JP2009036607A - Light quantity detection circuit and electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light quantity detection circuit enhancing photo-detection accuracy by correcting sensitivity lowering without changing manufacturing conditions, and an electrochemical device. <P>SOLUTION: The light quantity detection circuit includes a pair of photo-detection parts LS1 and LS2. One photo-detection part LS1 outputs an output signal Ia corresponding to the light quantity of outside light while the other photo-detection part LS2 outputs an output signal Ib corresponding to a light quantity obtained by dimming the outside light to 1/n by a dimming means. The detection circuit includes a multiplication part 11 for multiplying the output signal Ib of the photo-detection part LS2 by n, a multiplication part 12 for multiplying the output signal Ia of the photo-detection part LS1 by a constant a, a division part 13 for dividing the output value of the multiplication part 11 by the output value of the multiplication part 12, an addition part 14 for adding a constant b to the output value of the division part 13, and a division part 15 for dividing the output value of the multiplication part 11 by the output value of the addition part 14. The output value of the division part 15 is taken as the light quantity (illuminance L) of outside light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light amount detection circuit having an optical sensor for detecting the brightness of external light, and an electro-optical device including the same.

As a conventional light quantity detection circuit, utilizing the fact that the leakage current of a thin film transistor is proportional to the amount of received light, charging or discharging the voltage detection capacitor with this leakage current, and monitoring the voltage change across the capacitor It is known that the amount of light is detected by (see, for example, Patent Document 1).
By the way, it is known that the leakage current of a thin film transistor is proportional to the amount of received light, but its sensitivity (current value with respect to the amount of received light) is reduced by light exposure. For this reason, in the light amount detection circuit described in Patent Document 1, the light amount detection accuracy is lowered due to the sensitivity reduction.

In order to prevent this, a photoelectric conversion element is known in which a transistor generation method is improved to improve anti-deterioration characteristics (see, for example, Patent Document 2).
JP 2006-29832 A Japanese Patent Laid-Open No. 9-232620

  However, the photoelectric conversion element described in Patent Document 2 requires special manufacturing conditions. For example, an optical sensor is built in a display device using TFTs, or the display device and the optical sensor are connected with the same device. In the case of manufacturing, the manufacturing process is different from the characteristics suitable for display, and the manufacturing process becomes longer or the condition setting of the manufacturing apparatus is frequently changed.

  Therefore, an object of the present invention is to provide a light amount detection circuit and an electro-optical device that can improve sensitivity of light detection by correcting sensitivity reduction without changing manufacturing conditions.

In order to solve the above-described problems, a light amount detection circuit according to the present invention includes a pair of light detection units having a light sensor that detects external light, and a light sensor reading unit that reads output signals from the pair of light detection units. With
The pair of light detection units outputs an output signal that is a product of the deterioration function of the sensitivity of the light detection unit expressed by a function of the integrated light amount of incident light, the initial sensitivity of the light detection unit, and the amount of incident light. To do,
One light detection unit receives the external light as incident light, outputs an output signal corresponding to the amount of the external light, and the other light detection unit includes a light reduction unit that reduces external light, The light attenuated by the dimming means is incident as incident light, and an output signal corresponding to the amount of the attenuated light is output.
Correlation between the amount of incident light and the output signal in the one light detection unit, correlation between the amount of incident light and the output signal in the other light detection unit, and a sensitivity deterioration function in the one light detection unit and the other The light amount of the external light is detected based on each output signal read by the optical sensor reading unit based on a correlation with a sensitivity deterioration function in the light detection unit.

Thereby, the sensitivity fall can be corrected and the illuminance of the external light can be detected with high accuracy.
Also, a simultaneous equation consisting of the correlation between the amount of incident light and the output signal in one light detection unit and the correlation between the amount of incident light and the output signal in the other light detection unit is expressed as a sensitivity degradation function in one light detection unit. Can be corrected even if the integrated light quantity is unknown, and a circuit for detecting the integrated light quantity becomes unnecessary. Thus, simplification of the light quantity detection circuit can be realized.

