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

This paper explores passive switched capacitorbased RF receiver front ends for spectrum sensing. Widebandspectrum sensors remain the most challenging block in the softwaredefined radio hardware design. The use of passive switchedcapacitors provides a very low power signal conditioning front endthat enables parallel digitization and software control andcognitive capabilities in the digital domain. In this paper, existingarchitectures are reviewed followed by a discussion of high speedpassive switched capacitor designs. A passive analog FFT front enddesign is presented as an example analog conditioning circuit. Design methodology, modeling, and optimization techniques areoutlined. Measurements are presented demonstrating a 5 GHzbroadband front end that consumes only 4 mW power.