A Linearity-Improved 24–29-GHz GaN MMIC Doherty Power Amplifier With Reconfigurable Self-Adaptive Peaking Gate Bias Network

In this article, a linearity-improved millimeter-wave (mm-wave) gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) Doherty power amplifier (DPA) is presented for fifth-generation new radio (5G-NR) FR2 applications. To improve the linearity of the DPA while maintaining high back-off efficiency, a reconfigurable diode-based self-adaptive peaking gate bias network is proposed to keep the peaking amplifier off before the carrier amplifier reaches its maximum voltage swing and then effectively increase the gate bias voltage of the peaking amplifier when it is turned on during load modulation so that the gain compression and phase distortion of the DPA can be reduced. By changing the setting of the external series resistor and the external bias voltage, the effective gate bias of the power-stage peaking amplifier can be flexibly reconfigured. To verify the concept, a 24–29-GHz GaN MMIC DPA was designed using a 150-nm GaN on silicon carbide high-electron-mobility transistor (HEMT) process. The fabricated DPA can achieve a saturated power range of 34.8–36.1 dBm, with a corresponding power-added efficiency (PAE) of 25%–31.7%. The PAE of the DPA at 6-dB power back-off (PBO) ranges from 19% to 24.8% within the 24–29-GHz frequency band. The saturated gain of the DPA is higher than 13.5 dB, and the overall gain compression is lower than 4 dB across the whole operating band. When excited by a 400-MHz 5G-NR signal, the DPA can achieve very good linearity without using digital predistortion (DPD).