JP5089501B2 - Liquid crystal display device, light emitting device, light emission balance control device, and light emission intensity detection device - Google Patents

Description

  The present invention relates to a light emitting device such as a liquid crystal display device, and more particularly to a technique for controlling the light emission balance by detecting the light emission intensity of a plurality of color light sources.

  A light source module that mixes light from LEDs of three colors of R, G, and B to emit white light is used. This light source module is used for a backlight of a liquid crystal display.

  Since the emission color of the LED shifts due to temperature change, aging change, etc., feedback control is performed to compensate for this and maintain the original white light. For example, in patent document 1, the color sensor which detects each luminescent color of R, G, and B LED is provided, and the luminescence intensity for every color is obtained. For each of R, G, and B, the emission intensity of the LED is feedback-controlled so that the detected emission intensity becomes a desired emission intensity.

  Japanese Patent Application Laid-Open No. H10-228688 discloses a sensor provided with an illuminance sensor that detects the intensity of light without distinguishing colors, instead of the color sensor. In the technique of this document, the light emission intensity when all the R, G, and B LEDs are turned on is measured. Further, the light emission intensity when one of R, G, and B is sequentially turned off is measured. Based on the difference between the former and latter emission intensities, the respective emission intensities of R, G, and B are calculated. Then, feedback control is performed based on the calculated emission intensity of each of R, G, and B.

JP 2007-123153 A

JP2007-214053

  However, the technique disclosed in Patent Document 1 has a problem that three expensive color sensors are required for control and the configuration becomes complicated.

  On the other hand, the technique of Patent Document 2 has an advantage that the configuration can be simplified by using only one inexpensive illuminance sensor. However, the technique of Patent Document 2 does not disclose what adjustment is performed when the detection sensitivity for each color of the illuminance sensor is not uniform. In addition, no correspondence is shown for the decrease in accuracy caused by the difference in detection sensitivity for each color.

  The present invention solves the above problems and accurately detects the emission intensity of each color even when the detection sensitivity for each color of the optical sensor is uneven or insufficient. It is an object of the present invention to provide an apparatus that can be controlled in a controlled manner.

  Each independent aspect of the present invention is shown below.

(1) A liquid crystal display device according to the present invention includes a liquid crystal panel section, a red light source, a green light source, and a blue light source, and a light emitting section that functions as a backlight of the liquid crystal panel section. A light sensor for detecting the light emission intensity and a first state in which the red light source, the green light source and the blue light source are turned on, a second state in which only the red light source is turned off, and a blue light source are turned off. The light source selection detecting means for detecting the light emission intensity of the light emitting unit by the light sensor in each state, and the light emission intensity detected by the light sensor in each state. And a light emission control means for controlling the light emitting section so that each light source has a desired light emission intensity.

  Therefore, since the detection is performed without turning off the green light source having the best sensor sensitivity, the dynamic range can be increased, and an accurate color balance can be realized even if a low-performance optical sensor is used.

(2) A light-emitting device according to the present invention includes a light-emitting unit having a red light source, a green light source, and a blue light source, a light sensor that detects light emission intensity of the light-emitting unit, a red light source for the light-emitting unit, The lighting control is performed so that the first state in which the green light source and the blue light source are turned on, the second state in which only the red light source is turned off, and the third state in which only the blue light source is turned off. Light source selection detecting means for detecting the light emission intensity of the light emitting part by the optical sensor, and light emission for controlling the light emitting part so that each light source has a desired light emission intensity based on the light emission intensity detected by the optical sensor in each state. Control means.

  Therefore, since the detection is performed without turning off the green light source having the best sensor sensitivity, the dynamic range can be increased, and an accurate color balance can be realized even if a low-performance optical sensor is used.

(3) A light emission balance control device according to the present invention is a light emission balance of a light emitting device including a light emitting unit having a red light source, a green light source, and a blue light source, and an optical sensor for detecting the light emission intensity of the light emitting unit. A light emission balance control device for controlling a light source, wherein a first state in which a red light source, a green light source and a blue light source are turned on, a second state in which only the red light source is turned off, a blue light source And a light source selection detecting means for detecting the light emission intensity of the light emitting part by the light sensor in each state, and the light emission detected by the light sensor in each state. Emission control means for controlling the light emitting unit so that each light source has a desired emission intensity based on the intensity is provided.

  Therefore, since the detection is performed without turning off the green light source having the best sensor sensitivity, the dynamic range can be increased, and an accurate color balance can be realized even if a low-performance optical sensor is used.

(4) In the apparatus according to the present invention, the light source selection / detection means includes an amplifier that amplifies the detection signal from the optical sensor, and an A / D converter that converts the output of the amplifier into a digital signal. The amplification degree of the amplifier is changed in the first state, the second state, and the third state according to the detection sensitivity for green, blue.

  Therefore, the amplification degree can be changed according to the detection sensitivity of the optical sensor, and the ability of the A / D converter can be fully utilized, so that highly accurate measurement can be performed.

(5) In the device according to the present invention, the light source selection detecting means includes an amplifier that amplifies the detection signal from the optical sensor and an A / D converter that converts the output of the amplifier into a digital signal, and is detected by the optical sensor. The amplification degree of the amplifier is changed according to the emitted light intensity.

  Therefore, the amplification degree is changed according to the magnitude of the detection output of the optical sensor, and the ability of the A / D converter can be fully utilized, so that highly accurate measurement can be performed.

