JP2012142224A - Backlight device and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology which, without reducing the luminous efficiency of a display, can restrict fluctuations in brightness and color of light from a backlight.SOLUTION: A backlight device of the present invention includes: a plurality of light-emitting units which each are driven by a pulse signal input thereto and function as a backlight for a liquid crystal panel; setup means which, by altering the cycle, phase and duty ratio of a pulse signal input to at least a part of the plurality of light-emitting units, sets for each light-emitting unit a detection period, or a period in which only one light-emitting unit emits light; detection means which detects the amount of light emitted by a light-emitting unit to be detected, or the one which is emitting light in the detection period; and adjustment means which, if the amount of light detected by the detection means deviates from a prescribed value, adjusts at least one of the duty ratio and the pulse amplitude of the pulse signal input to the light-emitting unit to be detected so that the amount of light of the light-emitting unit to be detected becomes a prescribed value.

Description

  The present invention relates to a backlight device and a control method thereof.

The brightness and color of light from the backlight of the liquid crystal display vary due to deterioration with time of the LEDs constituting the backlight. Conventionally, techniques for suppressing such fluctuations have been proposed.
In the technique disclosed in Patent Document 1, any one of a red LED, a blue LED, and a green LED that constitutes a backlight is turned on during a vertical blanking period or a horizontal blanking period of a liquid crystal display. The amount of light of the lit LED is detected by an optical sensor, and the color of the backlight is adjusted by controlling the light emission amount of the LED according to the detection result.
Moreover, in the technique described in Patent Document 2, detection lighting is performed in which only a light emitting unit that is a target of light amount detection is turned on among a plurality of light emitting units each formed of a plurality of LEDs. By sequentially performing the detection lighting for each light emitting unit, the amount of light is detected for each light emitting unit. The luminance and color of the backlight are adjusted by controlling the light emission amount for each light emitting unit according to the detection result.

JP 2008-282936 A JP 2008-286854 A

However, in the technique disclosed in Patent Document 1, it is necessary to provide a vertical blanking period or a horizontal blanking period for light quantity detection. During this period, it is necessary to display a black screen with the liquid crystal element in a non-transmissive state (a state where light from the backlight is not transmitted) in order to prevent the LED from being seen by the user through the monitor. For this reason, the technique disclosed in Patent Document 1 has a problem that the light emission time of the display (light output time from the screen) is shortened, that is, the light emission efficiency of the display is lowered.
Also in the technique disclosed in Patent Document 2, it is necessary to make the liquid crystal element non-transparent in order to prevent the light emitted from the light emitting unit from being seen by the user during detection lighting. For this reason, the technique disclosed in Patent Document 2 has a problem in that the light emission efficiency of the display is reduced, as in the technique disclosed in Patent Document 1.

  Therefore, an object of the present invention is to provide a technique capable of suppressing variations in luminance and color of light from a backlight without reducing the light emission efficiency of the display.

  According to a first aspect of the present invention, a plurality of light emitting units that are driven by an input pulse signal and function as a backlight of a liquid crystal panel, and a pulse signal that is input to at least some of the plurality of light emitting units. By changing the cycle, phase, or duty ratio, a setting unit that sets a detection period, which is a period during which only one light emitting unit emits light, for each light emitting unit, and a light emitting unit that emits light during the detection period When the light emission amount detected by the detection means and the light emission amount detected by the detection means deviates from a predetermined value, the light emission amount of the detection target light emission portion becomes the predetermined value. As described above, the backlight device includes an adjusting unit that adjusts at least one of a duty ratio and a pulse amplitude of a pulse signal input to the detection target light emitting unit.

  A second aspect of the present invention is a control method of a backlight device having a plurality of light emitting units that are driven by an input pulse signal and function as a backlight of a liquid crystal panel, and at least of the plurality of light emitting units. A setting step for setting, for each light emitting unit, a detection period, in which only one light emitting unit emits light, by changing the period, phase, or duty ratio of a pulse signal input to some light emitting units; A detection step of detecting a light emission amount of a detection target light emission unit that is a light emission unit that emits light during a detection period, and when the light emission amount detected in the detection step deviates from a predetermined value, the detection target light emission unit An adjustment step of adjusting at least one of a duty ratio and a pulse amplitude of a pulse signal input to the detection target light emitting unit so that the amount of emitted light becomes the predetermined value. A control method for the backlight device, characterized by.

