A Low-Power Resonance Detector for Output Power Optimization in Wireless Power Transfer Systems

This paper introduces a class-D power amplifier (PA) incorporating a power-efficient resonance detection circuit designed for resonant wireless power transfer (WPT) systems. In the operation of resonant WPT systems, the process tolerance of the L-C resonant components on both sides introduce an imaginary part in the equivalent reflected impedance in the PA, resulting in a degradation of the power transferred to the secondary side. The magnitude of the imaginary part can vary depending on the measurement setup of the WPT system, including the coupling distance, misalignment of the coils, and output loading conditions. Therefore, a resonant detector is proposed to estimate the reactance on the primary side and assist in adjusting the magnitude of the compensation capacitance to ensure the resonance of the L-C tank. Additionally, this proposed detector consumes only 249uW during measurement, making it suitable to be employed in low-power applications.