The key to self-powered technique is initiative to harvest energy from the surrounding environment. Harvesting energy from an ambient vibration source utilizing piezoelectrics emerged as a popular method. Efficient interface circuits become the main limitations of existing energy harvesting techniques. In this paper, an interface circuit for piezoelectric energy harvesting is presented. An active full bridge rectifier is adopted to improve the power efficiency by reducing the conduction loss on the rectifying path. A parallel synchronized switch harvesting on inductor (P-SSHI) technique is used to improve the power extraction capability from piezoelectric harvester, thereby trying to reach the theoretical maximum output power. An intermittent power management unit (IPMU) and an output capacitor-less low drop regulator (LDO) are also introduced. Active diodes (AD) instead of traditional passive ones are used to reduce the voltage loss over the rectifier, which results in a good power efficiency. The IPMU with hysteresis comparator ensures the interface circuit has a large transient output power by limiting the output voltage ranges from 2.2 to 2 V. The design is fabricated in a SMIC 0.18 μm CMOS technology. Simulation results show that the flipping efficiency of the P-SSHI circuit is over 80% with an off-chip inductor value of 820 μH. The output power the proposed rectifier can obtain is 44.4 μW, which is 6.7× improvement compared to the maximum output power of a traditional rectifier. Both the active diodes and the P-SSHI help to improve the output power of the proposed rectifier. LDO outputs a voltage of 1.8 V with the maximum 90% power efficiency. The proposed P-SSHI rectifier interface circuit can be self-powered without the need for additional power supply.

In this paper, a power-enhanced active rectifier with high precision of current detection for piezoelectric energy harvesting (PEH) system is presented. A traditional two-stage active rectifier is adopted, which includes a first-stage negative voltage converter and an active diode. A comparator with offset control technique is proposed; thus the input-referred offset voltage of the proposed comparator can be less than 1[Formula: see text]mV. The current detected accuracy of the proposed offset-controlled comparator (OCC) is improved by more than 10 times over a traditional comparator. Output oscillations of the OCC are dramatically reduced attributing to the high precision of current detection. In addition, the OCC is also able to prevent the reverse leakage current. The design is implemented in an SMIC 0.18[Formula: see text][Formula: see text]m standard CMOS technology with a chip area of 0.22[Formula: see text]mm2. The measurement results show that the maximum output power, power conversion efficiency and figure of merit are 23.3[Formula: see text][Formula: see text]W, 90%, and 0.9, respectively, when the open-circuit voltage is 2.4[Formula: see text]V. The proposed rectifier can be self-powered without the additional external supply.

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