“AiP germinated together with Bluetooth wireless technology in the early days. From 2000 to 2001, researchers from the University of Birmingham and Georgia Institute of Technology successively proposed an antenna design concept integrated on the package for 5.8GHz Wi-Fi applications; 2006 Nanyang Technological University, Singapore In order to better promote packaged antenna technology, Professor Zhang Yueping proposed the concept of AiP for the first time by drawing on the concept of SiP, and has done a lot of related research in the following 10 years, and therefore won the highest award in the antenna industry in 2020. – Claus Antenna Award.
As an important part of the wireless communication system, the antenna is usually presented in two forms: discrete and integrated in the transceiver system formed with the chip. The former is commonplace, and the latter is mainly divided into Antenna-on-Chip (AoC) and Antenna-in-Package (AiP) two categories. AoC technology integrates the antenna and other circuits on the same chip through semiconductor materials and processes. Considering cost and performance, AoC technology is more suitable for the terahertz frequency band; AiP technology integrates the antenna with other circuits through packaging materials and processes. In the same package, due to the good consideration of antenna performance, cost and volume, it has been favored by the majority of chip and package manufacturers in recent years.
At present, almost all 60GHz wireless communication and gesture radar chips use AiP technology. In addition, AiP technology can also be found in 79GHz automotive radar, 94GHz phased array antenna, 122GHz/145GHz/160GHz sensors and 300GHz wireless link chips. figure.
Evolution of mmWave Radar
Let’s briefly review the history of AiP.
AiP germinated together with Bluetooth wireless technology in the early days. From 2000 to 2001, researchers from the University of Birmingham and Georgia Institute of Technology successively proposed an antenna design concept integrated on the package for 5.8GHz Wi-Fi applications; 2006 Nanyang Technological University, Singapore In order to better promote packaged antenna technology, Professor Zhang Yueping proposed the concept of AiP for the first time by drawing on the concept of SiP, and has done a lot of related research in the following 10 years, and therefore won the highest award in the antenna industry in 2020. – Claus Antenna Award.
The success of AiP technology is largely due to the renewed interest in research and development of 60GHz wireless systems. 2007 marked a new stage in the development of AiP technology. In that year, the IEEE listed the 60GHz frequency band as an unlicensed millimeter-wave frequency band. Since then, a large number of AiP researches in this frequency band have begun to emerge. In 2014, as 5G technology fully supports low-frequency sub-6G and millimeter-wave frequency bands (26/28/39GHz), AiP technology has become one of the important topics in the 5G field. The main difficulty lies in how to achieve high radiation efficiency and low cost. mass production.
According to data provided by Lu Yuzhao, COO of Gartland Microelectronics, it is estimated that by 2024, the capacity of global millimeter-wave radars will reach 400 million, AiP can bring 40% growth to the market, and the cost is compared with the current mainstream CMOS SoC. The chip will continue to drop.
“High performance, miniaturization, easy installation, low cost, etc. are the core competitive advantages of AiP chips.” Wang Dian, production technology director of Gartland Microelectronics, was interviewed by “Electronic Engineering Album”, based on Gartland AiP chip development Taking the ultra-short-range vehicle radar as an example, it describes how to integrate the RF front-end, radar signal processing baseband, microprocessor and high-frequency antenna in the form of packaging, and then match very few peripheral devices, so as to quickly complete the radar module The process of building (including power chip, Flash and CAN transceiver).
As a manufacturer dedicated to providing millimeter-wave radar chips and solutions, Caltland Microelectronics, founded in 2014, started AiP product development in 2017. After four generations, it successfully mass-produced two models containing AiP technology in the second quarter of this year. Millimeter-wave radar chip products: Alps series 77/79GHz automotive-grade millimeter-wave radar chips, and Rhine series 60GHz industrial-grade millimeter-wave radar chips.
