Hasan Ulusan

A Fully Integrated and Battery-Free Interface for Low-Voltage Electromagnetic Energy Harvesters

This paper presents a fully integrated and battery-free 90 nm interface circuit for ac/dc conversion and step up of low-voltage ac signals generated by electromagnetic (EM) energy harvesters. The circuit is composed of two stages: The rectifier in the first stage utilizes an improved ac/dc doubler structure with active diodes internally powered by a passive ac/dc doubler and custom-designed comparators to minimize the voltage drops. With this, the efficiency is enhanced to 67% while providing 0.61 V to 40 μA load. The second stage is a dc/dc converter utilizing a low-voltage charge pump with an on-chip ring oscillator for further voltage step up. The rectifier stage is functional down to 125 mV input peak voltage, and the full interface circuit can maintain more than 1 V dc at 1 MΩ load for input peak voltages higher than 0.4 V. The circuit delivers 2.48 V to a 4.4 MΩ load, when interfaced to an in-house EM harvester, operating under 10 Hz, 0.5 g vibration.

Towards a vibration energy harvesting WSN demonstration testbed

This paper presents initial results toward the implementation of a wireless sensor network (WSN) demonstration testbed powered up by vibration energy, as part of the E-CROPS project. The testbed uses MicaZ Motes, supplied by AA batteries. The power drawn by Motes in different modes of operation are measured. Design details of an electromagnetic harvester, and experimental results of charging AA batteries with this harvester at 10 Hz vibration generated in the laboratory, are presented.

A self-powered rectifier circuit for low-voltage energy harvesting applications

This paper presents a fully self-powered low voltage and low power active rectifier circuit for vibration-based electromagnetic (EM) energy harvesters. A passive AC/DC doubler is used to provide a supply voltage for the active rectifier circuit. The proposed circuit is designed using standard 90 nm TSMC CMOS technology. The simulation results show that the proposed active rectifier circuit has voltage conversion ratio higher than 150% when the input peak voltage is more than 100 mV at open-load condition. The maximum power conversion efficiency of the circuit is 92% with 500 mV input peak voltage and 40 kΩ load resistance. Moreover, the rectifier is able to operate with low frequency input signals commonly available from vibrational energy harvesters.

A self-powered and efficient rectifier for electromagnetic energy harvesters

This paper presents an interface circuit for efficient rectification of voltages from electromagnetic (EM) energy harvesters operating with very low vibration frequencies. The interface utilizes a dual-rail AC/DC doubler which benefits from the full cycle of the input AC voltage, and minimizes the forward bias voltage drop with an active diode structure. The active diodes are powered through an AC/DC quadrupler with diode connected (passive) transistors. The interface system has been validated to drive 22 μA load at 1.1 V, with 86% efficiency, when 0.1g vibration is applied to an in house energy harvester at 8 Hz. The circuit is functional down to 150 mV input. The rectified voltage deviates at most 38 mV from the theoretical value of twice the input peak voltage. The system was demonstrated for feasibility in portable applications through a prototype placed to the waist of a jogger.

Highly Integrated 3 V Supply Electronics for Electromagnetic Energy Harvesters With Minimum 0.4 V

This paper presents a self-powered interface enabling battery-like operation with a regulated 3 V output from ac signals as low as 0.4 Vpeak, generated by electromagnetic energy harvesters under low frequency vibrations. As the first stage of the 180 nm standard CMOS circuit, harvested signal is rectified through an ac/dc doubler with active diodes powered internally by a passive ac/dc quadrupler. The voltage is boosted in the second stage through a low voltage charge pump stimulated by an on-chip ring oscillator. The output is finally regulated to 3 V at the last stage. The voltage doubling rectification stage deviates by less than 40 mV from ideal expectation for the validated 0.15–1 V input voltage range. The full system delivers 3 V output to 4.4 MΩ load for input voltage of 0.4 V peak, which is the lowest operable input voltage in the literature. The demonstrated system generates 9 μW of dc power with 3 V stable output for 32 μW input, whereas the circuit is able to supply even more output power for higher input power levels. The maximum efficiency of the rectification stage is 86%, while the full system efficiency is 37% and 28% for unregulated and regulated operation, respectively, when interfaced to an in-house electromagnetic energy harvester under 8 Hz 0.1 g vibration.