  Furthermore, since the characteristics of the light detection unit itself are not improved (change in manufacturing conditions), for example, even when the display device and the optical sensor are manufactured in the same manufacturing apparatus, the manufacturing process becomes long. Nor is it necessary to frequently change the condition setting of the manufacturing apparatus.

  In the present invention, a first multiplication circuit that multiplies the output signal of the other light detection unit by a first constant that is the reciprocal of the transmittance in the dimming means, and the output of the one light detection unit. A second multiplication circuit that multiplies the signal by a second constant a; a first division circuit that divides the output value of the second multiplication circuit by the output value of the first multiplication circuit; A first adding circuit for adding the output value of the first dividing circuit and the third constant b, and a second dividing circuit for dividing the output value of the first dividing circuit by the output value of the first adding circuit It is preferable that the output value of the divider circuit is the amount of the external light.

As a result, the correlation between the sensitivity degradation function R _Non [p] in one light detection unit and the sensitivity degradation function R _CF [p] in the other light detection unit is expressed as R _CF [p] = a (R _Non [P] / R _CF
[P]) + b (a and b are constants), the sensitivity reduction can be appropriately corrected.
It is also possible to assume that the second constant a is “1” and the third constant b is “0”. In this case, the second multiplier circuit and the first adder circuit are omitted, and The amount of light can be detected, and the light amount detection circuit can be further simplified.

An electro-optical device according to the invention includes the light amount detection circuit,
A display panel having a plurality of scanning lines, a plurality of data lines, and a plurality of pixels provided corresponding to intersections of the plurality of scanning lines and the plurality of data lines;
An illumination unit for illuminating the display panel;
And a control circuit that controls the illumination unit based on an output value of the light amount detection circuit.

Accordingly, it is possible to obtain an electro-optical device that can correct the decrease in sensitivity of the light amount detection circuit, detect the illuminance of external light with high accuracy, and appropriately control the illumination unit.
In addition, since it does not improve the characteristics of the light detection unit itself (change of manufacturing conditions), even if the display panel and the optical sensor are manufactured with the same manufacturing apparatus, the manufacturing process becomes long, There is no need to change the condition settings of the manufacturing equipment frequently.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram illustrating a configuration of a light amount detection circuit 1 according to the present embodiment.
As shown in FIG. 1, the light amount detection circuit 1 acquires two analog information obtained from the pair of light detection units LS1 and LS2 and the light detection units LS1 and LS2, and is calculated from these read values. A reading unit 10 that outputs an illuminance L of external light.

FIG. 2 is a circuit diagram illustrating a configuration of the light detection units LS1 and LS2 of the present embodiment.
As shown in FIG. 2, in the light detection units LS1 and LS2, a capacitor C is connected in parallel between a drain electrode D _L and a source electrode S _L of a thin film transistor (TFT optical sensor), and the source electrode S _L and the capacitor C And the other terminal of the TFT photosensor drain electrode D _L and the capacitor C are connected to the second voltage source (V2). Become.

With such a configuration, when the switch element SW is turned on every predetermined period, a predetermined reference voltage Vs (for example, +2 V) is applied to the capacitor C from the reference voltage source and charged. Due to this charging, both ends of the capacitor C are charged with a potential difference between the reference voltage Vs and the second voltage V2, but the gate electrode G _L is applied with the gate voltage GV having the opposite polarity, so that the gate is turned off. When the switch element SW is turned off, the charging voltage is reduced by a leakage current generated by irradiating the TFT photosensor with light.

Then, after a predetermined reading time from the charging timing of the capacitor C, the voltage charged in the capacitor C can be read (detected), and the illuminance of external light can be detected based on the read charging voltage.
In the following description, a switch element (corresponding to SW in FIG. 2) provided in each light detection unit LSi (i = 1, 2) is referred to as SWi, and a capacitor (corresponding to C in FIG. 2) is referred to as Ci. .

