PIN-photodiode based pixel architecture for high-speed optical distance measurement systems

Abstract

Contact-less optical distance measurement systems are necessary to obtain 3D-information of an entire scene. To be able to determine depth information of the scene by a sensor without moving parts like e.g. scanner, it is necessary to measure the distance from the camera to an object in every single pixel. A new pixel for such a 3D-camera is presented. The operating principle is based on the time-of-flight (TOF) of laser light from 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 fast, efficient PIN-photodiode having a 3dB bandwidth of about 1.35 GHz, a single-stage transimpedance amplifier and an electronic mixer on a single silicon chip. By correlating the received optical signal and the original electronic modulation signal, the phase-shift between sent and received signal can be determined. By performing correlation with a delayed modulation signal it is possible to eliminate the influence of object reflectivity and background illumination. The measurement time for a single distance measurement is 500μs for a range up to 3.7m. The standard deviation at 2.5m is better than 3cm for a transmitted optical power of 1.44mW at a wavelength of 650nm. The OEIC was fabricated in a slightly modified BiCMOS 0.6μm process. The diameter of the photosensitive area of the integrated PIN-photodiode is 100μm. The effective pixel size is about 220x400μm². Therefore a fill factor of ~9% is reached.