(6) The apparatus according to the present invention is characterized by including an integration circuit for integrating the output of the amplifier and supplying the output to the A / D converter.

  Therefore, accurate emission intensity can be measured even if there is a deviation in the rise of the emission of each light source.

(7) A light emission intensity detecting device according to the present invention includes a light emitting unit having a first color light source, a second color light source, an nth color light source, an optical sensor for detecting the light emission intensity of the light emitting unit, The light emitting unit is controlled to turn on so that the n light sources are turned on, and only one of the n light sources is sequentially turned off. Luminescence intensity detection comprising: a light source selection detection unit that controls to detect the emission intensity of the light emitting unit; and a calculation unit that calculates the emission intensity of each light source based on the emission intensity detected by the optical sensor in each state. A device,
When the light intensity of each light source of the light emitting unit is adjusted so that light is emitted with a desired color balance and the light intensity of each light source is detected by the light sensor, the light source that provides the largest detection output is the maximum detection light source. The light source selection detecting means does not realize a combination of turning off the maximum detected light source and turning on the remaining light sources when only one of the n light sources is sequentially turned off and the remaining light sources are turned on. It is characterized by that.

  Therefore, since the detection is performed without turning off the light source having the largest sensor output, the dynamic range can be increased and detection with high accuracy can be performed.

(8) In the emission intensity detection device according to the present invention, the calculation means records in advance correction information for correcting a detection output decrease due to the detection sensitivity of the photosensor, and corrects the emission intensity based on the correction information. It is characterized by calculating.

  Therefore, accurate detection can be performed even if a low-performance optical sensor is used.

  In the embodiment, the “light source selection detection means” is the function of the MPU 34 realized by steps S2 to S7 and S9 in FIGS. 5 and 6, and the amplifier 24, the sample and hold circuit 27, and the A / D converter 32 in FIG. Corresponds to this. Note that the functions of steps S2 to S7 and S9 may be configured only by hardware by a logic circuit.

  In the embodiment, the “light emission control means” corresponds to the function of the MPU 34 realized by steps S17 to S20 in FIG. Note that this may also be configured only by hardware using a logic circuit.

  “Light emission balance” refers to a balance of light emission intensities of a plurality of color light sources that affects the color of light that is mixed and combined.

  “Light emission intensity” is a concept that includes not only the absolute value of the light emission intensity but also a relative value such as a ratio to the maximum value.

  The “amplification degree” refers to the degree of amplification in the amplifier, and is a concept including not only the case of 1 or more but also the case of less than 1.

BEST MODE FOR CARRYING OUT THE INVENTION

1. Functional Block Diagram FIG. 1 shows a functional block diagram of a liquid crystal display device according to one embodiment of the present invention. The liquid crystal panel unit 2 receives a video signal and displays an image. The back surface of the liquid crystal panel unit 2 includes a red light source 4, a green light source 6, and a blue light source 8, and a backlight light emitting unit that emits white light by mixing these colors is provided. The light source selection detecting means 12 is a first state in which all of the red light source 4, the green light source 6, and the blue light source 8 are turned on, a second state in which only the red light source 4 is turned off, and a first state in which only the blue light source 8 is turned off. Lighting control is performed so that the three states are obtained. Furthermore, the light source selection detection means 12 acquires the emission intensity detection output from the optical sensor 10 in each of the first, second, and third states.

  The light emission control unit 14 calculates the light emission intensities of the red light source 4, the green light source 6, and the blue light source 8 based on the light emission intensities detected in the first, second, and third states. That is, the light emission intensity of the red light source 4 is calculated by subtracting the light emission intensity in the second state from the light emission intensity in the first state. Further, the emission intensity of the blue light source 8 is calculated by subtracting the emission intensity in the third state from the emission intensity in the first state. Further, the emission intensity of the green light source 6 is calculated by subtracting the emission intensity of the red light source 4 and the blue light source 8 calculated above from the emission intensity in the first state.

  The light emission control means 14 makes the red light source 4, the green light source 6, and the blue light source so that the light emission intensities of the red light source 4, the green light source 6, and the blue light source 8 calculated in this way become the desired light emission intensity. The emission intensity of 8 is feedback controlled. In this way, it is possible to control to keep the emission color of the backlight light source white.

  In addition, the sensitivity with respect to each color of the optical sensor 10 is different. In general, the sensitivity to green is the best, and the sensitivity is often the worst in the order of red and blue.

[Reason for measuring cyan light, white light, and yellow light by the optical sensor 10]
Therefore, when the ratio of sensitivity to R, G, and B of the optical sensor 10 is R: G: B = 3: 10: 1 as in this embodiment, the ratio of sensitivity to C, W, and Y is C: W. : Y = 11: 14: 13. Therefore, the ratio between W = 14, which is the maximum sensitivity, and minimum sensitivity C = 11 is W / C = 14/11 = 1.27.

  On the other hand, as in Patent Document 2, when all of RGB are sequentially turned off, the ratio of sensitivity to C: M (magenta): Y is C: M: Y = 11: 4: 13. Therefore, the ratio between the maximum sensitivity Y = 13 and the minimum sensitivity M = 4 is Y / M = 13/4 = 3.25 times. Thus, if the ratio between the maximum sensitivity and the minimum sensitivity is increased, there is a problem that the dynamic range for magenta (M), which is the minimum sensitivity, is significantly reduced.

