A compact fully differential Doherty power amplifier

In this paper, a compact triple-transistor fully differential Doherty power amplifier (DPA) is investigated. Three active devices are combined in a very judicious way to amplify the differential signal in a way like what a typical Doherty amplifier does. Particularly, two out-of-phase carrier PAs are applied to operate in the low-power region for high efficiency. On the other hand, only one peaking PA is used in the high-power region, which shares its output evenly with the two carriers. The reduction of transistor number from four for a classic differential DPA to three greatly cuts down the realization cost and compacts the overall circuit. Theoretical analysis is given for deep understanding of the operation principle. To demonstrate the proposed technique, a prototype is implemented based on Cree's CGH40010 GaN HEMTs. Experimental result shows that 73% and 63% drain efficiencies are achieved at peak power and 6-dB back-off point, respectively.