SPAD-Based Sensors

3D imaging and multi-pixel rangefinding constitute one of the most important and innovative fields of research in image sensor science and engineering in the past years. In rangefinding, one computes the Time-Of-Flight of a ray of light, generated by a mono-chromatic or wide-spectral source, from the source through the reflection of a target object and to a detector. There exist at least two techniques to measure the Time-Of-Flight (TOF): a direct and an indirect technique. In direct techniques (D-TOF), the time difference between a START pulse, synchronized with the light source, and a STOP signal generated by the detector is evaluated. In indirect techniques (I-TOF), a continuous sinusoidal light wave is emitted and the phase difference between outgoing and incoming signals is measured. From the phase difference, the time difference is derived using well-known formulae. Single-photon avalanche diodes (SPADs) or Geiger-mode avalanche photodiodes (GAPDs) are detectors capable of capturing individual photons with very high time-of-arrival resolution, of the order of a few tens of picoseconds. They