FIG. 3 is a cross-sectional view of the optical sensor and the switch element constituting the light detection unit LS1.
As shown in FIG. 3, the TFT optical sensor and the switch element SW1 constituting the light detection unit LS1 are both made of TFTs and formed on the TFT substrate 2. That is, on the surface of the TFT substrate 2, the gate electrode G _L of the TFT photosensor, one terminal Ca of the capacitor C1, and the gate electrode G _S constituting one switch element SW1 are formed so as to cover these surfaces. A gate insulating film 17 made of silicon nitride, silicon oxide or the like is laminated.

Further, TFT constituting the top of the gate electrode G _L of the TFT ambient light photosensor and switch elements SW1
On the gate electrode G _S , semiconductor layers 19 _L and 19 _S made of amorphous silicon, polycrystalline silicon, or the like are formed via a gate insulating film 17, respectively.
On the gate insulator 17, a source electrode S _L and a drain electrode D _{L of} a TFT photosensor made of a metal such as aluminum or molybdenum, and a source electrode S _S and a drain electrode D of a TFT constituting one switch element SW1 are provided. _S is provided in contact with the respective semiconductor layers 19 _L and 19 _S.

Among these, TFTs constituting the source electrode S _L and the switch element SW1 of the TFT photosensor
The drain electrodes D _S are extended and connected to each other to form the other terminal Cb of the capacitor C1. Further, for example, a protective insulating film 18 made of an inorganic insulating material is laminated so as to cover the surface of the TFT photosensor, the capacitor C1 and the switch element SW1 made of TFT, and the surface of the switch element SW1 made of TFT. Is covered with a black matrix 21 so as not to be affected by external light.

  The light detection unit LS2 is the same as the light detection unit LS1 shown in FIG. 3, except that the surface of the TFT photosensor is covered with a color filter having a transmittance of 1 / n as a light reduction means. The pair of light detection units LS1 and LS2 have the same photoelectric conversion characteristics. Here, the color filter is for dimming so that the incident light amount of the light detection unit LS2 becomes 1 / n (n> 0) of the incident light amount of the light detection unit LS1.

In other words, external light is directly incident on the TFT light sensor of the light detection unit LS1 as incident light, and external light that has been reduced to 1 / n by the color filter is incident on the TFT light sensor of the light detection unit LS2. Will be incident.
The reading unit 10 in FIG. 1 performs on / off control of the switch elements SW1 and SW2 of the light detection units LS1 and LS2, and charges the capacitors C1 and C2 of the light detection units LS1 and LS2. At this time, the charging timing and one discharging period of the light detection unit LS1 and the light detection unit LS2 are set to be equal to each other. One discharge period is a period from the start of charging the capacitor Ci to the next start of charging. Further, the reading time from the start of charging until the charging voltage of the capacitor Ci is read is set equal in the light detection units LS1 and LS2.

And based on the read value Ia acquired from the light detection part LS1 in this way and the read value Ib acquired from the light detection part LS2, the process mentioned later is performed and the illumination intensity L is calculated | required.
FIG. 4 is a block diagram illustrating a configuration of the reading unit 10.
As shown in FIG. 4, the reading unit 10 includes a multiplication unit 11 that multiplies the read value Ib of the light detection unit LS2 and the reciprocal n of the transmittance, a read value Ia of the light detection unit LS1, and a predetermined constant. a multiplication unit 12 that multiplies a, a division unit 13 that divides the output value of the multiplication unit 12 by an output value of the multiplication unit 11, an addition unit 14 that adds the output value of the division unit 13 and a predetermined constant b, The dividing unit 15 outputs the illuminance L by dividing the output value of the multiplying unit 11 by the output value of the adding unit 14.

That is, the processing in the reading unit 10 corresponds to processing for calculating the illuminance L based on the following formula based on the read values Ia and Ib acquired from the respective light detection units.
L = nIb / {(aIa / nIb) + b} (1)
In the above equation (1), the constant n corresponds to the first constant, the constant a corresponds to the second constant, and the constant b corresponds to the third constant.

