JP2011085693A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve image definition by suppressing color change in a liquid crystal panel screen when changing the driving current for an LED backlight. <P>SOLUTION: The liquid crystal display device 1 is configured to control the light emission luminance of the LED backlight 10 by means of both a pulse width modulation system to change a duty showing a turn-on time per pulse period to turn on/off the LED backlight 10 and a current value control system to change the current value flowing in the LED. An image signal processing part 13 is configured to, when changing the current value of the LED, adjust the image signal in accordance with the current value of the LED so that the display hue of the liquid crystal panel 18 in accordance with the input image signal of a predetermined gradation may be always constant. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device including a liquid crystal panel and an LED backlight that illuminates the liquid crystal panel.

  In recent years, liquid crystal display devices such as liquid crystal televisions are becoming thinner. As a configuration example for realizing the thinning, there is one using an LED (Light Emitting Diode) as a backlight used in a liquid crystal television. The LED has a smaller volume than a cold cathode fluorescent lamp (CCFL) that is a line light source, and can increase the degree of freedom of the layout of the backlight. Further, LEDs are equivalent to CCFLs in terms of power consumption or are becoming lower than CCFLs.

Some liquid crystal televisions have an output mode in which the state of video and audio can be set to a user-desired state. Since the image quality is changed for each mode, the output mode is also called an image quality mode (corresponding to the image quality / sound quality mode in the embodiment of the present invention). Further, the brightness adjustment of the backlight may be changed by changing the image quality mode.
In addition, the light emission luminance level of the backlight can be arbitrarily adjusted by a user operation. In addition, there is a type in which the brightness around the liquid crystal television is detected and the light emission luminance of the backlight is automatically adjusted according to the brightness detection result.

  When changing the brightness of the backlight, PWM (Pulse Width Modulation) control is generally applied. This is because in PWM, the duty of PWM and the luminance of the backlight have a substantially linear relationship. When the backlight has high luminance, the PWM ON duty is increased, and when the backlight has low luminance, the PWM ON duty is decreased to control the light emission luminance of the backlight.

However, in the case of PWM control, if the PWM ON duty is extremely low, the efficiency of the power supply may be reduced or linear control may not be possible. Therefore, consider changing the LED drive current when changing the luminance of the backlight. When trying to obtain the same light emission brightness with the LED, the PWM ON duty is increased by reducing the LED drive current, and the efficiency of the power supply can be increased. That is, in general, in order to obtain the same light emission luminance with the LED, the power consumption is lower when the driving power is decreased and the PWM ON duty is increased.
Thus, by combining PWM control and current control, the control range of the LED can be expanded, and the efficiency of the power supply can be improved.

  For example, the backlight driving device disclosed in Patent Document 1 adjusts the on / off period of a static voltage regulator while changing the power source with a static voltage regulator to provide a power source in the form of a PWM pulse to the LED array. The amplitude of the PWM pulse is adjusted by adjusting the duty of the pulse, adjusting the level of the drive current detected by the LED array, and feeding it back by the electrostatic voltage regulator. As a result, analog dimming and PWM dimming can be controlled for each channel and LED type of the LED backlight, thereby achieving uniform brightness and uniform color in the entire backlight region.

JP 2006-216535 A

FIG. 8 is a diagram showing an example of the chromaticity change of the emission color when the LED drive current is changed. The forward current for driving the white LED and the change in chromaticity of the white LED are shown in the CIE chromaticity diagram. It is shown. As shown in FIG. 8, as a characteristic of the white LED, the color of light emission changes according to the forward current.
For example, a white LED uses a blue light emitting diode as a chip of a light emitting portion and covers it with a YAG-based phosphor, thereby transmitting light (yellow) obtained from fluorescence as a fluorescent light and the phosphor. This is a mixture of blue and white light emission. There is also a combination of a blue light emitting diode, a phosphor emitting red light, and a phosphor emitting green light so as to obtain white. Here, when the forward current of the white LED changes, the light emission intensity of the blue light emitting diode changes. When the blue light emission intensity changes, the light emission intensity from the phosphor also changes accordingly, the overall balance changes, and the color changes. FIG. 8 shows an example of a change in color with a change in forward current of such an LED. As shown in FIG. 8, the color of light emitted from the white LED changes as the forward current changes. If a white LED is used for the backlight, the change in the color naturally affects the color on the screen, which is not preferable because the image quality deteriorates.

