A Multi-Step Charge Transfer Interface Circuit Extracting Maximum Input Power from Piezoelectric Energy Harvester

We present a power-efficient interface circuit to extract the maximum possible input power from a piezoelectric energy harvester using a multi-step charge transfer (MSCT) technique. In this proposed article, MSCT pre-charges the piezoelectric capacitance, flips the piezoelectric output voltage, and extracts the stored charge in multiple stages. It improves the end-to-end power efficiency of the rectifier by reducing the conduction loss of the power converter stage while extracting the maximum possible stored energy across the piezoelectric intrinsic capacitance for a given CMOS process. The proposed rectifier has been designed and simulated in a 180 nm CMOS node. It extracts 14.39 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{W}$</tex> output power in one step and 16.34 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{W}$</tex> output power in four steps for the same input power. The MSCT achieves a maximum power efficiency of 68.5% and 83% with a 47 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{H}$</tex> and 220 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{H}$</tex> inductor, respectively. The simulation results show that the MSCT with four steps achieves an improvement of 13.85% compared to the single-step charge transfer in terms of power efficiency.