltage applied to each pixel of the liquid crystal panel 1 is temporarily applied with a voltage higher than a voltage for obtaining a necessary luminance, and then a voltage for obtaining a desired luminance. In other words, so-called overshoot driving is performed.

Details of overshoot drive will be described with reference to the drawings. FIG. 3 is a diagram showing the relationship between the luminance and the voltage applied to the pixel electrode and time when performing overshoot driving at a low temperature. FIG. 3 illustrates one pixel among the plurality of pixels of the liquid crystal panel 1, but it is assumed that the same overshoot drive is performed in all the pixels.

As shown in FIG. 3, the voltage necessary for obtaining the brightness of the previous frame (referred to as the first frame Fr1) is V1, and the voltage required for obtaining the brightness of the next frame (referred to as the second frame Fr2). Assuming that the voltage V2 is V2, when switching from the first frame Fr1 to the second frame Fr2, a voltage V3 obtained by adding an overshoot voltage ΔV1 to V2 is applied to the pixel electrode. The applied voltage is changed from V3 to V2 after a lapse of a predetermined time from frame switching.

In the liquid crystal panel 1, as the difference in applied voltage is larger, the speed of change in luminance becomes faster. Therefore, at the time of frame switching, a voltage V3 obtained by adding the overshoot voltage ΔV1 to the required voltage V2 is applied to rapidly change the luminance of the pixel (the inclination of the inclined portion in the figure becomes steep). Thereby, the time (response time) until the luminance is switched can be shortened, and the display quality of the image of the liquid crystal display device A can be improved.

In addition, the liquid crystal panel 1 has a characteristic that the change rate of brightness (response speed) changes depending on the temperature. That is, when the pixel temperature is high, the luminance is switched (rise of the sloped portion in the drawing) faster than when the pixel temperature is low. Therefore, when the pixel temperature is high, the luminance switching speed can be made equal even if the overshoot voltage value is smaller than when the pixel temperature is low.

FIG. 4 is a diagram showing the luminance of overshoot drive when the temperature is high in the same pixel as in FIG. 3, and the relationship between the voltage applied to the pixel electrode and time. As shown in FIG. 4, since the temperature of the pixel is high, the luminance is rapidly switched when switching from the first frame Fr1 to the second frame Fr2. Therefore, the overshoot voltage ΔV2 is lower than the overshoot voltage ΔV1. That is, when switching from the first frame Fr1 to the second frame Fr2, the voltage V4 applied to the pixel electrode is lower than the applied voltage V3 at low temperature. As described above, by changing the value of the overshoot voltage depending on the temperature, the change in luminance in the pixel can be made constant (substantially constant). Thus, by changing the overshoot drive according to the temperature, the luminance switching of the liquid crystal panel 1 can be made constant, and the display quality of the image of the liquid crystal display device A can be improved.

The overshoot voltage determination circuit 52 determines the overshoot voltage of each pixel based on such characteristics of the liquid crystal panel 1. The overshoot voltage determination circuit 52 refers to the overshoot voltage determination LUT 531 provided in the memory 53 and determines an overshoot voltage for each pixel. The overshoot voltage determination circuit 52 adds the determined overshoot voltage to the drive voltage data.

The memory 53 includes a readable / writable RAM, a read-only ROM, and the like, and is a storage device that can hold information. The drive voltage determination circuit 51 and the overshoot voltage determination circuit 52 are configured to always access the memory 53.

The overshoot voltage determination LUT 531 (overshoot voltage determination table) stored in the memory 53 includes a first overshoot parameter used when the pixel is at a low temperature and a second overshoot parameter used when the pixel is at a high temperature. It has. The first overshoot parameter is a larger value than the second overshoot parameter.

The overshoot voltage determination circuit 52 will be described in detail. The overshoot voltage determination circuit 52 calls the first overshoot parameter or the second overshoot parameter from the overshoot voltage determination LUT 531 based on the pixel information in the previous frame.

