Herein, we present the design technique of a resonant rectifier for piezoelectric (PE) energy\nharvesting. We propose two diode equivalents to reduce the voltage drop in the rectifier operation,\na minuscule-drop-diode equivalent (MDDE) and a low-drop-diode equivalent (LDDE). The diode\nequivalents are embedded in resonant rectifier integrated circuits (ICs), which use symmetric bias-flip\nto reduce the power used for charging and discharging the internal capacitance of a PE transducer.\nThe self-startup function is supported by synchronously generating control pulses for the bias-flip\nfrom the PE transducer. Two resonant rectifier ICs, using both MDDE and LDDE, are fabricated in\na 0.18 �¼m CMOS process and their performances are characterized under external and self-power\nconditions. Under the external-power condition, the rectifier using LDDE delivers an output power\nPOUT of 564 �¼W and a rectifier output voltage VRECT of 3.36 V with a power transfer efficiency of\n68.1%. Under self-power conditions, the rectifier using MDDE delivers a POUT of 288 �¼Wand a VRECT\nof 2.4 V with a corresponding efficiency of 78.4%. Using the proposed bias-flip technique, the power\nextraction capability of the proposed rectifier is 5.9 and 3.0 times higher than that of a conventional\nfull-bridge rectifier.
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