High-Frequency Self-Synchronized Load-Independent Class-E Rectifier Using Fixed-Point Crossing Detection

This paper presents an intra-cycle self-synchronized load-independent (LI) class-E rectifier based on a novel fixedpoint crossing detection (FPXD) method. Through circuit analysis, we identify that the drain-to-source voltage of the LI class-E rectifier consistently crosses a fixed voltage threshold at a specific phase angle prior to turn-on, independent of load resistance. This fixed crossing point serves as a reliable trigger for gate-drive signal generation. Therefore, the proposed approach enables intracycle synchronization without the need for additional resonant components or control circuitry. Analytical expressions for the fixed point are derived, and a systematic design procedure is provided. A 6.78 MHz, 20 W WPT prototype was implemented and tested. The rectifier maintained robust load-independent performance, demonstrating nearly constant output voltage and input reactance across varying loads. Compared with the zerocrossing detection (ZXD)-based intra-cycle synchronization, the proposed method achieved more precise switching, eliminating reverse conduction and switching losses, and reducing total rectifier effectively.