The backlight unit 2 of the liquid crystal display device A is an area active type backlight, and adjusts the luminance of the LED 23 in the area corresponding to the pixel in accordance with the luminance of the pixel. In such a liquid crystal display device A, when the luminance of the LED 23 is high, the temperature of the pixel corresponding to the area 200 in which the LED 23 is arranged increases, and when the luminance is low, the temperature decreases. On the other hand, the luminance of the pixel is a combination of the light transmittance of the liquid crystal panel 12 and the luminance of the LED 23, and the pixel temperature is not uniquely determined by the luminance. That is, even if the luminance of the pixel is low, the luminance of the LED 23 may be high and the temperature may be high, and even if the luminance of the pixel is high, the luminance of the LED 23 may be low and the temperature may be low.

Therefore, the overshoot voltage determination circuit 52 acquires the light emission luminance data of the LED 23 arranged in the area 200 corresponding to each pixel in the frame before the synchronization circuit 6, and based on the light emission luminance data of the LED 23, Select one overshoot parameter or second overshoot parameter. That is, when the emission luminance of the LED 23 in the area 200 corresponding to the pixel is low in the previous frame, the overshoot voltage determination circuit 52 determines that the pixel temperature is low and selects the first overshoot parameter. On the contrary, when the light emission luminance of the LED 23 is high in the previous frame, it is determined that the pixel temperature is high, and the second overshoot parameter is selected.

The overshoot parameter is given as a ratio to the drive voltage, and the overshoot voltage determination circuit 52 determines the overshoot voltage from the drive voltage data and the overshoot parameter.

The overshoot voltage determination circuit 52 includes a timer circuit therein, and controls the time for sending drive voltage data obtained by adding the overshoot voltage in the timer circuit. That is, the overshoot voltage determination circuit 52 sends drive voltage data obtained by adding the overshoot voltage to the drive voltage data to the liquid crystal driver 11 for a predetermined time from the frame switching, and after the predetermined time has elapsed, The drive voltage data not added is sent to the liquid crystal driver 11. The timer circuit may be provided outside the overshoot voltage determination circuit 52, and the overshoot voltage determination circuit 52 may confirm the time.

In addition, the drive voltage determination circuit 51 sends the overshoot voltage determination circuit 52 to the overshoot voltage determination circuit 52 for a predetermined time from the frame switching timing. Data may be sent out. In this case, a timer circuit may be provided inside the drive voltage determination circuit 51, or may be disposed outside the drive voltage determination circuit 51 and the overshoot voltage determination circuit 52 inside the liquid crystal controller 5. .

The liquid crystal driver 11 applies a voltage to the switching element of each pixel (subcell) based on the drive voltage data sent from the liquid crystal controller 5 to control the light transmittance of each pixel.

As shown above, by changing the overshoot voltage according to the pixel temperature, the overshoot can be terminated in a certain period regardless of the brightness of the previous frame or the brightness of the next frame. Apparatus A can display images with high accuracy.

In the above embodiment, the overshoot voltage determination LUT 531 is provided with two types of overshoot parameters, but is not limited to two types, and is further classified according to the luminance of the LED 23. Also good. Different overshoot parameters may be provided depending on the voltage difference between the previous frame and the subsequent frame. The overshoot voltage determination circuit 52 extracts the overshoot parameter from the overshoot voltage determination LUT 531 and determines the overshoot voltage. However, the present invention is not limited to this. For example, the overshoot voltage determination circuit 52 may determine the overshoot voltage by calculation from the temperature of the liquid crystal panel 12 and the voltage value determined by the drive voltage determination circuit 51.

In the liquid crystal controller 5, the overshoot voltage determination circuit 52 determines the overshoot voltage and adds the overshoot voltage to the drive voltage data, but is not limited to this. For example, the overshoot voltage determination circuit 52 multiplies the drive voltage data by a parameter including a predetermined weight, thereby treating the drive voltage data in the same manner as adding the overshoot voltage to the drive voltage data. 1 may be driven.

(Second Embodiment)
Another example of the liquid crystal display device according to the present invention will be described with reference to the drawings. FIG. 5 is an exploded perspective view of another example of the liquid crystal display device according to the present invention. As shown in FIG. 5, the liquid crystal display device B has the same configuration as the liquid crystal display device A except that the backlight unit 2b is different, and substantially the same parts are denoted by the same reference numerals. Detailed description of the same part is omitted.

