A 2.6 $\mu \text{W}$ –1.2 mW Autonomous Electromagnetic Vibration Energy Harvester Interface IC with Conduction-Angle-Controlled MPPT and up to 95% Efficiency

This paper presents an IC optimized to interface small-scaled electromagnetic vibration energy harvesters. The interface IC tracks the optimum conduction angle of the implemented active AC-DC input stage, enabling maximum power point tracking without the need for a system clock, harvester disconnection, or any external sensor. The optimum conduction angle tracking control nominally requires 815 nW. An energy buffer can autonomously be charged via the interface, employing a hysteretic input voltage-controlled inductive DC-DC boost converter, to 4.2 V for IC input powers between 2.6 μW and 1.2 mW with a peak power conversion efficiency of 95%. The 4.2 V is even reached when harvesting from weak vibrations of only 0.2 m/s
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acceleration peak amplitudes and input voltages of around 570 mV. Buffer charging with up to 91% of the maximal available harvester power is accomplished, and cold startup is enabled. The IC prototype in 0.35 μm CMOS draws a quiescent current of 272 nA from the energy buffer at 4.2 V and a quiescent power of 639 nW at 3 V. In order to supply an application, such as a wireless sensor node, the IC can be configured to generate a regulated voltage and to ensure reliable operation by means of an overvoltage protection.