Linear Hybrid Asymmetrical Load-Modulated Balanced Amplifier with Multi-Band Reconfigurability and Antenna-VSWR Resilience

TL;DR

The paper tackles the challenge of achieving high linearity and robustness to load mismatch in wideband power amplifiers for multi‑band, high‑PAPR wireless systems. It introduces the H‑ALMBA, a three‑way load‑modulated balanced amplifier that integrates a carrier path with two peaking paths and uses adaptive CA biasing ($V_{DD,CA}$) plus reconfigurable BA1/BA2 sequencing to sustain linearity and efficiency across bands. A comprehensive theory is developed, including unified load impedance expressions and CA‑BA phase offset optimization, complemented by emulated GaN device verification and extensive wideband measurements under matched and mismatched loads. The results demonstrate wideband linear AMAM/AMPM performance, strong mismatch resilience, and competitive efficiency, highlighting the approach as a viable candidate for future massive MIMO PAs and multi‑band deployments.

Abstract

This paper presents the first-ever highly linear and load-insensitive three-way load-modulation power amplifier (PA) based on reconfigurable hybrid asymmetrical load modulated balanced amplifier (H-ALMBA). Through proper amplitude and phase controls, the carrier, control amplifier (CA), and two peaking balanced amplifiers (BA1 and BA2) can form a linear high-order load modulation over wide bandwidth. Moreover, it is theoretically unveiled that the load modulation behavior of H-ALMBA can be insensitive to load mismatch by leveraging bias reconfiguration and the intrinsic load-insensitivity of balanced topology. Specifically, the PA's linearity and efficiency profiles can be maintained against arbitrary load mismatch through $Z_\mathrm{L}$-dependent reconfiguration of CA supply voltage ($V_\mathrm{DD,CA}$) and turning-on sequence of BA1 and BA2. Based on the proposed theory, an RF-input linear H-ALMBA is developed with GaN transistors and wideband quadrature hybrids. Over the design bandwidth from $1.7$-$2.9$ GHz, an efficiency of $56.8\%$$-$$72.9\%$ at peak power and $49.8\%$$-$$61.2\%$ at $10$-dB PBO are measured together with linear AMAM and AMPM responses. In modulated evaluation with 4G LTE signal, an EVM of $3.1\%$, ACPR of $-39$ dB, and average efficiency of up to $52\%$ are measured. Moreover, the reconfigurable H-ALMBA experimentally maintains an excellent average efficiency and linearity against arbitrary load mismatch at $2:1$ VSWR, and this mismatch-resilient operation can be achieved at any in-band frequencies. The overall measured performance favorably outperforms the state-of-the-art.

Figures (20)

• Figure 1: Overview of H-ALMBA with varactor-less reconfiguration for wide bandwidth and load insensitiveness.
• Figure 2: Generalized schematic of H-ALMBA consist of peaking and control amplifiers.
• Figure 3: Comparison of normalized fundamental currents between H-ALMBA and PD-LMBA modes.
• Figure 4: Comparison of normalized fundamental voltages of each path in H-ALMBA and PD-LMBA mode
• Figure 5: Comparison of load resistance between three sub-amplifiers in H-ALMBA and PD-LMBA.