Image sensor with capacitive amplifier and associated methods
First Claim
Patent Images
1. An image sensor comprising:
- an array of light sensitive pixels, each pixel comprising a photosensitive element that develops a charge in response to incident light, a sense node, a transfer gate connected to said photosensitive element for transferring the charge to the sense node, a reset gate connected to the sense node, a read gate connected to said reset gate, a source follower connected to the sense node and said read gate, and forming part of an output amplifier, a gain capacitor connected between the sense node and said read gate for forming part of a feedback path across the output amplifier, said gain capacitor being controlled by said read and reset gates for resetting the pixel to a desired voltage, and said reset gate being connected across said gain capacitor and said read gate being connected in series with said gain capacitor so that when said reset and read gates are both closed, the output amplifier operates as a unity gain amplifier.
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Abstract
An image sensor includes pixels which are of the four-transistor, PIN photodiode type. In each pixel, the charge on a photodiode is transferred by a transfer gate to a sensing node. Readout of reset and read voltages is via an amplifier. A gain capacitor is connected in feedback across the amplifier. Read and reset gates are controlled so that the pixel is reset to a virtual ground voltage controlled by the gain capacitor. This is independent of the pixel parasitic capacitance.
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Citations
24 Claims
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1. An image sensor comprising:
an array of light sensitive pixels, each pixel comprising a photosensitive element that develops a charge in response to incident light, a sense node, a transfer gate connected to said photosensitive element for transferring the charge to the sense node, a reset gate connected to the sense node, a read gate connected to said reset gate, a source follower connected to the sense node and said read gate, and forming part of an output amplifier, a gain capacitor connected between the sense node and said read gate for forming part of a feedback path across the output amplifier, said gain capacitor being controlled by said read and reset gates for resetting the pixel to a desired voltage, and said reset gate being connected across said gain capacitor and said read gate being connected in series with said gain capacitor so that when said reset and read gates are both closed, the output amplifier operates as a unity gain amplifier. - View Dependent Claims (2, 3, 4, 5)
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6. An image sensor comprising:
an array of pixels, each pixel comprising a photosensitive element that develops a charge upon receiving incident light, a sense node, a transfer gate connected to said photosensitive element for transferring the charge to the sense node, a reset gate connected to the sense node, a read gate connected to the sense node, a source follower connected to the sense node, and forming part of an output amplifier, and a capacitor connected to said read gate and said source follower for forming part of a feedback path across the output amplifier, said capacitor being controlled by said read and reset gates for resetting the pixel to a desired voltage, and said reset gate being connected across said gain capacitor and said read gate being connected in series with said capacitor so that when said reset and read gates are both closed, the output amplifier operates as a unity gain amplifier. - View Dependent Claims (7, 8, 9, 10)
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11. An image sensor comprising:
an array of light sensitive pixels arranged in rows and columns, each column comprising a column reset gate and an amplifier gate connected to said column reset gate, and each pixel comprising a photosensitive element that develops a charge in response to incident light, a sense node, a transfer gate connected to said photosensitive element for transferring the charge to the sense node, a reset gate connected to the sense node, a read gate connected to the sense node, a source follower connected to the sense node and said amplifier gate, and forming part of an output amplifier, and a gain capacitor connected to said read gate and to said column reset gate and said amplifier gate for forming part of a feedback path across the output amplifier, said gain capacitor being driven by said column reset gate and said amplifier gate for causing an output voltage of the output amplifier to be level-shifted to a desired voltage at an end of each reset and read cycle, and said reset gate being connected across said gain capacitor and said read gate being connected in series with said gain capacitor so that when said reset and read gates are both closed, the output amplifier operates as a unity gain amplifier. - View Dependent Claims (12, 13, 14, 15)
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16. A method for operating an image sensor comprising an array of light sensitive pixels, each pixel comprising four transistors and a PIN photodiode, the four transistors comprising a transfer transistor connected to the PIN photodiode, a reset transistor connected to a sense node, a read transistor connected to the reset transistor, and an output transistor connected to the sense node and the read transistor for forming part of an output amplifier, a gain capacitor connected between the sense node and the read gate for forming part of a feedback path across the output amplifier, and wherein the reset transistor is connected across a gain capacitor, and the read transistor is connected in series with the gain capacitor, the method comprising:
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developing a charge in response to each PIN photodiode receiving incident light;
transferring the charges from the PIN photodiodes to the sense nodes via the transfer transistors;
transferring the charges from the sense nodes to respective gain capacitors connected in feedback across respective output amplifiers; and
closing the reset and read transistors for causing the pixel output amplifier to operate as a unity gain amplifier. - View Dependent Claims (17, 18)
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19. A method for operating an image sensor comprising an array of light sensitive pixels, each pixel comprising a plurality of transistors and a PIN photodiode, the plurality of transistors comprising a transfer transistor connected to the PIN photodiode, a reset transistor connected to a sense node, a read transistor connected to the sense node, and an output transistor connected to the sense node for forming part of an output amplifier, a gain capacitor connected to the read gate and the output transistor for forming part of a feedback path across the output amplifier, and wherein the reset transistor is connected across the gain capacitor and the read transistor is connected in series with the gain capacitor, the method comprising:
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developing a charge in response to each PIN photodiode receiving incident light;
transferring the charges from the PIN photodiodes to the sense nodes via the transfer transistors;
transferring the charges from the sense nodes to respective gain capacitors connected in feedback across respective output amplifiers; and
closing both the reset and read transistors for causing the pixel output amplifier to operate as a unity gain amplifier. - View Dependent Claims (20, 21)
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22. A method for operating an image sensor comprising an array of light sensitive pixels arranged in rows and columns, each column comprising a column reset gate and an amplifier gate connected to the column reset gate, each pixel comprising a plurality of transistors and a PIN photodiode, the plurality of transistors comprising a transfer transistor connected to the PIN photodiode, a reset transistor connected to a sense node, a read transistor connected to the sense node, and an output transistor connected to the sense node and the amplifier gate for forming part of an output amplifier, the reset transistor being connected across the gain capacitor and the read transistor being connected in series with the gain capacitor, the method comprising:
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developing a charge in response to each PIN photodiode receiving incident light;
transferring the charges from the PIN photodiodes to the sense nodes via the transfer transistors;
transferring the charges from the sense nodes to respective gain capacitors connected in feedback across respective output amplifiers; and
closing both the reset and read transistors for causing the pixel output amplifier to operate as a unity gain amplifier. - View Dependent Claims (23, 24)
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Specification
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Current AssigneeSTMicroelectronics Limited (STMicroelectronics NV)
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Original AssigneeSTMicroelectronics Limited (STMicroelectronics NV)
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InventorsHenderson, Robert
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Primary Examiner(s)Porta, David
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Assistant Examiner(s)YAM, STEPHEN K
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Application NumberUS10/350,166Publication NumberTime in Patent Office985 DaysField of Search350/214.A, 350/208.1, 348300-308, 330/308US Class Current250/214.00ACPC Class CodesH04N 25/672 between adjacent sensors or...H04N 25/77 Pixel circuitry, e.g. memor...
