Effects of different VDD-drives in ET & EER transmitters

Envelope tracking (ET) technique transmitter employing a linear 0.5 W 1 GHz LDMOS PA (power amplifier) is studied. Four different methods for supply voltage modulation are discussed and measured results are given. Results show improvement both in efficiency and linearity when predistortion of the supply voltage is added. The same linear amplifier was used also in an envelope elimination and restoration (EER) system, and measurements show significant improvement in the linearity compared to the envelope tracking system, with no notable loss in the efficiency. Also the effect of feedthrough to the linearity was much lower than with a Class E PA in the same transmitter configuration.