ABSTRACT
Power amplifiers (PAs) are some of the important and costly devices in communication systems and they are nonlinear in a certain operating region. The 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). There 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% of the direct current (DC) power is lost and turns into heat. By increasing the number of the base stations and then the number of power amplifiers improves the efficiency of the power amplifier and reduces the cost of the system. Moreover, transmission formats (e.g., code division multiple access [CDMA] and orthogonal frequency division multiplexing [OFDM]) suffer from high peak-to-average power ratios (PAPRs) or the crest factor (CF), that is, large fluctuations of signal envelopes. To improve the power amplifier efficiency without compromising its linearity, power amplifier linearization is essential.
