This article proposes a novel eight-phase self-bias-flip piezoelectric energy harvesting interface with charge recycling and reusing (SBFRR) and a switched-piezoelectric energy harvester (PEH) dc–dc (SPDC) converter. The proposed scheme innovatively utilizes the inherent capacitors ( CP ) of four PEHs as energy sources, flying capacitors, and flipping capacitors for time-sharing reuse to achieve both a high-voltage flipping and dc–dc conversion efficiency, while avoiding the use of extra energy reservoirs. The design is fully integrated and fabricated in standard 0.18- μ m CMOS. Measurement result demonstrates that the voltage flipping efficiency of up to 80% is achieved. Compared with the ideal full-bridge rectifier (FBR), the measured maximum output power improving rate (MOPIR) can be increased to 4.88 × . In addition, with the four CP serving as flying capacitors to achieve SPDC conversion for maximum power point track (MPPT), an MOPIR of > 3.5 × can be maintained with a PEH input voltage from 0.78 to 4.9 V.

Synchronized switch harvesting on inductor (SSHI) is an efficient active rectifier to extract energy generated from piezoelectric transducer in piezoelectric energy harvesting system. Unlike passive rectifiers, SSHI rectifiers require a power supply to drive synchronized switches. Unfortunately, there is no stable supply when the system starts from the cold state. Most designs let the system work as a passive full bridge rectifier (FBR) to charge power capacitor until a supply is available. However, a FBR requires high open-circuit voltage (VOC) and the FBR’s output voltage cannot go over VOC. This prevents the system from starting the SSHI rectifier if VOC is low. This paper proposes a new transducer reconfiguration design to lower the required VOC by 4 $\times$ to start up the SSHI system from the cold state. The proposed system is designed in a 0.18$-\mu$m BCD process and post-layout simulations show that the successful cold-startup under low VOC voltage.

Owing to the advancement of vibration energy harvesting technology, many motion-powered battery-free Internet of things (IoT) applications have been reported in recent years. Since the ambient energy is usually weak, these IoT devices (a) mostly operate in intermittent or burst mode. The operation of these devices heavily depends on the level of stored energy. Conventional energy-aware solutions are carried out based on discrete general-purpose comparators or analog-to-digital converters (ADC) inside the system on chip (SoC) to monitor the storage level. Their power consumption is considerable in a low-power system. This paper presents a new energy-aware circuit, which can wake up or turn off the IoT devices according to the stored energy. Its standby quiescent current is at the sub-$\mu$A level. The proposed circuit also provides a regulated output voltage for IoT applications. This design is built with discrete analog components. It is low cost and has high feasibility. It is compatible with different kinds of micro-power generators.