  ADVANTAGE OF THE INVENTION According to this invention, the brightness | luminance and color variation of the light from a backlight can be suppressed, without reducing the luminous efficiency of a display.

An example of the structure of the liquid crystal display which concerns on a present Example. An example of arrangement | positioning of a light emission part and an optical sensor part. An example of a pulse signal input to each LED. An example of the operation state of each LED before adjusting the light emission amount. An example of the flowchart at the time of adjusting the light emission amount of a light emission part. An example of the operation state of each LED at the time of changing the period of a pulse signal. An example of the detected value and the initial value of the light emission amount. An example of the detected value and the initial value of the light emission amount. An example of the operation state of each LED at the time of adjusting the light emission amount of LED. An example of the operation state of each LED at the time of changing the phase of a pulse signal. An example of the operation state of each LED before adjusting the light emission amount. An example of the operation state of each LED at the time of changing the duty ratio of a pulse signal. An example of the flowchart at the time of adjusting the light emission amount of a light emission part. An example of the operation state of each LED at the time of changing the period of a pulse signal. An example of the detected value and the initial value of the light emission amount. An example of the operation state of each LED at the time of adjusting the light emission amount of LED.

<Example 1>
Hereinafter, a backlight device and a control method thereof according to Embodiment 1 of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram illustrating an example of a configuration of a liquid crystal display having a backlight device according to the present embodiment. As shown in FIG. 1, the liquid crystal display according to the present embodiment includes a video input unit 110, a video processing unit 120, a display unit 130, a backlight device 200, and the like.

The video input unit 110 is a video input terminal such as HDMI (High-Definition Multimedia Interface), DVI (Digital Visual Interface), or DisplayPort. The video input unit 110 is connected to a video output device such as a personal computer or a video player. The video input unit 110 receives a video signal output from the video output device, and outputs the received video signal to the video processing unit 120.
The video processing unit 120 performs image processing on the video signal output from the video input unit 110. The image processing performed by the video processing unit 120 corrects the luminance, color, gamma value, etc. of the video signal in accordance with the display characteristics of the display unit 130 described later. The video processing unit 120 outputs the video signal subjected to the image processing to the display unit 130.
The display unit 130 is, for example, a liquid crystal panel, and displays a video based on the video signal output from the video processing unit 120. A backlight (specifically, light emitting units 210 to 240 described later) is disposed on the back surface of the display unit 130. The backlight irradiates light from the back surface of the display unit 130, so that the viewer can see the video displayed on the display unit 130.

  The backlight device 200 includes a light emitting unit 210, a light emitting unit 220, a light emitting unit 230, a light emitting unit 240, an optical sensor unit 250, a light emission amount control unit 260, and the like. Note that the number of light emitting units is not limited to four. There may be fewer than four or more.

The light emitting unit 210 is driven by the input pulse signal (pulse signal output from the light emission amount control unit 260) and functions as a backlight of the display unit 130. In the present embodiment, the light emitting unit 210 includes a plurality of LEDs (red LED 211, blue LED 212, green LED 213) that emit light of different colors. The light emission amount of each color LED (light emitting element) can be controlled independently by controlling the pulse signal output from the light emission amount control unit 260. Each LED of the light emitting unit 210 is turned on when the pulse signal output from the light emission amount control unit 260 is High, and is turned off during the Low period. Therefore, when the duty ratio of the pulse signal output from the light emission amount control unit 260 (the ratio of the length of the High period to the length of one cycle of the pulse signal) increases, the High period of the pulse signal increases, and the LED Since the lighting period also becomes longer, the light emission amount of the LED increases. When the duty ratio of the pulse signal is reduced, the High period of the pulse signal is shortened and the lighting period of the LED is also shortened, so that the light emission amount of the LED is reduced. The light emitted from the red LED 211, the blue LED 212, and the green LED 213 is mixed, whereby white light is obtained from the light emitting unit 210.
The light emitting unit 220, the light emitting unit 230, and the light emitting unit 240 each have the same functional configuration as the light emitting unit 210.

