JP2014241277A - Illuminating device, control method thereof, and video display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow for exact unevenness correction by acquiring an exact sensor value, while enhancing the contrast ratio by lowering the duty ratio of a light source of a dark part in a video.SOLUTION: An illuminating device includes a plurality of light sources the light emission of which is controllable independently, control means for controlling the brightness of the plurality of light sources, respectively, by pulse width modulation control for adjusting the duty ratio of lighting period and unlighting period, and measuring means for measuring the brightness of a light source to be measured by receiving the light from the light source to be measured over a predetermined measurement period. When the lighting period of the light source at the time of measuring the light source to be measured is shorter than the predetermined period, the control means controls to make the lighting period of the light source to be measured longer than the predetermined period.

Description

  The present invention relates to a lighting device, a control method thereof, and a video display device.

In a video display device using liquid crystal, a backlight using a light source such as an LED is required. As a method of adjusting the luminance of an image with a liquid crystal display, there are a method of adjusting luminance by controlling liquid crystal and a method of adjusting the luminance of backlight. By using the latter method, it is possible to increase the contrast ratio in the screen, and there are advantages in that power consumption can be suppressed.
PWM control (pulse width modulation control) is often used as a means for adjusting the brightness of the backlight. In the PWM control, the backlight is turned on and off at a constant cycle, and the luminance of the backlight is adjusted by changing the ratio (duty ratio) between the turn-on period and the turn-off period. When the cycle of turning on and off is long, the blinking of light is visually recognized by human eyes, and flicker may be felt. For this reason, it is common to perform PWM control of the backlight at a high frequency of 200 Hz or higher. Therefore, for example, if the frame frequency of the video is 60 Hz, the backlight is repeatedly turned on and off several times during one frame of the video.
In addition, many LEDs are spread on the backlight using LEDs. The number of LEDs varies depending on the size of the display screen and the required brightness. Here, as shown in Fig. 13, the backlight is divided into 10 areas each consisting of one or more LEDs, and the light emission of the LEDs in each area can be controlled independently, and the phase of the PWM signal is different. It shall be possible to As shown in FIG. 14A, when the light emission timings of all the LEDs are the same, the time variation of the total current amount increases, leading to a decrease in power supply efficiency and an increase in power consumption. Therefore, as shown in FIG. 14B, there is a technique for suppressing fluctuations in the total current by changing the phase of the PWM signal and shifting the light emission periods of the LEDs in each area (for example, Patent Document 1).

There is an individual difference (variation) in the brightness of the LED, and even if the LED is turned on with a PWM signal having the same current amount and the same duty ratio, a difference in brightness occurs for each LED. In addition, the brightness varies from LED to LED due to temperature differences in the screen and deterioration due to aging. In addition, even when a plurality of LEDs are connected in series to form an LED block and control is performed for each LED block, luminance variation occurs for each LED block due to LED luminance variation. The variation in the brightness of each LED block becomes the brightness unevenness of the backlight and affects the display image. In order to enable high-definition video display, PWM for each LED block after accurately grasping the brightness variation of each LED block
It is effective to suppress the luminance unevenness of the backlight by changing the duty ratio of the signal.
As a method of suppressing the luminance unevenness of the backlight, there is a method of performing control such as obtaining a variation in luminance of the LED block using a luminance sensor and changing the duty ratio for each LED block based on the obtained result. Here, in order to accurately acquire the luminance sensor value for each LED block, it is effective to turn on only the corresponding LED block and turn off the other LED blocks to suppress the influence on the measurement value due to light leakage. Therefore, all the LED blocks other than the LED block that is the sensor value acquisition target are turned off during the predetermined sensor value acquisition period, and the sensor value of the LED block that is the sensor value acquisition target is acquired. Control to return to can be considered. Here, the sensor value acquisition period is a period that is long enough to measure the luminance of the LED block to be measured by the optical sensor and is short enough not to be visually recognized by human eyes.

FIG. 15A shows an example of a time chart of PWM control before and after the sensor value acquisition period when one block in area 1 is a sensor value acquisition block. As shown in Fig. 15A, during the sensor value acquisition period, only the sensor value acquisition block in area 1 is lit, and the other LEDs in area 1
The block (non-sensor value acquisition block) and all LED blocks in other areas are forcibly turned off. By acquiring the value measured by the luminance sensor during this sensor value acquisition period, it is possible to measure the luminance of the LED for one block. FIG. 15B is a time chart of PWM control when one block in area 4 is a sensor value acquisition block. In this way, the luminance of all the LED blocks can be measured by performing the same measurement while changing the LED blocks to be lit in the area.
Note that the luminance slightly decreases with forced extinction. Therefore, a process for suppressing fluctuations in luminance is performed by extending the lighting period of the LED block that has been forcibly turned off by the amount of light that has been turned off. For example, FIG. 15C shows a process in the case where the sensor value of one block in area 4 is acquired in PWM cycle 2 (FIG. 15B). Specifically, the PWM duty ratio of area 10 is increased in PWM cycle 1, and the PWM duty ratio of non-sensor value acquisition blocks in areas 1 to 3 and area 4 is increased in PWM cycle 2.

