High efficiency CMOS active rectifier with adaptive delay compensation

In this paper, a CMOS active rectifier having high power conversion efficiency (PCE) for a wide output load range has been designed for wirelessly powered biomedical applications. Mathematical analysis is presented to evaluate optimum design conditions to achieve high PCE. Adaptively biased fast and slow comparators are used in addition to the main comparator to eliminate the ON and OFF delays associated with the comparator and buffer chain. The proposed comparator design uses both halves of ac input in tandem for obtaining a precise output. A voltage-mode switching is used to reduce static power consumption of the control circuit. The design performs reliably over process, voltage, and temperature (PVT) variations. Simulation results show that the proposed rectifier can deliver a maximum power of 69.8 mW, while the comparator and the digital blocks consume only 1.5% of total power. A peak PCE of 93.5% with 240 Ω loading and a peak voltage conversion ratio (VCR) of 96.7% at 10 kΩ loading have been obtained.