Temperature dependent memory effects on a drain modulated GaN HEMT power amplifier

In this paper, the impact of self heating on the linearity of a drain modulated GaN HEMT power amplifier (PA) is studied. After characterizing the frequency response of junction temperature rise to power dissipation, as well as the effect of this variable on the PA modulation profiles, the dynamic envelope trajectory, under a two-tone test signal, appears to be slightly dependent on frequency spacing. Self heating related effects are shown to be negligible in presence of other nonidealities, as the case of feedthrough. In this way, punching a vector hole in the two-tone I/Q diagram and applying memoryless digital predistortion (DPD), will allow identifying the influence of self heating effects, over adjacent channel distortion. Finally, this long-term memory effect is proved to be responsible for only a minor residual distortion in a linearized EDGE polar transmitter.