JP2013140098A - Illuminance sensor and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illuminance sensor capable of accurately detecting ambient brightness and stably outputting a detection result of illuminance.SOLUTION: In an illuminance sensor 10, first and second digital signals ADC1 and ADC2 resulting from AD conversion of first and second light receiving signals Iin1 and Iin2 output by first and second light receiving parts 1 and 2 are input to a signal processing circuit 6. When it is determined that a ratio (ADC2/ADC1) between the first and second digital signals ADC1 and ADC2 is not beyond a precedently determined range, the signal processing circuit 6 outputs the first and second digital signals ADC1 and ADC2 to an output data storage circuit 7. On the other hand, when it is determined that the ratio (ADC2/ADC1) is beyond the precedently determined range, the signal processing circuit 6 does not output the first and second digital signals ADC1 and ADC2 to the output data storage circuit 7. A light receiving signal to be stored in the output data storage circuit 7 to be output can be selected in accordance with the setting of the range.

Description

  The present invention relates to an illuminance sensor that detects the brightness of light, and a display device including the illuminance sensor.

  When mobile devices such as mobile phones and electronic books are equipped with an illuminance sensor that detects the ambient brightness on the LCD panel in order to control the brightness of the backlight (the amount of light emitted) according to the ambient brightness. There is. In this case, power consumption can be suppressed, and visibility can be improved.

  A typical example of an illuminance sensor is a sensor using a silicon photodiode. Silicon photodiodes are widely used because of their small size and high response speed.

  However, the spectral sensitivity characteristics of silicon photodiodes are very different from human visual sensitivity, and the sensitivity in the infrared region is increased. Here, the relationship between the amount of received light and the photocurrent (photoelectric sensitivity) varies depending on the wavelength of incident light, and the relationship between this wavelength and photoelectric sensitivity is referred to as “spectral sensitivity characteristics”.

  For this reason, there is an increasing demand for a sensor having a spectral sensitivity characteristic close to human visibility while using a silicon photodiode as an illuminance sensor. As a method for realizing spectral sensitivity characteristics close to human visual sensitivity, a method for subtracting currents flowing through photodiodes having different spectral sensitivity characteristics is known. An illuminance sensor using such a method is disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2007-73591).

  FIG. 10 is a circuit diagram showing a configuration of a main part of the illuminance sensor proposed in Patent Document 1. As shown in FIG. As shown in FIG. 10, the illuminance sensor of Patent Document 1 uses a current mirror circuit.

  The illuminance sensor includes a photodiode PD1 and a photodiode PD2. A current Iin1 flows through the photodiode PD1 according to the ambient brightness, and a current Iin2 flows through the photodiode PD2 according to the ambient brightness. Flowing. The transistors QP1 and QP2 form a current mirror circuit, and the collector current of the transistor QP2 is a current (Iin1 × α) corresponding to the current Iin1 flowing through the photodiode PD1. α is an arbitrary coefficient.

  The photodiode PD1 and the photodiode PD2 have different spectral sensitivity characteristics with respect to the wavelength of light, and subtract a current (Iin1 × α) corresponding to the amount of current Iin1 flowing through the photodiode PD1 from the current Iin2 flowing through the photodiode PD2. As a result, it is possible to realize spectral sensitivity characteristics close to visual sensitivity with the illuminance sensor.

  On the other hand, a method of converting a sensor output into a digital value using an analog-digital conversion circuit is known. For example, by converting the output current into a digital value, processing by software is facilitated by a CPU or a microcomputer. In particular, the integration type analog-to-digital conversion circuit has a feature that can realize high-precision resolution with a simple configuration. This is suitable for a device such as an illuminance sensor that requires a high resolution (about 16 bits) while being low speed.

  FIG. 11 is a circuit diagram illustrating a configuration of a main part of an illuminance sensor including an analog-digital conversion circuit. The illuminance sensor includes a photodiode PD1 and a photodiode PD2. A current Iin1 flows through the photodiode PD1 according to the ambient brightness, and the photodiode PD2 according to the ambient brightness. Current Iin2 flows.

  The result of analog-digital conversion of the current Iin1 by the analog-digital conversion circuit ADC1 becomes a digital value ADCout1, and the result of analog-digital conversion of the current Iin2 by the analog-digital conversion circuit ADC2 becomes a digital value ADCout2. Then, the multiplier MLP multiplies the digital value ADCout1 by α (α is an arbitrary coefficient), and the subtractor SBT subtracts a value (ADCout1 × α) corresponding to the digital value ADCout1 from the digital value ADCout2 (ADCout2-ADCout1 × α) is output. According to this illuminance sensor, it is possible to realize spectral sensitivity characteristics close to visual sensitivity.

  On the other hand, Patent Literature 2 (Japanese Patent Application Laid-Open No. 2010-27418) discloses an illumination control system. This lighting control system includes a lighting control device that controls lighting of the lighting fixture so that the illuminance value detected by the illuminance sensor becomes the target value. In the illumination control system, the illuminance value detected by the illuminance sensor is less than the target value, and the illuminance value detected by the illuminance sensor in the next detection cycle after the lighting control device performs dimming control falls within a predetermined range. When there is no change exceeding, a correction control unit for returning to the dimming control state of the previous cycle is provided. According to this lighting control system, when an object is placed on the light receiving portion of the illuminance sensor and the illuminance value cannot be detected correctly by the illuminance sensor, the lighting control device prevents the output of the lighting fixture from being increased unnecessarily. it can.

JP 2007-73591 A JP 2010-27418 A

  FIG. 12 illustrates a schematic configuration of a display device 501 that is a portable device on which the illuminance sensor 502 is mounted. The illuminance sensor 502 is mounted on the board 503 of the display device 501, and the upper part of the illuminance sensor 502 is covered with the display panel 505 of the display device 501. The display panel 505 includes a transparent panel portion 505a that transmits light to the light receiving portion 502a of the illuminance sensor 502 and a panel portion 505b that does not transmit light.

  In this display device 501, when light 508 is incident on the display panel 505 obliquely from a light source 507 regarded as a point light source, the light transmitted through the transparent panel portion 505a is incident obliquely on the illuminance sensor 502. It is conceivable that part of the incident light is blocked by the panel portion 505 b that does not transmit light and does not reach the light receiving portion 502 a of the illuminance sensor 502. Therefore, when the display device 501 that is a portable device is tilted with respect to the light source, the illuminance detected by the illuminance sensor 502 changes significantly.

  In practical use, since the portable device is always used with a hand, the display panel 505 can be frequently tilted with respect to the light source by the movement of the user's hand. Here, since sunlight is sufficiently parallel light and a sufficient amount of light enters the light receiving unit 502a, the change in illuminance detected by the illuminance sensor 502 is not so great.

