24 GHz 'Radar on A Chip' designed at Caltech
March 2, 2004
Imagine the possibilities for 24 GHz transceiver, made completely out of silicon and smaller than a penny that included inputs for a phased array antenna. Those possibilities -- small low cost high speed data links, affordable anti-collision radar for automobiles, and sensors for robots (including robotic vacuum cleaners) to name a few -- could become reality now that the High Speed Integrated Circuits group at the California Institute of Technology has designed just such a device.
The Caltech press release, Caltech Engineers Design a Revolutionary Radar Chip focuses primarily on the applications of the device. Ali Hajimiri, associate professor of electrical engineering and leader of the group, explains, "The key is that we can integrate the whole system into one chip that can contain the entire high-frequency analog and high-speed signal processing at a low cost. It's less powerful than the conventional radar used for aviation, but, since we've put it on a single, inexpensive chip, we can have a large number of them, so they can be ubiquitous." RF Report readers may be more interested in the paper, A Fully Integrated 24-GHz 8-Path Phased-Array Receiver in Silicon by Hossein Hashemi (University of Southern California), Xiang Guan (Caltech) and Ali Hajimiri presented at the International Solid State Circuit Conference (ISSCC) in San Francisco in mid-February. The paper explains why 24-GHz is better for short range communications links than the 2.4 GHz or 5 GHz unlicensed bands in many applications - reduced antenna size, more isolation between floors in an office environment, and "less than proportionate increase of power consumption in a narrowband integrated radio implementation." The paper also explains the improvements possible with a phased array antenna. Diagrams and formulas explain how local oscillator phase shifting can be used to compensate for propagation delay and improve the signal-to-noise ratio. The paper includes detailed block diagrams and, in some cases, even circuits for components in the chip. Various directional patterns are plotted for the phased array in both 2-path and 4-path configurations. There are also microphotographs of the 3.5 mm by 3.3 mm die showing the layout of the system components on the chip. The Caltech press release describes one of the applications for the device as, "A chip the size of a thumbnail could be placed on the roof of your house, replacing the bulky satellite dish or the cable connections for your DSL. Your picture could be sharper, and your downloads lightning fast." After reading the paper, this doesn't seem likely, at least for satellite reception, as the antenna is not on the chip and the input noise figure for the device is only 5 dB. Details on a 24 GHz phased array antenna designed by the RF and Microwave Group at Caltech is described on their Phased Arrays for Networks page. The 8-path phased-array receiver chip appears to be a very powerful building block for a wide range of 24-GHz applications. It will be interesting to see how quickly the design becomes available in a commercial product!
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