Wednesday, August 19, 2020

Motion-Triggered SPAD Sensor

University of Edinburgh and ST paper "A 128 × 128 SPAD Motion-Triggered Time of Flight Image Sensor with In-Pixel Histogram and Column-Parallel Vision Processor" by Francesco Mattioli Della Rocca, Hanning Mai, Sam Hutchings, Tarek Al Abbas, Kasper Buckbee, Andreas Tsiamis, Peter Lomax, Istvan Gyongy, Neale Dutton, and Robert Henderson presents sensor with combined vision and ToF functionality. The paper is also published in JSSC.

"A 128 x 128 SPAD motion detection-triggered time of flight (ToF) sensor is implemented in STMicroelectronics 40 nm CMOS SPAD foundry process. The sensor combines vision and ToF ranging functions to acquire depth frames only when inter-frame intensity changes are detected. The 40 μm x 20 μm 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 column-parallel 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 32.5 kfps in vision modality and 500 fps in motion detection-triggered ToF over a measured 3.5 m distance with 1.5 cm 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."

"While most frame-comparison vision cameras require an out-of-pixel frame memory to store the previous frame, in this sensor the time-gated counters for ToF operation are repurposed in the vision modality to store consecutive intensity frames for processing by the embedded column-parallel processors."

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