Peter Mengel

A CMOS photosensor array for 3D imaging using pulsed laser

A 32×2 pixel optical time of flight range sensor in standard 0.5 μm CMOS acquires up to 20k BD-images/s combines CDS, S&H, multiple double short time integration, a high-speed synchronous shutter, and a phase synchronizer enabling exposures <30 ns with <5.2 W/m/sup 2/ NEP. This CMOS imager chip for 3D imaging applications contains a photodiode array and the aforementioned features enable optical TOF measurements of laser pulses reflected from a target. The 42 mm/sup 2/ chip dissipates 330 mW.

Fast range imaging by CMOS sensor array through multiple double short time integration (MDSI)

The presented novel approach for direct range image acquisition is based on a CMOS image sensor with extremely short integration time and a defined flash illumination by fast infrared laser diodes. Determining the light propagation time by the MDSI method on a chip, a single CMOS sensor chip measures simultaneously distances to a net of numerous target points in a few milliseconds with a resolution of typically 5 mm. The exclusive use of semiconductor components assures high robustness, small size and low cost under high volume production. Hence the fields of applications are very versatile, ranging from safety and security to transportation, traffic and industrial automation as well.

Three-Dimensional CMOS Image Sensor for Pedestrian Protection and Collision Mitigation

Future car safety systems increasingly depend on the availability of robust sensors with vital improved technical perception output. For this objective, we develop a pulsed laser based time of flight range sensor in fully solid-state microsystems technology for more reliable detection and classification of road users, vehicles and traffic obstacles. The development aims on pedestrian protection and mitigation of collisions comprising the short distance around vehicle perception up to 25 m. The 3D sensor technology based on a chip design of 64×8 pixels and image repetition rates of up to 100 Hz will be presented and the performance of a first 3D line sensor prototype will be demonstrated for typical road test scenarios. Furthermore, an outlook on the final 3D array camera development for road safety applications will be given.

Automated solder joint inspection system using optical 3-D image detection

An automated system has been developed for visually inspecting the solder joints of SMDs (Surface Mounted Devices). The system is capable of inspecting fine pitch components down to 0.3 mm pitch QFPs (Quad Flat Packages). A unique image detection method was also developed to obtain precise 3-D images of solder joints. The principle of a confocal microscope is employed but plural sensors are used to detect reflected light at different focusing positions simultaneously. The system is unaffected by secondary reflection and dead angles. The warp in a PC (Printed Circuit) board surface is calculated in real time using the detected 3-D images, and board height to be detected in successive areas is predicted based on this calculation. Real-time automatic focusing control is then performed using newly developed defect detection algorithms, the system can recognize leads, pads and solder fillets from the detected images. Because 3-D shape features are extracted and used for defect judgment, user-defined parameters have been made easy to understand and/or to modify. Operational evaluation of the system confirms a 100% defect detection rate and a very low false alarm rate (0.16%).

Modeling of a 3D CMOS sensor for time-of-flight measurements

A solid state 3D-CMOS camera system for direct time-of-flight image acquisition consisting of a CMOS imaging sensor, a laser diode module for active laser pulse illumination and all optics for image forming is presented, including MDSI & CDS algorithms for time-of-flight evaluation from intensity imaging. The investigation is carried out using ideal and real signals. For real signals the narrow infrared laser pulse of the laser diode module and the shutter function of the sensors column circuit were sampled by a new sampling procedure. A discrete sampled shutter function was recorded by using the impulse response of a narrow pulse of FWHM=50ps and an additional delay block with step size of Δτ = 0.25ns. A deterministic system model based on LTI transfer functions was developed. The visual shutter windows give a good understanding of differences between ideal and real output functions of measurement system. Simulations of shutter and laser pulse brought out an extended linear delay domain from MDSI. A stochastic model for the transfer function and photon noise in time domain was developed. We used the model to investigate noise in variation the laser pulse shutter configuration.

Three-dimensional CMOS image sensor with 4x64 pixel array

A 3D CMOS imager based on time-of-flight (TOF) has been developed and successfully tested. It uses an active pulsed class 1 laser operating at 905nm to illuminate a 3D scene. The scene depth is determined by measurement of the travel time of reflected pulses by employing a fast on-chip synchronous shutter. A so-called “Multiple Double Short Time Integration” (MDSI) enables suppression of the background illumination and correction for reflectivity variations in the scene objects. The sensor chip contains 2 pixel lines with each pixel containing twin photodiodes, thus the chip contains 4×64 sensors. The chip allows two operating modes; the first is the binning mode (mode0 and mode1 are activated), where the twin pixels are short-circuited (tow lines on the die) and the average signal is measured. The second mode is the high-resolution mode (either mode0 or mode1 is activated). In this mode the pixels operate separately (four lines on the die). The chip has been realized in 0.5μm n-well standard CMOS process. The pixel pitch is 130μm. To get a good fill factor, the readout circuitry is located at the sides of the chip.