  However, artificial light sources such as fluorescent lamps, LED bulbs, and incandescent lamps are likely to be point light sources, and the change in illuminance due to light from the light sources becomes significant due to a slight inclination of the portable device.

  The display device 501 detects ambient brightness by the illuminance sensor 502, controls the amount of light emitted from the backlight based on the detection result, and displays an easy-to-see screen corresponding to the illuminance around the display device 501 to the user. can do.

  However, as described above, when the light emission amount of the backlight is always controlled with respect to the illuminance changed with a slight inclination, the light emission amount of the backlight is frequently adjusted. This causes a problem that the illuminance of the display panel 505 frequently changes, which makes it troublesome for a person using the display device (portable device) 501.

  On the other hand, the illuminance sensor disclosed in Patent Document 1 described above achieves spectral sensitivity characteristics close to visual sensitivity, but the illuminance changes when the illuminance changes instantaneously (transiently) due to inclination to the point light source or the like. Since the output signal representing the value also changes, the above-described problem cannot be solved.

  Also in Patent Document 2 described above, since the illuminance sensor outputs the illuminance value detected at a predetermined detection cycle, the illuminance value changes even when the illuminance value output by the illuminance sensor changes temporarily. The lighting control that follows and controls the output of the luminaire will frequently work.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an illuminance sensor that can accurately detect ambient brightness and can stabilize the output of illuminance detection results.

In order to solve the above problems, an illuminance sensor according to the present invention includes a first light receiving unit that outputs a first light reception signal corresponding to received light,
A second light receiving unit that outputs a second light reception signal corresponding to the received light;
The first light receiving signal and the second light receiving signal are input, the first light receiving signal and the second light receiving signal are processed, and the phase of the second light receiving signal with respect to the first light receiving signal is processed. It is determined whether or not the difference exceeds a predetermined range, and when it is determined that the difference exceeds a predetermined range, the first and second received light signals are not output, A signal processing unit that outputs the first and second received light signals when it is determined that the difference does not exceed a predetermined range;
And an output storage unit for storing the first and second light reception signals output from the signal processing unit and for outputting the first and second light reception signals.

  According to the illuminance sensor of the present invention, the signal processing unit performs signal processing on the first and second light receiving signals output from the first and second light receiving units and performs the second processing on the first light receiving signal. When it is determined that the difference between the received light signals does not exceed a predetermined range, the first and second received light signals are output. On the other hand, the signal processing unit does not output the first and second received light signals when the difference between the second received light signal and the first received light signal exceeds the predetermined range. The first and second light reception signals output from the signal processing unit are stored in the output storage unit and output from the output storage unit.

  Therefore, when the difference between the first light receiving signal and the second light receiving signal is within the predetermined range, the light receiving signal stored in the output storage unit is updated and the output storage unit is updated. Can be output from. On the other hand, when the difference between the first received light signal and the second received light signal exceeds the predetermined range, the received light signal stored in the output storage unit is not updated, and The output storage unit outputs a conventional light reception signal.

  Therefore, according to the illuminance sensor of the present invention, it is possible to select the light reception signal to be stored and output in the output storage unit according to the setting of the range, so that the output of the illuminance detection result is stabilized. Can be planned.

  In the illuminance sensor of one embodiment, the spectral sensitivity characteristic of the first light receiving unit and the spectral sensitivity characteristic of the second light receiving unit are different from each other.

  According to this embodiment, the first and second light receiving signals of the first and second light receiving units having different spectral sensitivity characteristics are used to calculate the spectrum of ambient light incident on the first and second light receiving units. Change can be detected. In addition, the light receiving surfaces of the first and second light receiving units change with respect to the light from the point light source, so that the spectral sensitivity characteristics are different from each other and incident on the light receiving surfaces of the first and second light receiving units. When the amount of light to be changed changes, the ratio of the first and second light receiving signals output from the first and second light receiving units having different spectral sensitivity characteristics changes greatly. Therefore, it is possible to detect the type of light source and the inclination with respect to the point light source.

In the illuminance sensor of one embodiment, the first light receiving unit has sensitivity in a wavelength region from visible light to infrared light,
The second light receiving unit has a sensitivity peak in the wavelength region of infrared light.

  According to this embodiment, the first light-receiving unit having sensitivity in the wavelength region from the visible light to the infrared light and the second light-receiving unit having a sensitivity peak in the wavelength region of the infrared light have the visibility. This can be realized only with a silicon photodiode without using a suitable filter or the like, and the cost can be reduced.

In the illuminance sensor of one embodiment, the first and second light receiving signals are current signals,
The signal processor is
The ratio between the first received light signal and the second received light signal is calculated, and when the ratio is within a preset numerical range, the first and second received light signals are output, while the ratio The first and second light receiving signals are not output when is outside the numerical range.

  According to this embodiment, the current signal output from the first light receiving unit and the second signal due to changes in the inclination of the light receiving surfaces of the first and second light receiving units with respect to the light from the point light source. When the ratio with the current signal output by the light receiving unit fluctuates beyond a preset numerical range, the signal processing unit does not output the light receiving signals from the first and second light receiving units. Therefore, it is possible to stabilize the output of the illuminance detection result.

Further, in the illuminance sensor of one embodiment, one of the first light receiving unit and the second light receiving unit has a circular light receiving surface,
The other light receiving part of the first light receiving part and the second light receiving part has an annular light receiving surface surrounding the circular light receiving surface.

  According to this embodiment, when the incident angle of the light incident on the light receiving surface is changed, the inclination of the incident light is determined without depending on the direction around the normal line of the light receiving surface. It can be detected by the signal.

In the illuminance sensor of one embodiment, the first and second light receiving signals are current signals,
The signal processor is
A first analog-digital conversion circuit that outputs a digital signal obtained by analog-digital conversion of the first light-receiving signal;
A second analog-digital conversion circuit that outputs a digital signal obtained by analog-digital conversion of the second received light signal.

  According to this embodiment, the first and second light reception signals are converted into the first and second digital signals, thereby facilitating signal processing of the light reception signals. When the light reception signal is output as an illuminance measurement result to an external display device, since the display device generally includes a CPU or the like, the light reception signal as the illuminance measurement result is a digital signal. , Signal handling becomes easier.

  On the other hand, it is possible to record the light reception signal as an analog signal as it is, if a configuration such as accumulating electric charge in a capacitor is adopted, but the configuration becomes complicated and the circuit scale increases.

