JP2008096242A - Light quantity detector, and liquid crystal display device equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light quantity detector capable of measuring a light quantity, while suppressing influence of noise of light irradiated to an optical sensor. <P>SOLUTION: The light quantity detector 1 includes a resistance element 13, the optical sensor 21 constituted of an n-type thin film transistor, and a capacity 22. One end 13a of the resistance element 13 is connected to a power supply potential (VDD), and a source S of the optical sensor 21 and one electrode 22a of the capacity 22 are connected in parallel to the other end 13b of the resistance element 13, and the light quantity is measured based on a charging voltage when charging the capacity 22 by the power supply potential (VDD) through the resistance element 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light amount detection device and a liquid crystal display device including the same, and more particularly to a light amount detection device including an optical sensor formed of a thin film transistor and a liquid crystal display device including the same.

  In general, an electronic device such as a mobile phone equipped with a liquid crystal display device is often used in an environment with different external light conditions such as daytime or nighttime. It is preferable to control the brightness and image quality of the screen of the liquid crystal display device in accordance with the brightness. Therefore, conventionally, a method has been proposed in which external light is detected by a light amount detection device including an optical sensor formed of a thin film transistor (TFT) formed on a display panel of a liquid crystal display device (see, for example, Patent Document 1). ).

  FIG. 6 is a circuit diagram of a light amount detection apparatus provided with an optical sensor composed of a conventional thin film transistor proposed in Patent Document 1. In FIG. First, with reference to FIG. 6, a circuit configuration of a light amount detection apparatus 200 including a conventional optical sensor composed of a thin film transistor will be described. In this light quantity detection device 200, the one electrode 201a of the capacitor 201 and the source S of the first switching transistor 202 formed of an n-type thin film transistor are connected to the power supply potential (VDD). The other electrode 201b of the capacitor 201 and the drain D of the first switching transistor 202 are the gate G of the second switching transistor 203 configured by a p-type thin film transistor and the photosensor 204 configured by an n-type thin film transistor. It is connected to the source S via the node n1. The source S of the second switching transistor 203 is connected to the power supply potential (VDD), and the drain D is connected to the source S of the resistor 205 formed of an n-type thin film transistor. Further, the drain D of the optical sensor 204 and the drain D of the resistor 205 are grounded. Further, the output signal Vout of the light quantity detection device 200 is output via a node n2 between the second switching transistor 203 and the resistor 205.

  FIG. 7 is a timing chart for explaining the operation of a light quantity detection device including a conventional photosensor composed of thin film transistors, and a diagram showing the voltage characteristics of the gate of the second switching transistor. Next, with reference to FIG. 6 and FIG. 7, the operation of the light quantity detection device 200 having the conventional thin film transistor will be described.

  First, as shown in FIG. 7, by applying a predetermined voltage Vpulse (H level) to the gate G of the first switching transistor 202 for a certain period, the first switching transistor 202 is kept on for a certain period. Thus, the capacitor 201 is charged with the power supply potential (VDD).

  Next, when the voltage Vpulse of the gate G of the first switching transistor 202 becomes L level (0 V), the first switching transistor 202 is turned off. At this time, since the potential of the node n1 connected to the other electrode 201b of the capacitor 201 is the power supply potential (VDD), the drain D of the first switching transistor 202 connected to the node n1 and the source of the photosensor 204 The potential of S and the gate G of the second switching transistor 203 is the power supply potential (VDD). Therefore, in this state, the second switching transistor 203 formed of a p-type thin film transistor is in an off state.

  When the optical sensor 204 is irradiated with light, a leakage current is generated from the source S to the drain D of the optical sensor 204. The magnitude of this leakage current increases as the light intensity increases. A constant voltage Vbias is applied to the gate G of the optical sensor 204. The electric charge stored in the capacitor 201 is discharged from the drain D of the optical sensor 204 due to a leakage current generated by irradiating the optical sensor with light, and the potential of the node n1 is changed from VDD as indicated by a solid line c0 in FIG. Going down.

