MPPT-Controlled Adaptive Reconfigurable 5.8GHz RF Energy Harvesting Front-End in 65nm CMOS

The range of input power levels that allow a RF energy harvester to produce an output level required to power a WSN node is limited. The limitation is caused by the losses arising from the static configuration of the RF energy harvester that is not ideal for a wide range of input power levels expected from RF energy sources. A dynamic RF energy harvester where both the matching network and rectifier are reconfigurable to adapt to the input power level improves the sensitivity and provides voltage regulation, extending the operating range. To implement this, the number of stages in the rectifier cascade and the input impedance produced by the matching network are modified. Several configurations could produce the required output, but the most efficient configuration for different input power levels is chosen using a Maximum Power Point Tracking (MPPT) mechanism to maximize the power harvested from RF sources. Simulation results for a design implemented in 65nm CMOS process show an improvement of around 17dB in dynamic range and up to 20% in efficiency for a dynamic RF energy harvester implementing MPPT compared to a static RF energy harvester in producing a 1V output using a 5.8GHz input. Silicon test results show that the performance of the dynamic rectifier is close to simulated results at around -8dBm, 5.8GHz RF input while providing a form of voltage regulation at high power input that increases dynamic range and removing the need for large voltage limiter circuits.