JP2009002727A - Light quantity detecting circuit and electro-optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light quantity detecting circuit and an electro-optical device which can raise light detection accuracy by correcting sensitivity deterioration without changing manufacturing conditions. <P>SOLUTION: The light quantity detecting circuit is provided with a pair of light detecting sections LS1, LS2. The one light detecting section LS1 outputs an output signal Ia responsive to the quantity of external light, while the other light detecting section LS2 outputs an output signal Ib responsive to the quantity of the external light with its light quantity reduced to 1/n by a light reducing means. The detecting circuit is provided with a multiplying section 11 for multiplying the output signal Ib of the light detecting section LS2 by n<SP>2</SP>, a subtracting section 12 for subtracting the output signal Ia of the light detecting section LS1 from the output value of the multiplying section 11, a multiplying section 13 for multiplying (n-1) by an initial sensitivity K, and a dividing section 14 for dividing the output value of the subtracting section 12 by the output value of the multiplying section 13. The output value of the dividing section 14 is determined to be the light quantity (luminous intensity L) of the external 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.
Each output read by the optical sensor reading unit based on the correlation between the incident light amount and the output signal in the one light detection unit and the correlation between the incident light amount and the output signal in the other light detection unit The light quantity of the external light is detected based on the signal.

Thereby, the sensitivity fall can be corrected and the illuminance of the external light can be detected with high accuracy.
Also, by solving a simultaneous equation consisting of the correlation between the incident light amount and the output signal in one light detection unit and the correlation between the incident light amount and the output signal in the other light detection unit with the incident light amount and the integrated light amount, Even if the integrated light quantity is unknown, sensitivity correction can be performed, and a circuit for detecting the integrated light quantity is not required, so that the light quantity detection circuit can be simplified.

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 obtained by squaring the reciprocal of the transmittance of the dimming means, and the first multiplication circuit. A subtracting circuit for subtracting the output signal of the one light detection unit from the output value of the first subtractor, and a second constant obtained by multiplying the output value of the subtracting circuit by subtracting 1 from the reciprocal of the transmittance and the initial sensitivity. A division circuit for dividing, and the output value of the gradual calculation circuit is preferably the amount of the external light.

  Thus, the deterioration function can be defined by the form Exp [-ap] corresponding to the type of the optical sensor (a is a constant indicating the speed of deterioration, and p is the integrated light amount), and the sensitivity reduction can be appropriately corrected. . In addition, the deterioration function can be corrected with a simple circuit by setting the deterioration function to a Taylor expansion function up to the first order. Furthermore, since sensitivity correction can be performed without including the constant a indicating the speed of deterioration, sensitivity correction can be appropriately performed even if there is a variation in deterioration speed among optical sensors. If the second constant can be set to 1 by appropriately setting the unit of light quantity, the divider circuit is omitted and the light quantity of the external light is detected based on the output of the subtractor circuit. I can do it.

Furthermore, it is preferable to include a second multiplication circuit that generates the second constant by multiplying the initial sensitivity and a third constant that is a value obtained by subtracting 1 from the reciprocal of the transmittance. It is preferable to provide an initial sensitivity correction circuit that corrects the initial sensitivity according to the integrated energization time of the light detection unit.
As a result, it is possible to set the sensitivity and transmittance of each optical sensor, and the accuracy is improved, and it is possible to more appropriately correct the sensitivity decrease.

An electro-optical device according to the present invention includes a light amount detection circuit according to any one of the first to seventh inventions,
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 LS < ^b > ² and the square of the reciprocal number n (n ² ), and the output of the multiplication unit 11. A subtracting unit 12 that subtracts the read value Ia of the light detecting unit LS1 from the value, a value (n−1) obtained by subtracting “1” from the initial sensitivity K of the light detecting unit without light reducing means and the reciprocal number n of the transmittance. And a divider 14 that divides the output value of the subtractor 12 by the output value of the multiplier 13 and outputs the illuminance L.

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 = (n ² Ib−Ia) / {K (n−1)} (1)
In the above equation (1), the constant n ² corresponds to the first constant, the constant K (n−1) corresponds to the second constant, and the constant (n−1) corresponds to the third constant. is doing.

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 [p] KL,
Ib = R [p / n] KL / n (2)
Here, R [p] is a sensitivity deterioration function, and is a function of the integrated light quantity p, which is a time integration of the received light quantity. This deterioration function R [p] is obtained by an empirical rule by experiment or the like, and in this embodiment, for example, R [p] = Exp [−ap] (a is a constant).