By the way, in the liquid crystal display, when displaying black, the light of the backlight is shielded by closing the liquid crystal shutter. However, the liquid crystal shutter cannot be sufficiently shielded from light, and even if the liquid crystal shutter is closed, a slight leak of light may cause a so-called “black float” in which sufficient black cannot be expressed. Therefore, when the control is performed so that the luminance of the backlight is uniform over the entire screen, the contrast ratio in the screen is limited due to black floating. As a technique for solving this problem, there is a technique called local dimming. This is a technique for performing control to vary the luminance of the backlight for each area in the screen in accordance with the contrast of the video (for example, Patent Document 2). By performing local dimming, it is possible to suppress black float and increase the contrast ratio in the screen.

JP 2010-153359 A Japanese Patent Laid-Open No. 2001-142409

However, when local dimming control is performed, a portion with high luminance (high duty ratio) and a portion with low luminance (low duty ratio) appear locally depending on the input video. When the lighting period of the low duty ratio LED block is shorter than the lighting period necessary for sensor value detection, there is a problem that the sensor value cannot be accurately grasped. Conversely, if the lower limit value of the duty ratio is determined so as to ensure the period necessary for acquiring the sensor value in order to prevent an inaccurate sensor value from being acquired, the contrast ratio due to local dimming is limited. This makes it impossible to provide high-quality video.

In order to enable sensor value detection in a low-brightness block, increase the duty ratio and simultaneously decrease the current value to ensure the LED emission period necessary for sensor value detection while maintaining the same brightness. There are also other methods. However, in this method, the amount of light input to the sensor is reduced, so that the correction accuracy is deteriorated due to the deterioration of the S / N ratio. In addition, there is a problem that the color of the LED changes due to a change in the current value.

  The present invention has been made in view of the above problems, and it is possible to obtain accurate sensor values and perform accurate unevenness correction while increasing the contrast ratio by lowering the duty ratio of the light source in the dark part of the image. Objective.

The first aspect of the present invention is:
A plurality of light sources each capable of controlling light emission independently;
Control means for controlling the brightness of each of the plurality of light sources by pulse width modulation control for adjusting the duty ratio of the lighting period and the lighting period,
Measuring means for measuring the luminance of the light source of the measurement object by receiving light from the light source of the measurement object over a predetermined measurement period;
With
When the lighting period of the light source at the time of measurement of the light source to be measured is shorter than the predetermined period, the control unit performs control to make the lighting period of the light source to be measured longer than the predetermined period. Do,
It is a lighting device.

The second aspect of the present invention is:
A lighting device as described above;
A display panel capable of controlling a transmission amount of light emitted from the lighting device;
A video display device.

The third aspect of the present invention is:
A control method for an illumination device including a plurality of light sources capable of independently controlling light emission,
A control step of controlling the brightness of each of the plurality of light sources by pulse width modulation control for adjusting a duty ratio between a lighting period and a lighting period;
A measurement step of measuring the luminance of the measurement target light source by receiving light from the measurement target light source over a predetermined measurement period;
Including
In the control step, when the lighting period of the light source at the time of measuring the light source to be measured is shorter than the predetermined period, control is performed to make the lighting period of the light source to be measured longer than the predetermined period. Do,
It is the control method of an illuminating device.

A fourth aspect of the present invention includes a plurality of light sources capable of independently controlling light emission,
Control means for controlling the brightness of each of the plurality of light sources by pulse width modulation control for adjusting the duty ratio of the lighting period and the lighting period,
Measuring means for measuring the luminance of the light source of the measurement object by receiving light from the light source of the measurement object over a predetermined measurement period;
With
The illumination device performs control to shorten the response time of the sensor by providing a light emission time at a low current before the measurement period of the light source.

  According to the present invention, it is possible to accurately acquire sensor values even when the backlight lighting block is in a low luminance state. It becomes possible to provide.

