JP2009257813A - Light intensity detection circuit and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light intensity detection circuit, capable of accurately detecting external light by briefly compensating reduction of sensitivity caused by degradation of an element in an optical sensor. <P>SOLUTION: An illuminance-output characteristic of a light-sensing part LS1 is approximated by a plurality of straight lines. By compensating an output value L<SB>LS1</SB>of the light-sensing part LS1 by using an inclination compensation value ASLP and an offset compensation value AOFF for making the respective approximation lines coincide with an ideal characteristic line I, dispersion in the optical sensor output characteristics is compensated. Here, a reduction of sensitivity due to degradation of element of an optical sensor is compensated, by calculating the reduction ratio of sensitivity of an optical sensor (light degradation ratio D) of the light-sensing part LS1 from the output value L<SB>LS1</SB>of the light-sensing part LS1 and the output value L<SB>LS2</SB>of a light-sensing part LS2, and compensating the offset compensation value AOF, according to the rate of light degradation D. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light amount detection circuit and a display device that can accurately detect external light.

In the conventional display device, ambient brightness is detected and brightness of the backlight is adjusted accordingly in order to ensure visibility and reduce power consumption of the backlight.
As such a display device, there is known a device in which an optical sensor is mounted on a glass substrate in a display panel to detect external light, and the backlight luminance is adjusted according to the illuminance of the detected external light ( For example, see Patent Document 1).

By the way, it is generally known that various optical sensors and optical elements such as CCDs suffer from a decrease in sensitivity due to element deterioration when receiving strong light for a long time. Furthermore, it has been found that the optical sensor formed on the glass substrate of the liquid crystal panel has a significant decrease in sensitivity as compared with a general-purpose optical sensor IC or the like.
In view of this, as a display device that suppresses element deterioration caused by the optical sensor on the glass substrate, a device that devises the driving condition of the TFT optical sensor is known (for example, see Patent Document 2).
JP 2000-131137 A JP 2007-316196 A

However, in the liquid crystal panel, while the TFT for the photosensor wants to secure a light leakage current, the TFT of the pixel sometimes wants to suppress the light leakage current. As in the display device described in Patent Document 2, the process conditions are as follows. In addition, it is difficult to suppress element degradation caused by the optical sensor on the glass substrate by devising the driving conditions of the TFT.
Therefore, the present invention is a light quantity detection that can accurately correct external light detection by simply correcting a sensitivity decrease due to deterioration of the optical sensor element even when the optical sensor is mounted on a glass substrate. It is an object to provide a circuit and a display device.

  In order to solve the above problems, a light amount detection circuit according to the present invention includes a light detection unit having a light sensor for detecting external light and a light sensor reading unit for reading an output signal of the light detection unit. The light detection unit includes a first light detection unit that receives the external light as incident light and outputs an output signal corresponding to the amount of the external light, and a light reduction unit that attenuates the external light. The light attenuated by the dimming means is incident as incident light, and is composed of a second light detection unit that outputs an output signal corresponding to the amount of the attenuated light, One of the first and second light detection units is detected based on the output signal of the first light detection unit and the output signal of the second light detection unit read by the light sensor reading unit. A light deterioration rate calculation unit for calculating a light deterioration rate in the output signal of the unit, and the one light A light amount detection unit for detecting the light amount of the external light based on the illuminance-output characteristics in the initial state of the knowledge unit, the output signal of the one light detection unit, and the light deterioration rate calculated by the light deterioration rate calculation unit; It is characterized by providing.

  As a result, it is possible to provide a function for correcting variations in the output characteristics of the optical sensor due to the manufacturing process and a function for correcting a decrease in sensitivity due to element degradation of the optical sensor, and to accurately detect the illuminance of external light. it can. Furthermore, since the above-mentioned variation correction and sensitivity correction can be performed inside the IC that drives the optical sensor, there is no need for a new addition or cost increase as a system.

The light amount detection circuit according to the present invention is characterized in that, in the above, the optical sensor reading unit reads each output signal of the first and second optical detection units in a time division manner.
Thereby, the optical sensor reading unit can also function as a reading unit for the first light detection unit and a reading unit for the second light detection unit. Therefore, it is sufficient to provide the number of photosensor reading units equal to the number of first photodetection units (or the number of second photodetection units), and each of the first photodetection unit and the second photodetection unit. Compared with the case where a reading unit is provided, the IC chip size and power consumption can be reduced.

Furthermore, in the light amount detection circuit according to the present invention, in the above, the optical sensor reading unit reads the output signal of the one light detection unit a predetermined number of times, and then reads the output signal of the other light detection unit once. It is characterized by.
As a result, the output signal of one light detection unit is usually read to detect the amount of external light, and the output signal of the other light detection unit is read every predetermined period to intervene in deriving the light deterioration rate. Therefore, it is possible to derive the light deterioration rate without hindering external light detection.

Furthermore, the light amount detection circuit according to the present invention is characterized in that, in the above, the optical sensor reading unit reads an output signal of the other optical detection unit at an arbitrary timing.
Thus, for example, when the light amount detection circuit is mounted on the display device, the output signal of the other light detection unit is read only immediately after the display is turned on or immediately after the display is refreshed. The output signal can be read. Therefore, it is not necessary to always switch and read the output signal of the first light detection unit and the output signal of the second light detection unit, and the power consumption can be reduced.

Moreover, the light quantity detection circuit according to the present invention is characterized in that, in the above, the light deterioration rate calculation unit calculates the light deterioration rate by taking a moving average.
As a result, even when the external light intensity changes significantly between the moment when the output signal of the first light detector is acquired and the moment when the output signal of the second light detector is acquired, the light deterioration rate is miscalculated. Can be suppressed.

  Furthermore, in the light amount detection circuit according to the present invention, in the above, the light amount detection unit uses an offset correction value and an inclination correction value for making the approximate line of the illuminance-output characteristic coincide with a predetermined ideal characteristic line. The light signal of the outside light is detected by correcting the output signal of the one light detector, and the offset correction value and the light deterioration rate calculated by the light deterioration rate calculator An optical deterioration correction unit that corrects at least one of the inclination correction values is provided.

As a result, it is possible to correct the variation in the output characteristics of the optical sensor by the logic processing, and it is possible to simply feed back the logic processing of the sensitivity correction including the calculation of the light deterioration rate to the variation correction logic of the output characteristics. .
Further, in the light amount detection circuit according to the present invention, in the above, when the light deterioration rate calculated by the light deterioration rate calculation unit is equal to or greater than a predetermined value, the light deterioration correction unit performs the offset correction value and the inclination correction. It is characterized by correcting at least one of the values.