Therefore, in this embodiment, as described above, the first state in which all the light sources are turned on to obtain white light, the second state in which only the red light source is turned off to obtain cyan light, and only the blue light source is turned off. By measuring in the third state using yellow light, measurement is performed without turning off the most sensitive green light source 6 to increase the dynamic range and realize accurate detection.

2. Circuit Configuration Example FIG. 2 shows a specific circuit configuration example of the liquid crystal display device of FIG. In FIG. 2, constituent elements corresponding to those in FIG. 1 are denoted by the same reference numerals. The red LED 4, the green LED 6, and the blue LED 8 constitute a backlight light source.

  Details of the backlight source are shown in FIG. FIG. 3A is a cross-sectional view. The backlight source includes a prism sheet 5 that scatters light, a guide plate 7 that serves as a light path, and a reflector 9. As shown in FIG. 3B, one end of the short side portion of the guide plate 7 is provided with a large number of sets each including one red LED 4, two green LEDs 6, and one blue LED 8 per unit cell. Yes. This is because the light emission intensity of the green LEDs 4 is weaker than the light emission intensity of the red LEDs 4 and the blue LEDs 8, so that the light emission intensities of the LEDs of the respective colors are made uniform. Light from the red LED 4, green LED 6, and blue LED 8 is mixed in the guide plate 7 to become white light and is emitted from the prism sheet 5.

  In addition, a through hole 9a is provided in a part of the reflecting plate 9, and an optical sensor 10 is provided in the rear part. The optical sensor 10 does not detect only light of a specific wavelength, but detects the intensity of light over a predetermined wavelength range, and is called a so-called illuminance sensor.

  In this embodiment, the red LED 4, the green LED 6, and the blue LED 8 are provided on the short side, but may be provided on the long side. Moreover, it is good also as a direct type | mold structure which provided red LED4, green LED6, and blue LED8 in the back side of the prism sheet 5, without providing a guide plate.

  In FIG. 2, a PLL circuit 22a of the timing generation circuit 22 receives a horizontal synchronization signal (LCD panel synchronization signal) of a video signal and generates a signal synchronized therewith. The basic pulse generator 22b generates a basic pulse of about several tens of MHz based on the output of the PLL circuit 22a. The light emission pulse generator 22c divides the basic pulse to generate a light emission pulse (several hundred KHz to several MHz) as shown in FIG. 4A. This light emission pulse is given to the LED drive circuit 20 and used to turn on the red LED 4, the green LED 6, and the blue LED 8.

  In addition, the dimming pulse generation unit 22d of the timing generation circuit 22 adjusts each of the red, green, and blue dimming levels based on duty information from the MPU 34 (information on how many light emission pulses are turned on). An optical pulse is generated (see FIG. 4C).

  The LED drive circuit 20 receives the light emission pulse from the timing generation circuit 22 and applies the light emission pulse to the red LED 4 for lighting only during the period when the dimming pulse for red is on. Similarly, only during the period when the dimming pulse for green is on, this light emission pulse is applied to the green LED 6 to light it. Similarly, only during the period when the dimming pulse for blue is on, this light emission pulse is applied to the blue LED 8 to light it.

  Since the ON period of the dimming pulse is determined based on the duty information from the MPU 34, the MPU 34 can control the light emission time of each LED by changing the duty information. If the light emission time is shortened, the light intensity perceived by the human eye is reduced, and if the light emission time is lengthened, the light intensity perceived by the human eye is increased. Thereby, the balance of each color can be adjusted. In this embodiment, the dimming pulse is several hundred Hz.

  The detection output of the optical sensor 10 is converted into digital data by an A / D converter 32 through an amplifier 24 with variable gain and a sample / hold circuit 27, and is supplied to an MPU 34. The MPU 34 gives a command to the LED drive circuit 20 so that the red LED 4, the green LED 6, and the blue LED 8 are all turned on, the second state in which only the red light source is turned off and cyan light is emitted, blue In a third state where only the light source is turned off to obtain yellow light, the output from the optical sensor 10 in each state is acquired as digital data of the emission intensity.

Further, the MPU 34 calculates the emission intensity of the red LED 4, the emission intensity of the green LED 6, and the emission intensity of the blue LED 8 based on the emission intensity in the first state, the second state, and the third state. On the other hand, the luminance information storage unit 36 stores a desired red emission intensity, a desired green emission intensity, and a desired blue emission intensity set by the user. The MPU 34 compares the desired light emission intensity with the measured measurement intensity for each color, and controls the ON time of the dimming pulse so that they are equal. Details of the control process by the MPU 34 will be described in the process of the intensity measurement / dimming control program.

3. Processing of Intensity Measurement / Dimming Control Program FIGS. 5 to 7 show flowcharts of the intensity measurement / dimming control program recorded in the MPU 34. The MPU 34 counts the rise of the green dimming pulse (see FIG. 4D) from the dimming pulse generation unit 22d of the timing generation circuit 22. The reason why the dimming pulse for the green LED 6 is used is that the dimming pulse for the green LED 6 is turned on every cycle as will be described later. The reason why the rising edge is used as a reference is that the rising edge does not fluctuate even if the dimming time is adjusted as shown in FIG. 4C.

  When the count value COUNT of the light control pulse reaches a predetermined value, the MPU 34 turns off the red LED 4 and emits cyan light according to the value, and turns on all the LEDs and emits white light. The measurement is performed, and the blue LED 8 is turned off and yellow light is emitted for measurement.

