An MPPT-Integrated Bias-Flip Rectifier for Piezoelectric Energy Harvesting

Piezoelectric energy harvesting (PEH) is a promising approach to collecting ambient kinetic energy as the power supply for electronic devices. In many PEH designs, the maximum power point tracking (MPPT) technique is exploited to enhance the output power of the system. However, a typical PEH system requires a separate power stage for MPPT, which requires a large external rectified capacitor for MPPT operation and suffers from cascaded power efficiency loss. This paper presents an MPPT-integrated bias-flip rectifier where the MPPT and AC-DC rectifier are merged into one stage, resulting in fewer off-chip capacitors, faster MPPT, and less cascaded energy loss. The proposed circuit was fabricated in a $0.18 \mu \mathrm{m}$ CMOS process, and the measurement results show a $7.7 \times$ energy extraction enhancement.