Circuit structure for providing conversion gain of a pixel array

An image sensor system comprising:

• a pixel array including:
• a pixel cell comprising:
• a source follower transistor and a row select transistor;
• a first trace coupled to the source follower transistor;
• a second trace to receive from the row select transistor an output of the pixel cell;
• switch circuitry including:
• a first transistor coupled to a supply voltage and the source follow transistor, wherein the first transistor is coupled to the source follower transistor via a first portion of the first trace;
• a second transistor coupled to a sample and hold circuit and the source follow transistor, wherein the second transistor is coupled to the source follower transistor via a second portion of the first trace;
• a third transistor coupled to the supply voltage and the row select transistor, wherein the third transistor is coupled to the row select transistor via a first portion of the second trace;
• and
• a fourth transistor coupled to the sample and hold circuit and the row select transistor, wherein the fourth transistor is coupled to the row select transistor via a second portion of the second trace;
• the switch circuitry to transition between a first operational mode and a second operational mode based on a control signal, the first operational mode including the first transistor and the fourth transistor each being in a respective active state and the second transistor and the third transistor each being in a respective inactive state, the second operational mode including the first transistor and the fourth transistor each being in a respective inactive state and the second transistor and the third transistor each being in a respective active state.

A method comprising:

• at a pixel cell of a pixel array:
• accumulating charge at a photodiode in response to light incident upon the photodiode;
• with a transfer transistor coupled to the photodiode and a floating diffusion node, bringing the floating diffusion node to a voltage level based on the accumulated charge;
• and
• outputting from a source follower transistor an amplification signal based on the floating diffusion node being brought to the voltage level, wherein the source follower transistor conducts current carried via a source follower first trace, wherein the pixel cell outputs an analog signal based on the amplification signal;
• and
• with a control signal, transitioning switch circuitry of the pixel array between a first operational mode and a second operational mode, the switch circuitry including:
• a first transistor coupled to a supply voltage and the source follow transistor, wherein the first transistor is coupled to the source follower transistor via a first portion of the first trace;
• a second transistor coupled to a sample and hold circuit and the source follow transistor, wherein the second transistor is coupled to the source follower transistor via a second portion of the first trace;
• a third transistor coupled to the supply voltage and the row select transistor, wherein the third transistor is coupled to the row select transistor via a first portion of the second trace;
• and
• a fourth transistor coupled to the sample and hold circuit and the row select transistor, wherein the fourth transistor is coupled to the row select transistor via a second portion of the second trace;
• wherein the first operational mode includes the first transistor and the fourth transistor each being in a respective active state and the second transistor and the third transistor each being in a respective inactive state, and wherein the second operational mode includes the first transistor and the fourth transistor each being in a respective inactive state and the second transistor and the third transistor each being in a respective active state.