  When the count value COUNT of the dimming pulse is a multiple of 600 (β in FIG. 4D), the MPU 34 instructs the dimming pulse generation unit 22d to thin out one dimming pulse of the red LED 4 (in FIG. 4D). α). As a result, as indicated by α in FIG. 4D, the dimming pulse of the red LED 4 is thinned out by one pulse, and cyan light is emitted. Then, the amplification degree of the amplifier 24 (FIG. 2) is set to the cyan light amplification degree MC (9 times in this embodiment). In this embodiment, the amplification degree of the amplifier 24 is changed according to cyan light, white light, and yellow light. This is because the sensitivity of the optical sensor 10 differs depending on the light, and by changing the amplification degree accordingly, the ability of the A / D converter 32 is utilized as much as possible to increase the dynamic range and increase the accuracy. It is.

Next, the MPU 34 takes in the output of the optical sensor after A / D conversion (step S9). This capture is performed as follows. First, MPU34
When the count value COUNT of the dimming pulse reaches a predetermined value (here, when the count value COUNT is a multiple of 600), the first switch 26 is controlled to be turned on, and the output from the amplifier 24 is stored in the capacitor 30. . Next, the MPU 34 controls the first switch 26 to be turned off simultaneously with the rising γ of the next green dimming pulse. As a result, electric charges corresponding to the intensity of cyan light (mixed color of green and blue) (average intensity considering the dimming time) are held in the capacitor 30. At the same time, the MPU 34 instructs the A / D converter 32 to convert the charge accumulated in the capacitor 30 into digital data. The MPU 34 takes in the digital data of the emission intensity from the A / D converter 32. When the data is captured, the MPU 34 turns on the second switch 28 to discharge the capacitor 30. When a sufficient time has elapsed for discharging, the MPU 34 turns off the second switch 28 again.

  Next, in step S10, the MPU 34 determines whether or not the current measurement is the first measurement for the color. In the first measurement, the acquired emission intensity data is not used as a measurement value, but it is determined whether or not the capability of the A / D converter 32 is sufficiently used, and the amplification degree of the amplifier 24 is set appropriately. It is used as information. Here, since it is the first measurement of cyan light, the process proceeds to step S11.

  In step S <b> 11, the MPU 34 determines whether the captured emission intensity data is smaller than half of the capability of the A / D converter 32. For example, if the most significant bit of the output of the A / D converter 32 is not “1”, it can be determined that the captured emission intensity data is less than half of the capability. If it is determined that the A / D converter 32 has sufficient capacity, the MPU 34 further doubles the cyan light amplification MC. In this embodiment, since the initial value of the amplification factor MC for cyan light is 9 times, if it is doubled, it will be 18 times. The MPU 34 records the cyan light gain MC corrected in this way in an internal memory. If it is determined that the capacity of the A / D converter 32 has no margin, the cyan light gain MC set as the initial value is used as it is.

  Next, the MPU 34 clears the variable for measurement to “0” (step S13). Thereafter, step S2 and subsequent steps are repeated.

  When the count value COUNT-150 of the dimming pulse is a multiple of 600 (for example, when COUNT becomes 750 (δ in FIG. 4D)), the MPU 34 sets the amplification factor of the amplifier 24 to the amplification factor MW for white light ( Step S5). In this embodiment, the amplification factor MW for white light is 7 times. Then, white light is emitted without thinning out any dimming pulse. The MPU 34 takes in the output from the optical sensor 10 (step S9), and determines whether or not the white light gain is further doubled (step S11). Thereafter, step S2 and subsequent steps are repeated.

  When the count value COUNT-300 of the dimming pulse is a multiple of 600 (for example, when the COUNT value is 900 (ε in FIG. 4D)), the MPU 34 sets the amplification degree of the amplifier 24 to the amplification degree MY for yellow light. (Step S7). In this embodiment, the amplification factor MY for yellow light is 8 times. Then, a command is given to the dimming pulse generator 22d so as to thin out the blue dimming pulse by one pulse. As a result, yellow light is emitted (see φ in FIG. 4D). The MPU 34 takes in the output from the optical sensor 10 (step S9), and determines whether to further double the yellow light amplification degree (step S11). Thereafter, step S2 and subsequent steps are repeated.

  When the count value COUNT-450 of the dimming pulse is a multiple of 600 (for example, when the COUNT value is 1050 (ε in FIG. 4D)), the MPU 34 does not perform special processing.

  As described above, the first measurement for each color is performed, and the amplification degree of the amplifier 24 for each color is set.

  As shown below, the MPU 34 sums up the measurement values from the second measurement to the fifth measurement, and averages them to calculate an average measurement value. First, when the count value COUNT of the dimming pulse is a multiple of 600, the MPU 34 controls the dimming pulse generation unit 22d so as to emit cyan light by thinning out the red dimming pulse (step S3). Also, the cyan light amplification MC recorded in the memory is read, and the amplification of the amplifier 24 is set to this.

  The MPU 34 takes in the output of the optical sensor 10 at this time as emission intensity data C (step S9). Since this time is the second measurement for cyan light, the process proceeds to step S14, and the emission intensity data taken in the variable Ct for recording the cyan intensity is added (step S14). Next, it is determined whether or not five measurements have been completed for all colors. Here, since the measurement has not been completed, step S2 and subsequent steps are repeated.

  Next, when the count value COUNT-150 of the dimming pulse is a multiple of 600, white light emission intensity data is captured and added to the variable Wt for recording the white intensity in the same manner as described above.

