A 6.78-MHz Digital Rectifier-Based Single-Stage Wireless Charger Using Digital-Controlled CC–CV Technique for Implantable Biomedical Devices

This letter presents a digital rectifier-based single-stage wireless charger. The proposed charger regulates charging current by adjusting the size of the power switch digitally, and the power loss of the switch can be reduced adaptively according to the charging condition. The power conversion efficiency is consequently improved significantly. Furthermore, high charging resolution and low output voltage ripple have been achieved by introducing a successive approximation method. Compared with the conventional analog-controlled charging technique, the proposed digital control can shorten the mode transition time, and thus avoid potential battery overcharging. In addition, a high-speed current sensor operating at 6.78 MHz is proposed to guarantee the sensing accuracy. The proposed single-stage wireless charger is fabricated in a 0.18-µm bipolar CMOS DMOS process with a die area of 0.56 mm$^{2}$. The measured peak receiver efficiency of the proposed charger is 92.8%.