A 128 × 128 SPAD Dynamic Vision-Triggered Time of Flight Imager

Abstract

A 128 x 128 SPAD motion detection-triggered time of flight (ToF) sensor is implemented in 40nm CMOS. The sensor combines vision and ToF ranging functions to only acquire depth frames when inter-frame intensity changes are detected. The 40µm x 20µm pixel integrates two 16-bit time-gated counters to acquire ToF histograms and repurposes them to compare two vision frames without requirement for additional out-of-pixel frame memory resources. An embedded ToF and vision processor performs on-chip vision frame comparison and binary frame output compression as well as controlling the time-resolved histogram sampling. The sensor achieves a maximum 20kfps in vision modality and 500fps in motion detection-triggered ToF over a measured 2.55m range with 1.6cm accuracy. The vision function reduces the sensor power consumption by 70% over continuous ToF operation and allows the sensor to gate the ToF laser emitter to reduce the system power when no motion activity is observed.