JP2011107234A - Liquid crystal display device and light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device and a light emitting device capable of detecting intensity of light emission of each color highly precisely and controlling it by using an optical sensor irrespective of difference in duty of each PWM modulated light pulse of red, green, and blue colors in a unit light emission period of an LED. <P>SOLUTION: A light source selection detecting means A of this device 1 controls turning-on of each light source based on the PWM modulated light pulses aligned in rising for each other to switch among a first state where all of red color light source 11, green color light source 12, and blue color light source 13 are turned on in a first unit light emission period, a second state where only one kind of the light source is turned off in a second unit light emission period, and a third state where only one kind of the light source different from the light source turned off in the second state is turned off in a third unit light emission period. Furthermore, a signal inversion amplifier 30 inverts and amplifies output of the optical sensor PD in each state, and an integrator 51 integrates it to obtain intensity of light emission. A light emission control means B calculates each intensity of light emission of the red, green, and blue color light sources and drives and controls them based on the intensity of light emission detected in each state. <P>COPYRIGHT: (C)2011,JPO&INPIT

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 light sources of a plurality of colors.

As a light emitting device such as a liquid crystal display device, three types of LEDs that emit light of three primary colors, red (R), green (G), and blue (B), are used, and R emitted from these three types of LEDs, Some obtain white light by mixing G and B light. Since the emission colors of these LEDs shift due to temperature change, aging change, etc., feedback control is performed so as to compensate for this and maintain the original white light.

For example, in Patent Literature 1 and Patent Literature 2, a color sensor for detecting the emission color of each of R, G, and B LEDs is provided to obtain emission intensity for each color. 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.

However, the techniques disclosed in Patent Documents 1 and 2 have a problem that an expensive color sensor is required for control and the configuration is complicated.

In order to solve this problem, in Patent Document 3, in order to perform inexpensive control, instead of the color sensor, one optical sensor that detects the intensity of light without distinguishing colors is provided, and R, G, and B LEDs are provided. , And the intensity of light emitted when one of R, G, and B is sequentially turned off is measured. Based on the difference between the intensity of the former and the latter, each of R, G, and B is measured. It has been proposed to perform feedback control based on the emission intensity.
JP2007-123153 (FIG. 1) JP2008-210853 (FIG. 1, paragraphs [0019] to [0021]) JP2007-214053

However, regarding the acquisition of the light emission intensity in Patent Document 3, the photometry processing circuit captures an output signal from the photosensor at the time of receiving the trigger signal in accordance with the trigger signal from the photometry control signal circuit, and an amplification amplifier or A / A Although there is a description acquired with necessary circuit elements such as a D converter (see paragraph [0084]), since the light emission time of the LED is not linear with respect to time, only the A / D converter (instant light emission intensity) ) Is not able to reliably capture the signal output from the sensor.

Under such circumstances, the applicant intends to obtain the emission intensity of the united light emission period of the mixed LED, and provided a sample and hold circuit between the optical sensor and the A / D converter (FIG. 13A). ) For example, when acquiring the emission intensity of white light with different duty of each PWM (Pulse Width Modulation) dimming pulse of red, green and blue, the falling of the PWM dimming pulse of red, green and blue It became clear that the voltage from the photosensor input to the integrator of the sample and hold circuit could not be obtained accurately due to the irregularity (FIG. 13B). In particular, the acquisition accuracy deteriorates when the color temperature is set such that the duty of the PWM dimming pulse varies, such as 4000K or 10,000K. The cause is that the voltage in the one-color lighting period d3 is lower than the voltage charged in the capacitor C immediately before (three-color lighting period d1 + two-color lighting period d2), so that the capacitor C can no longer be charged. .

The present invention has been made in view of such problems, and its object is to use a single optical sensor to perform inexpensive control and to control each of PWM modulation of red, green, and blue during the unit light emission period of the LED. An object of the present invention is to provide a liquid crystal display device and a light emitting device capable of accurately detecting and controlling the light emission intensity of each color even if the duty of the pulse is different.

In order to achieve such an object, the present invention has the following configuration.
(1) The liquid crystal display device
LCD panel part,
A light source having a red light source, a green light source, and a blue light source, mixing each light source into white light, 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 in a first unit light emission period with respect to the light emitting unit based on each PWM dimming pulse whose rise is aligned with each other, a second unit The second state in which only one type of light source is turned off during the light emission period, and the third state in which only one type of light source that is different from that turned off during the second state in the third unit light emission period is turned off. And a light source selection detecting means for integrating the light emission intensity of the unit light emission period of the light emitting unit in each state in this integrator, including an integrator connected to the subsequent stage of the light sensor,
A light emission control means for controlling the light emitting unit so that each light source has a desired light emission intensity based on the light emission intensity of the unit light emission period integrated by the integrator in each state;
The light source selection detecting means includes a signal inverting amplifier connected between the optical sensor and the integrator, and the signal inverting amplifier inverts and amplifies the output signal of the optical sensor and outputs the signal to the integrator. And

Thus, the voltage applied to the integrator is controlled to gradually increase, and the integrator can reliably capture the light emission intensity of the mixed light source per unit light emission period. Therefore, accurate color balance control can be realized even if a low-performance optical sensor is used.

(2) The light emitting device
A light emitting unit that has light sources of at least two colors and emits light of a predetermined color by mixing the light sources;
An optical sensor for detecting the light emission intensity of the light emitting unit;
Based on the PWM dimming pulses whose rises are aligned with each other, in the first state in which the light sources of all colors are turned on in the first unit light emission period for the light emitting unit, one type in the second unit light emission period The lighting control is performed so that only the light source is extinguished, and an integrator connected to the subsequent stage of the photosensor is included, and with this integrator, the emission intensity of the unit emission period of the light emitting unit in each state Light source selection detection means for integrating
A light-emitting device comprising: a light-emission control unit that controls the light-emitting unit so that each light source has a desired light-emission intensity based on the light-emission intensity of the unit light-emission period integrated by the integrator in each state;
The light source selection detecting means has a signal inverting amplifier connected between the optical sensor and the integrator, and the signal inverting amplifier inverts and amplifies the output signal of the optical sensor and outputs the signal to the integrator. Features.

Thus, the voltage applied to the integrator is controlled to gradually increase, and the integrator can reliably capture the light emission intensity of the mixed light source per unit light emission period. Therefore, accurate color balance control can be realized even if a low-performance optical sensor is used.