The gate of the second switching transistor 203 formed of a p-type thin film transistor is connected to the node n1, and the potential of the node n1 drops due to the discharge due to the leakage current of the photosensor 204, and the second switching transistor 203 When the voltage falls below the gate threshold voltage (V _TH ), the second switching transistor 203 is turned on.

  Note that a constant voltage Va is applied to the gate G of the resistor 205, and the resistor 205 has a function as a resistance element having a constant resistance value. Thus, the voltage output as Vout after the second switching transistor 203 is turned on is a voltage between the potential difference between the power supply potential (VDD) and the ground (GND).

  Further, since the leakage current of the optical sensor 204 increases as the amount of light applied increases, the amount of light applied is smaller than the case indicated by the solid line c0, as indicated by the one-dot chain line c1 in FIG. The slope of the potential drop at the node n1 becomes small. That is, the larger the amount of light irradiated to the optical sensor 204, the shorter the time until the second switching transistor 203 is turned on. Conversely, the smaller the amount of light irradiated to the optical sensor 204, the more the second switching transistor 203 becomes. It takes longer to turn on. Accordingly, the predetermined voltage Vpulse applied to the gate G of the first switching transistor 202 is set to L level, and the time from when the first switching transistor 202 is turned off to when the second switching transistor 203 is turned on is measured. By doing so, it becomes possible to measure the amount of light irradiated to the optical sensor 204.

JP 2006-29832 A

  However, in the light amount detection device 200 described in Patent Document 1, since the source S of the optical sensor 204 is electrically connected to the gate G of the second switching transistor 203, the light irradiated to the optical sensor 204. When noise is included, the influence of this noise is directly transmitted to the gate G of the second switching transistor 203. For this reason, there exists a problem that the light quantity detection apparatus 200 is easy to receive to the influence of the noise of the light with which the optical sensor 204 is irradiated.

  The present invention has been made to solve the above-described problems, and one object of the present invention is to measure the amount of light while suppressing the influence of light noise applied to the optical sensor. Is to provide a simple light quantity detection device.

Means for Solving the Problems and Effects of the Invention

  In order to achieve the above object, a light amount detection device according to a first aspect of the present invention includes a resistor, a photosensor configured by a thin film transistor, and a capacitor, and one end of the resistor has a first reference potential. The other end of the resistor is connected to one of the source / drain of the photosensor and one electrode of the capacitor in parallel, and is charged when the capacitor is charged through the resistor by the first reference potential. The amount of light is measured based on the voltage.

  In the light quantity detection device according to the first aspect, as described above, the capacitor is charged via the first reference potential via the resistor, so that the capacitor is charged slowly rather than rapidly due to the resistor. Therefore, it is possible to average the noise component included in the light applied to the optical sensor while the capacity is charged. Thereby, the light quantity can be measured while suppressing the influence of noise of light irradiated on the optical sensor.

  The light amount detection device according to the first aspect preferably further includes a comparator that is connected to one electrode of the capacitor and compares the charging voltage of the one electrode of the capacitor with the comparison voltage, and the charging voltage is the same as the comparison voltage. Then, the amount of light is measured by measuring the charging time based on the output signal output from the comparator. Thus, if it comprises so that a comparator may be used, the light quantity irradiated to an optical sensor can be measured easily.

  The light quantity detection device according to the first aspect preferably further includes an A / D converter that is connected to one electrode of the capacitor and converts an analog signal into a digital signal. If comprised in this way, when charging a capacity | capacitance by 1st reference potential, since the charge amount which can be charged to a capacity | capacitance per fixed time changes with the magnitudes of the light quantity irradiated to a photosensor, a photosensor is irradiated. The magnitude of the amount of light can be measured by the A / D converter as the amount of change in the charge voltage of the capacitor after a certain time has elapsed since the start of charging of the capacitor with the first reference potential.

  In this case, preferably, the charge voltage after a certain time is measured by the A / D converter, and the light quantity is measured based on the amount of change in the value of the charge voltage per certain time. With this configuration, the measurement of the light amount is performed by a periodic process, so that it is not necessary to perform a complicated process for interrupting the irregular process from outside the light amount detection device. Thereby, control of a light quantity detection apparatus can be simplified.

