CMOS image sensor with improved fill factor
First Claim
Patent Images
1. An active pixel sensor (APS) circuit, comprising:
- (a) a photodetector which produces a node voltage at a node in accordance with light sensed by the photodetector;
(b) a first transistor coupled at a gate terminal to the node and directly coupleable at a source terminal to an output line coupled to a sample and hold circuit, wherein the first transistor is configured to operate in source follower mode to provide an output voltage on the output line having a magnitude related to the magnitude of the node voltage; and
(c) a second transistor having a source terminal coupled to the gate terminal of the first transistor, a gate terminal coupled to a phase reset signal, and a drain terminal coupled to a row voltage signal and to a drain terminal of the first transistor, wherein;
the phase reset signal switches high during times at which the charge stored in the photodetector is not being read to couple the gate terminal of the first transistor to the row voltage signal; and
the row voltage signal switches low during times at which the charge stored in the photodetector is not being read to switch off the first transistor, whereby the circuit is isolated from the output line when the charge stored in the photodetector is not being read.
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Abstract
An active pixel sensor circuit and method. According to one embodiment, a photodetector produces a voltage at a floating diffusion node in accordance with light sensed by the photodetector. An active element is coupled at a control terminal to the floating diffusion node and is directly couplable at an output terminal to an output line. The active element is configured to provide an output voltage on the output line having a magnitude related to the magnitude of the floating diffusion node voltage.
101 Citations
16 Claims
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1. An active pixel sensor (APS) circuit, comprising:
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(a) a photodetector which produces a node voltage at a node in accordance with light sensed by the photodetector; (b) a first transistor coupled at a gate terminal to the node and directly coupleable at a source terminal to an output line coupled to a sample and hold circuit, wherein the first transistor is configured to operate in source follower mode to provide an output voltage on the output line having a magnitude related to the magnitude of the node voltage; and (c) a second transistor having a source terminal coupled to the gate terminal of the first transistor, a gate terminal coupled to a phase reset signal, and a drain terminal coupled to a row voltage signal and to a drain terminal of the first transistor, wherein; the phase reset signal switches high during times at which the charge stored in the photodetector is not being read to couple the gate terminal of the first transistor to the row voltage signal; and the row voltage signal switches low during times at which the charge stored in the photodetector is not being read to switch off the first transistor, whereby the circuit is isolated from the output line when the charge stored in the photodetector is not being read. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. In an APS circuit comprising (1) a photodetector which produces a node voltage at a node in accordance with light sensed by the photodetector, (2) a first transistor coupled at a gate terminal to the node and directly coupled at a source terminal to an output line coupled to a sample and hold circuit, and (3) a second transistor having a source terminal coupled to the gate terminal of the first transistor, a method comprising the steps of:
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(a) switching a phase reset signal coupled to a gate terminal of the second transistor high during times at which a charge stored in the photodetector is not being read to couple the gate terminal of the first transistor to a drain terminal of the second transistor, wherein the drain terminal of the second transistor is coupled to a drain terminal of the first transistor and to a row voltage signal; and (b) switching the row voltage signal low during times at which the charge stored in the photodetector is not being read to switch off the first transistor, whereby the circuit is isolated from the output line, wherein, when the charge stored in the photodetector is being read, the first transistor is configured to operate in source follower mode to provide an output voltage on the output line having a magnitude related to the magnitude of the node voltage. - View Dependent Claims (10, 11)
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12. An image sensor, comprising an array of APS circuits, each APS circuit of the array comprising:
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(1) a photodetector which produces a node voltage at a node in accordance with light sensed by the photodetector; (2) a first transistor coupled at a gate terminal to the node and directly coupleable at a source terminal to a column output line for the array column for said each APS circuit, wherein said column output line is coupled to a sample and hold circuit, further wherein the first transistor is configured to operate in source follower mode to provide an output voltage on the column output line having a magnitude related to the magnitude of the node voltage; and (3) a second transistor having a source terminal coupled to the gate terminal of the first transistor, a gate terminal coupled to a phase reset signal, and a drain terminal coupled to a row voltage signal and to a drain terminal of the first transistor, wherein; the phase reset signal switches high during times at which the charge stored in the photodetector is not being read to couple the gate terminal of the first transistor to the row voltage signal; and the row voltage signal switches low during times at which the charge stored in the photodetector is not being read to switch off the first transistor, whereby the circuit is isolated from the column output line when the charge stored in the photodetector is not being read. - View Dependent Claims (13)
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14. In an image sensor comprising an array of APS circuits, wherein each APS circuit of the array comprises (1) a photodetector which produces a node voltage at a node in accordance with light sensed by the photodetector, (2) a first transistor coupled at a gate terminal to the node and directly coupled at a source terminal to a column output line for the array column for said each APS circuit, said column output line being coupled to a sample and hold circuit, and (3) a second transistor having a source terminal coupled to the gate terminal of the first transistor, a method comprising the steps of column output line for the array column for said each APS circuit, a method comprising the step of:
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(a) switching a phase reset signal coupled to a gate terminal of the second transistor high during times at which a charge stored in the photodetector is not being read to couple the gate terminal of the first transistor to a drain terminal of the second transistor, wherein the drain terminal of the second transistor is coupled to a drain terminal of the first transistor and to a row voltage signal; and (b) switching the row voltage signal low during times at which the charge stored in the photodetector is not being read to switch off the first transistor, whereby the at least one APS circuit is isolated from the column output line, wherein, when the charge stored in the photodetector is being read, the first transistor is configured to operate in source follower mode to provide an output voltage on the output line having a magnitude related to the magnitude of the node voltage. - View Dependent Claims (15, 16)
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Specification