(3) The liquid crystal display device
LCD panel part,
A light source having a red light source, a green light source, and a blue light source, mixing each light source into white light, 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 in a first unit light emission period with respect to the light emitting unit based on the PWM dimming pulses that are aligned with each other in falling, a second state The second state in which only one type of light source is turned off in the unit light emission period, and the third state in which only one type of light source that is different from the one turned off in the second state in the third unit light emission period is turned off. Light source selection detecting means for controlling lighting so as to be in a state, and having an integrator connected to the subsequent stage of the optical sensor, and integrating the light emission intensity of the light emitting unit in the respective light emitting units in each state by the integrator. ,
And a light emission control means for controlling the light emitting unit so that each light source has a desired light emission intensity based on the light emission intensity of the unit light emission period integrated by the integrator in each state.

Thus, the voltage applied to the integrator is controlled to gradually increase, and the integrator can reliably capture the light emission intensity of the mixed light source per unit light emission period. Therefore, accurate color balance control can be realized even if a low-performance optical sensor is used.

(4) The light emitting device
A light emitting unit that has light sources of at least two colors and emits light of a predetermined color by mixing the light sources;
An optical sensor for detecting the light emission intensity of the light emitting unit;
Based on the PWM dimming pulses whose falling edges are aligned with each other, the light source is turned on in the first unit light emission period in the first unit light emission period, and in one type in the second unit light emission period. The lighting control is performed so that only the light source of the light source is turned off, and the integrator is connected to the subsequent stage of the photosensor, and this integrator is used for the unit light emission period of the light emitting unit in each state. Light source selection detection means for integrating the emission intensity;
And a light emission control means for controlling the light emitting unit so that each light source has a desired light emission intensity based on the light emission intensity of the unit light emission period integrated by the integrator in each state.

Thus, the voltage applied to the integrator is controlled to gradually increase, and the integrator can reliably capture the light emission intensity of the mixed light source per unit light emission period. Therefore, accurate color balance control can be realized even if a low-performance optical sensor is used.

In this embodiment,
The “unit light emission period” corresponds to the PWM dimming period H in FIG.

Specifically, the “light source selection detection means” is the function of the microcomputer 70 realized by steps ST2 to ST4 and ST6 to ST8 in FIG. 5 and the PWM generation circuit 20, the current / voltage converter 30 in FIG. The amplifier 40, the sample and hold circuit 50, the post-stage amplifier 60, and the A / D converter 71 correspond to this. In the case of “each PWM dimming pulse whose falling is aligned with each other”, instead of the PWM generation circuit 20, the current / voltage converter 30 and the microcomputer 70, the PWM generation circuit 200 of FIG. A device 300 and a microcomputer 700 are applied. It should be noted that the functions of steps ST2 to ST4 and ST6 to ST8 may be configured only by hardware using a logic circuit.

Specifically, the “light emission control means” corresponds to the function of the microcomputer 70 (700) realized by steps ST9 to ST13 in FIG. 5 and the PWM generation circuit 20 (200). Note that steps ST9 to ST13 may also be configured only by hardware by a logic circuit.

Specifically, the “signal inverting amplifier” corresponds to the current / voltage converter 30 of FIG. 2A.

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

[First embodiment]
A first embodiment in which the present invention is applied to a liquid crystal display device will be described in detail with reference to the drawings.

1-1. Functional Block Diagram FIG. 1 shows functional blocks of the liquid crystal display device 1 according to the first embodiment of the present invention.

The liquid crystal display device 1 includes a liquid crystal panel unit 2, a light emitting unit 10, an optical sensor PD, a light source selection detection unit A, and a light emission control unit B. The liquid crystal panel unit 2 inputs a video signal and displays an image. The light emitting unit 10 includes a red light source 11, a green light source 12, and a blue light source 13, and each light source is mixed into white light and functions as a backlight of the liquid crystal panel unit 2.

The light source selection detecting means A turns on all of the red light source 11, the green light source 12, and the blue light source 13 in the first unit light emission period based on the PWM dimming pulses whose rises are aligned with each other. Only one type of light source that is different from the one that was turned off in the first state, the second state in which only one type of light source was turned off in the second unit emission period, and the second state in the third unit emission period. Lighting control is performed so as to be in the third state in which is turned off. Further, the light source selection detecting means A has a signal inverting amplifier 30 and an integrator 51. In each of the first, second and third states, the signal inverting amplifier 30 receives the output from the photosensor PD and performs inverting amplification. The integrator 51 integrates the inverted and amplified signal to obtain the emission intensity.

The light emission control means B calculates the light emission intensity of each of the red light source 11, the green light source 12, and the blue light source 13 based on the light emission intensity detected in each of the first, second, and third states. That is, the light emission intensity of the light source turned off in the second state is calculated by subtracting the light emission intensity in the second state from the light emission intensity in the first state. Further, the light emission intensity of the light source turned off in the third state is calculated by subtracting the light emission intensity in the third state from the light emission intensity in the first state. Further, the light emission intensities of the remaining light sources are calculated by subtracting the light emission intensities of the two types of light sources calculated above from the light emission intensities in the first state.

  The light emission control means B uses the red light source 11, the green light source 12, and the blue light source so that the light emission intensities of the red light source 11, the green light source 12, and the blue light source 13 calculated in this way become the respective desired light emission intensities. The emission intensity of the light source 13 is feedback controlled. Therefore, control can be performed so as to keep the emission color of the backlight light source white.

1-2. 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. In FIG. 2, reference numeral 1 denotes a liquid crystal display device. The liquid crystal display device 1 includes a liquid crystal panel unit 2, a light emitting unit 10 that irradiates the liquid crystal panel unit 2 from the back, an LED drive circuit 3 that drives the light emitting unit 10, and a dimming pulse S1 to the LED drive circuit 3. A PWM generation circuit 20 that supplies light, an optical sensor PD that detects the light emission intensity of the light emitting unit 10, a current / voltage converter (signal inversion amplification circuit) 30 that inverts and amplifies a signal detected by the optical sensor PD, A pre-amplifier 40 that amplifies the signal output from the current / voltage converter 30, a sample-and-hold circuit 50 that samples and holds the signal amplified by the pre-amplifier 40, and a signal acquired by the sample-and-hold circuit 50 A post-stage amplifier 60 that amplifies and a microcomputer 70 that controls the entire apparatus 1 are provided.

Here, since the liquid crystal panel part 2 can use a well-known thing, description about the structure is abbreviate | omitted.

The light emitting unit 10 includes a red LED 11, a green LED 12, and a blue LED 13, generates white light mixed by emitting light of these three colors, and irradiates the liquid crystal panel unit 2. Details of the light emitting unit 10 are shown in FIG. FIG. 3A is a cross-sectional view. The light emitting unit 10 includes a diffusion sheet that scatters light, a prism sheet 14, and one end of a short side portion of a guide plate 15 serving as a light path, one red LED 11 and one green LED 12 per unit cell, A large number of blue LEDs 13 incorporated therein are provided.

