Untersuchung von Photogate-PMD-Sensoren hinsichtlich qualifizierender Charakterisierungsparameter und -methoden

Since patent pending in 1996, the first realised photonic mixer device (PMD) structure in CMOS technology in 1997, several single pixel and line sensor structures with improved performance and the first 3D camera in 2001, up to current high resolution 3D cameras with active suppression of background illumination, PMD technology has reached readiness for marketing in 2005.
To achieve this development status, numerous sensor variations had to be evaluated to understand and to verify the basic working principle and to improve the pixel performance. To allow a qualitative comparison between different kinds of sensors, significant characterisation and performance parameters had to be defined and achieved under non-varying measurement conditions. Repeated accuracy of different samples during a long development period is achieved by the realisation of a special kind of measurement environment. It enables the accomplishment of automated measuring routines under constant and reproducible ambient conditions and therefore guarantees reliable measurement data acquisition.
Goals of this study are the configuration of a modular characterisation platform and the definition and implementation of appropriate PMD performance parameters.
Chapter 1 starts with a short introduction to the fundamentals of measuring, time of flight measurement, correlation, and a basic PMD principle description.
In chapter 2 the requirements for the measurement environment are listed. Concerning the demands on flexible optical and electrical signal generation for various kinds of different PMD sensors, a universal and modular characterisation platform is realised and described. It consists of optical signal generation modules, including automated power measurement and attenuation controls, and several electrical pattern generators.
Chapter 3 includes the definition of different PMD typical characterisation parameters. It starts with a nomenclature and interpretation, based upon the curve of video voltages, and describes the characterisation of some typical parameters for image sensors, like dark current and sensitivity. The PMD mixing efficiency is explained and rated for constant and modulated signal conditions. Based upon the mixing principle the resulting transfer and correlation functions are benchmarked by significant parameters like demodulation contrast, symmetry and stability of phase measurement. Chapter 3 concludes with different kinds of experimental evaluation methods to determine the optical dynamic characteristics.
Chapter 4 describes a basic approach to increase the optical signal dynamic range by the use of different non-linear integration characteristics. Based on a simplified PMD model the resulting optical dynamic range is evaluated by simulation. The achieved dynamic extension can be shown in measurement results for a standard high resolution PMD sensor under measurement conditions and the resulting distance accuracy of a real 3D scene.
The work concludes with a short summary and a view of the prospects for the future developments for PMD characterisation.