JP2009222550A - Light quantity detecting circuit and electro-optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light quantity detection circuit and an electro-optical device for improving light detection accuracy by suitably correcting deterioration of an optical sensor due to light irradiation. <P>SOLUTION: A light quantity detection circuit includes two TFT optical sensors TFTc, TFTs using a-Si. The TFTc is connected to a diode, and one electrode connected to a gate electrode is connected to a first voltage source 11 supplying a voltage Vg1 through a resistor Rc with a node A, and the other electrode is connected to a second voltage source 12 supplying a voltage Vg0. Concerning TFTs, a source electrode is grounded, the gate electrode is connected to the node A, and a drain electrode is connected to a light detection part, the resistor Rc is higher than a resistor in turning on TFTc, and is smaller than a resistor in turning off it, and when a threshold voltage of TFTs is Vth, Vg1>Vg0+Vth is satisfied. In light quantity detection, a positive bias voltage Vg0+Vth is applied on the gate electrode of TFTs, and external light is shaded on TFTc with a dimming means 15. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a light amount detection circuit in which deterioration of an optical sensor due to light irradiation is appropriately corrected to improve light detection accuracy, and an electro-optical device including the same.

Since the visibility of the display device varies depending on the brightness of the external light, conventionally, the brightness of the display device is controlled by detecting the brightness of the external light. As an optical sensor for detecting the brightness of such outside light, as disclosed in Patent Documents 1 and 2 below, amorphous-S
Utilizing the fact that the leakage current of a thin film transistor (hereinafter referred to as “TFT”) using i (hereinafter referred to as “a-Si”) is proportional to the amount of received light, this leakage current charges the voltage detection capacitor or Devices are known that detect the amount of light by discharging and monitoring the voltage change across the capacitor. In addition, the TFT photosensor is manufactured at the same time in the manufacturing process of the display device, and the TFT photosensor is integrated in the display device (see Patent Document 1 below).

For the light quantity detection by the TFT photosensor as described above, a change in the off current of the TFT (current when the TFT is in a non-conducting state as a switch) is used. This is because the change in off-current due to light irradiation is large, and it is easy to secure a dynamic range as a sensor.

By the way, it is known that the leakage current of a TFT using a-Si is proportional to the amount of received light, but its sensitivity (current value with respect to the amount of received light) is reduced by exposure to light. For this reason, in the light amount detection circuits disclosed in Patent Documents 1 and 2 below, the light amount detection accuracy decreases due to this sensitivity decrease. In order to prevent this, Patent Document 3 below discloses a photoelectric conversion element that improves the anti-deterioration characteristics by improving the generation method of the TFT photosensor.
JP 2006-29832 A JP 2002-131719 A Japanese Patent Laid-Open No. 9-232620

However, the photoelectric conversion element disclosed in Patent Document 3 requires special manufacturing conditions. For example, it is necessary to provide an optical sensor inside a display device using TFTs. In addition, when manufacturing a display device and an optical sensor in the same device, a manufacturing process different from the characteristics suitable for display is required, and the manufacturing process becomes longer or the condition setting of the manufacturing device is frequently changed. I will be forced.

The present invention has been made in view of the above-described problems, and includes a light amount detection circuit that has a sensitivity correction function with a simple configuration and can be manufactured in a simple process, and a display including the light amount detection circuit. The object is to provide an apparatus.

The light quantity detection circuit of the present invention is a light quantity detection circuit comprising a TFT photosensor using a-Si, wherein two TFT photosensors using a-Si are provided,
The one TFT photosensor is diode-connected, one electrode connected to the gate electrode is connected to the first voltage source through a resistor, and the other electrode is connected to the second voltage source,
The other TFT photosensor has a source electrode grounded and a gate electrode connected to the one TFT.
Connected to the connection point between one electrode of the optical sensor and the resistor, the drain electrode is connected to a light detection unit for monitoring the current flowing during detection,
The resistance value of the first resistor is higher than the resistance when the one TFT photosensor is on and smaller than the resistance when it is off,
The voltage of the first voltage source is Vg1, and the voltage of the second voltage source is a predetermined positive voltage Vg.
0, when the threshold voltage of the one TFT photosensor is Vth, Vg1> V when detecting the light quantity
A positive bias voltage Vg0 + Vth is applied to the gate electrode of the other TFT photosensor so as to satisfy the relationship of g0 + Vth,
The one light sensor is provided with a light control means for controlling the incidence of external light,
The dimming means operates so as to shield the one photosensor from incident light when detecting the amount of light.