In the illuminance sensor of one embodiment, the first and second analog-digital conversion circuits are
An integration circuit that includes an integration capacitor that stores electric charge according to an input current signal and that outputs a voltage corresponding to the amount of electric charge stored by the integration capacitor;
A comparison circuit that compares the output voltage of the integration circuit with a preset reference voltage and outputs a comparison result between the output voltage and the reference voltage as a binary pulse signal;
Includes a flip-flop that captures the pulse signal in synchronization with the clock signal and outputs a bit stream signal, and a counter that counts the active pulses of the bit stream signal, and outputs the count result of this counter as an analog-digital converted output value An output circuit to
An integration type analog-to-digital conversion circuit having a discharge circuit for discharging the integration capacitor of the integration circuit during an active pulse period of the bit stream signal.

  According to this embodiment, the current signal output from the light receiving unit is integrated (that is, averaged) by the integration circuit, so that an output voltage obtained by multiplying the current signal output from the light receiving unit by a certain coefficient is obtained. It can be input to the comparison circuit. Therefore, the output value of the output circuit can be output as accurate and stable illuminance information.

Moreover, in the illuminance sensor of one embodiment, the integration time of one time of the first and second analog-digital conversion circuits is within 100 milliseconds.
The signal processor is
The digital signal obtained by analog-to-digital conversion of the first and second received light signals is subjected to signal processing at a preset time interval equal to or longer than the integration time, and the difference between the second received light signal and the first received light signal is different. Is determined to exceed the preset range, and when it is determined that the difference does not exceed the preset range after a preset number of times, the first and second While the received light signal is converted from analog to digital, a digital signal is output.
A digital signal obtained by analog-to-digital conversion of the first and second light receiving signals when the number of times that the difference does not exceed a preset range is less than the preset number of times. Is not output.

  According to this embodiment, the difference between the second received light signal and the first received light signal is preset by performing signal processing on the digital signal from the first and second analog-digital conversion circuits. Since the digital signal based on the first and second light receiving signals is output when the number of times (for example, three times) continues within the preset range, stable illuminance information can be output. Further, since the integration time of one time of the first and second analog-digital conversion circuits is within 100 msec, artificial lighting (fluorescent lamp, incandescent lamp, etc.) driven by a household AC power supply (50/60 Hz) ) Is highly stable against illuminance fluctuations.

The display device of the present invention includes a display panel for displaying a screen,
A backlight for illuminating the display panel;
A backlight control unit for controlling the backlight;
An illuminance sensor according to any one of claims 1 to 7,
The backlight control unit
The brightness of the backlight is controlled based on the light reception signal output from the output storage unit included in the illuminance sensor.

  According to the display device of the present invention, since the illuminance sensor according to the present invention is provided, the brightness of the screen can be accurately controlled by controlling the luminance of the backlight according to the illuminance of the ambient light. Further, the backlight control unit can stably control the luminance of the backlight, and it is not necessary to repeat the control of the luminance of the backlight more frequently than necessary in response to a change in ambient brightness. Accordingly, the illuminance of the display screen can be stabilized and the power consumption can be reduced.

  According to the illuminance sensor of the present invention, the first and second light receiving signals of the first and second light receiving units are signal-processed by the signal processing unit, and the difference between the second light receiving signal and the first light receiving signal is different. Depending on whether or not is exceeding a predetermined range, it is possible to automatically select the light reception signal to be stored and output in the output storage unit, so that the output of the detection result of illuminance can be stabilized. Can be planned.

  By mounting the illuminance sensor of the present invention on a portable device, ambient light can be accurately detected even in various environments, a stable illuminance detection result can be output, and the power consumption of the portable device can be suppressed.

It is a block diagram which shows embodiment of the illumination intensity sensor of this invention. It is a flowchart explaining the operation | movement outline | summary of the said embodiment. It is a figure which shows typically an example of the structure of the 1st light-receiving part of the said embodiment. It is a figure which shows typically an example of the structure of the 2nd light-receiving part of the said embodiment. It is a graph which shows the spectral sensitivity characteristic of the said 1st, 2nd light-receiving part. It is a graph which shows output signal ratio when various light sources are input into the said 1st, 2nd light-receiving part. It is a figure which shows an example of the shape of the light-receiving surface of the 1st, 2nd light-receiving part of the said embodiment. It is a circuit diagram which shows the structure of the analog-digital conversion circuit with which the illumination intensity sensor of the said embodiment is provided. It is a wave form diagram which shows operation | movement of the said analog-digital conversion circuit. It is a block diagram which shows schematic structure of the display apparatus provided with the illumination intensity sensor of the said embodiment. It is a circuit diagram which shows the structure of the principal part of the conventional illumination intensity sensor provided with the current mirror circuit. It is a circuit diagram which shows the structure of the principal part of the conventional illumination intensity sensor provided with the analog-digital conversion circuit. It is a figure which shows typically the display apparatus carrying an illuminance sensor.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1 is a block diagram showing an embodiment of an illuminance sensor of the present invention. The illuminance sensor of this embodiment includes a first light receiving unit 1 and a second light receiving unit 2 that receive ambient environmental light. The first and second light receiving units 1 and 2 are configured by, for example, photodiodes and the like, and have a function of outputting a light reception signal corresponding to the received light as a current signal to a subsequent circuit.

  Further, the illuminance sensor of this embodiment includes a first analog-digital conversion circuit 3 (hereinafter referred to as a first analog-digital conversion circuit 3) to which a first current signal Iin1 as a first light reception signal from the first light receiving unit 1 is input. And a second analog-digital conversion circuit 5 (hereinafter referred to as a second analog-digital conversion circuit 5) to which a first current signal Iin2 as a second light reception signal from the second light receiving section 2 is input. AD conversion circuit 5). The first AD converter circuit 3 digitally converts the first current signal Iin1 and outputs a first digital signal ADC1. The second AD converter circuit 5 digitally converts the second current signal Iin2 and outputs a second digital signal ADC2.

  Further, the illuminance sensor of this embodiment includes a signal processing circuit 6 and an output data storage circuit 7 as an output storage unit. The first and second AD conversion circuits 3 and 5 and the signal processing circuit 6 constitute a signal processing unit. The signal processing circuit 6 performs predetermined signal processing, for example, first and second, on the first and second digital signals ADC1 and ADC2 input from the first and second AD conversion circuits 3 and 5, respectively. Data calculation, data comparison, etc. are performed on the digital signals ADC1 and ADC2. The signal processing circuit 6 determines whether or not to transfer the first digital signal ADC1 and the second digital signal ADC2 to the output data storage circuit 7 in accordance with the result of the signal processing.

