Extension of Quasi-Load Insensitive Class-E Doherty Operation with Complex Load Trajectories

This paper extends the quasi-load insensitive (QLI) Class-E Doherty power amplifier (PA) design methodology to address Doherty PA combiners with complex load impedance trajectories. The analysis of the Class-E PA power and efficiency load-pull contours shows that changing the class-E network resonance factor allows rotating the loadpull contours to achieve QLI operation with various Doherty combiners. Moreover, an alternative approach using a modified class-E network is proposed to overcome the frequency limitation that might be caused by the class-E network resonance factor choice. To validate the proposed methodology, a 40 W Doherty PA is designed and simulated using commercial GaN HEMT transistors achieving more than 70% Efficiency over 6-dB output power back-off at 3.8 GHz.