Wideband PA Design: The “Continuous” Mode of Operation Paul. J Tasker, Vince Carrubba, Peter Wright, Jonny Lees, Johannes Benedikt and Steve Cripps Centre for High Frequency Engineering, School of Engineering, Cardiff University, CF24 3AA, Cardiff, Wales, UK tasker@cf.ac.uk Abstract — The introduction and formulation of the “Continuous” modes of transistor operation has provided an alternative design route for the realization of high efficiency power amplifiers (PA’s) over a wide bandwidth (approaching an octave). The formulation of the “Continuous” modes provides a mathematical framework for extending the fundamental/harmonic impedance space over which the power and efficiency performance of the traditional PA modes, i.e. Class, B, Class F, etc, can be maintained. This mathematical framework has been experimentally validated using RF I-V waveform engineering measurements systems and the realization of demonstrator PA prototypes. Index Terms — Microwave measurements, microwave theory and techniques, power amplifiers, power transistors, wideband. I. INTRODUCTION The overall efficiency of wireless communication networks is predominantly determined by the Power amplifier (PA) stage. Low efficiency generally translates into increased running costs for base stations and reduced battery life for mobile handsets. In narrow band systems it has been possible to utilize “traditional” modes of operation, Class B, Class F, etc, to realize high efficiency PA’s. However, these modes require the output matching circuit to present short or open terminations to the relevant harmonics. This termination requirement presents a major circuit design challenge if the application requires wideband power amplifiers. The development of emerging 4G (Fourth Generation) multi-purpose wireless communication networks, such as LTE (Long Term Evolution) that provide higher data-rates (downlink peak rates of at least 100Mbit/s and uplink of at least 50Mbit/s) motivates the microwave community to improve PA performance also in terms of bandwidth. Hence, these new communication systems where increasing bandwidth is very important necessitate a new approach to design high efficiency power amplifiers going beyond the “traditional” modes of operation. In the “traditional” modes of operation, described in the Snider’s paper [1], utilized basic waveform building blocks. By avoiding the simultaneous presence of harmonic voltage and current components in their selection high efficiency results. Since, the resulting voltage and current components are harmonically rich, this necessitates the need for harmonic short or open circuit terminations in their practical realization. On going research activity [2-6] both theoretically and experimentally has indicated that there are alternative modes of operation that can also provide for high efficiency that do allow for the simultaneous, same frequency, presence of harmonic voltage and current components, i.e. Class E [5,6], Class J [3]. The formulation of the “Continuous” modes provides a mathematical framework to describe sets of fundamental/harmonic impedance reactive loci that support specific examples of this mixed mode of operation; delivering the same power and efficiency as the traditional modes on which they are based. II. THEORETICAL ANALYSIS The power and efficiency performance of Power Amplifiers is mathematically determined by analyzing the dynamic, time varying, voltage V(t) and current I(t) waveforms that are present on the Power Amplifiers Transistor Terminals. Vt () = ft () and It () = gt () (1) Class A, the reference mode of operation, with a theoretical maximum efficiency of 50%, is defined as both the voltage and current waveforms being sinusoidal. Vt () = ft () = V DC 1 - sin ωt ( ) ( ) It () = gt () = I max 2 1 + sin ωt ( ) ( ) (2) In this case the waveforms contain no harmonic components. Efficiency performance can be improved via the introduction of harmonic components to modify the shape of the current and/or voltage waveforms. In the work of Snider [1] the current waveform is modified to a half rectified sinusoidal waveform; 978-1-4673-0929-5/12/$31.00 ©2012 IEEE