LiDAR (Light Detection and Ranging) is the ranging technology increasingly used in applications such as mobile ranging, automotive ADAS (Advanced Driver Assistance System), gesture recognition and 3D mapping, and has incredible potential for market development. This article will show the trends of LiDAR and the Silicon Photomultiplier (SiPM) Direct Time of Flight (dToF) LiDAR Platform Development Kit introduced by onsemi.
LiDAR uses ToF technology for ranging
LiDAR was originally referred to as optical radar because none of the light sources used were lasers, but since the advent of lasers, lasers have been particularly suitable as a source of high-brightness, low-divergence coherent light, so the optical radar uses lasers as light sources. The name is collectively referred to as laser radars.
LiDAR is a system that integrates laser, global positioning system (GPS) and inertial navigation system (INS), which is used to obtain point cloud data and generate accurate digital three-dimensional model. The combination of these three technologies can obtain the surrounding three-dimensional real scene under the condition of consistent absolute measurement points.
The LiDAR system is mainly composed of laser, phased array, MEMS (microelectromechanical mirrors), scanner and optical components, photodetector and receiver electronic devices, positioning and navigation system, sensors and other major components. According to different design concepts, it can be classified into different types such as orientation-based, scanning mechanism-based and platform-based.
LiDAR uses time of flight (ToF) technology for ranging by measuring the time required for matter, particle or wave (sound wave or electromagnetic wave) to travel in the medium. It can either detect the traveling object in a direct way, called direct time of flight (dToF), or measure it with indirect scattered light, called indirect time of flight (iToF), and calculate the distance by calculating the time delay between the transmitted signal and its echo. iToF is suitable for short-distance depth sensing applications, and is used indoor and in environments where the sensor is not exposed to direct sunlight. dToF is suitable for both short-and long-range depth sensing applications.
SiPM sensor has required performance for LiDAR
SiPM is a sensor, which is a solid-state single photon sensitive device based on single photon avalanche diode (SPAD) implemented a conventional silicon substrate, capable of responding to the challenges of sensing, timing, and quantifying low-light signals as low as single photon levels. SiPM, which traditionally belongs to the field of photomultiplier tubes (PMT), now provides an attractive alternative, which combines the low-light detection capability of PMT and provides all the advantages of solid-state sensors. SiPM is characterized by low voltage operation, insensitivity to magnetic fields, mechanical rigidity and excellent response uniformity. Due to these characteristics, SiPM has rapidly achieved proven performance in the fields of medical imaging, hazard and threat detection, biophotonics, high energy physics and LiDAR.
Using SiPM as a photoelectric sensor has many advantages over alternative sensor technologies such as APD, PIN diode and PMT, especially for mobile and mass-produced products. SiPM is a single photosensitive, high performance, solid-state sensor, composed of closely arranged SPAD sensors with integrated quench resistors. It features high gain (~1x106), high detection efficiency (> 50%) and fast timing (sub-nanosecond rise time).
Photoelectron gain is generally more definitive than conventional PMT, resulting in a very low or even negligible excess noise factor. A fixed number of detected photons can have a higher SNR (signal-to-noise ratio) than PMT. In contrast, the random gain of PMT typically requires more detected photons to obtain the same SNR. If a large number of SPADs are arranged together, the dynamic range can be several orders of magnitude larger than PMT, thus achieving faster imaging rate or higher SNR without saturation. In addition, the mass production of silicon electronics makes the manufacturing cost of SiPM lower than of vacuum tubes.
SiPM sensor with high gain and high bandwidth
In the Internet of Things (IoT), there are increasing ranging and sensing applications that are expected to benefit from low power consumption and high performance SiPM technology. Especially LiDAR applications using near infrared (NIR) wavelengths that are safe for human eyes, such as automotive ADAS, 3D depth mapping, mobile, consumer and industrial ranging.
