77GHz radar signal processing flow chart and application solution

It is certain that the automotive millimeter wave market will usher in a wave of rapid growth! The reason is simple: automotive millimeter wave radar can effectively improve the active safety performance of the car and is an essential tool for achieving the ultimate goal of ADAS and unmanned driving.

The vehicle-mounted millimeter-wave radar transmits modulated millimeter waves through the array antenna, and then extracts the intermediate frequency signal by mixing the received echo signal with the local oscillation. The rear MCU unit runs 2-D Fourier transform and other processing to extract the relative speed, relative distance, relative angle, and relative movement direction of the vehicle and the target. The vehicle central processing unit 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.

Automotive safety regulations and ratings around the world will accelerate the rapid development of ADAS, thereby driving strong demand for automotive millimeter-wave radar.

Figure 1: Development of ADAS safety regulations in various countries (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 distance, and launching commercially available solutions. Among them, the 77GHz radar-related products developed by NXP have formed a large and thriving family. (Figure 2)

Figure 2: NXP 77GHz millimeter wave radar solution related product family

Today, we will introduce you to a classic 77GHz radar solution based on NXP products (see Figure 4 for the solution block diagram). This solution uses the "S32R274 (processor) + TEF810 (RF transceiver)" dual-chip architecture, which allows the vehicle to detect the surrounding environment and perceive potential collision risks, thereby improving vehicle safety performance. Currently, the solution has an evaluation kit available for customer evaluation, which includes complete hardware circuits such as microwave array antennas, as well as complete evaluation software based on S32R274 including beamforming, CFAR, etc., 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 solution can be summarized into the following four points:

1

RF transceiver chip

In NXP's entire 77GHz millimeter-wave radar solution, the automotive radar transceiver uses the TEF810 single-chip solution, which supports FMCW modulation and can be used for short-range, medium-range, and long-range automotive radar applications, covering the entire automotive radar frequency band from 76GHz to 81GHz.

TEF810 has a high degree of integration and achieves a very high cost-effectiveness. It integrates all the functional modules necessary for FMCW modulation, including an FMCW waveform generator flexibly controlled by a chirp signal, 3-way transmission links including binary key phase and output power stabilization circuit, and 4-way high-linearity and low-noise receiving links including ADC. In high-angle resolution applications, one chip can realize up to 12 virtual receiving links and achieve an angular resolution of 12 degrees.

Each receiving link includes a high-pass filter and a low-pass filter. The high-pass filter is used to filter out relatively strong low-frequency interference, and the low-pass filter can be used as an ADC anti-aliasing filter. Each receiving channel contains a 40MS/s 12-bit SAR ADC, followed by a digital decimation filter with decimation coefficients of 1, 2, 4.8 and 16. The quantized sampled signal can be transmitted to the S32R274 via LVDS, CSI2-DPHY, CIF and other interfaces for further processing.

TEF810 uses a standard SPI communication interface to transmit control and data alarm information. SPI supports a maximum transmission rate of 40Mbps. The chip contains a functional safety monitoring circuit that can track and monitor the operating status of key parameters such as chip temperature, RF link status, and phase-locked loop lock status. The internal circuit block diagram of TEF810 is shown in Figure 4.

Figure 4, TEF810 RF transceiver chip circuit block diagram

The transmit and receive antennas on the evaluation board use a 10-unit serially fed linear patch array. The array units conform to the Chebyshev optimal distribution. The 4 receiving antennas are spaced 0.5 wavelengths apart, and the 3 transmitting antennas are spaced 2 wavelengths apart. This can achieve a 3-transmit 4-receive MIMO configuration, which is equivalent to 12 virtual linear receiving arrays spaced 0.5 wavelengths apart. The central resonant frequency of the serially fed linear array is 79GHz, the gain at the center frequency is 12.9dBi, and the half-power bandwidth can achieve a vertical angle of 12 degrees and a horizontal angle of 80 degrees. The actual evaluation board is shown in Figure 5.

Figure 5: Antenna evaluation board

2

Radar Signal Processor

S32R274 is an automotive-grade, PowerPC-based 32-bit multi-core processor. As the data analysis and decision-making core in the 77GHz automotive radar solution, in addition to general software processing capabilities and rich automotive bus interfaces, S32R274 also has powerful radar signal processing capabilities to meet the computing power requirements of modern beamforming and fast chirp modulation. Its internally integrated unique signal processing acceleration unit can realize fast Fourier transform, window function processing, FIR filtering, peak retrieval, vector calculation and histogram analysis.

The S32R274 supports ASIL automotive safety applications and adds some anti-tamper features that meet SHE requirements. The S32R274 highly integrated processor can help customers achieve compact, safe, reliable, low-cost and high-performance radar solutions. The schematic diagram of the S32R274 evaluation board is shown in Figure 5.

Figure 6, S32R274 processor evaluation board

3

Software Development Tools

The software development tool RadarSDK provided with the above hardware solution is very convenient for customers to implement software development. It provides software labels for RF and SPT abstraction layers, which is convenient for customers to develop higher-level algorithms based on RadarSDK. The software includes basic 2D-FFT changes, two-dimensional peak search + constant false alarm rate detection, digital beamforming, and wave direction angle estimation. The signal processing flow chart is shown in Figure 7.

Figure 7, 77GHz radar signal processing flow chart

4

Comprehensive technical support

Finally, if you encounter any problems during development, don’t forget that Avnet is the agent distributor of NXP radar solutions and can provide you with comprehensive technical support including hardware and software! For more detailed information about the solution, please contact your Avnet sales representative immediately! Then you are ready to go to the NXP 77GHz millimeter wave radar market for gold!