  Further, when the count value COUNT-300 of the dimming pulse is a multiple of 600, the emission intensity data of yellow light is captured and added to the variable Yt for recording the yellow intensity in the same manner as described above.

  When the above process is repeated and measurement is performed five times for each color, the measured values for four times are added to the variables Ct, Wt, and Yt, respectively. When the measurement is completed five times, the MPU 34 calculates the cyan intensity Cf, the white intensity Wf, and the yellow intensity Yf by the following formula (step S16).

Cf = (Ct / MC) / 4
Wf = (Wt / MW) / 4
Yf = (Yt / MY) / 4
Here, MC, MW, and MY are amplification factors for cyan, white, and yellow, respectively, and are used when they are doubled in step S12.

  Next, the MPU 34 calculates the emission intensities of the blue LED 8, the green LED 6, and the red LED 4 based on the following formula based on the cyan intensity Cf, white intensity Wf, and yellow intensity Yf calculated above (step S17).

B = Wf-Cf
G = Wf-Yf
R = Wf-B-G
Here, B is the emission intensity of the blue LED 8, G is the emission intensity of the green LED 6, and R is the emission intensity of the red LED 4.

  Next, the MPU 34 reads out desired tristimulus values XREF, YREF, and ZREF set by the user from the luminance information storage unit 36 (step S18). Next, the MPU 34 is based on the factory adjusted values of the tristimulus values determined based on the values measured at the time of manufacture for the red LED 4, the green LED 6, and the blue LED 8, and the desired tristimulus values XREF, YREF, and ZREF set by the user. Then, the ratio (the ratio of the intensity to be detected by the optical sensor 10 with respect to the maximum intensity) of the target light emission intensity of the LEDs 4, 6, and 8 for each color is calculated (step S19). The calculation formula is as follows. Here, the tristimulus value is an XYZ color system in the CIE color system.

Here, the factory adjustment value of the tristimulus value is calculated by actual measurement at the time of manufacture as will be described later.

  The MPU 34 outputs duty information so that the ratios of R, G, and B obtained by measurement to the maximum intensities Rmax, Gmax, and Bmax are equal to the calculated target RREF, GREF, and BREF, respectively, and the dimming pulse Control is performed to change the ratio of the on-time (step S20). The dimming pulse generation unit 22d controls the on-time of the dimming pulse of each color based on the given red, green, and blue duty information.

  As described above, the color balance is adjusted using the average value of the five measurements. Note that when the measurement is completed five times, the control is repeated again from the first measurement.

[Reason for measuring cyan light, white light, and yellow light by the optical sensor 10]
In this embodiment, cyan light, white light, and yellow light are measured by the optical sensor 10. This is due to the following reasons.

  The sensitivity of each color of the optical sensor 10 is different. In general, the sensitivity to green is the best, and the sensitivity is often poor in the order of red and blue. For example, the ratio of sensitivity to R, G, and B of the optical sensor 10 used in this embodiment is R: G: B = 3: 10: 1.

  Therefore, as in Patent Document 2, when all of RGB are sequentially turned off, the ratio of sensitivity to C, M, and Y is C: M: Y = 11: 4: 13. Therefore, the ratio between the maximum sensitivity Y = 13 and the minimum sensitivity M = 4 is Y / M = 13/4 = 3.25 times. Thus, if the ratio between the maximum sensitivity and the minimum sensitivity is increased, there is a problem that the dynamic range for magenta (M), which is the minimum sensitivity, is significantly reduced.

  In this embodiment, cyan light, white light, and yellow light are measured, and the ratio of sensitivity to C, W, and Y is C: W: Y = 11: 14: 13. Therefore, the ratio between W = 14, which is the maximum sensitivity, and minimum sensitivity C = 11 is W / C = 14/11 = 1.27. Thereby, the nonuniformity of sensitivity between the measurement light can be reduced, the dynamic range can be increased, and the measurement accuracy can be improved.

  Further, as shown in FIG. 8, an experimental result is obtained that flicker perceived by human eyes is greater when only the green LED is turned off than when only the red LED or only the blue LED is turned off. It was. In FIG. 8, what is plotted with square points is an evaluation of how much flicker is felt by changing the dimming frequency when only the green LED is turned off. Plot-shaped points are plotted to evaluate how much flicker is felt by changing the dimming frequency when only the red LED is turned off. Plotted with triangular points are evaluations in five stages of how much the subject feels flicker by changing the dimming frequency when only the blue LED is turned off. The horizontal axis represents the dimming frequency, and the vertical axis represents the average flicker evaluation value.

  For example, in this embodiment, the frequency of the dimming pulse is 700 Hz, and even in this region, it is shown that flicker is felt when only the green LED or the red LED is turned off. From these experimental results, it can be concluded that it is preferable to avoid turning off only the green LED.

[Reason for weighting amplification]
As described above, the sensitivity ratio of the optical sensor 10 to cyan light, white light, and yellow light is C: W: Y = 11: 14: 13. Since the least common multiple is 11 × 14 × 13 = 2002, the ratio of the amplification factor MC for cyan light, the amplification factor MW for white light, and the amplification factor MY for yellow light is 182 (= 2002/11): 143 (= 2002/14): 154 (= 2002/13) is preferable. However, in this embodiment, in consideration of the capability of the AD converter 32, the amplification factor MC: MW: MY = 9: 7: 8 which is realistically approximated is selected. By setting the amplification degree MC: MW: MY to 9: 7: 8, the input at the time of AD conversion becomes 11 × 9: 14 × 7: 13 × 8 = 99: 98: 104, and the maximum and minimum ratio is ( 104/98) 1.06 times. Therefore, a good SN ratio can be obtained. The amplification degree MC: MW: MY may be further approximated to 5: 3: 4.

