A Dual-Mode RF Power Harvesting System with an On-Chip Coil in 180-nm SOI CMOS for Millimeter-Sized Biomedical Implants

In this paper, we present a dual-mode power harvesting system for millimeter-sized biomedical implants that are immune to the variation of wireless link parameters and loading. The design includes a multistage full-wave voltage rectifier, a power management unit, and a low dropout voltage regulator. Depending on the received RF power level and the required power by the load, power delivery is conducted in a continuous or duty-cycled mode. The system is fabricated in 180-nm silicon on insulator (SOI) CMOS technology with an active area of 2.56 mm² including an on-chip coil. RF power is transferred to the chip from a 2× 2 cm² coil through 10 mm of air at 434 MHz. The efficiency of the designed wireless link, which is the power transfer efficiency from the external coil to the on-chip coil, reaches up to 0.68% (-21.7 dB) at 10-mm separation through air. Keeping the transmitted RF power below 24 dBm, the system can provide a 1.08-V dc voltage for resistive loads larger than 20 k Ω continuously over time. When the harvested power is not enough to drive the load continuously, the system operates in the duty-cycled mode. Measurement results show that the system can drive a 1-k Ω load in the duty-cycled mode when the transmitted power level is 15 dBm.