  The output data storage circuit 7 is composed of a register or the like, and has a function of storing the first digital signal ADC1 and the second digital signal ADC2 input from the signal processing circuit 6, and the first digital signal. It has a function of outputting the ADC 1 and the second digital signal ADC2.

  Next, with reference to the flowchart of FIG. 2, the outline | summary of the illumination intensity measurement operation | movement by the illumination intensity sensor of this embodiment is demonstrated.

  First, illuminance measurement is started in step S101. The start of the illuminance measurement corresponds to turning on the power in hardware. In the case of a digital illuminance sensor, the start of the illuminance measurement corresponds to initialization of an operation setting register or the like.

  Next, it progresses to step S102 and the measurement of ambient light by the said 1st, 2nd light-receiving parts 1 and 2 is started. During this measurement period, the first and second light receiving portions 1 and 2 of the illuminance sensor convert the received light into first and second current signals Iin1 and Iin2, respectively, and are analog signals. The first and second current signals Iin1 and Iin2 are converted into first and second digital signals ADC1 and ADC2 by the first and second AD conversion circuits 3 and 5, respectively. Here, when the first and second AD conversion circuits 3 and 5 employ an integration circuit, the time required for measuring ambient light varies depending on the integration time of the integration circuit. Generally, the measurement is completed with an integration time of 100 milliseconds or less.

  In step S103, the signal processing circuit 6 performs the first digital signal ADC1 and the first digital signal ADC1 as signal processing for obtaining a determination value based on the first and second digital signals ADC1 and ADC2. 2 digital signal ADC2 is compared.

  Here, as an example, when the first and second light receiving units 1 and 2 have a configuration in which a filter that substantially matches the visibility is provided in the photodiode, the first and second light receiving units 1 and 2 The first and second current signals Iin1 and Iin2 are linear with respect to the illuminance.

  Further, for example, the first light receiving unit 1 and the second light receiving unit 2 have the same configuration, and the first current signal Iin1 from the first light receiving unit 1 and the second light receiving unit 2 When the current signal Iin2 of 2 does not match, it means that ambient light is not uniformly input to the first light receiving unit 1 and the second light receiving unit 2. The incident angle at which the light emitted from the point light source enters the light receiving surface of the first light receiving unit 1 and the incident angle at which the light emitted from the point light source enters the light receiving surface of the second light receiving unit 2 are: If they do not match, the first current signal Iin1 of the first light receiving unit 1 and the second current signal Iin2 of the second light receiving unit 2 do not match. Therefore, the first digital signal ADC1 and the second digital signal ADC2 do not match.

  The signal processing circuit 6 uses the signal processing to set, for example, the ratio (ADC2 / ADC1) between the first digital signal ADC1 and the second digital signal ADC2 as the determination value. This determination value represents the difference in the second current signal (second received light signal) Iin2 with respect to the first current signal (first received light signal) Iin1.

  In step S104, the signal processing circuit 6 determines whether the ratio (ADC2 / ADC1), which is a determination value obtained based on the digital signals ADC1 and ADC2, satisfies a predetermined range (condition). Determine whether or not. The setting of the range (condition) varies depending on the spectral sensitivity characteristics of the first and second light receiving units 1 and 2, the arrangement with respect to the light receiving surface, and the like.

  For example, when the first light receiving unit 1 and the second light receiving unit 2 have the same light receiving area and are arranged symmetrically on the light receiving surface of the illuminance sensor, the signal processing circuit 6 For example, when the ratio (ADC2 / ADC1) of the digital signal ADC1 and the digital signal ADC2 falls within the range of 0.9 to 1.1, it is determined that “the determination criterion is satisfied”. That is, when the deviation of the second digital signal ADC2 from the first digital signal ADC1 is within 10%, the signal processing circuit 6 determines that “the determination criterion is satisfied”. On the other hand, when the ratio (ADC2 / ADC1) of the digital signal ADC1 and the digital signal ADC2 is not within the range of 0.9 to 1.1, it is determined that “the determination criterion is not satisfied”.

  When the signal processing circuit 6 determines that “the determination criterion is satisfied”, the process proceeds to step S105, where the first digital signal ADC1 and the second digital signal ADC2 are transferred to the output data storage circuit 7, The first digital signal ADC1 and the second digital signal ADC2 stored in the output data storage circuit 7 are updated, and the process returns to step S102. On the other hand, when the signal processing circuit 6 determines that “the determination criterion is not satisfied”, the first digital signal ADC1 and the second digital signal ADC2 are not transferred to the output data storage circuit 7, but the output data storage circuit The first digital signal ADC1 and the second digital signal ADC2 stored in 7 are not updated, and the process returns to step S102.

  In the illuminance sensor of this embodiment, such operations from step S102 to step S105 are repeated.

  That is, in this example of the illuminance sensor, when the first digital signal ADC1 and the second digital signal ADC2 stored in the output data storage circuit 7 are not updated, the first measurement after the illuminance measurement is started. Unless otherwise, the output data storage circuit 7 holds the first and second digital signals ADC1 and ADC2 as the previous measurement data.

  As described above, in the present embodiment, as an example, when the deviation of the second digital signal ADC2 from the first digital signal ADC1 exceeds 10% of the digital signal ADC1, it is stored in the output data storage circuit 7. The first and second digital signals ADC1 and ADC2 that are being used are not updated. Therefore, for example, when the user holds the mobile device including the illuminance sensor in his / her hand, the mobile device is inclined and the incident light and the second light reception on the first light receiving unit 1 of the illuminance sensor are performed. The first and second digital signals ADC1 and ADC2 as signals representing the illuminance output from the output data storage circuit 7 do not vary when the light incident on the unit 2 becomes unbalanced beyond a certain range. In this way, a stable illuminance detection result can be output.

  In the above description, as an example, whether or not the ratio of the second digital signal ADC2 to the first digital signal ADC1 (ADC2 / ADC1) is within the range of 1.0 ± 0.1 is used as a criterion. However, the numerical range used as a criterion for determining the ratio (ADC2 / ADC1) is not limited to the range of 1.0 ± 0.1, of course, as 1.0 ± 0.2 or 1.0 ± 0.05. Alternatively, it is possible to set a desired numerical value range by setting the numerical value range to 1.0 ± β (β is a desired value of 0 to 0.5, for example).

  In addition, the spectral sensitivity characteristic of the first light receiving unit 1 and the spectral sensitivity characteristic of the second light receiving unit 2 may be the same, but the spectral sensitivity characteristic of the first light receiving unit 1 and the second light receiving unit 2 may be the same. The spectral sensitivity characteristic of the light receiving unit 2 may be different. For example, as described next with reference to FIGS. 3A and 3B, the first light receiving unit 1 is assumed to have a wide spectral sensitivity characteristic from visible light to infrared light, and the second light receiving unit 2 is mainly used. Further, it may be sensitive to infrared light.

