In March of this year, Apple released the new iPad Pro. The biggest upgrade is to carry the first dToF in Apple products. By projecting a dot matrix, it can obtain more accurate 3D scene information and enhance the AR application experience. With the approaching of Apple's autumn conference, the industry chain has also reported that iPhone 12 will also be equipped with dToF LiDAR, deepening the AR layout. As a benchmark for pushing down the industry chain, this wave of Apple operations has led many people to the idea of "dToF replacing iToF". Is this really the case?
dToF is long overdue, and mobile applications still need to solve two major problems. The application of
ToF on smart phones has long been commonplace. Now in 2020, almost all high-end flagship models are equipped with a ToF sensor as standard. Initially, this technology was used for distance sensing. Manufacturers applied the ToF module to the front panel of the mobile phone as a sensor for the screen-off function of the call. This can be traced back to the 2014 BlackBerry passport, LG G3 and other models.
In recent years, due to the increasing demand for 3D sensing and camera ranging, ToF has become more useful in smart phones. At present, most of the mobile phone ToF modules on the market adopt the iToF (indirect ToF) solution. As the name suggests, the principle of iToF is not to directly measure the flight time of the beam. According to Luo Wei, chief engineer of Huawei Camera, iToF generally modulates the emitted light wave into a periodic signal with a certain frequency, and indirectly calculates the light flight by measuring the phase difference between the transmitted signal and the signal arriving at the measured end and reflected back to the receiving end. Time, common schemes include four-step phase shifting method and two-step phase shifting method.
However, because iToF needs to collect multiple phases of image data to calculate the phase difference when outputting a frame of depth image, iToF has relatively high overall power consumption, and it is more difficult to increase the frame rate of the depth map. In order to solve these problems, iToF increases the signal-to-noise ratio by increasing the pulse instantaneous power and multi-pixel fusion Binning, thereby reducing power consumption and increasing the detection range. The advantage of iTof is that the pixel of the sensor is relatively small (5um, or even 3.5um), so the resolution can be higher. In the past few years when
has been widely used in iToF, it seems that "the thunder is louder and the rain drops". Whether it is a mobile phone manufacturer or a research organization, while constantly touting the application of ToF in the mobile phone field is about to explode, for consumers, ToF has not brought them particularly obvious changes. I believe that no one will choose simply because of ToF. Buy a mobile phone. Of course, this is largely due to the lack of application scenarios and software ecology, so that ToF has not ushered in a real market "burst".
Just when many people felt that ToF was a bit tasteless, the LiDAR on the new iPad Pro launched by Apple brought ToF to the forefront. At present, the ToF technical route can be roughly divided into iToF and dToF (direct ToF) two solutions, and the LiDAR on the iPad is the latter.
Regarding the difference between iToF and dToF, Bai Yangong, senior technical support manager at ams, said that dToF is actually simpler and more direct than iToF in principle. The principle of dToF is to use the process time from the light source emission to the reflection of the measured object to the receiving end divided by two, and then multiplied by the speed of light to directly obtain the distance data to the measured object.
"Compared with iToF, dToF has the following advantages: real distance detection, fast response, low power consumption and accuracy of multi-object detection. Especially iToF cannot recognize the quantity when detecting multiple objects. , Only a median distance value can be fed back.” Bai Yangong added.
So the question is, since dToF is even simpler than iToF in principle, why did dToF officially enter the consumer's field of vision until the application on the iPad Pro this year?
In this regard, Liu Yang, CEO of Juyou Intelligent Technology Co., Ltd., believes that the two main reasons are cost and application scenarios. "According to the current technology maturity and the current status of introduction, dToF still costsIt is higher than iToF, and has higher requirements on the light-emitting part in structure, and therefore the application scene is more limited to the scene at a longer distance. In the mobile terminal, the more mature and more cost-effective iToF was first introduced. Due to the mobile terminal's demand for multi-sensing, including Apple, it also began to try on the iPad Pro, and dToF began to receive more attention. In fact, dToF is not a new technology, and it has been applied in other fields as early as possible, and it is mainly more suitable for remote scenarios. "Z2z
In fact, although it seems that the principle of dToF is relatively simple, there are still many difficulties in the process of implementation. dToF is mainly composed of three parts: the transmitting end VCSEL, the receiving end SPAD (single photon avalanche diode), TDC ( Time-to-digital conversion circuit). Compared with iToF, dToF has higher requirements on both the transmitting end and the receiving end.
For the transmitting end, the power of VCSEL light source directly affects the working distance of dToF. To achieve such The iPad Pro has a working distance of about 5 meters, it is necessary to increase the power of the VCSEL light source, or shorten the pulse period to ns level to increase the instantaneous power. On the other hand, on the receiving end SPAD, the process itself is complicated and the cost is high. It is monopolized by foreign manufacturers, and how to improve its resolution in a limited volume is still to be resolved. Therefore, the difficulty of miniaturization and high cost are the main reasons that dToF has not been widely used in mobile devices for 3D sensing.
