The increasing demand in electronic portability imposes low power consumption as a key metric to analog and digital circuit design. Tunnel FET ( TFET ) devices have been explored mostly in digital circuits, showing promising results for ultra-low power and energy efficient circuit applications. The TFET presents a low inverse sub-threshold slope ( SS ) that allows a low leakage energy consumption, desirable in many digital circuits, especially memories. In Ultra-Low Input Power Conversion Circuits based on Tunnel-FETs , the TFET is explored as an alternative technology also for ultra-low power and voltage conversion and management circuits, suitable for weak energy harvesting ( EH ) sources. The TFET distinct electrical characteristics under reverse bias conditions require changes in conventional circuit topologies. In this book, ultra-low input power conversion circuits based on TFETs are designed and analyzed, evaluating their performance as rectifiers, charge pumps and power management circuits ( PMC ) for RF and DC EH sources.