A 6.78 MHz Single-Stage Wireless Power Transmitter Using a 3-Mode Zero-Voltage Switching Class-D PA

A 6.78 MHz single-stage transmitter (TX) using a reconfigurable regulating class-D power amplifier (PA) for wireless power transfer (WPT) applications is presented. Based on a 3-mode modulation scheme, the TX achieves power regulation and transmission with only one power stage. A discontinuous-conduction-mode (DCM) zero-voltage switching (ZVS) scheme is adopted to reduce switching loss. A control loop is set to regulate the output voltage of the WPT receiver (RX) by automatically adjusting the transmitting power. With dual-loop control and a proportional-integral (PI) compensation scheme, the loop achieves tight regulation and fast response. The controller is implemented digitally to benefit from the AirFuel (R) embedded Bluetooth communication link. The PA was fabricated with a high-voltage 0.35 mu m CMOS process, and the digital controller with a standard 0.35 mu m CMOS process, respectively. Measurement results show that the output voltage of the RX was correctly regulated to 11.7 V under a load change of 50mA to 500mA, and the WPT system could deliver a maximum power of 7.3 W to the RX over a distance of 4.0 cm, and achieved TX to RX peak efficiency of 57.3%.

Automated summary

This study presents a 6.78 MHz single-stage transmitter using a reconfigurable regulating class-D power amplifier for wireless power transfer applications. The transmitter achieves power regulation and transmission with only one power stage, adopts a DCM-ZVS scheme to reduce switching loss, and utilizes a dual-loop control with PI compensation for tight regulation and fast response. The system demonstrates correct output voltage regulation under load changes, delivers maximum power to the receiver over a distance, and achieves a peak efficiency of 57.3%.