A CMOS 13.56-MHz high-efficiency low-dropout-voltage 40-mW inductive link power supply utilizing on-chip delay-compensated voltage doubler rectifier and multiple LDOs for implantable medical devices

Abstract

A near-field 13.56-MHz 20mA inductive energy transmission device with ferrite core spiral coils and CMOS power regulator is designed and tested. The power regulator is composed of active voltage doubler (VD) rectifier and low-dropout regulators (LDOs). In order to avoid large space requirement of coil and further increase its efficiency in the implantable medical devices (IMDs), the coils are constructed in the spiral shape with a ferrite core. In the VD with the comparator, the input offset voltage is adjustable for delay compensation and a start-up control circuit is added to achieve robust start-up mechanism. On-chip delay compensation control is implemented to prevent from reverse current conduction and increase the efficiency. Three fully-integrated LDOs with rectifier output voltage of 2V to 1.8V are realized: LDO for analog circuits (ALDO), LDO for digital circuits (DLDO) and LDO for reference-voltage circuits (RLDO). Thus the performance of individual LDO can be optimized. Both ALDO and RLDO have low crosstalk noise from DLDO. The measured ripple voltage of rectifier output is 10.4mV. The power conversion efficiency (PCE) of 85% with 20mA output current. The measured dropout voltage is 384mV. As compared with other designs, the proposed Inductive link power supply has lower ripple voltages and dropout voltage, and higher PCE.