Linear-Mode Gain-Modulated Avalanche Photodiode Image Sensor for Time-of-Flight Optical Ranging

In this paper, a CMOS image sensor based on avalanche photodiodes (APDs) for time-of-flight optical ranging is presented. In-pixel phase-sensitive detection was obtained thanks to the modulation of APD avalanche gain. A pixel based on this principle with 30-μm pixel pitch and 25.7% fill factor was designed, and a 64 × 64 APD image sensor was fabricated in a 0.35-μm standard CMOS process. The maximum demodulation contrast measured on the array exceeds 85% at 25-MHz modulation frequency. High-frequency modulation was demonstrated on single test pixels, where a demodulation contrast as high as 80% was measured at 200-MHz modulation frequency. A 3-D camera working at a frame rate up to 200 frames/s was realized and characterized.