Design of 74% Fractional Bandwidth Continuous-Mode Doherty Power Amplifier Using Compensation Susceptance

This brief presents a novel design method of broadband continuous-mode Doherty power amplifier (CM-DPA) using compensation susceptance. In particular, at power back-off point, the compensation susceptance is added at the current source plane of the carrier PA to make it operates in continuous mode, which thus enhances the back-off efficiency and extends the bandwidth. Meanwhile, considering the influence of the parasitic parameters of the PA in practical design, the designed compensation susceptance at the current source plane is equivalently transformed into the compensation susceptance at the package plane of the carrier PA. Additionally, at saturation point, the load impedances at the package plane of both carrier and peaking PAs can meet the impedance conditions of drain efficiency more than 60%. Based on the proposed method, a 74% fractional bandwidth CM-DPA operating from 1.1 to 2.4 GHz is designed and measured. Under the continuous-wave excitation, the measured 6-dB back-off efficiency is 46.8%–63% and the saturation efficiency is 59.1%–78.8%. The measured small-signal gain and back-off gain are 10–12 dB and 9.1–10 dB, respectively.