A 1-W, 6.78-MHz Wireless Power Transfer System With Up-to-16.1% Light-Load Efficiency Improvement and Instant Response Through Single-Cycle-Based DTX Control

This article presents a 6.78-MHz wireless power transfer system with transmission power control. The proposed receiver (RX) with a simplified 0X/1X structure can achieve single-stage regulation in series–series resonant tank, where the charge and discharge cycle are only dependent on the hysteresis comparator. Asymmetric pulsewidth modulation is adopted in the proposed transmitter (TX), where the duty ratio (<inline-formula><tex-math notation="LaTeX">${D}_{\text{TX}}$</tex-math></inline-formula>) is switched based on the charge or discharge cycle of RX. With the proposed single-cycle-based <inline-formula><tex-math notation="LaTeX">${D}_{\text{TX}}$</tex-math></inline-formula> control, the <inline-formula><tex-math notation="LaTeX">${D}_{\text{TX}}$</tex-math></inline-formula> will be switched to 0.25 in the discharge cycle, while it is 0.5 in the charge cycle for maximum power transmission. Therefore, the end-to-end (E2E) efficiency especially at light-load conditions can be improved, and the recovery time is nearly instant when loading changes suddenly, i.e., neglectable voltage droop can be achieved. The RX is implemented by a printed circuit board and the TX is fabricated in a 0.18-<italic>μ</italic>m CMOS technology. In the measurement, an output power range from 10 to 1000 mW is achieved with 60.6% peak E2E efficiency. The significant E2E efficiency improvement is observed over 10–255 mW and the maximum improvement is 16.1%. The measured load transient response verifies that the proposed design has instant response and neglectable voltage droop.