Christian Moranz

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).

Energy Harvesting and Chip Autonomy

Energy harvesting micro-generators provide alternative sources of energy for many technical and personal applications. Since the power delivered by such miniaturized devices is limited they need to be optimized and adapted to the application. The associated electronics not only has to operate at very low voltages and use little power it also needs to be adaptive to the fluctuating harvesting conditions. A joint development and optimization of transducer and electronics is essential for improved efficiency.

A 96.7% efficient boost converter with a stand-by current of 420 nA for energy harvesting applications

This paper presents a voltage hysteresis controlled boost converter working in boundary mode for low power energy harvesting applications. Efficiencies up to 96.7% are reached. A flipped voltage follower based OTA-C integrator ensures current control with a static current consumption of 8.2 μA in the active phase and 420 nA in the standby phase. The boost converter can handle input voltages down to 0.9 V. The output voltage is adjustable from 1.3 V up to the technology limit of 3.3 V. The boost converter uses an external commercially available coil of 680 μH and operates at switching frequencies around 150 kHz. The circuit is realized in a 0.35 μm technology.

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.

A Solar Cell Powered Adaptive Charging Circuit for CMOS Integrated Micro Fuel Cells

This paper presents an autonomous interface circuit which uses solar cells to automatically recharge chip integrated micro fuel cell accumulator arrays. These accumulators comprise a fuel cell for powering systems and a hydrolysis cell for charging the integrated hydrogen storage. The charging current is continuously monitored and the interface circuit automatically maximizes and controls the charging current. The solar cells powering the charging process are projected to be part of the chip package. The presented system, in combination with a previously developed voltage regulator and integrated sensors or actuators enables the implementation of fully integrated energy autonomous systems.