• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.35-38
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• 2018

This paper describes a low-power MPPT interface for DC-type energy harvesting sources. The proposed circuit consists of an MPPT controller, a bias generator, and a voltage detector. The MPPT controller consists of an MPG (MPPT Pulse Generator) with a schmitt trigger, a logic gate operating according to energy type (light, heat), and a sample/hold circuit. The bias generator is designed by employing a beta multiplier structure, and the voltage detector is implemented using a bulk-driven comparator and a two-stage buffer. The proposed circuit is designed with $0.35{\mu}m$ CMOS process. The simulation results show that the designed circuit consumes less than 100nA of current at an input voltage of less than 3V and the maximum power efficiency is 99.7%. The chip area of the designed circuit is $1151{\mu}m{\times}940{\mu}m$.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.39-42
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• 2018

In this paper, a low-power MPPT interface circuit for vibration energy harvesting sources is presented. The designed circuit rectifies the harvested ac type energy to the dc type energy required to drive the system, and periodically samples and holds the open circuit voltage (Voc) through the MPPT controller, and transfers the harvested power to the load while maintaining the input voltage at 1/2 of the maximum available power point. All circuits have been designed using a 0.35-um CMOS technology, and the operation has been verified through simulation. Simulation results show that the designed circuit consumes 98nA of current at 3V input voltage and the maximum power efficiency is 99.21%. The designed chip occupies $1.281mm{\times}1.236mm$.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.31-34
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• 2018

This paper presents a low-power buck-boost converter for multi-input energy harvesting systems. The designed circuit combines the energy harvested from three input channels in real time and stores it in a storage capacitor. The structure of the buck-boost converter is simplified by using one external inductor and applying time division technique using an arbiter. In addition, to improve the efficiency of the system, the controller circuits of the converter are designed so that current consumption is minimized. The proposed circuit is designed with $0.35{\mu}m$ CMOS process. Simulation results show that the designed circuit consumes up to 490nA of current when all three input channels are active, and the maximum power efficiency is 92%. The chip area of the designed circuit is $1310{\mu}m{\times}1100{\mu}m$.

• Journal of IKEEE
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• v.19 no.2
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• pp.201-209
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• 2015

This paper describes a battery charger using photovoltaic energy harvesting with MPPT control. The proposed circuit harvests maximum power from a PV(photovoltaic) cell by employing MPPT(Maximum Power Point Tracking) control and charges an external battery with the harvested energy. The charging state of the battery is controlled according to the signals from a battery management circuit. The MPPT control is implemented using linear relationship between the open-circuit voltage of a PV cell and its MPP voltage such that a pilot PV cell can track the MPP of a main PV cell in real time. The proposed circuit is designed in a $0.35{\mu}m$ CMOS process technology and its functionality has been verified through extensive simulations. The maximum efficiency of the designed entire system is 86.2% and the chip area including pads is $1.35mm{\times}1.2mm$.

• Korean Journal of Soil Science and Fertilizer
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• v.49 no.5
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• pp.621-626
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• 2016

The present study evaluated the variations in soil microbial population of controlled horticultural land used for lettuce (Lactuca sativa) cultivation by their fatty acid methyl ester and chemical properties. We utilized four treatment groups, no treatment (NT), culture medium (CM), Bacillus subtilis S37-2 (KACC 91281P) ${\times}10^6CFU\;mL^{-1}$ (BS1), and Bacillus subtilis $S37-2{\times}10^7CFU\;mL^{-1}$ (BS2) and analyzed these variations throughout the before treatment and harvesting stage. The chemical properties such as pH, organic matter, available phosphate, and electrical conductivity in soils before treatment and harvesting stage showed no significant difference among the treatments. Total numbers of bacteria and microbial biomass C in soil treated with BS1 were larger than those of NT, CM, and BS2, whereas total number of fungi at the harvesting stage was significantly lower in the BS1 soil than in the NT and CM soils (P < 0.05). On basis of leaf length, leaf width, leaf number and leaf weight, the growth characteristics lettuce on the soil treated with BS1 and BS2 was faster than those of NT and CM soils. Yield of lettuce with treated BS1 and BS2 were 35% and 29% more than that of NT, respectively.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.520-523
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• 2016

This paper describes a DC-DC converter with MPPT control for thermoelectric energy harvesting. The designed circuit converts low voltage harvested from a thermoelectric generator into higher voltage for powering a load. A start-up circuit supplies VDD to a controller, and the controller turns on and off a NMOS switch of a main-boost converter. The converter supplies the boosted voltage to the load through the switch operation. Bulk-driven comparators can do the comparison under low voltage condition and are used for voltage regulation. Also, bulk-driven comparators raise system's efficiency. A peak conversion efficiency of 76% is achieved. The proposed circuit is designed in a 0.35um CMOS technology and its functionality has been verified through simulations. The designed chip occupies $933um{\times}769um$.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.267-270
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• 2014

This paper presents a CMOS interface circuit for vibration energy harvesting. The proposed circuit consists of an AC-DC converter and a DC-DC boost converter. The AC-DC converter rectifies the AC signals from vibration devices(PZT), and the DC-DC boost converter generates a boosted and regulated output at a predefined level. A full-wave rectifier using active diodes is used as the AC-DC converter for high efficiency, and a schottky diode type DC-DC boost converter is used for a simple control circuitry. A MPPT(Maximum Power Point Tracking) control is also employed to harvest the maximum power from the PZT. The proposed circuit has been designed in a 0.35um CMOS process. The chip area is $530um{\times}325um$. Simulation results shows that the maximum efficiencies of the AC-DC converter and DC-DC boost converter are 97.7% and 89.2%, respectively. The maximum efficiency of the entire system is 87.2%.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.577-580
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• 2014

In this paper an auto-switching dual-input energy harvesting circuit is proposed. Since the maximum power points of a thermoelectric generator(TEG) output and a vibration device(PEG) output is 1/2 of their open-circuit voltage, an identical MPPT controller can be used for both energy sources. The proposed circuit monitors the outputs of the TEG and PEG, and chooses the energy source generating a higher output using an auto-switching controller, and then harvests the maximum power from the selected device using a MPPT controller. The harvested energy is boosted through a charge pump and stored in a storage capacitor. The stored energy is provided to a load through a PMU(Power Management Unit). The proposed circuit is designed in a $0.35{\mu}m$ CMOS process and its functionality has been verified through extensive simulations. The designed chip occupies $1.4mm{\times}1.2mm$ including pads.

• Korean Journal of Materials Research
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• v.17 no.12
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• pp.660-663
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• 2007

Piezoelectric energy harvesting from our surrounding vibration has been studied for driving the wireless sensor node. To change the vibration energy into the electric-energy efficiently, the natural frequency of cantilever needs to be adjusted to that of a vibration source. When adding 6.80g mass on the end of the fabricated cantilever, a natural frequency shifts from 136 Hz into 49.5 Hz. In addition, electro-mechanical coupling factor increased from 10.20% to 11.90% and resulted in the 1.18 times increase of maximum output power.

• Journal of IKEEE
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• v.20 no.4
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• pp.373-377
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• 2016

This paper presents a low power boost converter using offset controlled Zero Current Sensor (ZCS) control for thermoelectric energy harvesting.[1] [5] Offset controlled ZCS uses adjustable pre-offset that is controled by 6bit code each connected gate of NMOS for switching. Offset controlled ZCS demonstrates an efficiency that is higher than using analog comparator ZCS and that is smaller area than using delay line ZCS. Experimentally, the offset controlled ZCS system consumes 10 times less power than analog comparator ZCS based system at similar performance.