Exploiting Phase for Extended Efficiency Range in Symmetrical Doherty Power Amplifiers

Abstract

This work presents a symmetrical Doherty power amplifier (DPA) that exhibits an extended high-efficiency range with respect to output power backoff (OBO). The presented theoretical analysis illustrates that certain phasing constraints placed at the Doherty combining node can achieve extended load modulation and enhanced efficiency for a DPA with symmetric carrier and peaking devices, without sacrificing maximum output power. This proposed design approach has been validated with measurements on a gallium nitride (GaN) DPA operating from 2.1–2.3 GHz. Under continuous-wave (CW) excitation, the power amplifiers (PAs) delivers 43.6 dBm of output power at 3-dB compression and exhibits a drain efficiency (DE) of 54% at 9-dB OBO, which demonstrates an extended OBO efficiency range compared to a conventional symmetrical DPA. The measured DPA achieves 51% DE with a 20-MHz LTE input signal. This work is the first time that current combine phasing has been presented as a method to achieve extended Doherty load modulation, hence resulting in an extended efficiency range over OBO.