As for mobile phone ToF products, Liu Yang said that at present it is still a foreign supply chain dominated by SONY, and Juyou Smart is also actively cooperating with mobile phone customers, especially in promoting some of its unique TOF chips and system technologies. In terms of dToF, Domestic breakthroughs have been made in key VCSELs and SPADs in China. For example, the research team of Professor Zhu Zhangming and Yang Yintang of Xidian University released the dToF SPAD lidar sensor chip in early June. The single chip integrates the core photosensitive device SPAD finishing and precise ranging Circuit, a variety of ranging accuracy optimization and anti-background light interference algorithms and other functions, with a resolution of 32×32×4, a refresh rate of over 30fps, and a long-distance high-precision detection of 12-15 meters under 200mW power consumption, It is the farthest detection range of dToF SPAD in the current report.
It can be seen that with the increase in market demand in the future and more players joining the dToF market competition, the cost of dToF may drop rapidly. But I want to further and AR , Face recognition and other applications, still need to work harder on the resolution of small-size SPAD.
dToF replaces iToF? Scene adaptation is the key
Judging from the performance of iPad Pro, dToF is indeed an AR application experience belt There has been a lot of improvement. A senior industry insider told "Huaqiang Electronics" that from a technical point of view, in addition to high ranging accuracy and strong anti-interference ability, dToF's advantages in ranging distance and multi-object recognition capabilities make dToF can perform well in the AR field. This is the main reason why Apple chose dToF technology.
At present, dToF has been widely used in many fields. Bai Yangong said: "Now we can see applications There are many directions and application areas, such as the application of distance detection in sweeping robots, and proximity sensing in large screens such as laptops. Screen lock screen unlocking applications, safety distance detection in factories, stable landing of drones and collision detection, etc. DToF can be used as long as it is an application scenario that requires absolute distance measurement. "Z2z
" is like the TMF8 series dToF sensor of ams, which integrates an optical filter, which can eliminate strong light and minimize the interference of external light on the sensor; at the same time, it is a common problem for optical components-oil pollution can also be well suppressed , And this is almost impossible for iToF to solve, dToF can minimize the impact. "Z2z
So now that dToF has so many advantages, will it replace iToF as the preferred technology for mobile devices in the future?
As mentioned above, dToF still has problems such as high cost and low resolution compared to iToF. According to senior industry insiders, the low resolution of dToF is mainly due to the fact that SPAD’s single pixel size cannot be too small. Although this yearPanasonic released a 1200×900 resolution SPAD dToF sensor on ISSCC with 65nm CMOS process, but due to volume power consumption, it is more used in automotive LiDAR.
Regarding whether dToF will replace iToF, Liu Yang believes that technology and scene adaptation are the most important: “ToF technology will not stay in the current situation, regardless of whether dToF and iToF will continue to evolve, or even continue to integrate, so there is no need to use these The technical name is the direction of calibration. Making a better ToF and making a ToF more suitable for related application scenarios is the key." A senior industry insider at
believes that iToF still has the power to compete with dToF in the consumer electronics field. He said:" We also see that iToF technology has also been improving. Algorithms and circuit design are used to improve the ranging accuracy, distance and anti-interference ability of the iToF system. Therefore, in the consumer electronics field where the ranging range is generally small, iToF It may not be lost to dToF. In the future, which technology will be the dominant technology in the consumer electronics field, it is difficult to draw conclusions.”
According to past practices, after Apple embraces dToF technology, it is likely that the supply chain will intensively follow up. For existing ToF manufacturers, this may be a harbinger of intensified industry competition. How should they face it?
“We think it’s not that Apple embraced dToF, but that Apple has tried a ToF technology that is more suitable for their current application.” Juyou Smart CEO Liu Yang believes, “Although some companies may follow suit, we are more focused The development of ToF technology that is more suitable for customer applications and has commercial value is not limited to dToF and iToF. We are also developing related and more advantageous ToF technologies, including hybrid ToF technology and high dynamic pixel control technology, and look forward to subdividing applications To provide customers with more professional ToF solutions, such as higher resolution, smaller FOM factor, better system cost, higher accuracy, etc."
Therefore, dToF and iToF, as two branches of ToF technology, have different Technical features will have their own room for development in different application scenarios. Liu Yang believes that the current dToF technology has lower power consumption and relatively consistent accuracy values at longer distances, but there are indeed problems with insufficient accuracy, insufficient resolution, and high cost. Therefore, there may be some problems on the rear of the mobile phone. Application opportunities.
At the same time, ToF technology is still evolving and merging. Juyou Intelligent said that the future ToF technology will be more suitable for applications, more dynamic, higher precision and resolution, and it will be more system integration.化. In addition, the innovation of the light-emitting part will be a key, and Juyou Smart is also vigorously developing related chips and solutions in the light-emitting drive and control part. In short, in order to solve more complex application requirements, ToF technology will continue to evolve and become more diverse. . We have been talking about
AR/VR applications for many years, but the progress has been slow due to restrictions on equipment performance, network, display, and sensing technology. Today, under the stimulation of 5G, Apple's AR ecological construction, and Huawei's Hetu application, ToF has clearly entered a period of rapid development, and the "endorsement" of major terminal companies has provided a solid backing for ToF's application prospects. For manufacturers related to the ToF industry, how to grasp the pain points of terminal applications, quickly follow up the changes in application demand, and expand their own basic technological advantages are the keys to gaining a foothold in the Red Sea market in the future.
