Almudena Suárez received the degree in electronic physics and the Ph.D. degree from the University of Cantabria, Santander, Spain, in 1987 and 1992, respectively, and the Ph.D. degree in electronics from the University of Limoges, Limoges, France, in 1993. At present, she is a Full Professor at the University of Cantabria, and a member of its Communications Engineering Department. She has authored two books on the Analysis and design of microwave circuits, and has published about 50 papers in IEEE journals. She belongs to the technical committees of the IEEE International Microwave Symposium and European Microwave Conference. She was an IEEE Distinguished Microwave Lecturer for the period 2006-2008, has been the leading researcher in several Spanish R&D projects and has taken part in a number of Spanish and European projects in collaboration with industries. She is the coordinator of the research area “Electronic and Communications Technology” of the Spanish national evaluation agency ANEP.
Abstract
Microwave circuits are usually analyzed with harmonic balance, which only provides steady-state solutions, with no information on their stability properties. If the simulated solution is unstable, the solution measured for the same conditions will be qualitatively different from the simulated one. Instabilities are associated to undesired oscillations, frequency divisions or hysteresis. These phenomena often invalidate the circuit design, thus increasing the production cycles and the final cost.
The paper presents recent advances on stability-analysis methods, applied to power amplifiers, which often exhibit undesired behavior. Techniques will be provided to detect the most common types of bifurcations, or qualitative changes of the solution stability when a parameter is varied continuously. The bifurcation loci provide instability contours versus practical design parameters and can be used to evaluate the relevance of the instability on the overall amplifier performance and to stabilize the amplifier. Various examples of usual instability phenomena in power amplifiers will be presented. The bifurcation analysis techniques are combined with pole-zero identification in order to detect an undesired coexistence of stable solutions, that is, the coexistence of the stable amplifier solution with an undesired one, associated to a hysteresis phenomenon. This involves jumps between stable solutions which may be of the same or different type and affects the instability contours. The hysteresis phenomenon will be analyzed in depth and efficient techniques will be provided for its prediction and suppression.