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3
poWEr aMplifiErs in
WirElEss coMMunications
3.1 Introduction
Power amplifiers (PAs) are some of the important and costly devices
in communication systems and they are nonlinear in a certain operat-
ing region. e nonlinearity of the PA has several undesired impacts,
such as spectral broadening that causes adjacent channel interference
(ACI) and in-band distortion that causes phase distortion, which is
measured by error vector magnitude (EVM). ere are several ways to
tackle the nonlinearity problem of PAs. One simple solution is to back
off the PA from its saturation point to force it to operate within its
linear region. But in this way a significant loss in power efficiency will
occur, typically less than 10% (Wright, 2002), and more than 90