Lidar solution based on SPAD/SiPM technology

Lidar (LiDAR) is a ranging technology that has been increasingly used in applications such as automotive advanced driver assistance systems (ADAS), gesture recognition, and 3D mapping in recent years. Especially in the automotive field, with the trend of sensor fusion, LiDAR combines imaging, ultrasound, and millimeter wave radar to complement each other to provide vehicles with all-round perception and pave the way for safer autonomous driving.ON semiconductor provides this full range of sensor solutions and the technology is far ahead. It is one of the market leaders in single-photon avalanche diode (SPAD) and silicon photomultiplier (SiPM) sensor technologies. It provides a complete LiDAR solution, including systems, sensors, and output.

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

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, histogram, 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 which integrates SiPM and image sensor, and the latest 400 x 100 SPAD array Pandion.

Lidar solution based on SPAD/SiPM technology

Figure 1: Block diagram of a typical LiDAR system

What are SPAD, SiPM and ToF

SPAD is a photodiode that works in Geiger Mode, just like a photon trigger switch, in an “on” or “off” state. SiPM is composed of multiple independent SPAD sensors, each of which has its own quenching resistance, which overcomes the shortcoming that a single SPAD cannot measure multiple photons at the same time. Time of flight (ToF) refers to the time it takes to send light pulses to the target and then the sensor receives the light returning from the target. Through the speed of light and ToF, the target distance can be calculated. The concept is very simple, but it is subject to many challenges in the real world, including harsh environments such as light conditions, low reflectivity targets, and long distances. There are currently two ToF measurement techniques: 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 the histogram data. If the SNR is increased, the detection can be realized at a longer distance. ToF LiDAR can be used in many applications, such as robotics, drones, industrial, mobile, automotive ADAS and autonomous driving and augmented reality (AR)/virtual reality (VR).

SiPM and SPAD are becoming emerging LiDAR detectors

SiPM and SPAD can detect low-reflectivity targets with a distance of more than 200 m and 5%. They can also work in bright sunlight. The resolution is excellent, and the smallest possible aperture and solid-state design enable compact system integration into the car. It has a very cost advantage 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 product consistency. ON Semiconductor is currently a global supplier that is truly capable of mass production of SiPM products. The voltage and gain of millions of sensors it provides are very consistent, which is easy to calibrate the system and reduce manufacturing costs.

2. Comply with vehicle regulations (IATF 16949, AEC Q102, -40 to 1050C operating temperature, PPAP compliance)

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. From the beginning of the design, automotive certification was considered to design sensors and packaging.

3. High photon detection rate (PDE) at 905 nm

ON Semiconductor’s SiPM now has the best-in-class PDE, exceeding 12%, and will reach 30% in 2020.

4. High gain

The gain of SiPM is 10,000 times that of avalanche photodiodes (APD) and 1 million times that of PIN diodes. Crosstalk

SiPM array scanning LiDAR system

The 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 the field of view (AoV) 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 sample multiple vertical points at the same time, 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 image and LiDAR

FUSEONE combines a 2-megapixel automotive-grade image sensor and a SiPM-based flash LiDAR, and uses a software application to fuse the camera and LiDAR to obtain target distance, movement speed and other data. The high-sensitivity SiPM detector and phantom intelligent algorithm achieve enhanced distance capabilities. Since there is no need for mechanical radar scanning, FUSEONE is extremely cost-effective. 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 band pass filter. Xilinx FPGA is used for edge processing and full waveform acquisition, with an AoV of 25° x 3.6°, under the outdoor lighting conditions of 20 klux, pedestrian detection can reach 45 m and car detection can reach 85 m.

Pandion SPAD array realizes long-distance scanning LiDAR

The 400×100 SPAD array has CMOS logic devices, the array size is 14 mm × 3 mm, the pixel pitch is 38.6 um, and the rolling shutter readout (100-channel parallel readout) is adopted, and the passive quenching active reset (PQAR) feature can be obtained

Lidar solution based on SPAD/SiPM technology

Figure 2: Pandion detects targets with different distances and different reflectivities

Lidar solution based on SPAD/SiPM technology

Figure 3: Intensity image obtained by Pandion using photon counting

Lidar solution based on SPAD/SiPM technology

Figure 4: Pandion intensity image at low light level

Summarize

SiPM and SPAD technologies are the key to the realization of the receiver function in the LiDAR system. Based on the Geiger mode avalanche principle, a compact, high-gain sensor is realized. ON Semiconductor is the market leader of these technologies and provides a complete LiDAR solution, including SiPM sensors, The SiPM array scanning LiDAR system, the FUSEONE system that integrates SiPM flash LiDAR and images, and the Pandion SPAD array have the advantages of robustness, high cost performance, and compliance with vehicle regulations. They are actively researched and innovated, while providing designers with extensive field application support and related Application notes and video libraries, product demonstration systems, simulation data of verified models, etc., to solve design challenges and promote innovation.

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