A 13.56 MHz Efficient Active Rectifier with Quasi-Constant Delay Compensation Scheme for Implantable Medical Devices

An active rectifier operating at 13.56 MHz in the ISM frequency band for wirelessly powered implantable medical devices is presented. This rectifier compensates for the transmission delay accurately over a wide input voltage range, enabling efficient energy conversion compared to previous rectifiers. A quasi-constant delay comparator is proposed to minimize the variation in delay of the active diode under significant input voltage changes. Then, a delay compensation technique based on controlled offset voltage is utilized to eliminate reverse current. Furthermore, the one-shot circuit is employed to address the issue of multiple conduction of the active diode within a single period. The proposed rectifier is implemented in 0.18μm CMOS technology. The post-layout simulation results show that the delay variation of the active diode is only 63 ps when the input voltage VAC ranges from 1.45V to 3.8V. Additionally, the rectified output voltage ranges from 1.2V to 3.3V, with the power conversion efficiency (PCE) of 90.1% to 94.8%. And the maximum output power of 90.8 mW is obtained for a load resistor of 120 Ω.