  In this embodiment, the sample and hold circuit 27 is used to integrate the detection signal from the optical sensor 10. In addition to the sample and hold circuit built in the A / D converter 32, a sample and hold circuit 27 is provided separately before the A / D converter 32.

  As shown in FIG. 9, even if a rectangular light emission pulse is given to each LED, the light emission intensity does not change in the same way as the light emission pulse. That is, the light emission intensity at the edge portion of the light emission pulse does not follow it sharply, but has a dull shape (trapezoid). In addition, as shown in FIG. 3, in order to make the emission intensity uniform, one red LED and one blue LED are provided in the unit cell, whereas two green LEDs are provided. This is because the emission intensity of the green LED is weak. As a result, the steepness of the two connected green LEDs is worse than that of one red LED or blue LED.

  Therefore, as conventionally performed, the method of calculating the light intensity as a whole by measuring the light intensity by the optical sensor 10 and multiplying it by the ON time of the dimming pulse lacks accuracy. In particular, an error due to the difference in absorbance between green and other colors is not taken into account, and this is a cause that cannot be accurately determined.

  Therefore, in this embodiment, a sample and hold circuit 27 is provided at the input stage of the A / D converter 32 so that the output of the optical sensor 10 is integrated for one cycle of the dimming pulse. FIG. 10A shows a dimming pulse. FIG. 10B shows a light emission pulse, and FIG. 10C shows an output of the optical sensor 10 that detects the light of each LED that emits light. With the rise of the dimming pulse, the MPU 34 turns on the switch 26 of the sample hold circuit 27. As a result, the output of the optical sensor 10 is accumulated in the capacitor 30.

  The MPU 34 turns off the switch 26 immediately before the dimming pulse is turned off and turned on again. Thereby, even if the edge of the light emission intensity of each LED is dull, it is possible to measure the actual light emission intensity by integrating the light emission intensity for the ON period of the dimming pulse including these.

  The MPU 34 turns off the switch 26 and gives a conversion command to the A / D converter 32. As a result, the integrated value of the output of the optical sensor 10 accumulated in the capacitor 30 is given to the MPU 34. When receiving data from the A / D converter 32, the MPU 34 turns on the switch 28 to discharge the capacitor 30, and turns on the switch 28 again to prepare for the next measurement.

  As described above, by integrating the output of the optical sensor 10 and supplying it to the A / D converter, the rise of the emission of each LED 4, 6, 8 after receiving the pulse, the emission pulse, Even if there is an edge inclination of the dimming pulse itself, it is possible to accurately measure the emission intensity.

In the above embodiment, the MPU 34 is controlled to count the dimming pulses and thin out the dimming pulses. However, a lighting control pulse as shown in FIG. 4D may be generated based on the dimming pulse. In this case, the MPU 34 does not need to count the dimming pulses, and can be controlled to thin out the dimming pulses by the rising or falling edge of the lighting control pulse.

4). Tristimulus Factory Adjustment Value Setting Processing In the above control, the tristimulus factory adjustment value is used. This factory adjustment value is calculated based on actual measurement as follows for each optical sensor 10 incorporated in the display device.

  First, only the red LED 4 is turned on, and measurement is performed using a highly accurate sensor capable of measuring tristimulus values X, Y, and Z. Thereby, the X component RX, the Y component RY, and the Z component RZ of the stimulation value of the red light from the red LED 4 can be obtained. Similarly, the X component GX, Y component GY, and Z component GZ of the stimulus value of green light from the green LED 6 and the X component BX, Y component BY, and Z component BZ of the stimulus value of blue light from the blue LED 8 are obtained. .

  RX, RY, RZ, GX, GY, GZ, BX, BY, BZ thus obtained, and the X component WX of the stimulation value of white light when all of the red LED 4, the green LED 6, and the blue LED 8 are turned on, The relationship between the Y component WY and the Z component WZ is as follows.

Here, WX, WY, and WZ are stimulation values of white light when the red LED 4, the green LED 6, and the blue LED 8 are caused to emit light. RGB is the ratio of the intensity of each LED 4, 6, 8 to the maximum intensity. Therefore, when each LED is lit at the maximum intensity (when the ON period of the dimming pulse is maximum), r = 1, g = 1, and b = 1.

  When the red LED 4, green LED 6, and blue LED 8 are turned on at the maximum brightness assumed, and the stimulation values WX, WY, and WZ of white light are measured, the calculation is performed with r = 1, g = 1, and b = 1 in the above equation. The stimulus values WX, WY, and WZ calculated by

  Next, the intensities R, G, and B of the red LED 4, the green LED 6, and the blue LED 8 are detected using the optical sensor 10 that is actually incorporated in the display device. This is performed by measuring the intensity of cyan light, white light, and yellow light and calculating the intensity of each color based on the method described in the above embodiment (see step S17).

  Here, the Y component of the above formula (2), that is, RY, GY, BY is in a relationship that is almost equal to the intensity R, G, B. Therefore, if the sensitivity of each color of the optical sensor 10 is uniform and has the same capability as the high-precision sensor, RY, GY, BY and R, G, B should be equal. Actually, since the capability of the optical sensor 10 is inferior, R, G, and B are smaller than RY, GY, and BY. Therefore, based on the measured R, G, and B, the above equation (2) is modified as follows.