The light quantity detection circuit of the present invention includes a TFT using a-Si as an optical sensor. However, a sensor function is a phenomenon in which an on-current of a TFT is changed by light irradiation instead of a conventional TFT off-current. It is what you use. And the light quantity detection circuit of this invention is this aS.
Two TFT photosensors using a-Si are provided to compensate the characteristics of the TFT photosensor using i by light irradiation, and one TFT photosensor is used to compensate the gate bias voltage of the other TFT photosensor. is doing.

In the light amount detection circuit of the present invention, the resistance value of the first resistor is set to be higher than the resistance when the one TFT photosensor is on and smaller than the resistance when it is off, and the first voltage source When the light voltage is Vg1, the second voltage source voltage is a predetermined positive voltage Vg0, and the threshold voltage of the one TFT photosensor is Vth, the relationship of Vg1> Vg0 + Vth is satisfied at the time of light amount detection. Therefore, the positive bias voltage V is applied to the gate electrode of the other TFT photosensor.
g0 + Vth is applied.

On the other hand, when the TFT photosensor using a-Si is irradiated with light, the threshold voltage Vth varies. However, in the present invention, since the two TFT photosensors are exposed to outside light, the other TF is used.
The threshold voltage of the T photosensor varies substantially in the same way as the threshold voltage of the one TFT photosensor.
Therefore, even if Vth of two TFT photosensors fluctuate together, the other TF is detected at the time of light quantity detection.
Since the positive bias voltage applied to the gate electrode of the T photosensor is Vg0 + Vth, a positive bias voltage of a constant Vg0 is always applied to the other TFT photosensor with reference to the threshold voltage.

Here, the one light sensor is provided with a light control means for controlling the incidence of external light, and the light control means operates to shield the one light sensor from the incident light when detecting the amount of light. In addition, when the amount of light is not detected, the one photosensor is irradiated with external light in the same manner as the other photosensor, and the characteristics change with the same tendency as the other photosensor. With this configuration, the light amount detection circuit of the present invention can apply the threshold voltage Vth according to the characteristic deterioration of the optical sensor without depending on the surrounding illuminance when detecting the light amount. As this light control means, a liquid crystal shutter provided with a light amount detector or a fine mechanical shutter using a micromachining structure can be used.

Therefore, according to the light amount detection circuit of the present invention, even if the TFT optical sensor using two a-Si has a variation in characteristics due to light irradiation, the voltage applied to the gate electrode of the other TFT optical sensor is When the threshold voltage Vth is used as a reference, a constant bias voltage Vg0 is always a positive bias voltage, so that the characteristic variation of the other TFT photosensor due to light irradiation is substantially compensated. Therefore, according to the light amount detection circuit of the present invention, it is possible to provide a TFT with a simple configuration of sensitivity correction function.
Variations due to light irradiation of the optical sensor can be accurately corrected.

In addition, according to the light amount detection circuit of the present invention, since the on-current of the TFT photosensor is measured, the amount of current is much larger than the off-current as in the conventional example. Therefore, it is possible to use a TFT photosensor smaller than that of the conventional type that measures off-current as in the conventional example. In addition, according to the light amount detection circuit of the present invention, according to the light amount detection circuit of the present invention, the input / output characteristics are linear with respect to the logarithm of the irradiation light amount, and the adjustment range of the drive voltage is wide. The element size to be configured and the design freedom of the potential monitor are increased.

In the light quantity detection circuit of the present invention, the voltage Vg1 of the first voltage source can be a constant voltage.

When the voltage Vg1 of the first voltage source is a constant voltage, the circuit configuration is simplified, and the second voltage source is also a predetermined positive voltage Vg0, that is, a constant voltage source, so that output fluctuation is small. Stable operation is possible.

In the light amount detection circuit of the present invention, the voltage Vg1 of the first voltage source periodically changes so as to satisfy the relationship of Vg1> Vg0 + Vth when the light amount is detected and satisfy the relationship of Vg1 <Vg0 + Vth when the light amount is not detected. It is preferable that

When a positive bias voltage is constantly applied to a TFT photosensor using a-Si, characteristic fluctuation (deterioration) due to energization stress occurs. Degradation due to energization stress of the TFT photosensor proceeds at a remarkable and faster speed than degradation due to light irradiation. Therefore, in the light amount detection circuit of the present invention, the voltage Vg1 of the first voltage source that determines the gate application voltage is changed with time, and when the light amount is not detected, both TFT lights are satisfied so as to satisfy the relationship Vg1 <Vg0 + Vth. A reverse bias voltage is applied to the gate electrode of the sensor. Therefore, according to the light quantity detection circuit of the present invention, it is possible to obtain a light quantity detection circuit with less characteristic fluctuation due to energization stress.

