Towards Generalized Doherty Power Amplifier Design for Broadband and Multiband Operation

Conventional Doherty power amplifier (CDPA) theory is limited to single carrier operation, leading to non-generic structure. This paper presents a new analysis that generalizes and improves CDPA theory. We show that by introducing a theoretical parameter "a" at the output combiner we can redefine the relationships among the output combiner elements for more design flexibility than in the CDPA. Furthermore we show how the approach links several design approaches published previously. The approach allows us to increase bandwidth permitting broadband operation up to 25% fractional bandwidth with dual band operation yielding even higher percentage bandwidth. A specific design, called the Broadband General Doherty power amplifier (BB GDPA), is given to illustrate the approach and is shown to improve the performance of a previously published 2.14/2.655 GHz parallel Doherty power amplifier (PDPA). Simulations show a drain efficiency (DE) increase of up to 8.5% at peak power (PP) level and 13.4% at back-off power (BOP) level. Using GaN HEMTs a maximum DE of 85% and 63% at an average of 43-dBm peak power and BOP levels respectively were measured.