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A vertically illuminated photodetector based on Ge-on-SOI, which operates at 8 Gb/s for reverse bias as low as 0.5 V, is presented. The integrated photodetector also features low dark current and good photogenerated carrier collection efficiency.

Optical time-of-flight (TOF) distance measurements can be performed using so-called smart lock-in pixels. By sampling the optical signal 2, 4 or n times in each pixel synchronously with the modulation frequency, the phase between the emitted and reflected signal is extracted and the object's distance is determined. The high integration-level of such lock-in pixels enables the real-time acquisition of the three-dimensional environment without using any moving mechanical components. A novel design of the 2-tap lock-in pixel in a 0.6 μm semiconductor technology is presented. The pixel was implemented on a sensor with QCIF resolution. The optimized pixel design allows for high-speed operation of the device, resulting in a nearly-optimum demodulation performance and precise distance measurements which are almost exclusively limited by photon shot noise. In-pixel background-light suppression allows the sensor to be operated in an outdoor environment with sunlight incidence. The highly complex pixel functionality of the sensor was successfully demonstrated on the new SwissRanger SR3000 3D-TOF camera design. Distance resolutions in the millimeter range have been achieved while the camera is operating with frame rates of more than 20Hz.

The time-of-flight (TOF) principle is a well known principle to acquire a scene in all three dimensions. The advantages of the knowledge of the third dimension are obvious for many kinds of applications. The distance information within the scene renders automatic systems more robust and much less complex or even enables completely new solutions. A solid-state image sensor containing 124 x 160 pixels and the corresponding 3D-camera, the so-called SwissRanger camera, has already been presented in detail in [1]. It has been shown that the SwissRanger camera achieves depth resolutions in the sub-centimeter range, corresponding to a measured time resolution of a few tens of picoseconds with respect to the speed of light (c~3•108 m/s). However, one main drawback of these so-called lock-in TOF pixels is their limited capacity to handle background illumination. Keeping in mind that in outdoor applications the optical power on the sensor originating from background illumination (e.g., sun light) may be up to a few 100 times higher than the power of the modulated illumination, the sensor requires new pixel structures eliminating or at least reducing the currently experienced restrictions in terms of background illumination. Based on a 0.6 µm CMOS/CCD technology, four new pixel architectures suppressing background illumination and/or improving the ratio of modulated signal to background signal at the pixel-output level were developed and will be presented in this paper. The theoretical principle of operation and the expected performance are described in detail, together with a sketch of the implementation of the different pixel designs at silicon level. Furthermore, test results obtained in a laboratory environment are published. The sensor structures are characterized in a high background-light environment with up to sun light conditions. The distance linearity over a range of a few meters with the mentioned light conditions is measured. At the same time, the distance resolution is plotted as a function of the target distance, the integration time and the background illumination power. This in-depth evaluation leads to a comparison of the various background suppression approaches; it also includes a comparison with the traditional pixel structure in order to highlight the benefits of the new approaches. The paper concludes by providing parameter estimations which enables the outlook to build a sensor with a high lateral resolution containing the most promising pixel.

A new miniaturised 256 pixel silicon line sensor, which allows for the acquisition of depth-resolved images in real-time, is presented. It reliably and simultaneously delivers intensity data as well as distance information on the objects in the scene. The depth measurement is based on the time-of-flight (TOF) principle. The device allows the simultaneous measurement of the phase, offset and amplitude of a radio frequency modulated light field that is emitted by the system and reflected back by the camera surroundings, without requiring any mechanical scanning parts. The 3D line sensor will be used on a mobile robot platform to substitute the laser range scanners traditionally used for navigation in dynamic and/or unknown environments.

A new pixel structure for the demodulation of intensity modulated light waves is presented. The integration of such pixels in line and area array sensors finds application in time-of-flight three-dimensional imaging. In 3D range imaging an illumination module sends a modulated optical signal to a target, where it is reflected back to the sensor. The phase shift of the reflected signal compared to the emitted signal is proportional to the distance to one point of the target. The detection and demodulation of the signal is performed by a new pixel structure named drift field pixel. The sampling process is based on the fast separation of photogenerated charge due to lateral electrical fields below a high-resistive transparent poly-Si photogate. The dominant charge transfer phenomenon of drift, instead of diffusion as in conventional CCD pixels, allows much higher modulation frequencies of up to 1 GHz and a much higher ultimate distance accuracy as a consequence. First measurements performed with a prototype pixel array of 3x3 pixels in a 0.8 micron technology confirm the suitability of the pixels for applications in the field of 3D-imaging. Depth accuracies in the sub centimeter range have already been achieved.

A new miniaturized camera system that is capable of 3-dimensional imaging in real-time is presented. The compact imaging device is able to entirely capture its environment in all three spatial dimensions. It reliably and simultaneously delivers intensity data as well as range information on the objects and persons in the scene. The depth measurement is based on the time-of-flight (TOF) principle. A custom solid-state image sensor allows the parallel measurement of the phase, offset and amplitude of a radio frequency (RF) modulated light field that is emitted by the system and reflected back by the camera surroundings without requiring any mechanical scanning parts. In this paper, the theoretical background of the implemented TOF principle is presented, together with the technological requirements and detailed practical implementation issues of such a distance measuring system. Furthermore, the schematic overview of the complete 3D-camera system is provided. The experimental test results are presented and discussed. The present camera system can achieve sub-centimeter depth resolution for a wide range of operating conditions. A miniaturized version of such a 3D-solid-state camera, the SwissRanger 2, is presented as an example, illustrating the possibility of manufacturing compact, robust and cost effective ranging camera products for 3D imaging in real-time.