Here, R′Y, G′Y, and B′Y are replaced with the measured values of R, G, and B. R′X and R′Z are calculated by the following formulas. That is, R′X and R′Z are corrected according to the ratio between RY and R′Y.

G′X, G′Z, B′X, and B′Z can be calculated by the same formula.

  Next, the red LED 4, the green LED 6, and the blue LED 8 are caused to emit light at a predetermined maximum intensity, and the intensity W of the white light is detected by the optical sensor 10. The intensity W at this time should be equal to W′Y calculated by calculation when r = 1, g = 1, and b = 1 in the above equation (3). However, since Equation (3) is an approximate equation, they do not match. Therefore, the measured value W is set to W ″ Y in equation (3), and W′X and W′Z are corrected based on the ratio of W ″ Y and W′Y (similar to equation (4)) Correct W) X and W''Z. The same correction is performed for the right side of Equation (3) based on the ratio of W ″ Y to W′Y. Therefore, the following formula is obtained.

  If this equation is modified, the following equation is obtained. This equation is obtained when the light parameters WX, WY, and WZ of light having a desired color are given, and the intensity detected by the optical sensor 10 when the red LED 4, the green LED 6, and the blue LED 8 try to develop this color. The ratio of the maximum intensity is indicated by r, g, and b.

When shipped from the factory, R ″ X, R ″ Y, R ″ Z, G ″ X, G ″ Y, G ″ Z, B ″ X, B ″ Y, B in Equation (6) '' Z is recorded in the memory of the MPU 34 as a factory adjustment value of tristimulus values. Note that r, g, and b in Expression (6) correspond to RREF, GREF, and BREF in Expression (1).

5. Other embodiments
(1) In the above embodiment, the signal from the optical sensor 10 is integrated using the sample and hold circuit 27 having a relatively long time constant. However, if the A / D converter 32 can sample at a very high speed, the digital intensity at each time point may be acquired without performing integration, and the emission intensity may be obtained by summing the digital data.

(2) In the above embodiment, an example is shown in which feedback control is performed so as to achieve a desired color balance based on the measured light intensities R, G, and B of the red LED 4, the green LED 6, and the blue LED 8. However, the measured light intensities R, G, and B of the red LED 4, the green LED 6, and the blue LED 8 may be used for other controls. The present invention can also be applied to calculate the light intensities R, G, and B of the red LED 4, the green LED 6, and the blue LED 8.

  In this case, the emission intensity of the blue LED measured by a highly accurate sensor with varying intensity was obtained based on white light and cyan light by the method of the present invention when the intensity was similarly varied. A correspondence table or calculation formula with the measurement value of the blue LED is recorded in advance in the MPU 34 or the like. Similarly, the green LED emission intensity measured by a high-precision sensor with varying intensity, and the green LED obtained based on white light and yellow light by the method of the present invention when the intensity is similarly varied Correspondence table or calculation formula with the measured value of the red LED emission intensity measured with a highly accurate sensor by changing the intensity, and the red LED obtained by the method of the present invention when the intensity is changed in the same way A correspondence table or calculation formula with the measured values is recorded in advance in the MPU 34 or the like.

  At the time of actual measurement, the method of the present invention is used to calculate the intensities of the red LED, green LED 6 and blue LED 8 based on cyan light, white light and yellow light. By applying a correspondence table or calculation formula recorded in advance to this, an accurate strength can be obtained.

(3) In the above-described embodiment, the amplification degree set in advance according to the sensitivity is used in accordance with whether the measurement is cyan light, white light, or yellow light. However, in the first measurement, the amplification degree of the amplifier 24 is set to the reference amplification degree (the smallest amplification degree), and according to the magnitude of the output of the A / D converter 32 obtained at this time, A / D The amplification degree may be set so that the capability of the D converter 32 can be sufficiently exhibited, and the second and subsequent measurements may be performed. For example, the amplification degree of the amplifier 24 can be set so that the output of the amplifier 24 becomes a predetermined ratio (for example, 90%) of the maximum capacity of the A / D converter 32.

(4) In the above embodiment, control is performed using the tristimulus values XYZ. However, the control may be performed using other values such as RGB values.

(5) In the above-described embodiment, the case where desired white light is obtained has been described.

(6) The present invention can be applied not only to the backlight of a liquid crystal display device but also to the light source of a projector, the realization of a desired color in an LED display, the realization of a desired color in illumination, and the like.

(7) Although the LED has been described in the above embodiment, the present invention can be similarly applied to other light sources. Further, the present invention can be applied not only in the case of mixing three colors but also in the case of mixing two colors or mixing four or more colors. In this case, it is preferable to perform measurement without turning off the color with the largest sensor output by combining the sensor sensitivity and the light emission intensity among the colors. That is, the turn-off control is not performed like the green LED in the above embodiment.

