Outphasing Class-E Power Amplifiers: From Theory to Back-Off Efficiency Improvement

Abstract

Abstract-This paper presents an analysis of outphasing class-E Power Amplifiers (OEPAs), using load-pull analyses of single class-E PAs. This analysis is subsequently used to rotate and shift power contours and rotate the efficiency contours to improve the efficiency of OEPAs at deep power back-off, to improve the Output Power Dynamic Range (OPDR) and to reduce switch voltage stress. To validate the theory a 65nm CMOS prototype, using a pcb transmission-line based power combiner was implemented. The OEPA provides +20.1dBm output power from VDD=1.25V at 1.8GHz with more than 65% Drain Efficiency (DE) and 60% Power Added Efficiency (PAE). The presented technique enables more than 49dB OPDR and 37% DE and 22% PAE at 12dB back-off with reduced switch voltage stress.

A +20 dBm Highly Efficient Linear Outphasing Class-E PA Without AM/AM and AM/PM Characterization Requirements

“…For high efficiency at back-off as well as at maximum output power, non-isolating power combiners are required. Non-isolating combiners ensure high efficiency (ideally 100%) by providing optimum impedances both at maximum output power power as well as at a specific power back-off level [3], [4]. Employing non-isolating power combiners, however, results in loadpulling between the two branch PAs that cause input-output phase difference to deviate from ∆θ in = ∆θ out yielding nonlinearity (distortion).…”

“…In [4] the authors showed that, depending on the class-E PA parameters and on the OEPA branch amplifiers' load trajectories, identical voltage source modeling of switch mode class-E PAs is valid only under specific conditions. Moreover, in this current work, we show that the output impedance of a class-E PA is load-dependent which then necessitates a new theoretical model to describe the linearity performance of outphasing transmitters employing class-E PAs as branch amplifiers.…”

“…In [4], we presented a general theory of the OEPAs based on the (time domain) load-pull analyses of the branch class-E PAs. The work in [4] addressed the output power, efficiency, output power dynamic range (OPDR) and reliability related maximum switch voltage while the linearity was not the prime focus of that paper.…”

“…In [4], we presented a general theory of the OEPAs based on the (time domain) load-pull analyses of the branch class-E PAs. The work in [4] addressed the output power, efficiency, output power dynamic range (OPDR) and reliability related maximum switch voltage while the linearity was not the prime focus of that paper. In this work the linearity of OEPAs is studied theoretically and validated by measurement results of an OEPA employing two class-E branch PAs implemented in a standard 65nm CMOS technology and using an off-chip transmission-line based power combiner at 1.8GHz (similar to our work in [4]).…”

“…To find |V out | as a function of |V in | (and therefore to characterize AM/AM distortion), similar to our work in [4], the load-pull analyses of single branch PAs were leveraged. For this, consider the load-pulling of the top branch class-E PA by changing Z 1 .…”