Simplified Emulation of Active Load Modulation for a Millimeter-Wave GaN MMIC Doherty Power Amplifier Design

Based on large-signal simulations, this article proposes a simplified method to emulate the active load modulation between the carrier and peaking transistors in a Doherty power amplifier (DPA) design. In contrast to the conventional load-pull method, the proposed method contributes to emulating the active load modulation between the load-modulated transistors with considering their nonlinear interaction. It offers the advantages of predicting the real-world performance of the load-modulated transistors and providing the optimum load-modulation trajectories to be synthesized in a DPA design. To verify the proposed method, a two-way millimeter wave (mmWave) gallium nitride (GaN) microwave monolithic integrated circuit (MMIC) DPA is designed from 25.5 to 27 GHz. The measured results show that the realized MMIC DPA achieves power-added efficiency (PAE) higher than 30% at saturation, 27% at 6-dB back-off, and 21.5% at 8-dB back-off, with a saturated output power higher than 31.4 dBm across the band. When tested using a 400-MHz modulated signal with digital predistortion (DPD), the MMIC DPA shows adjacent channel power ratio (ACPR) levels better than -40 dBc over the band.

Automated summary

This article proposes a simplified method to emulate the active load modulation between the carrier and peaking transistors in a Doherty power amplifier (DPA) design based on large-signal simulations. The proposed method considers the nonlinear interaction between the load-modulated transistors, providing the advantages of predicting their real-world performance and synthesizing optimum load-modulation trajectories in a DPA design. The measured results of a designed mmWave GaN MMIC DPA show high power-added efficiency, saturated output power, and low adjacent channel power ratio levels when tested with a modulated signal using digital predistortion.