Wide Power Range RF Energy Harvester for Powering Ultralow-Power Devices

Harvesting radio frequency (RF) energy is an attractive solution for powering ultralow-power (ULP) devices. However, harvesting efficiently from different RF power levels is still a challenge. This work presents a wide power range RF harvester composed of a rectifier circuit and a power management integrated circuit (PMIC). Such a wide range is achieved by associating two independent rectifiers in parallel, one specifically optimized for low RF powers. In the association, the inductive matching technique is employed in each rectifier. It consists of an inductive branch comprised of a lumped inductor and a short-circuited stub whose values are selected to minimize ohmic losses. The operation range is controlled via the inductive branch values and by following the optimal load of the rectifier circuit with the PMIC, based on the input power level. The harvester is designed at 889 MHz and manufactured by using off-the-shelf components. Measured efficiencies of 29% and 63% are obtained at −20 and 0 dBm, respectively, demonstrating the wide power range with high efficiency at low powers. At −20 dBm, the rectifier association keeps the PMIC active and delivers hundreds of nW at a regulated voltage of 1.8 V, which is suitable for ULP devices.