  FIG. 3A schematically shows a specific example of the structure of the first light receiving unit 1 having a wide spectral sensitivity characteristic from visible light to infrared light. The first light receiving unit 1 is formed on a general P-type semiconductor substrate 31. An N-type well (Nwell) 32 is formed in the P-type semiconductor substrate (Psub) 31, and a P-type diffusion layer (Pdif) 33 is formed in the N-type well 32. A deep junction photodiode PDir is formed in a junction region between the P-type semiconductor substrate 31 and the N-type well 32. A shallow junction photodiode PDvis is formed in the junction region between the N-type well 32 and the P-type diffusion layer 33. As shown in FIG. 3A, the anode of the photodiode PDir and the anode of the photodiode PDvis are connected to the ground (GND). The cathode of the photodiode PDir is connected to the cathode of the photodiode PDvis.

  Thereby, at the connection point 35 between the cathode of the photodiode PDir and the cathode of the photodiode PDvis, a current Iall (= Iir + Ivis) obtained by adding the light reception current Iir at the photodiode PDir and the light reception current Ivis at the photodiode PDvis is added. Flowing. Therefore, in the first light receiving unit 1, the light receiving currents Iir and Ivis of the two photodiodes PDvis and PDir having different junction depths are added together and output.

  FIG. 3B schematically shows a specific example of the structure of the second light receiving unit 2 mainly having sensitivity to infrared light. As shown in FIG. 3B, the second light receiving unit 2 is different from the first light receiving unit 1 shown in FIG. 3A only in that the anode of the photodiode PDvis is connected to the cathode of the photodiode PDir. In this way, by short-circuiting the anode and the cathode of the photodiode PDvis, only the light reception current Iir in the photodiode PDir is output from the second light receiving unit 2.

  In the first and second light receiving portions 1 and 2 as specific examples shown in FIGS. 3A and 3B, if light is incident only from above the P-type semiconductor substrate 31, the junction is generally shallow. The spectral sensitivity characteristic of the photodiode PDvis formed in the part is different from the spectral sensitivity characteristic of the photodiode PDir formed in the part where the junction is deep.

  FIG. 4 is a spectral sensitivity characteristic diagram in which the horizontal axis represents the wavelength (nm) of incident light, and the vertical axis represents normalized sensitivity. In FIG. 4, the spectral sensitivity characteristic K1 of the photodiode PDvis in which the junction is formed in a shallow portion is indicated by a solid line. Further, the spectral sensitivity characteristic K2 of the photodiode PDir formed at the deep junction is indicated by a dotted line. A spectral sensitivity characteristic K3 indicated by a broken line is a spectral sensitivity characteristic obtained by adding the spectral sensitivity characteristic K1 of the photodiode PDvis and the spectral sensitivity characteristic K2 of the photodiode PDir.

  As shown by the spectral sensitivity characteristic K1, the shallow junction photodiode PDvis has sensitivity from the visible light region to the infrared region. On the other hand, the photodiode PDir having a deep junction has a peak sensitivity in the infrared region as indicated by the spectral sensitivity characteristic K2.

  Accordingly, the light receiving currents Iir and Ivis of two photodiodes PDvis and PDir having different junction depths are summed and output, and the output current Iall of the first light receiving unit 1 (FIG. 3A) and the photodiode PDir This is clearly different from the output current Iir of the second light receiving unit 2 (FIG. 3B) from which only the received light current Iir is output.

  For example, since illumination such as a fluorescent lamp or white LED hardly includes infrared light, the output as the first light receiving signal of the first light receiving unit 1 having sensitivity from visible light to infrared light. Compared with the signal Iall, the output signal Iir as the second light receiving signal of the second light receiving unit 2 mainly having sensitivity to infrared light is small. On the other hand, when a light source having a strong infrared component such as sunlight or an incandescent lamp is used, the output signal Iir of the second light receiving unit 2 becomes larger than when a fluorescent lamp or a white LED is the light source.

Here, a ratio Ratio derived by dividing the output signal Iir from the second light receiving unit 2 by the output signal Iall from the first light receiving unit 1 is defined by the following equation (1).
Ratio = Iir / Iall (1)
The ratio Ratio defined by the above equation (1) varies depending on the spectrum of the light source. That is, if the light source is a fluorescent lamp, a white LED, or the like, the ratio Ratio is low, and if the light source is sunlight, an incandescent lamp, or the like, the ratio Ratio is high.

  FIG. 5 is a graph showing a simulation result with the horizontal axis representing the type of light source and the vertical axis representing the ratio Ratio defined by the above equation (1).

  The light sources F2, F6, F7, F8, F10, F11, and F12 shown on the horizontal axis in FIG. 5 each represent a fluorescent lamp using a spectrum defined by the CIE (International Commission on Illumination). Further, D65 on the horizontal axis represents standard light defined by the CIE, and D55 represents auxiliary standard light defined by the CIE. These D65 and D55 represent the daylight sunlight spectrum. The incandescent lamp on the horizontal axis is the spectrum of the A light source defined by the CIE. The white LED on the horizontal axis is a spectrum corresponding to a general daylight white color (WhiteLED), and the WarmWhite LED on the horizontal axis is a spectrum corresponding to a light bulb color (WarmWiteLED).

  As can be seen from FIG. 5, in the fluorescent lamp and the white LED, the ratio Ratio (= Iir / Iall) is about 0.29 to 0.4, and in the spectra D65 and D55 representing daylight in the daytime, The ratio Ratio is 0.5 to 0.55. Further, it can be seen that in the incandescent lamp (A light source), the ratio Ratio is about 0.75. That is, it can be seen that the type of the light source of the incident light to the first and second light receiving units 1 and 2 can be physically determined by the value of the ratio Ratio defined by the above equation (1).

  Therefore, the ratio (= Iir / Iall) is calculated by the signal processing circuit 6 based on the digital signal ADC1 from the first light receiving unit 1 and the digital signal ADC2 from the second light receiving unit 2. Incorporating the function to transfer the calculated ratio Ratio to the output data storage circuit 7 makes it possible to determine the type of ambient light source being measured.

  Here, when the balance between the light incident on the first light receiving unit 1 and the light incident on the second light receiving unit 2 is lost, the ratio Ratio also changes. For example, when the ratio Ratio at the time of the current illuminance measurement changes greatly with respect to the ratio Ratio at the time of the previous illuminance measurement, the type of the surrounding light source changes, or the amount of light input to the first light receiving unit 1 This corresponds to a case where the ratio and the amount of light input to the second light receiving unit 2 change.