  In other words, in a backlight using an LED, by combining PWM control and current control, the control range of the LED can be expanded and the efficiency of the power supply can be improved. When the drive current is changed, there is a problem that the color of light emission changes and the color on the screen of the illuminated liquid crystal panel also changes.

  The present invention has been made in view of the above circumstances, and in a configuration using an LED as a backlight, the color change of the liquid crystal panel screen is suppressed and the image quality is improved when the LED drive current is changed. An object of the present invention is to provide a liquid crystal display device.

  In order to solve the above problems, a first technical means of the present invention includes a liquid crystal panel that displays an input video signal and a backlight that uses an LED that illuminates the liquid crystal panel, and turns on / off the LED. A liquid crystal display device for controlling the light emission luminance of an LED by both a pulse width modulation method for changing a duty indicating a lighting time per cycle in a pulse and a current value control method for changing a current value flowing through the LED. If the gradation of the input video signal is the same when the LED current value is changed, the video signal is adjusted according to the LED current value so that the display color of the liquid crystal panel is always constant. It is characterized by doing.

  The second technical means is characterized in that, in the first technical means, the color adjustment is adjustment of RGB balance of the video signal.

  According to a third technical means, in the first or second technical means, a relationship between a dimming setting value for controlling the light emission luminance of the backlight and a current value to be supplied to the LED is determined in advance. A memory that stores in advance adjustment values for adjusting the color tone of the image signal when applying the adjustment value according to the current value determined according to the dimming setting value when the backlight is emitted. It is characterized by adjusting.

  According to a fourth technical means, in the first to third liquid crystal display devices, the adjustment value for adjusting the color is an RGB γ correction value corresponding to a current value. It is a thing.

  According to the present invention, in a configuration in which an LED is used as a backlight, it is possible to suppress the color change of the liquid crystal panel screen when the LED drive current is changed and to improve the image quality.

It is a block diagram which shows the structural example of the liquid crystal display device by this invention. FIG. 2 is a functional block diagram for further explaining the LED control unit, the LED driving unit, and the LED backlight of FIG. 1. It is a figure which shows an example of a light control table. It is a figure which shows an example of the electric current setting value according to image quality and a sound quality mode, and the light control table to be used. It is a figure for demonstrating the setting example of the ON duty of PWM according to the brightness of a backlight. It is a figure which shows the relationship between the light control setting value of a backlight according to image quality and sound quality mode, and screen brightness | luminance. It is a figure which shows the example of arrangement | positioning of the backlight applicable to the liquid crystal display device of this invention. It is a figure which shows an example of the chromaticity change of the luminescent color when changing the drive current of LED.

  FIG. 1 is a block diagram showing a configuration example of a liquid crystal display device according to the present invention, and shows an embodiment configured as a liquid crystal television. The liquid crystal display device 1 includes an LED backlight 10, a tuner unit 11, an operation unit 12, a video signal processing unit 13, a main control unit 14, an LED drive unit 15, an external light illuminance detection unit 16, a liquid crystal control unit 17, a liquid crystal panel 18, And a ROM (Read Only Memory) 19.

  The main control unit 14 directly or indirectly controls the entire liquid crystal display device 1 such as the video signal processing unit 13 and the LED driving unit 15, and includes an LED control unit 14 a that controls the LED driving unit 15. The operation unit 12 receives a user operation and transmits the operation content to the main control unit 14. The operation unit 12 can be configured by a main body operation unit provided as a button or the like on the main body of the liquid crystal display device 1 and / or a reception unit that receives an operation signal from an attached remote controller.

  The tuner unit 11 has an antenna for receiving broadcast waves connected to the antenna input terminal, demodulates the broadcast waves input from the antenna input terminal, and outputs the demodulated wave to the video signal processing unit 13. The video signal processing unit 13 performs various signal conversion processes for displaying the video signal input from the tuner unit 11 on the liquid crystal panel 18. By providing the tuner unit 11, the liquid crystal display device can be configured as a liquid crystal television device.

