Validation and Physical Interpretation of the Power-Amplifier Polar Volterra Model

Although the Cartesian signal decomposition has been the preferred representation in baseband polynomial power-amplifier (PA) behavioral models, this is not the only 2-D reference frame that could be considered for representing the input complex envelope signal. Indeed, in this paper, we demonstrate that, if the alternative polar representation is considered, the resulting Volterra series model is much more adequate to model the physical behavior of PA devices. This is the feature that supports the design of an innovative PA model, denominated the Polar Volterra model, which is more flexible and general than the traditional Volterra series commonly used in PA baseband modeling. The closeness of the new model formulation with the PA physical operation enabled, for the first time in PA low-pass equivalent behavioral modeling, the theoretical derivation of a Volterra series model directly from the PA circuit analysis. In fact, as the proposed model directly isolates such PA physical characteristics, a significant reduction of the number of model coefficients is achieved when compared with the traditional Cartesian Volterra model. Finally, validation results that highlight the advantages of the Polar Volterra model are presented. These were based on the laboratory measurements performed on two PAs with distinct architectures: a conventional class-AB amplifier and a polar transmitter.