  In this embodiment, the light emission amount of the LED is controlled by changing (controlling) the pulse width (duty ratio) of the pulse signal (PWM (Pulse Width Modulation)). The method is not limited to this. In the LED, the light emission amount increases as the drive current (pulse amplitude of the pulse signal) output from the light emission amount control unit 260 increases, and the light emission amount decreases as the drive current decreases. Therefore, the light emission amount of the LED may be controlled by changing the pulse amplitude of the pulse signal (PAM (Pulse Amplitude Modulation)). You may combine both said PWM and PAM. That is, the light emission amount of the light emitting unit can be controlled by adjusting at least one of the duty ratio of the pulse signal and the pulse amplitude.

  The optical sensor unit 250 detects the amount of input light (specifically, light emitted from the light emitting unit). In the present embodiment, the optical sensor unit 250 detects the amount of input light separately for a red component, a blue component, and a green component. For example, the optical sensor unit 250 includes a color sensor and an A / D converter. The color sensor detects the light amounts of the red component, blue component, and green component of the light emitted from the light emitting unit. The color sensor outputs a detection value (detection signal) for each color to the A / D converter. The A / D converter converts red, blue, and green detection values output from the color sensor into digital values (digital signals). The A / D converter outputs the red, blue, and green detection values converted into digital values to the light emission amount control unit 260.

FIG. 2 shows an example of the arrangement of the light emitting unit 210, the light emitting unit 220, the light emitting unit 230, the light emitting unit 240, and the optical sensor unit 250. In FIG. 2, the display unit 130 (display surface) is also shown for easy understanding of the arrangement. In FIG. 2, the light emitting unit 210 is located at the upper left, the light emitting unit 220 is located at the lower left, the light emitting unit 230 is located at the upper right, and the light emitting unit 240 is located at the lower right. The light emitting unit 210 includes a red LED 211, a blue LED 212, and a green LED 213. The light emitting unit 220 includes a red LED 221, a blue LED 222, and a green LED 223. The light emitting unit 230 includes a red LED 231, a blue LED 232, and a green LED 233. The light emitting unit 240 includes a red LED 241, a blue LED 242, and a green LED 243. The optical sensor unit 250 is located at the center of the display surface.

  The light emission amount control unit 260 controls each light emitting unit. Specifically, the light emission amount control unit 260 controls a pulse signal input to the LED of each light emitting unit based on the red detection value, the blue detection value, and the green detection value detected by the optical sensor unit 250. FIG. 3 shows a timing chart of pulse signals input to each LED of the light emission unit 210 by the light emission amount control unit 260. In FIG. 3, the frame rate of the video signal displayed on the display unit 130 is, for example, 60 Hz. The length of one cycle of the pulse signal input to the red LED 211, blue LED 212, and green LED 213 by the light emission amount control unit 260 is 1 for each of the images displayed on the display unit 130 (video signals input to the display unit 130). Shorter than the frame period. That is, the red LED 211, the blue LED 212, and the green LED 213 are each input with a pulse signal having a plurality of cycles during one frame of the image displayed on the display unit 130. Details of the control of each light emitting unit by the light emission amount control unit 260 will be described later.

Next, an example of the operation of the backlight device when adjusting the luminance and color of light from the backlight (light emission amount of the light emitting unit) will be described.
FIG. 4 is a timing chart showing the operating state of each LED before adjusting the light emission amount. In FIG. 4, the duty ratio of pulse signals input to the LEDs 211 to 213 of the light emitting unit 210, the LEDs 221 to 223 of the light emitting unit 220, the LEDs 231 to 233 of the light emitting unit 230, and the LEDs 241 to 243 of the light emitting unit 240 in FIG. The periods are equal to each other. Hereinafter, the pulse signal before adjusting the light emission amount of the light emitting unit is referred to as a reference signal.
In this embodiment, the light emission amount of each light emitting unit is adjusted. For example, the light emission amount control unit 260 switches the light emitting unit to be adjusted in synchronization with the synchronization signal from the video processing unit 120. However, the method of switching the light emitting unit to be adjusted is not limited to this. The light emitting unit to be adjusted may be switched regardless of the synchronization signal (the video processing unit 120 may not output the synchronization signal to the light emission amount control unit 260).