Thereby, when the light deterioration rate is within the allowable range, the light deterioration correction logic process can be stopped.
Furthermore, in the light amount detection circuit according to the present invention, in the above, the light deterioration rate calculation unit has a ratio between an output signal of the first light detection unit and an output signal of the second light detection unit in advance. The light deterioration rate is calculated based on a light deterioration correction coefficient that is a ratio with a set initial ratio.

Thereby, the sensitivity correction function can be realized without changing the structure of the optical sensor.
Further, in the light amount detection circuit according to the present invention, in the above, the first and second light detection units include a thin film transistor as the light sensor, and a capacitor connected between a source electrode and a drain electrode of the thin film transistor. , Each having a switch element connected to one terminal of the capacitor and the source electrode, and the photosensor reading unit is charged to a reference voltage when the switch element is on, and when the switch element is off The voltage value of the capacitor, which decreases due to a leakage current generated when light is applied to the thin film transistor, is read as an output signal.

Thereby, the light quantity irradiated to the optical sensor unit can be detected by the fluctuation of the potential of the capacitor.
In addition, a display device according to the present invention includes any one of the light amount detection circuits described above, an illumination unit that illuminates the display panel, and a control unit that controls the illumination unit based on an output value of the light amount detection circuit. It is characterized by that.

  Thereby, the light intensity detection circuit can accurately detect the illuminance of outside light and appropriately control the illuminating unit such as the backlight. Therefore, the display device that ensures the visibility of the display panel and reduces the power consumption can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a liquid crystal display device 1 as a display device of the present embodiment. Here, a transflective liquid crystal display device is illustrated as the liquid crystal display device 1. 2 is a cross-sectional view taken along line XX of FIG.
As shown in FIGS. 1 and 2, the display panel of the liquid crystal display device 1 is made of an active matrix substrate (hereinafter referred to as a thin film transistor (TFT) or the like made of a transparent insulating material such as a glass substrate and having a thin film transistor (TFT) or the like mounted thereon. A liquid crystal layer 14 is formed between a color filter substrate (hereinafter referred to as a CF substrate) 25 having a color filter or the like formed on the surface, and polarizing plates are provided on the upper and lower surfaces of the two substrates. The configuration is pasted.

  Of these, the TFT substrate 2 has a gate line 4 and a source line 5 formed in a matrix in the display area DA, a pixel electrode is formed in a portion surrounded by the gate line 4 and the source line 5, and the gate line 4 A thin film transistor (TFT) as a switching element connected to the pixel electrode is formed at the intersection between the source line 5 and the source line 5. Reference numeral LS1 is a light detection unit for detecting external light, and reference numeral LS2 is a light detection unit for light degradation reference, which is provided at the outer peripheral edge of the display area DA as will be described later. These wirings, TFTs, and pixel electrodes are schematically shown as a first structure 3 in FIG.

  As shown in FIG. 1, the TFT substrate 2 is provided with a flexible wiring substrate FPC for connecting to an image supply device (not shown) for driving the liquid crystal display device 1 on the short side portion thereof. Data lines and control lines led out from the image supply device through are connected to the liquid crystal driver IC. Signals such as a VCOM signal, a source signal, and a gate signal for driving the liquid crystal are generated in the liquid crystal driver IC and supplied to the common line 11, the source line 5, and the gate line 4 on the TFT substrate 2, respectively.

  A plurality of transfer electrodes 10 a to 10 d are provided at the four corners of the TFT substrate 2. These transfer electrodes 10a to 10d are directly connected to each other through a common line 11 or to each other in a liquid crystal driver IC. Each of the transfer electrodes 10a to 10d is electrically connected to a counter electrode 26 described later, and a counter electrode voltage output from the liquid crystal driver IC is applied to the counter electrode 26.

  In the CF substrate 25, a color filter composed of a plurality of colors such as R (red), G (green), and B (blue) and a black matrix are formed on the surface of the glass substrate. The CF substrate 25 is disposed so as to face the TFT substrate 2, and the black matrix is disposed at a position corresponding to at least the gate lines 4 and the source lines 5 of the TFT substrate 2, and a color filter is formed in a region partitioned by the black matrix. Is provided. These color filters and the like are schematically shown as the second structure 27 in FIG. The CF substrate 25 is further provided with a counter electrode 26 made of a transparent electrode made of indium tin oxide or the like, and the counter electrode 26 is formed over the entire display area DA.

The sealing material 6 is applied around the display area DA of the TFT substrate 2 except for an injection port (not shown). Further, the contact material 10A for connecting both the substrates is made of, for example, conductive particles whose surfaces are plated with metal and a thermosetting resin. Then, the bonding of the TFT substrate 2 and the CF substrate 25 is performed by the following procedure, for example.
First, the TFT substrate 2 is set in the first dispenser device, and the sealing material 6 is applied in a predetermined pattern. Next, the TFT substrate 2 is set in the second dispenser device, and the contact material 10A is attached to each transfer electrode 10a˜. Apply on 10d. After that, the spacers 15 are uniformly distributed over the display area DA of the TFT substrate 2 and a temporary fixing adhesive is applied to the portion of the CF substrate 25 where the sealing material 6 and the contact material 10A come into contact. Thereafter, the TFT substrate 2 and the CF substrate 25 are bonded together, and the temporary fixing adhesive is cured to complete the temporary fixing.

Then, when both the temporarily fixed substrates 2 and 25 are heat-treated, the thermosetting resin of the sealing material 6 and the contact material 10A is cured, and an empty liquid crystal display panel is completed. When the liquid crystal 14 is injected into the empty liquid crystal display panel from an injection port (not shown) and the injection port is closed with a sealing material, the transflective liquid crystal display device 1 is completed.
A backlight having a well-known light source (or illumination unit) (not shown), a light guide plate, a diffusion sheet, and the like is disposed below the TFT substrate 2. The luminance of the backlight is controlled by a backlight control circuit described later provided outside the display panel.

Next, the structure of the light detection units LS1 and LS2 will be described.
FIG. 3A is a cross-sectional view of an optical sensor and a switch element that constitute the optical detection unit LS1.
The thin film transistor (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 G1 _L of the TFT photosensor, one terminal Ca1 of the capacitor C1, and the gate electrode G1 _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, a semiconductor made of amorphous silicon, polycrystalline silicon, or the like is disposed on the gate electrode G1 _L of the TFT photosensor and on the gate electrode G1 _S of the TFT constituting the switch element SW1 via a gate insulating film 17, respectively. Layers 191 _L and 191 _S are formed.
On the gate insulator 17, a source electrode S1 _L and a drain electrode D1 _{L of} a TFT photosensor made of a metal such as aluminum or molybdenum, and a source electrode S1 _S and a drain electrode D1 of a TFT constituting one switch element SW1 are provided. _S is provided in contact with each of the semiconductor layers 191 _L and 191 _S.