In this embodiment, the red LED 11, the green LED 12, and the blue LED 13 are provided on the short side, but may be provided on the long side. Alternatively, the guide plate 15 may be omitted, and a direct-type configuration in which the red LED 11, the green LED 12, and the blue LED 13 are provided on the back side of the prism sheet 14 may be employed.

  As shown in FIG. 3A, the optical sensor PD is provided at the rear portion where a through hole 16 a is provided in a part of the reflector 16. This optical sensor PD does not detect only light of a specific wavelength but detects light emission intensity over a predetermined wavelength range, and is a so-called photosensor or illuminance sensor photodiode. Therefore, it becomes cheaper than a color sensor.

The PWM generation circuit 20 of FIG. 2 may be provided inside the microcomputer 70, but in order to reduce the burden on the microcomputer 70, an FPGA is used.
(Field Programmable Gate Array) Specifically, as shown in FIG. 4, the serial interface unit 21, the pulse width setting register 22, the count clock (reference clock) CLK, the dimming cycle information setting unit 23, the counter 24, and the red dimming count comparator 25. , A green light adjustment count comparator 26, a blue light adjustment count comparator 27, and the like.

The pulse width setting register 23 stores duty information Rduty, Gduty, and Bduty (14 bits each) output from the microcomputer 70. The duty information Rduty, Gduty, and Bduty are used to set the pulse width when the red LED 11, the green LED 12, and the blue LED 13 are PWM-controlled.

The dimming cycle information setting unit 23 generates the count clock CLK based on the divided pulse and sets it in the PWM pulse cycle setting register of the counter 24 as count-up cycle information.

For example, the counter 24 has a count clock CLK set to 20 MHz and a count-up cycle set to 1 kHz. The count-up cycle is set to a value corresponding to the PWM dimming cycle H that is the unit light emission period of the LED. Accordingly, the counter 24 automatically resets the count value when the count clock CLK for the PWM dimming period H is counted.

Red light control count comparator 25 The red light control count comparator 25 compares the count value of the counter 24 with the duty information Rduty stored in the pulse width setting register 22 as a threshold value. When the threshold value is not exceeded, “High level” is output, and when the threshold value is exceeded, “Low level” is output. Similarly, the green light control count comparator 26 compares the count value of the counter 24 with the duty information Gduty stored in the pulse width setting register 22 as a threshold value, and the count value exceeds the threshold value for the LED drive circuit 3. If not, “High level” is output, and if the threshold value is exceeded, “Low level” is output, and the blue light adjustment count comparator 27 uses the duty information Bduty stored in the pulse width setting register 22 as a threshold value for the counter 24. When the count value does not exceed the threshold value, “High level” is output to the LED driving circuit 3, and when the threshold value is exceeded, “Low level” is output.

In this way, the signals output from the red dimming count comparator 25, the green dimming count comparator 26, and the blue dimming count comparator 27 are the red PWM dimming pulse S1r, green PWM dimming pulse S1g, and blue, respectively. The PWM dimming pulse S1b is supplied to the LED drive circuit 3. Since the PWM dimming pulses S1r, S1g, and S1b are generated based on the count value of the counter 24, the rising edges (Low level → High level) of the PWM dimming pulses S1r, S1g, and S1b are aligned. (See FIGS. 2 and 4).

The LED drive circuit 3 receives the PWM dimming pulses S1r, S1g, and S1b from the PWM generation circuit 20, and turns on the red LED 11 only when the PWM dimming pulse S1r for red is at a high level. Similarly, the green LED 12 is lit only during a period in which the PWM dimming pulse S1g for green is at a high level. Similarly, only when the PWM dimming pulse S1b for blue is at a high level, it is applied to the blue LED 13 to light it.

The current / voltage converter 30 includes an operational amplifier 31 and a feedback resistor R1. A non-inverting amplification terminal (+) of the operational amplifier 31 is connected to a power source (+ 3.3V) and a cathode of the optical sensor PD, and an inverting input terminal. (−) Is connected to the anode of the optical sensor PD and the feedback resistor R1 whose other end is connected to the output terminal. By adopting such a configuration, the current flowing through the optical sensor PD can be converted into a voltage (S2 in FIG. 2), and this can be inverted and amplified to be output, which functions as a signal inverting amplifier (FIG. 2). S3).

The preamplifier 40 includes an operational amplifier 41, a resistor R2, and a feedback resistor R3. The non-inverting amplification terminal (+) of the operational amplifier 41 is connected to the output terminal of the current / voltage converter 30 and the inverting input terminal (−). Are connected to a resistor R2 having the other end grounded and a feedback resistor R3 having the other end connected to the output terminal. With this configuration, the signal output from the current / voltage converter 30 is amplified and output.

Here, the reason why the preamplifier 40 is arranged in the subsequent stage of the current / voltage converter 30 will be described. Assuming that the voltage input to the integrator 51 is Vin and the output voltage is Vout, the relationship of the following equation is established, and the voltage integrated in the integrator 51 rises exponentially as shown in FIG.
Vout = (1−e ^ (− t / CR)) * Vin

In order to output the light amount of the optical sensor PD with the integrator 51 while maintaining linearity, it is necessary to use the light sensor PD in a region where the slope of the output voltage rise with respect to the charging time maintains linearity. For example, as shown in FIG. 8, when the output voltage of the current / voltage converter 30 is 3.3 V (Vin) and the integrator 51 is driven based on the voltage value, linearity is maintained only at a voltage of 1 V or less. Since this cannot be performed (region F in FIG. 8), the dynamic range in the integrator 51 becomes small. Therefore, it is necessary to secure the dynamic range of the integrator 51 by increasing the voltage value Vin from the current / voltage converter 30 by the pre-stage amplifier 40. Accordingly, it is necessary to amplify and output the signal output from the current / voltage converter 30.
If the time constant of the integrator 51 is reduced to perform sample and hold in a region where the linearity cannot be obtained (region G in FIG. 8), the slope of the voltage rise of the integrator 51 varies depending on the time, and thus the linearity of the emission intensity cannot be obtained. .

The sample and hold circuit 50 includes a first electronic switch SW1, a second electronic switch SW2, and an integrator 51. The integrator 41 includes a circuit resistor R4 and a capacitor C. The capacitor C accumulates the amount of light output from the optical sensor PD, and the first electronic switch SW1 and the second electronic switch SW2 are turned on and off by the sample and hold signals SH1 and SH2 from the microcomputer 70. Thus, the light emission intensity in the unit light emission period (PWM dimming cycle) of the LED light source is integrated.

The post-stage amplifier 60 includes an operational amplifier 61, a resistor R5, and a feedback resistor R6, and amplifies the amount of light accumulated in the capacitor C of the sample and hold circuit 50.

