New Powerful Sensory Tool in Automotive Safety Systems Based on PMD-Technology

Abstract

The application of electronic imaging for driver support and occupant safety is actually one of the most challenging tasks in automotive research activities. Most efforts aim to apply two-dimension al imagers in CCD-, CMOS- and TFA-technology so far. Now a further imaging technology has been developed : the PMD-technology, which directly enables 3D-imaging by means of the time-offlight (TOF) principle . This approach offers an extremel y high potential for new solutions in this application field . The PMD-Technology opens up amazing new perspectives for occupant detection systems as well as the observation of vehicles outer area (see Fig . 1.).

This Photonical Mixing Detector or Photonic Mixer Device (PMD) , respectively, represents a new electro-optic device that provides a smart interface between the world of incoherent optical signals and the world of their electronic signal processing. As a new micro-photonic semiconductor device it can be integrated and arranged to an array of smart PMD-pixels enabling the whole 3D-scene to be described by an equivalent array of scaled voxels (volume pixture elements). The multiple electrooptical mixing and correlation process provides the depth information for each pixel in addition to the intensity value and the colour information. In contrast to that , conventional electronic processing of fast incoherent optical signals generally requires at least a photodetector for optoelectronic signal conversion, a broadband and high dynamic amplifier, and an electronic mixer/correlator for each spatial point , altogether causing a large amount and high sensitivity to tim e drift failures . The new device, unifying the detection and mixing process within some ten square μm , shows an electro optical transfer characteristic comparable to the basic differential amplifier circuit with an optically driven current source . Compared with conventional solutions the receiver volume is reduced by a factor of about 100 .000 thus principally enabling receiver arrays of 100.000 PMD-pixels . Small arrays of PMD-pixels have been designed and implemented in standard CMOS technology, including signal pre-processing stages. In addition to the amazing PMD-simplicity the accuracy of depth measurements has been increased by more than factor ten compared to conventional TOF-systems. This 3D-imaging camera technique offers a huge amount of new applications in automotive safety systems and intelligent driver support. The PMD-camera will be predestined to solve urgent problems as, e.g. the smart airbag - detecting the passenger-presence, -position , -size and -weight and additionally provid ing precrash information, collision avoidance, automatic park assistance and so on.