Digitally Assisted High-Voltage High-Current CMOS Active Rectifier for Implantable Devices

A CMOS active rectifier for implantable medical devices capable of high current and high voltage operation is presented. The rectifier uses a combination of cross-coupled PMOS devices and NMOS-based active diodes to enhance power conversion efficiency (PCE). Active diodes are realized using digitally-assisted switched-offset comparators to reduce losses due to reverse current. The switched offset is optimized using the digitally-assisted loop by continually sensing the AC input to prevent conduction losses. High voltage operation is achieved using a combination of 18V and 5V devices available in the ON semiconductor triple gate 0.18µm CMOS process. The active rectifier operates over a wide range of frequencies from 100kHz to 1MHz to support wireless power transfer for implantable devices. For an AC input voltage of 5V at frequency of 200kHz, the proposed active rectifier achieves a peak rectified output voltage of 4.66V and peak PCE of 92% for a load of 50Ω.