Next, the calculation principle of the above equation (1) will be described.
As described above, in the present embodiment, the two light detection units LS1 and LS2 are provided, and the light detection unit LS2 is configured so that the incident light amount of the light detection unit LS2 is 1 / n of the incident light amount of the light detection unit LS1. The light reduction means is provided.
Accordingly, when light having a certain illuminance L is irradiated, the following simultaneous equations are obtained by the correlation between the read values Ia and Ib of the respective light detection units and the illuminance L.

Ia = R _Non [p] KL,
Ib = R _CF [p] KL / n (2)
Here, R _Non [p] is a deterioration function of the sensitivity of the optical sensor in the absence of the light reduction means, R _CF
[P] is a deterioration function of the sensitivity of the optical sensor in the presence of the light reduction means, and is a function of the integrated light quantity p, which is the time integration of the received light quantity.

These deterioration functions are obtained by empirical rules based on experiments and the like. In the present embodiment, the deterioration function R _Non [p] and the deterioration function R _CF [p] _satisfy the following relational expression. To do.
R _CF [p] = a (R _Non [p] / R _CF [p]) + b (3)
Here, a and b are constants obtained by experiments or the like, and take values such as a = 1.08 and b = −0.06.

By the way, from the equation (2),
Ia / Ib = (R _Non [p] KL) / (R _CF [p] KL / n)
= N (R _Non [p] / R _CF [p]) (4)
And this
R _Non [p] / R _CF [p] = (1 / n) · (Ia / Ib) (5)
Therefore, if this is substituted into the equation (3),
R _CF [p] = (a / n) · (Ia / Ib) + b (6)
Get. In this way, the deterioration function R _CF [p] with the dimming means can be expressed in a form that does not include the integrated light quantity p. Based on the equations (6) and (2), the above (1 ) Formula can be obtained. In the present embodiment, since the initial sensitivity K is a constant, the initial sensitivity K does not appear in the above equation (1) by including the initial sensitivity K in the constants a and b.

The formula of the illuminance L obtained in this way does not include the integrated light quantity p, and the illuminance L can be calculated even if the integrated light quantity p is unknown.
In FIG. 4, the multiplication unit 11 corresponds to the first multiplication circuit, the multiplication unit 12 corresponds to the second multiplication circuit, the division unit 13 corresponds to the first division circuit, and the addition unit 14 corresponds to the first multiplication circuit. The dividing unit 15 corresponds to the second dividing circuit.

Next, the operation of the embodiment of the present invention will be described.
Now, it is assumed that outside light is irradiated on the TFT photosensor. At this time, the reading unit 10 turns on the switch elements SW1 and SW2 of the light detection units LS1 and LS2, and charges the capacitors C1 and C2 of the light detection units LS1 and LS2 with the reference voltage Vs, respectively. Then, after that, the reading unit 10 switches the switch elements SW1 and SW2 to the off state, and the charging voltages charged in the capacitors C1 and C2 are the same due to the leakage current generated when the TFT light sensor is irradiated with the external light. Reduced by discharge characteristics.

Thereafter, when a predetermined reading time has elapsed, the reading unit 10 reads the charging voltages of the capacitors C1 and C2, and performs the processing shown in FIG. 4 as the reading values Ia and Ib to calculate the illuminance L.
By the way, utilizing the fact that the leakage current of the thin film transistor is proportional to the amount of light received, the light amount detection circuit for charging or discharging the voltage detection capacitor with this leakage current and detecting the light amount by the voltage change between both ends of this capacitor is Although widely used, it is known that the sensitivity of the thin film transistor (the current value with respect to the amount of received light) is reduced by light exposure, and the reduction in sensitivity reduces the light amount detection accuracy.

  In order to prevent this, a photoelectric conversion element is known in which the transistor generation method is improved to improve the anti-deterioration characteristics. In this case, however, special manufacturing conditions are required. For example, a display using a TFT When an optical sensor is built in the device or a display device and an optical sensor are manufactured in the same device, the manufacturing process becomes different from the characteristics suitable for display, and the manufacturing process becomes longer. Or forced to change the condition settings of the manufacturing equipment frequently.