  In this case, it is preferable to further include a control unit connected to the other end of the resistor and the output of the A / D converter, and the control unit includes a timer that measures a predetermined time. If comprised in this way, since the charge voltage of the capacity | capacitance for every fixed time is measured by the timer contained in a control part measuring a fixed time, the light quantity irradiated to a photosensor is easily measured. be able to.

  In the light quantity detection device according to the first aspect, preferably, the other of the source / drain of the photosensor and the other electrode of the capacitor are connected to a second reference potential that is lower than the first reference potential. With this configuration, a potential difference can be generated between one and the other of the source / drain of the photosensor and between one electrode and the other electrode of the capacitor, so that the source / drain of the photosensor can be easily changed from one to the other. Leakage current can flow and capacity discharge can be performed.

  The light quantity detection device according to the first aspect preferably further includes a switch circuit disposed between the one electrode of the capacitor and the second reference potential that is lower than the first reference potential, and the switch circuit includes: The capacitor is discharged by connecting the one electrode of the capacitor and the second reference potential in the on state, and the capacitor is charged by disconnecting the connection of the one electrode of the capacitor and the second reference potential in the off state. According to this configuration, the capacitor can be easily discharged when the switch circuit is in the on state, and the capacitor can be easily charged when the switch circuit is in the off state.

  In the light quantity detection device according to the first aspect, preferably, an integrating circuit is configured by a resistor and a capacitor. If comprised in this way, since the charge of the capacity | capacitance by a 1st reference electric potential is performed slowly rather than rapidly by the integration circuit comprised from a resistor and a capacity | capacitance, it is easily contained in the light irradiated to a photosensor. Noise components can be averaged while the capacity is charged.

  A liquid crystal display device according to a second aspect of the present invention includes the light amount detection device according to the first aspect. If comprised in this way, the liquid crystal display device containing the light quantity detection apparatus which can measure light quantity, suppressing the influence of the noise of the light irradiated to an optical sensor can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a plan view of a liquid crystal display device including a light amount detection device according to a first embodiment of the present invention. FIG. 2 is a circuit diagram of the light quantity detection device according to the first embodiment of the present invention. First, with reference to FIG. 1 and FIG. 2, the structure of the light quantity detection apparatus 1 by 1st Embodiment of this invention is demonstrated.

  The light quantity detection device 1 according to the first embodiment is arranged in a liquid crystal display device 100 as shown in FIG. The liquid crystal display device 100 includes a liquid crystal display panel 50. The light quantity detection unit 20 of the light quantity detection device 1 is installed in the liquid crystal display panel 50, and the drive IC unit 10 of the light quantity detection device 1 is installed outside the liquid crystal display panel 50.

  On the glass substrate 51 of the liquid crystal display panel 50, the light amount detection unit 20, the display unit 52, the H driver 53, and the V driver 54 of the light amount detection device 1 are formed. The H driver 53 is provided for driving (scanning) the drain line, and the V driver 54 is provided for driving (scanning) the gate line. In the display unit 52, the pixels 60 are arranged in a matrix. Note that the display unit 52 shows only a configuration for one pixel for simplification. Each pixel 60 includes an n-channel transistor 61, a pixel electrode 62, a counter electrode 63 common to the pixels 60 arranged to face the pixel electrode 62, a liquid crystal 64 sandwiched between the pixel electrode 62 and the counter electrode 63, In addition, the auxiliary capacitor 65 is used. The drain D of the n-channel transistor 61 is connected to the drain line, and the source S is connected to the pixel electrode 62 and one electrode of the auxiliary capacitor 65. The gate G of the p-channel transistor 61 is connected to the gate line.

