High Conversion Gain Image Sensor With Tunable Floating Diffusion Capacitance

The patent applies dynamics by making the floating diffusion node capacitance variable rather than fixed. A tuning circuit dynamically adjusts the capacitance value based on lighting conditions: using lower capacitance for high conversion gain in low-light scenarios, and higher capacitance to prevent saturation in bright environments. This resolves the contradiction by allowing the system to adapt its capacitance characteristic to different operating conditions.

The patent changes the capacitance parameter of the floating diffusion node from a fixed value to a variable value that can be tuned. By introducing a tuning circuit that modifies the capacitance parameter according to scene brightness, the system achieves high conversion gain when needed while avoiding saturation, thus resolving the fundamental trade-off between these two opposing requirements.

The patent makes the capacitance dynamic and可调 (tunable) rather than fixed by geometry. Even with small pixel cell sizes that constrain physical capacitance, the tuning circuit can dynamically adjust the effective capacitance value to optimize conversion gain. This allows high resolution to be maintained while still achieving high conversion gain through active capacitance control.

The patent changes the capacitance parameter from being solely determined by physical geometry (which is constrained by small pixel size) to being controllable through an electronic tuning circuit. This parameter change enables the system to achieve high conversion gain in small pixels by electronically adjusting the capacitance value rather than relying on purely geometric factors.