In the light amount detection circuit of the present invention, the light detection unit is connected between a capacitor connected between the drain electrode of the other TFT and the ground, and between the drain electrode and a predetermined constant voltage source. And a detection time from when the switch element is turned off until the voltage at both ends of the capacitor is discharged to a predetermined threshold voltage.

According to the light amount detection circuit of the present invention, the input / output characteristics are linear with respect to the logarithm of the light amount.
It is easy to handle as a circuit that detects with a time constant (time to reach a predetermined potential), and high resolution can be secured in a wide light quantity range. Also, because the drive voltage change range is wide,
The degree of freedom in designing the element size constituting the sensor and the potential monitoring capacitor is also increased.

Furthermore, the electrochemical optical device of the present invention includes any one of the light quantity detection circuits described above,
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 that illuminates the display panel;
A light control circuit for controlling the illumination unit based on an output value of the light amount detection circuit;
It is characterized by providing.

According to the electro-optical device of the present invention, the electro-optical device can correct the characteristic variation of the light amount detection circuit, detect the amount of external light with high accuracy, and appropriately control the illumination unit. Can do. In the electro-optical device of the present invention, since the manufacturing conditions of the light detection unit itself are not changed, the manufacturing process is performed even when the display panel and the optical sensor are manufactured by the same manufacturing device. Will not be long, and will not be forced to change the frequent setting of the manufacturing equipment.

The best mode for carrying out the present invention will be described below with reference to the drawings and examples. However,
The embodiments described below exemplify a light amount detection circuit for embodying the technical idea of the present invention, and are not intended to specify the present invention as this light amount detection circuit. It is equally applicable to those of other embodiments within the scope. In each drawing used for the description in this specification, each layer and each member are displayed in different scales so that each layer and each member can be recognized on the drawing. However, it is not necessarily displayed in proportion to the actual dimensions.

FIG. 1 is an overall view of an electro-optical device with a built-in optical sensor. FIG. 2A is a light amount detection circuit diagram of the first embodiment at the time of light amount detection, and FIG. 2B is a light amount detection circuit diagram of the first embodiment at the time of non-detection of the light amount. FIG. 3 is a light quantity-current characteristic diagram of the TFT photosensor before light deterioration. FIG. 4 is a diagram showing the light quantity-current characteristics of the TFT photosensors before and after photodegradation. FIG. 5 is a light intensity-current characteristic diagram of the first embodiment before and after light degradation. FIG. 6 is a light amount detection circuit diagram of the second embodiment. 7A to 7D are diagrams illustrating changes in voltage across the capacitor _CW of the second embodiment. FIG.
FIG. 8A is a light amount detection circuit diagram of the second embodiment, and FIG. 8B is a diagram showing a Vg1 drive waveform of the second embodiment.

A specific example of a liquid crystal display panel as an electro-optical device to which the present invention is applied will be described with reference to FIG. The liquid crystal display panel 1 includes a pair of active matrix substrates (hereinafter referred to as “active matrix substrates”).
AR substrate) 2 and a color filter substrate (hereinafter referred to as CF substrate) 5, and the AR substrate 2 is a CF substrate so that a projecting portion 2 </ b> A having a predetermined space is formed when the AR substrate 2 is arranged opposite to the CF substrate 5. A material having a size larger than 5 is used, and a sealing material (not shown) is attached to the outer periphery of the AR substrate 2 and the CF substrate 5, and liquid crystal and spacers are enclosed inside.

Various wirings and the like are formed on the facing surfaces of the AR substrate 2 and the CF substrate 5. this house,
The CF substrate 5 includes a black matrix provided in a matrix in accordance with the pixel area in the display area DA of the AR substrate 2, and, for example, red (R) and green (G) provided in an area surrounded by the black matrix. ), A color filter made of blue (B), and a common electrode that is electrically connected to the electrode on the AR substrate 2 side and is provided so as to cover the opposing surface of the CF substrate 5. Although specific configurations of the color filter, the black matrix, and the common electrode are not shown, they are opposed to the light amount detection unit LS formed on the AR substrate 2 and various lead lines L and L ₀ derived from the light amount detection unit LS. It is extended to the place to do. Further, a backlight (not shown) is provided on the back surface of the AR substrate 2 as illumination means. This backlight is controlled by the output of the light quantity detector LS.

