Coupling-aware efficiency modeling of outphasing power amplifiers for wearable wireless power transfer

Area of Science:

• Electrical Engineering
• Wireless Communication Systems
• Power Electronics

Background:

• Outphasing power amplifiers (PAs) are crucial for efficient wireless power transfer (WPT) due to their constant-envelope operation.
• Wearable WPT efficiency is significantly impacted by the interplay between power combiners and inductive link impedance, which is coupling-dependent.
• Existing models lack a systematic characterization of these combined effects.

Purpose of the Study:

• To develop a system-level analytical framework for modeling outphasing PAs, Wilkinson and Chireix combiners, and coupling-dependent WPT loads.
• To determine optimal operating conditions for wearable WPT systems as a function of the coupling coefficient.
• To provide practical design insights for selecting appropriate combiner architectures.

Main Methods:

• A novel system-level analytical framework was developed.
• The framework jointly models outphasing PA operation, Wilkinson and Chireix combiner behavior, and WPT load variations.
• Circuit-level harmonic balance simulations were used to validate the analytical trends.

Main Results:

• For Wilkinson combiners, optimal outphasing is at 0°, with efficiency limited by link coupling.
• For Chireix combiners, peak efficiency occurs at the compensation angle (θc), modulated by coupling.
• Chireix combiners (θc=60°-70°) can outperform Wilkinson by 8% at moderate coupling (k≈0.2), while Wilkinson is more robust for weak/varying coupling (k<0.15).

Conclusions:

• The proposed framework enables explicit determination of optimal operating conditions for wearable WPT systems.
• Chireix and Wilkinson combiners exhibit distinct performance characteristics influenced by coupling conditions.
• Actionable guidelines are provided for early-stage design and architecture selection without complex simulations.