Design and Analysis of Continuous-Mode Doherty Power Amplifier With Second Harmonic Control

While continuous-mode Doherty power amplifier (CM-DPA) can achieve high efficiency at output back-off (OBO) power levels, their achievable bandwidth and load modulation have not yet been fully investigated. This brief reveals that the bandwidth of CM-DPA is limited by the impedance trajectories of the peaking transistors. In particular, the peaking transistor degrades the bandwidth in the high power region and limits the fractional bandwidth (FBW) of the CM-DPA. Moreover, based on post-matching Doherty architecture, an analytical method for harmonic control in CM-DPAs is presented. A broadband CM-DPA with harmonic control is implemented, fabricated and measured. The CM-DPA delivers a saturation output power (Psat) of 42.6-44.4 dBm from 1.50 to 2.55 GHz, i.e., FBW of 51.8%. The drain efficiencies in the interested frequency band are 50.7%-69.7% and 43.3%-57% at the Psat and 6-dB OBO power levels, respectively.