A 24-28-GHz GaN MMIC Synchronous Doherty Power Amplifier With Enhanced Load Modulation for 5G mm-Wave Applications

• Published in: IEEE transactions on microwave theory and techniques Vol. 70; no. 8; pp. 3910 - 3922
• Main Authors: Liu, Rui-Jia, Zhu, Xiao-Wei, Xia, Jing, Zhao, Zi-Ming, Dong, Qin, Chen, Peng, Zhang, Lei, Jiang, Xin, Yu, Chao, Hong, Wei
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.08.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: 5G mobile communication; Bandwidth; Dispersion; Doherty power amplifier (DPA); Frequencies; Gallium nitride; gallium nitride (GaN); Gallium nitrides; High electron mobility transistors; Impedance; Integrated circuits; Load matching; load modulation; Millimeter waves; millimeter-wave (mm-wave); MMIC (circuits); Modulation; monolithic microwave-wave integrated circuit (MMIC); Power amplifiers; Saturation; Semiconductor devices; Silicon carbide; Topology; Transistors; Transmission lines
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2022.3176818

In this article, a load-modulation enhanced wideband compact high-efficiency millimeter-wave (mm-wave) gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) synchronous Doherty power amplifier (DPA) is presented. A synchronous DPA architecture is used to ensure the optimal saturation performance at the mm-wave band. Based on the analysis of load-modulation behavior, the bandwidth of the DPA can be extended by decreasing the phase dispersion factor <inline-formula> <tex-math notation="LaTeX">\alpha </tex-math></inline-formula>. A simple optimal tuning-based method is proposed to design an equivalent <inline-formula> <tex-math notation="LaTeX">\lambda </tex-math></inline-formula>/4 transmission line (EQWTL) with the minimal <inline-formula> <tex-math notation="LaTeX">\alpha </tex-math></inline-formula> for a given topology. Furthermore, the influence of the power division ratio <inline-formula> <tex-math notation="LaTeX">\sigma </tex-math></inline-formula> on the proposed DPA's load-modulation behavior has also been analyzed and a proper load modulation can be realized by splitting more power to the peaking branch properly. For verification, a 24-28-GHz GaN MMIC synchronous DPA has been designed using a 0.15-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> GaN on silicon carbide high-electron-mobility transistor process. Both the load modulation and the matching of the fundamental and the second harmonic load impedances can be realized by a modified bandpass-type EQWTL with a minimal <inline-formula> <tex-math notation="LaTeX">\alpha </tex-math></inline-formula> easily. Experimental results show that the fabricated DPA can achieve the output power of 35.4-36 dBm and the power-added efficiency (PAE) of 27.8%-36.8% at saturation. The PAE at 6-dB power back-off (PBO) is 18.3%-30.1% and the 9-dB PBO PAE is higher than 14.3% in the whole frequency band. An average PAE of 27.4% with good linearity is obtained when excited by a 400-MHz modulated signal after linearization.