Joachim Leicht

Autonomous and self-starting efficient micro energy harvesting interface with adaptive MPPT, buffer monitoring, and voltage stabilization

This paper presents an efficient autonomous micro energy harvesting interface optimized for high-resistive vibration-driven electromagnetic energy transducers. A novel active voltage doubler and an energy processing scheme with adaptive maximum power point tracking (MPPT) is implemented. The interface enables wide voltage range harvesting for amplitudes between 0.44 V and 4.15V. Harvesting with tracking efficiencies of up to 93% and total efficiencies of up to 72% is enabled. In order to supply energy harvesting applications such as low power wireless sensor nodes a programmable voltage stabilization is implemented. The prototype chip is fabricated in a 0.35 μm CMOS process and is self-supplied needing no start-up help.

A Parallel-SSHI Rectifier for Piezoelectric Energy Harvesting of Periodic and Shock Excitations

Piezoelectric harvesters are capable of generating energy out of ambient vibrations. Dedicated interface circuits can significantly increase the harvesting capabilities compared with passive rectifiers. This paper presents an autonomous piezoelectric energy harvesting system in a 0.35-μm CMOS process. The implemented interface is based on the parallel-SSHI technique and can harvest from periodic and shock excitations. Regular operation is enabled for input voltages as low as 670 mV. It extracts up to 6.81 times more power compared with an ideal full-bridge rectifier depending on the generator characteristics and excitation conditions. The device is capable of cold startup and provides a stable output voltage for powering an application.

20.6 Electromagnetic vibration energy harvester interface IC with conduction-angle-controlled maximum-power-point tracking and harvesting efficiencies of up to 90%

An electromagnetic vibration energy harvester (EMH) is an electromechanical mass-spring-damper system transducing electrical energy out of ambient vibrations. Resistive load matching [1] as well as maximum power point (MPP) AC-DC conversion [2] are highly suitable techniques for enhancing the electrical energy output of an EMH. The presented interface IC (Fig. 20.6.1) enables MPP AC-DC conversion by tracking the optimum conduction angle and by employing a hysteretic input voltage controlled inductive DC-DC boost converter. All control signals are derived from the harvester voltage itself. Thus, no additional sensor, harvester disconnection, or DC-DC converter duty-cycle control are needed. Additionally, the implemented voltage conditioning provides over-voltage protection (OVP) and application voltage regulation (VR).

A 200ns settling time fully integrated low power LDO regulator with comparators as transient enhancement

The design of a low power low drop out voltage regulator with no off-chip capacitor and fast transient responses is presented in this paper. The LDO regulator uses a combination of a low power operational trans-conductance amplifier and comparators to drive the gate of the PMOS pass element. The amplifier ensures stability and accurate setting of the output voltage in addition to power supply rejection. The comparators ensure fast response of the regulator to any load or line transients. A settling time of less than 200ns is achieved in response to a load transient step of 50mA with a rise time of 100ns with an output voltage spike of less than 200mV at an output voltage of 3.25 V. A line transient step of 1V with a rise time of 100ns results also in a settling time of less than 400ns with a voltage spike of less than 100mV when the output voltage is 2.6V. The regulator is fabricated using a standard 0.35μm CMOS process and consumes a quiescent current of only 26 μA.

21.2 A 4µW-to-1mW parallel-SSHI rectifier for piezoelectric energy harvesting of periodic and shock excitations with inductor sharing, cold start-up and up to 681% power extraction improvement

A piezoelectric energy harvester (PEH) converts vibration-induced mechanical stress into electrical charge. This conversion is optimized for cantilever-based generators when excited continuously in resonance. However, this is rarely achieved using ambient vibrations, where changes in excitation frequencies (fEX) and magnitudes, or shock excitations are more common [1]. The implemented system (Fig. 21.2.1) is a fully autonomous energy-harvesting interface based on the parallel-synchronized-switch harvesting-on-inductor (SSHI) technique, also known as bias-flip [2], and can work with periodic as well as shock excitations. It allows enhanced ambient energy extraction by operating at an ideal rectified voltage (VBUF) [2] set by means of an optimal power point circuit (OPP). It operates with different harvesters and a wide variation of accelerations and excitation frequencies. The system achieves cold start-up and provides a configurable output voltage (VLDO) that can power systems such as wireless sensor nodes, biomedical or hand-held devices. It can use a single inductor by means of an inductor-sharing block (IS), and has over-voltage protection (OVP).