Among these, the source electrode S1 _L of the TFT photosensor and the drain electrode D1 _S of the TFT constituting the switch element SW1 are connected to be extended to form the other terminal Cb1 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 light shielding layer 211 so as not to be affected by external light.

The surface of the TFT photosensor is covered with a color filter 22 having a transmittance of 1 / n as a dimming means.
Further, on the opposite CF substrate 25 on which the light detection unit LS1 is disposed, as shown in FIG. 2, a counter electrode 26 is extended to a position facing the light detection unit LS1, and the light detection unit LS1 is connected to the light detection unit LS1. The drain electrode D1 _L of the TFT photosensor to be configured and the other terminal Cb1 on the ground terminal GR side of the capacitor C1 are connected to the counter electrode 26 via the transfer electrode 10b.

FIG. 3B is a cross-sectional view of the light sensor and the switch element that constitute the light detection unit LS2.
The light detection unit LS2 is different from the light detection unit LS1 shown in FIG. 3A except that the surface of the TFT optical sensor is covered with the color filter 22 but the color filter 22 is not provided. Has the same configuration as that of the light detection unit LS1, and the pair of light detection units LS1 and LS2 have the same photoelectric conversion characteristics.

That is, the color filter 22 is for dimming so that the incident light amount of the light detection unit LS1 is 1 / n (n> 0) of the incident light amount of the light detection unit LS2, and the light detection unit LS1. The light attenuated by the color filter 22 is incident as incident light, and external light is incident on the light detection unit LS2 as incident light.
3A and 3B show the case where the color filter 22 is formed on the TFT substrate 2 for the sake of clarity, but the color filter 22 is formed on the CF substrate 25 as shown in FIG. In this case, the color filter 22 is formed in the portion corresponding to the light detection unit LS1 of the CF substrate 25, and the color filter 22 is not formed in the portion corresponding to the light detection unit LS2.

FIG. 4 is a circuit diagram illustrating a configuration of the light detection units LS1 and LS2. Since the light detection unit LS1 and the light detection unit LS2 have the same circuit configuration, here, the light detection units LS1 and LS2 are collectively referred to as the light detection unit LS, and the switch elements SW1 and SW2 are the switch elements SW and capacitors. C1 and C2 will be described as capacitors C. The gate electrodes G1 _L and G2 _L are the gate electrode G _L , the source electrodes S1 _L and S2 _L are the source electrode S _L , and the drain electrodes D1 _L and D2 _L are the drain electrode D _L.

Light detecting section LS, the capacitor C is connected in parallel between the drain electrode D _L and the source electrode S _L of the TFT ambient light photosensor, one terminal of the source electrode S _L and the capacitor C via the switching element SW reference connected to a voltage source, further, a configuration in which the other terminal of the drain electrode D _L and the capacitor C of the TFT ambient light sensor is connected to the counter electrode (VCOM).
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. By this charging, both ends of the capacitor C are charged with a potential difference between the reference voltage Vs and the counter electrode voltage VCOM. However, the gate electrode G _L is charged with the gate voltage GV having the opposite polarity, and thus 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 is read (detected), whereby the backlight or the like can be controlled.
Here, the charging timing and one discharge period of the light detection unit LS1 and the light detection unit LS2 are set to be equal to each other. In addition, 1 discharge period is a period from the charging start time of the capacitor | condenser C to the next charging start time, and is set to 0.5 [s]-1.0 [s] in this embodiment, for example. Further, the reading time from the start of charging until the charging voltage of the capacitor C is read is also set equal in the light detection units LS1 and LS2.

FIG. 5 is a block diagram showing a detailed configuration of the backlight control circuit.
As shown in FIG. 5, the backlight control circuit includes a reading unit 31 that acquires analog information obtained from the light detection units LS1 and LS2, a sensitivity correction value output unit 32, and an optical sensor variation correction unit 33 (hereinafter referred to as “photosensor variation correction unit 33”). A correction processing unit 33), a filter processing unit 34, a B / L luminance conversion unit 35, and a B / L luminance control unit 36 that controls the backlight 37.

The reading unit 31 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. Further, the reading unit 31 switches the switch SW _{LS in} FIG. 5 and reads the charging voltage charged in the capacitor C1 or C2 of the light detection unit LS1 or LS2 at a predetermined timing. Instead of the method of directly reading the charging voltage, the discharging time until the voltage drops to a predetermined voltage may be read.

FIG. 6 is a timing chart of optical sensor output detection.
As shown in FIG. 6, the reading unit 31 reads the outputs of the light detection units LS1 and LS2 in a time-sharing manner. Specifically, every time the output of the light detection unit LS1 is read a predetermined number of times (here, 13 times), the output of the light detection unit LS2 is read once. That is, at the timing of reading the output of the light detection unit LS2, the output detection of the light detection unit LS1 is in a standby state.

Then, the analog information obtained this way to convert A / D, the illuminance data L _LS1 from the light detection unit LS1, illuminance data L _LS2 from the light detecting portion LS2 is obtained, the illuminance data L _LS1 sensitivity correction value The illuminance data L _LS2 is output to the sensitivity correction value output unit 32 and output to the output unit 32 and the correction unit 33.
The sensitivity correction value output unit 32 calculates a light deterioration rate D indicating the degree of sensitivity decrease due to element deterioration in the light sensor of the light detection unit LS1 based on the illuminance data L _LS1 and L _LS2 , and the light deterioration rate D Then, a sensitivity correction value COFF, which will be described later, is calculated and output.

FIG. 7 is a block diagram showing details of the sensitivity correction value output unit 32.
As shown in FIG. 7, the sensitivity correction value output unit 32 includes a deterioration coefficient calculation unit 32a, a memory circuit 32b, a light deterioration rate calculation unit 32c, and a sensitivity correction value calculation unit 32d.
Illuminance data L _LS1 and L _LS2 are input to the deterioration coefficient calculation unit 32a. The deterioration coefficient calculation unit 32a first has a measurement ratio α (= L _LS1) which is a ratio between the illuminance data L _LS1 and the illuminance data L _LS2. / L _LS2 ) is calculated. Next, the deterioration coefficient calculation unit 32a reads the initial ratio β, which is the measurement ratio in the initial state, stored in the memory circuit 32b in advance, and the light deterioration correction coefficient K (the ratio between the measurement ratio α and the initial ratio β). = Α / β).

