Digital Linearization of RF Power Amplifiers

The effect of power amplifier (PA) nonlinearities on the output spectrum and methods for measuring the nonlinearities are reviewed. An adaptive approach for modeling the intermodulation distortion (IMD) at the output of a digital transmitter, due to the interaction of a modulated signal with a nonlinear PA, is presented. It is shown that digital predistortion (DPD) can be used to compensate for the IMDs otherwise generated. DPD coefficient estimator structures are described as part of adaptive methods used to minimize IMD power measured at the transmitter output. Three types of estimator structures are compared.