In addition, since it is known that the sensitivity reduction depends on the integrated light quantity, which is the time integration of the received light quantity, it may be possible to correct the sensitivity with the integrated light quantity. It is necessary to continue metering. This includes a case where photometry is not required and a case where the apparatus does not operate, which is not realistic.
On the other hand, the present embodiment can correct the decrease in sensitivity without improving the characteristics of the transistor itself (changing the manufacturing conditions), so that the light quantity can be detected with high accuracy and the above-described manner. In addition, it is not necessary to lengthen the manufacturing process or frequently change the condition setting of the manufacturing apparatus. Furthermore, sensitivity correction is possible even if the integrated light quantity is unknown.

  Thus, in the above-described embodiment, one of the pair of light detection units outputs an output signal corresponding to the amount of external light, and the other light detection unit is dimmed by the dimming means. Outputs an output signal corresponding to the amount of incident light, correlates the amount of incident light and the output signal in one light detector, the correlation between the amount of incident light and the output signal in the other light detector, and one light detection The amount of external light is detected based on each output signal based on the correlation between the sensitivity deterioration function in the first light detection unit and the sensitivity deterioration function in the second light detection unit.

Thereby, the sensitivity fall can be corrected and the illuminance of the external light can be detected with high accuracy.
Also, a simultaneous equation consisting of the correlation between the amount of incident light and the output signal in one light detection unit and the correlation between the amount of incident light and the output signal in the other light detection unit is expressed as a sensitivity degradation function in one light detection unit. Can be obtained by using the correlation between the sensitivity detection function and the sensitivity degradation function of the other light detection unit, so that the correction formula can be obtained without including the integrated light quantity. This eliminates the need for a circuit for detecting the integrated light amount, and simplifies the light amount detection circuit.
Furthermore, since the characteristics of the light detection unit itself are not improved (change in manufacturing conditions), for example, even when the display device and the optical sensor are manufactured in the same manufacturing apparatus, the manufacturing process becomes long. Nor is it necessary to frequently change the condition setting of the manufacturing apparatus.

In addition, a first multiplication circuit that multiplies the output signal of the other light detection unit by a first constant that is the reciprocal of the transmittance of the light reduction means, and a second constant for the output signal of the one light detection unit. a second multiplication circuit that multiplies a, a first division circuit that divides an output value of the second multiplication circuit by an output value of the first multiplication circuit, and an output value of the first division circuit A first adder circuit for adding a third constant b; and a second divider circuit for dividing the output value of the first divider circuit by the output value of the first adder circuit. Therefore, the correlation between the sensitivity degradation function R _Non [p] in one light detection unit and the sensitivity degradation function R _CF [p] in the other light detection unit is expressed as follows: R _CF [p] = a (R _Non [p] / R _CF [p]) + b (a and b are constants)
Sensitivity reduction can be corrected appropriately.

  In the above embodiment, the case where the reading unit 10 actually calculates the illuminance L using the arithmetic circuit shown in FIG. 4 has been described. However, the read values Ia and Ib of the respective light detection units are used as input variables. A look-up table to be prepared is prepared, and the illuminance L can be obtained by referring to this table. Also, the read values Ia and Ib of the respective light detection units can be input and directly calculated by the CPU based on the above equation (1).

Furthermore, in the above embodiment, it is possible to assume that a = 1 and b = 0 in the relationship between the deterioration function R _Non [p] and the deterioration function R _CF [p] expressed by the above equation (3). . In this case, the equation (3) is
R _CF [p] = R _Non [p] / R _CF [p] (7)
And the equation (1) is
L = n ² Ib ² / Ia (8)
Thus, the illuminance L can be obtained based on the equation (8).

