Design of Oscillator and Charge Pump for the Startup of Ultra-Low-Voltage Energy Harvesters

This paper presents a design procedure for the minimization of the startup voltage of energy-harvesting boost converters. The analysis of both an LC oscillator and a charge pump under ultra-low-voltage operation, based on the physics-based MOSFET and diode models, is performed. Considering the interaction between these two blocks, a routine that minimizes the startup voltage of boost converters is proposed. The technique provides the oscillator characteristics, number of stages and sizing of the charge-pump devices. The methodology, applied to a cold startup in a 180 nm CMOS technology, provides a fully integrated design with a minimum input voltage of only 53 mV, for an output of 500 mV at 100 nA of current consumption.