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Energy harvesting techniques provide solutions for powering battery-free circuits or even for charging storage elements such as batteries or super capacitors. In this paper a self-starting switched-capacitor approach based on three-stage charge pump that is appropriate to thermoelectric and photo-voltaic energy harvesting, is carried out in a 28 nm ultra-thin buried oxide (UTBB) fully-depleted silicon-on-insulator (FD-SOI) CMOS technology. By taking advantage of the FD-SOI substrate characteristics, the forward-body-biasing (FBB) technique is applied in order to improve switch conductances. In addition, a sizing exploration of standard N-type and flipped-well P-type devices operating as switches is advanced, in order to provide optimum balance between their conductances. Extensive simulation results validate the proper operation of the charge pump at a minimum input voltage of 150 mV, and show a maximum efficiency peak of 63.3% at an input voltage of 350 mV and load a current of 500 nA. [ABSTRACT FROM AUTHOR]

This paper presents a low-profile and autonomous piezoelectric energy harvesting system consisting of an extraction rectifier and a maximum power point tracking (MPPT) circuit for powering portable electronics. Synchronized switch harvesting on capacitor-inductor (SSHCI) technique with its unique two-step voltage flipping process is utilized to downsize the ponderous external inductor and extend application areas of such harvesting systems. SSHCI implementation with small flipping inductor-capacitor combination enhances voltage flipping efficiency and accordingly attains power extraction improvements over conventional synchronized switch harvesting on inductor (SSHI) circuits utilizing bulky external components. A novel MPPT system provides robustness of operation against changing load and excitation conditions. Innovation in MPPT comes from the refresh unit, which continually monitors excitation conditions of piezoelectric harvester to detect any change in optimum storage voltage. Compared with conventional circuits, optimal flipping detection inspired from active diode structures eliminates the need for external adjustment, delivering autonomy to SSHCI. Inductor sharing between SSHCI and MPPT reduces the number of external components. The circuit is fabricated in 180 nm CMOS technology with 1.23 mm2 active area, and is tested with custom MEMS piezoelectric harvester at its resonance frequency of 415 Hz. It is capable of extracting 5.44x more power compared to ideal FBR, while using $100~\mu $ H inductor. Due to reduction of losses through low power design techniques, measured power conversion efficiency of 83% is achieved at 3.2 V piezoelectric open circuit voltage amplitude. Boosting of power generation capacity in a low profile is a significant contribution of the design. [ABSTRACT FROM AUTHOR]

This paper proposed a high efficiency boost converter targeting thermoelectric generator energy harvesting. The proposed converter adopts the critical conduction mode rather than the discontinuous mode to reduce the conduction loss, which can improve the peak efficiency at high input power. To reduce the minimum input voltage, an adaptive on-resistance switch, which can automatically change the high side and low side on-resistance according to the input voltage, is used. To maximize the output power, a maximum power point tracking circuit is designed to track the internal source resistance. Radio frequency (RF) kick-up and low voltage startup are used to improve the cold start voltage. The proposed converter is implemented in a 0.18- $\mu \text{m}$ standard CMOS process, which occupies a chip area of about 0.48 mm2. Measurement results show that the peak efficiency of the converter can be up to 90.8% and 60% at 180 and 20 mV of the open-circuit voltage, respectively. Owing to the cold startup circuit, the proposed converter can start successfully with 260-mV open-circuit voltage or −16-dBm RF input. Moreover, the open-circuit voltage can be further lowered to 12 mV with 1.5- $\mu \text{W}$ output power after startup. [ABSTRACT FROM AUTHOR]

An efficient self-powered synchronous electric charge extraction CMOS interface circuit dedicated to piezoelectric harvesters is proposed in this paper. Self-powered peak detection (PKD) and switch circuits are used to reduce quiescent current so that the backup or pre-charged power can be saved. A new low phase lag (LPL) PKD circuit is designed to improve the synchronous extraction efficiency, which only requires one detection capacitor to perform positive and negative PKD. The circuit can be set at general mode (G-mode) or LPL mode (LPL-mode). Under LPL-mode, the phase lag can be reduced typically by 50%, the synchronous extraction efficiency can obtained up to 94%, while the output power can reach 659~\mu \textW when the piezoelectric transducer original open-circuit voltage V\mathrm{ oc,org}=5 V, which is 3.56 times of that of full-bridge rectifier standard energy harvesting circuit at the maximum power point. The minimum harvesting startup voltage is 1.7 V and is independent of the energy storage capacitor voltage V\mathrm{ DC} . The harvesting efficiency can still reach 71.3% at V\mathrm{ oc,org}=5 V. The size of the active area is 0.5 mm2 in a 0.18- \mu \textm CMOS technology. Circuit may be invoked as a functional block for energy autonomous wireless sensor network node of the Internet of Things. [ABSTRACT FROM PUBLISHER]

This paper presents a piezoelectric-based power management solution for battery-free wireless remote switches (BWSs). The proposed BWS IC, including a piezoelectric (PE) energy harvester and a buck converter, can collect the energy generated by a single PE-button press, and then supply that energy to a wireless transmitter to send a message. By combining a rectifier using the synchronized switch harvesting on inductor technique and a 6:1 series–parallel switched-capacitor converter, the proposed PE energy harvester can maximize the collected amount of energy, while supplying it at a low output voltage. In addition, by employing a switching-based start-up scheme and a variable ON-time pulse-frequency modulation scheme, the proposed buck converter can reduce the loss associated with charging the output capacitor during start-up, and then deliver the largest possible energy to the load, while maintaining low voltage ripples and high-power efficiency. A prototype BWS IC fabricated with high-voltage 250-nm CMOS technology was shown to be capable of harvesting a total energy of 246~\mu \textJ from a single button-pressing of a 300-mm2 lead magnesium niobate-lead titanate PE disc. More than 200~\mu \textJ was delivered to the load, sufficient to transmit a 4-B-long message via a 2.4-GHz wireless USB channel over a 10-m distance. [ABSTRACT FROM AUTHOR]

