It is certain that the automotive millimeter wave market will usher in a wave of rapid growth! The reason is simple: vehicle -mounted millimeter-wave radar can effectively improve the active safety performance of automobiles, and is an essential artifact to achieve the ultimate goal of ADAS and unmanned driving.
The vehicle-mounted millimeter-wave radar transmits the modulated millimeter-wave through the array antenna, and then mixes the received echo signal with the local oscillator to extract the intermediate frequency signal, and then runs the 2-D Fourier transform in the rear MCU unit to extract the difference between the vehicle circumference and the target. Information such as relative speed, relative distance, relative angle, and relative movement direction. The central processing unit of the car will perform intelligent processing based on the extracted information, and give the driver warning information, or take active intervention measures in time to ensure active safety performance and reduce the probability of accidents.
The automotive safety regulations and ratings in countries around the world will accelerate the rapid development of ADAS, thereby driving the strong demand for automotive millimeter-wave radar.
Figure 1. The development process of ADAS security regulations in various countries (Image source: China Investment Securities)
In response to this market trend, various technology manufacturers are actively investing in the research and development of 77GHz millimeter-wave radars with higher resolution and longer sensing distances, and have launched commercial solutions. Among them , the products related to the 77GHz radar developed by NXP have formed a large family of "people prosperous". (figure 2)
Figure 2, NXP 77GHz millimeter wave radar solution related product family
Today, we will "Amway" a classic 77GHz radar scheme based on NXP products (see Figure 4 for the scheme block diagram). The solution adopts the "S32R274 (processor) + TEF810 (radio frequency transceiver)" dual-chip architecture, which allows the vehicle to detect the surrounding environment and perceive potential collision risks, thereby improving vehicle safety performance. At present, an evaluation kit is available for customers to evaluate the solution. The kit includes complete hardware circuits such as microwave array antennas, as well as complete evaluation software including beamforming and CFAR based on S32R274, allowing customers to quickly start their own radar design.
Figure 3, NXP 77GHz millimeter wave radar solution system block diagram
The reasons for recommending this scheme can be summed up in the following four points:
1
RF transceiver chip
在NXP整个77GHz毫米波雷达方案中，汽车雷达收发器采用的是TEF810单芯片方案，它支持FMCW调制方式，可用于短距、中距、长距车载雷达应用，能够覆盖76GHz到81GHz的全汽车雷达频段。
TEF810具有高集成度并且实现了极高的性价比，内部集成了所有FMCW调制方式所必须的功能模块，包括用啁啾信号灵活控制的FMCW波形生成器、3路发射链路包含二元键相以及输出功率稳定电路、4路包含ADC的高线性和低噪声的接收链路，在高角度分辨率应用中，可以用一颗芯片实现最高12路虚拟接收链路，实现12度的角度分辨率。
每个接收链路包括高通滤波器和低通滤波器，高通滤波器用于滤除比较强的低频干扰，低通滤波器可以由于ADC抗混叠滤波器，每个接收通道包含有40MS/s的12-bit SAR ADC, ADC后跟有抽取系数为1、2、4.8和16的数字抽取滤波器。量化后的采样信号可以经由LVDS，CSI2-DPHY，CIF等接口传到S32R274做进一步的处理。
TEF810采用标准SPI通信接口用于传输控制和数据告警信息，SPI最高支持40Mbps传输速率。芯片内部含有功能安全监控电路，可追踪监控关键参数的运行状况比如芯片温度，射频链接状况以及锁相环的锁定状态等。TEF810内部电路框图如图4所示。
图4，TEF810射频收发芯片电路框图
评估板上的收发天线采用10单元串联馈电的直线贴片阵列，阵列单元符合契比雪夫最优分布，4路接收天线间隔0.5个波长，3个发天线间隔为2个波长，这样可以实现3发4收的MIMO配置，等效于12个间隔为0.5波长虚拟线性接收阵列。串联馈电直线阵列中心谐振频率为79GHz，中心频率处的增益为12.9dBi，半功率带宽可以实现垂直角12度，水平角80度。评估板实物如图5所示。
图5，天线评估板实物图
2
雷达信号处理器
S32R274是一款汽车级的、基于PowerPC架构的32-bit多核处理器，作为77GHz车载雷达方案中数据分析决策核心，除了具有通用软件处理能力和丰富的汽车总线接口，S32R274更具有强大的雷达信号处理能力，满足现代波束赋形和快啁啾调制对计算能力的要求，其内部集成的独特的信号处理加速单元可实现快速傅里叶变换、窗函数处理、FIR滤波、峰值检索、矢量计算以及柱状图分析等。
S32R274支持ASIL汽车安全应用以及增加了一些符合SHE要求的防篡改特征。S32R274高集成度处理器可以帮助客户实现紧凑，安全可靠，低成本高性能的雷达解决方案。S32R274评估板示意图如图5。
图6，S32R274处理器评估板
3
软件开发工具
和上述硬件方案配套提供的软件开发工具RadarSDK非常便于客户实现软件开发，它提供了RF和SPT抽象层的软件标示，便于客户基于RadarSDK开发更高级别算法，软件包含基本的2D-FFT变化、二维峰值搜索+恒虚警率检测、数字波束赋形。波达方向角估计。信号处理流程框图如图7。
图7，77GHz雷达信号处理流程框图
4
全方位技术支持
最后，如果你在开发中如果遇到任何问题，别忘了安富利（Avnet）是NXP雷达解决方案的代理分销商，能够为你提供包括硬件和软件全方位的技术支持！想要获取方案的更多细节信息，请马上联系你身边的安富利销售代表吧！然后你就准备着到NXP 77GHz毫米波雷达市场中淘金吧！