  The light deterioration correction coefficient K calculated by the deterioration coefficient calculating unit 32a is input to the light deterioration rate calculating unit 32c, and the light deterioration rate calculating unit 32c calculates the light deterioration rate D based on the light deterioration correction coefficient K. . Specifically, the light deterioration rate D is acquired with reference to a look-up table stored in the memory circuit 32b and corresponding to the light deterioration correction coefficient K and the light deterioration rate D. The light deterioration rate D acquired in this way is output to the sensitivity correction value calculation unit 32d.

At this time, it is preferable to calculate the light deterioration rate D by taking a moving average. In this embodiment, since the reading unit 31 reads the outputs of the light detection units LS1 and LS2 in a time-sharing manner, the _ambient light illuminance is remarkably _generated at the moment when the illuminance data L _LS1 is acquired and at the moment when the illuminance data L _LS2 is acquired. May be different. Therefore, by taking the moving average, it is possible to suppress erroneous calculation of the light deterioration rate D even when the illuminance of outside light changes rapidly as described above.

In order to reduce the size of the lookup table, data may be thinned out and stored. In this case, when the value of the light deterioration correction coefficient K is not included in the lookup table, the light deterioration rate D may be derived by performing an interpolation operation using neighboring data.
Here, the light deterioration correction coefficient K will be described.
Since the optical sensor output is directly proportional (or inversely proportional) to the amount of incident light in the ideal state, assuming that the initial sensitivity of the light detection unit LS1 is Xa0 and the initial sensitivity of the light detection unit LS2 is Xb0, the light detection unit LS1 at the illuminance L0. The optical sensor output Pa (L0 / n) and the optical sensor output Pb (L0) of the light detection unit LS2 at the illuminance L0 are expressed as follows.

Pa (L0 / n) = Xa0 · (L0 / n),
Pb (L0) = Xb0 · (L0) (1)
Thus, the initial ratio β is Pa (L0 / n) / Pb (L0) = (1 / n) · (Xa0 / Xb0). This initial ratio β is a function of the initial sensitivities Xa0, Xb0 and n irrespective of the external light illuminance L0, and the measurement ratio at an arbitrary illuminance L can be set as the initial ratio β.

  Further, the photosensor deteriorates due to light exposure and the photosensitivity is lowered, so that the photocurrent is lowered with respect to the initial state. Such a decrease in photosensitivity can be obtained by a function R (p) of the integrated light quantity p, which is the total of the light quantity irradiated from the initial state. If the integrated light amount in the light detection unit LS2 after a certain time has elapsed is p, the integrated light amount in the light detection unit LS1 is p / n.

Accordingly, when the sensitivity of the light detection unit LS1 after receiving the light exposure of the integrated light amount p / n is Xa1, and the sensitivity of the light detection unit LS2 after receiving the light exposure of the integrated light amount p is Xb1, the deterioration in the illuminance L1. The light sensor output Paa (L1 / n) of the subsequent light detection unit LS1 and the light sensor output Pbb (L1) of the light detection unit LS2 after deterioration in the illuminance L1 are expressed as follows.
Paa (L1 / n) = Xa1 · (L1 / n) = R (p / n) · Xa0 · (L1 / n),
Pbb (L1) = Xb1 · L1 = R (p) · Xb0 · L1 (2)
Accordingly, the measurement ratio α is Paa (L1 / n) / Pbb (L1) = (1 / n) · (R (p / n) / R (p)) · (Xa0 / Xb0). Since the measurement ratio α does not depend on the external light illuminance L1, the same measurement ratio can be obtained even if the measurement ratio α is obtained with an arbitrary illuminance L.

From the initial ratio β and the measurement ratio α thus determined, the light degradation correction coefficient K = α / β = (Paa (L1 / n) / Pbb (L1)) / (Pa (L0 / n) / Pb (L0)) = R (p / n) / R (p), which is calculated as a function of the integrated light quantity p.
With this light deterioration correction coefficient K, it is possible to know the degree of deterioration in the TFT light sensors of the light detection units LS1 and LS2.

Next, the light deterioration rate D will be described.
The photodegradation rate D is the light sensor output Paa (L1 / n) of the light detection unit LS1 measured when light of a certain illuminance L1 is incident, and the light sensor output Pa (L1 / n) in the initial state. The ratio is expressed as D = Paa (L1 / n) / Pa (L1 / n) = R (p / n). This value is determined by the deterioration state regardless of the amount of incident light.

The light deterioration rate D corresponds to the light deterioration correction coefficient K described above, and the light deterioration rate D can be obtained from the light deterioration correction coefficient K by obtaining this correspondence in advance.
The sensitivity correction value calculation unit 32d refers to a lookup table that is stored in advance in the memory circuit 32b and associates the light deterioration rate D with the sensitivity correction value COFF, obtains the sensitivity correction value COFF from the light deterioration rate D, and This is output to the correction unit 33 in FIG. At this time, when the light deterioration rate D is less than a predetermined value (for example, 10%), the sensitivity correction value COFF is set to zero. Since the light deterioration rate D and the sensitivity correction value COFF can be approximated by a linear function as shown in FIG. 8, the sensitivity correction value COFF can also be calculated from a calculation formula.

The illuminance data L _LS1 output from the reading unit 31 and the sensitivity correction value COFF output from the sensitivity correction value output unit 32 are input to the correction unit 33, and the correction unit 33 determines the light detection unit based on these data. The illuminance L of the incident light of LS1 is calculated.

FIG. 9 is a diagram for explaining the procedure for calculating the illuminance L. FIG.
In an ideal state where light leakage due to ambient temperature heat leakage or light other than external light (backlight leakage light, etc.) can be ignored, the output of the photosensor is directly proportional to (or inversely proportional to) the incident light illuminance as shown by the broken line I. )

However, when an optical sensor is formed on a glass substrate as in the present embodiment, sufficient photocurrent may not be ensured in a low illuminance region, or the output may be saturated in a high illuminance region. Therefore, the output characteristics of the optical sensor are nonlinear characteristics as indicated by the solid line Iout. Furthermore, the output intensity of the optical sensor shifts due to variations in the manufacturing process.
Therefore, in consideration of such variations in the output characteristics of the optical sensor, the optical sensor output value L _LS1 is corrected to accurately detect the light. In addition, as shown in FIG. 10, when the optical sensor receives strong light for a long time and the integrated illuminance increases, the sensitivity decreases due to element deterioration and the optical sensor output changes. The optical sensor output value L _LS1 is corrected in consideration of D.

