In RF energy harvesting, network architectures employ a hub as both a radiating source and data collector. Because an RF harvester is implemented through a multi-stage rectifier, however, its sensitivity is largely dictated by the threshold voltage of the rectifier diodes or transistors. To compensate for this limitation, a CMOS RF energy harvester based on a multi-stage rectifier for efficient conversion of alternating current (AC) to DC power has been presented by Giuseppe Papotto, Francesco Carrara, and Giuseppe Palmisano from Italy's Universit di Catania.
The circuit is based on a multi-stage rectifier that uses a fully passive, threshold self-compensation scheme. To achieve threshold compensation, the designers can exploit the inherent properties of the voltage waveforms at the nodes of the rectifying chain. To maximize the harvester's overall power-conversion efficiency, the researchers also propose a computer-aided-design (CAD) oriented design methodology.
The researchers designed a 915-MHz harvester with an integrated input-matching network and 17-stage self-compensated rectifier. It was fabricated in 90-nm CMOS. The system's rectifier can deliver a 1-V output to a capacitive load from an input of just -24 dBm. When driving a 1-MO load, the device can supply a 1.2-V output with just -18.8-dBm input power. See "A 90-nm CMOS Threshold-Compensated RF Energy Harvester," IEEE Journal Of Solid-State Circuits, Sept. 2011, p. 1985.