By integrating a variety of RF, analog and digital components (including DSP and MCU) onto a single CMOS chip, Texas Instruments has staked a claim to all automotive radar applications, both outside and inside the vehicle.
Primary automotive radar applications can be broadly grouped into corner radars and front radars. Corner radars (rear and front) are typically short-range radar sensors that can be used for blind-spot detection (BSD), lane-change assist (LCA) and front/rear cross-traffic alert (F/RCTA), while front radars are typically mid- and long-range radars responsible for autonomous emergency braking (AEB) and adaptive cruise control (ACC).
TI’s AWR mmWave (77- to 81-GHz ) sensor portfolio for automotive scales from a long-range front radar, the AWR1243 transceiver (used in conjunction with the TDA3x processor), to the AWR 1642 single-chip radar for short range applications. There’s also the AWR1443 single-chip radar for diverse proximity-sensing applications such as door/trunk opener, ground clearance measurement and in-cabin applications such as occupancy sensing and gesture-based control.
TI’s announcement represents an accelerating shift in the industry toward the 77-GHz frequency band – from 24 GHz — due to emerging regulatory requirements, as well as the larger bandwidth availability, smaller sensor size and performance advantages. Compared to 24 GHz, the use of 76–81 GHz for these applications enables high-range resolution (up to 4 cm range resolution is possible) and higher-velocity resolution (which is important for parking-assist applications), and also results in a smaller form factor for the antennas, which is a significant advantage.
For sure, light detection and ranging (LiDAR) has been getting much attention for ADAS and autonomous vehicles, often with the assumption that it will replace radar in many instances because of its accuracy and falling cost. However, radar does have inherent advantages: It is unaffected by lighting conditions; it is relatively unaffected by fog, rain or snow; it’s RF so it can “see” through and around objects; and from an aesthetic point of view they can be hidden behind bumpers or doors, unlike LiDAR, or sonar (Figure 1).
While LiDAR technology has been advancing rapidly, so too has radar. Early in 2016, NXP made a splash at CES with the announcement of what was the smallest, single-chip 77-GHz radar transceiver. It measured 7.5 x 7.5 mm, was designed for short-range radar applications, and at the time of the announcement NXP claimed high resolution, but did not have figures on hand to support the claim. It is being field tested by Google engineers and in radar specialist Hella’s automotive CompactRadar solution.
Resolution claims for NXP’s product are still unavailable. Still, TI claims its sensor portfolio delivers “up to three times more accurate sensing than current mmWave solutions on the market.”
Regardless, the key point at that time was that the NXP device operated at 77 GHz, using RFCMOS. Traditionally, compound semiconductor material such as silicon germanium (SiGe) had been the go-to technology for adequate performance at millimeter wave bands (30 GHz to 300 GHz). However, CMOS is cheaper and also allows for potentially higher levels of integration and lower power consumption. Still, SiGe does have size and performance advantages at these higher frequencies, as well as high temperature tolerance, which has benefits as devices get closer to the engine block. These are just some of the reasons Infineon Technologies uses SiG for the front end of its own 76- to 77-GHz automotive radar solution for long-range applications like adaptive cruise control and collision warning, which recognize objects at a range of up to 250 meters.
TI’s radar ICs are designed around the use of linear frequency-modulation, continuous-wave (FMCW) radar, with multiple receive/transmit antennas for beamforming for more accurate range resolution. However, with FMCW, range resolution also depends upon the sweep bandwidth of the chirp: a sweep bandwidth of 300 MHz can resolve down to 0.5 meters; a 1-GHz sweep can resolve to 15 cm; and a 4-GHz sweep bandwidth can give a range resolution as low as 3.75 (Figure 3).
The resolution of a given solution of course depends upon other factors, including distance and relative speed, but according to TI, the sensor series can detect at ranges of up to 300 meters, resolve down to 50 µm, and work at velocities of up to 300 km/hr. They occupy a footprint of 10.4 mm2 and consume as little as 150 mW. Built-in, self-test (BIST) f allows the AWR1x series to meet ISO 26262, automotive safety integrity level (ASIL) B.
While TI has not released information on the cost of the ICs, it does have a $299 EVM specific to each version for the series to help designers get started.
With the AWR1x series, designers can cost-effectively, and with a single platform, design for applications all the way from 3D ranging and pedestrian detection at 300 meters, down to more localized, short-range detection applications, such as detecting when an opening door is about to hit another car or wall.
The applications are many, but the single, scalable platform, with low-cost, highly integrated solutions and software support, make them possible (Chart).