This paper presents an all-NMOS RF-DC rectifier with internal$V_{\mathrm {TH}}$cancellation (IVC) technique to achieve an ultra-wide high-PCE input power range for RF energy harvesting. The all-NMOS topology replaces the PMOS transistor in the conventional cross-coupled rectifier with a diode-like NMOS transistor to obtain the maximum current driving capability while effectively reducing the reverse leakage current at higher input power, combining the strengths of diode-based and cross-coupled rectifiers. The IVC unit is used to compensate for the threshold voltage of the diode-like rectifying transistor on the output side and improve the PCE at low input power. As a result, the sensitivity and the input power range are improved simultaneously. The proposed rectifier is fabricated with a 0.18-$\mu $m standard CMOS technology. The measurement results show that the IVC all-NMOS rectifier achieves 55% PCE, −15.5 dBm sensitivity and 18.6 dB input power range when operating at 900 MHz with a 30 k$\Omega $load.

This brief presents a high-sensitivity battery-free radio frequency (RF) energy harvesting system with ultralow-power auxiliary modules. The proposed design implements two-stage energy conversion based on burst charging mode, achieving ultrahigh sensitivity by using an intermittent charging method that eliminates the charge pump’s loading effect on the RF rectifier. An all-nMOS RF--dc rectifier with internal${V}_{\mathrm {TH}}$cancellation (IVC) technique achieves an ultrawide high-power conversion efficiency (PCE) input power range for an RF energy harvesting. Furthermore, a${V} _{\mathrm {TH}}$-based voltage reference is introduced, enabling subthreshold operation of transistors with picowatt-level power consumption, thereby simultaneously improving both PCE and sensitivity. The proposed RF energy harvesting system is implemented with a 0.18-$\mu $m standard CMOS technology. The results show that the system achieves a 55% PCE, a −33-dBm sensitivity, and a 17-dB input power range at 2.4 GHz.

This paper presents a 6.78MHz reconfigurable four-phase dual-output series resonant rectifier that integrates hysteresis control and the triple-mode double-frequency current wave modulation (DFCWM) technique. The rectifier accomplishes AC-DC rectification and dual-output voltage regulation within a single power stage, achieving high efficiency and a reduced number of off-chip components. The combination of hysteresis control with the triple-mode DFCWM enables rectification and voltage regulation without crossover adjustments through four independent phases. Without altering the external LC resonant frequency, more uniform power conversion and reduced output voltage ripple are achieved, while also enhancing the transient response speed of the load. When simulating with a 0.18-μm CMOS process, the dual-output voltages can be adjusted to 1.1V and 2.2V, reaching a maximum output power of 0.7W with a peak power conversion efficiency (PCE) of 89.2%. Furthermore, a rapid transient load response can be observed when the load current varies between 20mA and 200mA.

This paper presents a triple-output piezoelectric energy harvesting (PEH) system with parallel synchronized switch harvesting on capacitors (P-SSHC) rectifier based on shared capacitors. By analyzing the principle of the P-SSHC rectifier, this paper supports the rationality of using shared capacitors to construct the multi-voltage conversion ratio (VCR) switch capacitor (SC) DC-DC converters. In addition, the adoption of a parallel structure in the multi-output SC DC-DC converters reduces the cross-regulation. Simulation results show that the proposed system not only has good input power adaptability (1/3X,1X,2X) but can also provide triple voltage (0.5V, 1V, 2V) with less cross-regulation. The maximum output power is 14.4μW when peak-to-peak open circuit voltage is 1.7V.

This paper proposes a piezoelectric energy harvesting interface circuit using multiple charge extractions and the multiple precharge (MCE-MPC) technique. This circuit is able to extract energy from PEH efficiently using a miniscule inductor and has the advantage of controllable precharge energy. It improves output power and extraction efficiency by using precharge and multiple transfers techniques. When the inductor value is 50μH, the output power of MCE-MPC is increased by 101.92% and 24.60% compared with synchronous electric charge extraction (SECE) and multi-shot SECE (MCE), respectively, and 7.62% compared with multiple charge extractions with bias-flip (MCEBF) when precharging the piezoelectric voltage to the same value. When the inductor value is 1mH, an extraction efficiency of 102.9% can be obtained by MCE-MPC.

This work presents the novel integration of a reconfigurable piezoelectric energy harvester array (RPA) with a parallel synchronized switch harvesting on inductor (P-SSHI) rectifier. The proposed design realizes maximum power point tracking (MPPT) by adjusting RPA with changes in vibration amplitude. Compared with the traditional interface systems based on monolithic piezoelectric energy harvester (PEH), this design can operate in a wider range of input voltage, removing the need for a DC-DC converter, essential in the traditional design. This adaptability eliminates the need for extra-passive components and reduces switching loss. RPA can be also configured in series to reduce the inherent capacitance of PEHs, effectively improving the extraction efficiency of P-SSHI rectifier. Simulations of this system show that the efficiency of the RPA/P-SSHI combined system can be kept above 66% within an input voltage range from 0.03V to 4.39V.

In piezoelectric energy harvesting (PEH), synchronous electric charge extraction (SECE) has the benefit of load independence. To reduce the energy dissipation on parasitic resistance, multi-shot SECE (MCE) was implemented to split the charge extraction process. In this paper, a multiple charge extraction with bias-flip (MCEBF) interface circuit is proposed. It not only reduces the dissipation in charge extraction but also enlarges the extractable energy of piezoelectric structure by adding a bias-flip action. MCEBF can also generate positive and negative voltage rails via buck-boost topology to supply power for double-rail devices. The analytical and experimental comparison among SECE, MCE, and MCEBF under different controls are also provided. In experiments, MCEBF offers a 57.3% improvement over SECE and 24% over MCE, in terms of harvested power.