In recent years, pervasive computing has become an important topic in automobile industry. Besides well-known driving assistant systems such as ABS, ASR and ESP several small tools that support driving activities were developed. The most important reason for integrating new technologies is to increase the safety of passengers as well as road users. The Centre Suisse d'Electronique et de Microtechnique SA (CSEM) Zurich presented the CMOS/CCD real-time range-imaging technology, a measurement principle with a wide field of applications in automobiles. The measuring system is based on the time-of-flight measurement principle using actively modulated radiation. Thereby, the radiation is emitted by the camera's illumination system, reflected by objects in the field of view and finally imaged on the CMOS/CCD sensor by the optics. From the acquired radiation, the phase delay and hence the target distance is derived within each individual pixel. From these distance measurements, three-dimensional coordinates can then be calculated. The imaging sensor acquires its environment data in a high-frequency mode and is therefore appropriate for real-time applications. The basis for decisions which contribute to the increased safety is thus available. In this contribution, first the operational principle of the sensor technology is outlined. Further, some implementations of the technology are presented. At the laboratories of the Institute of Geodesy and Photogrammetry (IGP) at ETH Zurich an implementation of the above mentioned measurement principle, the SwissRanger, was investigated in detail. Special attention was focused on the characteristics of this sensor and its calibration. Finally, sample applications within the automobile are introduced.
KEYWORDS: 3D-TOF imaging, Sensors, 3D image processing, Time of flight imaging, Cameras, Sun, Modulation, Solid state electronics, Image sensors, Time metrology
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.
KEYWORDS: Demodulation, Modulation, Signal detection, Distance measurement, Electrons, Sensors, Camera shutters, Signal processing, 3D image processing, Diffusion
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.
KEYWORDS: Optical coherence tomography, Sensors, Signal to noise ratio, Demodulation, Signal detection, Mirrors, Photons, Image sensors, 3D image processing, Modulation
Optical Coherence Tomography (OCT) is an optical imaging technique allowing the acquisition of three-dimensional images with micrometer resolution. It is very well suited to cross-sectional imaging of highly scattering materials, such as most biomedical tissues. A novel custom image sensor based on smart pixels dedicated to parallel OCT (pOCT) is presented. Massively parallel detection and signal processing enables a significant increase in the 3D frame rate and a reduction of the mechanical complexity of the complete setup compared to conventional point-scanning OCT. This renders the parallel OCT technique particularly advantageous for high-speed applications in industrial and biomedical domains while also reducing overall system costs. The sensor architecture presented in this article overcomes the main challenges for OCT using parallel detection such as data rate, power consumption, circuit size, and optical sensitivity. Each pixel of the pOCT sensor contains a low-power signal demodulation circuit allowing the simultaneous detection of the envelope and the phase information of the optical interferometry signal. An automatic photocurrent offset-compensation circuit, a synchronous sampling stage, programmable time averaging, and random pixel accessing are also incorporated at the pixel level. The low-power demodulation principle chosen as well as alternative implementations are discussed. The characterization results of the sensor exhibit a sensitivity of at least 74 dB, which is within 4 dB of the theoretical limit of a shot-noise limited OCT system. Real-time high-resolution three-dimensional tomographic imaging is demonstrated along with corresponding performance measurements.
The relentless progress of semiconductor technology makes it possible to provide image sensors and pixels with additional analog and digital functionality. Growing experience with such photosensor functionality leads to the development of modular building blocks that can be employed for smart pixels, single-chip digital cameras and
functional image sensors. Examples given include a non-linear pixel response circuit for high-dynamic range imaging offering a dynamic range of more than 180 dB, low-noise amplifiers and avalanche-effect pixels for high-sensitivity detection performance that approaches single-photoelectron resolution, lock-in pixels for optical time-of-flight range cameras with sub-centimeter distance resolution and in-pixel demodulation circuits for optical coherence tomography
imaging. The future is seen in even higher levels of integration, such as system-on-a-chip machine vision cameras (“seeing chips”), post-processing with non-silicon materials for the extension of the detection range to the X-ray, ultraviolet and infrared spectrum, the exploitation of all properties of the incident light and imaging of fields other than electromagnetic radiation
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.
CMOS image sensors offer over the standard and ubiquitous charge-coupled devices several advantages, in terms of power consumption, miniaturization, on-chip integration of analog- to-digital converters and signal processing for dedicated functionality. Due to the typically higher readout noise of CMOS cameras compared to CCD cameras applications demanding ultimate sensitivity were so far not accessible to CMOS cameras. This paper present an analysis of major noise sources, concepts to reduce them, and results obtained ona single chip digital camera with a QCIF resolution of 144 by 176 pixels and a dynamic range in excess of 120 dB.
This article presents the design and realization of a CMOS digital image sensor optimized for button-battery powered applications. First, a pixel with local analog memory was designed, allowing efficient sensor global shutter operation. The exposure time becomes independent on the readout speed and a lower readout frequency can be used without causing image distortion. Second, a multi-path readout architecture was developed, allowing an efficient use of the power consumption in sub-sampling modes. These techniques were integrated in a 0.5 um CMOS digital image senor with a resolution of 648 by 648 pixels. The peak supply current is 7 mA for a readout frequency of 4 Mpixel/s at Vdd equals 3V. Die size is 55 mm2 and overall SNR is 55 dB. The global shutter performance was demonstrated by acquiring pictures of fast moving objects without observing any distortion, even at a low readout frequency of 4 MHz.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.