Sony's long-range SPAD dToF lidar exposed

Last year, Japan's Sony Corporation entered the field of autonomous driving in a high-profile manner through the prototype car "VISION-S".

VISION-S has completed development and has been on the road in Austria since the beginning of this year.

Recently, Sony has unveiled a stacked dToF (direct time of flight) ranging sensor for automotive LiDAR, using SPAD pixels as detection units.

The main features of this LiDAR developed by Sony are that it can measure distances up to 300 meters at intervals of 15 cm with high accuracy and high speed, and it can maintain high reliability even in drastic temperature changes from -40°C to 125°C and in adverse weather conditions.

Main Specifications

1. The principle of SPAD dToF

There are generally three measurement mechanisms for depth sensors: structured light (such as iPhone's FaceID), camera array (camera), and ToF (for lidar). Structured light and camera array are based on geometric principles for indirect depth estimation, while ToF (time-of-flight) measures the flight time between emitted light and reflected light and directly estimates the target distance based on the speed of light.

ToF can be divided into two categories: indirect time of flight (iToF) and direct time of flight (dToF). The difference between the principles of dToF and iToF lies mainly in the difference between emitted and reflected light.

dToF directly emits a light pulse and measures the time interval between the reflected light pulse and the emitted light pulse to obtain the flight time of light and calculate the distance.

iToF does not emit a single light pulse, but a sine wave modulation with regularly changing light and dark intensities. By detecting the phase difference between the received reflected modulated light and the emitted modulated light, the flight time is measured, thereby estimating the distance.

By the way, Apple’s latest iPad Pro and iPhone 12 Pro’s lidar also use dToF technology.

Advantages of dToF:

dToF can achieve both longer ranging distance and higher ranging accuracy.

dToF is less sensitive to ambient light interference and can be used in scenes with different light intensities.

SPAD (Single Photon Avalanche Diode) is a common detection unit in dToF sensors. SPAD is a pixel structure that can detect weak light, that is, it uses the avalanche multiplication effect to amplify the electrons generated from a single incident photon, so that weak light can be detected.

Using SPAD as the detection unit in the lidar dToF sensor can achieve long-distance and high-precision depth measurement.

The principle of SPAD pixels

The so-called stacking method is to connect the SPAD pixel chip and the logic chip through Cu-Cu to achieve conductivity. This method can improve design flexibility and productivity while achieving miniaturization and high performance.

Stacked structure

2. More and more companies are focusing on LiDAR

Japan's semiconductor-related companies such as Sony and Canon have entered the field of autonomous driving vehicle sensors by virtue of their long-term accumulation in the field of CMOS image sensors and have relatively leading technology.

For example, Pioneer partnered with Canon to develop 3D-LiDAR sensors in April 2019 and has released a small, high-performance mass-produced model 3D-LiDAR. In January 2021, at CES 2020, Pioneer launched a next-generation 3D-LiDAR prototype capable of measuring distances up to 500 meters. Toshiba has focused its research and development on LiDAR-related technologies, and in April 2019, it disclosed a measurement algorithm technology that improves the distance measurement resolution of LiDAR. In July 2020, Toshiba developed a series of light receiving technologies for solid-state LiDAR that can support L4 or higher autonomous driving.

There are two ways to achieve autonomous driving: one is to use LiDAR, and the other is not to use LiDAR. Currently, the former is the majority, and more and more companies are focusing on the development of LiDAR.

According to a market forecast report, the market size of laser sensors, including LiDAR, is expected to expand 200 times from 2017 to 2030.

In addition, Apple's recent contact with multiple LiDAR suppliers to develop self-driving EVs has also become a hot topic of discussion. Looking at the entire autonomous driving industry, it can be said that the development of LiDAR companies is unstoppable.