The Design of a CM-Range Energy Efficient Dual-Mode Wireless Data Link

Sunday, April 05, 2009
7:00 PM
Free and open to the public

Continued scaling has been driving down the cost of consumer electronic devices for over forty years, bringing a steady increase in the number of electronic platforms and functions that an individual relies upon. The combination of the high density of terminals with the availability of cheap, high-performance computation is now pushing communication features to start rivaling computational ones as the main selling points for electronic systems. A steady reduction in the energy dissipation and system cost for wireless and mixed signal subsystems, typically not directly impacted by scaling, is required to continue this trend.

Techniques to bring such improvements are the topic of this talk. I will first show examples of my past work in the data acquisition and wake-up receiver spaces. Next, I will focus on a wireless link specifically designed to provide energy efficient peer-to-peer connectivity at 1 Mbps rate over a 5 cm distance. Such a link could be used as a low-energy ad-hoc networking/cooperation channel between handheld terminals, or as the main data link in a highly distributed computing or sensing and actuation system. The link is optimized to operate at a total energy cost below 60pJ/bit, while occupying a size lower than 1cm2 (including the antenna), and rely on no crystal reference or other precision off-chip component. Pulse based transmission is used to minimize the transmitter average power consumption without degrading efficiency or requiring high-Q impedance transformation elements. In order to achieve the high-level of miniaturization demanded, a methodology to co-design the circuits, the antenna and the propagation channel is developed and applied to determine the optimal carrier frequency for transmission.

The results show that the optimized 5 cm wireless channel has minimal multi-path, and can transfer sufficient power to turn on a diode connected directly to the antenna. The receiver utilizes therefore direct AM-detection, eliminating both the cost of LO generation and that of RF gain. To further minimize overhead, a modulation scheme is chosen that allows to merge data demodulation and synchronization in a single digital block. This demodulator also provides real-time BER estimation used to reconfigure the front-end to a linear synchronous downconverter and enhance interference immunity. The resulting communication scheme shows over 10dB of improvement in tolerable SIR for the case for single-pulse detection over a correlating receiver, corresponding to a 10x energy improvement for the same bit-error rate and throughput compared to DSSS interference mitigation technique. Finally, I will discuss some future directions regarding the application of short range wireless technology and other low-power techniques to increase integration and performance in bio/chemical sensor interfaces.

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Simone Gambini

Ph.D. candidate
University of California at Berkeley