First, the light emission amount control unit 260 adjusts the light emission amount of the light emitting unit 210. FIG. 5 shows a flowchart when the light emission amount control unit 260 adjusts the light emission amount of the light emitting unit 210.
In step 11, in order to detect the light emission amount of the light emitting unit 210, the light emission amount control unit 260 changes the cycle of the pulse signal input to at least some of the light emitting units among the plurality of light emitting units included in the backlight device 200. To do. Further, in the present embodiment, the light emission amount control unit 260 maintains the light emission amount of the light emitting unit per one frame period of the video displayed on the display unit 130 as the cycle of the pulse signal input to the light emitting unit. Change to For example, the period of the pulse signal input to each LED constituting the light emitting unit 210 is changed to twice the period of the reference signal.
FIG. 6 is a timing chart showing the operation state of each LED after step 11 (when the light emission amount control unit 260 changes the cycle of the pulse signal). As shown in FIG. 6, the period of the pulse signal input to the red LED 211, blue LED 212, and green LED 213 of the light emission unit 210 by the light emission amount control unit 260 is twice the period of FIG. 4 (the period of the reference signal). It has changed. Even if the period of the pulse signal is changed to twice, the time during which the LED is lit during one frame period does not change, so the light emission amount of the light emitting unit 210 does not change. Therefore, the video displayed on the display unit 130 is not affected by the change in the period.

By the processing of step 11, only the light emitting unit 210 emits light (specifically, all the LEDs 211 to 213 constituting the light emitting unit 210 emit light simultaneously), and the light emitting units 220, 230, and 240 do not emit light ( A period ts1) in FIG. 6 is set. Thus, a period during which only one light emitting unit emits light is referred to as a detection period.
In this embodiment, the period during which only the light emitting unit 210 emits light may be set by changing the cycle of the pulse signal input to each LED of the light emitting units 220, 230, and 240.

  In step 12, the optical sensor unit 250 detects the light emission amount (specifically, the respective light emission amounts of the LEDs 211 to 213) using the light emitting unit 210 that emits light during the detection period as a detection target light emitting unit. The optical sensor unit 250 outputs the red color detection value, the blue color detection value, and the green color detection value detected during the period ts1 to the light emission amount control unit 260. The light emission amount control unit 260 acquires a red detection value, a blue detection value, and a green detection value from the optical sensor unit 250.

  In step 13, the light emission amount control unit 260 changes the light emission amount of the light emitting unit 210 detected in step 12 and the previous detection value (predetermined value; initial value), that is, the luminance and color of light from the light emitting unit 210. The value detected by the optical sensor unit 250 is compared with the value detected. Specifically, the detection value acquired in step 12 is compared with the initial value for each color. The initial value is, for example, a detection value detected by the optical sensor unit 250 in a factory manufacturing process. When the light emission amount of the light emitting unit 210 detected at step 12 is deviated from a predetermined value, that is, when there is an LED among the LEDs 211 to 213 whose detection value obtained at step 12 is deviated from the initial value. , Go to step 14. If the light emission amount of the light emitting unit 210 detected in step 12 is not deviated from a predetermined value, the light emission amount of the light emitting unit 210 has not changed, and the light emission amount control unit 260 changes the light emission amount of the light emitting unit 210. Do not do.

In step 14, the light emission amount control unit 260 adjusts the duty ratio of the pulse signal input to the light emitting unit 210 so that the light emission amount of the light emitting unit 210 becomes an initial value. Specifically, the duty ratio of the pulse signal input to the LED is adjusted so that the light emission amount of the LED whose detection value acquired in step 12 is deviated from the initial value becomes the initial value. More specifically, for each color, in accordance with the amount of change in the detected value (difference between the detected value acquired in step 12 and the initial value), the LED of that color (light emitting unit 210) so that the amount of change becomes zero. The duty ratio of the pulse signal input to the LED is changed. Note that not the duty ratio but the pulse amplitude may be adjusted, or both the duty ratio and the pulse amplitude may be adjusted.
An example of the acquired detection value of each color and the initial value of each color is shown in FIG. In FIG. 7, since the blue detection value is smaller than the initial value, it can be seen that the light emission amount of the blue LED 212 is reduced. Therefore, the light emission amount control unit 260 performs control to increase the duty ratio of the pulse signal input to the blue LED 212 of the light emitting unit 210 so that the light emission amount of the blue LED 212 approaches the initial value. FIG. 9 is a timing chart showing the operation state of each LED when the light emission amount control unit 260 changes the duty ratio of the pulse signal (when the light emission amount of the LED is adjusted). In FIG. 9, the High time within one cycle of the pulse signal of the blue LED 212 is increased by ΔB1, and the Low time is decreased by ΔB1 (the duty ratio is increased). Thereby, since the lighting period of the blue LED 212 becomes longer, the light emission amount of the blue LED 212 increases.
The light emission amount control unit 260 repeatedly performs the operation shown in the flowchart of FIG. 3 described above.
As described above, the light emission amount of the light emitting unit 210 is adjusted.

