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A miniature and high-efficiency interface circuit based on parallel synchronous switch harvesting on capacitors (P-SSHC) for piezoelectric energy harvesting (PEH) is proposed in this paper. This interface circuit consists of a two-stage synchronous rectifier and the P-SSHC circuit. The two-stage synchronous rectifier, composed of a negative voltage converter (NVC) and an active diode (AD), achieves higher efficiency compared with the full-bridge rectifier (FBR). In addition, the two-stage synchronous rectifier detects the zero-crossing moment of the input current; therefore, an extra current zero-crossing detection circuit is eliminated, which simplifies the structure of the interface circuit, reduces power consumption and improves peak converting efficiency. The P-SSHC circuit aims to improve the power extraction capability of the rectifier. The P-SSHC achieves considerable voltage flipping efficiency with very small volume compared to the parallel synchronized switch harvesting on inductor (P-SSHI), which is more suitable for volume sensitive applications. The proposed interface circuit is designed in SMIC 0.35[Formula: see text][Formula: see text]m CMOS process. Simulation results show that it achieves a [Formula: see text] output power improvement compared with FBR for the case of a 3.4[Formula: see text]V open-circuit voltage, the voltage flipping efficiency is as high as 83.6% and the peak power converting efficiency is up to 91.5%. The overall volume of the capacitors used in this paper is only 0.6[Formula: see text]mm3, which is much smaller than the inductor used by conventional P-SSHI interface circuit.

This paper presents a two-stage synchronous rectifier interface circuit for piezoelectric energy harvesting (PEH) system. The proposed rectifier includes a first-stage negative voltage converter, a second-stage adaptive on-resistance active diode, and combines a precise switch-on-time controlled P-SSHI circuit. The traditional active two-stage synchronous rectifier has lower current detection accuracy and hardly achieves high efficiency rectification over a wide input current range. An adaptive on-resistance active diode (AOR active diode) is proposed to replace the traditional active diode to achieve higher current zero-crossing detection accuracy, improve the input current range and the output power of the rectifier. The proposed diode allows the rectifier to maintain high rectification efficiency over a wider input current range. Further, a parallel synchronized switch harvesting on inductor (P-SSHI) with precise switch-on-time controlled circuit is proposed to achieve higher voltage flipping efficiency and improve the power extraction capability of the rectifier. By using the AOR active diode and the P-SSHI with precise switch-on-time controlled circuit, a good performance improvement has been achieved for the proposed interface circuit. The design is fabricated in an SMIC 0.35[Formula: see text][Formula: see text]m standard CMOS technology with a die size of [Formula: see text][Formula: see text]mm2. The simulation results indicate that the proposed circuit achieves more than 80% power converting efficiency and its peak efficiency is 85%. The current zero-crossing detection accuracy of the proposed AOR active diode is less than 10[Formula: see text][Formula: see text]A. The proposed PEH interface circuit extracts up to 2.81 times more output power compared with a traditional rectifier. The voltage flipping efficiency of the P-SSHI circuit is up to 90%, which can effectively improve the power extraction capability of the rectifier. Moreover, the proposed circuit can be self-powered and cold started up.