An Outphasing Power Amplifier for a Software-Defined Radio Transmitter

Abstract

A software-defined radio (SDR) transmitter needs a universal modulator and power amplifier to support any modulation in any band. There is a simple solution, namely, a Cartesian I-Q upconverter followed by a linear power amplifier, but for complex modulations its power conversion efficiency is often under 10%. Therefore, the search continues for a more efficient solution. One possibility is to harness the high efficiency of a saturated power amplifier but somehow make it deliver amplitude-modulated waveforms. Polar modulation has found use in enabling EDGE on GSM handsets, but we believe outphasing, or linear amplification using nonlinear components (LINC), offers a more enduring solution for a broader class of modulations.