Broadband Sequential Load Modulated Balanced Amplifier With Extended Design Space Using Second Harmonic Manipulation

This article presents the design methodology of a broadband radio frequency (RF)-input sequential load modulated balanced amplifier (SLMBA) with extended high-efficiency design space, by introducing the second-harmonic load manipulation over an enlarged range for the control amplifier (CA). The extension of CA load design space not only can provide the time-domain-varying drain current waveform inside the entire design continuum but also allows maintaining high efficiency at output power back-off (OBO) over an extended operation bandwidth. To validate the theory, a broadband SLMBA operating at 2.05-3.65 GHz was designed and fabricated using packaged gallium nitride (GaN) transistors. The implemented power amplifier (PA) attains a measured 45.2-46.8-dBm peak output power. Drain efficiency (DE) of 61.2%-79.7% at saturation and 50.5%-66.2% at 8-dB OBO is achieved throughout the designed bandwidth. When tested with a 100-MHz long-term evolution (LTE) signal with a peak-to-average-power ratio (PAPR) of 8 dB, the proposed SLMBA achieves 50.7%-63.5% average DE over 2.05-3.55 GHz and better than −45.1 dBc adjacent channel power ratio (ACPR) after digital predistortion (DPD).