PWM Image Sensor Charge-to-Time Conversion for High Dynamic Range

The patent transforms the traditional charge-to-voltage conversion approach into a charge-to-time conversion approach. The pixel sensor measures the time required to accumulate a threshold number of electrons from incoming photons, creating a time-based representation of light intensity. This parameter transformation enables high dynamic range imaging because the measurement is limited by the detection period rather than pixel saturation, allowing accurate capture of both bright and dark regions in a single shot without motion artifacts.

The patent transitions from a two-dimensional charge accumulation model (where electrons are stored in a fixed-capacity node) to a one-dimensional time-based measurement model. By measuring the duration required to accumulate a fixed threshold charge rather than measuring the final charge amount, the system effectively adds a time dimension to the measurement process. This allows the dynamic range to be determined by the detection period length rather than the pixel's physical charge storage capacity, enabling high pixel density without sacrificing dynamic range.

The patent implements a periodic detection process where each pixel independently measures the time to accumulate a threshold charge during a defined detection period. The system uses a rolling shutter mechanism that sequentially activates different rows or groups of pixels at different time offsets. This periodic, segmented approach allows the entire scene to be captured with a single effective exposure time, minimizing motion blur while maintaining sufficient light collection for low-light conditions through the time-based measurement approach.