Impedance matching for broadband piezoelectric energy harvesting

This paper presents a system design for broadband piezoelectric energy harvesting by means of impedance matching. An inductive load impedance is emulated by controlling the output current of the piezoelectric harvester with a bipolar boost converter. The reference current is derived from the low pass filtered voltage measured at the harvester terminals. In order to maximize the harvested power especially for nonresonant frequencies the filter parameters are adjusted by a simple optimization algorithm. However the amount of harvested power is limited by the efficiency of the bipolar boost converter. Therefore an additional switch in the bipolar boost converter is proposed to reduce the capacitive switching losses. The proposed system is simulated using numerical parameters of available discrete components. Using the additional switch, the harvested power is increased by 20%. The proposed system constantly harvests 80% of the theoretically available power over frequency. The usable frequency range of ±4Hz around the resonance frequency of the piezoelectric harvester is mainly limited due to the boost converter topology. This comparison does not include the power dissipation of the control circuit.

Energy-Harvesting Applications and Efficient Power Processing

In comparison to the original chapter in CHIPS 2020 Manoli et al. (CHIPS 2020—A Guide to the Future of Nanoelectronics: 329–420, 2012) [1], this chapter presents more application-oriented research with a focus on wearable devices and condition monitoring. It also covers electronic circuit components and systems employed in extracting, processing, and storing the harvested power. In the meantime, many innovative enhancements in terms of efficiency and applicability have been achieved by developing dedicated CMOS integrated circuits.

Physical insight into electromagnetic kinetic energy transducers and appropriate energy conditioning for enhanced micro energy harvesting

This paper proposes a new method for modeling electromagnetic kinetic energy transducers and gives analytical expressions that enable the design of efficient energy conditioning circuitry. The introduced transducer modeling approach achieves high accuracy without requiring a large set of parameters. The presented transducer characterization allows physical insight into fully assembled and packaged transducers in order to extract the required transducer model parameters without knowledge of the individual components. Moreover, the electromagnetic coupling, the parasitic damping, and the optimal load can be modeled with a dependence on the external excitation. Precise co-simulation with CMOS integrated energy conditioning circuitry is possible implementing this model in a circuit simulator.

Thermoelectric energy harvesting system for demonstrating autonomous operation of a wireless sensor node enabled by a multipurpose interface

This paper demonstrates the autonomous operation of a wireless sensor node exclusively powered by thermoelectric energy harvesting. Active operation of a wireless sensor system is demonstrated successfully by means of an on-line programmable emulation kit that enables various thermoelectric energy harvesting scenarios. Moreover, this emulation kit accomplishes autonomous wireless sensor node operation by interfacing a small-scaled thermogenerator via a CMOS integrated autonomous multipurpose energy harvesting interface circuit performing maximum power point tracking.

A fully integrated charge pump using parasitics to increase the usable capacitance by 25 % and the efficiency by up to 18 % with poly-poly capacitors

In this paper, an advanced layout scheme of an integrated capacitor is presented which improves the efficiency of a poly-poly capacitor based voltage doubler charge pump. The main losses in voltage doubler charge pumps are mathematically described and the importance of low stray capacitances are discussed. By means of the improved poly-poly capacitor layout, the usable capacitance is increased while the stray capacitance is reduced. To quantify the improvements, a standard charge pump architecture is fabricated in a 0.35 μm CMOS technology with three different capacitor types. The presented measurement results show an efficiency of up to 77.9 % and an improvement by up to 18 % if compared to the same charge pump architecture using a standard capacitor. While following all design rules, the improved poly-poly capacitor layout scheme achieves almost the efficiency of a double metal-metal capacitor which allows typically for the highest efficiency of fully integrated charge pumps.