Research And Design Of Reconfigurable Charge Pump Energy Harvester Based On MPPT

In recent years,the development momentum of the Internet of Things（IOT）has been continuously enhanced,technological innovations have emerged one after another,and application scenarios have been continuously enriched,becoming the key infrastructure supporting the development of the digital economy.Io T smart node usually contains loads such as sensor,signal processor,wireless transceiver,and energy storage element.Energy sources such as photovoltaic,thermoelectric,piezoelectric,radio frequency and biological are used to power nodes.Due to strict volume budgets,the output power of these energy sources is generally in the microwatt level.The energy harvesters convert and regulate the output voltages of the above energy sources to the target values,and perform maximum power point tracking（MPPT）.Common DC-DC converters include low-dropout linear regulator（LDO）,switched-inductance DC-DC converter and charge pump.LDO is applied to step-down conversion,which has the advantages of high integration and small area,however,the output voltages of energy sources are usually low,which need to be boosted by the converters to supply the loads.Switched-inductor DC-DC converter is used for boost or buck conversion and offer high power conversion efficiency at high throughput power,but at the expense of bulky off-chip inductor.The charge pump is also used in boost or buck conversion,and has high power conversion efficiency in the case of low throughput power.Charge pump is only composed of MOS transistors and capacitors,it can be integrated inside the chip and is more suitable for Io T smart node with strict volume budgets.The loads expect to obtain the maximum power,so that the energy storage element can be charged faster under light load,and the load voltage can be raised as much as possible to ensure the normal operation of the loads when the load is heavy.A practical challenge in the design of energy harvesters is that energy sources have environment-dependent properties,and the maximum power points depend on different environmental variables,such as light intensity and temperature.Therefore,the MPPT technology is required to implement measures such as input impedance modulation to increase the input power of energy harvester and reduce the loss as much as possible,so that it can continuously output the maximum power in the changing environment.Aiming at the problem that the MPPT accuracy of the two-dimensional MPPT technology formed by conversion ratio modulation and switching frequency modulation decreases with the increase of the maximum power point voltage,a reconfigurable charge pump energy harvester based on MPPT is proposed in this thesis,which has nearly continuous conversion ratio.Adopting the One-dimensional MPPT technology that combines coarse adjustment and fine adjustment of the conversion ratio,it can maintain sufficient MPPT accuracy in a wide range of input voltage and has stronger adaptability to changing environment.The main work completed by the thesis is as follows:（1）Discussed the working principle of basic charge pump and reconfigurable charge pump,analyzed the causes of charge pump loss,and proposed loss optimization schemes.（2）Took photovoltaic cell as an example to discuss the principle,model and output characteristics of energy sources,and MPPT algorithm,input impedance modulation technology and low power output power detection technology was discussed.（3）Designed the reconfigurable charge pump energy harvester circuit.The reconfigurable charge pump energy harvester is composed of reconfigurable charge pump,dual frequency oscillator,buffer capacitor voltage hysteresis controller and MPPT finite state machine.The reconfigurable charge pump energy harvester circuit was simulated under different conditions,and the reconfigurable charge pump layout was designed.The reconfigurable charge pump energy harvester designed in this thesis adopts 0.18μm CMOS process,having nearly continuous conversion ratio in the range of 1～2（15）/（16）,the input voltage range is 0.65～1.8V,the output voltage is 1.8V,and the dynamic peak efficiency with MPPT is 76%.The overall performance meets the design specifications.