Feature: Sensors


Figure 2: Comparison of LiDAR-based depth sensing methods


will degrade less rapidly than a SWIR system, providing more consistent performance across all-weather conditions. Considering all this, NIR is generally accepted as the preferred


wavelength for automotive LiDAR. It allows the use of silicon- based devices as opposed to more expensive materials, such as InGaAs, and perhaps more importantly, components are available from multiple suppliers. While both NIR and SWIR are capable of eye-safe operation, NIR uses lower-power lasers and can meet automotive LiDAR requirements. From a commercial perspective, NIR is significantly cheaper –


an always significant consideration in automotive applications. A survey by IHS Markit (Amsrud, 2019) showed cost of about $4-20 per channel for lasers and detectors, whereas for a comparable SWIR system this is around $275. Even with further development and increased volumes, predictions are that NIR will remain between 10x and 100x cheaper than SWIR.


LiDAR component technology One of the most important elements of any LiDAR system is the sensing element that captures and quantifies the reflected laser light. While several technologies can be used for this, silicon photomultipliers (SiPMs) generally offer the best performance, primarily because their high gain permits them to detect single photons, in the order of 1,000,000. As a result, SiPMs have become more widely used in recent years, becoming the sensor of choice for LiDAR depth-sensing applications. Tese devices can deliver the highest SNR performance for long-distance ranging in high- contrast conditions, compared to legacy detectors like avalanche photodiodes (APDs) which offer much lower gain and need to integrate incoming signals. Additional benefits, including lower supply biases, better


uniformity and reduced sensitivity to temperature changes, make SiPMs an ideal upgrade for systems that use APDs. Te higher sensitivity of SiPMs also enables the use of smaller form-factor


28 July/August 2021 www.electronicsworld.co.uk


optics, allowing for easier LiDAR integration into vehicles. As SiPMs are produced in a high-volume CMOS process, these high-performance devices have the lowest detector cost, further enabling the proliferation of LiDAR. Te ArrayRDM-0112A20-QFN from ON Semiconductor is a


monolithic 1×12 array of 0.47mm x 1.12mm SiPM pixels based on the advanced, proprietary, RDM SiPM CMOS process, specifically developed for high sensitivity to NIR light. It achieves industry- leading 18.5% photon detection efficiency (PDE) at 905nm wavelengths, with a response of over 100kA/W. Te high internal gain of the SiPM allows sensitivity down to


the single-photon level, which in combination with the high PDE detects the faintest return signals, enabling LiDAR to operate over greater distances, even with low-reflective targets. Te array is packaged in a robust 10mm x 5.2mm QFN package allowing access to the twelve individual pixels. Specifically designed for automotive LiDAR systems (including


Flash, mechanical or MEMS scanning LiDAR), the array is the first to carry AEC-Q102 approval for automotive qualification, developed in accordance with IATF 16949.


Incredibly useful LiDAR is an incredibly useful technology, because it determines depth rapidly and accurately, whether as a single point or a 3D map of an object or large site as part of a scanning system. One key decision to make when planning a LiDAR design, however, is the wavelength of the IR light to be used. Based upon performance, component availability and commercial considerations, NIR is most oſten the preferred choice. In most LiDAR implementations, the laser light source can


be relatively simple, but the choice of detector has a significant impact on system performance. Te latest SiPM array from ON Semiconductor offers excellent detection performance and is the first SiPM detector to carry AEC-Q102 approval.


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