Analysis and Design of RF Energy-Harvesting Systems with Impedance-Aware Rectifier Sizing

Because of the interaction between the internal blocks of an RF energy harvesting (RFEH) system, sizing a rectifier only for high power conversion efficiency (PCE) is insufficient for improving global power harvesting efficiency (PHE). This paper analyzes and sizes the rectifier by taking its input and output impedances into account with a two-port model that combines the rectifier AC and DC characteristics. The AC characteristic in this model is used for impedance-aware rectifier sizing. We target a low input-impedance rectifier for better impedance matching between the receiver antenna and the rectifier. The DC characteristic describes the rectifier power loss allocation and estimates its maximum power point. A proposed parasitic-aware matching network sizing methodology predicts the PHE is finally limited by Ohmic loss in the matching network at a low incident power level. For overcoming this limitation, this paper also analyzes the impact of multiple rectifier stages on RFEH with a high peak-to-average power ratio (high-PAPR) incident waveform for improving the PHE. We design an RFEH prototype with a sized 28nm CMOS two-stage cross-coupled rectifier. Measurement results show sensitivity as low as -28.3 dBm with a peak PHE of 31.1% at -16.5 dBm 2.45-GHz high-PAPR incident power. It has sufficient high output impedance to prevent reverse leakage without the need for an additional self-gating circuit.