RADIANCE-S: The Key to Calibration in ToF 3D Sensing Module Assembly

COVID-19 is leading the world into an automation boom despite of the inconveniences it has brought to us. Undoubtedly, COVID-19 is influencing our daily life in both physically and mentally. People are concerned in being infected and hence keeping social distance to avoid face-to-face interaction. However, many daily activities are unavoidable including working and communication. Therefore, human-machine collaboration is playing an important role in today’s situation, such that people can remain their activities without leaving home.

In recent years, HMI (Human-Machine Interface) with 3D sensing has already introduced in our daily life. Coming, automation will be gradually replacing some unnecessary human-contact with a more convenience and concern-free way.

Figure 1. FedEx Robot Delivery with LIDAR Sensor
(Source: FedEx)

Figure 2. Face Recognition in Smartphone Security (Source: Spaceo.ca)

Fast and precise sensing is the most valuable items for HMI to enable the automation world. Since late 2018, Time-of-Flight (ToF), one of the 3D depth sensing technology, has become the new trend and has been widely implemented in various industries. For example the front/rear camera of Smartphones, industrial robotics vision enhancement in achieving industrial 4.0 or Smart Factory for automated production, automotive driving and in-car driver monitoring system with identification profiling and gesture recognition system.

APPLICATIONS

Leading the Smartphone market, Huawei, Oppo, Vivo, LG and Samsung have launched respective models with ToF 3D sensing camera for photo-taking enhancement, facial recognition in e-payment or personal security to contactless gesture navigation in 2019. It is estimated that Smartphone equips with ToF 3D sensing camera will be increased with a projection of 183 million or more in 2020 and beyond. Meanwhile, ToF 3D sensing technology is more widely adopted in today’s automotive industry. From LiDAR (Light Detection and Ranging) applications for driver-assisted driving to advanced driver assistance systems (ADAS). The reliability and performance accuracy of the ToF system are the major priority to the safety concern for the automotive makers, which have also brought different forms of challenges to the lens module manufacturers.

CHALLENGES

ToF 3D sensing technology can be divided into two major categories: Direct-ToF (d-ToF) and Indirect-ToF (i-ToF). Regarding to different applications and requirements, manufacturers will have different approaches within these two sensing methods.
- Direct-ToF (d-ToF): Measuring the time taken for emitted and returned laser to calculate the distance information
- Indirect-ToF (i-ToF): Measuring the phase shift between emitted and returned laser for distance calculation

Figure 3. Principle of ToF 3D Sensing

In general, i-ToF 3D sensing is more common in consumer electronics, but only the fly in the ointment is that this distance calculation method may exhibit some systems errors.

ToF 3D sensor is formed by different modules. Synchronization is required for each module for normal operation. However, there must have some system and intrinsic errors involved during the synchronization which are unavoidable:

1. Periodic Error in Correlated Waveform
a. Non-sinusoidal sign – distortion or misidentification
b. Phase error – changes in modulation waveform shape or emitted optical power between different samples

2. Synchronization Error in Laser and Sensor
a. Imitation synchronization difference between laser emitter and receiving sensor
b. Difference in input voltage during ToF setup and actual operation
3. Pixel Dependent Coordination Offset
a. Actuarial errors due to noise distribution
4. Thermal Induced Error
a. Laser Diode Driver’s performance changes with temperatures
Currently, the market acceptancy is typically in ±10mm error tolerance. As for some markets like security commentary and online electronic payment, more stringent error requirements are needed.

TESTING & CALIBRATION – HIGH VOLUME MANUFACTURING

Recognizing the system and intrinsic error involved, calibration in modular level will be provided by high-end manufacturer, in order to meet the requirements of high-end products. The necessary calibration steps are:
• Profiling and compensating the periodic error
• Computing and offsetting the intrinsic optics distortion
• Characterizing the synchronization difference between sensor and the laser emitter
• Harmonizing the pixels’ level consistency

Apart from minimizing the system error by calibration and testing, some high-end manufacturers will also provide a tailor-made and one-stop solutions for ToF 3D sensing technology to their customers with key values propositions:

• Automated production with minimal operator intervention – increase product yield by optimizing the production process and reducing costs
• Scalable modular design with cascaded modules
• Easily conversion for modules of different sizes to adapt to the ever-changing ToF market
• High volume yield output with consistency
• To exceed market accuracy requirements with higher accuracy and being ready for the future

As the World Number 1 CMOS Image Sensor equipment manufacturer, ASM Pacific Technology Ltd. (ASMPT) has launched their newest product development, RADIANCE-S, a spectacular design by global expertise which has met customers’ needs in high-volume production, high yield and accurately minimize the system errors by ToF 3D sensor module assembly to end-of-line calibration in one machine. RADIANCE is a today’s and future’s solution to fulfil the high-volume manufacturing in ToF 3D sensing technology.
• Inline architecture for fast volume operation with pallets transferring between calibration modules seamlessly
• 2D code tracking of pallets and units for real-time system monitoring
• Fast and easy changing of sensor module with quick change pallet design and self-responding settings call up via recognizing the corresponding unit ID

Entire system is well designed to be modular with possible insertion of new modules for up-scaling of production and plugging in new testing or calibration features easily. With calibration accuracy as a prime focus of RADIANCE-S, it has an excellent performs on multipath, input current and voltage consistency, ToF sensor module’s temperature influence and modulating frequencies controls. RADIANCE-S serves to complete ASMPT’s portfolio in camera module and ToF 3D sensing module assembly production equipment with ToF 3D sensor end-of-line calibration and testing solution. To lead the automation, ASMPT is enabling the digital world.