The microcomputer 70 includes an A / D converter 71, a reference information storage unit 72, an output information storage unit 73, an arithmetic processing unit 74, a counter 75, and the like. The reference information storage unit 72 stores tristimulus values Xref, Yref, and Zref. Based on these values, the arithmetic circuit 74 calculates a desired light emission intensity of the red LED 11, a desired light emission intensity of the green LED 12, and a desired light emission of the blue LED 13. The intensity is calculated from Equation 1. The output information storage unit 73 stores duty information Rduty corresponding to the red LED 11, duty information Gduty corresponding to the green LED 12, duty information Bduty corresponding to the blue LED 13, and the like.

The duty information Rduty, Gduty, and Bduty determine ON periods of the red PWM dimming pulse S1r, the green PWM dimming pulse S1g, and the blue PWM dimming pulse S1b, respectively. Therefore, the light emission time of each LED can be controlled by changing the duty information Rduty, Gduty, and Bduty. If the light emission time is shortened, the light emission intensity perceived by human eyes is reduced. Thereby, the balance of each color can be adjusted. In this embodiment, the frequency of the dimming pulse S1 is set to 1 kHz (set to the count-up cycle of the counter 24 in the PWM generation circuit 20 described above).

The sample and hold signals SH1 and SH2 are signals for charging and discharging the capacitor C of the sample and hold circuit 50, and are synchronized with the green PWM dimming pulse S2g output from the PWM generation circuit 20. The reason for synchronizing with the green PWM dimming pulse S1g is that the green PWM dimming pulse S1g is turned on every cycle as described later. The light emission intensity in the unit light emission period (PWM dimming cycle) of the LED light source is detected.

The detection output of the optical sensor PD is given to the microcomputer 70 via the current / voltage converter (signal inverting amplifier) 30, the pre-stage amplifier 40, the sample / hold circuit 50, and the post-stage amplifier 60. The microcomputer 70 gives a command to the PWM generation circuit 20 so that the red LED 11, the green LED 12, and the blue LED 13 are all turned on within the first unit light emission period, and the second unit light emission period. In the second state, only the red LED 11 is turned off to obtain cyan light, and in the third unit light emission period, only the blue LED 13 is turned off to obtain yellow light, and the light sensor PD in each state is used. Is obtained as digital data of emission intensity.

Further, the arithmetic circuit unit 74 of the microcomputer 70 is based on the emission intensity in the first state, the second state, and the third state, the emission intensity of the red LED 11, the emission intensity of the green LED 12, and the emission intensity of the blue LED 13. Is calculated. Meanwhile, the tristimulus values Xref, Yref, and Zref set by the user are stored in the reference information storage unit 72, and the desired light emission intensity of the red LED 11 and the desired light emission of the green LED 12 are calculated by the arithmetic circuit 74 from the values. The intensity and the desired light emission intensity of the blue LED 13 are calculated from Equation 1 described later.

The arithmetic circuit 74 of the microcomputer 70 compares the desired light emission intensity with the measured light emission intensity for each color, and controls the on-time of the PWM dimming pulse S1 so that both are equal. Details of the control processing by the microcomputer 70 will be described in the processing of the emission intensity measurement / dimming control program described later.

"Reason for inverting the light quantity detected by the optical sensor PD by the current / voltage converter (signal inverting amplifier) 30"
The applicant obtains the light emission intensity of the united light emission period of the mixed LED and has provided the sample and hold circuit 50 between the optical sensor PD and the A / D converter 71 (FIG. 13A). When the emission intensity of white light with different duty of each of the PWM dimming pulses S1r, S1g, S1b of red, green, and blue is acquired, the PWM dimming pulses S1r, S1g, S1b of red, green, and blue are set up. It became clear that the voltage from the photosensor PD input to the integrator 51 of the sample and hold circuit 50 could not be obtained accurately because the drops were uneven (FIG. 13B). In particular, the acquisition accuracy deteriorates when the color temperature is set such that the duty of the PWM dimming pulse varies, such as 4000K or 10,000K. The reason is that the voltage in the one-color lighting period d3 is lower than the voltage charged in the capacitor C immediately before (three-color lighting period d1 + two-color lighting period d2), and therefore the capacitor C is not charged.

Therefore, a current / voltage converter (signal inverting amplifier) 30 is provided between the optical sensor PD and the sample and hold circuit 50. With this arrangement, the current / voltage converter (signal inverting amplifier) 30 inverts the amount of light detected by the optical sensor PD based on the PWM dimming pulses S1r, S1g, and S1b whose rises are aligned with each other. By doing so, the input voltage applied to the sample-and-hold circuit 50 works so that the one where the light emission intensity is strong becomes smaller. That is, as shown in FIG. 9A, the capacitor C of the integrator 51 is charged in the order of voltage from low to high regardless of the duty variation in each PWM dimming pulse S1r, S1g, S1b. Charging is performed reliably during the one-color lighting period d3, and the capacitor C can reliably capture the emission intensity of the mixed light source per unit emission period. Therefore, accurate color balance control can be realized even if a low-performance optical sensor is used. Therefore, even if one light sensor is used to perform inexpensive control and the duty of each of the red, green, and blue PWM dimming pulses S1r, S1g, and S1b is different in the unit light emission period of each LED, each color is accurately obtained. It is possible to provide a liquid crystal display device and a light emitting device that can detect and control the emission intensity of the light.

1-3. Processing of emission intensity measurement / dimming control program
FIG. 5 shows a flowchart of the emission intensity measurement / dimming control program stored in the microcomputer 70.

The counter 75 of the microcomputer 70 counts the rising edge of the green PWM dimming pulse S1g (see FIG. 6) of the PWM generation circuit 20. The counter 75 can count seven pulses, and is reset to 0 when the eighth pulse is input (FIG. 6A). The reason why the green PWM dimming pulse S1g is used is that the green PWM dimming pulse S1g is turned on every cycle as described later. The reason why the rising edge is used as a reference is that the rising edge does not vary even if the light control time is adjusted as shown in FIG. 6C.

When the count value COUNT of the green PWM dimming pulse S1g reaches a predetermined value, the microcomputer 70 turns off the red LED 11 and emits cyan light according to the value, and turns on all the LEDs. Measurement is performed by emitting white light and performing measurement by turning off the blue LED 13 and emitting yellow light.

First, the microcomputer 70 resets the count value of the counter 75 (step ST1).

When the count value of the counter 75 becomes 1 (β1 in FIG. 6C, YES in step ST2), the microcomputer 70 gives the duty information Rduty = 0 corresponding to the red LED 11 to the pulse width setting register 23 of the PWM generation circuit 20. The red PWM dimming pulse S1r is controlled to be thinned out by one pulse (step ST3). Thereby, as shown by α in FIG. 6C, the red PWM dimming pulse S1r is thinned out by one pulse, and cyan light is emitted during this unit light emission period.