Specifically, as shown in FIG. 9, the incident light illuminance has three illuminances: low illuminance (L0 to L1 [Lx]), medium illuminance (L1 to L2 [Lx]), and high illuminance (L2 to L3 [Lx]). The area is divided into regions, and the output characteristics of the optical sensor in each region are approximated by straight lines Iout1, Iout2, and Iout3, respectively, and an inclination correction value ASLP and an offset correction value AOFF defined so that these approximate lines coincide with the ideal straight line I. _{Is used} to correct the light sensor output value L _LS1 to calculate the illuminance L.

Here, the straight lines Iout1 to Iout3 are straight lines connecting the operating point at the maximum illuminance and the operating point at the minimum illuminance in each region.
The inclination correction values ASLP1 to ASLP3 [unsigned (m−1) bits] and offset correction values AOFF1 to AOFF3 [signed m bits] are defined so that these straight lines Iout1 to Iout3 coincide with the ideal straight line I, respectively. To do.

Then, the illuminance L after variation correction is expressed by the following equation (1) using the inclination correction value ASLP and the offset correction value AOFF.
L = (L _LS1 + AOFF) × ASLP / 2 ^m−1 (3)
Here, the set of correction values (ASLP, AOFF), depending on the optical sensor output value L _LS1, inclination correction value (ASLP1, AOFF1), set to one of (ASLP2, AOFF2) and (ASLP3, AOFF3) Is done.

Further, if the optical sensor output values corresponding to the illuminances L0 and L1 are Pout (L0) and Pout (L1), respectively, and the ideal output values corresponding to the illuminances L0 and L1 are I (L0) and I (L1), respectively, a straight line The inclination correction values ASLP1 and AOFF1 corresponding to Iout1 are each expressed by the following equations.
AOFF1 = {I (L1) × Pout (L0) −I (L0) × Pout (L1)} / {I (L0) −I (L1)} (4)
ASLP1 = {I (L0) / (Pout (L0) + AOFF1) + I (L1) / (Pout (L1) + AOFF1)} × 2 ^m−2 (5)
Further, if the optical sensor output values corresponding to the illuminances L2 and L3 are Pout (L2) and Pout (L3), respectively, and the ideal output values corresponding to the illuminances L2 and L3 are I (L2) and I (L3), respectively, a straight line The inclination correction values ASLP2 and AOFF2 corresponding to Iout2 are expressed by the following expressions (6) and (7), and the inclination correction values ASLP2 and AOFF2 corresponding to the straight line Iout3 are expressed by the following expressions (8) and (9).

AOFF2 = {I (L2) × Pout (L1) −I (L1) × Pout (L2)} / {I (L1) −I (L2)} (6)
ASLP2 = {I (L1) / (Pout (L1) + AOFF2) + I (L2) / (Pout (L2) + AOFF2)} × 2 ^m−2 (7)
AOFF3 = {I (L3) × Pout (L2) −I (L2) × Pout (L3)} / {I (L2) −I (L3)} (8)
ASLP3 = {I (L2) / (Pout (L2) + AOFF3) + I (L3) / (Pout (L3) + AOFF3)} × 2 ^m−2 (9)
In this way, the output characteristic Iout of the optical sensor is approximated by connecting a plurality of linear functions, and the illuminance L is detected based on the approximate line and the optical sensor output value L _LS1 .

Further, in the present embodiment, the offset correction value AOFF is corrected based on the sensitivity correction value COFF output from the sensitivity correction value output unit 32. That is, as shown in the following equation (10), the sensitivity correction value COFF corresponding to the light deterioration rate D is added to the offset correction value AOFF, thereby correcting the offset correction value AOFF and calculating the illuminance L.
L = (L _LS1 + AOFF + COFF) × ASLP / 2 ^m−1 (10)
In this way, the correction unit 33 first determines which of the three illuminance regions the illuminance L _LS1 output from the reading unit 31 is, and based on the determination result, the above ( Select an appropriate correction value set from among the correction value sets (ASLP1, AOFF1), (ASLP2, AOFF2), and (ASLP3, AOFF3) calculated based on equations (4) to (9) and stored in the memory. To do. Next, the selected correction value set is corrected based on the sensitivity correction value COFF corresponding to the light deterioration rate D output from the sensitivity correction value output unit 32, and the final correction value set (ASLP, AOFF + COFF) is corrected. ) Then, using the correction value group (ASLP, AOFF + COFF) obtained in this way, the corrected illuminance L is calculated based on the above equation (10).

The corrected illuminance L is obtained by correcting variations in the initial output characteristics of the optical sensor and a decrease in sensitivity due to element degradation.
Further, the illuminance L output from the correction unit 33 is input to the filter processing unit 34 in FIG. 5, and noise is removed by a median filter. Here, the median filter outputs, for example, the median value of 13 pieces of data.

Then, the B / L luminance conversion unit 35 compares the illuminance L filtered by the filter processing unit 34 with a predetermined illuminance threshold value, and outputs the result to the B / L luminance control unit 36. Here, the illuminance threshold value is set to a value that optimizes the display appearance with respect to the brightness of the corresponding backlight and the illuminance of the external light, or to reduce power consumption.
Then, the B / L luminance control unit 36 controls the backlight 37 to an optimal luminance based on the comparison result in the B / L luminance conversion unit 35.

  In FIG. 5, the light detection unit LS2 corresponds to the first light detection unit, the light detection unit LS1 corresponds to the second light detection unit, the reading unit 31 corresponds to the optical sensor reading unit, and the optical sensor variation correction is performed. The unit 33 corresponds to the light amount detection unit, the sensitivity correction value output unit 32 corresponds to the light deterioration rate calculation unit, and the filter processing unit 34, the B / L luminance conversion unit 35, and the B / L luminance control unit 36 serve as the control unit. Correspondingly, the backlight 37 corresponds to the illumination part.

Next, the operation of the first embodiment of the present invention will be described.
First, the liquid crystal display device 1 is irradiated with light in four stages such that the illuminance of incident light of the light detection unit LS1 becomes L0, L1, L2, and L3, respectively, and the optical sensor output value of the light detection unit LS1 at each illuminance. Pout (L0), Pout (L1), Pout (L2), and Pout (L3) are acquired. Then, using these photosensor output values Pout (L0) to Pout (L3), the inclination correction values ASLP1 to ASLP3 and the offset correction values AOFF1 to AOFF3 are calculated based on the above equations (4) to (9). And stored in the memory.

