An all-digital, CMOS zero current switching circuit for thermal energy harvesting

This paper introduces an all digital, CMOS zero current switching (ZCS) circuit that enables a wide dynamic and a fine resolution zero current detection range for high gain (50 mV input to 1.35 V output) inductor-based DC-DC converter. Using only a 3-bit design, more than 1.5 μs dynamic range with 50 ns delay resolution is achieved. The prototype chip is designed and simulated using 65 nm low-power CMOS technology and occupies less than 0.04 mm² area. Post-layout SPICE simulations confirm that 85% efficiency can be achieved for the overall system. The proposed circuit is part of a system that targets energy harvesting from human body thermal energy to enable long lifetime operation for wearable and biomedical devices.