| With the development of microelectronics technology in recent years,demand is growing for microelectronic system such as portable electronic devices and implantable medical equipment.However,the battery is still the main power supply for microelectronic system.Batteries cannot meet the needs because of its poor durability,pollution to the environment and material consumption.Moreover battery replacement has become extremely difficult especially for the working position which is difficult to touch(such as the human body).Therefore,the power supply technology has become a hotspot which can provide green,renewable,harmless energy.Now power consumption of microelectronic system has reduced from milliwatt to microwatt magnitude,so harvesting energy from its work environment and transforming it to electricity becomes one of the feasible solutions.Energy can be harvested from environment such as mechanical,thermal,light,electromagnetic,human body to replace traditional sources.One of the most popular methods of energy harvesting is by using piezoelectric material.Piezoelectric energy harvesting is attractive mainly due to its simplicity and universal.In this dissertation,based on the piezoelectric cantilever beam we mainly studied the equivalent circuit model of piezoelectric energy harvesting and its interface circuits.First,we briefly introduced the piezoelectric effect,two electromechanical coupling patterns 31 and 33.Using piezoelectric cantilever beam as analysis object,this dissertation established the model of piezoelectric cantilever beam and deduced the calculation formula of output power.We also analyzed the effects of the cantilever beam structure on the output power.The equivalent circuit model of piezoelectric cantilever beam is setted up and the output voltage and power of the equivalent circuit model with resistance is also analyzed.Then,based on the Switch-Only rectifier,a high efficiency self-resetting rectifier for piezoelectric energy harvesting systems is proposed.The rectifier increased the efficiency of energy conversion by using two switches to reset the transducer capacitor when the current I_P is zero.The active diode(operational amplifier+CMOS)is adopted to reduce the voltage drop along the conduction path and thereby increases the power extraction and conversion capability.Additionally,the control circuit for the proposed rectifier is simple and does not require an external supply voltage.The layout area is 320μm×180μm.The post simulation results show the voltage conversion efficiency can reach up to 98.2%and the maximum power conversion efficiency is 90.1%when the input current source I_P=100μA in parallel with internal capacitor C_P=25nF and internal resistor R_P=1MΩ.Furthermore,based on traditional rectifiers and threshold compensations,we do researches in the technique of substrate bias,the sub-threshold,DTMOS structure and self-powered to improve the performance of the rectifier.By using Cadence Spectre two ultra-low-voltage high-efficient CMOS active rectifiers are present for piezoelectric energy harvesting applications.When the input voltage amplitude is low enough,the circuit can automatically shut down by adopting input-powered,thereby avoiding unnecessary energy loss.The negative voltage converter respectively adopted substrate bias and DTMOS structure,effectively reduce the threshold voltage of MOS.By using a bulk-driven comparator,the lowest input voltage amplitude can be reduced to 0.2V.Based on standard SMIC 0.18μm CMOS technology,the two CMOS active rectifiers are tested and post simulated respectively.The results show that when the input voltage equals to 0.2V@100Hz with load resistance 40KΩ,the voltage conversion efficiency and the energy conversion efficiency of the rectifier using substrate biasing can reach up to86%and 85%respectively.The frequencies in the range of 10Hz-500Hz can be rectified.The voltage conversion efficiency and the energy conversion efficiency of the rectifier based on the DTMOS can be as high as 80%and 78%respectively when the input voltage equals to 0.18V.The work frequency is 10Hz-1KHz. |