As shown in FIG. 5, in the backlight unit 2b, LEDs 23 are arranged on the LED panel 20b. The backlight unit 2b has a high installation density in the central part, and the LED 23 is arranged so that the installation density decreases as it approaches the edge part, in accordance with the characteristics of the human eye that is difficult to recognize the luminance of the edge part. .

In the backlight unit 2b, all the LEDs 23 emit light with a constant light emission luminance. That is, the planar light emitted from the backlight unit 2b has a luminance distribution with a high center portion and a low edge portion. Yes. Further, since the backlight unit 2b does not perform active area driving, the liquid crystal display device B does not require the synchronization circuit 6. Since the liquid crystal panel unit 1 is irradiated with the planar light emitted from the backlight unit 2b, the pixels in the central portion of the liquid crystal panel 12 of the liquid crystal panel unit 1 become high temperature, and the pixels in the peripheral portion are The temperature distribution becomes low. Therefore, an overshoot voltage determination LUT 532 stored in the memory 53 of the liquid crystal controller 5 is provided corresponding to the temperature distribution of the liquid crystal panel 12.

The overshoot voltage determination LUT 532 will be described with reference to the drawings. FIG. 6 is a schematic diagram showing the temperature distribution of the liquid crystal panel, and FIG. 7 is an overshoot voltage determination LUT showing overshoot parameters in each region shown in FIG. In FIG. 6, the liquid crystal panel 12 is divided into five temperature ranges. In FIG. 6, hatching is performed so that each region can be easily recognized.

As shown in FIG. 6, in the liquid crystal panel 12, the first region Ar1 to the fifth region Ar5 are formed concentrically from the central portion. When the backlight unit 2b is used, the density of the LED 23 and the temperature distribution of the liquid crystal panel 12 have a correlation, that is, the temperature of the liquid crystal panel 12 is high in a portion where the LED 23 is high and the density of the LED 23 is low. The temperature of the liquid crystal panel 12 is also lowered.

From these, it can be said that the overshoot voltage determination LUT 532 corresponds to the density of the LEDs 23 of the backlight unit 2b. That is, when the backlight unit 2b is used, the temperature of the liquid crystal panel 12 has the following relationship. The first region Ar1 at the center of the liquid crystal panel 12 is a region having a temperature of T1 or higher. A second region Ar2 adjacent to the outer periphery of the first region Ar1 is a region having a temperature of T2 or more and less than T1. Similarly, the third region Ar3 adjacent to the outer periphery of the second region has a temperature of T3 or higher and lower than T2, and the fourth region Ar4 adjacent to the outer periphery of the third region has a temperature of T4 or higher and lower than T3, and is the fifth outermost region Ar5. Is a region where the temperature is lower than T4.

As shown in FIG. 7, the overshoot voltage determination LUT 532 has different overshoot parameters depending on the temperature distribution of the liquid crystal panel 12 in each of the first region Ar1 to the fifth region Ar5. That is, the overshoot voltage determination LUT 532 has an overshoot parameter Op1 in the first region Ar1, an overshoot parameter Op2 in the second region Ar2, an overshoot parameter Op3 in the third region Ar3, and an overshoot parameter Op3 in the fourth region Ar4. The overshoot parameter Op5 is given to the shoot parameter Op4 and the fifth region Ar5, respectively.

Since the temperatures of the first region Ar1 to the fifth region Ar5 are determined under the condition of T1> T2> T3> T4, the overshoot parameter is larger as the temperature is lower, and is smaller as the temperature is higher. That is, Op1 <Op2 <Op3 <Op4 <Op5.

The overshoot voltage determination circuit 52 confirms which region the pixel is in, acquires an overshoot parameter corresponding to the region, and calculates an overshoot voltage. For example, when calculating the overshoot voltage of the pixel in the first region Ar1, the overshoot voltage determination circuit 52 acquires the overshoot parameter Op1 corresponding to the first region Ar1 from the overshoot voltage determination LUT 531. The overshoot voltage is calculated by this method.