  Therefore, the configuration of the reading unit 10 at this time is a configuration in which the multiplication unit 12 and the addition unit 14 in FIG. 4 are omitted, as shown in FIG. That is, the division unit 13 is configured to divide the output value of the multiplication unit 11 by the read value Ia, and the division unit 15 is configured to divide the output value of the multiplication unit 11 by the output value of the division unit 13. In this way, the light amount detection circuit can be simplified.

Although the initial sensitivity K is a fixed value here, the initial sensitivity K can be made variable according to the integrated energization time.
At this time, the correction formula of illuminance L is
L = nIb / K {(aIa / nIb) + b} (9)
Or assuming a = 1 and b = 0,
L = n ² Ib ² / KIa (10)
And Thus, the initial sensitivity K appears in the correction formula for the illuminance L. For example, the integrated energization time T sequentially stored in the rewritable nonvolatile memory is read, and the initial sensitivity K corresponding to the integrated energization time T is set. The reading unit 10 obtains the illuminance L.

  When performing illuminance detection using the correction equation shown in the above equation (9), the reading unit 10 multiplies the read value Ia by the constant aK instead of the constant a in the multiplication unit 12 of FIG. Instead of the constant b, a constant bK may be added to the output value of the division unit 13. Further, in the case of performing illuminance detection using the correction formula shown in the above formula (10), the reading unit 10 multiplies the read value Ia by a constant K instead of the constant a in the multiplication unit 12 of FIG. The adder 14 may be omitted, and the divider 15 may divide the output value of the multiplier 11 by the output value of the divider 13.

  Here, the initial sensitivity K may be directly calculated using a function of the integrated energization time T, or a lookup table having the integrated energization time T as an input variable is prepared and calculated with reference to the table. May be. Note that the initial sensitivity K is calculated to be larger as the integrated energization time T is longer. In this way, by changing the initial sensitivity according to the integrated energization time, the illuminance detection value can be corrected appropriately even when the sensitivity drop depends on the integrated energization time at the time of metering. Accurate illuminance detection can be realized.

In the above embodiment, a case where a TFT photosensor is applied as the photosensor has been described. However, any photo-electric conversion such as a well-known photodiode, phototransistor, photo TFT, photoSCR, photoconductor, photocell, etc. An element can be applied.
Next, the electro-optical device 100 to which the above-described light amount detection circuit 1 is applied will be described.
FIG. 6 is a diagram illustrating a configuration of the electro-optical device 100 to which the light amount detection circuit 1 is applied.

As shown in FIG. 6, the electro-optical device 100 includes a liquid crystal panel 101, a light control circuit 102, a backlight 103 as an illumination unit, and a control circuit 104. The liquid crystal panel 101 includes an image display area A, a scanning line driving circuit 201, a data line driving circuit 202, and a light amount detection circuit 1 on the element substrate.
Here, since the liquid crystal panel 101 has a structure in which a pair of an element substrate on which a transistor is formed and a counter substrate on which a color filter is formed sandwiches a liquid crystal layer, the light amount detection circuit 1 is provided on the element substrate. In this case, by providing the light reduction filter of the light detection unit LS2 in the light amount detection circuit 1 not on the light detection unit but on the corresponding part of the counter substrate, the light detection unit LS2 is incident on the light detection unit LS2 without increasing the manufacturing process. The light to be able to be dimmed.

  The control circuit 104 generates various signals and supplies them to the scanning line driving circuit 201 and the data line driving circuit 202. In the image display area A, a plurality of pixels P1 are formed in a matrix, and the transmittance can be controlled for each pixel P1. Light from the backlight 103 is emitted through the pixel P1. Thereby, gradation display by light modulation becomes possible. The dimming circuit 102 adjusts so that the backlight 103 emits light with luminance according to illuminance data indicating the illuminance of the external light (ambient light) output from the light amount detection circuit 1.

  The visibility of the displayed image depends on the brightness of the environment. Therefore, the dimming circuit 102 compares the illuminance of the ambient light output from the light amount detection circuit 1 with a predetermined illuminance threshold. For example, when the illuminance of the ambient light corresponds to natural light during the day, the backlight The light emission luminance of 103 is set high so that a bright screen is displayed. On the other hand, when the ambient light illuminance corresponds to a dark environment at night, the light emission luminance of the backlight 103 is set low.

