8uW to 1mW Input Power Management IC Design for RF Energy Harvester

Abstract

This master thesis project aims to design a power management block which is suitable for RF energy harvesting application with input power range from 8uW to 1mW. RF energy harvesting applications are low power Wireless Sensor Network or Transceiver with working duty cycle and average power consumption is from tens of uW to hundreds of uW. Based on the transceiver working condition, general power management block system can be designed in a two stages architecture including the Harvest Interface Stage and Load regulation Stage with storage element in between. The purpose of Harvest Interface is to regulated input voltage according to varying input power condition and Load regulation in system is to regulated output voltage for the target application. The Storage Element in between can store energy coming from Harvest Interface and discharge it according to the load. In terms of low input power situation (8uW in this project), the total power management system should be designed to be ultra low power loss. This project focused on the design of Harvest Interface Stage with the full bridge MOSFET rectifier to be the input of Harvest Interface and output connected to the Storage Element. Power loss estimation was done to evaluate topologies of Harvest Interface Stage. Then, inductive DC/DC boost converter was chosen to be the topology. Next, the switches control principle was analysed and low power switches control design was implemented to regulated input voltage of DC/DC boost converter. In addition, in order to track the varying input power, a power detector has been made which consists of 9bits ADC, DAC, RC integrator and Maximum Power Point Tracking [MPPT] digital design to continuously track the maximum power point by comparing new cycle power value with previous cycle power value. The output of power detector will give a input voltage reference for DC/DC boost converter to regulate its input voltage. The saturated input voltage reference indicates the maximum PCE from rectifier to DC/DC boost converter. Finally, Schematic and Layout were done in this project and simulations were implemented for both schematic and layout. Maximum Power Point Tracker [MPPT] can track 8uW power source with only 1 percent power loss inaccuracy and for 1mW power source, 7.5 percent inac- curacy power loss will occur. DC/DC converter [Without MPPT] power conversion efficiency post layout simulation(RC Extraction) for 8uW input power is 70 percent and 89 percent for 1mW input power source.