Analog/RF physical layer issues for UWB systems

Ultra-wideband communications systems offer unique challenges and opportunities for RF circuit design. Proper understanding of the trade-offs that system specifications impose upon the circuit designer is essential in optimizing a system for UWB. The defining attribute of UWB is the wide fractional bandwidth of the signal. This wide bandwidth can be achieved in several ways: with carrierless systems, with a wide-bandwidth single carrier spread-spectrum system, with a multi-carrier system such as OFDM, via frequency hopping, or via some combination of these methods. This paper provides detailed impact analysis of wide fractional bandwidth on RF frontend circuits and examines the various tradeoffs. In particular, wide-bandwidth channels limit the instantaneous Q allowable in the signal path. This requires modifications of the traditional narrowband design methods. Some of the issues discussed in this paper include: issues of broadbanding, power impact, fast hopping tradeoffs, power amplifier, and antenna issues.