Power amplifier behavioural model mismatch sensitivity and the impact on digital predistortion performance

This paper presents an investigation of power amplifier behavioural model performance sensitivity to in-band reflections. The measurement system and model extraction process is presented together with the results and an analysis of the effect of parameter variations in a digitally predistorted system. A load-pull system is used together with a digital baseband model extraction system to identify the impact on modelling performance. The results show that the model performance varies greatly with in-band reflection magnitude and phase on the amplifier output. It is also shown that a digital predistortion based on a model extracted at matched conditions, where it gives an excellent improvement of 20 dB in adjacent channel leakage ratio (ACLR), gives a poor improvement of 7 dB for miss-matched conditions with as low reflections as Γ = 0.2 (return loss 14 dB). This indicates that in-band reflections need to be considered and adaptive predistortion used also for low VSWR system like base-stations for telecommunication.