A 13.56 MHz 40 mW CMOS High-Efficiency Inductive Link Power Supply Utilizing On-Chip Delay-Compensated Voltage Doubler Rectifier and Multiple LDOs for Implantable Medical Devices

In this paper, a 13.56 MHz CMOS near-field inductive link power supply (ILPS) that can deliver 20 mA output current for implantable medical devices (IMDs) is proposed and fabricated. In the proposed ILPS, the pair of inductive link coils is constructed in the spiral shape with a ferrite core to save space and increase efficiency. Experimental results have shown that the near-field coils can transmit power at the resonant frequency of 13.56 MHz with the transmission efficiency up to 76.3%. The CMOS power regulator is composed of active voltage doubler rectifier (VD) and low-dropout regulators (LDOs). In the active 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 with SR-latches is proposed to prevent from error glitch switching on offset voltage control and achieve accurate delay compensation so that the reverse current conduction can be avoided and the efficiency can be increased. Three fully-integrated LDOs with rectifier output voltage of 2 V to 1.8 V are realized for analog (ALDO), digital (DLDO), and reference-voltage (RLDO) circuits. Thus the performance of individual LDO can be optimized. The measured output ripple voltage of the active VD is 10.4 mV. The power conversion efficiency (PCE) is 85% under 20 mA output current. The measured dropout voltage is 384 mV. As compared with other designs, the proposed ILPS has lower ripple voltages, lower dropout voltage, and higher PCE.