Design of S-band high-efficiency class-F/class-F^-1 GaN HEMT power amplifiers

In order to solve the problem that the class-F and the inverse class-F (class-F^-1) power amplifiers (PAs) affected by the parasitics of the packaged transistor, resulting in a low efficiency performance and complicated circuit structure, a novel output matching circuit is proposed. Firstly, the DC bias line with harmonic tuning was equipped in the harmonic control circuits, thus simplifying the complexity of the harmonic control circuits. Then, an L-type transmission line circuit was adopted to replace the traditional L-C lumped components, which matched the harmonic impedances presented by the parasitics, thus the class-F or class-F^-1 harmonic impedance conditions at the intrinsic drain of transistor can be realized. Finally, two series transmission lines transformed the optimum fundamental impedance into 50 Ω load. For demonstration, the class-F PA and class F^-1 PA using the CGH40010 GaN HEMT device are designed and fabricated, which operating at 2.4 GHz. Measurement results show that the peak power added efficiency (PAE) of the class-F PA reaches 75.5%, the corresponding output power is 40.8 dBm; the peak PAE of the class-F^-1 PA is 77.6%, and the corresponding output power is 40.3 dBm. The proposed method simplifies the complexity of the PA circuit, can easily compensate the parasitics of transistor, and provides a feasible solution for designing high efficiency PAs using GaN HEMT active devices.