High Voltage and High Current CMOS Active Rectifier with Digital Offset Compensation for Implantable Devices

Abstract

A CMOS active rectifier for wirelessly powered implantable devices operating at a frequency of 100-500kHz, input voltage of 5-18V and a load current of 100mA-200mA is presented. The diodes used in the conventional rectifier are replaced by PMOS and NMOS transistors, which help in obtaining high power conversion efficiency and voltage conversion efficiency. The PMOS and NMOS transistors used for the rectification are high voltage devices 18v/5v (VDS/ VGS). Dedicated switching mechanisms are used for protection of the devices at higher voltages. The NMOS transistors are operated as active diodes, using a high voltage differential common gate comparator with adjustable offset. The proposed comparators are implemented with a dynamic switched current offset mechanism to reduce the reverse current and a NOR gate based SR-latch is used to prevent the multiple pulsing. A calibration circuit is proposed to detect the reverse current present in the circuit and dynamically vary the amount of current offset added to the comparator to reduce the reverse current. ONC18TG18 CMOS technology, a 180nm process by ON semiconductor is used for the design of the rectifier. A peak PCE of 92% and VCE of 93.2% is obtained for a 50Ω loading.