1 is a block diagram showing a schematic configuration of a video display device according to a first embodiment. The figure which shows the PWM control of 1st Embodiment The figure which shows the PWM control at the time of the frequency change of 1st Embodiment The figure which shows the PWM control at the time of sensor value acquisition of 1st Embodiment The figure which shows the PWM control at the time of sensor value acquisition of 1st Embodiment The figure which shows the PWM control at the time of sensor value acquisition of 1st Embodiment The figure which shows the PWM control at the time of sensor value acquisition of 1st Embodiment The figure which shows the PWM control at the time of sensor value acquisition of 1st Embodiment The figure which shows PWM control at the time of duty ratio change of 2nd Embodiment The figure which shows PWM control at the time of sensor value acquisition of 2nd Embodiment The figure which shows the division | segmentation and duty ratio setting of the LED control block of 3rd Embodiment The figure which shows the division | segmentation and duty ratio setting of the LED control block of 3rd Embodiment The figure which shows the control at the time of the sensor value acquisition of 4th Embodiment Diagram showing backlight area division Diagram showing PWM control in the prior art Diagram showing PWM control and brightness compensation during sensor value acquisition in the prior art

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 is a block diagram showing an outline of a video display device 100 including the illumination device according to the first embodiment as a backlight device. The video display device 100 according to the present embodiment is a liquid crystal display using a liquid crystal element. The video display apparatus 100 analyzes the video signal input from the video input unit 101 by the video analysis unit 102 and determines the luminance of the display video and the backlight. The LCD control unit 103 controls the LCD panel (display panel) 104 so that the video determined by the video analysis unit 102 can be displayed, and aligns the liquid crystal of each pixel of the LCD panel 104 so that the video can be displayed. . Further, the backlight control unit 105 sets a necessary current value, a PWM duty ratio, and the like for the LED driver 106 so that the backlight luminance determined by the video analysis unit 102 is realized. Here, a liquid crystal display device will be described as an example, but the present invention can be applied to an arbitrary video display device using a display panel capable of controlling the transmission amount of light emitted from a backlight device (illumination device). is there.

The LED driver 106 has a plurality of channels, and each channel has a backlight 107.
Is connected to the LED block (light source). The LED block is a block in which a plurality of LEDs are connected in series. In the present embodiment, the backlight 107 is divided into a plurality of LED blocks in the vertical direction and the horizontal direction. Each LED block corresponds to a light source that can control light emission independently. The LED driver 106 controls the brightness of the LED block by pulse width modulation control (PWM control) that adjusts the duty ratio of the lighting period and the extinguishing period within one cycle under the conditions set by the backlight control unit 105. In the present embodiment, an area composed of a plurality of LED blocks as shown in FIG. 11 is defined, and the phase of the PWM signal is different for each area.

The luminance sensor 108 measures the luminance of the LED block to be measured by receiving the light emitted from the backlight 107 over a predetermined measurement period. The measurement result of the luminance sensor 108 is output to the sensor control unit 109. The sensor control unit 109 operates in synchronization with the backlight control unit 105. That is, the backlight control unit 105 forcibly turns off the non-sensor value acquisition LED block, which is a light source other than the light source for which the sensor value is to be acquired, during a period when the sensor control unit 109 acquires the sensor value.

The sensor control unit 109 acquires the luminance of the sensor value acquisition target LED block by acquiring the output value from the luminance sensor 108 during the sensor value acquisition period. The sensor control unit 109 feeds back the sensor value for each LED block to the backlight control unit 105. Based on the sensor value for each LED block acquired from the sensor control unit 109, the backlight control unit 105 adjusts the PWM control by the LED driver 106 so as to reduce the luminance unevenness of the backlight 107 as much as possible. The backlight 107 irradiates the LCD panel 104, and the irradiated light is transmitted according to the transmittance of each pixel of the LCD panel 104, whereby an image that can be observed by the observer is displayed on the video display unit 110.

Here, FIG. 2 shows a PWM control time chart when the LED block duty ratio in the sensor acquisition area is small and the LED lighting period per PWM cycle is shorter than the period required for sensor acquisition. Here, for simplification of explanation, explanation is given for the case where the duty ratio of all the areas is the same, but in reality, there may be a case where the duty ratio is different for each control unit block in each area or even in the same area due to local dimming. It is done. Here, it is assumed that the duty ratio of the LED block is 5% and the lighting period necessary for sensor acquisition is 250 μsec. When the PWM frequency is 360 Hz and the duty ratio is 5%, the lighting period per PWM cycle is about 139 μsec (= 1% / 360 sec 5%), which is insufficient for the period required for sensor value acquisition. In this case, in this embodiment, control is performed to reduce the frequency of the PWM signal of the block from which the sensor is acquired (hereinafter also referred to as PWM frequency) to such an extent that a lighting period necessary for acquiring the sensor value is obtained.