The AR substrate 2 has short sides 2a, 2b and long sides 2c, 2d facing each other, and one short side 2b side is an overhang portion 2A. A semiconductor for a source driver and a gate driver is provided in the overhang portion 2A. A chip Dr is mounted, and a light quantity detection unit LS including the light quantity detection circuit of the present invention is disposed on the other short side 2a side.

The AR substrate 2 has a plurality of gate lines GW _{1 to} GW _n (n = 2) arranged at predetermined intervals in the row direction (lateral direction) in FIG. 3, 4, ...
And a plurality of data lines S insulated from these gate lines and arranged in the column direction (vertical direction)
W _{1 to} SW _m (m = 2, 3, 4,...), And these data lines SW _{1 to} SW _m and gate lines GW _{1 to} GW _n are wired in a matrix and intersect with each other. Lines GW _{1 to} GW
_In each region surrounded by _n and the data lines SW _{1 to} SW _m , switching elements (not shown) that are turned on by scanning signals from the gate lines GW _{1 to} GW _n and the data lines SW _{1 to} SW _m
A pixel electrode (not shown) to which a video signal from is supplied via a switching element is formed.

Each area surrounded by the gate lines GW _{1 to} GW _n and the data lines SW _{1 to} SW _m constitutes a so-called pixel, and an area in which these pixels are formed becomes a display area DA, that is, an image display section. ing. For example, a TFT is used as the switching element.

Each of the gate lines GW _{1 to} GW _n and each of the data lines SW _{1 to} SW _m is extended outside the display area DA and is routed to an outer peripheral area outside the display area to be a source driver and a gate driver semiconductor chip. Connected to Dr. Further, the AR substrate 2 has a light amount detection unit L on one long side 2d side.
The lead-out lines L ₀ and L derived from the S optical sensor are connected to terminals T ₁ and T ₂ to which an external control circuit is connected.

[First Embodiment]
Next, the light amount detection circuit 10A of the first embodiment will be described with reference to FIGS. First
As shown in FIG. 1, the light amount detection circuit 10A of the light amount detection unit LS of the embodiment includes two a-S.
TFT photosensors TFTc and TFTs using i are provided. The two TFT photosensors TFTc and TFTs are manufactured in the same size and integrally.

One TFT photosensor TFTc operates as a compensation TFT, and the gate electrode Gc and the drain electrode Dc are connected to form a diode connection. The drain electrode Dc is connected to the first power supply 11 whose power supply voltage is Vg1 through the first resistor Rc. Hereinafter, a connection point between the drain electrode Dc and the first resistor Rc is referred to as a node A.
Further, the source electrode Sc is connected to the second power source 12 having the predetermined second voltage Vg0.

Also, one TFT photosensor TFTc is provided with a light control means 15, and the one TFT
Incidence and non-incidence of external light can be controlled with respect to the optical sensor TFTc. As this light control means, a liquid crystal shutter provided together with a light amount detector, a fine mechanical shutter using a micromachining structure, or the like is used. Note that this light control means does not allow external light to enter one TFT photosensor TFTc when detecting the amount of light, and one TF when detecting no amount of light.
Control is performed so that external light is incident on the T-light sensor TFTc.

The other TFT photosensor TFTs operates directly as a TFT photosensor. In the other TFT photosensor TFTs, the gate electrode Gs is connected to the node A of the one TFT photosensor Tc, the source electrode Ss is grounded, and the drain electrode Ds.
Is connected to a terminal 13 for monitoring the current at the time of sensor drive voltage supply and detection. A circuit for monitoring the supply of the sensor driving voltage to the other TFT photosensor TFTs and the current at the time of detection is well known to those skilled in the art and is not shown in the figure.

