Light quantity detection circuit and display panel using the same
First Claim
1. A light quantity detection circuit comprising:
- a photosensor comprising a thin film transistor comprising a gate electrode disposed on a substrate, a semiconductor layer disposed on the substrate, an insulating film disposed between the gate electrode and the semiconductor layer, the photosensor converting light incident thereon into an output comprising an electric signal, and the semiconductor layer comprising a channel, a source disposed at one end of the channel and a drain disposed at another end of the channel;
a first resistor connected with the photosensor in parallel;
a switching transistor comprising a gate receiving the output of the photosensor and a first and second terminals between which a current runs in response to the output of the photosensor, the first terminal of the switching transistor being connected with a first power terminal and the second terminal of the switching transistor being connected with a second power terminal;
a second resistor connecting the first terminal of the switching transistor and the first power terminal; and
an output terminal connected with a wiring connecting the second resistor and the first terminal of the photosensor.
1 Assignment
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Accused Products
Abstract
Since a photosensor using a diode is incapable of perform refresh because of the structure, and the leak characteristics are unstable, the diode is not suitable for the photosensor. On the other hand, in a photosensor using a thin film transistor, since light quantity is very small, there has been a problem that feedback is difficult. A detection circuit converting an output current into a voltage is added to a photosensor using a thin film transistor. Thus, it is possible to convert a very small current into a voltage in a desired range enabling feedback. In addition, by varying resistors, capacitors, and the number of TFTs connected in the photosensor included in the circuit, it is made possible to change the sensitivity of the photosensor.
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Citations
27 Claims
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1. A light quantity detection circuit comprising:
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a photosensor comprising a thin film transistor comprising a gate electrode disposed on a substrate, a semiconductor layer disposed on the substrate, an insulating film disposed between the gate electrode and the semiconductor layer, the photosensor converting light incident thereon into an output comprising an electric signal, and the semiconductor layer comprising a channel, a source disposed at one end of the channel and a drain disposed at another end of the channel;
a first resistor connected with the photosensor in parallel;
a switching transistor comprising a gate receiving the output of the photosensor and a first and second terminals between which a current runs in response to the output of the photosensor, the first terminal of the switching transistor being connected with a first power terminal and the second terminal of the switching transistor being connected with a second power terminal;
a second resistor connecting the first terminal of the switching transistor and the first power terminal; and
an output terminal connected with a wiring connecting the second resistor and the first terminal of the photosensor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A light quantity detection circuit comprising:
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a photosensor comprising a thin film transistor comprising a gate electrode disposed on a substrate, a semiconductor layer disposed on the substrate, an insulating film disposed between the gate electrode and the semiconductor layer, the photosensor converting light incident thereon into an output comprising an electric signal, and the semiconductor layer comprising a channel, a source disposed at one end of the channel and a drain disposed at another end of the channel;
a first capacitor comprising a first terminal receiving the output of the photosensor and a second terminal applied with a reference voltage;
a first switching transistor allowing a current flow between a first and second terminals thereof, the first terminal of the first switching transistor being connected with the first terminal of the first capacitor;
a second capacitor comprising a first terminal connected with the second terminal of the first switching transistor and a second terminal applied with the reference voltage;
a second switching transistor comprising a first terminal connected with the first terminal of the second capacitor and a second terminal applied with the reference voltage; and
a timing device supplying timing signals to the first and second switching transistors so that electric charges are stored in the first capacitor in response to the output of the photosensor, the electric charges stored in the first capacitor are transferred to the second capacitor by turning on the first switching transistor, and an output voltage is outputted from the first terminal of the second capacitor while the second switching transistor is turned off. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17)
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18. A light quantity detection circuit comprising:
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a photosensor comprising a thin film transistor comprising a gate electrode disposed on a substrate, a semiconductor layer disposed on the substrate, an insulating film disposed between the gate electrode and the semiconductor layer, the photosensor converting light incident thereon into an output comprising an electric signal, and the semiconductor layer comprising a channel, a source disposed at one end of the channel and a drain disposed at another end of the channel;
a first switching transistor allowing a current flow between a first and second terminals thereof, the first terminal of the first switching transistor receiving the output of the photosensor;
a first capacitor comprising a first terminal connected with the second terminal of the first switching transistor and a second terminal applied with a reference voltage;
a second switching transistor allowing a current flow between a first and second terminals thereof, the first terminal of the second switching transistor being connected with the first terminal of the first capacitor and the second terminal of the second switching transistor being connected with a power terminal;
a third switching transistor allowing a current flow between a first and second terminals thereof, the first terminal of the third switching transistor being connected with the first terminal of the first capacitor;
a second capacitor comprising a first terminal connected with the second terminal of the third switching transistor and a second terminal applied with the reference voltage;
a fourth switching transistor allowing a current flow between a first and second terminals thereof, the first terminal of the fourth switching transistor being connected with the power terminal, the second terminal of the fourth switching transistor being applied with the reference voltage, and a gate of the fourth switching transistor being connected with the first terminal of the second capacitor;
a resistor connecting the power terminal and the first terminal of the fourth switching transistor;
an output terminal connected with a wiring connecting the resistor and the first terminal of the fourth switching transistor; and
a timing device supplying timing signals to the first, second and third switching transistors so that electric charges are supplied from the power terminal to the first capacitor by turning on the second switching transistor, at least part of the electric charges supplied to the first capacitor is discharged through the photosensor by turning on the first switching transistor, and the electric charges remaining in the first capacitor are transferred to the second capacitor by turning on the third switching transistor. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25)
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26. A display panel comprising:
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a display unit formed on a substrate, the display unit comprising;
a plurality of drain lines and a plurality of gate lines that are arranged in a matrix configuration, a plurality of display pixels, each of the display pixels being connected with one of the drain lines and one of the gate lines; and
a light quantity detection circuit comprising a photosensor converting light incident thereon into an electric signal; and
an external control circuit supplying control signal and a power for driving the display pixels and supplying the control signal, the power or the control signal and power to the light quantity detection circuit for an operation thereof. - View Dependent Claims (27)
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Specification