Next, the microcomputer 70 takes in the output of the optical sensor PD obtained from cyan light and performs A / D conversion (step ST4). This capture is performed as follows. First, when the count value of the green PWM dimming pulse S1g becomes 1, the microcomputer 70 controls the first electronic switch SW1 to be turned on, and accumulates the output from the preamplifier 40 in the capacitor C.

Next, the microcomputer 70 controls the first electronic switch SW1 to be turned off simultaneously with the rise β2 of the next green PWM dimming pulse S1g. As a result, a charge corresponding to the emission intensity of cyan light (mixed color of green and blue) (emission intensity considering the dimming time) is held in the capacitor C. At the same time, the microcomputer 70 takes in the electric charge accumulated in the capacitor C, takes in the electric charge accumulated in the capacitor C, converts it by the A / D converter 71, and takes it in as digital data of the emission intensity. When the data is captured, the microcomputer 70 turns on the second electronic switch SW2 to discharge the capacitor C. When a sufficient time has elapsed for discharge, the microcomputer 70 turns off the second electronic switch SW2.

Next, in step ST5, it is determined whether or not the count value of the counter 75 has become 7. Here, since 1 has been counted, the microcomputer 70 determines that the measurement of white light and yellow light has not yet been performed, and skips Steps ST5 and ST2 with NO, and proceeds to the process of Step ST6.

In step ST6, when the count value of the counter 75 becomes 3 (β3 in FIG. 6C), the microcomputer 70 exits with YES and does not perform any special processing. That is, white light is emitted without thinning out any adjustment pulse.

Simultaneously with the fourth rising edge of the next green PWM dimming pulse S1g (β4 in FIG. 6C), the first electronic switch SW1 is controlled to be turned off. Thereby, the electric charge according to the light emission intensity of white light (the light emission intensity considering the dimming time) is held in the capacitor C. At the same time, the microcomputer 70 takes in the electric charge accumulated in the capacitor C, takes in the electric charge accumulated in the capacitor C, converts it by the A / D converter 71, and takes it in as digital data of the emission intensity. When the data is captured, the microcomputer 70 turns on the second electronic switch SW2 to discharge the capacitor C. When a sufficient time has elapsed for discharging, the microcomputer 70 turns off the second electronic switch SW2 again (step ST4).

On the other hand, if NO in step 6 and the count value of the counter 75 reaches 5 (β5 in FIG. 6C), the microcomputer 70 generates a dimming pulse so as to thin out the blue dimming pulse by one pulse. Duty information Bduty = 0 corresponding to the blue LED 13 is given to the pulse width setting register 23 of the unit 20 for control (steps ST7 and ST8, γ in FIG. 6C). Thereby, yellow light is emitted.

Simultaneously with the rise of the next green PWM dimming pulse S1g (β6 in FIG. 6C), the first electronic switch SW1 is controlled to be turned off. As a result, a charge corresponding to the emission intensity of yellow light (mixed color of green and red) (emission intensity considering the dimming time) is held in the capacitor C. At the same time, the microcomputer 70 takes in the electric charge accumulated in the capacitor C, takes in the electric charge accumulated in the capacitor C, converts it by the A / D converter 71, and takes it in as digital data of the emission intensity. When the data is captured, the microcomputer 70 turns on the second electronic switch SW2 to discharge the capacitor C. When a sufficient time has elapsed for discharging, the microcomputer 70 turns off the second electronic switch SW2 again (step ST4).

When the microcomputer 70 captures the emission intensity of cyan light, white light, and yellow light output from the optical sensor PD (YES in step ST5), the captured cyan emission intensity C, white emission intensity W, yellow emission intensity. Based on Y, the light emission intensity of the blue LED 11, the green LED 12, and the red LED 11 is calculated based on the following equation (step ST9).

R = WC
B = W−Y
G = W-R-B
Here, B is the emission intensity of the blue LED 13, G is the emission intensity of the green LED 12, and R is the emission intensity of the red LED 11.

Next, the microcomputer 70 reads out the desired tristimulus values Xref, Yref, and Zref set by the user from the reference information storage unit 72 (step ST10). Next, the microcomputer 70 adjusts the factory adjustment value of the tristimulus value determined based on the values measured at the time of manufacture for the red LED 11, the green LED 12, and the blue LED 13, and desired tristimulus values Xref, Yref, Zref by user settings. Based on the above, the target light emission intensity (ratio from the maximum light emission intensity, the ratio of the light emission intensity to be detected by the optical sensor PD to the maximum light emission intensity) of each color LED 11, 12, 13 is calculated (step ST11). 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 described later.

The microcomputer 70 calculates the duty information Rduty, Gduty, Gduty so that the ratios of R, G, B obtained by measurement to the maximum emission intensities Rmax, Gmax, Bmax are equal to the calculated target Rref, Gref, Bref, respectively. Bduty is output and control is performed to change the ratio of the ON time of the PWM dimming pulse (step ST12). The PWM generation circuit 20 controls the on-time of the dimming pulse of each color based on the given red, green, and blue duty information Rduty, Gduty, and Bduty. Then, the count value of the counter 75 is reset to 0 (step ST13).

The color balance is adjusted as described above. Note that color balance adjustment may be performed using an average value of a plurality of measurements. In that case, a sudden change does not occur.

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

The sensitivity of each color of the photosensor PD 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, in this embodiment, the ratio of sensitivity to red, blue, and green of the photosensor PD used is R: G: B = 3: 10: 1.

Therefore, as in Patent Document 3, when all of R, G, and B are tried in order, 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. 7A, an experimental result is obtained that flicker felt by human eyes is larger when only the green LED 12 is turned off than when only the red LED or only the blue LED is turned off. It was. In FIG. 7A, what is plotted at the point of “■” is an evaluation of how much flicker is felt by changing the dimming frequency when only the green LED 12 is turned off. Plotted with “x” points is an evaluation of how much flicker is felt by changing the dimming frequency when only the red LED 11 is turned off. Plotted at the point of “▲” is an evaluation of the degree of flicker that the subject feels by changing the dimming frequency when only the blue LED 13 is extinguished in five stages. 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 PWM dimming pulse S1 is 1 kHz, and even in this region, it is shown that flicker is felt when only the green LED 12 or the red LED 11 is turned off. From such experimental results, it can be concluded that it is preferable to turn off only the green LED 12.