  Here, in the present embodiment, as shown in FIGS. 1 and 2, the driving IC unit 10 installed outside the liquid crystal display panel 50 includes a CPU 11, a switch circuit 12, a resistance element 13, a comparator 14, and the like. Is included. The CPU 11 and the resistance element 13 are examples of the “control unit” and “resistor” of the present invention, respectively. The comparator 14 is an example of the “comparator” in the present invention. As shown in FIG. 2, the CPU 11 is connected to the control terminal of the switch circuit 12 and the output side of the comparator 14. The CPU 11 has a function of generating an H (High) level signal and an L (Low) level signal as a start control signal to the switch circuit 12. Thereby, ON / OFF of the switch circuit 12 is controlled. Note that the switch circuit 12 is set to be turned off by an H level signal of the start control signal and to be turned on by an L level signal of the start control signal. Further, the CPU 11 starts from the time when the switch circuit 12 is turned off (when charging is started in the capacitor 22 described later) until the comparison voltage of the comparator 14 becomes equal to the charging voltage of the capacitor 22 described later. It has a timer 11a for measuring time. The comparator 14 outputs an L (Low) level signal if the voltage of the signal input to the comparator 14 is equal to or lower than the comparison voltage, and H if the voltage of the signal input to the comparator 14 is equal to or higher than the comparison voltage. It has a function of outputting a (High) level signal. One end 13 a of the resistance element 13 is connected to the power supply potential (VDD), and the other end 13 b is connected to one terminal of the switch circuit 12. The other terminal of the switch circuit 12 is grounded.

  As shown in FIG. 2, the light amount detection unit 20 includes an optical sensor 21 configured by an n-type thin film transistor and a capacitor 22. The source S of the photosensor 21 and the one electrode 22 a of the capacitor 22 are connected to each other and to the other end 13 b of the resistance element 13. In the first embodiment, an integrating circuit is configured by the resistance element 13 and the capacitor 22. Since the integration circuit includes the resistance element 13, the integration circuit has a feature that the capacitor 22 is charged more slowly than in the case where the resistance element 13 is not provided. In addition, the time required for charging can be changed by changing the resistance value of the resistance element 13. Further, the drain D of the photosensor 21 and the other electrode 22b of the capacitor 22 are grounded. One electrode 22 a of the capacitor 22 is connected to the comparator 14.

  FIG. 3 is a timing chart for explaining the operation of the light quantity detection device according to the first embodiment of the present invention, and a diagram showing the voltage characteristics of the capacitance. Next, with reference to FIG. 2 and FIG. 3, operation | movement of the light quantity detection apparatus 1 by 1st Embodiment of this invention is demonstrated.

  First, as shown in FIG. 3, the switch circuit 12 is maintained in an on state for a certain period by maintaining the L level start control signal for a certain period. As a result, the one electrode 22a of the capacitor 22 is grounded via the switch circuit 12, so that the capacitor 22 is discharged. Next, the switch circuit 12 is turned off by raising the start control signal to the H level. As a result, the capacitor 22 is charged with the power supply potential (VDD) via the resistance element 13.

  In the state where the capacitor 22 is charged, as shown in FIG. 2, when light is irradiated to the optical sensor 21, a leakage current is generated from the source S to the drain D of the optical sensor 21. The magnitude of this leakage current increases as the light intensity increases. Note that a constant voltage −Vg is applied to the gate G of the photosensor 21 formed of an n-type thin film transistor, and the n-type thin film transistor constituting the photosensor 21 is in an off state. Although the time required for charging the capacitor 22 is delayed due to the leakage current generated by irradiating the light to the optical sensor 21, the charging voltage Cw of the capacitor 22 is as shown by the solid line a0 in FIG. It rises over time.

  As shown in FIG. 3, after the elapse of time T0, the charging voltage Cw of the capacitor 22 becomes the same as the comparison voltage of the comparator 14, and the comparator 14 outputs an H level signal. A time T0 required for the charge voltage Cw of the capacitor 22 to be equal to the comparison voltage is measured by the timer 11a of the CPU 11.