FIG. 3 shows a diagram when the PWM frequency at the time of measurement in the sensor value acquisition area in area 1 is 180 Hz. Since the duty ratio is the same 5%, the lighting period per PWM cycle is about 278 μsec. By doing so, the lighting period becomes longer than the time required for sensor value acquisition, so that the sensor value can be accurately acquired. FIG. 4 shows how sensor values are acquired in this case. For LED blocks other than the sensor value acquisition target LED block, as shown in FIG. 4, the decrease in the lighting period, which has been cut off by forced extinction, is compensated by increasing the duty ratio to prevent a decrease in luminance. In this example, since the duty ratio of the PWM signal of each LED block is small and a plurality of blocks do not light up at the same time, only the sensor value non-acquisition block in the same area 1 is cut off. However, this is not the case when the duty ratio of other areas is high due to local dimming. When the duty ratio of the other area is high, it is necessary to appropriately extend the duty ratio for preventing the luminance reduction for areas other than area 1. In any case, by reducing the PWM frequency of the block from which the sensor value is acquired in this way, the lighting period of the measurement target block becomes longer, so that the sensor value can be acquired.

  In the example of FIG. 4, the frequency of the sensor value acquisition block is changed over the entire one frame period. However, in actuality, it may be changed only during the PWM period necessary for sensor value acquisition. For example, FIG. 5 shows a case where the frequency is changed only in the PWM cycle including the sensor value acquisition period when the frequency is changed to 180 Hz as in the case of FIG. That is, the PWM cycle may be reduced only in a period including the sensor value measurement time in one frame period.

If the frequency cannot be changed in units of LED control blocks, the frequency may be changed in the minimum unit (units of a plurality of LED blocks) in which the frequency can be changed.
For example, if the frequency can be changed for each area, the frequency may be changed similarly in the sensor value non-acquisition block of area 1 as shown in FIG. Also in this case, the frequency may be changed only in a necessary PWM cycle instead of in units of frames as in the case of FIG. If the minimum unit that can change the frequency is the entire screen, the frequency of the entire screen may be changed.

Next, control when the duty ratio further decreases will be described. When the duty ratio is reduced to 3%, the lighting period per PWM cycle is about 83 μsec. At this time, even if the frequency is changed to 180 Hz as shown in FIG. 3, the lighting period per one cycle is about 166 μsec, so that it does not reach 250 usec necessary for sensor value acquisition. Therefore, in this case, the frequency is further reduced to 120 Hz. The state of sensor acquisition at that time is shown in FIG. When PWM frequency is 120Hz, duty ratio is 3%
When set to, the lighting period per PWM cycle is 250 usec, so the sensor value can be acquired.

When the duty ratio is reduced to 3% or less, even if the frequency is changed to 120 Hz, the lighting period per PWM cycle does not reach 250 usec which is the sensor value acquisition necessary period. In that case, the frequency is further lowered. For example, if the PWM frequency is set to 90 Hz, the sensor value can be acquired. Here, when the PWM period is 180 Hz as shown in FIG. 4, three periods of 180 Hz coincide with one frame (60 Hz) of the video. When the PWM period is 120 Hz as shown in FIG. 7, the two periods of 120 Hz coincide with one frame (60 Hz) of the video. However, if the PWM period is 90Hz, it cannot be matched with one frame (60Hz) of the video. Therefore, when the PWM frequency is set to 90 Hz, different frequencies are combined in one frame as in the case of FIG. FIG.
Shows the situation when a 90Hz PWM frequency is combined with one period and a 360Hz PWM frequency is combined with two periods. As a combination of frequencies in one frame of video, for example, another combination such as one cycle of 90 Hz and one cycle of 180 Hz may be used.

Similarly, when the duty ratio drops to 1.5%, the sensor value can be acquired by lowering the PWM frequency to 60 Hz, which is the same as the video.

