Switchable Capacitor for Imaging Device Input Node

The capacitor is configured to be switchably connected to the floating diffusion, allowing the capacitance value of the input node to be dynamically adjusted between two states: connected (higher capacitance for expanded dynamic range) and unconnected (lower capacitance for higher charge-voltage conversion efficiency). This dynamic reconfiguration enables the system to adapt to different signal conditions.

The invention changes the capacitance parameter of the input node by switching the capacitor's connection state. When the capacitor is connected, the input node capacitance increases to expand dynamic range; when disconnected, the capacitance decreases to improve charge-voltage conversion efficiency. This parameter switching allows optimization for different operating conditions.

Rather than providing a large capacitor that would always occupy significant area, the invention uses a capacitor that can be dynamically switched. The capacitor only occupies active space when connected to provide linearity for large charge quantities, and can be disconnected when high dynamic range is needed, effectively sharing the area requirement between two functional states.

The capacitor serves multiple functions depending on its connection state: it provides linearity improvement for large charge quantities when connected, and enables dynamic range expansion when disconnected. This multi-functionality allows a single capacitor structure to address different signal conditions without requiring separate dedicated components for each function.