  Examples of the case where the type of light source around the illuminance sensor changes include a case where a user moves in or out of a building with a portable device incorporating the illuminance sensor. The time interval for updating the output of the output data storage circuit 7 of the illuminance sensor should be sufficiently early with respect to such a change in environment (change in light source type). Therefore, the time interval for updating the output is not limited to the time interval of 100 ms described above as an example, and may be a time interval longer than 100 ms.

  For example, the signal processing circuit 6 calculates the ratio Ratio at a certain time interval (for example, 100 milliseconds), and the calculated ratio Ratio is repeated three times in the predetermined range (for example, 0.9 to 1. The data update adjustment function for outputting the data (ratio Ratio and digital signals ADC1, ADC2) to be stored in the output data storage circuit 7 for the first time when the output data storage circuit 7 is stabilized within the range 1) and updating the storage data of the output data storage circuit 7 It is preferable to provide. As a result, the amount of control (backlight brightness, etc.) based on the output signal of the illuminance sensor changes frequently so that the output signal output from the output data storage circuit 7 of the illuminance sensor does not change frequently. Can be avoided.

  The data update adjustment function can be easily realized by adding to the signal processing circuit 6 a recording circuit for recording the ratio Ratio, a counter for counting the number of calculation of the ratio Ratio, and the like.

  According to the above-described data update adjustment function, after the ratio of the surrounding light sources is changed, the output data of the illuminance sensor is updated after the ratio Ratio is stabilized for, for example, 300 msec. The illuminance sensor is incorporated in a display device, for example, and updates output data (ratio Ratio and digital signals ADC1 and ADC2) every 300 milliseconds, for example, when the direction of the display device relative to the light source is stable. When the display device is tilted with respect to the point light source and the ratio Ratio falls outside the predetermined range (for example, a range of 0.9 to 1.1), the illuminance sensor does not update the output data. According to the illuminance sensor having the data update adjustment function, the output data is output until the ratio Ratio calculated every predetermined time interval (for example, 100 milliseconds) is stabilized within the predetermined range three times in succession. Do not update. Therefore, according to the illuminance sensor, a signal representing the measured illuminance can be stably output.

  The predetermined range may be a ratio of 0.9 to 1.1, 0.8 to 1.2, or 0.95 to 1.05. It is good also as a range. Further, the ratio Ratio may be 1.0 ± β (β is a desired value of 0 to 0.5, for example). In addition, the output data may be updated when the ratio Ratio calculated every predetermined time interval is stabilized within the predetermined range twice in succession, and is calculated every predetermined time interval. The output data may be updated when the ratio Ratio is continuously maintained four times in the predetermined range. Further, the output data may be updated when the ratio Ratio calculated for each predetermined time interval is stabilized within the predetermined range for four or more desired times.

  Further, in the specific example shown in FIGS. 3A and 3B, the first light receiving unit 1 has the spectral sensitivity characteristic K3 of FIG. 4, and the second light receiving unit 2 has the spectral sensitivity characteristic K2 of FIG. However, this is just an example. For example, it is assumed that the first light receiving unit 1 has a spectral sensitivity characteristic that is close to or substantially coincides with the visual sensitivity characteristic using a filter, and the second light receiving unit 2 does not have the filter and has the spectral sensitivity characteristic K3 in FIG. As described above, the photodiode may have a wide sensitivity from visible light to infrared light.

  Further, as shown in the plan view of FIG. 6, the light receiving surface 1 </ b> A of the first light receiving unit 1 has a circular shape, and the light receiving surface 2 </ b> A of the second light receiving unit 2 has a circular shape of the first light receiving unit 1. It is good also as the annular | circular shape which surrounds 1 A of this light-receiving surface. In this case, the direction in which the incident light on the light receiving surfaces 1A and 2A is inclined with respect to the normal line of the light receiving surfaces 1A and 2A is independent of the inclination direction regardless of the direction around the normal line Based on the digital signal ADC1 from the first light receiving unit 1 and the digital signal ADC2 from the second light receiving unit 2, the inclination of the light source with respect to the light receiving surfaces 1A and 2A can be detected.

  Next, a specific example of the AD conversion circuits ADC1 and ADC2 included in the above embodiment will be described with reference to FIGS. In this embodiment, the first AD converter circuit ADC1 and the second AD converter circuit ADC2 have the same configuration, and therefore, in the description of this specific example, the AD converter circuit ADC will be collectively referred to. The first and second light receiving currents Iin1 and Iin2 input to the first and second AD conversion circuits ADC1 and ADC2, respectively, are collectively referred to as an input current Iin.

  FIG. 7 is a circuit diagram showing the configuration of the AD converter circuit ADC, and FIG. 8 is a waveform diagram showing the operation of the AD converter circuit ADC.

  As shown in FIG. 7, the AD converter circuit ADC includes a charging circuit (integrating circuit) 71 that stores charges, a discharging circuit 72 that discharges charges, and an output voltage Vsig and a reference voltage Vref of the charging circuit 71. A comparison circuit 73 that compares the levels is included, and a control circuit (output circuit) 74 that outputs a digital value ADCout based on an output signal Comp that is a comparison result by the comparison circuit 73.

  The charging circuit 71 is provided with an amplifier AMP1 and a capacitor (integrating capacitor) C1 that constitute an integrator, and charges corresponding to the input current Iin are stored in the capacitor C1. The discharge circuit 72 is provided with a reference current source I1 for generating a reference current Iref for discharging the charge stored in the capacitor C1, and a switch SW2 for switching on / off of the discharge. .

  The comparison circuit 73 is provided with a comparator CMP1 and a switch SW1. The comparator CMP1 compares the output voltage Vsig of the charging circuit 71 with the reference voltage Vref generated by the reference voltage source V1, and outputs a signal Comp. The data conversion period in which the input current Iin is converted to the digital value ADCout is determined by turning on / off the switch SW1. When the switch SW1 is turned on, the reference voltage Vref generated by the reference voltage source V1 is applied to the charging circuit 71, and the capacitor C1 is charged. When the switch SW1 is turned off, the output voltage Vsig of the charging circuit 71 and the reference voltage Vref are compared with each other by the comparator CMP1, and the output signal Comp as the comparison result is H (high) level and L (low). ) Is input to the control circuit 74 as a binary level pulse signal. The input current Iin is converted into a digital value ADCout while the switch SW1 is off.

