Load-Modulated Double-Balanced Amplifier with Quasi-Isolation to Load

This paper presents a novel Double-Balanced power amplifiers (PAs) architecture with an intrinsic isolation to load. Derived from the generic load modulated Balanced Amplifier (LMBA), by designing the single-ended control amplifier (CA) as another balanced PA, the load-modulated double-balanced amplifier (LMDBA) can inherit the intrinsic load-mismatch tolerance of balanced amplifier without any reconfiguration and load-impedance sensing. A proof-of-concept is demonstrated using two balanced GaN power amplifiers and branch-line quadrature hybrid couplers at 2.1 GHz. The implemented PA achieves an efficiency of 76.2% at peak power and 69.5% at 10-dB output back-off (OBO) under the matched condition of load. An efficiency up to 72.5% at peak power and up to 64.1% at 10-dB OBO are measured under 2 : 1 VSWR of load. In modulated evaluation with a 20-MHz OFDM signal, an EVM of 1.9%, ACPR of −41 dB is measured under matched condition after Digital Pre-Distortion (DPD). The PA’s linearity profiles are well sustained experimentally against 2 : 1 VSWR of load mismatch, e.g., 2.1% of EVM and up to −39.5 dB of ACPR.