Apparatus and methods for dark level compensation in image sensors using dark pixel sensor metrics
First Claim
1. A complementary metal oxide semiconductor (CMOS) image sensor, comprising:
- a CMOS pixel sensor array comprising a plurality of rows of CMOS pixel sensors, each row of CMOS pixel sensors comprising at least one dark pixel sensor; and
a dark level compensation circuit that controls an offset applied to an image signal generated by a CMOS pixel sensor of the CMOS pixel array responsive to an aggregate dark level metric derived from dark pixel image signals produced by the dark pixel sensors.
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Abstract
An image sensor comprises a plurality of pixel sensors, e.g., CMOS pixel sensors, including a plurality of dark pixels. A dark level compensation circuit that controls an offset applied to an image signal generated by a pixel sensor responsive to an aggregate dark level metric, e.g., a mean dark level, derived from dark pixel image signals produced by the dark pixel sensors. For example, the dark level compensation circuit for CMOS image sensor using a column parallel architecture may generate an offset control signal that varies an offset of a reference signal used by an analog to digital converter (ADC) circuit that converts an analog image signal from a pixel sensor to a dark level compensated digital image signal.
122 Citations
25 Claims
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1. A complementary metal oxide semiconductor (CMOS) image sensor, comprising:
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a CMOS pixel sensor array comprising a plurality of rows of CMOS pixel sensors, each row of CMOS pixel sensors comprising at least one dark pixel sensor; and
a dark level compensation circuit that controls an offset applied to an image signal generated by a CMOS pixel sensor of the CMOS pixel array responsive to an aggregate dark level metric derived from dark pixel image signals produced by the dark pixel sensors. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An image sensor, comprising:
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a plurality of pixel sensors that produce respective analog image signals, the plurality of pixel sensors including a plurality of dark pixel sensors;
an analog to digital converter (ADC) circuit that receives an analog image signal generated by a pixel sensor of the plurality of pixel sensors and that produces a digital image signal therefrom subject to an offset controlled by an offset control signal; and
a dark level compensation circuit that generates the offset control signal responsive to analog image signals produced by the dark pixel sensors. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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19. A method of operating an image sensor, comprising:
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generating dark pixel image signals from dark pixel sensors on multiple rows of a CMOS pixel sensor array;
generating an offset control signal from the dark pixel image signals;
producing an image signal from a pixel sensor of the CMOS pixel sensor array; and
applying an offset to the image signal responsive to the offset control signal. - View Dependent Claims (20, 21, 22)
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23. A method of operating an image sensor comprising a plurality of pixel sensors, the method comprising:
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generating dark pixel image signals from a plurality of dark pixel sensors included in the plurality of pixel sensors;
generating an offset control signal from the dark pixel image signals;
applying the offset control signal to an analog to digital converter (ADC) circuit that receives an analog image signal produced by a pixel sensor of the plurality of pixel sensors to produce a dark level compensated digital image signal. - View Dependent Claims (24, 25)
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Specification