Broadband Sequential Load Modulated Balanced Amplifier With Extended Design Space Using Second Harmonic Manipulation
Chenhao Chu, Jingzhou Pang, Ramzi Darraji, Sagar K. Dhar, Tushar Sharma, Anding Zhu
Abstract
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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8$</tex-math> </inline-formula> dB, the proposed SLMBA achieves 50.7%–63.5% average DE over 2.05–3.55 GHz and better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 45.1 dBc adjacent channel power ratio (ACPR) after digital predistortion (DPD).