As described above, by changing the PWM frequency, the sensor value can be obtained accurately while lowering the minimum value of the duty ratio, and it is possible to improve both the contrast ratio and reduce unevenness. . For example, when the PWM frequency of the sensor value acquisition block is halved, the minimum value of the duty ratio can be lowered to ½, so that the contrast ratio can be doubled. Similarly, when the PWM frequency of the sensor value acquisition block is 1/3, the contrast ratio can be tripled, and when the PWM frequency of the sensor value acquisition block is 1/4, the contrast ratio can be quadrupled. By reducing the PWM frequency of the sensor value acquisition block to 60Hz, which is the same as the frame frequency, the contrast ratio becomes six times. However, if the frequency is lowered, low frequency flicker may occur. Although the flicker is relatively less felt at low luminance than at high luminance, it is necessary to consider how far the frequency can be lowered by a trade-off with the contrast ratio. For example, if priority is given to reducing flicker, the PWM frequency should be reduced to 1/2 (180 Hz), and if priority is given to increasing the contrast ratio, the PWM frequency should be reduced to 1/6 (60 Hz). Forgive me.

  By changing the PWM frequency according to the sensor value acquisition as described above, the sensor value can be accurately measured even when the PWM duty ratio is low. Can be provided.

(Second embodiment)
In the present embodiment, a description will be given of a case where the sensor value can be acquired by changing the duty ratio within one frame period instead of changing the PWM frequency. In Fig. 9, the duty ratio is expanded in the third PWM cycle of the frame, and the expanded portion is then replaced with the other 5
A state when the duty ratio is reduced in each PWM cycle is shown. As in the case of the first embodiment, assuming that the LED lighting period required for sensor value acquisition is 250 μsec, when the PWM frequency is 360 Hz and the duty ratio is 5%, the lighting period per PWM cycle is about 139 μsec. In the present embodiment, the shortage of the LED lighting period is dealt with by increasing the duty ratio in the PWM period of sensor value acquisition.

In the sensor value acquisition cycle, if the duty ratio is increased to about 9.1%, a lighting period of 250 μsec can be secured. Since the lighting period for 111 μsec is extended in the sensor value acquisition cycle, it is necessary to shorten the lighting period in the other five cycles in order to suppress the luminance fluctuation in one frame. Since the lighting period to be shortened in the other five cycles is 22.2 μsec, the duty ratio of each cycle may be reduced and set to about 4.2%. FIG. 10 shows how the sensor is acquired by changing the lighting duty ratio as described above. That is, in the sensor value acquisition block of area 1, the duty ratio of the PWM signal is increased during the sensor value acquisition period, while the duty ratio is decreased during other periods. In the area other than area 1 sensor value non-acquisition block and area 1, the duty ratio of the PWM signal is basically not changed. However, in the sensor value non-acquisition block in area 1, it is forcibly turned off during the sensor value acquisition period.
In order to guarantee it, the duty ratio is extended.

In the present embodiment, the PWM frequency does not change, but the luminance increases or decreases within one frame. For this reason, if the difference between the duty ratio in the sensor value acquisition period and the duty ratio in other periods is large, it may be easy to feel low-frequency flicker as in the case of the first embodiment. Therefore, in the present embodiment as well, as in the case of the first embodiment, the lower limit of the duty ratio is determined in consideration of the trade-off between the improvement in image quality due to the improvement in contrast and the low-frequency flicker.

As described above, by changing the PWM duty ratio within one frame, sensor values can be obtained accurately even when the LED block is in a low-brightness state, providing a display with high contrast and low-brightness unevenness. It becomes possible to do.

In the present embodiment, the fluctuation in luminance is suppressed by uniformly reducing the duty ratio in other periods (other than during measurement) by increasing the duty ratio during the sensor value acquisition period (when measuring). . However, it is not always necessary to uniformly reduce the duty ratio of each cycle. Further, it is not necessary to reduce the duty ratio in all PWM periods other than during measurement within one frame period. If the amount of decrease in the duty ratio in each cycle other than during measurement is determined so that the total decrease in the duty ratio is the same as the increase in the duty ratio, fluctuations in luminance can be suppressed. Note that it is preferable to increase and decrease the duty ratio within one video frame period.

It is also possible to combine the first embodiment and the second embodiment. That is, the PWM frequency of the block from which the sensor value is acquired may be lowered and the duty ratio of the block may be adjusted.

(Third embodiment)
In the first and second embodiments, the lighting period of the LED block from which the sensor value is to be acquired is lengthened in order to be able to acquire the sensor value, and the sensor value acquisition period is to suppress the luminance fluctuations associated therewith. The lighting period of the LED block in other than is shortened. On the other hand, in the present embodiment, the brightness variation is suppressed by shortening the lighting period of other LED blocks (typically, LED blocks around the sensor value acquisition target LED block) in the sensor value acquisition period. . That is, in the first and second embodiments, the sensor value can be obtained by adjusting the lighting period of the LED block in the time direction in the same block. Sensor value can be acquired by adjusting in the direction. Here, as in the first and second embodiments, the case where the sensor value cannot be obtained because the LED lighting period is insufficient due to the low PWM duty ratio will be described.