Here, the case where the present invention is applied to an electro-optical device using liquid crystal has been described, but the present invention can also be applied to an electro-optical device using an electro-optical material other than liquid crystal. For example, electrophoresis using a display panel using an OLED element such as an organic EL or a light emitting polymer as an electro-optical material, or a microcapsule containing a colored liquid and white particles dispersed in the liquid as the electro-optical material Display panels, twist ball display panels using twist balls that are painted in different colors for areas of different polarity as electro-optical materials, toner display panels using black toner as electro-optical materials, high pressure such as helium and neon The present invention can be applied to various electro-optical devices such as a plasma display panel using a gas as an electro-optical material.

It is a block diagram which shows the structure of the light quantity detection circuit of embodiment in this invention. It is a circuit diagram of a photon detection part. It is sectional drawing of the photosensor and switch element on a TFT substrate. It is a block diagram which shows the detailed structure of a reading part. It is a block diagram which shows the other example of a reading part. 1 is a diagram illustrating a configuration of an electro-optical device to which a light amount detection circuit of the present invention is applied.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Light quantity detection circuit, 10 ... Reading part, 11 ... Multiplication part, 12 ... Multiplication part, 13 ... Division part, 14 ... Addition part, 15 ... Division part, 100 ... Electro-optical apparatus, LS1, LS2 ... Light detection part, SW1, SW2 ... switch element, C1, C2 ... capacitor, Vs ... reference voltage

Claims (6)

A pair of light detection units having a light sensor for detecting outside light, and a light sensor reading unit for reading output signals from the pair of light detection units,
The pair of light detection units outputs an output signal that is a product of the deterioration function of the sensitivity of the light detection unit expressed by a function of the integrated light amount of incident light, the initial sensitivity of the light detection unit, and the amount of incident light. To do,
One light detection unit receives the external light as incident light, outputs an output signal corresponding to the amount of the external light, and the other light detection unit includes a light reduction unit that reduces external light, The light attenuated by the dimming means is incident as incident light, and an output signal corresponding to the amount of the attenuated light is output.
Correlation between the amount of incident light and the output signal in the one light detection unit, correlation between the amount of incident light and the output signal in the other light detection unit, and a sensitivity deterioration function in the one light detection unit and the other A light quantity detection circuit that detects the light quantity of the external light based on each output signal read by the optical sensor reading section based on a correlation with a sensitivity deterioration function in a light detection section.   A first multiplication circuit that multiplies the output signal of the other light detection unit by a predetermined first constant, and a first multiplication circuit that divides the output signal of the one light detection unit by the output value of the first multiplication circuit. 1 division circuit, and a second division circuit that divides the output value of the first multiplication circuit by the output value of the first division circuit, and the output value of the second division circuit is The light amount detection circuit according to claim 1, wherein the light amount is a light amount.   The light quantity detection circuit according to claim 2, wherein the first constant is a reciprocal of the transmittance of the dimming unit.   A second multiplication circuit that multiplies an output signal of the one light detection unit by a predetermined second constant; and a first division circuit that multiplies the output value of the second multiplication circuit by the first multiplication. 4. The light quantity detection circuit according to claim 2, wherein the light amount detection circuit divides by an output value of the circuit.   A first adder circuit that adds a predetermined third constant to the output value of the first divider circuit; and the second divider circuit outputs the output value of the first adder circuit to the first value. The light quantity detection circuit according to claim 2, wherein the light amount detection circuit divides by an output value of the division circuit. A light amount detection circuit according to any one of claims 1 to 5,
A display panel having a plurality of scanning lines, a plurality of data lines, and a plurality of pixels provided corresponding to intersections of the plurality of scanning lines and the plurality of data lines;
An illumination unit for illuminating the display panel;
An electro-optical device comprising: a light control circuit that controls the illumination unit based on an output value of the light amount detection circuit.

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