This paper presents a 60mV input voltage start-up system for thermoelectric energy harvesting. A new process tolerant inverter cell is proposed, which is functional at supply voltages as low as 60mV. Using the proposed unit cell, a ring oscillator has been implemented. The ring oscillator is followed by 40 charge-pump stages, an ultra-low-power level detector and a boost converter. The energy harvesting system can generate an output voltage of 1V and delivers a maximum power of 4.5 µW from a 60mV supply. This system has been implemented in a standard 0.18 µm CMOS technology, uses neither zero-threshold voltage (normally-on) NMOS nor MEMS switches and occupies 3.3 mm 2 .

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