Here, the resistance value of the first resistor Rc is higher than the resistance when one TFT photosensor TFTc is on, and smaller than the resistance when it is off. When the threshold voltage of one TFT photosensor TFTc is Vth, the power supply voltage of the first voltage 11 is Vg1 at the time of detecting the amount of light.
> Vg0 + Vth is satisfied. Then, the positive bias voltage Vg0 + Vth is applied to the gate electrode Gs of the other TFT photosensor Ts. Here, the voltage Vg1 of the first voltage source is a constant voltage. With this configuration,
Since the circuit configuration is simplified and the second voltage source is also a positive voltage Vg0 determined in advance, that is, a constant voltage source, a stable operation with little fluctuation in output is possible.

Here, the characteristics of the TFT photosensor before and after photodegradation will be described with reference to FIGS. FIG.
This shows the influence of light irradiation on the Vg-Is characteristics in the case of the other TFT photosensor TFTs alone before photodegradation. In addition, according to FIG. 3, it turns out that the electric current value Is is changing by light irradiation. For example, when Vg = 2V, the change is 0.03 mA with a light intensity of 0 LX, 10000 L
X is 0.28 mA.

Now, the initial threshold voltage Vth of the two TFT photosensors TFTs and TFTc is 1.5V.
Suppose that In the light quantity detection circuit 10A shown in FIG. 2, Vg0 = 0.5V, Vg1 = 1.
When 0V is applied, the potential of the node A becomes Vg0 + initial Vth = 0.5 + 1.5 = 2.0V, and 2.0V is applied to the gates of TFTc and TFTs. At this time, the current flowing between the source and drain of the TFTs changes as shown by arrows in FIG.

Next, FIG. 4 shows a comparison with a state in which the characteristics are changed by long-time light irradiation. The characteristic indicated by the dotted line in the figure is the characteristic after light degradation. The threshold voltage Vth of the two TFT photosensors TFTs and TFTc is shifted from the initial 1.5V to 4.4 by shifting the characteristic curve to the right as shown by the horizontal arrows.
It is 5V. At this time, in the circuit configuration shown in FIG. 2, the potential of the node A is Vg0 + V
th (after deterioration) = 0.5 + 4.5 = 5.0 V, and the current value changes depending on the amount of light irradiation as indicated by the vertical arrow in FIG.

That is, in the present invention, when the amount of light is not detected, two TFT photosensors TFTs and TFTs
Since both c are exposed to light, the threshold voltage Vth of both TFT photosensors TFTs and TFTc
Fluctuate in substantially the same way. Since the threshold voltage Vth varies depending on the light incident on the TFT c itself, it is necessary to block the incident light on the TFT c and output the threshold voltage in the dark state when detecting the amount of light. For this reason, the TFT c is provided with a dimming means for controlling the incidence / non-incidence of light, and operates so as to be in a light-shielding state during the detection operation of the sensor. By performing the detection operation in this way, even if both of the two TFT photosensors fluctuate, the voltage applied to the node A is Vg0 + Vth when detecting the amount of light. A bias voltage obtained by adding a constant offset voltage Vg0 to the voltage Vth is applied.

FIG. 5 shows the relationship between the light amount before and after the light deterioration detected by the light amount detection circuit 10A of the first embodiment and the value of the current flowing through the other photosensor TFTs. From the results shown in FIG.
It can be seen that even if the threshold voltage Vth of both TFT photosensors TFTs and TFTc changes due to light deterioration, the current of the other TFT photosensor TFTs constituting the photosensor hardly changes. That is, even if the characteristics of both the TFT photosensors TFTs and TFTc deteriorate, the function as the light quantity detection circuit is maintained normally. Accordingly, the light amount detection circuit 1 of the first embodiment.
According to 0A, although the sensitivity correction function has a simple configuration, it is possible to accurately correct fluctuations caused by light irradiation of the TFT photosensor.

[Second Embodiment]
In the light amount detection circuit 10A of the first embodiment, two TFT photosensors TFTs and T
The other TFT photosensor TFTs operating as a photosensor so that a constant positive bias voltage Vg0 is always applied to the gate electrodes Gs and Gc of FTc with reference to the threshold voltage Vth.
An example of measuring the current flowing through is shown. However, the other TF that acts as an optical sensor
As a measurement circuit for the current flowing through the T photosensor TFTs, a conventional circuit for measuring the current flowing at the time of reverse bias voltage can be employed.