Next, the light emission amount control unit 260 adjusts the light emission amount of the light emitting unit 220 using the light emitting unit 220 as a detection target light emitting unit. The method for adjusting the light emission amount of the light emitting unit 220 is the same as the method for adjusting the light emission amount of the light emitting unit 210.
In order to detect the light emission amount of the light emitting unit 220, the light emission amount control unit 260 changes the cycle of the pulse signal input to each LED constituting the light emitting unit 220 to twice the cycle of the reference signal. Thereby, the detection period (only the light emitting unit 220 emits light (specifically, all the LEDs 221 to 223 constituting the light emitting unit 220 emit light simultaneously) and the light emitting units 210, 230, and 240 do not emit light) Is set.
The optical sensor unit 250 detects the light emission amount (specifically, the respective light emission amounts of the LEDs 221 to 223) using the light emitting unit 220 emitting light during the detection period as a detection target light emitting unit. The optical sensor unit 250 outputs the detected red detection value, blue detection value, and green detection value to the light emission amount control unit 260. The light emission amount control unit 260 acquires a red detection value, a blue detection value, and a green detection value from the optical sensor unit 250.

An example of the acquired detection value of each color and the initial value of each color is shown in FIG. In FIG. 8, since the green detection value is larger than the initial value, it can be seen that the light emission amount of the green LED 223 is increased. Therefore, the light emission amount control unit 260 performs control to reduce the duty ratio of the pulse signal input to the green LED 223 of the light emitting unit 220 so that the light emission amount of the green LED 223 approaches the initial value. In FIG. 9, the High time in one cycle of the pulse signal of the green LED 223 is decreased by ΔG2, and the Low time is increased by ΔG2 (the duty ratio is decreased). Thereby, since the lighting period of the green LED 223 is shortened, the light emission amount of the green LED 223 is reduced.
The light emission amount control unit 260 repeatedly performs the operation described above.
As described above, the light emission amount of the light emitting unit 220 is adjusted.

The light emission amount of the light emitting unit 230 and the light emitting unit 240 is adjusted in the same manner as the light emitting unit 210 and the light emitting unit 220.
The light emission amount control unit 260 periodically performs the operation of adjusting the light emission amount of each light emitting unit as described above to suppress a change in the light emission amount of each light emitting unit. Accordingly, variations in luminance and color of white light that the backlight device 200 irradiates the display unit 130 are reduced.

As described above, according to the present embodiment, only one light emitting unit emits light by changing the cycle of the pulse signal input to at least some of the light emitting units of the backlight device 200. A detection period that is a period to be set is set for each light emitting unit. Then, based on the detection result of the light amount in the detection period, the duty ratio and pulse amplitude of the pulse signal input to the detection target light emission unit, and thus the light emission amount of the detection target light emission unit are adjusted. Thereby, the fluctuation | variation of the light emission amount of the light emission part by the time-dependent deterioration etc. of LED which comprises a light emission part can be suppressed, and the brightness | luminance and color fluctuation | variation of the light from a backlight can be reduced. In this embodiment, since it is not necessary to display black (black screen) on the display unit 130, it is possible to suppress a decrease in light emission efficiency of the display.
Also, in this embodiment, when setting the detection period, the period of the pulse signal input to the light emitting unit is such that the light emission amount of the light emitting unit per one frame period of the image displayed on the liquid crystal panel is maintained. Changed to Therefore, it is possible to eliminate a decrease in the light emission efficiency of the display.

