Micro Energy Harvesting Circuit Design For WBAN Application

With the rapid development of semiconductor technology, Wireless Body AreaNetwork (WBAN) which focuses on human body health has attracted more and moreattention of researchers from domestic and abroad. However, the problem of power supplylimits the progress to small size and portable device for WBAN. Therefore, this paperproposes a micro energy harvesting circuit based on the power needs analysis of WBANand aims to power zl70102which is designed by Zarlink company for WBAN application.This paper first introduces the methods of energy harvesting including thermalenergy harvesting, solar energy harvesting, RF energy harvesting and vibration energyharvesting. By comparing the advantages and disadvantages of various energy harvestingmethods, vibration energy harvesting is selected as the optimal solution for WBANapplication. Then the piezoelectric effect and the equivalent circuit model of piezoelectricare presented. After that, based on the design specifications, the circuit system adopts PulseFrequency Modulation (PFM), voltage feedback to control switch regulator in order toimprove energy efficiency. Finally, the main blocks including rectifier, bandgap voltagereference, oscillator and comparators are analyzed in detail and the entire micro energyharvesting is simulated in Cadence through SMIC0.18μm process.The simulated results show the output voltage of micro energy harvesting circuit isstable at1.8V, the maximum load current is5mA, volatge ripple is28mV, the powerefficiencies are93%at5mA full load and78%at50μA light load. Due to the storagecapacitor can obtain145μW energy from piezoelectric device, so the minimum equivalentharvesting energy is107μW which could basically satisfy the power needs of zl70102.