For example, as shown in FIG. 11A, it is assumed that the screen is divided into five in the vertical direction (R1 to R5) and eight in the horizontal direction (C1 to C8), and the duty ratio can be set for each divided block. Note that this division example is one example, and the number of divisions may actually be larger or smaller than this.

FIG. 11B shows a setting example of the duty ratio of each divided block. Here, it is assumed that the luminance of the blocks in the upper left of the screen (R1 to R3, C1 to C3) is low and the duty ratio of these blocks is set to 5%. In this case, as in the case of the first embodiment, accurate sensor value measurement cannot be performed. Therefore, in the present embodiment, when the lighting period of the LED block from which sensor values are to be acquired is not sufficient with respect to the sensor value acquisition time, another method for enabling acquisition of the sensor values of the block is shown. . In the present embodiment, by adjusting the duty ratio with the peripheral block, it is possible to obtain the sensor value of the block while preventing the luminance change from occurring in a wide area including the peripheral block.

First, a control method in the case of acquiring the sensor value of the upper left R1C1 block will be described.
In FIG. 11B, the duty ratio of the R1C1 block is 5%. If the duty ratio required to acquire the sensor value at the PWM frequency of 300 Hz is 9% or more, the lighting period is insufficient at this duty ratio, and the sensor value cannot be acquired. Therefore, the sensor value is obtained by lowering the duty ratio of the peripheral blocks and adding the reduced duty ratio to the duty ratio of the R1C1 block to obtain the sensor value. Here, the duty ratios of the three blocks R1C2, R2C1, and R2C2 are reduced as peripheral blocks. Since the duty ratio of R1C1 is 5% and the duty ratio at which sensor values can be acquired is 9%, the duty ratio of the R1C1 block needs to be increased by 4% or more. 4% / 3 ≒ 1.33% when trying to allocate a duty ratio of 4% uniformly in the above 3 blocks. If the duty ratio is changed in integer units, the duty ratio of the R1C1 block can be increased to a level where the sensor value can be acquired by decreasing the duty ratio of each block by 2%. First, reduce the duty ratio of the three blocks from 5% to 3%. At the same time, the duty ratio for a total of 6% corresponding to the duty ratio reduction of 3 blocks is added to the R1C1 block and changed from 5% to 11%. FIG. 11C shows the distribution of the adjusted duty ratio.

In this state, the R1C1 block can secure a lighting period in which the sensor value can be sufficiently acquired, so that an accurate sensor value can be grasped. Similarly, for example, when acquiring the sensor value of the R2C2 block, the duty ratio of the surrounding blocks is also lowered and added to the R2C2 block. Here, the peripheral blocks are eight blocks R1C1, R1C2, R1C3, R2C1, R2C3, R3C1, R3C2, and R3C3. When exchanging the duty ratio in eight blocks, it is possible to compensate for the shortage of the duty ratio of the R2C2 block by lowering each block by 1%. Therefore, the duty ratio of the eight blocks is lowered from 5% to 4%, and the total duty ratio of 8% is added to the R2C2 block to be 5% to 13%. By operating this duty ratio, the sensor value of the R2C2 block can be acquired. In this way, when acquiring sensor values for blocks with a duty ratio of less than 9%, the duty ratio with the surrounding blocks can be adjusted in the same way, and sensor values can be acquired without changing the luminance over a wide area. can do. Also, the method for adjusting the duty ratio with the surrounding blocks is not limited to that shown in this embodiment. For example, when the duty ratio of the sensor acquisition block is 8%, adjustment may be performed only with the immediately adjacent block. Conversely, when the duty ratio of the R1C1 block is 5% as described above, the duty ratio of the adjacent three blocks is not increased by 2%, but each block including the surrounding blocks is also increased by 1%. You may make it raise.

In addition, only the method for adjusting the duty ratio of the backlight is shown here, but in order to avoid the occurrence of luminance unevenness due to the duty ratio adjustment as much as possible, the liquid crystal transmittance is adjusted at the same time so that the luminance unevenness is not visually recognized. It is also preferable to do so. In other words, by reducing the liquid crystal transmittance of the part corresponding to the LED block with the increased duty ratio by that amount, and increasing the liquid crystal transmittance of the part corresponding to the LED block with the reduced duty ratio by that amount, uneven brightness occurs. It is preferable to suppress.

As described above, in this embodiment, the duty ratio of the block from which the sensor value is acquired is extended by adjusting the duty ratio of the peripheral blocks. In this way, since the sensor value can be accurately acquired even when the LED block is in a low luminance state, a display with high contrast and low luminance unevenness can be provided.

