A 24–28-GHz Single-Chip GaN MMIC T/R Front-End Using Doherty Power Amplifier as Embedded Switches in Rx Mode

This article presents a novel millimeter-wave (mm-wave) single-chip gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) transmit–receive (T/R) front-end for 5G-NR FR2 applications. Unlike the conventional T/R front-ends that use single-pole double-throw (SPDT) switches, which suffer from insertion loss, nonlinearity, and limited power handling in transmit (Tx) mode, the proposed approach uses the Doherty power amplifier (DPA) in the Tx path to function as embedded switches during receive (Rx) operation directly, which can simultaneously achieve high efficiency at large power back-off (PBO) in Tx mode and good isolation in Rx mode. To validate the concept, a fully integrated 24–28-GHz GaN MMIC T/R front-end was designed and fabricated using a 120-nm GaN-on-SiC high-electron-mobility transistor (HEMT) process. In Tx mode, the two-stage DPA delivers a saturated output power of 34.2–35.2 dBm with a peak power-added efficiency (PAE) of 22%–28%. The PAE at 6-dB PBO ranges from 15.4% to 19.3%. When excited by a 400-MHz 5G-NR signal, excellent linearity is achieved after using digital predistortion (DPD). In Rx mode, a wideband three-stage low-noise amplifier (LNA) provides a noise figure (NF) of 3.3–4.8 dB and a gain of 18–21.5 dB, including the switch loss.