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This study presents a novel triple hybrid system that combines simultaneously generated power from thermoelectric (TE), vibration-based electromagnetic (EM) and piezoelectric (PZT) harvesters for a relatively high power supply capability. In the proposed solution each harvesting source utilizes a distinct power management circuit that generates a DC voltage suitable for combining the three parallel supplies. The circuits are designed and implemented in 180 nm standard CMOS technology, and are terminated with a schottky diode to avoid reverse current flow. The harvested AC signal from the EM harvester is rectified with a self-powered AC-DC doubler, which utilizes active diode structures to minimize the forward- bias voltage drop. The PZT interface electronics utilizes a negative voltage converter as the first stage, followed by synchronous power extraction and DC-to-DC conversion through internal switches, and an external inductor. The ultra-low voltage DC power harvested by the TE generator is stepped up through a charge-pump driven by an LC oscillator with fully- integrated center-tapped differential inductors. Test results indicate that hybrid energy harvesting circuit provides more than 1 V output for load resistances higher than 100 kΩ (10 μW) where the stand-alone harvesting circuits are not able to reach 1 V output. This is the first hybrid harvester circuit that simultaneously extracts energy from three independent sources, and delivers a single DC output.

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This paper presents a performance enhancement feature for a novel power management circuit to generate 1.8 V from the low DC voltage rectified at the output of the vibration-based electromagnetic (EM) energy harvesters. The proposed 180 nm circuit utilizes a low voltage charge pump based boost converter with variable output-stages, and an autonomous regulator circuit with negative feedback topology. 2 and 3 stage charge pump options in the variable stage configuration has been validated to extend the supported input voltage range at the same load, or alternatively maintain higher efficiency operation at a higher load range. The simulation results showed that under no-load condition the output voltage reached to 1.8 V for input voltage of 0.65 V and 0.48 V with 2 and 3 stage outputs, respectively. The power conversion efficiency of the power management circuit can be kept stable around 55% by switching from 2 to 3 stages after 3.5 μA.

Triple Hybrid Energy Harvesting Interface Electronics

This study presents a novel hybrid system that combines the power generated simultaneously by a vibration-based Electromagnetic (EM) harvester and a UHF band RF harvester. The novel hybrid scavenger interface uses a power management circuit in 180 nm CMOS technology to step-up and to regulate the combined output. At the first stage of the system, the RF harvester generates positive DC output with a 7-stage threshold compensated rectifier, while the EM harvester generates negative DC output with a self-powered AC/DC negative doubler circuit. At the second stage, the generated voltages are serially added, stepped-up with an on-chip charge pump circuit, and regulated to a typical battery voltage of 3 V. Test results indicate that the hybrid operation enables generation of 9 μW at 3 V output for a wide range of input stimulations, which could not be attained with either harvesting mode by itself. Moreover the hybrid system behaves as a typical battery, and keeps the output voltage stable at 3 V up to 18 μW of output power. The presented system is the first battery-like harvester to our knowledge that generates energy from two independent sources and regulates the output to a stable DC voltage.

Stage optimization in regulated step-up for low voltage electromagnetic energy harvesters

This paper presents a new self-powered low voltage rectifier implementation for vibration-based electromagnetic (EM) energy harvesters. The proposed circuit is an improved version of the previously reported rectifier, which was designed in TSMC 90 nm CMOS technology. The circuit is designed in lower cost UMC 180 nm CMOS technology, and uses a passive AC/DC quadrupler structure to supply the external power of the utilized active components. Simulation results show that the maximum power conversion efficiency of the circuit is 94% with 500 mV input peak voltage and 8 kΩ load resistance. Lower than 4 mV voltage drop is achieved for input peak voltage above 200 mV at open-load condition. The circuit is able to operate with low frequency input signals, which are commonly available from electromagnetic vibration energy harvesters.

A Self-Powered Hybrid Energy Scavenging System Utilizing RF and Vibration Based Electromagnetic Harvesters

In this paper a 90 nm power management circuit for vibration based electromagnetic energy harvesters is introduced to generate 1 V from the rectified DC voltage. A mode selector block is designed to detect the output DC voltage level of the rectifier and adjust the mode of the driver block. In order to set the output to the desired level, a regulation system with negative feedback topology is utilized. The circuit is able to operate with input voltages as low as 0.25 V. The simulation results also show that the power conversion efficiency of the regulated system is almost constant for wide range of input voltages.