An analysis of performance degradation of a memoryless DPD due to frequency response of an envelope amplifier in an EER Power Amplifier

Dynamic supply voltage techniques, such as an EER (Envelope Elimination and Restoration) PA (Power Amplifier), have attracted significant attention recently due to their high power efficiency under back-off operation. EER PAs generally possess strong nonlinearity compared to a conventional PAs, memoryless DPD (Digital Predistortor) is therefore indispensable for maintain signal quality. However, the level of residual distortion compensation with a memoryless DPD of a two tone test is dependent on the tone spacing. In this paper, we identify that the frequency response of an envelope amplifier causes a significant degradation to the performance of a combined memoryless DPD and EER PA. A simple and useful model is proposed for the analysis of this degradation. Furthermore, we demonstrate that IMD3 (third-order intermodulation distortion) for a two tone test separation between 100 kHz and 4 MHz is improvement by up to 25dB by the memoryless DPD with a frequency response compensation envelope amplifier.