Abstract
This paper proposes an on−chip, ultra−low−power cold−start circuit for a low−voltage, fast start−up of a boost converter for autonomous thermal energy harvesting from slight temperature differences. An improved charge transfer obtained from a Schmitt trigger (ST) clock booster enables voltage multiplication of the low input voltage during a cold start, providing low power consumption and a high boosting ratio. The start−up charge pump operates with an on−chip clock generated by an ultra−low−voltage ring oscillator that comprises modified Schmitt trigger (ST) delay cells, as previously reported by the authors. The proposed start−up architecture combines a previously reported advantageous one−shot control mechanism to start the boost converter efficiently. Theoretical analysis supports the proposed start−up scheme, and it is implemented in 22 nm FD−SOI CMOS technology. Simulation results show that, when combined with an inductive boost converter, the proposed harvesting system starts operating in 1.2 s when harvesting energy from a 48 mV DC source. To the best of the authors’ knowledge, 48 mV is the lowest reported minimum start−up voltage for a simulated fully integrated start−up circuit operating without additional sources of energy. The complete primary boost converter that was simulated requires a standard 82 μH off−chip inductor.