Assuming that the display on the liquid crystal panel is turned on at time t0 in FIG. 6, at time t1, the reading unit 31 reads the charging voltage charged in the capacitor C1 of the light detection unit LS1, and the illuminance data L from the read value. Calculate _LS1 .
At this time, assuming that the low-illuminance external light that satisfies L _LS1 ≦ Pout (L1) is applied to the TFT optical sensor, the correction unit 33 uses the above equations (4) and (5). The calculated offset correction value AOFF1 and inclination correction value ASLP1 are selected as the offset correction value AOFF and inclination correction value ASLP, and the illuminance L is calculated based on the above equation (10). Here, it is assumed that the sensitivity correction value COFF is set to zero in the initial state.

The illuminance L has been subjected to variation correction of the optical sensor output characteristics, and is approximately equal to the actual illuminance of incident light.
On the other hand, when high-illuminance outside light that satisfies L _LS1 > Pout (L2) is applied to the TFT optical sensor, the correction unit 33 calculates based on the above equations (8) and (9). The offset correction value AOFF3 and the inclination correction value ASLP3 are selected as the offset correction value AOFF and the inclination correction value ASLP, and the illuminance L is calculated based on the above equation (10).

As described above, since the inclination correction value ASLP and the offset correction value AOFF are changed depending on whether the optical sensor output value is in the low illuminance region or the high illuminance region, the optical sensor output characteristic is nonlinear. In addition, correction corresponding to variations in output characteristics of each illuminance region is possible, and illuminance calculation can be performed appropriately.
This external light detection using the light detection unit LS1 is repeated 13 times until time t2.

At time t3, the reading unit 31 reads the charging voltage charged in the capacitor C2 of the light detection unit LS2, and calculates the illuminance data L _LS2 from the read value.
The sensitivity correction value output unit 32 is a deterioration factor calculation unit 32a, and a measurement ratio α (= L _LS1 / L _LS2) which is a ratio between the illuminance data L _LS1 acquired at time t2 and the illuminance data L _LS2 acquired at time t3. ) And a light deterioration correction coefficient K (= α / β) that is a ratio between the measurement ratio α and the initial ratio β stored in the memory circuit 32b in advance. Further, the light deterioration rate D is obtained from the light deterioration correction coefficient K with reference to the lookup table stored in the memory circuit 32b.

FIG. 11 is a diagram illustrating changes in the optical sensor outputs of the light detection units LS1 and LS2.
The light detection unit LS1 has a dimming unit, and the amount of incident light is different between the light detection unit LS1 and the light detection unit LS2. Therefore, as shown in FIG. 11, the optical sensor of the light detection unit LS2 having a large amount of received light undergoes faster element deterioration, and the output ratio of the two optical sensors changes according to the integrated illuminance. Therefore, it is possible to estimate the degree of element deterioration in the optical sensor of the light detection unit LS1 based on the change in the output ratio.

Further, the sensitivity correction value calculation unit 32d refers to the lookup table stored in the memory circuit 32b, acquires the sensitivity correction value COFF from the light degradation rate D, and stores it in the memory.
At this time t3, the illuminance data L _LS1 is not acquired and the ambient light is not detected. Therefore, the on / off control of the backlight 37 maintains the state at the time t2.
At time t4, the reading unit 31 reads the charging voltage charged in the capacitor C1 of the light detection unit LS1, and calculates the illuminance data L _LS1 from the read value. Then, the correction unit 33 determines the illuminance area of the external light based on the illuminance data L _LS1 and selects the offset correction value AOFF and the inclination correction value ASLP corresponding to the illuminance area. Also, the sensitivity correction value COFF stored in the memory at time t3 is read, and the illuminance L is calculated based on the above equation (10).

The illuminance L calculated in this way is data that has been subjected to correction of variation in optical sensor output characteristics and correction of reduction in sensitivity due to element degradation, and is approximately equal to the actual incident light illuminance.
Note that when the light deterioration rate D is less than 10%, the sensitivity correction value COFF is set to zero. Therefore, correction of sensitivity reduction due to element deterioration is not performed, and the integrated illuminance increases and the light deterioration rate D becomes 10%. When the value is greater than or equal to%, the sensitivity correction value COFF is calculated, and the reduction in sensitivity due to element deterioration is corrected.

FIG. 12 is a diagram for explaining the effect of this embodiment. As is clear from FIG. 12, when the sensitivity reduction is corrected based on the sensitivity correction value COFF corresponding to the light deterioration rate D, the change in the optical sensor output is compared with the case without correction. It can be seen that it can be resolved with high accuracy.
In general, in general-purpose optical sensor ICs, the allowable range of output error is often set to about 20% or less. Therefore, by performing sensitivity correction when the light degradation rate D becomes 10% or more as in the present embodiment, a photosensor with higher accuracy than a general-purpose photosensor IC can be obtained.

As described above, the first embodiment includes the function of correcting the variation in the output characteristics of the optical sensor due to the manufacturing process and the function of correcting the decrease in sensitivity due to the element degradation of the optical sensor. Can be detected.
At this time, the illuminance-output characteristic of the light detection unit is approximated by connecting a plurality of linear functions, and the amount of incident light is detected based on the approximate line and the output value of the light detection unit. Can be corrected with high accuracy even when the is non-linear, and the illuminance of outside light can be accurately detected.

Further, the approximate line divides the illuminance-output characteristic of the light detection unit into at least two external light illuminance regions, and is a straight line connecting the operating point at the maximum illuminance and the operating point at the minimum illuminance in each region. Therefore, the approximate line used for detecting the amount of external light can be set relatively easily.
Further, the amount of external light is detected by correcting the output value of the light detection unit using the offset correction value and the inclination correction value for matching each straight line to the ideal characteristic line. Variations can be corrected by logic processing, and sensitivity correction logic processing including calculation of the light deterioration rate can be simply fed back to the output characteristic variation correction logic.

Further, since the optical sensor reading unit reads each output signal of the pair of optical detection units in a time-sharing manner, it is not necessary to provide the optical sensor reading unit in each optical detection unit. Therefore, the IC chip size and power consumption can be reduced as compared with the case where each light detection unit is provided with a reading unit.
Furthermore, since the optical sensor reading unit reads the output signal of one photodetection unit a predetermined number of times, and then reads the output signal of the other photodetection unit once, it normally reads the output signal of one photodetection unit. The amount of external light can be detected and the output signal of the other light detection unit can be read every predetermined period to intervene in the derivation of the light deterioration rate. A derivation can be made. At this time, by matching the predetermined number of times with the number of data of the median filter, the filter processing can be performed appropriately.

