A 13.56 MHz CMOS Active Rectifier With Switched-Offset and Compensated Biasing for Biomedical Wireless Power Transfer Systems

摘要

A full-wave active rectifier switching at 13.56 MHz with compensated bias current for a wide input range for wirelessly powered high-current biomedical implants is presented. The four diodes of a conventional passive rectifier are replaced by two cross-coupled PMOS transistors and two comparator- controlled NMOS switches to eliminate diode voltage drops such that high voltage conversion ratio and power conversion efficiency could be achieved even at low AC input amplitude $vert V_{rm AC}vert$. The comparators are implemented with switched-offset biasing to compensate for the delays of active diodes and to eliminate multiple pulsing and reverse current. The proposed rectifier uses a modified CMOS peaking current source with bias current that is quasi-inversely proportional to the supply voltage to better control the reverse current over a wide AC input range (1.5 to 4 V). The rectifier was fabricated in a standard 0.35 $mu{rm m}$ CMOS N-well process with active area of 0.0651 ${rm mm}^{2}$. For the proposed rectifier measured at $vert V_{rm AC}vert=3.0 {rm V}$, the voltage conversion ratios are 0.89 and 0.93 for $R_{rm L}=500 Omega$ and 5 ${rm k}Omega$, respectively, and the measured power conversion efficiencies are 82.2% to 90.1% with $vert V_{rm AC}vert$ ranges from 1.5 to 4 V for $R_{rm L}=500 Omega$.