A Scalable N -Step Equally Split SSHI Rectifier for Piezoelectric Energy Harvesting With Low-Q Inductor

In piezoelectric energy harvesting, the large inherent capacitor ( $C_{\text {P}}$ ) of a piezoelectric transducer (PT) results in significant charge loss and low-power extraction. To improve the power extraction, various interface circuits using a flip process have been proposed, such as synchronized switch harvesting on inductor (SSHI) rectifier and synchronized switch harvesting on capacitor (SSHC) rectifier. The flip process reduces the influence of large $C_{\text {P}}$ and the charge loss by using external elements. However, to extract high power, each rectifier requires a bulky inductor with a high quality factor (Q) and numerous external capacitors, respectively, which increases the system’s volume. Therefore, to solve the tradeoff issue between the extracted power and the volume of the system, this article proposes a scalable N-step equally split synchronized-switch harvesting-on-inductor (ES-SSHI) rectifier. By splitting the flip process into equal N-step, the ES-SSHI rectifier reduces an inductor RMS current and conduction loss. Moreover, the duty signals of each split phase are regular and symmetric, which enables a single controller to generate multiple flip duty signals and allows for predicting the zero-crossing point of the inductor current, ultimately reducing the controller loss. The proposed system was fabricated in the 180-nm CMOS process. The measured results demonstrate that the proposed ES-SSHI rectifier achieves a power extraction improvement of 1170% over the full-bridge rectifier (FBR) even with a subcubic millimeter scale low-Q inductor, reducing the system’s volume.