In addition, since the light deterioration rate is calculated based on the light deterioration correction coefficient that is the ratio between the output signal ratio of the pair of light detection units with different incident light amounts and the initial ratio stored in advance, the structure of the optical sensor The sensitivity correction function can be realized without any change.
Furthermore, since the light degradation rate is calculated by taking a moving average, when acquiring the output signal of each light detection unit in time division, the moment when the output signal of one light detection unit is acquired and the other light detection Even when the external light intensity changes significantly from the moment when the output signal of the unit is acquired, it is possible to prevent the light deterioration rate from being erroneously calculated.

  Further, since the sensitivity correction is performed when the light deterioration rate is equal to or greater than a predetermined value, the sensitivity correction process can be stopped when the light deterioration rate is within an allowable range. Therefore, it is possible to prevent the sensitivity correction process from being erroneously operated by deriving the light deterioration rate due to the variation in the initial characteristics. Furthermore, if the allowable range is set to be stricter than the allowable range of a general-purpose optical sensor IC, a highly accurate optical sensor can be obtained.

Furthermore, since the output value correction of the optical sensor can be completed inside the IC that drives the optical sensor, the sensitivity can be reduced due to deterioration of the device due to long-term use without any new additions or cost increase as a system. By correcting, it is possible to obtain a highly accurate external light detection result over a wide range from low illuminance to high illuminance.
In addition, since the light amount detection circuit as described above is applied to a display device that performs backlight control, the backlight can be appropriately controlled using the accurate external light illuminance detected by the light amount detection circuit. A display device that can ensure visibility and reduce power consumption can be obtained.

In the first embodiment, the case where the optical sensor output of the light detection unit LS2 is acquired once every time the optical sensor output of the light detection unit LS1 is acquired 13 times has been described. However, the light detection unit LS1 The number of times of obtaining the optical sensor output can be set to an arbitrary number.
Next, a second embodiment of the present invention will be described.
In the second embodiment, the illuminance data L _LS2 from the light detection unit _LS2 is acquired at a predetermined timing such as immediately after the display is turned on or immediately after refreshing.

FIG. 13 is a timing chart of optical sensor output detection in the second embodiment.
When it is detected at time 10 that the display of the liquid crystal panel is turned on by the SLPOUT command, at time t11, the reading unit 31 reads the charging voltage charged in the capacitor C2 of the light detection unit LS2, and from the read value. Illuminance data L _LS2 is calculated.
Next, at time t12, the reading unit 31 reads the charging voltage charged in the capacitor C1 of the light detection unit LS1, and calculates the illuminance data L _LS1 from the read value. Further, the sensitivity correction value output unit 32 uses the deterioration coefficient calculation unit 32a to calculate a measurement ratio α (= L _LS1 / L _LS2 ) that is a ratio between the illuminance data L _LS1 and the illuminance data L _LS2 acquired at time t11. In addition to the calculation, a light deterioration correction coefficient K (= α / β), which is a ratio between the measurement ratio α and the initial ratio β stored in advance in the memory circuit 32b, is calculated. Further, the light deterioration rate D is obtained from the light deterioration correction coefficient K with reference to the lookup table stored in the memory circuit 32b. Further, the sensitivity correction value calculation unit 32d refers to the lookup table stored in the memory circuit 32b, acquires the sensitivity correction value COFF from the light degradation rate D, and stores it in the memory.

Then, the correction unit 33 discriminates the illuminance area of the outside light based on the illuminance data L _LS1 , selects the offset correction value AOFF and the inclination correction value ASLP according to the illuminance area, and also the sensitivity correction value stored in the memory. COFF is read and the illuminance L is calculated based on the above equation (10).
The illuminance L calculated in this way has been subjected to correction of variations in optical sensor output characteristics and correction of sensitivity reduction due to element deterioration, and has a value substantially equal to the actual incident light illuminance.

The external light detection using the light detection unit LS1 is repeated until the refresh operation is performed at time t13.
At time t13, when it is detected that the refresh operation has been performed by the SLPOUT command, at time t14, the reading unit 31 reads the charging voltage charged in the capacitor C2 of the light detection unit LS2, and reads the read value. Illuminance data L _LS2 is calculated from

At time t15, the reading unit 31 calculates the illuminance data L _LS1 , and the sensitivity correction value output unit 32 calculates the light deterioration rate D based on the illuminance data L _LS1 and the illuminance data L _LS2 acquired at time t14. Ask. Further, the sensitivity correction value calculation unit 32d acquires the sensitivity correction value COFF from the light deterioration rate D and stores it in the memory.
In this way, the sensitivity correction value COFF is updated, and thereafter, the sensitivity correction is performed with the sensitivity correction value COFF obtained at time t15 until the SLPOUT command is detected again.

As described above, in the second embodiment, the illuminance data is acquired from the degradation detection light detection unit only immediately after the display of the liquid crystal panel is turned on or after the refresh operation is performed. It is not necessary to always switch and read the illuminance data from the light detection unit and the illuminance data from the deterioration detection light detection unit, and power consumption can be reduced.
In each of the above embodiments, the case where a color filter having a transmittance of 1 / n is applied as the light reducing means has been described. However, by covering a part of the surface of the TFT photosensor with a light shielding layer, incident light can be reduced. It can also be dimmed.

In each of the above-described embodiments, the case where the light detecting unit LS1 for detecting external light is provided with the light reducing unit has been described. However, the light detecting unit LS1 for detecting external light and the light detecting unit LS2 for light degradation reference However, it is sufficient that the incident light quantity is different, and a light reduction unit can be provided in the light deterioration reference light detection unit LS2.
Furthermore, in each of the above-described embodiments, the case where the light detection unit for detecting external light and the light detection unit for detecting light degradation are provided one by one. However, when the size of the display panel is large, external light is used. A plurality of detection light detection units may be provided.

In each of the above embodiments, the case where the offset correction value AOFF is corrected by adding the sensitivity correction value COFF corresponding to the light deterioration rate D to the offset correction value AOFF has been described. The offset correction value AOFF can also be corrected by multiplying by the sensitivity correction value COFF ′ corresponding to the light deterioration rate D.
Further, the values of the illuminance determination thresholds L0 to L3 can be changed according to the characteristics of the optical sensor. Thereby, it is possible to cope with variations in individual optical sensor characteristics.