In this embodiment, when the light sensor unit 250 detects the light emission amount of each light emitting unit, the detection period is set by changing the cycle of the pulse signal input to the light emitting unit by the light emission amount control unit 260. It had been. However, the detection period setting method is not limited to this. For example, the detection period may be set by changing the phase of the pulse signal. It is preferable that the phase of the pulse signal input to the light emitting unit is changed so that the light emission amount of the light emitting unit per one frame period of an image displayed on the liquid crystal panel is maintained.
FIG. 10 is a timing chart showing the operation state of each LED when the light emission amount control unit 260 changes the phase of the pulse signal.
In FIG. 10, the phase of the pulse signal input to the red LED 211, blue LED 212, and green LED 213 of the light emission unit 210 by the light emission amount control unit 260 is shifted from the phase of the reference signal. Thereby, a period during which only the light emitting unit 210 emits light (period ts3 in FIG. 10), that is, a detection period is set. Even if the phase of the pulse signal is shifted (changed), the amount of light emitted from the light emitting unit 210 does not change because the LED lighting time does not change during one frame period. Therefore, the video displayed on the display unit 130 is not affected by the change in phase. In this case, the optical sensor unit 250 detects the amount of light during the period ts3 in FIG.

Further, the detection period may be set by changing the duty ratio of the pulse signal. It is preferable that the duty ratio of the pulse signal input to the light emitting unit is changed so that the light emission amount of the light emitting unit per one frame period of an image displayed on the liquid crystal panel is maintained. This method is effective when there is an LED that is lit during the entire period, such as the blue LED 222 of the light emitting unit 220 shown in FIG. 11 (when the pulse signal is High during the entire period).
FIG. 12 is a timing chart showing the operation state of each LED when the light emission amount control unit 260 changes the duty ratio of the pulse signal.
In FIG. 12, the pulse signal output from the light emission amount control unit 260 to each LED of the light emitting unit 210 has a reduced drive current (pulse amplitude) and an increased duty ratio compared to the state of FIG. Since the amplitude and the duty ratio are changed so as to increase the duty ratio by increasing the duty ratio by reducing the light emission amount by reducing the amplitude, the light emission amount of the light emitting unit 210 is the same as the state shown in FIG. is there. In FIG. 12, the pulse signal output from the light emission amount control unit 260 to the blue LED 222 of the light emitting unit 220 has an increased amplitude and a reduced duty ratio compared to the state of FIG. Since the amplitude and the duty ratio are changed so that the light emission amount is decreased by decreasing the duty ratio by the increase in the light emission amount by increasing the amplitude, the light emission amount of the blue LED 222 is the same as the state shown in FIG. . Therefore, the video displayed on the display unit 130 is not affected by the change in the amplitude and duty ratio.
By changing the duty ratio of the pulse signal as described above, a period during which only the light emitting unit 210 emits light (period ts4 in FIG. 12), that is, a detection period is provided. In this case, the optical sensor unit 250 detects the amount of light during the period ts4 in FIG.

  Further, in this embodiment, each light emitting unit is composed of red, blue, and green LEDs. However, the configuration of each light emitting unit is not limited to this. For example, each light emitting unit may be composed of LEDs of four or more colors, or may be composed of only white LEDs (LEDs that emit white light by an input pulse signal). In the case where each light emitting unit is composed only of a white LED, a photodiode can be used as an optical sensor.

<Example 2>
In the first embodiment, the optical sensor unit detects the light amounts of the three colors of red, blue, and green at the same time, and outputs a detection value for each color. In this embodiment, the case where the optical sensor unit outputs only one detection value will be described. Hereinafter, a description will be given focusing on differences from the first embodiment.
A configuration of a liquid crystal display having a backlight device according to the present embodiment will be described with reference to FIG. Note that description of functions similar to those of the first embodiment is omitted.

  In this embodiment, the optical sensor unit 250 detects the amount of light emitted from the light emitting unit without dividing it into the amount of light of each color. The optical sensor unit 250 includes, for example, a photodiode and an A / D converter. The photodiode detects the amount of light emitted from the red LED, blue LED, and green LED of each light emitting unit. Unlike a color sensor, a photodiode cannot distinguish and detect light of a red component, a blue component, and a green component. The photodiode outputs the detection value to the A / D converter. The A / D converter converts the detection value output from the photodiode into a digital value. The A / D converter outputs the detection value converted into the digital value to the light emission amount control unit 260.

