Feedthrough-compensated image sensor

An integrated-circuit image sensor having pixels disposed in constituent rows and columns of a pixel array, the integrated-circuit image sensor comprising:

• a first photodetector that accumulates photocharge in response to incident light;
• a first and second capacitive nodes;
• a first transfer gate disposed between the photodetector and the first capacitive node and having a control terminal coupled to a transfer-gate control line that extends in a row-wise direction across the pixel array;
• an output transistor having a control terminal coupled to the first capacitive node and an output terminal switchably coupled to a column output line that extends in a column-wise direction across the pixel array;
• and
• a conversion-gain transistor coupled between the first and second capacitive nodes and having a control terminal coupled to a conversion-gain-select line that extends in the column-wise direction across the pixel array.

An integrated-circuit image sensor having pixels disposed in constituent rows and columns of a pixel array, the integrated-circuit image sensor comprising:

• a photodetector that accumulates photocharge throughout an exposure interval;
• a first and second capacitive nodes;
• a transfer gate disposed between the photodetector and the first capacitive node and having a control terminal coupled to a transfer-gate control line that extends in a row-wise direction across the pixel array;
• an output transistor having a control terminal coupled to the first capacitive node and an output terminal switchably coupled to a column output line that extends in a column-wise direction across the pixel array;
• a conversion-gain transistor coupled between the first and second capacitive nodes and having a control terminal coupled to a conversion-gain-select line;
• and
• control circuitry to generate in succession, at conclusion of the exposure interval:
• a high-conversion-gain readout signal on the column output line by driving the transfer-gate control line to a state that enables photocharge conduction via the transfer gate while driving the conversion-gain-select line to a first state that renders the conversion-gain transistor in a non-conducting state to electrically isolate the second capacitive node from the first capacitive node, and
• a lower-conversion-gain readout signal on the column output line, while the transfer-gate control line is driven to the state that enables photocharge conduction via the transfer gate, by driving the conversion-gain-select line to a second state that renders the conversion-gain transistor in a conducting state to electrically couple the second capacitive node from the first capacitive node.

A method of operation within an integrated-circuit image sensor having pixels disposed in constituent rows and columns of a pixel array, the method comprising:

• accumulating photocharge within a photodetector during an exposure interval;
• and
• generating in succession at conclusion of the exposure interval:
• a high-conversion-gain readout signal by enabling conduction of the photocharge accumulated within the photodetector to a first capacitive readout node;
• and
• a lower-conversion-gain readout signal by switchably coupling a second capacitive node to the first capacitive readout node and enabling conduction, at least to the second capacitive node, of photocharge remaining within the photodetector after generation of the high-conversion-gain readout signal.