  The control circuit 74 is provided with a flip-flop FF and a counter COUNT. The output signal Comp of the comparison circuit 73 is latched by the flip-flop FF, and the resulting bit stream signal Charge is input to the discharge circuit 72 and the counter COUNT, respectively. Here, the counter COUNT counts the number of L (Low) levels (the number of discharges) of the bit stream signal Charge. That is, the counter COUNT counts active pulses, and outputs the count result as a digital value ADCout which is an analog-digital conversion value corresponding to the input current Iin.

  The switch SW2 of the discharge circuit 72 is turned on / off based on the bit stream signal Charge. When the switch SW2 of the discharge circuit 72 is turned on, electric charge is stored in the capacitor C1 of the charge circuit 71 by the discharge circuit 72. When the switch SW2 is turned off, the charge of the capacitor C1 of the charging circuit 71 is discharged according to the input current Iin.

  Next, the operation of the AD converter circuit ADC will be specifically described based on the waveform diagram of FIG. In FIG. 8, clk indicates the waveform of the clock signal, SW1 indicates the signal level input to the switch SW1, and SW2 indicates the signal level input to the switch SW2.

  When an H (high) level signal is input to the switch SW1, the switch SW1 is turned off, and conversion of the input current Iin to the digital value ADCout is started. When an H (high) level signal is input to the switch SW2, the switch SW2 is turned off, and the charge stored in the capacitor C1 of the charging circuit 71 is discharged according to the input current Iin (precharge operation). ). As a result, the output voltage Vsig of the charging circuit 71 decreases. First, since the output voltage Vsig of the charging circuit 71 and the reference voltage Vref are set to be the same, the output voltage Vsig of the charging circuit 71 is lower than the reference voltage Vref during the discharging period.

  Thereafter, when an L (low) level signal is input to the switch SW2, the switch SW2 is turned on, and the capacitor C1 of the charging circuit 71 is charged by the discharging circuit 72. As a result, the output voltage Vsig of the charging circuit 71 increases. At some point, the output voltage Vsig of the charging circuit 71 exceeds the reference voltage Vref. The output voltage Vsig of the charging circuit 71 and the reference voltage Vref are compared by the comparator CMP1, and when the output voltage Vsig of the charging circuit 71 exceeds the reference voltage Vref, the H (high) level output signal Comp is compared with the comparator CMP1. Is output from.

  When the H (high) level output signal Comp is input to the flip-flop FF of the control circuit 74, the flip-flop FF latches the output signal Comp, and at the rise of the next clock signal clk, the H (high) level. The bit stream signal Charge is output.

  When the H-level bit stream signal Charge is input to the switch SW2, the switch SW2 is turned off and the charge stored in the capacitor C1 of the charging circuit 71 is discharged. As a result, the output voltage Vsig of the charging circuit 71 decreases. At some point, the output voltage Vsig of the charging circuit 71 falls below the reference voltage Vref. When the output voltage Vsig of the charging circuit 71 is lower than the reference voltage Vref, an L-level output signal Comp is output as an active pulse indicating that the output of the comparator CMP1 is at the active level. Note that the active pulse of the output signal Comp may be set to either L level or H level, and can be selected as appropriate according to the operation logic of the circuit.

  When the L-level output signal Comp is input to the flip-flop FF of the control circuit 74, the flip-flop FF latches the output signal Comp so that the control circuit 74 takes in the output signal Comp, and the flip-flop FF The L level bit stream signal Charge is output at the rising edge of the clock signal clk.

  When the L-level bit stream signal Charge is input to the switch SW2, the switch SW2 is turned on. Here, the bit stream signal Charge is a time-series arrangement of L level signals (active pulses), and the switch SW2 is turned on during the L level period (active pulse period).

  The AD conversion circuit ADC shown in FIG. 7 repeats the above-described operation, and the counter COUNT counts the number of discharges Count of the discharge circuit 72 during the period in which the switch SW1 is turned off, that is, the data conversion period Tconv. The digital value ADCout corresponding to the input current Iin can be output.

Here, the charge amount Qconv charged by the input current Iin in the data conversion period Tconv is calculated by the following equation (2).
Qconv = Iin × Tconv (2)

Further, assuming that the period of the clock signal clk is Tclk, the amount of charge Qclk discharged at a time by the reference current Iref flowing through the discharge circuit 72 is calculated by the following equation (3).
Qclk = Iref × Tclk (3)

Since the charge amount Qconv charged in the data conversion period Tconv and the sum of the charge amount Qclk discharged in the data conversion period Tconv are equal, the following equation (4) is obtained from the above equations (2) and (3). It holds.
Iin x Tconv = Iref x Tclk x Count (4)

From the above equation (4), the following equation (5) is derived.
Count = (Iin × Tconv) / (Iref × Tclk) (5)

The minimum resolution of the AD conversion circuit ADC is determined by (Iref × Tclk) = Qclk. Here, assuming that the minimum resolution is n, the charging period Tconv is set by the following equation (6).
Tconv = Tclk × 2 ⁿ (6)

Substituting this equation (6) into the above equation (5) leads to the following equation (7).
Count = (Iin / Iref) × 2 ⁿ (7)

  For example, when the resolution n = 16 bits, the counter COUNT outputs a value corresponding to the input current Iin in the range of 0 to 65535. Thereby, the integration type analog-digital conversion circuit ADC can perform analog-digital conversion with a wide dynamic range and high resolution.

Next, a case where the AD conversion circuit ADC having the above-described configuration is applied to the first AD conversion circuit ADC1 will be described. In the first AD converter circuit ADC1, when the first received light current Iin1 flowing through the first light receiving unit 1 is analog-to-digital converted with the reference current Iref of the discharge circuit 72, the number of discharges Count1 of the discharge circuit 72 is expressed by the following equation ( 8). In the following equation (8), n is the minimum resolution.
Count1 = (Iin1 / Iref) × 2 ⁿ (8)

  At this time, the flip-flop FF of the control circuit 74 in the analog-digital conversion circuit ADC1 outputs the bit stream signal Chargel that is accurately at the H (high) level by the number of discharges Count1.

  Next, the schematic configuration of the display device 81 including the illuminance sensor of the above embodiment is shown in the block diagram of FIG. The display device 81 includes the illuminance sensor 82, a backlight control unit 83, a backlight 84, and a display panel 85.

  The said backlight 84 is a light source for irradiating the display panel 85 which displays a screen from a back surface, for example, has red LED, green LED, and blue LED. The illuminance sensor 82 receives ambient light of the display device 81, measures the brightness, and outputs a digital signal Dout to the backlight control unit 83 as a measurement result. The backlight control unit 83 controls the luminances of the red LED, the green LED, and the blue LED of the backlight 84 based on the digital signal Dout. Thereby, the light emission amount of the backlight 84 is controlled according to the color component of the ambient light. According to the display device 81, by mounting the illuminance sensor 82 according to the embodiment, the light emission amount of the backlight 84 can be stably controlled, and the control of the light emission amount of the backlight 84 is not repeated more than necessary. Therefore, it leads to reduction of power consumption.

