A Battery-Free BLE Backscatter Communication Chip for Wearable Systems

Abstract

This letter presents a backscatter chip that features bidirectional communication with commodity bluetooth low-energy (BLE) transceivers. For uplink, the chip reflects a reverse-whitened BLE tone into single-sideband (SSB) GFSK-modulated BLE packets via a proposed replica VCO-based GFSK modulator and an inductor-free SSB reflector. For downlink, the BLE packets are frequency down-converted passively by utilizing a reverse-whitened BLE tone followed by a proposed self-calibrated GFSK demodulator to recover the downlink data at ultralow power with improved robustness. A dual-linearly polarized microstrip patch antenna (DPMPA) is integrated to enable concurrent RF energy harvesting and communication in a wearable form factor. Implemented in 65-nm CMOS, the chip consumes $1.4~\mu $ W for downlink and $15.8~\mu $ W for uplink. Wireless tests demonstrated a 50 cm downlink and >3 m uplink ranges at 20 dBm EIRP.