chapter  6
Power Amplifier Linearization
Pages 42

Power amplifiers (PAs) are necessary components in communication systems and they are nonlinear in a certain operating region. Power amplifier nonlinearity results in spectral broadening, which leads to adjacent channel interference (ACI) and superfluous radiation. One way to avoid these impacts is to back off the power amplifier from its saturation point or from the nonlinear region, but this causes degradation in power amplifier efficiency that is not desired (typically less than 10%) (Wright, 2002). More than 90% of the direct current (DC) power is lost and turns into heat, hence other methods need to be investigated in which the spectrum broadening can be suppressed while the power efficiency is maintained. In the new broadband communication technologies, the power amplifier exhibits more severe nonlinearity. The transmission formats, such as wideband code division multiple access (WCDMA) and orthogonal frequency division multiplexing (OFDM), have high peak-to-average power ratios (PAPRs), which means large fluctuations in their signal envelopes. By increasing the number of base stations and then the number of power amplifiers, an improvement in efficiency of the power amplifier reduces the cost of the system. To enhance the power amplifier efficiency and maintain linearity of the power amplifier, a linearization technique is pivotal to combat nonlinearity.