Research And Design Of AC-DC-DC Booster Used In Micro Energy Harvesting

In the past few years,the development of wireless sensor networks and communication nodes has aroused great interest of researchers.The wireless sensor networks have a positive impact on many aspects of our human existence.However,the sensor is facing severe challenges in power supply.Therefore,how to extract useful power from the surrounding environment for sensor has aroused widespread concern.Vibration energy conversion is one of the effective ways to collect energy.A piezoelectric energy harvesting and management circuit is presented in this paper.The main work done the following:(1)The collection structure of vibration energy and the research status of piezoelectric energy management circuit are analyzed in detail,and their development trends are also introduced.(2)The equivalent model of piezoelectric micro-generator is analyzed,and the working principle of AC-DC rectifier and DC-DC booster circuit for vibration energy collecting circuit is expounded.(3)A high efficiency,wide input voltage amplitude range rectifier is designed.The rectifier consists of a pair of cross-coupled connected NMOS transistors and two active diodes.The crosscoupled transistors function as switches with only a small voltage drop when either of them is turned on.The active diodes are two comparators controlled PMOS transistors work as ideal diodes with even no voltage drops and no reverse current.When the amplitude of the input voltage is 0.5V and the frequency is 100 Hz,the voltage conversion efficiency and the energy conversion efficiency of the rectifier can reach 98% and 95%,respectively.And it can work at a wide range of input voltage amplitudes of 0.45 V up to 1.8V.High gate-source breakdown voltage process can be used to enlarge the maximum input voltage amplitude without decreasing the efficiency.(4)A digitally controlled boost converter is designed based on the high performance of pulsefrequency modulation under low-power load.The booster converter is responsible for boosting the low voltage from the rectifier to a regulated DC voltage for the sensor power supply.This circuit works in a discontinuous conduction mode.By detecting the voltage of the node,the drive signal is controlled to break off when the inductance current is zero.When the input voltage is 500 mV and the output is 1.8V,the energy conversion efficiency of the circuit can reach 85%.(5)Additional,this paper presents a low power reference voltage source.When the power supply is 0.9V,the temperature coefficient is 8.67 ppm /℃,and the power consumption is only 5n W.The cadence specter simulation result under a standard 0.18μm CMOS process shows that the output voltage can be basically stabilized at 1.8V and the energy conversion efficiency of the system can reach 80% under a 0.5V input amplitude with 100 Hz frequency,and the ripple voltage can be controlled within 25 mV.