Gartland vehicle ultra-short-range radar AiP chip
The radar chip size of these two integrated antennas is only 12.2mm*12.2mm, with four transmitters and four receivers, built-in radar signal processing baseband, FMCW waveform generator and high-speed ADC. The peripheral only needs power supply and flash memory to form a complete millimeter Wave radar module, at the same time, the user can choose 3 transmit channels arbitrarily to control the transmit characteristics. The chip can also support the pitch and horizontal direction MIMO technology, providing the ability to solve the pitch angle and higher accuracy in the horizontal direction.
Three launch modes can be switched at will
On this basis, we can continue to build a full-scenario chip solution covering 360 degrees around the car – through the cascade of a single Alps SoC or two Alps SoCs, it can meet the needs of forward radar; a single Alps SoC (2 rounds of 4 Receive or 4 transmit and 4 receive) can meet the needs of front angle/back angle radar; through Alps AiP, the needs of ultra-short-range radar around the car can be realized. Obviously, the complete solution of the radar chip around the car is realized through a chip platform, which not only reduces the development difficulty, but also saves the development time and development cost, and is also conducive to the standardization of the sensor hardware.
Unprecedented technical challenges
Of course, to complete the development of such an ultra-short-range radar, there will be challenges including ground clutter, physical design, antenna performance design, electrical connection, packaging technology and materials, chip module co-design, heat dissipation, reliability, and automated testing. A series of challenges, Wang Dian said that in order to help downstream manufacturers overcome these challenges together, Caltland Microelectronics has done a lot of work on chip development, production and underlying software.
Taking Alps AiP as an example, the designer needs to place 5240 vias, 161 signal lines, 12 antenna units and 4 groups of power dividers within an area of 12*12 mm2. The minimum line width is only 25um, and the ratio is provided. Use bandwidth redundancy at least 200% higher than the design bandwidth. In addition, in order to make a complete packaged antenna millimeter-wave radar system chip with high reliability, more than 6,000 hours of reliability experiments are required to meet the requirements of vehicle quality and life.
Ultra-short-range radar requires a large elevation viewing angle, so that the detection of height information of short-range objects will be more abundant, but it also means that more ground clutter will be detected at the same time.
The way Gartland solves the problem of ground clutter is to accumulate multiple frames of data and compare it with the characteristic curve fitted by a large amount of measured a priori information – beyond this curve, it is considered to be the real measured object. Targets, below this curve, are suppressed. The distance, amplitude, and even speed and pitch information of the target are helpful for fitting such characteristic curves. At the same time, through the actual measurement of Gatland, it was found that different pavement materials, such as cement, asphalt, and dirt roads, have their own characteristics. In addition, by supporting the adaptive characteristic curve, adding more characteristic variables such as speed and pitch information, combined with online training, when the vehicle enters different road conditions, the characteristic curve can be dynamically adjusted, which will have a better effect on clutter suppression. .
Source: Gatland Microelectronics
Due to the limitation of physical space, the angle distortion generated by the integrated antenna coupling is nonlinear. The nonlinear distortion causes the angle solution to deteriorate, and the difficulty of angle measurement increases. Here, antenna calibration is required.
The traditional calibration method only uses linear conversion compensation, which is not ideal for nonlinear distortion. For this challenge, Gatland creatively uses a new neural network algorithm (RBF-NN) for antenna calibration. For such a neural network architecture, the input layer is the measured angle θ of the antenna, through the middle hidden layer, the transfer function φ, and finally summed to obtain a calibrated value of the angle as the output.
In the above figure, the left side is the original data of angle measurement, which has nonlinear distortion; the middle is the traditional calibration method, and the angle error after calibration is about 5 degrees; the right side uses the RBF-NN neural network calibration algorithm, the angle The error is within 1 degree, and the effect is very obvious. (Information source: Gartland Microelectronics)
Usually, the azimuth field of view of the ultra-short-range radar is large. In the scene of dense traffic, the probability of receiving interference will be greater, and the demand for anti-interference will be stronger. The AiP chip of Caltland Microelectronics adopts a systematic strategy To fight interference: 3 modes to avoid interference, 1 mechanism to eliminate interference.