In this way, by determining the overshoot parameter for each region, the period until switching from the previous frame to the next frame in all regions can be made constant (almost constant), and the display quality of the video is improved. It is possible. In the present embodiment, the area is divided into five areas, but the present invention is not limited to this. The area is further finer or coarser depending on the size of the liquid crystal display device A (liquid crystal panel 12) and the density change of the LEDs 23. It may be divided.

(Third embodiment)
Still another example of the liquid crystal display device according to the present invention will be described with reference to the drawings. FIG. 8 is an exploded perspective view of the liquid crystal display device according to the present invention. The liquid crystal display device C shown in FIG. 8 has the same configuration as the liquid crystal display device shown in FIGS. 1 and 2, etc., except that the backlight unit 2c is different. Detailed description of the same part is omitted.

As shown in FIG. 8, the backlight unit 2 c includes a light guide plate 25 and a plurality of LEDs 23 mounted side by side on the LED panel 20. As shown in FIG. 8, the light guide plate 25 is a rectangular plate-like transparent plate similar to the liquid crystal panel 12, and the LED panel 20 is disposed close to both of the pair of short sides of the light guide plate 25. More specifically, the LED panel 20 is disposed so that the mounting surface of the LED 23 faces the short side of the light guide plate 25. The light emitted from the LED 23 enters the light guide plate 25 from the light incident surfaces formed on both short sides of the light guide plate 25, and is emitted from the exit slope which is one main surface.

The temperature distribution of the light guide plate will be described with reference to the drawings. 9 is a temperature distribution diagram of the liquid crystal panel of the liquid crystal display device shown in FIG. 8, and FIG. 10 is a table showing an example of an overshoot voltage determination LUT.

In the backlight unit 2 c, the LED 23 is disposed in the vicinity of the short side of the light guide plate 25. For this reason, the temperature of the light guide plate 25 has a distribution such that the temperature is higher in the portion near the short side and lower as it is closer to the center. The liquid crystal panel 12 disposed adjacent to the light guide plate 25 also has a high temperature in the vicinity of the short side and a low temperature in the center (see FIG. 9).

Therefore, in the overshoot voltage determination LUT 533 provided in the memory 53 of the liquid crystal controller 5, the overshoot parameter Opc1 of the first region Cr1 close to the short side is lower than the overshoot parameter Opc2 of the second region Cr2 at the center. (See FIG. 10).

The overshoot voltage determination circuit 52 refers to the overshoot voltage determination LUT 533. When the pixel is included in the first region Cr1, the overshoot parameter Opc1 is used, and when the pixel is included in the second region Cr2, the overshoot voltage is determined. The parameter Opc2 is acquired and the overshoot voltage is calculated.

In this way, by dividing the region by the temperature of the light guide plate 25 and determining the overshoot parameter for each region, the period until switching from the previous frame to the next frame is constant (almost constant) in all regions. It is possible to improve the display quality of the video.

In the present embodiment, the liquid crystal panel 12 is divided into two regions according to the temperature, but the present invention is not limited to this, and the liquid crystal panel 12 may be further divided according to the temperature distribution. In addition, the light incident surface of the light guide plate 25 is a surface with both short sides, but is not limited to this, and as long as it is a side surface, it may be only one surface, and all three surfaces or all four surfaces may enter. It may be formed as an optical surface. Moreover, it is not limited to these, It is also possible to utilize the backlight unit which has a light-guide plate which has a light-incidence surface in a side surface. In such a case as well, an overshoot voltage determining LUT having an overshoot parameter corresponding to the temperature distribution of the light guide plate may be provided.

(Other embodiments)
In the liquid crystal display device, a temperature distribution is likely to occur in the liquid crystal panel immediately after the power is turned on, and heat is applied or the temperature of the liquid crystal panel approaches a uniform temperature while being driven for a long time. Therefore, the liquid crystal controller 5 acquires an overshoot parameter from the overshoot voltage determination LUT and determines an overshoot voltage until a predetermined time elapses after the power is turned on. As the fixed time elapses, the temperature of the liquid crystal panel approaches uniform, and the response speed of the pixels becomes equal. Accordingly, the overshoot voltage may be determined using the same overshoot parameter for all pixels.