[Relationship between extinction frequency and flicker]
Although FIG. 7A shows the result when the turn-off timing is sufficiently delayed, the relationship between the turn-off frequency and flicker was confirmed. As shown in FIG. 7B, when the light is turned off at a turn-off frequency of 150 Hz or more, human eyes It was verified that he did not notice. In the case of the present embodiment, the unit light emission period integrated by the integrator 51 corresponds to one period of the dimming frequency, and two periods are required for color measurement. Therefore, it is desirable to perform light control at a light control frequency that is twice or more the number of colors to be measured. For example, when measuring three colors, a dimming frequency of 900 Hz or more is required.

1-4. 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 photosensor PD incorporated in the display device.

First, only the red LED 11 is turned on, and measurement is performed from the front of the LCD 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 11 can be obtained. Similarly, the X component Gx, the Y component Gy, and the Z component Gz of the green light stimulus value from the green LED 12 and the X component Bx, the Y component By, and the Z component Bz of the blue light stimulus value from the blue LED 13 are obtained. .

Rx, Ry, Rz, Gx, Gy, Gz, Bx, By, Bz obtained in this way, and the X component Wx of the stimulation value of white light when all the red LED 11, green LED 12, and blue LED 13 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 11, the green LED 12, and the blue LED 13 are caused to emit light. RGB is the ratio of the emission intensity of each LED 11, 12, 13 to the maximum emission intensity. Therefore, when each LED is turned on at the maximum light emission intensity (when the ON period of the dimming pulse is maximum), r = 1, g = 1, and b = 1.

When the red LED 11, the green LED 12, and the blue LED 13 are turned on at the assumed maximum brightness and the stimulation values Wx, Wy, and Wz of white light are measured, the calculation is performed as r = 1, g = 1, and b = 1 in the above formula. The stimulus values Wx, Wy, and Wz calculated by

Next, the emission intensity R, G, B of the red LED 11, the green LED 12, and the blue LED 13 is detected using the optical sensor PD that is actually incorporated into the display device 1. This is performed by measuring the emission intensity of cyan light, white light, and yellow light as described in the above embodiment, and calculating the emission intensity of each color based on this (see step ST9).

Here, the Y component of the above equation 2, that is, Ry, Gy, By, is in a relationship that is substantially equal to the emission intensity R, G, B. Therefore, if the sensitivity of the photosensor PD with respect to each color 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 PD is inferior, the above equation 2 is modified as follows based on R, G, and B.

Here, R′y, G′y, and B′y are replaced with the measured R, G, and B values. R′y and R′z are calculated by the following equations. That is, R′x and R′z are corrected in accordance with 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 11, the green LED 12, and the blue LED 13 are caused to emit light at a predetermined maximum emission intensity, and the emission intensity W of white light is detected by the optical sensor PD. The light emission 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 Expression 3 is an approximate expression, the two do not match. Therefore, the measured value W is set to W ″ y, W′x and W′z are corrected based on the ratio of W ″ y and W′y, and W ″ x, Get W ″ z. Also, the same correction is performed on the right side based on the ratio of W ″ y and W′y. Therefore, the following expression is obtained.

If this equation is modified, the following equation is obtained. This formula shows that when light parameters Wx, Wy, and Wz of desired colors are given, the emission intensity detected by the optical sensor PD when the color is to be developed by the red LED 11, the green LED 12, and the blue LED 13 is determined. The ratio of the maximum emission 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 "y, B" z in Equation 6 are tristimulus. The value is recorded in the memory of the microcomputer 70 as a factory adjustment value. Note that r, g, and b in Equation 6 correspond to Rref, Gref, and Bref in Equation 1, and W ″ x, W ″ y, and W ″ z correspond to Xref, Yref, and Zref.

In addition, R ″ x, R ″ y, R ″ z, G ″ x, G ″ y, G ″ z, B ″ x, B ″ y, B ″ y, and B ″ z in Expression (6) are the above-described Rx. , Ry, Rz, Gx, Gy, Gz, Bx, By, Bz may be recorded.

Although the first embodiment in which the present invention is applied to a liquid crystal display device has been described in detail with reference to the drawings, it goes without saying that the present invention can be applied to a light emitting device excluding the liquid crystal unit panel unit 2.

In addition to the R, G, and B light sources, the present invention is also applicable to combinations of reddish white, greenish white, and bluish white light sources that are close to white, with a focus on efficiency, and blue and yellow light source combinations. Is possible.

In the above embodiment, the counter 75 of the microcomputer 70 counts the green PWM dimming pulse S1g, and controls to thin out the PWM dimming pulse S1 during measurement. However, the counter 75 may be provided in the PWM generation circuit 20, and the PWM dimming pulse S1 may be controlled to be thinned out by the logic circuit on the PWM generation circuit 20 side based on the count value.

[Second Embodiment]
In the first embodiment, the amount of light detected by the photosensor PD based on the PWM dimming pulses S1r, S1g, and S1b whose rises are aligned with each other is supplied to the sample and hold circuit 50 by the signal inverting amplifier 30. It was made to apply so that the one where emitted light intensity was strong might become small. On the other hand, in the second embodiment, the light quantity detected by the photosensor PD is output to the sample and hold circuit 50 based on the PWM dimming pulses S1r ′, S1g ′, and S1b ′ aligned with the falling edges. However, it is characterized in that it is applied so that the one having a higher emission intensity becomes larger. Accordingly, as in the first embodiment, the capacitor C is applied in the order of low to high (FIG. 9B), and the capacitor C can reliably capture the emission intensity of the mixed light source per unit emission period. Therefore, accurate color balance control can be realized even if a low-performance optical sensor is used.

The second embodiment of the present invention will be described below with reference to the drawings. In the first embodiment, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

2-1. Functional Block Diagram FIG. 10 shows functional blocks of the liquid crystal display device 100 according to the first embodiment of the present invention.

The liquid crystal display device 100 includes a liquid crystal panel unit 2, a light emitting unit 10, an optical sensor PD, a light source selection detection unit A ′, and a light emission control unit B. The liquid crystal panel unit 2 inputs a video signal and displays an image. The light emitting unit 10 includes a red light source 11, a green light source 12, and a blue light source 13, and each light source is mixed into white light and functions as a backlight of the liquid crystal panel unit 2.

The light source selection detecting means A ′ turns on all of the red light source 11, the green light source 12, and the blue light source 13 in the first unit light emission period based on each PWM dimming pulse whose falling is aligned. The first state, the second state in which only one type of light source is turned off in the second unit light emission period, and one type different from that turned off in the second state in the third unit light emission period. Lighting control is performed so as to be in a third state in which only the light source is turned off. Furthermore, the light source selection detection means A ′ has an integrator 51, and acquires the emission intensity by integrating the output from the photosensor PD with the integrator 51 in each of the first, second, and third states. .

