The Design Of Light Energy Harvest Circuit Based On Switch Capacitor In Dim Lighting

IoT smart node chips generally have low power consumption in the sleep state,an energy harvesting circuit can be used to convert external energy to supply power to the chip,reducing the energy consumption of the battery.Compared with other energy sources,solar energy has a higher power density and is an ideal energy harvesting source.In order to meet the all-weather and all-round energy supply of smart nodes,it is necessary to realize energy harvesting in dim lighting(300lux)environment.The implementation method of energy harvesting in dim lighting is systematically elaborated in this design.According to the output characteristics of single solar cell under low light intensity,a cold start circuit based on a dynamic charge transfer switch charge pump is designed,which can start at a minimum input voltage of 200m V.In order to adapt to the low power input of an external energy source,a boost circuit scheme of a switched capacitor structure is adopted,and a series-parallel topology with a configurable conversion ratio is used to raise the input voltage.By classifying the output voltage range(0.2V～0.7V)of a single photovoltaic cell,the clock circuit and the switch capacitor topology are adjusted at different voltages to obtain the boost conversion ratio,and the conversion efficiency of the energy harvesting circuit is improved.Finally,by adjusting the hysteresis of the cold start and the switched capacitor boost topology output voltage,the dual-voltage self-power supply of the energy harvesting circuit is realized,and the power supply stability of the circuit is improved.This design completed the energy harvesting circuit based on the TSMC 40nm process,with a layout area is 0.22mm~2.The post-simulation results show that under the full process corner,within the temperature range of-20～80℃,the cold start circuit can start at a minimum input voltage of 200m V and an input current of 40μA,with the output power of a monolithic photovoltaic cell under 300lux illumination is simulated.After the cold start is completed,the boost circuit first outputs 850m V,and then stably outputs a0.8V voltage through the linear regulator,which can provide a minimum load current of 1μA for always-on block circuit of smart node chips.At the TT corner and 27℃,the energy conversion efficiency of the harvesting circuit for continuous energy harvesting at an input voltage of 200mV and 400mV is 32% and 46%.