Next, an example of the operation of the backlight device when adjusting the luminance and color of light from the backlight (light emission amount of the light emitting unit) will be described.
In this embodiment, the detection period is set so that the plurality of LEDs constituting the detection target light emitting unit emit light one by one.
This will be specifically described below. In addition, the operation state of each LED before adjusting the light emission amount is as shown in FIG.

First, the light emission amount control unit 260 adjusts the light emission amount of the light emitting unit 210. FIG. 13 shows a flowchart when the light emission amount control unit 260 adjusts the light emission amount of the light emitting unit 210.
In step 21, the light emission amount control unit 260 changes the cycle of the pulse signal output to the red LED 211 to twice the cycle of the reference signal.
FIG. 14 is a timing chart showing the operation state of each LED when the period of the pulse signal output to the red LED 211 by the light emission amount control unit 260 is changed. As shown in FIG. 14, the cycle of the pulse signal output from the light emission amount control unit 260 to the red LED 211 of the light emitting unit 210 is changed to twice the cycle of FIG. Thereby, a detection period (period ts5 in FIG. 14) in which only the red LED 211 emits light is set.
In step 22, the optical sensor unit 250 detects the light emission amount of the red LED 211 during the detection period. The optical sensor unit 250 outputs the detection value detected in the period ts5 to the light emission amount control unit 260.

In step 23, the light emission amount control unit 260 changes the cycle of the pulse signal output to the blue LED 212 to twice the cycle of the reference signal. At this time, the cycle of the pulse signal output to the red LED 211 is restored.
In step 24, the optical sensor unit 250 detects the light emission amount of the blue LED 212 during a period (detection period) in which only the blue LED 212 emits light. The optical sensor unit 250 outputs a detection value detected during the detection period in which only the blue LED 212 emits light to the light emission amount control unit 260.

In step 25, the light emission amount control unit 260 changes the cycle of the pulse signal output to the green LED 213 to twice the cycle of the reference signal. At this time, the cycle of the pulse signal output to the blue LED 212 is restored.
In step S <b> 26, the optical sensor unit 250 detects the light emission amount of the green LED 213 during a period (detection period) in which only the green LED 213 emits light. The optical sensor unit 250 outputs the detection value detected during the detection period in which only the green LED 213 emits light to the light emission amount control unit 260.

  In step 27, the light emission amount control unit 260 compares the acquired detection value (the light emission amount detected in step 22, step 24, or step 26) with the initial value for each color. If any of the LEDs 211 to 213 has an acquired detection value that deviates from the initial value, the process proceeds to step 28. If it does not exist, the light emission amount of the light emitting unit 210 does not change, and therefore the light emission amount control unit 260 does not change the light emission amount of the light emitting unit 210.

In step 28, the light emission amount control unit 260 determines the pulse signal input to the LED of that color (the LED of the light emitting unit 210) so that the change amount becomes 0 according to the change amount of the detection value for each color. Adjust the duty ratio.
An example of the acquired detection value of each color and the initial value of each color is shown in FIG. In FIG. 15, since the detection value of the blue LED 212 is smaller than the initial value, it can be seen that the light emission amount of the blue LED 212 is reduced. Therefore, the light emission amount control unit 260 performs control to increase the duty ratio of the pulse signal output to the blue LED 212 of the light emitting unit 210 so that the detection value detected by the optical sensor unit 250 approaches the initial value. Moreover, in FIG. 15, since the detection value of green LED213 is larger than an initial value, it turns out that the light emission amount of green LED213 is increasing. Therefore, the light emission amount control unit 260 performs control to reduce the duty ratio of the pulse signal output to the green LED 213 of the light emitting unit 220 so that the detection value detected by the optical sensor unit 250 approaches the initial value.

