A 13.56-MHz Active Rectifier With SAR-Assisted Coarse-Fine Adaptive Digital Delay Compensation for Biomedical Implantable Devices

This letter presents an active rectifier with SAR-assisted coarse-fine adaptive digital delay compensation technique for biomedical implantable devices. Both on- and off-delays are compensated by adjusting the comparator offset. In order to achieve accurate zero-voltage switching against process, voltage, and temperature variations, a two-step coarse-fine digital tuning method is introduced. The coarse-tuning phase and the fine-tuning phase are controlled by a 7-bit SAR controller and a 3-bit bidirectional counter, respectively. Meanwhile, the tuning frequency is designed to be much smaller than the switching frequency to minimize the power consumption. The proposed rectifier has been fabricated in 0.18-$\mu \text{m}$ CMOS process with a core area of 0.203 mm
²
and a maximum output power of 54 mW. With the input ac voltage ranging from 1.5 to 2 V, the measurement results show that the peak power conversion efficiency and voltage conversion ratio are 92.6% and 95.7% for the load resistor of 2 $\text{k}\Omega $ , respectively.