Analysis and Suppression of Memory Effects in Envelope Elimination and Restoration (EER) Power Amplifiers

A frequency domain cancellation technique was used to examine nonlinearities and associated memory effects of the modulation characteristics of RF power amplifiers (PAs) used in envelope elimination and restoration (EER) systems. Using offset sinusoidal modulation on the drain of a GaAs power amplifier (PA), a measure of the distortion in the amplitude modulation (AM) characteristic, as well as the undesired phase modulation (PM) may be obtained by examining the harmonics of the modulation sidebands. While care was taken to avoid significant frequency response variations in the envelope amplifier and bias feeds, phase deviation of the sideband harmonics relative to the carrier was still observed. Furthermore, it was found that proper termination of the second harmonic of the RF carrier at the PA output reduced this phase deviation, hence allowing for simpler static compensation of the amplitude modulation characteristic.