FIG. 16 is a timing chart showing the operation state of each LED when the light emission amount control unit 260 changes the duty ratio of the pulse signal (when the light emission amount of the LED is adjusted). In FIG. 16, the High time within one cycle of the pulse signal of the blue LED 212 is increased by ΔB3, and the Low time is decreased by ΔB3. Thereby, since the lighting period of the blue LED 212 becomes longer, the light emission amount of the blue LED 212 increases. Further, the High time in one cycle of the pulse signal of the green LED 213 is decreased by ΔG4, and the Low time is increased by ΔG4. Thereby, since the lighting time of the green LED 213 is shortened, the light emission amount of the green LED 213 is reduced.
The light emission amount control unit 260 repeatedly performs the operation shown in the flowchart of FIG. 13 described above.
As described above, the light emission amount of the light emitting unit 210 is adjusted.

The light emission amount of the light emitting unit 220, the light emitting unit 230, and the light emitting unit 240 is adjusted in the same manner as the light emitting unit 210.
The light emission amount control unit 260 periodically performs the adjustment operation of the light emission amount of each light emitting unit as described above, and suppresses the change in the light emission amount of each light emitting unit detected by the optical sensor unit 250. Accordingly, variations in luminance and color of white light that the backlight device 200 irradiates the display unit 130 are reduced.

  As described above, according to the present embodiment, even when the optical sensor unit 250 cannot distinguish the detection values of the respective colors, the same effects as those of the first embodiment can be obtained. In addition, since it is not necessary for the optical sensor unit 250 to distinguish the detection values of the respective colors, the same effects as those of the first embodiment can be obtained with a more inexpensive configuration. Specifically, since the photosensor unit 250 can be configured using a photodiode instead of a color sensor, the same effect as in the first embodiment can be obtained with a configuration that is less expensive than a configuration using a color sensor. Can do.

200 Backlight Device 210, 220, 230, 240 Light Emitting Unit 250 Optical Sensor Unit 260 Light Emission Control Unit

Claims (8)

A plurality of light emitting units that are driven by the input pulse signal and function as a backlight of the liquid crystal panel;
By changing the period, phase, or duty ratio of a pulse signal input to at least some of the light emitting units among the plurality of light emitting units, a detection period, in which only one light emitting unit emits light, is set for each light emitting unit. Setting means to set to,
Detecting means for detecting a light emission amount of a detection target light emitting unit which is a light emitting unit emitting light during the detection period;
The duty of the pulse signal input to the detection target light emission unit so that the light emission amount of the detection target light emission unit becomes the predetermined value when the light emission amount detected by the detection unit is deviated from the predetermined value. Adjusting means for adjusting at least one of ratio and pulse amplitude;
A backlight device comprising: The setting means sets the cycle, phase, or duty ratio of the pulse signal input to the light emitting unit so that the light emission amount of the light emitting unit per one frame period of an image displayed on the liquid crystal panel is maintained. The backlight device according to claim 1, wherein the backlight device is changed. The light emitting unit is composed of a plurality of LEDs that emit light of different colors,
The detection means detects the amount of input light separately for each color of the plurality of LEDs,
3. The backlight device according to claim 1, wherein in the detection period, all LEDs constituting the detection target light emitting unit emit light simultaneously. The light emitting unit is composed of a plurality of LEDs that emit light of different colors,
3. The backlight device according to claim 1, wherein a plurality of LEDs constituting the detection target light emitting unit emit light one by one during the detection period. 3. The backlight device according to claim 1, wherein the light emitting unit includes a white LED that emits white light in response to an input pulse signal. 4. The backlight device according to claim 3, wherein the detection unit is a color sensor. The backlight device according to claim 4, wherein the detection unit is a photodiode. A method for controlling a backlight device that is driven by an input pulse signal and has a plurality of light emitting units that function as a backlight of a liquid crystal panel,
By changing the period, phase, or duty ratio of a pulse signal input to at least some of the light emitting units among the plurality of light emitting units, a detection period, in which only one light emitting unit emits light, is set for each light emitting unit. A setting step to set to
A detection step of detecting a light emission amount of a detection target light emitting unit that is a light emitting unit emitting light during the detection period;
The duty of the pulse signal input to the detection target light emission unit so that the light emission amount of the detection target light emission unit becomes the predetermined value when the light emission amount detected in the detection step deviates from a predetermined value. An adjustment step for adjusting at least one of the ratio and the pulse amplitude;
A control method for a backlight device, comprising:

Images