(Fourth embodiment)
In the present embodiment, a method for enabling sensor value acquisition even at a low duty ratio by devising an LED lighting method will be described. “Sensor measurement time” includes the response time from when the LED whose luminance is to be measured emits light until the sensor responds and the value stabilizes, and the acquisition time of the sensor value such as AD conversion. . In the first to third embodiments, the sensor value can be acquired by extending the lighting period of the LED block. In contrast, in this embodiment,
The sensor value can be acquired by shortening the response time of the sensor.

As shown in FIG. 12A, a sensor response time is provided from when the LED of a block to be acquired is lit until when sensor value acquisition is actually started. This sensor response time will not be a problem if there is enough duty ratio to obtain the sensor value, but if the duty ratio becomes low, this response time becomes a bottleneck, and before the sensor value acquisition finishes as shown in Fig. 12B, The lighting period ends.

Therefore, in this embodiment, when the lighting period of the LED block from which the sensor value is to be acquired is shorter than the sensor value acquisition time, the light emission period for lighting the LED block with a current lower than normal is set as the sensor value acquisition period. Provide in front. This light emission period can be said to be a precharge period in which the sensor is precharged. By performing lighting with a normal current amount after the precharge period, the sensor response time is greatly shortened, and the sensor value measurement can be started quickly. At this time, the length of the lighting period is set so that the sum of the light emission amount during the precharge period and the light emission amount during the measurement period is not different from the light emission amount during the lighting period other than during measurement (when no precharge period is provided). It will be adjusted. FIG. 12C shows the situation at that time. As described above, even when the light emission amount is the same, by using the precharge period by the low current light emission, the response time is shortened, and the LED light emission amount can be grasped by the sensor even in the low luminance state.

By providing a precharge period with varying current as described above, sensor values can be obtained accurately even when the LED block is in a low-brightness state, providing a display with high contrast and low-brightness unevenness. It becomes possible to do.

(Other)
The above embodiments can be implemented in combination. For example, the first and / or
Alternatively, when it is not sufficient to extend the lighting period of the LED block by the method of the second embodiment, the lighting period of the LED block to be measured is further extended by adjusting the brightness with the peripheral block by the method of the third embodiment. Can do. Similarly, the method of the fourth embodiment also includes the first to
It can be implemented in any combination with the method of the third embodiment.

105 Backlight controller
107 Backlight
109 Sensor controller

Claims (30)

