Lidar analysis based on SPAD SiPM technology

What is lidar and what does it do? Lidar (LiDAR) is a ranging technology that has been increasingly used in recent years for applications such as automotive advanced driver assistance systems (ADAS), gesture recognition and 3D mapping. Especially in the automotive field, with the trend of sensor fusion, LiDAR combines imaging, ultrasonic waves, and millimeter wave radar to complement each other and provide all-round perception for cars, paving the way towards safer autonomous driving. ON Semiconductor provides this full range of sensor solutions and is far ahead in technology. It is one of the market leaders in single photon avalanche diode (SPAD) and silicon photomultiplier (SiPM) sensor technology, providing a complete LiDAR solution, including systems, sensors, and outputs. and laser driver solutions.

ON Semiconductor’s complete LiDAR solution

A LiDAR system has 6 main hardware functional blocks: transmission, reception, beam steering, optics, output and power management. A typical LiDAR system block diagram is shown in Figure 1. Among them, ON Semiconductor can provide SiPM/SPAD, laser driver reference design, power management, amplification and processing, timing, histograms, point cloud generation and even systems. Mature analog SiPM products include C series, J series, and R series. The system includes SiPM array scanning LiDAR demonstrator (more than 100 m scanning distance), FUSEONE that fuses SiPM with image sensors, and the latest 400 x 100 SPAD array Pandion.

What are SPAD, SiPM and ToF

SPAD is a photodiode that works in Geiger Mode (Geiger Mode), which is like a photon-triggered switch and is in an "on" or "off" state. SiPM is composed of multiple independent SPAD sensors, each sensor has its own quenching resistance, thereby overcoming the shortcoming of a single SPAD that cannot measure multiple photons at the same time. Time of flight (ToF) refers to the time required to send a pulse of light to a target and then for the sensor to receive the light back from the target. Through the speed of light and ToF, the target distance can be calculated. The concept is simple, but it is subject to many challenges in the real world, including harsh environments such as lighting conditions, low reflectivity targets, and long distances. There are currently two ToF measurement technologies: single laser pulse method and multiple laser pulse method. The single laser pulse method refers to measuring the return time of a single pulse each time and requires a high signal-to-noise ratio (SNR). The multi-laser pulse method refers to measuring the return time of multiple pulses each time, and obtaining the distance through histogram data. If the SNR is improved, longer-distance detection can be achieved. ToF LiDAR can be used in many applications, such as robots, drones, industry, mobile, automotive ADAS and autonomous driving, augmented reality (AR)/virtual reality (VR), etc.

SiPM and SPAD are emerging as LiDAR detectors

SiPM and SPAD can detect low reflectivity targets at a distance of more than 200 m, 5%, can operate in bright sunlight, have excellent resolution, and have the smallest possible aperture and solid-state design to enable compact system integration into cars. And it has great cost advantages and is becoming an emerging LiDAR detector.

Automotive LiDAR sensor requirements

1. Strict consistency. Since SiPM/SPAD works in Geiger mode, it is difficult to control the consistency of the product. ON Semiconductor is currently the only supplier in the world that is truly capable of mass-producing SiPM products. The voltage and gain of the millions of sensors it provides are very consistent, making it easy to calibrate the system and reduce manufacturing costs.

2. Comply with automotive regulations (IATF 16949, AEC Q102, -40 to 1050C operating temperature, PPAP compliant). ON Semiconductor has accumulated many years of professional experience in automotive production and has a very complete quality supervision and control system for automotive regulatory products. , the sensors and packaging were designed with automotive certification in mind from the beginning.

3. High photon detection efficiency (PDE) at 905 nm. ON Semiconductor’s SiPM now has a best-in-class PDE of more than 12% and will reach 30% in 2020.

4. High gain, the gain of SiPM is 10,000 times that of avalanche photodiode (APD) and 1 million times that of PIN diode, with crosstalk <20, providing excellent SNR.

SiPM array scanning LiDAR system

This SiPM array scanning LiDAR contains 16 905 nm laser diodes, an electromechanical rotating mirror for beam steering, ON Semiconductor's monolithic 1 x 16 SiPM array and processing electronics, and has an angle of view (AoV) of 80° x 5.53 °, pulse width 1 ns, system peak power 400 W, system size 22 cm x 18 cm x 13 cm. This system uses a 1D array to simultaneously sample multiple vertical points, combined with horizontal single-axis scanning, to obtain a complete image of the field of view and achieve real-time imaging of long-distance low-reflectivity targets.

FUSEONE System: Fusion of Imagery and LiDAR

FUSEONE combines a 2-megapixel automotive-grade image sensor and SiPM-based flash LiDAR. It integrates cameras and LiDAR through software applications to obtain target distance, movement rate and other data. The highly sensitive SiPM detector and phantom intelligent algorithm achieve enhanced distance capabilities. Since no mechanical radar scanning is required, FUSEONE has great cost advantages. The system uses 8 SiPMs and 2 905 nm laser diodes with a pulse width of 20 ns and a peak power of 80 W. The receiver optical path uses a 43 nm bandpass filter. Xilinx FPGA is used for edge processing full waveform acquisition with an AoV of 25°. x 3.6°, under outdoor lighting conditions of 20 klux, pedestrian detection reaches 45 m, and car detection reaches 85 m.

Pandion SPAD array enables long-distance scanning LiDAR

The 400×100 SPAD array has CMOS logic devices, the array size is 14 mm × 3 mm, and the pixel pitch is 38.6 um. It adopts rolling shutter readout (100-channel parallel readout), and the passive quench active reset (PQAR) characteristics can be obtained <5 ns recovery time, breakdown voltage reaches above 3.3 V. Different from traditional point clouds, Pandion SPAD LiDAR has formed images

Summarize

SiPM and SPAD technologies are the key to realizing the receiver function in LiDAR systems. They are based on the Geiger mode avalanche principle to achieve compact, high-gain sensors. ON Semiconductor is the market leader in these technologies and provides complete LiDAR solutions, including SiPM sensors, The SiPM array scanning LiDAR system, the FUSEONE system that combines SiPM flash LiDAR and images, and the Pandion SPAD array have the advantages of being robust, cost-effective, and compliant with vehicle regulations. They actively develop and innovate, and at the same time provide designers with extensive on-site application support and related Solve design challenges and drive innovation with annotations and video libraries, product demonstration systems, simulation data for validated models, and more. The above is the lidar solution based on SPAD SiPM technology. I hope it can help you.