  In addition, the degree of time delay required for charging the capacitor 22 varies depending on the amount of light applied to the optical sensor 21. That is, if the amount of light applied to the optical sensor 21 is large, the leakage current increases, so the degree of delay increases. Conversely, if the amount of light applied to the optical sensor 21 is small, the leakage current decreases, so the delay is delayed. The degree of becomes smaller. As shown by the one-dot chain line a1 in FIG. 3, when the amount of light to be irradiated is larger than that indicated by the solid line a0, the slope of the charging voltage Cw of the capacitor 22 becomes small, and the charging voltage Cw of the capacitor 22 becomes the comparison voltage. The time T1 until it becomes the same is longer than T0. In other words, the time until the H level signal is output from the comparator 14 becomes longer as the amount of light irradiated to the optical sensor 21 is larger, and conversely, as the amount of light irradiated to the optical sensor is smaller, the level from the comparator 14 becomes higher. The time until the signal is output is shortened. Therefore, the magnitude of the amount of light applied to the optical sensor 21 is measured based on the length of time from the start of charging of the capacitor 22 until the H level signal is output from the comparator 14.

  In the first embodiment, as described above, the capacitor 22 is charged by the power supply potential (VDD) via the resistor element 13, so that the capacitor 22 is slowly charged instead of rapidly due to the resistor element 13. Therefore, the noise component included in the light applied to the optical sensor 21 can be averaged while the capacitor 22 is charged. Thereby, it is possible to measure the amount of light while suppressing the influence of noise of light applied to the optical sensor 21.

  In the first embodiment, as described above, the comparator 14 is connected to the one electrode 22a of the capacitor 22 and compares the charging voltage of the one electrode 22a of the capacitor 22 with the comparison voltage. By measuring the amount of light by measuring the charging time based on the output signal output from the comparator 14 when they become the same, it is possible to easily measure the amount of light irradiated to the optical sensor. .

  In the first embodiment, as described above, since the drain D of the optical sensor 21 and the other electrode 22b of the capacitor 22 are grounded, the source S and drain D of the optical sensor 21 and the capacitance 22 Since there is a potential difference between the one electrode 22a and the other electrode 22b, a leakage current can easily flow from the source S to the drain D of the optical sensor 21, and the capacitor 22 can be discharged.

  In the first embodiment, as described above, the switch circuit 12 is provided between the one electrode 22a of the capacitor 22 and the ground (GND), and the switch circuit 12 has the capacitor 22 in the on state. The switch circuit 12 is turned on by grounding the electrode 22a to discharge the capacitor 22 and disconnecting the connection of the electrode 22a and the ground to the capacitor 22 in the off state. In this case, the capacitor 22 can be easily discharged, and when the switch circuit 12 is in the off state, the capacitor 22 can be easily charged.

  In the first embodiment, as described above, the integrating circuit is configured by the resistor element 13 and the capacitor 22, so that the charging of the capacitor 22 by the power supply potential (VDD) is configured by the resistor element 13 and the capacitor 22. Since the integration circuit performs the operation slowly rather than rapidly, the noise component included in the light irradiated to the optical sensor 21 can be easily averaged while the capacitor 22 is charged.

  In the first embodiment, as described above, the light amount detection device 1 is provided in the liquid crystal display device 100 including the liquid crystal display panel 50, and the optical sensor 21 and the capacitor 22 are arranged in the liquid crystal display panel 50. In addition, the resistance element 13 is disposed outside the liquid crystal display panel 50. By disposing the resistance element 13 outside the liquid crystal display panel 50 in this way, it is possible to reduce the variation in performance during the manufacture of the resistance element 13 as compared with the case where the resistance element 13 is formed on the liquid crystal display panel 50. Therefore, the detection accuracy of the light quantity detection device 1 can be increased.

  Note that all or a part of the driving IC unit 10 including the resistance element 13 may be formed on the liquid crystal display panel 50 by SOG (System On Glass) technology. As a result, the number of semiconductor components can be reduced, the assembly can be simplified, and the external circuit board can be reduced, so that the overall size and weight can be reduced.

(Second Embodiment)
FIG. 4 is a circuit diagram of a light amount detection apparatus according to the second embodiment of the present invention. With reference to FIG. 4, in the second embodiment, unlike the first embodiment, a light amount detection apparatus 2 including an A / D converter 15 instead of the comparator 14 will be described.

