Multi-Junction SPAD Pixel Bias Control for PDE Modulation

Each SPAD pixel is divided into multiple avalanche diodes (e.g., four diodes arranged in a 2x2 grid), allowing independent control of each diode's bias voltage. This segmentation enables the pixel to operate in different sensitivity modes by activating one, two, three, or all four diodes, thereby modulating the effective active area and preventing saturation in high-ambient light conditions while maintaining the ability to detect single photons.

The bias control circuit dynamically adjusts the reverse-bias voltage of individual avalanche diodes based on illumination conditions. In low-light conditions, higher bias voltages are applied to maximize photon detection efficiency. In high-ambient light conditions, the bias voltage is reduced or individual diodes are deactivated to prevent saturation, allowing the system to adapt to varying lighting environments without sacrificing detection performance.

Multiple avalanche diodes within a single SPAD pixel are electrically and functionally merged through shared readout circuitry and common timing detection mechanisms. The output signals from individual diodes are combined and processed by a unified timing circuit that maintains consistent time-of-arrival resolution across all diodes. This merging approach allows the system to utilize the increased effective active area provided by multiple diodes while preserving precise timing performance through a coordinated detection and processing architecture.