Floating Diffusion Capacitance Control for Adaptive Image Sensor Gain

The patent implements dynamic control of the floating diffusion node capacitance by introducing multiple selection transistors (first selection transistor, second selection transistor) that can be selectively activated based on illuminance conditions. This allows the capacitance value to be dynamically adjusted between different states, enabling the conversion gain ratio to adapt to varying lighting environments while maintaining a relatively simple circuit structure.

The patent applies local quality by making different parts of the pixel circuit have different functions. Specifically, the first selection transistor and second selection transistor are designed with different characteristics to provide distinct capacitance adjustment options. This allows the circuit to optimize image quality under different illuminance conditions by selectively activating the appropriate transistor, while keeping the overall circuit complexity manageable through targeted local modifications rather than comprehensive redesign.