High precision pixel circuit and method thereof

A pixel circuit, comprising:

• a photo-sensitive element, configured to operably generate charge in response to incident radiation;
• a floating diffusion node;
• a reset transistor, configured to operably dissipate charge on the floating diffusion node;
• a transfer gate, connected between the photo-sensitive element and the floating diffusion node, configured to operably control transfer of charge to the floating diffusion node;
• a buffer amplifier having an input connected to the floating diffusion node, configured to operably generate a buffered output signal according to a voltage on the floating diffusion node;
• an amplifier circuit;
• a first sample-and-hold (S/H) stage;
• and
• a second S/H stage, wherein the first S/H stage and the second S/H stage are connected in cascade between the buffer amplifier and the amplifier circuit;
• wherein the second S/H stage is configured to operably sample, or to operably sample and hold the buffered output signal to generate a second S/H signal, and the first S/H stage is configured to operably sample and hold the second S/H signal to generate a first S/H signal;
• wherein the amplifier circuit is electrically connected to the output of the first S/H stage and an output of the second S/H stage independently;
• wherein during a first time period of a global exposure cycle, the second S/H stage samples the buffered output signal having a first voltage to generate the second S/H signal having the first voltage, and the first S/H stage samples and holds the second S/H signal to generate the first S/H signal having the first voltage, wherein the first voltage relates to a first state of the floating diffusion node;
• wherein during a second time period of the global exposure cycle, the second S/H stage samples and holds the buffered output signal having a second voltage to generate the second S/H signal having the second voltage, wherein the second voltage relates to a second state of the floating diffusion node;
• wherein during a third time period, the first S/H signal having the first voltage and the second S/H signal having the second voltage are sensed by the amplifier circuit independently for generating a first output signal and a second output signal correspondingly.