The light quantity detection circuit 10B according to the second embodiment will be described with reference to FIGS. In FIG. 6, the same components as those in the light quantity detection circuit 10A of the first embodiment shown in FIG. Light amount detection circuit 1 of the second embodiment
The difference between 0B and the light amount detection circuit 10A of the first embodiment is that the capacitor C is connected between the drain electrode Ds of the other TFT photosensor TFTs operating as a photosensor and the ground.
The drain electrode Ds is connected to the reference voltage source 14 and the terminal 13 for monitoring the voltage across the capacitor Cmon by the switch element Sw. Further, the operation of the light control means 15 in FIG. 6 is the same as that of the light amount detection circuit 10A of the first embodiment. In the following, the connection point between the drain electrode Ds of the other TFT photosensor TFTs and the capacitor Cmon is referred to as a node B.

In this light quantity detection circuit 10B, first, Sw is connected to the reference voltage source 14, and the constant voltage Va,
For example, 2V is applied to the node B, and the capacitor Cmon is charged with Va. Next, the switch element Sw is switched to the terminal 13 for monitoring, and the amount of light is detected by outputting the detection time until the node B is discharged until the voltage at the node B reaches a predetermined threshold voltage.
Note that the terminal 13 may always be connected to the drain electrode Ds of the other TFT photosensor TFTs so as to be turned on / off with the reference voltage source 14. With such a configuration, the potential fluctuation of the node B caused by the change in the electric charge accumulated in the capacitor Cmon due to the current flowing through the other TFT photosensor TFTs is read by the voltage detection circuit connected to the terminal 13. Then, by measuring the time from when the switch is switched until it reaches a predetermined potential, it is converted into the magnitude of the current value, that is, the amount of light. The light quantity detection circuit 10 of the second embodiment
Even in the case of B, since the voltage of the node A is always Vg0 + Vth, both T
Even if the characteristics of the FT photosensors TFTs and TFTc deteriorate, the function as the light quantity detection circuit is maintained normally.

The response characteristics of the light amount detection circuit 10B of the second embodiment are as shown in FIGS. 7A to 7D. As shown in FIGS. 7A to 7D, it can be seen that the amount of light can be converted from the time from when the switch is switched to when a predetermined potential is reached. According to the light amount detection circuit 10B of the second embodiment, since the input / output characteristics are linear with respect to the logarithm of the light amount, it is easy to handle as a circuit that detects with a time constant (time to reach a predetermined potential) and is wide. High resolution can be secured in the light amount range. Moreover, since the change range of the drive voltage is wide, the degree of freedom in designing the element size and the potential monitoring capacitor constituting the sensor is also increased.

[Third Embodiment]
In the light quantity detection circuits 10A and 10B of the first and second embodiments, an example in which a constant positive bias voltage Vg0 is always applied to the threshold voltage Vth to the gate electrodes Gs and Gc of the two TFT photosensors TFTs and TFTc is shown. It was. However, TFT photosensors using a-Si are subject to characteristic degradation due to energization stress when a positive bias voltage is constantly applied. This TFT
Degradation due to energization stress of the optical sensor proceeds at a remarkable and faster speed than degradation due to light irradiation.

Therefore, in the light amount detection circuit 10C of the third embodiment, two TFT photosensors TF are used.
A predetermined positive bias voltage is applied to the gate electrodes Gs and Gc of Ts and TFTc when a light amount is detected, and a reverse bias voltage is applied when the light amount is not detected. The light quantity detection circuit 10C of the third embodiment will be described with reference to FIG. In the light amount detection circuit 10C of the third embodiment, the circuit configuration is the same as that of the light amount detection circuit 10B of the second embodiment as shown in FIG. As shown in FIG. 8B, the configuration is different in that the voltage Vg1 of the voltage source is changed with time. Further, the operation of the light control means 15 in FIG. 8 is the same as that of the light amount detection circuit 10A of the first embodiment.

That is, in the light amount detection circuit 10C of the third embodiment, the voltage of the node A is Vg1> Vg0 at the time of light amount detection, as in the case of the light amount detection circuit 10A of the first embodiment.
The relationship of + Vth is satisfied, but the relationship of Vg1 <Vg0 + Vth is satisfied so that the reverse bias voltage is obtained when the amount of light is not detected. In order to achieve such a reverse bias voltage, for example, Vg1 = −5V may be set. According to the light amount detection circuit 10C of the third embodiment as described above, a light amount detection circuit with less characteristic fluctuation due to energization stress can be obtained.

In the light quantity detection circuit 10C of the third embodiment, the other TF as an optical sensor is used.
Although an example in which the same circuit as that of the second embodiment light amount detection circuit 10B is used as the measurement circuit for the current flowing through the T light sensor TFTs has been described, the same circuit as that of the first embodiment light amount detection circuit 10A can be used. That is obvious.

