An impedance-based model for the evaluation of IM3 in commercial amplifiers with memory

A simple model that captures nonlinear memory effects in wideband amplifiers is presented in this work. The model is formulated in the frequency domain and defines an equivalent hypothetical load impedance that explains asymmetries, in magnitude and phase, in two-tone IMD products. To test the model, a commercial amplifier has been widely characterized using an inexpensive measurement setup for the acquisition of magnitude and phase of IMD components in a two-tone test. Model parameters have been fitted to measurements by using a least-squares optimization procedure. The extracted impedance has been approximated by a simple passive network, obtaining a good correspondence with IM3 measurements. The modeled hypothetical impedance allows a better understanding of the generation of IMD dependent on modulation bandwidth