Image sensor with switchable in-pixel binning during readout

An integrated-circuit image sensor, comprising:

• a photodetection element to accumulate a photocharge;
• first and second floating diffusion nodes switchably coupled to the photodetection element via first and second transfer gates, respectively;
• an in-pixel binning transistor that switchably couples the first and second floating diffusion nodes;
• and
• readout control circuitry to:
• switch on the first transfer gate to enable transfer of a first portion of the photocharge from the photodetection element to the first floating diffusion node;
• switch on the second transfer gate to enable transfer of a second portion of the photocharge from the photodetection element to the second floating diffusion node;
• generate a first readout value based on the first portion of the photocharge in the first floating diffusion node;
• switch on the in-pixel binning transistor to create a composite floating diffusion node that combines capacitances of the first and second floating diffusion nodes;
• and
• generate a second readout value based on the second portion of the photocharge in the composite floating diffusion node.

A method of operation of an integrated-circuit image sensor, comprising:

• accumulating a photocharge within a photodetection element;
• operating readout control circuitry to generate a first readout value and a second readout value from the photodetection element, including:
• switching on a first transfer gate to enable transfer of a first portion of the photocharge from the photodetection element to a first floating diffusion node;
• switching on a second transfer gate to enable transfer of a second portion of the photocharge from the photodetection element to a second floating diffusion node;
• generating the first readout value based on the first portion of the photocharge in the first floating diffusion node;
• switching on an in-pixel binning transistor between the first and second floating diffusion nodes to create a composite floating diffusion node that combines capacitances of the first and second floating diffusion nodes;
• and
• generating the second readout value based on the second portion of the photocharge in the composite floating diffusion node.