Time-of-flight based pixel architecture with integrated double-cathode photodetector

Abstract

ABSTRACT For various industrial applications contact-less optical 3D distance measurement systems with active illumination are suitable. A new approach for a pixel of such a 3D-camera chip for applications in displacement and 3D-shape measurement is presented here. The distance information is gained by measuring the Time-of-Flight (TOF) of photons transmitted by a modulated light source to a diffuse reflecting object and back to the receiver IC. The receiver is implemented as an opto-electronic integrated circuit (OEIC). It consists of a double-cathode photodetector performing an opto-electronic correlation, a decoupling network and an outp ut low-pass filter on a single silicon chip. The correlation of the received optical signal and the electronic modulation si gnal enables the determination of the phase-shift between them. The phase-shift is directly proportional to the distan ce of the object. The measurement time for a single distance measurement is 20 ms for a range up to 6.2 m. The standard deviation up to 3.4 m is better than 1cm for a transmitted optical power of 1.2 mW at a wavelength of 650 nm. The OEIC was fabricated in a slightly modified 0.6 µm BiCMOS technology with a PIN-photodetector. The photosensitive area of the integrated PIN-photodetector is 120×115 µm². A fill factor of ~67 % is reached. Keywords: time-of-flight, optical distance m easurement, OEIC, opto-electronic correlation, PIN photodetector