When this deterioration function R [p] is Taylor-expanded, the following equation is obtained.
R [p] = 1-ap + a 2 p 2/2-a 3 p 3/6 + a 4 p 4 / 24- ··· ......... (3)
Then, when the degradation function R [p] is cut up to the first order term and R [p] = 1−ap is substituted into the simultaneous equations of the above equation (2),
Ia = (1-ap) KL,
Ib = (1-ap / n) KL / n (4)
When this is solved for the illuminance L and the integrated light quantity p, the above equation (1) is obtained.

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. Further, by adopting a form of R [p] = 1-ap that employs terms up to the first order by Taylor expansion of the deterioration function, the constant a indicating the speed of deterioration is not included, and the deterioration speed for each optical sensor. The illuminance L can be calculated with high accuracy even if there is a variation of.

In FIG. 4, the multiplication unit 11 corresponds to the first multiplication circuit, the subtraction unit 12 corresponds to the subtraction circuit, the multiplication unit 13 corresponds to the second multiplication circuit, and the division unit 14 corresponds to the first division circuit. It corresponds to the circuit.
Next, the operation of the first 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.

FIG. 5 is a diagram for explaining the effect of the present embodiment. In FIG. 5, the thick solid line represents the sensitivity characteristic when the present embodiment is applied, and the thin line represents the sensitivity characteristic when the correction is not performed as in the present embodiment.
As is clear from FIG. 5, when the illuminance calculation is not performed as in the present embodiment, the sensitivity is reduced when the integrated light quantity is 10 kL × H or more. It turns out that it corrects appropriately.

  Thus, in the first 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 reduced by the light reduction means. Outputs an output signal corresponding to the amount of incident light that has been emitted, and shows 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. Based on each output signal, the amount of external light is detected.

Thereby, the sensitivity fall can be corrected and the illuminance of the external light can be detected with high accuracy.
Also, by solving a simultaneous equation consisting of the correlation between the incident light amount and the output signal in one light detection unit and the correlation between the incident light amount and the output signal in the other light detection unit with the incident light amount and the integrated light amount, Even if the integrated light quantity is unknown, sensitivity correction can be performed, and a circuit for detecting the integrated light quantity is not required, so that the light quantity detection circuit can be simplified.

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.
Further, a first multiplier circuit that multiplies the output signal of the other light detection unit by the square of the reciprocal of the transmittance in the light reduction means, and the output value of the one light detection unit from the output value of the first multiplication circuit. A subtracting circuit for subtracting a signal; a second multiplying circuit for multiplying an initial sensitivity by a value obtained by subtracting 1 from the reciprocal of the transmittance; and dividing an output value of the subtracting circuit by an output value of the second multiplying circuit. Thus, a division circuit for calculating the light quantity of the external light is provided, so that the deterioration function is expressed in the form Exp [−ap] (a is a constant indicating the speed of deterioration, and p is the integrated light quantity. ), The sensitivity reduction can be appropriately corrected.

In addition, the deterioration function can be corrected with a simple circuit by setting the deterioration function to a Taylor expansion function up to the first order. Furthermore, since sensitivity correction can be performed without including a constant a indicating the speed of deterioration, even if there is a variation in deterioration speed among optical sensors, sensitivity correction is appropriately performed regardless of the variation. be able to.
In the first 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 reading values Ia and Ib of the respective light detection units are calculated. A lookup table as an input variable 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, if the initial sensitivity K and the transmittance of the color filter for darkening are constant within the allowable error range between products, the multiplication unit 13 is omitted, and the initial sensitivity K and transmission of the light detection unit without the light reduction means. The division unit 14 can be simplified to a configuration in which the output value of the subtraction unit 12 is divided by using a constant obtained by multiplying a value (n−1) obtained by subtracting “1” from the reciprocal number n of the rate. Furthermore, since the number to be divided is a constant, by adjusting the unit system with the device using the output value of this light amount detection circuit, the number to be divided can be set to 1, and the dividing unit 14 can be omitted. It can be simplified. That is, the output value of the subtracting unit 12 can be used as the illuminance L.

Furthermore, in the first embodiment, a case has been described in which terms up to the first order in the above equation (3) are adopted as the deterioration function R [p]. Can also be requested. For example, adopted terms up to the second order of the equation (3), when the R [p] = 1-ap + a 2 p 2/2, and solving the simultaneous equations represented by equation (1), the illumination L Is expressed by the following equation.

