LiDAR is a key sensor technology for future driving. For autonomous vehicles a fast and reliable three dimensional monitoring of the environment is essential for managing a wide variety of common traffic situations. Since these kinds of systems use typically light in the near infrared range, ambient light of the sun is a serious problem due to its high intensity compared to the laser source. Therefore, reducing the influence of ambient light on the distance measurement is very important. In this paper we present a 2 × 192 pixel SPAD-based direct time-of-flight line sensor for flash LiDAR applications with high ambient light rejection integrated in standard CMOS technology. Two commercially available 905 nm laser diodes emitting short pulses are employed for scene illumination. For time measurement an in-pixel timeto- digital-converter with a resolution of 312.5 ps and full range of 1.28 μs has been implemented. Each pixel uses four vertically arranged single SPADs for background light rejection based on the detection of temporal correlated photons. This technique allows the discrimination of the received laser pulse buried in the superimposed background light and, hence, to improve the measurement quality. Additionally, different parameters of the coincidence detection circuit, such as coincidence depth and time, can be varied during operation to enable a real time adjustment to the present ambient light condition, which is measured between each laser shot by operating the sensor in photon counting mode. By using this technique the sensor allows a reliable distance measurement at various ambient and target conditions.
Optical inspection systems require fast image acquisition at significantly enhanced resolution when utilized for advanced machine vision tasks. Examples are quality assurance in print inspection, printed circuit board inspection, wafer inspection, real-time surveillance of railroad tracks, and in-line monitoring in flat panel fabrication lines. Ultra-highspeed is an often demanded feature in modern industrial production facilities, especially, where it comes to high volume production. A novel technology in this context is the new high-speed sensor for line-scan camera applications with unmatched line rates up to 200 kHz (tri-linear RGB) and 600 kHz (b/w), presented in this paper. At this speed, the multiline- scan sensor provides full color images with, e.g., a spatial resolution of 50 μm at a transport speed of 10 m/s. In contrast to conventional Bayer pattern or three-chip approaches, the sensor presented here utilizes the tri-linear principle, where the color filters are organized line-wise on the chip. With almost 100% fill-factor, the tri-linear technology assures high image quality because of its robustness against aliasing and Moiré effects leading to improved inspection quality, less false positives and thus less waste in the production lines.
The performance of a fabricated CMOS line sensor based on the lateral drift-field photodiode (LDPD)1 concept is described. A new pixel structure was designed to decrease the charge transfer time across the photoactive area. Synopsys TCAD simulations were performed to design a proper intrinsic lateral drift-field within the pixel. The line sensor was fabricated in the 0.35 μm CMOS technology, and further characterized using a tailored photon-transfer method2 and the EMVA 1288 standard3. The basic parameters such as spectral responsivity, photo-response non-uniformity and dark current were measured at fabricated sensor samples. A special attention was paid to charge transfer time characterization4 and the evaluation of crosstalk between neighboring pixels – two major concerns attained during the development. It is shown that the electro-optical characteristics of the developed line sensor are comparable to those delivered by CCD line sensors available on the market, which are normally superior in performance compared to their CMOS based counterparts, but offering additional features such as the possibility of time gating, non-destructive readout, and charge accumulation over several cycles: approaches used to enhance the signal-to-noise ratio (SNR) of the sensor output.
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.