The liquid crystal display device 1 of this example includes an output mode (image quality / sound quality mode) for setting a video or audio state to a user-desired state. As the output mode, for example, “standard mode”, “dynamic mode”, “game mode”, “PC mode”, “AV memory mode”, etc. are set.
The “standard mode” is a mode indicating that the image quality / audio settings are standard values. The “dynamic mode” is a clear and vivid image that allows sports programs to be viewed as powerful. The dynamic mode can be used as a demo mode (also referred to as a storefront mode) for PR of the characteristics of the device at a storefront of a store, for example. Usually, the dynamic mode is executed with the best image quality and brightness prepared in the video display device. The “game mode” is a mode in which video such as a video game is displayed with gentle brightness and is displayed gently on the eyes, and the “PC mode” is a screen mode for PC. The “AV memory mode” is a mode in which arbitrary adjustment contents can be stored for each input.

The liquid crystal display device 1 has a plurality of image quality / sound quality modes as described above, and one image quality / sound quality mode can be selected from them. The image quality / sound quality mode is selected according to a user operation from the operation unit 12. Alternatively, the video signal processing unit 13 may determine the type and characteristics of the video indicated by the video signal and automatically select based on the determination result.
The video signal processing unit 13 performs various types of video processing that match the selected image quality / sound quality mode on the input video signal, and outputs the video signal to the liquid crystal control unit 17.

  The liquid crystal control unit 17 performs control to sequentially write the video signal output from the video signal processing unit 13 from the top line of the liquid crystal panel 18. The liquid crystal panel 18 performs vertical scanning by sequentially writing and updating the scanning video signal. The video signal written on the liquid crystal panel 18 is held for one frame period (0.5 frame when driving the liquid crystal panel at double speed and 0.25 frame when driving the liquid crystal panel at 4 speed). The The liquid crystal panel 18 is a non-self-luminous panel and is illuminated by the LED backlight 10.

  The external light illuminance detection unit 16 includes an OPC (Optical Picture Control) sensor (also referred to as a brightness sensor) that detects the illuminance of external light around the liquid crystal display device 1. The light emission luminance of the LED backlight 10 can be automatically increased or decreased according to the illuminance of the ambient light around the liquid crystal display device 1 detected by the OPC sensor.

With the above configuration, the main control unit 14 passes the dimming control signal and the mode switching signal to the LED control unit 14a. The LED control unit 14 a controls the light emission of the LED backlight 10 via the LED driving unit 15.
The mode switching signal is a signal indicating the image quality / sound quality mode after switching. The mode switching signal corresponds to a signal indicating a mode selected in response to a user operation on the operation unit 12, or a signal indicating an image quality / sound quality mode determined by determining the type and characteristics of a video signal.

  The dimming control signal is generated as a signal indicating the dimming setting value according to the brightness adjustment by the user operation on the operation unit 12 or the detection result of the brightness sensor. The dimming setting value is set corresponding to the range of the luminance ratio that can be adjusted by the backlight (for example, 20 to 100%). In this example, when the dimming setting value is the minimum, the luminance ratio 20 %, And the luminance ratio is set to 100% when the dimming setting value is maximum.

  When the dimming setting is automatically performed by the brightness sensor, the liquid crystal display device displays a dimming setting screen for performing the dimming setting according to a predetermined user operation, and the mode of the automatic dimming mode by the brightness sensor is displayed. The user can arbitrarily set ON / OFF. If the automatic light control is ON, the light emission luminance of the backlight is automatically adjusted according to a preset condition according to the detection result of the brightness sensor. For example, when the periphery of the liquid crystal display device becomes dark, control is performed so that the light emission luminance of the backlight is also reduced accordingly. At this time, the level of the light emission luminance (luminance ratio) of the backlight is determined by the dimming setting value.

  On the other hand, when the dimming setting value is set by a user operation, an arbitrary dimming setting value can be set by the user operation on the dimming setting screen. For example, the brightness level is displayed by a bar chart, and an arbitrary level between the beginning and the maximum of the dimming setting value can be set by a user operation. At this time, for example, the dimming setting value from the minimum to the maximum may be divided into a plurality of stages so that one of the plurality of stages can be selected. As an example, the minimum level of the dimming setting value is set to −16, the maximum level is set to +16, and the user can select any number (integer value) from −16 to +16.

