A 2.4-GHz Wideband Wireless Harvester With Integrated Autonomous RF Input-Frequency Tracking for FCC-Compatible Chip-Scale Battery Charging

Abstract

RF-powered Internet of Things (IoT) sensor duty cycles are limited due to low available energy at long range in the absence of a battery. Additionally, RF energy harvesters with high- $Q$ interfaces between the antenna and rectifier suffer from poor sensitivity for RF input frequencies outside their narrow bandwidth. In this article, we address these challenges and present a channel-agnostic far-field 2.4-GHz energy harvester achieving: 1) dynamic RF input frequency tracking for wideband sensitivity; 2) FCC-compatible frequency-hopped input harvesting; and 3) optimal battery charging capability for powering energy-constrained IoT applications. An enhanced antenna-rectifier interface is designed with 2-dB better stand-alone sensitivity and $5\times $ lower leakage using a bulk-connected rectifier. Input frequency tracking is achieved over 15-MHz bandwidth using a fast-settling auto-zeroing amplifier that senses the rectifier’s first-stage output. Chip-scale pulsed battery charging is achieved from cold-start over $10\times $ RF available power ranging from −27 to −17 dBm with > 22% efficiency across the entire range. State-of-the-art battery charging is achieved at −21.5-dBm incident power and 4.18% duty cycled (1-h-per-day charging) FCC-compliant frequency-hopped RF input assuming a steady-state 100-nA load. The compact harvester IC occupies 2 mm2 in a 65-nm CMOS technology and the antenna and IC integrated together in a chip-on-board approach occupy 2.125 cm2 of PCB area.

Keywords

• Antenna
• battery charging
• boost converter
• cold start
• energy harvester
• FCC-compatible