  In the above embodiment, the difference between the first received light signal and the second received light signal is obtained from the ratio between the first received light signal and the second received light signal. Any value may be used as long as it is a value representative of the difference between the second received light signal and the second received light signal. In the above embodiment, the first and second light receiving units 1 and 2 are provided. However, the first, second, and third light receiving units are provided, and the signal processing circuit 6 is connected to the first light receiving unit. It is also possible to determine whether or not the difference between the second and third light receiving signals of the second and third light receiving units with respect to the first light receiving signal of one light receiving unit exceeds a predetermined range. Good. In this case, when the signal processing circuit 6 determines that the difference exceeds a predetermined range, the signal processing circuit 6 does not output the first to third light reception signals, while the difference is determined in advance. The first to third light receiving signals are output when it is determined that the specified range is not exceeded. In addition, the first to n-th n (n is a natural number of 4 or more) light-receiving units are provided, and the second to n-th light-receiving units corresponding to the first light-receiving signal of the first light-receiving unit You may provide the signal processing circuit which judges whether the difference of n light received signal exceeds the predetermined range. When the signal processing circuit determines that the difference exceeds a predetermined range, the signal processing circuit does not output the first to n-th received light signals, while the difference exceeds a predetermined range. If it is determined that it is not, the first to nth light receiving signals are output.

  Further, the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope described in the claims, and the present invention can be obtained by appropriately combining technical means disclosed in the above-described embodiment. Embodiments to be made are also included in the technical scope of the present invention.

  Since the illuminance sensor of the present invention can stably output a signal representing the detected illuminance, it can be suitably used for a display device, particularly a portable device.

DESCRIPTION OF SYMBOLS 1 1st light-receiving part 2 2nd light-receiving part 3 1st AD converter circuit 5 2nd AD converter circuit 6 Signal processing circuit 7 Output data storage circuit 31 P-type semiconductor substrate 32 N-type well 33 P-type diffusion layer 35 Connection point PDvis Shallow junction photodiode PDir Deep junction photodiode ADC AD conversion circuit 71 Charging circuit 72 Discharging circuit 73 Comparison circuit 74 Control circuit 81 Display device 82 Illuminance sensor 83 Backlight controller 84 Backlight 85 Display panel AMP1 Amplifier C1 capacitor CMP1 comparator SW1, SW2 switch FF flip-flop COUNT counter

Claims (9)

A first light receiving unit that outputs a first light receiving signal corresponding to the received light;
A second light receiving unit that outputs a second light reception signal corresponding to the received light;
The first light receiving signal and the second light receiving signal are input, the first light receiving signal and the second light receiving signal are processed, and the phase of the second light receiving signal with respect to the first light receiving signal is processed. It is determined whether or not the difference exceeds a predetermined range, and when it is determined that the difference exceeds a predetermined range, the first and second received light signals are not output, A signal processing unit that outputs the first and second received light signals when it is determined that the difference does not exceed a predetermined range;
An illuminance sensor comprising: an output storage unit that stores the first and second light reception signals output from the signal processing unit and outputs the first and second light reception signals. The illuminance sensor according to claim 1,
An illuminance sensor, wherein the spectral sensitivity characteristic of the first light receiving unit and the spectral sensitivity characteristic of the second light receiving unit are different from each other. The illuminance sensor according to claim 2,
The first light receiving unit has sensitivity in a wavelength region from visible light to infrared light,
The illuminance sensor, wherein the second light receiving unit has a sensitivity peak in a wavelength region of infrared light. In the illuminance sensor according to any one of claims 1 to 3,
The first and second light receiving signals are current signals,
The signal processor is
The ratio between the first received light signal and the second received light signal is calculated, and when the ratio is within a preset numerical range, the first and second received light signals are output, while the ratio The illuminance sensor, wherein the first and second light receiving signals are not output when is outside the numerical range. The illuminance sensor according to any one of claims 1 to 4,
One of the first light receiving unit and the second light receiving unit has a circular light receiving surface,
The illuminance sensor, wherein the other light receiving portion of the first light receiving portion and the second light receiving portion has an annular light receiving surface surrounding the circular light receiving surface. The illuminance sensor according to any one of claims 1 to 5,
The first and second light receiving signals are current signals,
The signal processor is
A first analog-digital conversion circuit that outputs a digital signal obtained by analog-digital conversion of the first light-receiving signal;
An illuminance sensor, comprising: a second analog-digital conversion circuit that outputs a digital signal obtained by analog-digital conversion of the second received light signal. The illuminance sensor according to claim 6.
The first and second analog-digital conversion circuits are:
An integration circuit that includes an integration capacitor that stores electric charge according to an input current signal and that outputs a voltage corresponding to the amount of electric charge stored by the integration capacitor;
A comparison circuit that compares the output voltage of the integration circuit with a preset reference voltage and outputs a comparison result between the output voltage and the reference voltage as a binary pulse signal;
Includes a flip-flop that captures the pulse signal in synchronization with the clock signal and outputs a bit stream signal, and a counter that counts the active pulses of the bit stream signal, and outputs the count result of this counter as an analog-digital converted output value An output circuit to
An illuminance sensor, comprising: an integration type analog-digital conversion circuit having a discharge circuit for discharging an integration capacitor of the integration circuit during an active pulse period of the bit stream signal. The illuminance sensor according to claim 6 or 7,
The integration time of one time of the first and second analog-digital conversion circuits is within 100 milliseconds,
The signal processor is
The digital signal obtained by analog-to-digital conversion of the first and second received light signals is subjected to signal processing at a preset time interval equal to or longer than the integration time, and the difference between the second received light signal and the first received light signal is different. Is determined to exceed the preset range, and when it is determined that the difference does not exceed the preset range after a preset number of times, the first and second When the number of times that the difference is not exceeding the preset range is less than the preset number, the digital signal obtained by analog-to-digital conversion of the received light signal is output. An illuminance sensor characterized by not outputting a digital signal obtained by analog-to-digital conversion of the first and second received light signals. A display panel for displaying a screen;
A backlight for illuminating the display panel;
A backlight control unit for controlling the backlight;
An illuminance sensor according to any one of claims 1 to 7,
The backlight control unit
A display device, wherein brightness of the backlight is controlled based on the light reception signal output from the output storage unit included in the illuminance sensor.

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