A Broadband Doherty-like Power Amplifier with Large Power Back-off Range

This paper proposes a novel power amplifier (PA) topology which can realize PA operation with high power back-off range (OBO) and wide bandwidth. Here a short-circuit reactance instead of an additional PA branch is introduced into the isolated port of a coupler to provide the frequency dependency required for broadband load impedance modulation. In addition, the corresponding complex load impedances at each normalized frequency are given to achieve high OBO based on the use of the same transistor in both the carrier PA and peak PA branches. The behaviours of the proposed PA as a function of input power are also derived based on the appropriate complex load impedance. To validate the proposed topology, a PA with 9 dB OBO operating across 1.0-3.0 GHz is designed, fabricated, and tested. Measurements illustrate that the PA can deliver a saturated output power from 44 dBm to 45 dBm over 1.0-3.0 GHz, with a drain efficiency ranging from 62% to 71%. Drain efficiencies are from 41% to 48% at the OBO of 9 dB.