A Fast Cold-Start Integrated System for Ultra-Low Voltage SC Energy-Harvesting Circuits

Energy-harvesting circuits are promising candidates to enable ultra low power Internet-of-Things devices. In the case of solar-powered circuits, they suffer from output voltage variations due to unstable incident light intensity. Those circuits require power management circuitry to supply a stable voltage to the main circuit despite the light-source variations. Self-starting the power management circuit from an ultra low-voltage (ULV) source is a challenging task, and this work introduces the design of a cold-start integrated system based on a ring-oscillator, clock-boosting techniques and a charge pump for use in an energy harvesting DC-DC converter for ULV applications. The cold-start circuit must provide a 650 mV, 10 µW signal to drive the main converter. It is designed in 180-nm CMOS technology and requires a minimum start-up voltage of 195.79 mV, providing a start-up time of 30.7 µs.