  When the dimming set value is set by a user operation, automatic dimming by the brightness sensor is automatically turned off. By these processes, a specific dimming setting value based on the brightness sensor or user dimming is set. In this case, in the case of automatic dimming by the brightness sensor, the dimming set value dynamically changes according to the ambient brightness.

  The ROM 19 is a storage unit that stores an RGB balance adjustment value for each dimming set value for adjusting a change in light emission color according to the LED drive current. The ROM 19 may be provided inside the main control unit.

FIG. 2 is a functional block diagram for further explaining the LED control unit, the LED driving unit, and the LED backlight of FIG.
The LED control unit 14a controls the light emission luminance of the LED 41 by using both PWM control and current control. The PWM control is a control for changing a duty (ON duty) indicating a lighting time per cycle in a pulse for turning on / off the LED 41. The ON duty D can be expressed as D = τ / T, where T is the lighting / extinguishing cycle of the LED 41 and τ is the lighting period in one cycle. The current control is control for selecting a current value (forward current value) to be supplied to the LED 41 from a plurality of preset current values and applying it to LED driving.

The LED control unit 14 a includes a dimming control unit 22, a PWM signal generation unit 23, and an LED current control unit 24, and further includes a memory that stores the dimming table 21.
The dimming table 21 associates the dimming setting value determined based on the setting by the user operation as described above and the detection result of the brightness sensor, the ON duty of the backlight, and the current setting value to be passed through the LED. It is remembered. The ON duty and current set value are set for each image quality / sound quality mode.

  The dimming control unit 22 refers to the dimming table 21 and determines an ON duty and a current setting value to be used for the image quality / sound quality mode according to the image quality / sound quality mode indicated by the input mode switching signal. The dimming control unit 22 outputs the determined ON duty to the PWM signal generation unit 23 and outputs the determined current setting value to the LED current control unit 24.

  The PWM signal generation unit 23 generates a pulse signal according to the input ON duty and outputs the pulse signal to the LED drive unit 15. Further, the LED current control unit 24 generates a current control signal for controlling the current so that the input current set value is obtained, and outputs the current control signal to the LED driving unit 15.

  The LED drive unit 15 includes an LED voltage generation unit 31 and an LED driver 32. The LED driver 32 outputs a signal for generating an LED drive voltage based on the current control signal input from the LED current control unit 24. The LED voltage generator 31 outputs a drive voltage to the LED 41 according to the input signal. Also. The LED driver 32 outputs the pulse signal input from the PWM signal generation unit 23 to the LED 41.

Thereby, the current of the current set value determined by the dimming control unit 22 is applied to the LED 41 in accordance with the PWM signal having the ON duty determined by the dimming control unit 22.
In this way, the LED control unit 14a drives the LED drive unit 15 and turns on the LED 41 while referring to the value of the dimming table 21 based on the dimming control signal and the mode switching signal.

  FIG. 3 is a diagram illustrating an example of the dimming table. The dimming table 21 includes a dimming table a and a dimming table b. In each table a and b, a dimming set value, an ON duty, and a current set value are associated. The dimming setting value is determined based on the setting by the user operation or the detection result of the brightness sensor. The dimming tables a and b are selected and used according to the image quality / sound quality mode. In this example, the dimming setting value is divided into 20 to 100% backlight luminance adjustment ranges of 33 levels (2.5% intervals) from -16 to +16, and each dimming setting value level Further, it is assumed that the ON duty and the current set value are set. FIG. 3 shows some of the setting values of the dimming setting table.

  FIG. 4 is a diagram illustrating an example of a current setting value corresponding to an image quality / sound quality mode and a dimming table to be used. In this example, for each image quality / sound quality mode of the dynamic mode and standard mode, a current setting value and a dimming table used in each image quality / sound quality mode are shown. In the dynamic mode, I1 is used as a fixed current value, and the ON duty and current value are controlled according to the dimming table a. In the standard mode, I1 and I2 (I2 <I1) are used as current setting values, and the ON duty and current value are controlled according to the dimming table b.