1 is a functional block diagram of a liquid crystal display device according to an embodiment of the present invention. It is a circuit example of the light emission balance control apparatus by one Embodiment of this invention. It is a figure which shows the detail of a backlight light source. 4A shows a basic pulse, FIG. 4B shows a light emission pulse, and FIG. 4C shows a dimming pulse. FIG. 4D is a diagram illustrating a relationship between the dimming pulse and the lighting control pulse. It is a flowchart of the control program recorded on MPU34. It is a flowchart of the control program recorded on MPU34. It is a flowchart of the control program recorded on MPU34. It is a graph which shows the relationship between a light control frequency and flicker. It is a figure which shows the relationship between the light emission pulse and the light emission intensity of LED. It is a figure which shows the relationship between a light control pulse, a light emission pulse, and an optical sensor output.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Liquid crystal panel part 4 ... Red light source 6 ... Green light source 8 ... Blue light source 10 ... Optical sensor 12 ... Light source selection detection means 14 ... Light emission control means

Claims (9)

LCD panel part,
A light emitting unit having a red light source, a green light source, and a blue light source, and functioning as a backlight of the liquid crystal panel unit;
An optical sensor for detecting the light emission intensity of the light emitting unit;
A first state in which the red light source, the green light source, and the blue light source are turned on, a second state in which only the red light source is turned off, and a third state in which only the blue light source is turned off with respect to the light emitting unit. Light source selection detecting means for detecting the light emission intensity of the light emitting unit in each of the states so that the green light source with the best sensitivity to the light sensor is not turned off by controlling the lighting,
Based on the light emission intensity detected by the optical sensor in each state, light emission control means for controlling the light emitting unit so that each light source has a desired light emission intensity,
A liquid crystal display device comprising: A light emitting unit having a red light source, a green light source, and a blue light source;
An optical sensor for detecting the light emission intensity of the light emitting unit;
A first state in which the red light source, the green light source, and the blue light source are turned on, a second state in which only the red light source is turned off, and a third state in which only the blue light source is turned off with respect to the light emitting unit. Light source selection detecting means for detecting the light emission intensity of the light emitting unit in each of the states so that the green light source with the best sensitivity to the light sensor is not turned off by controlling the lighting,
Based on the light emission intensity detected by the optical sensor in each state, light emission control means for controlling the light emitting unit so that each light source has a desired light emission intensity;
A light emitting device comprising: A light emission balance control device for controlling the light emission balance of a light emitting device comprising a light emitting unit having a red light source, a green light source, and a blue light source, and an optical sensor for detecting the light emission intensity of the light emitting unit,
A first state in which the red light source, the green light source, and the blue light source are turned on, a second state in which only the red light source is turned off, and a third state in which only the blue light source is turned off with respect to the light emitting unit. Light source selection detecting means for detecting the light emission intensity of the light emitting unit in each of the states so that the green light source with the best sensitivity to the light sensor is not turned off by controlling the lighting,
Based on the light emission intensity detected by the optical sensor in each state, light emission control means for controlling the light emitting unit so that each light source has a desired light emission intensity,
A light emission balance control device. In the apparatus in any one of Claims 1-3,
The light source selection detecting means includes
An amplifier for amplifying a detection signal from the optical sensor;
An A / D converter for converting the output of the amplifier into a digital signal;
An apparatus for changing the amplification degree of the amplifier in the first state, the second state, and the third state in accordance with detection sensitivities of the photosensor for red, green, and blue. In the apparatus in any one of Claims 1-4,
The light source selection detecting means includes
An amplifier for amplifying a detection signal from the optical sensor;
An A / D converter for converting the output of the amplifier into a digital signal;
An apparatus characterized in that the amplification degree of the amplifier is changed according to the light emission intensity detected by the optical sensor. The apparatus of claim 4 or 5,
An apparatus comprising an integrating circuit for integrating the output of the amplifier and supplying the output to the A / D converter. A light emitting unit having a first color light source, a second color light source, an nth color light source;
An optical sensor for detecting the light emission intensity of the light emitting unit;
The light emitting unit is controlled to turn on so that the n light sources are turned on, and only one of the n light sources is sequentially turned off. Light source selection detecting means for controlling to detect the light emission intensity of the light emitting unit,
Calculation means for calculating the light emission intensity of each light source based on the light emission intensity detected by the optical sensor in each state;
A luminescence intensity detecting device comprising:
When the light intensity of each light source of the light emitting unit is adjusted so that light is emitted with a desired color balance and the light intensity of each light source is detected by the light sensor, the light source that provides the largest detection output is the maximum detection light source. ,
The light source selection detection means does not realize a combination of turning off the maximum detection light source and turning on the remaining light sources when sequentially turning off only one of the n light sources and turning on the remaining light sources. A light emission intensity detecting device characterized by the above. The emission intensity detection device according to claim 7,
The light emission intensity detection device, wherein the calculation means records correction information for correcting a detection output decrease due to detection sensitivity of the optical sensor in advance, and calculates and corrects the light emission intensity based on the correction information. . A light emission intensity detection method for detecting light emission intensity of each light source of a light emitting unit having a first color light source, a second color light source, ... an nth color light source, using an optical sensor,
The light emitting unit is controlled to turn on so that the n light sources are turned on, and only one of the n light sources is sequentially turned off. Control to detect the light emission intensity of the light emitting part,
In the emission intensity detection method for calculating the emission intensity of each light source based on the emission intensity detected by the optical sensor in each state,
When the light intensity of each light source of the light emitting unit is adjusted so that light is emitted with a desired color balance and the light intensity of each light source is detected by the light sensor, the light source that provides the largest detection output is the maximum detection light source. ,
The light emitting light source selection unit does not realize a combination of turning off the maximum detection light source and turning on the remaining light source when sequentially turning off only one of the n light sources and turning on the remaining light sources. An emission intensity detection method characterized by the above.

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