A highly efficient Doherty power amplifier employing optimized carrier cell

We have proposed a novel design of the Doherty power amplifier (PA) to improve the efficiency at a back-off output power level. It is shown that the carrier PA having 100 Omega load impedance is not an optimum for maximizing the efficiency at the back-off level due to the knee voltage effect. Thus, we introduce a Doherty PA having a load impedance larger than 100 Omega when the peaking PA is turned off. For experimental demonstration, we have implemented and tested the Doherty PA using Cree GaN HEMT CGH40045 devices at 2.655 GHz. The measured results clearly show that the proposed Doherty PA delivers better efficiency at the back-off output power level than the conventional PA due to the better load condition for improving efficiency.