A Simplified Broadband Design Methodology for Linearized High-Efficiency Continuous Class-F Power Amplifiers

TLDR

The paper presents a design approach for achieving approximated continuous Class‑F power amplifier modes over wide bandwidths. By exploiting the nonlinear device capacitance to shape voltage and current waveforms, identifying high‑efficiency reactance‑plane regions, and applying a distributed simplified real‑frequency synthesis algorithm, the design reduces to a fundamental matching problem enabling wideband operation. Using a 10‑W Cree GaN HEMT, the authors measured over 70 % efficiency across a 51 % bandwidth (1.45–2.45 GHz) with 11–16.8 W output, and achieved linearized adjacent‑channel power ratios below –53 dBc (20 MHz LTE) and –49 dBc (40 MHz W‑CDMA), representing the best performance for broadband switch‑mode PAs.

Abstract

This paper describes the design approach employed for achieving approximated continuous Class-F power amplifier (PA) modes over wide bandwidths. The importance of the nonlinear device capacitance for wave-shaping the continuous Class-F voltage and current waveforms is highlighted, thus reducing the device sensitivity to second and third harmonic impedance terminations. By identifying the high-efficiency regions on the reactance plane for harmonic band placement, the design can be reduced to a fundamental matching problem. The distributed simplified real frequency technique synthesis algorithm can then be utilized to achieve wideband operation. Using a 10-W Cree GaN HEMT device, greater than 70% efficiency has been measured over a 51% bandwidth from 1.45 to 2.45 GHz, with output powers of 11-16.8 W. The nonlinear PA was then linearized using digital predistortion with 20-MHz long-term evolution and 40-MHz eight-carrier W-CDMA excitation signals, to attain adjacent channel power ratios below -53 and -49 dBc, respectively. To the best of the authors' knowledge, the measured results represent the best performance obtained from a broadband switch-mode PA, and the best linearized switch-mode performance using 20- and 40-MHz modulated signals.