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International Journal of Antennas and Propagation
Volume 2014, Article ID 947373, 20 pages
Research Article

Passive Switched Capacitor RF Front Ends for Spectrum Sensing in Cognitive Radios

1University of Minnesota, Minneapolis, MN 55455, USA
2IBM T. J. Watson Research Center, Yorktown Heights, NY 10598, USA
3Army Research Laboratory, Adelphi, MD 20783, USA

Received 16 November 2013; Accepted 22 March 2014; Published 1 June 2014

Academic Editor: Amor Nafkha

Copyright © 2014 Bodhisatwa Sadhu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This paper explores passive switched capacitor based RF receiver front ends for spectrum sensing. Wideband spectrum sensors remain the most challenging block in the software defined radio hardware design. The use of passive switched capacitors provides a very low power signal conditioning front end that enables parallel digitization and software control and cognitive capabilities in the digital domain. In this paper, existing architectures are reviewed followed by a discussion of high speed passive switched capacitor designs. A passive analog FFT front end design is presented as an example analog conditioning circuit. Design methodology, modeling, and optimization techniques are outlined. Measurements are presented demonstrating a 5 GHz broadband front end that consumes only 4 mW power.