Matteo Filippi

Micropower Design of a Fully Autonomous Energy Harvesting Circuit for Arrays of Piezoelectric Transducers

This paper presents a self-powered energy harvesting circuit based on synchronous charge extraction with a single shared inductor for power conversion from arrays of independent piezoelectric transducers. The number of handled elements can be easily increased at the expense of few additional components and without affecting performance. The energy harvesting circuit was characterized with three 0.5 × 12.7 × 31.8 mm3 piezoelectric cantilevers subject to different types of vibrations. Throughout all operating conditions, the circuit was able to extract the maximum power independently from every transducer. Compared to passive energy harvesting interfaces, the output power is significantly higher, with worst-case increases ranging from +75% to +184%. The circuit starts up passively and is based on ultralow power active control, which consumes during operation at 3 V a fraction of the extra harvested power as low as 10 μW per source. As part of the best tradeoff between harvested and intrinsic power, an overall energy efficiency up to 74% was achieved.

A Load-Modulated Rectifier for RF Micropower Harvesting With Start-Up Strategies

In this paper, we introduce a new load-modulated two-branch rectifier, designed to dynamically cooperate with an ultra-low power management unit (PMU), interposed between the rectenna and application circuits. The design targets batteryless RF energy harvesting applications with typical input power ranging from ~ 10 to ~ 100 μW. Energy is stored in a low leakage capacitor. In order to allow activation in discharged states, the PMU implements a low-voltage start-up stage, whose current consumption is specifically optimized for biasing the rectifier accordingly. When a sufficient voltage is reached, the PMU activates a more efficient boost converter stage with maximum power point tracking capabilities and micro-power consumption. Such two circuits are designed to provide two very different loading conditions to the rectifier. A joint design of the nonlinear rectifier paths and of the two PMU subsystems based on two specific optimizations of the matching networks is proposed, along with a circuit solution for automatically switching between the start-up stage and the boost converter. In order to validate the concept, a microstrip prototype operating at 900 MHz with a discrete components PMU is characterized, although the proposed idea is fully technology independent. With respect to a conventional rectifier, the proposed design allows the system to operate with significantly lower input power, while preserving efficiency during steady-state power conversion.

A Nanocurrent Power Management IC for Multiple Heterogeneous Energy Harvesting Sources

This paper presents a fully autonomous power converter IC for energy harvesting from multiple and multitype sources, such as piezoelectric, photovoltaic, thermoelectric, and RF transducers. The converter performs an independent self-adapting input power tracking process for each source. The peak power conversion efficiency measured during single-source operation is 89.6%. With all sources enabled, the intrinsic current consumption is as low as 47.9 nA/source. A self-starting battery-less architecture has been implemented in a 0.32-μm STMicroelectronics BCD technology with a 2142 μm × 2142 μm die area. The IC only requires a single-shared inductor and an external storage capacitor for the basic working configuration. With respect to other multisource energy harvesters, this design specifically introduces a series of nanopower design techniques for extreme minimization of the intrinsic consumption during operation. The small chip size combined with the limited number of required external component, the high conversion efficiency, and the state-of-the-art intrinsic nanocurrent consumption make the IC suitable for many critical applications with very limited available power, such as wearable devices or unobtrusive wireless sensor networks.

A Nanopower Synchronous Charge Extractor IC for Low-Voltage Piezoelectric Energy Harvesting With Residual Charge Inversion

The paper presents a power converter for piezoelectric energy harvesting implementing a modified version of a synchronous electrical charge extraction with quiescent current as low as 160 nA. The input energy is increased of more than 200% for weak vibrations, by inverting the residual charge left on the capacitance of the transducer after each energy extraction. Moreover, a power management policy, named two-way energy storage, is introduced in order to improve significantly the efficiency of the energy harvesting system in battery-less systems during the startup phase, when the energy storage is fully depleted. The converter behaves as a buck-boost converter, and the measured peak efficiency is 85.3%. The IC has been designed in a 0.32-μm microelectronic technology from STMicroelectronics in an active area of 0.95 mm2.

A Nanocurrent Power Management IC for Low-Voltage Energy Harvesting Sources

This paper presents the nanopower design of an integrated 1-μW-to-5-mW power management circuit. The circuit integrates a boost converter with maximum power point tracking, a low drop-out voltage regulator (LDO), and a start-up circuit for battery-less activation from discharged states. The IC implements a dynamic two-way power routing policy that ensures a fast start-up from discharged states even with very large energy storage capacitors. In order to reduce the intrinsic power, asynchronous control logic was adopted. The circuit was implemented in a STMicroelectronics 0.32-μm microelectronic technology. The power conversion section and the LDO draw, respectively, stand-by currents of 121 and 414 nA in the active modes. The circuit achieves a peak conversion efficiency of 77.1% and a minimum start-up voltage of 223 mV.

A nano-power power management IC for piezoelectric energy harvesting applications

This paper describes a power management IC for piezoelectric energy harvesting which integrates an active AC-DC converter with residual charge inversion together with a smart self-supply architecture to speed up the start-up phase and increase harvesting effectiveness. Due to randomness of available power and to its typical intrinsic limitation to tens of μW the IC has been carefully designed to reduce quiescent current down to 150 nA while the efficiency is estimated to be at least 81%. Moreover this allows the system to be fully autonomous even with very low input energy. The IC has been designed in a 0.32 μm BCD technology from STMicroelectrics and its area is 4.6 mm2.

A nano-power energy harvesting IC for arrays of piezoelectric transducers

This paper describes a multi-source energy harvester IC for arrays of independent transducers, designed in a 0.32μm STMicroelectronics BCD technology, that can manage up to 5 AC-DC channels (e.g. piezoelectric transducers). The IC implements a boost converter based on synchronous electrical charge extraction. A single external inductor is time-shared among all transducers and access conflicts are handled by an arbiter circuit implemented as an asynchronous FSM. The designed converter is fully autonomous and suitable for battery-less operation. The circuit area is 4.6 mm2 and has a power consumption of 175 nW/source at 2.5 V while efficiency ranges between 70% and over than 85%.

A Sub-μ A Stand-By Current Synchronous Electric Charge Extractor for Piezoelectric Energy Harvesting

In the field of energy harvesting there is a growing interest in power management circuits with intrinsic sub-μ A current consumptions, in order to operate efficiently with very low levels of available power. In this context, integrated circuits proved to be a viable solution with high associated nonrecurring costs and design risks. As an alternative, this article presents a fully autonomous and battery-less circuit solution for piezoelectric energy harvesting based on discrete components in a low-cost PCB technology, which achieves a comparable performance in a 32 × 43 mm2 footprint. The power management circuit implements synchronous electric charge extraction (SECE) with a passive bootstrap circuit from fully discharged states. Circuit characterization showed that the circuit consumes less than 1μ A with a 3V output and may achieve energy conversion efficiencies of up to 85%. In addition, the circuit is specifically designed for operating with input and output voltages up to 20V, which grants a significant flexibility in the choice of transducers and energy storage capacitors.

A 40 nA/source energy harvesting power converter for multiple and heterogeneous sources

This paper presents a fully autonomous integrated circuit for power conversion from multiple and heterogeneous energy harvesting transducers. Five input channel are dedicated to vibrational harvesting and exploiting multi-frequency operations. Additional four input channels are dedicated to manage DC sources. An independent MPPT is applied on each channel. A relevant feature of the design is the use of specific nano-power design techniques which reduce the converter quiescent consumption down to 40 nA/source and still keep energy conversion efficiency up to 82.8%. Only few external components are required: an external capacitor for energy storage, a single inductor and four capacitors for MPPT on DC sources.