  FIG. 5 is a diagram for explaining an example of setting the PWM ON duty according to the brightness of the backlight. Here, it is assumed that the standard mode and the dynamic mode can be set as the image quality / sound quality mode. As described above, the standard mode is a mode indicating that the image quality / audio output by the liquid crystal display device is a standard value, and the dynamic mode is a video display with the best image quality / brightness on the liquid crystal display device. It is set as a mode.

  The brightness of the backlight that can be set in the liquid crystal display device is set to a luminance ratio of 20 to 100%. The backlight dimming setting value has a luminance ratio of 20% at the minimum value and 100% at the maximum value. In the standard mode, the PWM ON duty is controlled according to the straight lines 51a and 51b. Here, the current value I2 is selected until the backlight luminance ratio is the lowest 20% -72.5%. When the current value I2 is used, in the standard mode, the ON duty is 100% when the backlight luminance ratio is 72.5%. The current value I2 is described in the dimming table b shown in FIG. 3 as a current setting value selected in the standard mode at the dimming setting value 20-72.5%. In the standard mode, the brightness (brightness ratio) of the backlight is changed by changing the PWM ON duty while the current setting value is fixed at I2 in the range of the dimming setting value 20-72.5%. To change. By changing the ON duty, the brightness of the backlight changes in proportion to the ON duty.

  In the standard mode, when the dimming setting value (in this case, luminance ratio 72.5%) at which the ON duty is 100% at the current value I2 is 1 step brighter dimming setting value (in this example, luminance ratio 75%), The current value and ON duty are switched. That is, if the luminance ratio exceeds 72.5%, it cannot be handled with the current value I2, so the luminance ratio of the backlight is changed by switching the current value to I1 (I2 <I1) and changing the PWM duty. To control. In the standard mode, the PWM duty is set to 90% when the luminance ratio of the backlight is 100%.

  The reason why a different current value is used in the standard mode is that the power consumption is reduced by lowering the current value I2 lower than the current value I1 used at a high brightness ratio below the intermediate brightness ratio of the backlight. Is to plan. For example, the current value can be fixed to I1 and controlled like the straight line 51c only by the PWM duty. However, due to the characteristics of the LED, the current value is reduced and the duty is increased by increasing the duty. Is low power consumption. Therefore, from the viewpoint of low power consumption, the backlight luminance ratio is controlled by using a plurality of current values in the standard mode.

  On the other hand, in the dynamic mode, the PWM duty is controlled according to the straight line 51d. In the dynamic mode, when the backlight luminance ratio is in the range of 20-100%, the current setting value I1 that is the same as the current setting value used in the standard mode luminance ratio in the range of 75-100% is set as a fixed value. Set the brightness by changing the duty. In the dynamic mode, the PWM duty is set to 100% when the backlight luminance ratio is 100%.

FIG. 6 is a diagram illustrating the relationship between the dimming setting value of the backlight and the screen brightness according to the image quality / sound quality mode. As shown in FIG. 6, the brightness of the backlight and the screen brightness of the liquid crystal panel have a proportional relationship. When the backlight becomes brighter, the screen brightness increases in proportion to it.
In the dynamic mode and the standard mode, dimming is performed according to the dimming table in FIG. The standard mode is indicated by a straight line 52a, and the dynamic mode is indicated by a straight line 52b. Thus, a screen brighter in the dynamic mode can be obtained with the same dimming setting value.

(Color correction processing according to the present invention)
As described above, when the drive current (forward current) of the LED changes when the light emission luminance of the backlight using the LED is changed using both the current value and the PWM, the color of the light emission of the LED is It changes as the forward current changes. In order to eliminate this color change, in the embodiment according to the present invention, the color balance of light emission is changed by the LED drive current by changing the RGB balance of the video signal according to the dimming setting value. However, if it is supplemented by the video signal and the gradation of the input video signal is the same, the video can always be displayed on the liquid crystal panel 18 with a constant color.

