A low-power integrated power converter for an electromagnetic vibration energy harvester with 150 mV-AC cold startup, frequency tuning, and 50 Hz AC-to-DC conversion

This paper demonstrates the first fully-functional integrated power converter designed to interface a MEMS-based electromagnetic (EM) vibration energy harvester for near-50 Hz operation. The IC accomplishes (i) cold startup from a 50 Hz-150-mV-peak AC input to a 1.1-V output, (ii) conjugate impedance matching for maximum power extraction along with resonant frequency tuning and (iii) input-AC-to-output-DC voltage conversion. Cold startup is achieved using an on-chip Meissner oscillator with an off-chip transformer. Thereafter, a self-timed current-feedback-based H-bridge circuit is turned on for conjugate impedance matching with on-chip control and an off-chip microcontroller for impedance synthesis. The regular-operation H-bridge circuit delivers 820 uW to a load capacitor at 71% efficiency at resonance. It also performs frequency tuning to deliver 650 uW (57%-efficiency) at 50% off-resonance, thereby demonstrating robustness to possible harvester-resonance variations due to manufacturing tolerances. This makes it the first demonstration of a full-system low-power interface IC for vibrational energy harvesters. The prototype is fabricated in 0.18 um CMOS process with an active area of 1.5 mm ² .