This paper presents a new method for detecting and reversing the polarity of a low-voltage thermoelectric generator (TEG) in inductor-based converters. The proposed technique makes use of the inductor response to a voltage change due to the flip in the TEG polarity. The inductor voltage provides two distinguishable states which correspond to the normal and the reversed TEG polarity. A switch matrix circuit is then used to correct the polarity by physically reversing the TEG connection. The detection circuit along with the switch matrix provide a positive input voltage from the TEG to the inductor-based converter. The proposed technique is an efficient polarity detection with all-digital implementation, fully integrated, small area and power overhead. The prototype chip is fabricated in 65-nm CMOS and occupies an area of 0.09 mm2. Measurement results confirm a maximum efficiency of 70% at 50 mV TEG voltage and 40~\mu \text A output current. The proposed technique is part of an autonomous thermal energy harvesting system that detects and corrects the TEG polarity. [ABSTRACT FROM AUTHOR]

This paper presents a piezoelectric energy harvesting circuit, which integrates a Synchronized Switch Harvesting on Inductor (SSHI) circuit and an active rectifier. The major design challenge of the SSHI method is flipping the capacitor voltage at optimal times. The proposed SSHI circuit inserts an active diode on each resonant loop, which ensures flipping of the capacitor voltage at optimal times and eliminates the need to tune the switching time. The diodes of the SSHI circuit are also used as a rectifier to further simplify the controller. The key advantage of the proposed circuit is a simple controller, which leads to low power dissipation of the proposed circuit to result in high efficiency. The proposed circuit is self-powered and capable of starting even when the battery is completely drained. The circuit was fabricated in BiCMOS 0.25~\mu \text m technology with a die size of 0.98 \times 0.76 mm2. Measured results indicate that the proposed circuit increases the amount of power harvested from a piezoelectric cantilever by 2.1 times when compared with a full bridge (FB) rectifier and achieves a power conversion efficiency of 85%. The proposed circuit dissipates about 24~\mu \text {W} while the controller alone only 1.5~\mu \text {W}$ . [ABSTRACT FROM AUTHOR]

A maximum-power-point-tracking DC-DC boost converter to harvest energy from sub-\muW power sources is presented. For available input-power levels below 1 \muW, voltage boosting is achieved by operating all circuits in the sub-threshold region, and by switching the DC-DC converter at tens of Hz, thereby reducing switching losses. The paper further explores the possibility of energizing the DC-DC inductor for an optimum duration, such that switching and resistive losses are minimized. The sub-\muW energy harvesting circuit uses an area of 0.2 mm^2 on a standard 180 nm CMOS process, and utilizes an auxiliary voltage source for start-up. The designed and fabricated system is more than 50% efficient when the available power is greater than 2 \muW. The circuit can harvest energy whenever the available power is more than 0.3 \muW. Efficiency at 0.3 \muW is 25%, at 0.5 \muW is 37% and at 1 \muW is 48%. The complete IC consumes 50 nA for internal operations and the input voltage can be as low as 70 mV. [ABSTRACT FROM PUBLISHER]

The design and analytical modeling of a high efficiency energy harvester comprising a passive voltage-boosting network (VBN) and a switching charge pump rectifier (CPR) is presented in this paper. To improve the power conversion efficiency (PCE), the VBN increases the voltage at the input of the CPR and provides control signals for switching. Unlike traditional Schottky and diode-connected MOS transistor rectifiers, the proposed orthogonally switching CPR (OS-CPR) comprises MOS transistors as voltage-controlled switches. Analytical models for the OS-CPR are developed and presented. Circuit-level optimization techniques are employed to reduce conduction and switching losses. Simulated in a 90 nm standard CMOS technology (IBM 9RF), a 5-stage 915 MHz OS-CPR achieves a dc voltage of 1.35 V and a PCE of 11.9% with a 1 M\Omega load at -18.2 dBm available input power (PS,AV). To show technology scalability of the design, the OS-CPR is also validated using AMS 0.18 \mum high-voltage (HV) CMOS technology. When benchmarked with traditional rectifiers, the OS-CPR (under similar conditions) achieves a higher PCE and a higher output dc voltage. The OS-CPR is easily scalable to operate over multiple sub-GHz ISM frequency bands. [ABSTRACT FROM PUBLISHER]

The potential application space for miniaturized systems like wireless microsensors is expansive, from reconnaissance mission work and remote sensors to biomedical implants and disposable consumer products. Conforming to microscale dimensions, however, constrains energy and power to such an extent that sustaining critical power-hungry functions like wireless communication is problematical. Harvesting ambient kinetic energy offers an appealing alternative, except the act of transferring energy requires power that could easily exceed what the harvester generates in the first place. This paper reviews piezoelectric and electrostatic harvester circuits, describes how to design low-power switched-inductor converters capable of producing net energy gains when supplied from piezoelectric and electrostatic transducers, and presents experimental results from prototype embodiments. In the electrostatic case shown, the controller dissipated 0.91 nJ per cycle and the switched-inductor precharger achieved 90.3% efficiency to allow the harvester to net a gain of 2.47 nJ per cycle from a capacitor that oscillated between 157 and 991 pF. The piezoelectric counterpart harnessed 1.6 to 29.6 \mu \W from weak periodic vibrations with 0.05–0.16-\m/s^2 accelerations and 65.3 \mu \J from (impact-produced) nonperiodic motion. [ABSTRACT FROM PUBLISHER]