Image sensor with configurable pixel circuit and method

An image sensor comprising a plurality of pixel circuits each comprising:

• a photodiode connected between ground and a floating diffusion (FD) node,
• a reset transistor (MRST) configured to be connected between a first voltage supply and the floating diffusion (FD) node,
• a source follower transistor (MSF), wherein a drain of the source follower transistor (MSF) is connected to a second voltage supply, a gate of the source follower transistor (MSF) is connected to the floating diffusion (FD) node and a source of the source follower transistor (MSF) is connected to a row select transistor (MSEL), and
• the row select transistor (MSEL) is connected between the source of the source follower transistor (MSF) and a common column output,
• wherein each pixel circuit is configured to provide an output signal corresponding to a light incident on the photodiode;
• and
• wherein, to configure each pixel circuit to selectively output a linear integration signal or a logarithmic signal, each pixel circuit further comprises:
• a bias transistor (MVB) connected between the second voltage supply and the drain of the source follower transistor (MSF),
• a second additional transistor (MS2) configured to connect a drain of the bias transistor (MVB) to a drain of the reset transistor (MRST), and
• a third additional transistor (MS3) configured to connect the reset transistor (MRST) to the first voltage supply, and
• a fourth additional switch transistor (MS4) configured to connect the drain of the reset transistor (MRST) and a gate of the reset transistor (MRST).

A method for reconfiguring an image sensor comprising a plurality of pixel circuits, the method comprising:

• providing a photodiode connected between ground and a floating diffusion (FD) node,
• providing a reset transistor (MRST) connected between a first voltage supply and the floating diffusion (FD) node,
• providing a source follower transistor (MSF), wherein a drain of the source follower transistor (MSF) is connected to a second voltage supply, a gate of the source follower transistor (MSF) is connected to the floating diffusion (FD) node and a source of the source follower transistor (MSF) is connected to a row select transistor (MSEL), and
• connecting the row select transistor (MSEL) between the source of the source follower transistor (MSF) and a common column output,
• outputting an output signal corresponding to a light incident on the photodiode;
• providing each pixel circuit with an output selection transistor,
• configuring each pixel circuit using a corresponding one of the output selection transistors to selectively output a linear integration signal or a logarithmic signal;
• connecting a first additional transistor (MVB) between the second voltage supply and the drain of the source follower transistor (MSF), and
• providing a second additional transistor (MS2) configured to connect a drain of the first additional transistor (MVB) to a drain of the reset transistor (MRST), and
• providing a third additional transistor (MS3) configured to connect the reset transistor (MRST) to the first voltage supply, and
• providing a fourth additional transistor (MS4) configured to connect the drain of the reset transistor (MRST) to a gate of the reset transistor (MRST).