A 13.56-MHz Wireless Power Transfer System With a Wide Operating Distance and Load Range for Biometric Smartcards

This article presents a wireless power transfer system for an increased dynamic range of link distance and load with extended controllability of transmitting power. Under wide link distance and load variation, rectification and regulation in a single-stage to provide a stable 3-V dc voltage $V_\text {L}$ from a 13.56-MHz sinusoidal waveform at the receiver (RX) $LC$ tank is performed. For high end-to-end power transfer efficiency and robust operation under link and load variations, the transmitting power $P_\text {TX}$ is controlled by the reflected impedance from the RX to the transmitter (TX). To extend the controllability of the $P_\text {TX}$ , antennae with high quality factors and a series-connected RX $LC$ tank structure are applied. A working-only-when-needed rising edge detector and a $\Delta \Sigma$ -based falling edge detector for low power and accurate zero current detection are presented. A digital $\Delta \Sigma$ -based voltage regulation controller is adopted for stable dc supply with fast transient response. The implemented IC in a standard 65-nm CMOS process measures 0.14-mm $^\text{2}$ active silicon area. The proposed work operates under a wide range of link distance (30–185 mm) with a large load dynamic range (10000×, 60 $\Omega$ –600 k $\Omega$ ).