The light emission control unit B calculates the light emission intensities of the blue light source 11, the green light source 12, and the blue light source 13 based on the light emission intensities detected in the first, second, and third states. That is, the light emission intensity of the light source turned off in the second state is calculated by subtracting the light emission intensity in the second state from the light emission intensity in the first state. Further, the light emission intensity of the light source turned off in the third state is calculated by subtracting the light emission intensity in the third state from the light emission intensity in the first state. Further, the light emission intensities of the remaining light sources are calculated by subtracting the light emission intensities of the two types of light sources calculated above from the light emission intensities in the first state.

  The light emission control means B uses the red light source 11, the green light source 12, and the blue light source so that the light emission intensities of the red light source 11, the green light source 12, and the blue light source 13 calculated in this way become the respective desired light emission intensities. The emission intensity of the light source 13 is feedback controlled. Therefore, control can be performed so as to keep the emission color of the backlight light source white.

2-2. Circuit Configuration Example FIG. 11 shows a specific circuit configuration example of the liquid crystal display device of FIG. In FIG. 11, the same reference numerals are given to the components corresponding to the components in FIG. 10. In FIG. 11, reference numeral 100 denotes a liquid crystal display device. The liquid crystal display device 1 includes a liquid crystal panel unit 2, a light emitting unit 10 that irradiates the liquid crystal panel unit 2 from the back, an LED drive circuit 3 that drives the light emitting unit 10, and a dimming pulse S1 to the LED drive circuit 3. PWM generating circuit 200 for supplying ', an optical sensor PD for detecting the light emission intensity of the light emitting unit 10, a current / voltage converter 300 for converting the current flowing through the optical sensor PD into a voltage, and the converted voltage A pre-amplifier 40 to be amplified, a sample-and-hold circuit 50 that samples and holds the signal amplified by the pre-stage amplifier 40, a post-stage amplifier 60 that amplifies the signal acquired by the sample-and-hold circuit 50, and control of the entire apparatus 100 And a microcomputer 700 that supervises the above.

Similar to the PWM generation circuit 20, the PWM generation circuit 200 of FIG. Specifically, as shown in FIG. 12, serial interface units 21 and 22, a pulse width setting register 23, a count clock (reference clock) CLK, a dimming cycle information setting unit 23, a counter 24, and a red dimming count A comparator 250, a green light adjustment count comparator 260, a blue light adjustment count comparator 270, and the like are provided.

The pulse width setting register 23 stores duty information Rduty ', Gduty', and Bduty '(14 bits each) output from the microcomputer 70. The duty information Rduty ', Gduty', Bduty 'is used for setting the pulse width when the red LED 11, the green LED 12, and the blue LED 13 are PWM-controlled.

The dimming cycle information setting unit 23 generates the count clock CLK based on the divided pulse and sets it in the PWM pulse cycle setting register of the counter 24 as count-up cycle information.

For example, the counter 24 has a count clock CLK set to 20 MHz and a count-up cycle set to 1 kHz. The count-up cycle is set to a value corresponding to the PWM dimming cycle H that is the unit light emission period of the LED. Accordingly, the counter 24 automatically resets the count value when the count clock CLK for the PWM dimming period H is counted.

The red light control count comparator 250 compares the count value of the counter 24 with the duty information Rduty 'stored in the pulse width setting register 22 as a threshold value, and the LED drive circuit 3 does not exceed the threshold value. Outputs “Low level” and outputs “High level” when the threshold value is exceeded. Similarly, the green light control count comparator 260 compares the count value of the counter 24 with the duty information Gduty ′ stored in the pulse width setting register 22 as a threshold value, and the count value of the LED drive circuit 3 is set to the threshold value. When not exceeding, “Low level” is output, and when exceeding the threshold value, “High level” is output, and the blue light control count comparator 270 uses the duty information Bduty ′ stored in the pulse width setting register 22 as a threshold value. Compared with the count value of the counter 24, if the count value does not exceed the threshold value, the LED drive circuit 3 outputs "Low level", and if it exceeds the threshold value, it outputs "High level".

In this way, the signals output from the red light control count comparator 250, the green light control count comparator 260, and the blue light control count comparator 270 are the red PWM light control pulse S1r ′ and the green PWM light control pulse S1g ′, respectively. The blue PWM dimming pulse S2b ′ is supplied to the LED drive circuit 3. Since each PWM dimming pulse S1r ′, S1g ′, S1b ′ is generated based on the count value of the counter 24, the falling (High) of each waveform of the PWM dimming pulses S1r ′, S1g ′, S1b ′. Level → Low level) are aligned (see FIGS. 11 and 12).

The LED drive circuit 3 receives the PWM dimming pulses S1r ', S1g', and S1b 'from the PWM generation circuit 200, and turns on the red LED 11 only when the PWM dimming pulse S1r' for red is at a high level. Similarly, the green LED 12 is lit only during a period in which the PWM dimming pulse S1g 'for green is at a high level. Similarly, the blue LED 13 is lit only during a period when the PWM dimming pulse S1b 'for blue is at a high level.

The current / voltage converter 300 includes an operational amplifier 31 and a feedback resistor R1, and the non-inverting amplification terminal (+) of the operational amplifier 31 is connected to the anode of the photosensor PD with the other end of the cathode grounded. The other end of the terminal (−) is grounded together with the feedback resistor R1 connected to the output terminal. With such a configuration, the current detected by the optical sensor PD can be converted into a voltage and output (signal S3 in FIG. 11).

The pre-amplifier 40 includes an operational amplifier 41, a resistor R2, and a feedback resistor R3. The non-inverting amplification terminal (+) of the operational amplifier 41 is connected to the output terminal of the current / voltage converter 300 and the inverting input terminal (−). Are connected to a resistor R2 having the other end grounded and a feedback resistor R3 having the other end connected to the output terminal. With this configuration, the voltage output from the current / voltage converter 300 is amplified and output.

The sample-and-hold circuit 50 and the post-stage amplifier 60 are the same as those in the first embodiment, and a description thereof will be omitted.

The microcomputer 700 includes an A / D converter 71, a reference information storage unit 720, an output information storage unit 730, an arithmetic processing unit 740, a counter 75, and the like. The reference information storage unit (including the reference information setting unit) 720 stores tristimulus values set by the user. The desired emission intensity of the red LED 11, the desired emission intensity of the green LED 12, and the blue LED 13 The desired emission intensity is calculated from Equation 1. The output information storage unit 730 stores duty information Rduty 'corresponding to the red LED 11, duty information Gduty' corresponding to the green LED, duty information Bduty 'corresponding to the blue LED, and the like.

