Giulio Ricotti

Electronic interface for Piezoelectric Energy Scavenging System

The paper focuses on an electronic interface for systems, called Piezoelectric energy scavenging systems (PESS), which convert the energy of mechanical vibrations into electrical energy using a piezoelectric transducer. The output of the transducer is a strong and irregular function of time hence, to obtain a suitable supply source, an AC-DC conversion is needed. Classical rectifiers (half/full bridge or voltage doubler) with an output storage capacitor do not fit very well, since they work as peak detectors, converting only input voltages which are higher than their output voltage. The paper shows an electronic interface which is able to efficiently harvest the energy associated to the randomic voltage waveform delivered by a piezoelectric transducer. Its working principle is based on an inductive step-up converter; an active driving circuit is used to set the phases of the converter. The energy is stored into a capacitor which is also used to supply the active elements of the step-up converter, realizing a completely autonomous energy scavenging system. For this reason the whole circuitry has been designed with a very low-power consumptions, about 700 nA. A prototype was diffused in 5 V CMOS STMicroelectronics technology and measurements showed its effectiveness.

Active autonomous AC-DC converter for Piezoelectric Energy Scavenging Systems

The paper focuses on an electronic interface which can be used into Piezoelectric Energy Scavenging Systems (PESS). These systems convert the energy of mechanical vibrations into electrical energy using a piezoelectric transducer to realize a power supply for low power electronic systems. To obtain a suitable supply source an AC-DC conversion of the output signal of these transducers is needed and, since the output power level of the energy scavenger can be very low, the conversion should be as efficient as possible. This paper shows an active voltage doubler AC-DC converter for PESS. A novel driving circuitry topology is presented; it has the advantage to be tolerant with respect to the process variations. The converter uses exclusively a fraction of the harvested energy to supply itself and a bias circuit has been designed to make the total current consumption supply independent. A test chip was diffused in 5 V CMOS STMicroelectronics technology. Experimental results show the effectiveness of this solution and efficiencies higher than 90% have been obtained for different load values.

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.

Active self supplied AC-DC converter for piezoelectric energy scavenging systems with supply independent bias

The paper focuses on an electronic interface which can be used into piezoelectric energy scavenging systems (PESS). These systems convert the energy of mechanical vibrations into electrical energy using a piezoelectric transducer to realize a power supply for low power electronic systems. To obtain a suitable supply source an AC-DC conversion of the output signal of these transducers is needed and, since the output power level of the energy scavenger can be very low, the conversion should be as efficient as possible. This paper shows an active voltage doubler AC-DC converter for PESSs. A novel driving circuitry topology is presented; it has the advantage to be tolerant with respect to the process variations. The converter uses exclusively a fraction of the harvested energy to supply itself and a bias circuit has been designed to make the total current consumption supply independent. The simulation results show that the efficiency of the AC-DC converter can be as high as 94%. The circuit will be diffused in 0.35 mum CMOS STMicroelectronics technology.

Self-Supplied Integrable Active High-Efficiency AC-DC Converter for Piezoelectric Energy Scavenging Systems

In recent years a lot of studies focused on energy-scavenging systems (ESS). An important motivation for these studies is the development of portable devices (PD) and of wireless sensor networks (WSN). An ESS can be partitioned in two sections: the energy-scavenger itself and the electronic interface. The first one is the energy transducer while the second one is the electronic circuit which manages the energy. One of the most important objectives of the electronic interface is to realize the required ac-dc conversion. Since the output power level of the energy-scavenger can be very low, the conversion should be as efficient as possible. The goal of this paper is to design an active, high efficiency voltage doubler ac-dc converter for piezoelectric ESS which exclusively uses a fraction of the harvested energy to supply its active devices. The circuit was diffused in 0.35mum BCD6s technology. The simulation results show that it is possible to obtain a maximum efficiency of the ac-dc converter equal to 91%. Premiliminary experimental measurements were performed and the results obtained are in good agreement with simulations

Integrated stabilized photovoltaic energy harvester

In this paper a photovoltaic power generator is presented. The energy harvesting device exploits the power generated by several on-chip micro-photovoltaic cells, connected in series, to provide the supply voltage and the reference voltages for an integrated voltage regulator. The regulator operates also with low illumination levels or large load currents, and tolerates a wide variation of the voltage produced by the micro-photovoltaic cell chain. In order to allow the series connection of several photovoltaic cells, we used an SOI technology, where parasitic p-n junctions to the substrate are not present.

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%.

Integrated self-supplied system for environmental temperature sensing

In this paper we present a 4-mm2 battery-less temperature sensor, designed to collect and periodically transmit information to an ambient monitoring system. It consists of a 0.35-µm BCD SOI technology based chip including an ultra-low power integrated circuit and an energy harvesting supply unit made by 34 series-parallel connected photovoltaic cells. Each cell consists of a trench insulated p-n junction. Series connections among cells are possible because of the lack, guaranteed by the SOI insulation, of the substrate parasitic diode, typical in standard CMOS technology. The system is fully compliant with real-time applications and can work in low illumination conditions and with large variations of the photovoltaic voltage.

Single-chip smart power camera controller with photodiode current measurement down to 3 nA

This IC, together with an external 8 b microcontroller, implements all signal conditioning, measuring and power actuation functions required by a photographic camera. All IC functions are programmed by an external microcontroller through a 16 b SPI interface. The internal low-drop regulator (0.1 V drop, 30 mA) supplies both the internal circuitry and the external microcontroller. A bandgap voltage reference is used for low sensitivity to temperature variation. To preserve battery life, the micro can shut down itself and the system by writing a bit that switches off the regulator and brings system current consumption under 500 nA.

Comparison of Two Autonomous AC-DC Converters for Piezoelectric Energy Scavenging Systems

Piezoelectric Energy Scavenging Systems (PESS) are used to convert the energy of mechanical vibrations into electrical energy exploiting the piezoelectric effect. Their output is a voltage which strongly varies in time; to obtain a suitable supply source an AC-DC conversion of the output voltage of these transducers is needed. Since the output power level of the energy transducer can be very low, the conversion should be as efficient as possible.