In order to take advantage of the high gain and bandwidth of SiPM sensor, dToF can be used to provide accurate ranging with the lowest power budget. The high sensitivity of onsemi’s SiPM allows the use of low-power lasers to improve eye safety. onsemi has created a software model that allows accurate determination of system performance under various input conditions, and a hardware ranging platform with SiPM sensors. To take advantage of the high gain and bandwidth of SiPM sensor, dToF can be used to provide accurate ranging up to 23 meters without affecting battery life.
The SiPM sensor introduced by onsemi provides single photon detection from 250 nm to 1,100 nm, supports low voltage to easily implement system requirements, has low power characteristics, allows low power design with lower operating voltages and simple read-out electronics, high bandwidth and fast response time, minimizes ranging measurement time, takes advantage of low laser power dToF ranging technology, has low noise and high gain characteristics, good SNR, adopts standard CMOS manufacturing processes, is low cost, highly uniform and scalable production, and uses small side SMT package to provide only 1 mm sensors.
SiPM dToF LiDAR platform development kit
The SiPM dToF LiDAR platform development kit launched by onsemi shows a complete ranging application and helps developers familiarize themselves with the underlying technology and all necessary building blocks. In addition, this kit helps to evaluate the core components of the system, such as SiPM sensors. Through the test points provided on the hardware and various functions and configurable parameters on the GUI, developers may evaluate the kit in a quick and user-friendly manner, and accelerate the application development.
This highly integrated SECO-RANGEFINDER-GEVK development kit is a LiDAR platform using SiPM dToF. The development board provides plug-and-play function. It is composed of SiPM, a single photosensitive, high performance, solid-state sensor and a complete development kit for single-point rangefinder applications, suitable for industrial and commercial applications requiring cost optimization.
The development kit is based on the latest NIR SiPM from onsemi (RB series) and integrates all necessary system components, including all the essential sub-systems for the application involving laser and reference circuit (Tx), receiving circuit (Rx), power management systems, and core FPGA and UART communication. This kit includes a multifunctional GUI enabling a complete evaluation of the range-finding performance as well as the adjustment of system variables such as the buffer number of pulses or the bias voltage for the SiPM-RB photomultiplier.
SECO-RANGEFINDER-GEVK development kit can be used for dToF operation for single point applications and has > 0.11m to 23m detectable range. It features out-of-the-box operation with a dedicated user-friendly GUI with adjustable system variables and optimized system cost. It has built-in time-to-digital converter (TDC), approximately 85ps bin width based on FPGA (ice3), automatic TDC calibration (FPGA reference clock), support for different power options, including USB (5V) and PMOD connector (3.3 V), and optimized system cost.
The laser and optical devices used in the kit include RB series SiPM sensor, 905nm laser diode transmitter, 650-1050 nm coated BK7 Plano-convex lenses for maximized measurement distance, 905±5nm band pass optical filter (FWHM: 30±5 nm) for Rx, which can achieve the highest sensitivity in the selected spectrum, comply with the power requirements of BS EN 60825 1:2014 for Class 1 laser products under normal operating conditions and single fault conditions, and the laser safety standards IEC/EN 60825-1:2014 and 21 CFR 1040.10 and 1040.11 (except for the deviation pursuant to Laser Notice No. 56) and are FDA-certified.
This development platform also includes scalable systems with Bluetooth® development kit (BDK−GEVK) and various other sensors and actuators, and provides a variety of software, including software adjustable settings suitable for various industrial and IoT applications and FPGA-based TDC, readout, communication interface and control of two regulated bias supplies. This development platform can be used in indoor navigation and ranging (detection distance up to 23m), collision detection, 3D mapping and other applications.
Conclusion
With the gradual maturity of LiDAR-related technologies, the cost has gradually decreased to an acceptable level in the market. Combined with the development of autonomous driving technology, more cars have begun to use the LiDAR system to detect distance, avoid collision and create 3D mapping. In addition, in the consumer product market, products such as sweeping robots and drones are also important application fields of LiDAR, with great market potential in the future. It is worthwhile for interested manufacturers to speed up their steps to invest in related product development and seize market opportunities.