Startup And Optimization Techniques For Energy Harvesting Interface Circuits With Ultra-low Input Voltage

The 4th Industrial Revolution has been accelerated by technology breakthroughs to enable the Internet of Things(IoT)where millions of devices can be connected together and to the Internet.With the development of the Internet of Things,device scale is getting smaller,and its application occasions are getting wider.A large number of Internet of Things devices can be seen put into use in wearable devices,implanting medical devices,smart home and other fields.For these wireless nodes,the traditional wired power supply scheme is obviously no longer applicable.When wired power becomes clearly not usable for a large number of IoT devices,battery is considered a better option for inexpensive and reliable source with the popularity and advantages of Li-Ion battery technologies.However,as operation time and performance of IoT devices increases,larger battery capacity is required,leading to undesirably larger size and weight of the energy storage and the host systems.Therefore,finding a source of power which is clean,reliable and virtually unlimited has become a crucial need that drives attention of researchers around the world.In recent years,many research teams have proposed to use environment friendly energy resources instead of traditional batteries to power wireless sensor devices,such as solar cell,thermoelectric generator(TEG),piezoelectric transducer(PZT)and so on.Among these alternative sources of power,thermoelectric generators have attracted more and more attention in wearable device applications due to advantages of high power density,low power,low cost and suitability for small size devices.Although TEG can generate microwatt-level power to power wearable devices,its output voltage is too low.Therefore,how to ensure that the energy harvesting system can start up normally and enter stable working state under ultra-low input voltage has become an important research content in the design of the energy harvesting system.In this paper,an energy harvesting interface circuit is designed for Thermoelectric energy harvesting system and other DC output energy harvesting systems.In order to ensure that the system can work normally under the low input voltage,the designed system uses a two-stage self-start circuit to realize the normal start of the circuit and enter stable working state without battery.In order to obtain the maximum power from TEG,the circuit is integrated with maximum power point tracking(MPPT)module.In order to improve the energy conversion efficiency,the designed circuit adopts the zero-current switch(ZCS)technology to reduce the transistor loss and improve the conversion efficiency of the boost converter.In addition,the designed system also includes ultra-low power reference generator,ultra-low power and low temperature coefficient main clock source,voltage detection circuit and other modules.The energy harvesting interface circuit with ultra-low input voltage designed in this paper adopts 55nm CMOS process,the lowest self-start voltage is 220mV,the lowest steadystate operating voltage is 15mV,and the output voltage is 1.2V.When the TEG open circuit voltage is 120mV,the maximum conversion efficiency of the Boost converter is 77.74%.