Minimum distortion power polynomial model (MDP-PM) of nonlinear power amplifiers and its application on analog predistorters

With the increasing demands of power efficiency and linearity on power amplifiers (PAs), there are more and more demands for some new and easy modeling methods of PA nonlinearities. One direction of these trends is to get better polynomial models which are extensively used in the design of analog predistorters (PDs) to combat nonlinearity and in the estimation of the intermodulation products for PAs. Because of the difficulty in modeling a PA and for ease of comparison, most of the polynomial models reported in the literature are based on a simple TWTA model (Saleh´s (1981) model) instead on actual PA devices. In this paper, we propose a method for obtaining a general order polynomial model from an existing model such as Saleh´s model, or from the input-output statistical characteristics of a PA device. We also obtain the analytical representation of its coefficients. The method is based on minimizing the power of the distortion between the output of a PA and the output of the model based on it. Thus the model is named the minimum distortion power polynomial model (MDP-PM). We have obtained the coefficients of the proposed MDP-PMs up to order 7 based on Saleh´s model to illustrate our results. Then, we show the application of this model in analog PD designs, whereas the resulted PD devices outperform those given in the literature by 0.8 dB for order 3 and by 0.2 dB for order 5