A VHF Wide-Input Range CMOS Passive Rectifier With Active Bias Tuning

Tiny implantable medical devices in millimeter size demand advanced wireless power solutions that operate at hundreds of megahertz and mainly use passive rectifiers for ac-dc power conversion. A conventional cross-connected (CC) rectifier can operate with high frequency and low input voltage but only achieves good efficiencies in a very narrow input power range, due to the shoot-through and reverse currents. This work presents a CMOS passive rectifier with active bias tuning (ABT), allowing a widely extended input range with high power conversion efficiency (PCE). In addition, we compensate for the process, voltage, and temperature variations with the ABT scheme that leads to a robust design for very-high-frequency (VHF) operation. Meanwhile, we propose a peak V-OUT searching scheme to indicate the charging/discharging directions for the ABT. We obtain a bias-voltage balancing among stacked rectifier stages with a switched-capacitor network. The proposed rectifier is fabricated in a 65-nm CMOS process. Measurement results of three chips show that the proposed rectifier improves the PCE over a wide input range, with an average maximum PCE of 64.4%.