Measurement & Extraction of the Low-Frequency Dynamics of an Envelope Tracking Amplifier Using Multisine Excitations
Both efficiency and linearity of an Envelope Tracking Power Amplifier depend on the tight synchronization between a Low- and High-Frequency path. The presence of reactive elements in this Low-Frequency path, as well as an inevitable delay difference between both paths, results in a dynamic mismatch that can seriously degrade the overall performance of the device. This work introduces a method that is able to extract these Low-Frequency dynamics without requiring access to any internal nodes of the device. The proposed extraction procedure makes use of the combination of a linear parameter-varying framework and a specific signal excitation strategy which uses a multisine excitation to mimic the operational conditions of the amplifier. A trustworthy model for the Low-Frequency dynamics is an important component necessary for building an adequate pre-distortion tool that is able to eliminate a bad dynamic match.