Back-Off Range Extension of Doherty Power Amplifier Using Parasitic Capacitance Compensation

Abstract

Efficiencies of a Doherty power amplifier (DPA) at output back-off (OBO) levels are limited by the parasitic parameters of transistors. To deal with this issue, an effective approach is proposed in this letter to enhance efficiency and the OBO range of a DPA. An equivalent negative capacitance network (ENCN) is utilized to compensate for reactive impedances of the carrier amplifier, which can significantly boost efficiency at the deep back-off. For validation, an asymmetric DPA utilizing the out-phased current combining method is designed to achieve an extended OBO range. When the operating frequency is 2.55 GHz in continuous-wave measurement, the implemented DPA can obtain drain efficiencies of 54.8% at 11.6-dB OBO level and 74.4% at saturation (43.1 dBm), respectively.