  Specifically, the RGB balance adjustment value is stored in advance in a storage means such as the ROM 19 for each dimming setting value, and the RGB balance adjustment value is determined from the dimming setting value used in the liquid crystal display device. To adjust the chromaticity. The RGB balance adjustment value defines γ correction for each of the RGB channels. Here, since the liquid crystal display device performs the control as shown in FIG. 5, the current value of the LED at that time is determined according to the dimming setting value of the backlight. In this case, one of the currents I1 and I2 is assumed to be used according to the dimming setting value.

In this case, in the liquid crystal display device, RGB adjustment values are stored in the ROM in advance so that the color of the liquid crystal panel at the current I1 becomes a predetermined x, y value (coordinate values on the CIE chromaticity diagram). The RGB balance adjustment values are stored in the ROM so that the color of the liquid crystal panel at the current I2 becomes the same x and y coordinate values as at the current I1. Then, since the current value to be used is known according to the backlight dimming setting value, the color correction is performed by applying the adjustment value corresponding to the current value to the input video signal. As a result, even when the LED drive currents are different, high-quality video expression can be performed without changing the color of the screen on the liquid crystal panel.
In FIG. 1, the part that performs these controls is the main control unit 14, and the color correction processing corresponding to the current value is performed by the video signal processing unit 13. The ROM 19 that stores the RGB balance adjustment values is set as a memory that can be read by the main control unit 14.

An example of a method for generating RGB balance adjustment values will be described.
First, the backlight LED drive current is set to I1 or I2 to emit light. Then, the screen of the liquid crystal panel is photographed by the camera, and the coordinate values x and y on the CIE chromaticity diagram are measured by the chromaticity meter based on the photographed image. Next, based on the measured coordinate values, the image quality is adjusted so that the coordinate values x and y become predetermined target values. When it is determined that the coordinate values x and y of the display screen displayed on the liquid crystal panel 18 as a result of the adjustment correspond to the target coordinate values, the adjustment values at that time are stored in the memory (ROM) of the video display device. And the subsequent image display is performed using the adjustment value. Next, the LED drive current is set to I2, and the same operation is performed to store the adjustment value in the memory.

  As a specific example of adjusting the coordinate values x and y, for example, two gray screens are displayed on the liquid crystal panel 18 and a dark gray with a predetermined gradation is displayed on one side and a light gray with another predetermined gradation is displayed on the other side. To do. For light gray and dark gray, target coordinate values x and y are determined for each. In adjusting the RGB balance, adjustment is performed based on the display screen of the light gray and the dark gray so that target coordinate values x and y are obtained for each gray.

  In actual adjustment, first, dark gray is selected, and adjustment of the adjustment value that defines the relationship between the input gradation and the output gradation is performed. The liquid crystal display device holds a default RGBγ table and defines the relationship between the input gradation and the output gradation. The operator adjusts the output value in the dark gray tone with respect to the default value. This adjustment function is provided for each of RGB, and the operator appropriately adjusts one or a plurality of γ tables of RGB so that the coordinate values x and y that are dark gray targets are obtained. Next, the operator adjusts the gain for the light gray output value. Here, the output value of dark gray that has already been adjusted is fixed, and the slope of the output value is changed according to gain adjustment in light gray. A gain adjustment function is also provided for each of RGB, and the operator appropriately adjusts one or a plurality of γ tables of RGB so that the above-described bright gray target coordinate values x and y are obtained.

  The adjustment value adjusted by the processing as described above is held in the ROM of the liquid crystal display device, and the image is displayed based on the adjustment value by performing γ correction using the adjustment value. That is, when the current setting value of the backlight LED is I1, RGB adjustment is performed using the adjustment value of I1, and when the current setting value is I2, RGB adjustment is performed using the adjustment value of I2. I do. Whether the LED current setting value is I1 or I2 can be determined by the image quality / sound quality mode and the backlight dimming setting value at that time. For example, if the control as shown in FIG. 5 is performed, in the standard mode, the current setting value is I2 when the dimming setting value is 20 to 72.5% in the luminance ratio, and the adjustment value of the current setting value I2 is used for γ. When the dimming set value is 75 to 100% in luminance ratio, the current set value is I1, and γ correction is performed using the adjustment value of the current set value I1. As a result, even when the LED drive current changes and the light emission color of the LED changes, it is possible to display an image with the same color by adjusting the video signal.

