On-chip starter circuit for switched-inductor DC-DC harvester systems

Because wireless microsystems can only incorporate tiny batteries, they typically exhaust stored on-board energy quickly. Fortunately, harvesting ambient energy is a viable means of extending their operational lifetimes, except starting and re-starting miniaturized microwatt harvesters from nocharge conditions is difficult. The challenge is drawing usable energy from millivolt signals under micro-scale constraints. This paper proposes a nonlinear on-chip starter that borrows the harvester´s steady-state inductor to start the system from nocharge conditions. Simulations show that the starter draws power from 250-500 mV to charge 100 pF to 3 V in 48 μs. The 100-pF temporary supply then powers the harvester´s 1-V, 4-μA controller to charge 100 nF by 100 mV in 65-μs cycles until the 100-nF battery charges enough to supply the system.