3D ranging with a single-photon imaging array

Several applications require systems for 3D ranging acquisition, where both high frame-rate and high sensitivity (for either very dark environments or opaque objects) are a must. We exploited a monolithic chip with 32 x 32 Single-Photon Avalanche Diode smart-pixels for 3D ranging applications based on an Indirect Time-of-Flight (iTOF) technique. The scene is illuminated by a sinusoidally modulated LED and the reflected light is acquired by the imager in different timeslots, for measuring the phase delay of outgoing vs. incoming signal, hence computing the distance between the sensor and objects in the scene. All 1024 array pixels are synchronously enabled by a global gate signal, which allows photon counting in well-defined time-slots within each frame. The frame duration is set in accordance to the desired SNR. We report on measurements performed on chips fabricated in a standard high-voltage 0.35 μm CMOS technology, which feature 40% photon detection efficiency at 450 nm and 20% at 650nm. The single-photon sensitivity allowed the use of just few LEDs at 650 nm and 20MHz for acquiring a scene with a maximum distance of 7.5 m, with better than 10 cm distance resolution and frame-rates higher than 50 frames/s.