Modified output impedance matching solution for load modulation power amplifier performance enhancing

In this study, a modified load-modulated power amplifier (LMPA) structure is presented. Unlike the traditional LMPA (Doherty power amplifier) with quarter-wave line transformers, in this presented LMPA, the two-point matching network for the main amplifier and two-side matching network for the auxiliary amplifier are applied to achieve the back-off efficiency enhancing. The matching networks of the traditional DPAs are analysed and their limiting conditions to achieve optimal performance at back-off and peak power are deduced. A pre-matching is added to transform the load impedance (50 Ω) to complex impedance, then more freedom degrees are introduced to design the two point matching network, which results in the conditions for achieving optimal performance are more relaxed. In this way, the max output power at peak power and the optimal efficiency power at back-off can be achieved for the LMPA simultaneously. To verify the structure, an example LMPA base on GaN devices is designed. The measured max output power is about 43.8 dBm with drain efficiency (DE) of 64.9%. The measured 6 dB back-off DE is 54.9% and 4.5 dB back-off efficiency is 60.1%, which is about 15.2% higher than the class AB power amplifier.