A hybrid Cartesian loop and envelope modulated PA linear transmitter architecture

A high efficiency and linearity P A solution is presented based on hybrid linearisation schemes that employ complementary techniques to overcome the weakness (or constraints) of either method on its own. I n particular, the high linearity of Cartesian loop is combined with the high efficiency of Envelope Elimination and Restoration (EER). The results of a prototype hybrid linearised PA built using digital generation of the phase and amplitude signals for the EER amplifier, and utilizing a digital Cartesian feedback loop are presented. Limitations of the amplitude modulator on system performance are demonstrated using PWM and delta-modulated switching amplifiers. I. INTRODUCTION Linearisation of power amplifiers to meet spectral emission standards has been extensively researched and many techniques have been proposed e.g. predistortion, Cartesian loop, Envelope Elimination and Restoration @ER), polar loop, LMC, and CALLUM[l]. The techniques have allowed very high degrees of linearity, or traded wider bandwidth for moderate returns of linearity. The different techniques also have various efficiency trade-offs. In order to meet the linearity specification of current standards employing linear-modulation