L = (− aIa + aIbn ⁴ + √ (−a ² n ² (Ia ² + Ib ² n ⁴ −2 IaIbn (1 + (− 1 + n) n)))) / (ak (−1 + n) (1 + n ² )) 5)
L = − (a (Ia + Ibn ⁴ ) + √ (−a ² n ² (Ia ² + Ib ² n ⁴ −2 IaIbn (1 + (− 1 + n) n)))) / (ak (−1 + n) (1 + n ² )) ...... (6)
Then, the illuminance L is calculated using the physically meaningful expression (the expression in which the illuminance L is a positive value) among the above expressions (5) and (6). Thereby, sensitivity correction can be performed with higher accuracy.

In the first embodiment, the deterioration function R [p] = Exp [−ap] has been described. However, the deterioration function R [p] corresponding to the type of the optical sensor can be applied. . Also in this case, the illuminance L can be obtained by obtaining a specific form of the deterioration function R [p] and solving the simultaneous equations represented by the above equation (2).
Next, a second embodiment of the present invention will be described.

In the second embodiment, while the initial sensitivity K is set to a fixed value in the first embodiment described above, the initial sensitivity K is made variable according to the integrated energization time.
FIG. 6 is a block diagram illustrating a configuration of the light amount detection circuit 1 according to the second embodiment. As shown in FIG. 6, the light amount detection circuit 1 of the present embodiment is the same as that shown in FIG. 6 except that an initial sensitivity correction unit 20 that changes and outputs the initial sensitivity K according to the integrated energization time is added. Since it has the same configuration as that of the single light quantity detection circuit 1, the description will focus on the different parts.

  The initial sensitivity correction unit 20 reads, for example, the integrated energization time T sequentially stored in a rewritable nonvolatile memory, and outputs the initial sensitivity K corresponding to the integrated energization time T to the reading unit 10. In the reading unit 10, the multiplication unit 13 multiplies the initial sensitivity K output from the initial sensitivity correction unit 20 by a constant (n−1), and outputs the result to the division unit 14. Yes.

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. At this time, the initial sensitivity K is calculated to be larger as the accumulated energization time T is longer.
In FIG. 6, the initial sensitivity correction unit 20 corresponds to the initial sensitivity correction circuit.

As described above, in the second embodiment, since the initial sensitivity is changed according to the integrated energization time, the illuminance detection value is appropriately corrected even when the sensitivity decrease depends on the integrated energization time during photometry. It is possible to realize illuminance detection with higher accuracy.
In each of the above embodiments, the case where a TFT photosensor is applied as the photosensor has been described. However, any photo-electrical device such as a known photodiode, phototransistor, photoTFT, photoSCR, photoconductor, photocell, or the like can be used. A conversion 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. 7 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. 7, 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, the light reduction filter of the light detection unit LS2 of the light amount detection circuit 1 is provided not on the light detection unit but on a corresponding part of the counter substrate, so that the light detection unit LS2 does not increase the manufacturing process. Incident light can be reduced.

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 (environment 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 figure for demonstrating the effect of this invention. It is a block diagram which shows the structure of the light quantity detection circuit in 2nd Embodiment. 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 ... Subtraction part, 13 ... Multiplication part, 14 ... Division part, 20 ... Initial sensitivity output part, 100 ... Electro-optical apparatus, LS1, LS2 ... Light detection Part, SW1, SW2 ... switch element, C1, C2 ... capacitor, Vs ... reference voltage

Claims (8)

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.
Each output read by the optical sensor reading unit based on the correlation between the incident light amount and the output signal in the one light detection unit and the correlation between the incident light amount and the output signal in the other light detection unit A light amount detection circuit for detecting a light amount of the external light based on a signal.   A first multiplication circuit that multiplies the output signal of the other light detection unit by a predetermined first constant, and a subtraction that subtracts the output signal of the one light detection unit from the output value of the first multiplication circuit. The light amount detection circuit according to claim 1, further comprising: a circuit, wherein an output value of the subtraction circuit is a light amount of the external light.   3. A first division circuit that divides an output value of the subtraction circuit by a predetermined second constant, wherein the output value of the first division circuit is used as the amount of the external light. The light quantity detection circuit described.   4. The light quantity detection circuit according to claim 2, wherein the first constant is a value obtained by squaring the reciprocal of the transmittance of the dimming unit.   5. The light amount detection circuit according to claim 3, wherein the second constant is a value obtained by multiplying the initial sensitivity by a value obtained by subtracting 1 from the reciprocal of the transmittance.   6. The light quantity according to claim 3, further comprising: a second multiplication circuit that multiplies the initial sensitivity by a predetermined third constant to generate the second constant. Detection circuit.   The light quantity detection circuit according to claim 3, further comprising an initial sensitivity correction circuit that corrects the initial sensitivity in accordance with an integrated energization time of the light detection unit. A light amount detection circuit according to any one of claims 1 to 7,
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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