In the first to third embodiments, only the light amount detection circuits 10A to 10C that compensate for the light deterioration of the TFT optical sensor are shown. However, the light amount detection circuits 10A to 10C are used to form an electro-optical device. To apply, you can do the following. That is, the visibility of the display image depends on the brightness of the surrounding environment. Therefore, the light amount value of the ambient light output from the light amount detection circuits 10A to 10C is compared with the predetermined light amount threshold value. For example, when the light amount of the ambient light corresponds to natural light during the day, the light emission of the backlight is performed. Set the brightness higher and display a bright screen. On the other hand, when the amount of ambient light corresponds to a dark environment at night, the light emission luminance of the backlight is set low.

Here, the case where the light amount detection circuit of the present invention is applied to an electro-optical device using liquid crystal has been described, but it 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.

1 is an overall view of an electro-optical device with a built-in optical sensor. FIG. 2A is a light amount detection circuit diagram of the first embodiment at the time of light amount detection, and FIG. 2B is a light amount detection circuit diagram of the first embodiment at the time of non-detection of the light amount. It is an illumination intensity-current characteristic view of a TFT photosensor before light degradation. It is the figure which put in order and showed the illumination intensity-current characteristic of the TFT photosensor before and behind light degradation. It is an illumination intensity-current characteristic figure of a 1st embodiment before and behind light degradation. It is a light quantity detection circuit diagram of a 2nd embodiment. 7A to 7D are diagrams illustrating changes in voltage across the capacitor _CW of the second embodiment. FIG. 8A is a light amount detection circuit diagram of the third embodiment, and FIG. 8B is a diagram showing a Vg1 drive waveform of the third embodiment.

Explanation of symbols

1: Liquid crystal display device 2: TFT substrate 2A: Overhang portion 5: CF substrate 10, 10A,
10B, 10C: Light quantity detection circuit 11: First voltage source 12: Second voltage source 13: Terminal 14: Reference voltage source LS: Light quantity detection unit L: Power supply line (lead-out wiring) L ₀ : Output line (lead-out wiring) A, B: Node

Claims (5)

In a light amount detection circuit including a thin film transistor photosensor using amorphous-Si,
Two thin film transistor photosensors using amorphous-Si are provided,
The one thin film transistor photosensor is diode-connected, one electrode connected to the gate electrode is connected to the first voltage source via a resistor, and the other electrode is connected to the second voltage source,
In the other thin film transistor photosensor, a source electrode is grounded, a gate electrode is connected to a connection point between one electrode of the one TFT photosensor and a resistor, and a drain electrode is a light for monitoring a current flowing during detection. Connected to the detector,
The resistance value of the first resistor is higher than the on-state resistance of the one thin film transistor photosensor and smaller than the off-state resistance,
The voltage of the first voltage source is Vg1, and the voltage of the second voltage source is a predetermined positive voltage Vg.
0, when the threshold voltage of the one thin film transistor photosensor is Vth,
The positive bias voltage Vg0 + Vth is applied to the gate electrode of the other thin film transistor photosensor so as to satisfy the relationship of Vg1> Vg0 + Vth,
The one light sensor is provided with a light control means for controlling the incidence of external light,
The light control circuit is characterized in that the light control means operates to block the one light sensor from incident light when detecting the light amount. 2. The light quantity detection circuit according to claim 1, wherein the voltage Vg1 of the first voltage source is a constant voltage. The voltage Vg1 of the first voltage source periodically changes so as to satisfy a relationship of Vg1> Vg0 + Vth when the light amount is detected and satisfy a relationship of Vg1 <Vg0 + Vth when the light amount is not detected. The light quantity detection circuit according to 1. The light detection unit includes a capacitor connected between a drain electrode of the other thin film transistor and the ground, and a switch element connected between the drain electrode and a predetermined constant voltage source, and the switch element 4. The light amount detection circuit according to claim 1, wherein a detection time from when the capacitor is turned off until the voltage at both ends of the capacitor is discharged until the voltage reaches a predetermined threshold voltage is output. A light amount detection circuit according to any one of claims 1 to 4,
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 that illuminates the display panel;
A light control circuit for controlling the illumination unit based on an output value of the light amount detection circuit;
An electro-optical device comprising:

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