A plurality of light sources each capable of controlling light emission independently;
Control means for controlling the brightness of each of the plurality of light sources by pulse width modulation control for adjusting the duty ratio of the lighting period and the lighting period,
Measuring means for measuring the luminance of the light source of the measurement object by receiving light from the light source of the measurement object over a predetermined measurement period;
With
When the lighting period of the light source at the time of measurement of the light source to be measured is shorter than the predetermined period, the control unit performs control to make the lighting period of the light source to be measured longer than the predetermined period. Do,
Lighting device. The control means lengthens the lighting period of the light source by lowering the frequency of pulse width modulation for the light source to be measured,
The lighting device according to claim 1. The frequency of the pulse width modulation is higher than the frame frequency,
The control means lowers the frequency of pulse width modulation for the light source to be measured over the entire one frame period including the measurement time.
The lighting device according to claim 2. The frequency of the pulse width modulation is higher than the frame frequency,
The control means lowers the frequency of pulse width modulation for the light source to be measured only in the period including the measurement time,
The lighting device according to claim 2. The control means lowers the frequency of pulse width modulation only for the light source to be measured,
The illuminating device of any one of Claims 2-4. The control means lowers the frequency of pulse width modulation for a plurality of light sources including the light source to be measured,
The illuminating device of any one of Claims 2-4. The control means increases a lighting period of the light source by increasing a duty ratio at the time of measurement with respect to the light source to be measured.
The lighting device according to claim 1. The control means is for reducing the duty ratio for the light source within one frame period including the measurement time for the light source to be measured and in at least any period other than the measurement time. The sum of minutes is equal to the increase in duty cycle,
The lighting device according to claim 7. The control means decreases the duty ratio of at least one of the light sources around the light source to be measured, and increases the duty ratio of the light source to be measured;
The lighting device according to claim 1. The total decrease in the duty ratio of the light source around the light source to be measured is the same as the increase in the duty ratio of the light source to be measured.
The lighting device according to claim 9. A plurality of light sources each capable of controlling light emission independently;
Control means for controlling the brightness of each of the plurality of light sources by pulse width modulation control for adjusting the duty ratio of the lighting period and the lighting period,
Measuring means for measuring the luminance of the light source of the measurement object by receiving light from the light source of the measurement object over a predetermined measurement period;
With
When the lighting period of the light source at the time of measuring the light source to be measured is shorter than the predetermined period, the control unit is configured to measure the measurement target with a current lower than the current in the measurement period before the measurement period. Control to provide a light emission period to turn on the light source,
Lighting device. The total of the light emission amount in the light emission period and the light emission amount in the measurement period is equal to the light emission amount in the lighting period other than during measurement,
The lighting device according to claim 11. The control means forcibly turns off light sources other than the light source when measuring the light source to be measured.
The illuminating device of any one of Claims 1-12. The control means increases the duty ratio of the pulse width modulation by an amount corresponding to the forced extinction period for the light source that is forcibly extinguished,
The lighting device according to claim 13. The lighting device according to any one of claims 1 to 14,
A display panel capable of controlling a transmission amount of light emitted from the lighting device;
A video display device comprising: The lighting device according to claim 9;
A display panel capable of controlling a transmission amount of light emitted from the lighting device;
With
Reducing the amount of light transmitted through the display panel corresponding to the light source with the increased duty ratio, and increasing the amount of light transmitted through the display panel corresponding to the light source with the decreased duty ratio;
Video display device. A control method for an illumination device including a plurality of light sources capable of independently controlling light emission,
A control step of controlling the brightness of each of the plurality of light sources by pulse width modulation control for adjusting a duty ratio between a lighting period and a lighting period;
A measurement step of measuring the luminance of the measurement target light source by receiving light from the measurement target light source over a predetermined measurement period;
Including
In the control step, when the lighting period of the light source at the time of measuring the light source to be measured is shorter than the predetermined period, control is performed to make the lighting period of the light source to be measured longer than the predetermined period. Do,
Control method of lighting device. In the control step, the lighting period of the light source is lengthened by lowering the pulse width modulation frequency for the light source to be measured.
The control method of the illuminating device of Claim 17. In the control step, the frequency of pulse width modulation for the measurement target light source is lowered over the entire one frame period including the measurement time of the measurement target light source.
The control method of the illuminating device of Claim 18. In the control step, only during the period including the measurement time of the light source to be measured, the frequency of pulse width modulation for the light source to be measured is lowered.
The control method of the illuminating device of Claim 18. In the control step, the frequency of pulse width modulation is lowered only for the light source to be measured,
The control method of the illuminating device of any one of Claims 18-20. In the control step, the frequency of pulse width modulation is lowered for a plurality of light sources including the light source to be measured.
The control method of the illuminating device of any one of Claims 18-20. In the control step, the lighting period of the light source is lengthened by increasing the duty ratio at the time of measurement for the light source to be measured.
The control method of the illuminating device of Claim 17. In the control step, the duty ratio for the light source is decreased within one frame period including the measurement time for the light source to be measured and at least in any period other than the measurement time. The sum of minutes is equal to the increase in duty cycle,
The control method of the illuminating device of Claim 23. In the control step, the duty ratio of at least one of the light sources around the light source to be measured is decreased, and the duty ratio of the light source to be measured is increased.
The control method of the illuminating device of Claim 17. The total decrease in the duty ratio of the light source around the light source to be measured is the same as the increase in the duty ratio of the light source to be measured.
The control method of the illuminating device of Claim 25. A control method for an illumination device including a plurality of light sources capable of independently controlling light emission,
A control step of controlling the brightness of each of the plurality of light sources by pulse width modulation control for adjusting a duty ratio between a lighting period and a lighting period;
A measurement step of measuring the luminance of the measurement target light source by receiving light from the measurement target light source over a predetermined measurement period;
Including
In the control step, when the lighting period of the light source at the time of measurement of the light source of the measurement object is shorter than the predetermined period, the measurement object is lower than the current in the measurement period before the measurement period. Control to provide a light emission period to turn on the light source,
Control method of lighting device. The total of the light emission amount in the light emission period and the light emission amount in the measurement period is equal to the light emission amount in the lighting period other than during measurement,
The control method of the illuminating device of Claim 27. In the control step, when measuring the light source to be measured, the light source other than the light source is forcibly turned off.
The control method of the illuminating device of any one of Claims 17-28. In the control step, for the light source that is forcibly turned off, the duty ratio of the pulse width modulation is increased by an amount corresponding to the forced turn-off period.
The control method of the illuminating device of Claim 29.

Images