Global Shutter Pixel Circuit for Higher Saturation Charge Capacity

The patent merges the sense node capacitance and floating diffusion capacitance into a unified charge holding system. By connecting these two capacitance elements, the total capacitance becomes the sum of both, allowing the system to hold more saturated charges than either element could individually (10 fF + 10 fF = 20 fF total), thus resolving the contradiction between simple structure and sufficient charge capacity.

The patent changes the capacitance parameter by introducing an additional capacitive element (floating diffusion) with comparable capacitance value (about 10 fF) to the existing sense node capacitance. This parameter change doubles the total charge holding capacity while maintaining the simplicity of the PN junction and wiring capacitance design.

The patent segments the total capacitance into two distinct functional parts: sense node capacitance for charge accumulation and floating diffusion capacitance for charge transfer and signal generation. This segmentation allows the system to achieve higher total capacitance (20 fF) while maintaining optimal noise characteristics by distributing the capacitance function across two elements rather than concentrating it in one.

The floating diffusion acts as an intermediary element between the sense node and the readout circuit. It mediates the charge transfer process, allowing the sense node to accumulate charges at optimal capacitance (10 fF) while the floating diffusion provides additional capacitance (10 fF) during the transfer phase, thus increasing total saturated charges without degrading noise performance.