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This paper considers the compensation of linear and nonlinear distortions which are present in RF part of envelope tracking (ET) amplifier. In particular, we consider the compensation of magnitude and phase responses of analog filters, amplifier nonlinearity, and possible time misalignment between signals in RF and envelope branches. We propose a new adaptive predistorter architecture for ET amplifiers. Our analytical results indicate that the proposed architecture is a more general than the state-of-the-art architecture and is guaranteed to work with any ET amplifier. Furthermore, our simulations show that in order to keep adjacent channel power ratio below -60 dB, at least 9th order polynomial predistorter is needed. A comparable performance is obtained with look-up-table based predistorter having only 16 entries.