Here, in order to align the falling edges (High level → Low level) of the red PWM dimming pulse S1r ′, green PWM dimming pulse S1g ′, and blue PWM dimming pulse S2b ′ supplied to the LED drive circuit 3. In addition, duty information Rduty ′, Gduty ′, and Bduty ′ that determine the level must be considered. In the first embodiment, the duty information Rduty, Gduty, and Bduty are output from the micro computer 70 and the rise of each PWM dimming pulse is aligned. In the second embodiment, the duty information R duty is output from the micro computer 700. By outputting “= 1−Rduty, Gduty” = 1−Gduty, Bduty ′ = 1−Bduty to the PWM generation circuit 200, the falling edges of the PWM dimming pulses S1r ′, S1g ′, and S1b ′ may be aligned. it can. The other processes of the emission intensity measurement / dimming control program stored in the microcomputer 700 are the same as those in the first embodiment, and will be omitted.

Accordingly, as in the first embodiment, the capacitor C is applied in the order of low to high (FIG. 9B), and the capacitor C can reliably capture the emission intensity of the mixed light source per unit emission period. Therefore, accurate color balance control can be realized even if a low-performance optical sensor is used.

[5. Other Embodiments]
(1) In the above embodiment, the case where desired white light is obtained has been described, but the present invention can also be applied to a case where a desired color is desired.

(2) The present invention can be applied not only to the backlight of the liquid crystal display device 1 but also to the realization of a desired color in a projector light source and an LED display, the realization of a desired color in illumination, and the like.

(3) 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 performing two-color mixing such as a combination of magenta and cyan, yellow and green, or cyan and red, or mixing of 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 10 according to a first embodiment of the present invention. FIG. 2A shows a circuit example of the liquid crystal display device 10 according to the first embodiment of the present invention, and FIG. 2B is a diagram showing waveform timing of the circuit. It is a figure which shows the detail of a backlight light source. It is a detailed circuit example of the PWM generation circuit 20 by 1st embodiment of this invention. 3 is a flowchart of a control program stored in a microcomputer 70. It is a figure which shows the relationship between a PWM light control pulse, the mixed color light to measure, and the count value of the counter. FIG. 7A is a diagram illustrating a relationship between a dimming frequency and flicker. FIG. 7A illustrates a result when the extinction timing is sufficiently delayed, and FIG. 7B is a diagram illustrating a relationship between the extinction frequency and flicker. It is a figure which shows the relationship between the electrical storage period and output voltage in a common integrator. It is a figure which shows the output waveform (the input waveform of the input voltage input into the sample hold circuit 50, and the waveform of the integrated input voltage) of this invention, FIG. A shows what is based on 1st Embodiment, B shows that according to the second embodiment. It is a functional block diagram of the liquid crystal display device 100 by 2nd embodiment of this invention. FIG. 11A shows a circuit example of the liquid crystal display device 10 according to the second embodiment of the present invention, and FIG. 11B is a diagram showing the timing of the waveform of the circuit. It is a detailed circuit example of the PWM generation circuit 200 by 2nd embodiment of this invention. FIG. 13A shows a general sample and hold circuit, and FIG. 13B is a waveform diagram showing the relationship between the input voltage input to the sample and hold circuit and the integrated input voltage.

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device 2 ... Liquid crystal panel part 10 ... Light emission part 11 ... Red light source
DESCRIPTION OF SYMBOLS 12 ... Green light source 13 ... Blue light source 30 ... Signal inversion amplifier 51 ... Integrator PD ... Optical sensor A, A '... Light source selection detection means B ... Light emission control means

Claims (4)

A liquid crystal panel,
A light source having a red light source, a green light source, and a blue light source, mixing each light source into white light, 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 in a first unit light emission period with respect to the light emitting unit based on each PWM dimming pulse whose rise is aligned with each other, a second unit The second state in which only one type of light source is turned off during the light emission period, and the third state in which only one type of light source that is different from that turned off during the second state in the third unit light emission period is turned off. And a light source selection detecting means for integrating the light emission intensity of the unit light emission period of the light emitting unit in each state in this integrator, including an integrator connected to the subsequent stage of the light sensor,
A liquid crystal display device comprising: a light emission control means for controlling the light emitting unit so that each light source has a desired light emission intensity based on the light emission intensity of the unit light emission period integrated by the integrator in each state;
The light source selection detecting means has a signal inverting amplifier connected between the optical sensor and the integrator, and the signal inverting amplifier inverts and amplifies the output signal of the optical sensor and outputs the signal to the integrator. A characteristic liquid crystal display device. A light emitting unit that has light sources of at least two colors and emits light of a predetermined color by mixing the light sources;
An optical sensor for detecting the light emission intensity of the light emitting unit;
Based on the PWM dimming pulses whose rises are aligned with each other, in the first state in which the light sources of all colors are turned on in the first unit light emission period for the light emitting unit, one type in the second unit light emission period The lighting control is performed so that only the light source is extinguished, and an integrator connected to the subsequent stage of the photosensor is included, and with this integrator, the emission intensity of the unit emission period of the light emitting unit in each state Light source selection detection means for integrating
A light-emitting device comprising: a light-emission control unit that controls the light-emitting unit so that each light source has a desired light-emission intensity based on the light-emission intensity of the unit light-emission period integrated by the integrator in each state;
The light source selection detecting means has a signal inverting amplifier connected between the optical sensor and the integrator, and the signal inverting amplifier inverts and amplifies the output signal of the optical sensor and outputs the signal to the integrator. A light emitting device characterized. LCD panel part,
A light source having a red light source, a green light source, and a blue light source, mixing each light source into white light, 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 in a first unit light emission period with respect to the light emitting unit based on the PWM dimming pulses that are aligned with each other in falling, a second state The second state in which only one type of light source is turned off in the unit light emission period, and the third state in which only one type of light source that is different from the one turned off in the second state in the third unit light emission period is turned off. Light source selection detecting means for controlling lighting so as to be in a state, and having an integrator connected to the subsequent stage of the optical sensor, and integrating the light emission intensity of the light emitting unit in the respective light emitting units in each state by the integrator. ,
And a light emission control means for controlling the light emitting unit so that each light source has a desired light emission intensity based on the light emission intensity of the unit light emission period integrated by the integrator in each state. apparatus. A light emitting unit that has light sources of at least two colors and emits light of a predetermined color by mixing the light sources;
An optical sensor for detecting the light emission intensity of the light emitting unit;
Based on each PWM dimming pulse whose falling is aligned, a first state in which light sources of all colors are turned on in the first unit light emission period for the light emitting unit, one kind in the second unit light emission period The lighting control is performed so that only the light source is extinguished, and an integrator is connected to the subsequent stage of the photosensor, and the integrator emits light in the unit light emission period in each state. Light source selection detection means for integrating the intensity;
And a light emission control means for controlling the light emitting unit so that each light source has a desired light emission intensity based on the light emission intensity of the unit light emission period integrated by the integrator in each state. .