Furthermore, in each of the above-described embodiments, the case where the external light illuminance is divided into three regions (four-point correction) has been described, but it can also be divided into four or more regions. As described above, by increasing the number of divisions, it is possible to improve the accuracy of variation correction of the optical sensor characteristics.
In each of the above embodiments, the case where the offset correction value AOFF is corrected according to the light deterioration rate D has been described. However, the inclination correction value ASLP can also be corrected, and further, the offset correction value AOFF and the inclination correction value can be corrected. It is also possible to correct both with the ASLP.

Furthermore, in each of the above embodiments, the case where the light deterioration rate D is obtained by referring to the lookup table stored in the memory circuit 32b based on the light deterioration correction coefficient K has been described. A circuit that realizes a function of the light deterioration rate D using the coefficient K as a variable may be provided, and the light deterioration rate D may be derived by calculation.
In each of the above embodiments, the case where the memory circuit 32b stores a preset initial ratio β has been described. In an initial state (factory shipment state), light having a predetermined reference illuminance is irradiated, The optical sensor outputs of the light detection units LS1 and LS2 in the initial state may be measured, and the initial ratio β obtained by calculation based on these may be stored in the memory circuit 32b.

In each of the above embodiments, the case where the present invention is applied to a transflective liquid crystal display device has been described. However, the present invention can also be applied to a transmissive liquid crystal display device and a reflective liquid crystal display device. In the case of a reflective liquid crystal display device, a front light may be used instead of the backlight or side light.
Further, in each of the above embodiments, the case where the present invention is applied to a display device using a backlight such as a liquid crystal display device has been described. However, the present invention is also applied to a display device using an organic electroluminescent light emitting element or the like. Is possible. In this case, the light emission amount or control data of the organic electroluminescence light emitting element or the like may be corrected based on the output value of the light amount detection circuit.

  Further, in the above embodiment, the case where a TFT photosensor is applied as the photosensor has been described. However, any photo-electric conversion such as a known photodiode, phototransistor, photo TFT, photoSCR, photoconductor, photocell, etc. An element can be applied.

1 is a plan view schematically showing a display panel seen through a color filter substrate of a liquid crystal display device according to an embodiment of the present invention. It is XX sectional drawing of FIG. It is sectional drawing of the photosensor and switch element on a TFT substrate. It is a circuit diagram of a photon detection part. It is a block diagram which shows the detailed structure of backlight control. It is a timing chart of optical sensor output detection. It is a block diagram which shows the detail of a light degradation rate output part. It is a figure which shows the relationship between a photodegradation rate and a sensitivity correction value. It is a figure for demonstrating the calculation procedure of external light illumination intensity. It is a figure which shows the relationship between integrated illumination intensity and the change rate of an optical sensor output. It is a figure which shows the change of the optical sensor output of light detection part LS1 and LS2. It is a figure explaining the effect of this embodiment. It is a timing chart of the optical sensor output detection in 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 2 ... TFT substrate, 4 ... Gate line, 5 ... Source line, 11 ... Common line, 22 ... Color filter (dimming means), 25 ... CF substrate, 26 ... Counter electrode, 31 ... Reading part 32 ... Sensitivity correction value output unit, 32a ... Deterioration coefficient calculation unit, 32b ... Memory circuit, 32c ... Light deterioration rate calculation unit, 32d ... Sensitivity correction value calculation unit, 33 ... Correction unit, 34 ... Filter processing unit, 35 ... B / L luminance conversion unit, 36 ... B / L luminance control unit, 37 ... backlight, LS1, LS2 ... light detection unit, SW1, SW2 ... switch element, C1, C2 ... capacitor, Vs ... reference voltage

Claims (10)

A light amount detection circuit comprising a light detection unit having a light sensor for detecting external light and a light sensor reading unit for reading an output signal of the light detection unit,
The light detection unit includes a first light detection unit that receives the external light as incident light and outputs an output signal corresponding to the amount of the external light, and a light reduction unit that attenuates the external light, The light attenuated by the dimming means is incident as incident light, and includes a second light detection unit that outputs an output signal corresponding to the amount of the attenuated light,
One of the first and second light detection units is detected based on the output signal of the first light detection unit and the output signal of the second light detection unit read by the light sensor reading unit. A light deterioration rate calculation unit for calculating a light deterioration rate in the output signal of the unit;
The light quantity of the external light is detected based on the illuminance-output characteristic in the initial state of the one light detection unit, the output signal of the one light detection unit, and the light deterioration rate calculated by the light deterioration rate calculation unit. A light amount detection circuit comprising: a light amount detection unit.   The light amount detection circuit according to claim 1, wherein the optical sensor reading unit reads each output signal of the first and second light detection units in a time-sharing manner.   3. The light amount detection circuit according to claim 2, wherein the optical sensor reading unit reads the output signal of the other light detection unit once after reading the output signal of the one light detection unit a predetermined number of times.   The light amount detection circuit according to claim 2, wherein the light sensor reading unit reads an output signal of the other light detection unit at an arbitrary timing.   5. The light amount detection circuit according to claim 2, wherein the light deterioration rate calculation unit calculates the light deterioration rate by taking a moving average. 6. The light amount detection unit corrects the output signal of the one light detection unit by using an offset correction value and an inclination correction value for matching the approximate line of the illuminance-output characteristic with a predetermined ideal characteristic line. Detecting the amount of the external light,
6. A light deterioration correction unit that corrects at least one of the offset correction value and the tilt correction value based on the light deterioration rate calculated by the light deterioration rate calculation unit. 2. A light quantity detection circuit according to item 1.   The light deterioration correction unit corrects at least one of the offset correction value and the inclination correction value when the light deterioration rate calculated by the light deterioration rate calculation unit is a predetermined value or more. 7. A light quantity detection circuit according to 6.   The light deterioration rate calculation unit calculates a light deterioration correction coefficient that is a ratio of a ratio between an output signal of the first light detection unit and an output signal of the second light detection unit and a preset initial ratio. 8. The light amount detection circuit according to claim 1, wherein the light deterioration rate is calculated based on the light deterioration rate.   The first and second light detection units are connected to a thin film transistor as the light sensor, a capacitor connected between a source electrode and a drain electrode of the thin film transistor, and one terminal of the source electrode and the capacitor. And the photosensor reading unit is charged with a reference voltage when the switch element is in an on state, and leaks when light is emitted to the thin film transistor when the switch element is in an off state. The light amount detection circuit according to claim 1, wherein a voltage value of the capacitor that decreases is read as an output signal. A light amount detection circuit according to any one of claims 1 to 9,
A display device comprising: an illumination unit that illuminates a display panel; and a control unit that controls the illumination unit based on an output value of the light amount detection circuit.

Images