  In the light quantity detection device 2 according to the second embodiment, as shown in FIG. 4, an analog signal is converted into a digital signal between the source S of the optical sensor 21 and the one electrode 22 a of the capacitor 22 and the CPU 11. A / D converter 15 is arranged. Further, the CPU 11 includes a timer 11b for measuring a certain time T from the start of charging of the capacitor 22. In addition, the other structure of 2nd Embodiment is the same as that of the said 1st Embodiment.

  FIG. 5 is a timing chart for explaining the operation of the light quantity detection device according to the second embodiment of the present invention, and a diagram showing the voltage characteristics of the capacitance. Next, with reference to FIG. 4 and FIG. 5, operation | movement of the light quantity detection apparatus 2 by 2nd Embodiment of this invention is demonstrated.

  First, as shown in FIG. 5, the switch circuit 12 is kept on for a certain period by maintaining the L level start control signal for a certain period. As a result, the one electrode 22a of the capacitor 22 is grounded via the switch circuit 12, so that the capacitor 22 is discharged. Next, the switch circuit 12 is turned off by raising the start control signal to the H level. As a result, the capacitor 22 is charged with the power supply potential (VDD) via the resistance element 13.

  When light is applied to the optical sensor 21 while the capacitor 22 is charged, a leakage current is generated from the source S to the drain D of the optical sensor 21. Note that a constant voltage −Vg is applied to the gate G of the photosensor 21 formed of an n-type thin film transistor, and the n-type thin film transistor constituting the photosensor 21 is in an off state. In the second embodiment, the charging voltage Cw of the capacitor 22 is measured by the CPU 11 after being converted into a digital signal by the A / D converter 15. Although the time required for charging the capacitor 22 is delayed as compared with the case where no light is irradiated to the optical sensor 21 due to a leakage current generated when the optical sensor 21 is irradiated with light, it is indicated by a solid line b0 in FIG. As described above, the output of the A / D converter 15 rises with time. In the second embodiment, the timer 11b of the CPU 11 measures the fixed time T from the start of charging of the capacitor 22, and the charging voltage Cw of the capacitor 22 at the time when the fixed time T elapses passes through the A / D converter 15. And measured by the CPU 11.

  Further, as shown by a one-dot chain line b1 in FIG. 5, when the amount of light to be irradiated is larger than the case indicated by the solid line b0, the slope of the output of the A / D converter 15 (the charging voltage Cw of the capacitor 22) becomes small. The change amount ΔV1 of the charging voltage Cw of the capacitor 22 per certain time T is smaller than ΔV0 in the case indicated by the solid line b0. That is, as the amount of light applied to the optical sensor 21 increases, the leakage current also increases, so that the change amount ΔV0 of the charging voltage Cw per certain time T decreases. Therefore, the magnitude of the amount of light applied to the optical sensor 21 is measured based on the output of the A / D converter 15 (charge voltage Cw of the capacitor 22) after a predetermined time T has elapsed.

  In the second embodiment, as described above, the A / D converter 15 that is connected to the one electrode 22a of the capacitor 22 and converts an analog signal into a digital signal is provided, so that the capacitor 22 is charged by the power supply potential (VDD). When performing, the amount of charge that can be charged to the capacitor 22 per fixed time T varies depending on the amount of light irradiated to the optical sensor 21, so that the amount of light irradiated to the optical sensor 21 depends on the power supply potential (VDD). It can be measured by the A / D converter 15 as the amount of change in the charging voltage of the capacitor 22 after the elapse of a certain time T from when the charging of 22 is started.

  In the second embodiment, as described above, the charging voltage Cw after the lapse of the predetermined time T is measured by the A / D converter 15 and the light amount is calculated based on the amount of change in the value of the charging voltage Cw per fixed time T. By measuring, the measurement of the light quantity is performed by a periodic process, so that it is not necessary to perform a complicated process for interrupting the irregular process from the outside of the light quantity detection device 2. Thereby, control of the light quantity detection apparatus 2 can be simplified.

  In the second embodiment, as described above, the CPU 11 connected to the other end 13b of the resistance element 13 and the output of the A / D converter 15 is provided, and the CPU 11 includes the timer 11b that measures a predetermined time. Thus, since the timer included in the CPU 11 measures the predetermined time, the charge voltage Cw of the capacitor 22 is measured every predetermined time T via the output of the A / D converter 15. The amount of light to be irradiated can be measured.

