Radar targets cars, conscious buildings

CMOS radar chips have been one recent area of focus for imec, the nanoelectronics research organization located in Leuven, Belgium. In collaboration with Vrije Universiteit Brussel, imec presented a radar transmitter implemented in plain 28-nm digital CMOS at the International Solid-State Circuits Conference 2014. With a supply voltage of 0.9 V and an output power above 10 dBm, the continuous-wave radar transmitter operates in the 79-GHz band.

Vito Giannini, Ph.D., principal scientist for imec’s green radio program and a coauthor of the ISSCC paper, was on hand at the recent International Microwave Symposium in Tampa to elaborate on the current status of the project. imec, he said, has been working with millimeter-wave technology for some time, particularly in the 60-GHz band for gigabit-per-second wireless HD streaming as well as heterogeneous radio-access networks, allowing small cells to connect to each other without requiring fiber optics.

But currently a particular focus, he said, is on radar applications in the 79-GHz band. Building on the transmitter presented at ISSCC, the organization now has developed a receiver fully integrated with the transmitter chip. The next steps will be to integrate data converters and potentially processors. (Giannini and his colleagues presented a paper titled “How extreme ADCs enable the future of nanoscale RF” at IMS.) “The result,” he said, “would be a single fully integrated platform with everything you need to do sensing—position, speed, and direction of a potential target.”

That target, Giannini said, could be a car, or it could be a person. “We are actually focusing mainly on person-detection because it has broader applications—not just in the automotive market, but in other scenarios such as conscious homes, where you detect how people move in a house, for instance, and adapt some functionality accordingly,” he said. “Falling detection is one possible application, but we’re also thinking of adaptive lighting in a room based on how people are moving and what they are doing.”

If you are reading, for example, a radar-based directed-lighting system could point light at your book, where it’s needed, and avoid the need for potentially privacy-compromising cameras in every room to accomplish the same task. Giannini noted that infrared also is a technology that could serve such applications, but it has the disadvantage of short range and might require multiple sensors. In contrast, a phased-array radar chip mounted in a centrally located light bulb could survey an entire room.

In addition to automotive and conscious-building applications, Giannini sees potential applications for phased-array CMOS radar in robotics. “If we want robots to be autonomous,” he said, “they will need sensors that allow them to move in any kind of conditions and situations.” Such robots, he said, will benefit from the very small form factor that imec currently is targeting—a phased-array system one square centimeter in size including antennas, all within a fully integrated CMOS flip-chip package mounted on a PCB.

Giannini cited key radar performance specifications: “One key number is the depth resolution, in the radial direction. That depends on the bandwidth of your system.” The imec system’s 4-GHz bandwidth offers a record-setting 7-cm depth resolution, which is up to a factor of four better than other state-of-the-art systems that rely on different modulation schemes. Current automatic cruise-control systems already on the market, he said, achieve depth resolution as good as 50 cm, which is adequate for that application. But for pedestrian detection, he said, “It is very critical to have depth resolution of better than 10 cm.”

Another key spec, he said, is angular resolution, which depends on how big you make your array of antennas. “Currently,” he said, “we target a system that has 5-degree angular resolution with a very wide field of view of 120 degrees.” He added that image sensors, which imec also researches, bring unique benefits to such applications, and he said, “People are thinking of actually combining the two technologies in a kind of sensor fusion.”

Speaking of yet another sensor technology—the lidar used in Google’s autonomous vehicles—Giannini said that lidar is a very good and accurate technology, although at this time costs are still on the high side.

But the main disadvantage of the technology, he said, is that it is less reliable when you need it the most—in bad weather, with rain and fog. That, he said, is where radar stands out, having proven its usefulness in demanding aerospace and military applications. “If we can manage to reduce the cost and size of such systems,” he said, “we can try to employ them in daily applications that can benefit normal people.” That’s the key idea behind imec’s CMOS radar initiative.