CCD/CMOS Lock-In Pixel for Range Imaging: Challenges, Limitations and State-of-the-Art

Smart lock-in pixels for real-time range imaging have been developed at CSEM during the last few years. These pixels, based on a combined CCD/CMOS process, are capable of demodulating intensity-modulated optical signals in parallel. By integrating some hundreds or thousands of them on one single chip, real-time 3D-imaging becomes possible by indirectly measuring the time-of-flight. The basic challenges and requirements of the pixels, making them usable for a wide range of 3D-applications, are the handling of strong signal variations over the imaged scenery, background light suppression techniques and high distance accuracy. These challenges and according difficulties in real implementations are discussed. Limitations of the pixels, both physically as well technologically, are derived and the basic need for current and future research and development is shown. The state-of-the-art pixel, as implemented in the so-called SwissRanger camera, is used for demonstrating the nature of the before mentioned challenges and limitations.