Broadband front-ends for software-defined radios

A new approach to multiband radios was introduced at UCLA which covers the whole frequency band in use today from 800 MHz up to 6 GHz. This approach enables a practical Software-Defined Radio (SDR) which can tune to any band and demodulate any signal in this frequency range or maybe beyond that in near future. This dissertation starts by presenting an overview of the current approach of the industry to multiband receivers as well as previous attempts at designing SDR circuits. It also explains the evolution of the UCLA SDR architecture and discusses the design specifications for the front-end. While this part of the dissertation provides the necessary background, its main focus is on the design and analysis of the SDR broadband front-end circuits: the broadband low-noise amplifier (LNA) and the downconversion mixer.;A broadband noise-cancelling LNA was designed in CMOS technology which has large gain (19--17 dB), good input impedance matching and low noise-figure (3--4 dB) across the entire spectrum in use today. The concept of noise-cancellation is explained and the design trade-offs and implementation challenges are presented based on fabricated prototypes in two CMOS technologies: TSMC 0.18-mum and STMicroelectronics 90-nm. Measured results are also presented.;Based on the fundamental understanding of the noise and nonlinearity processes in passive mixers, a very low flicker noise mixer was designed. Detailed analysis of the noise and nonlinearity mechanisms of this mixer are explained which are backed up by simulations and real life measurements of the UCLA SDR. The mixer was fabricated in STMicroelectronics 90-nm CMOS technology as part of the SDR front-end.