In addition, a sensor for detecting the temperature of the central portion and the edge portion of the liquid crystal panel is attached, and an overshoot voltage determination LUT is used for each pixel until the difference value of the detected temperature becomes a certain value or less. After the overshoot voltage is determined and the temperature difference value becomes a certain value or less, the overshoot voltage may be determined using the same overshoot parameter for all the pixels.

As mentioned above, although embodiment of this invention was described, this invention is not limited to this content. The embodiments of the present invention can be variously modified without departing from the spirit of the invention.

The present invention can be used as a display device for devices such as a thin television device, a thin display device, and a mobile phone.

DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 11 Liquid crystal driver 12 Liquid crystal panel 2 Backlight 20 LED panel 21 LED controller 22 LED driver 23 LED
3 image data acquisition unit 4 image signal processing unit 41 Y / C separation circuit 42 signal processing circuit 43 color demodulation circuit 44 contrast adjustment circuit 45 gamma correction circuit 46 signal generation circuit 5 liquid crystal controller 51 drive voltage determination circuit 52 overshoot voltage determination circuit 53 memory

Claims

A liquid crystal panel having pixel electrodes arranged opposite to each other;
Liquid crystal panel driving means for driving the liquid crystal panel;
A liquid crystal display device disposed on the back surface of the liquid crystal panel and provided with a backlight having an LED as a light source;
The liquid crystal panel driving means applies a voltage higher than a voltage necessary for driving when applying a voltage to the pixel electrode,
Voltage determining means for determining a driving voltage necessary for driving the pixel electrode of the liquid crystal panel based on image information to be displayed;
A liquid crystal display device comprising overshoot voltage determining means for determining an overshoot voltage to be added to the drive voltage based on the temperature of the pixel electrode and the drive voltage.
The liquid crystal panel driving means further includes an overshoot voltage determination table having a plurality of overshoot parameters for determining the overshoot voltage,
The liquid crystal display device according to claim 1, wherein the overshoot voltage determining unit determines an overshoot voltage based on the overshoot parameter.
The liquid crystal panel driving means includes time measuring means for measuring a predetermined time from the moment when the frame is switched,
The liquid crystal panel driving means applies a voltage obtained by adding the driving voltage and the overshoot voltage to the pixel electrode for a predetermined time from the moment when the frame is switched,
3. The liquid crystal display device according to claim 1, wherein the driving voltage is applied to the pixel electrode.
The time measuring means is included in the overshoot voltage determining means,
The overshoot voltage determining means outputs a voltage obtained by adding an overshoot voltage to the drive voltage immediately after the frame is switched, and outputs the drive voltage as it is after a predetermined time has elapsed. The liquid crystal display device described.
The liquid crystal display device according to any one of claims 1 to 4, wherein the backlight has the LEDs arranged two-dimensionally on the back surface of the liquid crystal panel.
6. The liquid crystal display device according to claim 5, wherein the backlight is configured such that the LEDs are arranged so that the density of the central portion is high and the density of the peripheral portion is low.
The liquid crystal display device according to any one of claims 1 to 4, wherein the backlight includes a light guide plate having a light incident surface on a side surface on which light from the LED is incident.
The liquid crystal display device according to claim 1, wherein the overshoot voltage determination table includes the overshoot parameter in accordance with a temperature distribution of the liquid crystal panel.
The overshoot voltage determination table divides the liquid crystal panel into a plurality of regions for each temperature level,
The liquid crystal display device according to claim 8, wherein an overshoot parameter is provided for each region.
The backlight is divided into a plurality of areas, and includes a backlight controller that can independently adjust the luminance of the LEDs included in the area,
The apparatus includes a synchronization unit that acquires luminance information for each LED frame in each area and sends the luminance information to the overshoot voltage determination unit.
The liquid crystal display device according to claim 5, wherein the overshoot voltage determining unit determines the temperature of the pixel based on luminance information of an LED that emits light incident on the pixel in the previous frame.