A GaN Filtering Doherty Power Amplifier With On-Chip Multifunctional Power Divider

In this letter, a filtering Doherty power amplifier (DPA) monolithic microwave integrated circuit (MMIC) with an on-chip multifunctional power divider (PD) is presented. The PD is implemented at the interstage of the DPA, achieving harmonic control, filtering, and phase compensation functions simultaneously. By integrating the filter into the interstage, separate functional circuits can be eliminated, as well as achieving improved efficiency and minimized chip area. A two-stage DPA MMIC operating at the 2.6–3.8 GHz is realized using 0.25- $\mu $ m gallium nitride (GaN) high-electron mobility transistor (HEMT) technology. The fabricated device exhibits small-signal filtering characteristics and a flat gain response, achieving a saturated output power of 33.1–34.1 dBm with 52.8%–55.1% drain efficiency (DE). The DE maintains 40%–45% at 6-dB output back-off (OBO), while linearity measurements with 64-quadrature amplitude modulation (QAM) signals show performance with <2.76% error vector magnitude (EVM) and −32 dBc adjacent channel leakage ratio (ACLR).