  The remaining effects of the second embodiment are similar to those of the aforementioned first embodiment.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiment but by the scope of claims for patent, and includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the above-described embodiment, an example using an optical sensor configured by an n-type thin film transistor has been described. However, the present invention is not limited thereto, and an optical sensor configured by a p-type thin film transistor may be used.

  Moreover, although the example which arrange | positions a capacity | capacitance on a display panel was shown in the said embodiment, this invention is not limited to this, You may arrange | position a capacity | capacitance outside a display panel.

  In the above embodiment, the drain of the photosensor and the other electrode of the capacitor are grounded. However, the present invention is not limited to this, and the drain of the photosensor and the other electrode of the capacitor are connected to the ground potential ( It may be connected to a reference potential lower than the power supply potential (VDD) other than GND). Further, the drain of the photosensor and the other electrode of the capacitor may be connected to different reference potentials that are lower than the power supply potential (VDD).

It is a top view of the liquid crystal display device provided with the light quantity detection apparatus by 1st Embodiment of this invention. It is a circuit diagram of the light quantity detection apparatus by 1st Embodiment of this invention. It is the figure for showing the timing chart for demonstrating operation | movement of the light quantity detection apparatus by 1st Embodiment of this invention, and the characteristic of the voltage of a capacity | capacitance. It is a circuit diagram of the light quantity detection apparatus by 2nd Embodiment of this invention. It is the timing chart for demonstrating operation | movement of the light quantity detection apparatus by 2nd Embodiment of this invention, and the figure showing the characteristic of the voltage of a capacity | capacitance. It is a circuit diagram of the light quantity detection apparatus provided with the optical sensor comprised by the conventional thin-film transistor. It is the timing chart for demonstrating operation | movement of the light quantity detection apparatus provided with the optical sensor comprised by the conventional thin-film transistor, and the figure showing the characteristic of the voltage of the gate of a 2nd switching transistor.

Explanation of symbols

11 CPU (control unit)
11a timer 11b timer 12 switch circuit 13 resistance element (resistor)
14 Comparator
15 A / D converter 21 Optical sensor 22 Capacitance

Claims (9)

A resistor,
An optical sensor comprising a thin film transistor;
With capacity,
One end of the resistor is connected to a first reference potential;
One end of the source / drain of the photosensor and one electrode of the capacitor are connected in parallel to the other end of the resistor,
A light amount detection device that measures a light amount based on a charging voltage when the capacitor is charged through the resistor by the first reference potential. A comparator connected to one electrode of the capacitor and comparing a charging voltage and a comparison voltage of the one electrode of the capacitor;
The light quantity detection device according to claim 1, wherein the light quantity is measured by measuring a charging time based on an output signal output from the comparator when the charging voltage becomes equal to the comparison voltage.   The light quantity detection device according to claim 1, further comprising an A / D converter connected to one electrode of the capacitor and converting an analog signal into a digital signal.   The light quantity detection device according to claim 3, wherein the charge voltage after a predetermined time is measured by the A / D converter and the light quantity is measured based on a change amount of the value of the charge voltage per fixed time. A control unit connected to the other end of the resistor and the output of the A / D converter;
The light quantity detection device according to claim 4, wherein the control unit includes a timer that measures the predetermined time.   6. The device according to claim 1, wherein the other of the source / drain of the photosensor and the other electrode of the capacitor are connected to a second reference potential that is lower than the first reference potential. The light quantity detection device described. A switch circuit disposed between one electrode of the capacitor and a second reference potential that is lower than the first reference potential;
The switch circuit connects the one electrode of the capacitor and the second reference potential in an on state to discharge the capacitor, and connects the one electrode of the capacitor to the second reference potential in an off state. The light quantity detection device according to claim 1, wherein the capacity is charged by cutting the capacitor.   The light quantity detection device according to claim 1, wherein an integrating circuit is configured by the resistor and the capacitor.   The liquid crystal display device provided with the light quantity detection apparatus of any one of Claims 1-8.

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