High-Efficiency Ultrasound Energy Harvesting Interface With Auto-Calibrated Timing Control From −25 °C to 85 °C

This work presents a high-efficiency ultrasound energy harvesting interface with auto-calibrated timing control, featuring: 1) the proposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{\text {P}}$ </tex-math></inline-formula> auto-calibration, consisting of the half bias-flip time (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t_{\text {half}}$ </tex-math></inline-formula>) detection and adaptive closed-loop time calibration (ACTC) to improve the system’s robustness against piezoelectric transducer (PZT) materials and environmental variations; 2) the proposed charge recycling (CR) bootstrapping driver to reduce conduction loss and improve the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{\text {P}}$ </tex-math></inline-formula> auto-calibration accuracy as well as the peak voltage flipping efficiency (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\eta _{\text {flip}}$ </tex-math></inline-formula>); and 3) the proposed coarse detection and fine calibration technique to eliminate the inherent timing offset and increase the acceptable input excitation frequency range. The fabricated chip prototype in 0.18-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>m silicon on insulator (SOI) CMOS process can adapt to both PZT5A (nominal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C_{\text {P}}}~{\sim }~114$ </tex-math></inline-formula> pF) and PZT5H (nominal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C_{\text {P}}}~{\sim }~190$ </tex-math></inline-formula> pF) and is capable of operating over a wide temperature range from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${-} 25~{^{\circ }}$ </tex-math></inline-formula>C to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$85~{^{\circ }}$ </tex-math></inline-formula>C. The proposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{\text {P}}$ </tex-math></inline-formula> auto-calibration and CR bootstrapping driver can improve the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\eta _{\text {flip}}$ </tex-math></inline-formula> to as high as 93.6% at an output power of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$496.6~{\mu }$ </tex-math></inline-formula>W. With the proposed coarse detection and fine calibration technique, this work demonstrates a high measured peak power conversion efficiency (PCE) of 94.5%, corresponding to a ~23% improvement when compared with the prior ultrasound energy harvesting interface while achieving a favorable figure of merit (FoM) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8.13{\times }$ </tex-math></inline-formula>.