  Note that the above RGB balance adjustment value generation method is an example applicable to the embodiment of the present invention, and other known methods can be appropriately applied to the RGB balance adjustment method. . In any case, an adjustment value for adjusting the change in the color of light emission due to the change in the current value of the LED according to the RGB balance of the video signal may be stored in advance. Further, in the dimming table shown in FIG. 3, the dimming set value is divided into 33 stages of −16 to +16, and the ON duty and the current set value are set for every 2.5% of the luminance ratio. The dimming setting value may be set steplessly, or the dimming setting value can be set steplessly, and the ON duty and current setting value are calculated by calculation for the set dimming setting value. May be.

  In addition, some liquid crystal televisions and the like are controlled such that the feature quantity such as the average brightness of the image displayed on the screen is detected and the light emission brightness of the backlight is dynamically changed according to the feature quantity. However, the embodiment according to the present invention can also be applied to such control. In this case, the LED drive current value may be determined according to the dimming setting value determined with respect to the feature amount of the video, and the RGB balance may be adjusted according to the determination result.

  FIG. 7 is a diagram showing an example of the arrangement of the backlight applicable to the liquid crystal display device of the present invention. The LED backlight 10 whose arrangement is illustrated in FIG. 7 is configured as an array type LED backlight. However, the liquid crystal display device of the present invention is not limited to the example described here, and a matrix type LED backlight or the like in which LEDs are laid on a substrate having the same size as the screen can be mounted.

  The LED backlight 10 includes a plurality of LED substrates 101 on which a plurality of white LEDs 102 are mounted on a chassis 105. The LED substrate 101 has a horizontally long rectangular strip shape, and is arranged such that the longitudinal direction of the rectangle coincides with the horizontal direction of the screen of the liquid crystal display device. Further, a harness 103 is provided to connect the LED boards 101 divided in two in the horizontal direction, and a harness 104 is provided to connect one LED board 101 and an external driver board. Further, a connector 106 to which the harnesses 103 and 104 are connected is installed on each LED board 101. In the liquid crystal display device according to the present invention, the division in the horizontal direction of the LED substrate 101 as illustrated in FIG. 7 is not essential.

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 10 ... LED backlight, 11 ... Tuner part, 12 ... Operation part, 13 ... Video signal processing part, 14 ... Main control part, 14a ... LED control part, 15 ... LED drive part, 16 ... Out Light illuminance detection unit, 17 ... liquid crystal control unit, 18 ... liquid crystal panel, 19 ... ROM, 21 ... dimming table, 22 ... dimming control unit, 23 ... PWM signal generation unit, 24 ... LED current control unit, 31 ... LED voltage Generation unit, 32... LED driver, 41... LED, 101... LED board, 102 .. white LED, 103 and 104 .. harness, 105.

Claims (4)

A pulse width that changes a duty cycle indicating a lighting time per cycle in a pulse that has a liquid crystal panel that displays an input video signal and a backlight that uses an LED that illuminates the liquid crystal panel, and that turns on and off the LED. A liquid crystal display device that controls the light emission luminance of the LED by both a modulation method and a current value control method for changing a current value flowing through the LED,
If the gradation of the input video signal is the same when the LED current value is changed, the video signal is adjusted according to the LED current value so that the display color of the liquid crystal panel is always constant. A liquid crystal display device.   2. The liquid crystal display device according to claim 1, wherein the color adjustment is an adjustment of RGB balance of a video signal. The liquid crystal display device according to claim 1 or 2,
The relationship between the dimming setting value for controlling the light emission luminance of the backlight and the current value flowing through the LED is predetermined,
A memory that stores in advance an adjustment value for adjusting the color of the video signal according to the current value;
A liquid crystal display device, wherein when the backlight is caused to emit light, the video signal is adjusted by applying the adjustment value according to a current value determined according to the dimming setting value.   4. The liquid crystal display device according to claim 1, wherein the adjustment value for adjusting the color is an RGB γ correction value corresponding to the current value. 5. .

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