Image Sensor Floating Diffusion Charge Overflow Management

The photoelectric conversion region is divided into multiple unit pixels, each with its own floating diffusion region. This segmentation allows independent charge accumulation and overflow management, enabling wide dynamic range without requiring a single large photoelectric conversion region, thus reducing manufacturing costs.

The patent introduces a temporal dimension to charge accumulation by implementing multi-stage overflow collection. Charges are accumulated not only spatially in the floating diffusion region but also temporally across multiple integration periods, expanding the dynamic range capability without increasing the physical size of the photoelectric conversion region.

By dividing the system into multiple unit pixels with individual floating diffusion regions, the patent reduces the dark current impact on each pixel. The segmented architecture allows better control and cancellation of dark current effects through differential measurement techniques, improving dark level performance while maintaining wide dynamic range.

The floating diffusion region acts as an intermediary charge storage node between the photoelectric conversion region and the readout circuitry. This intermediary structure isolates the dark current generation from the final signal measurement, allowing for better dark level performance through techniques like correlated double sampling that can cancel dark current effects.

The patent implements dynamic overflow management where the floating diffusion region can adaptively collect charges based on the incident light intensity. During high illuminance conditions, the system dynamically switches to collecting overflow charges from multiple unit pixels, maintaining optimal signal-to-noise ratio while extending the measurable dynamic range.

The system changes the operational parameters of charge accumulation based on illuminance levels. At low to medium illuminance, individual unit pixels accumulate charges normally. At high illuminance, the system activates overflow collection mode where excess charges are redirected to the floating diffusion region, maintaining measurement precision across the full dynamic range.

The patent uses segmentation of the photoelectric conversion region into unit pixels, each capable of independent overflow detection. This segmentation enables simple overflow detection circuitry that can be replicated across pixels, achieving multi-mode charge accumulation functionality without proportionally increasing overall device complexity.

The floating diffusion region is designed with multi-functionality, serving as both the primary charge accumulation node for individual pixels and as an overflow collection node for multiple pixels simultaneously. This universal design allows the same hardware structure to handle multiple charge accumulation modes without requiring additional dedicated circuitry for each mode.