First, combined with the flexible FMCW waveform generator of the AiP chip, possible interference is avoided by randomly changing the chirp configuration parameters in a frame of data, which is also an effective way to prevent synchronization interference.
Scrambling (Phase Scrambling, PS), changing the phase of the waveform;
Shift Chirp (Chirp Shifting, CS) to change the trigger point of the rising edge;
Frequency Hopping (Frequency Hopping, FH), keep the sweep bandwidth unchanged, change the start and cutoff frequencies.
When working in the same frequency band but with different modulation slopes, the transmitted signal overlaps with the echo signals of other radars, which will cause interference. This interference may bring an additional frequency component, or generate a larger amplitude, which will In the time domain, the noise floor is obviously raised.
Usually, such interference can be roughly divided into: the high frequency region of the head, the low frequency region of the middle and the high frequency region of the tail. Our anti-jamming strategy is divided into two steps. The first step is to locate the interference, which is judged by the absolute amplitude value of the signal and the amplitude difference between two adjacent points. The second step is to filter out the interference, using two strategies: 1. Direct filtering, 2. Use a pre-estimated amplitude to replace the amplitude of the interference.
In the above figure, the left side is the original state of the interference on the time-domain spectrum. It can be clearly observed that there are two interference sources, resulting in a significant increase in the noise floor; the middle is the effect of filtering out the interference by using the estimated amplitude; the right side is the direct filtering effect effect after interference. (Information source: Gartland Microelectronics)
In addition to cars, there are many things that can be done based on AiP millimeter-wave radar
In addition to the 360-degree full-scene application mentioned above, considering that millimeter-wave radar has a keen “insight” ability to some micro-movements of objects, the industry is taking this opportunity to apply millimeter-wave radar technology in the car cockpit In a large number of innovative application scenarios such as live detection, intelligent air conditioning, and indoor personnel tracking.
In the cockpit detection reference design mentioned by Wu Xiang, product manager of Galtland Microelectronics, the millimeter-wave radar can accurately detect the thoracic cavity caused by the human body’s breathing, heartbeat and other subtle vital signs at a long distance. , Abdominal cavity micro-motion, so it can detect and measure the presence of human vital signs in the car in a non-contact way, OEM or OEM only need to install AiP millimeter wave radar sensor in the rearview mirror or the position of the dome light in the car. And if the breathing and heartbeat detection technology is added to the air conditioner, the air conditioner can independently determine whether to enter the sleep mode through the speed of the person’s breathing.
In smart air conditioning and indoor personnel tracking solutions, millimeter-wave radar with multi-channel antenna technology can not only distinguish adults, children and pets, but also support the measurement of room area. For the detection of human fretting features such as breathing, it can track stationary and people who remain stationary for a long time, and at the same time automatically filter other object movements, such as fans, curtains, green plants, etc.
The addition of millimeter-wave radar to the video surveillance market is also becoming a new trend. According to Wu Xiang, the current surveillance cameras based on optical CMOS sensors, even if AI technology is introduced, will still greatly reduce the recognition degree and bring false alarms when the weather, ambient light is not good, or the distance is long. However, if combined with the small-volume AiP millimeter-wave radar sensor, the false alarm rate can be reduced with relatively low computing power and cost.
Dr. Zhang Yueping once said, “In the eyes of RF IC engineers, the antenna was just a piece of metal. Now they realize that without a good antenna solution, no matter how well designed RF IC is, it is a piece of quartz.” The world has expanded to many fields such as automobile, industry, packaging, materials and technology, microwave, radar and communication, and continued to provide global users with higher performance, easier to use and lower energy consumption millimeter wave radar technology, and to create a safer society for the society. , a smarter environment, this is not only Gatland’s mission, but also a responsibility shouldered by industry pioneers like Gatland.
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