Method and apparatus for reducing kTC noise in an active pixel sensor (APS) device
First Claim
Patent Images
1. An apparatus comprising:
- a sensor including a plurality of pixels arranged in an array, each pixel including;
a photodetector;
a node, adapted for providing a supply voltage;
a reset transistor connected between the photodetector and the supply voltage node;
a sampling branch operative to sample a reset signal from the pixel; and
a readout controller operative to perform a reference reset operation by asserting a reset signal on a gate of the reset transistor at a voltage greater than a reference voltage, wherein the reference voltage is a minimum voltage which causes the reset transistor to conduct and clamp the pixel to the supply voltage, and to control the sampling branch to sample the reset signal during the reference reset operation.
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Abstract
An image sensing device, such as a CMOS Active Pixel Sensor (APS) device, includes an array of pixels. Each pixel includes a reset transistor connected between a photodetector and a supply voltage. In a readout operation, a signal integrated onto the photodetector is sampled onto a holding capacitor. The photodetector is then reset in a reference reset operation during which the photodetector is clamped to the supply voltage. A reset signal is sampled from the pixel while the photodetector is clamped to the supply voltage. Reset, or kTC, noise in the reset signal may be filtered by a source-follower transistor in the pixel.
31 Citations
21 Claims
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1. An apparatus comprising:
a sensor including a plurality of pixels arranged in an array, each pixel including;
a photodetector;
a node, adapted for providing a supply voltage;
a reset transistor connected between the photodetector and the supply voltage node;
a sampling branch operative to sample a reset signal from the pixel; and
a readout controller operative to perform a reference reset operation by asserting a reset signal on a gate of the reset transistor at a voltage greater than a reference voltage, wherein the reference voltage is a minimum voltage which causes the reset transistor to conduct and clamp the pixel to the supply voltage, and to control the sampling branch to sample the reset signal during the reference reset operation. - View Dependent Claims (2, 3, 4)
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5. An apparatus comprising:
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a rolling shutter sensor comprising a plurality of three transistor (3T) pixels arranged in an array, each pixel including;
a photodetector;
a node, adapted for providing a supply voltage;
a reset transistor connected between the photodetector and the supply voltage node;
a sampling branch operative to sample a reset signal from the pixel; and
a readout controller, wherein said readout controller is operative to perform a reference reset operation by asserting a reset signal on a gate of the reset transistor at a voltage greater than a minimum voltage which causes the reset transistor to conduct and clamp the pixel to the supply voltage, to control the sampling branch to sample the reset signal during the reference reset operation, and to decrease the supply voltage by a threshold voltage of the reset transistor while the reset signal is being sampled.
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6. An apparatus comprising:
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a freeze-frame shutter sensor including a plurality of five transistor (5T) pixels arranged in an array, each pixel including;
a photodetector;
a node, adapted for providing a supply voltage;
a reset transistor connected between the photodetector and the supply voltage node;
a sampling branch operative to sample a reset signal from the pixel; and
a readout controller operative to perform a reference reset operation by asserting a reset signal on a gate of the reset transistor at a voltage greater than a minimum voltage which causes the reset transistor to conduct and clamp the pixel to the supply voltage, and to control the sampling branch to sample the reset signal during the reference reset operation.
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7. A method comprising:
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resetting a sensing node in a pixel by asserting a reset signal at a gate of a reset transistor at a level higher than a reference voltage, wherein the reference voltage is a minimum voltage which causes the reset transistor to conduct and clamp the sensing node to a supply voltage; and
sampling a reset value while the reset signal is asserted and the sensing node is clamped to the supply voltage. - View Dependent Claims (8, 9, 10, 11)
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12. A method comprising the steps of:
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resetting a sensing node in a pixel by asserting a reset signal at a gate of a reset transistor at a level higher than a minimum voltage which causes the reset transistor to conduct and clamp the sensing node to a supply voltage; and
sampling a reset value while reducing the supply voltage when the reset signal is asserted and the sensing node is clamped to the supply voltage. - View Dependent Claims (13)
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14. A method comprising:
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resetting a sensing node in a pixel by asserting a reset signal at a gate of a reset transistor at a level higher than a minimum voltage which causes the reset transistor to conduct and clamp the sensing node to a supply voltage to reset a photodetector in a freeze-frame shutter Active Pixel Sensor (APS) device; and
sampling a reset value while the reset signal is asserted and the sensing node is clamped to the supply voltage. - View Dependent Claims (15)
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16. A method for reducing kTC noise in a Complemenary Metal Oxide Semiconductor (CMOS) sensor device, the method comprising:
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asserting a reset signal at a gate of a reset transistor at a voltage greater than a reference voltage, wherein the reference voltage is a minimum voltage which causes the reset transistor to conduct and clamp a pixel to a supply voltage; and
reading a reset value for said pixel in the sensor while a sensing node in the pixel is clamped to said supply voltage. - View Dependent Claims (17, 18, 19, 20, 21)
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Specification