• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.523-526
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• 2001

In this paper, we design and fabricate the high-efficiency and low-power switched-capacitor DC-DC converter. This converter consists of internal oscillator, output driver and output switches. The internal oscillator has 100kHz oscillation frequency and the output switches composed of one pMOS transistor and three nMOS transistors. According to the configuration of two external capacitors, the converter has three functions that are the Inverter, Doubler and Divider. The proposed converter is fabricated through the 0.8$\mu\textrm{m}$ 2-poly, 2-metal CMOS process. The simulation and experimental result for fabricated IC show that the proposed converter has the voltage conversion efficiency of 98% and power efficiency more than 95%.

• Korean Journal of Optics and Photonics
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• v.19 no.1
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• pp.9-14
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• 2008

In this paper, a new type of Yagi-Uda antenna that operates in the terahertz frequencies is designed. The proposed Yagi-Uda antenna can obtain high input resistance of approximately $2000{\Omega}$ at the resonance frequency by using a full-wavelength dipole instead of a half-wavelength dipole as the driver element. The current leakage into the bias line was minimized by applying the photonic bandgap structure to the bias line. By designing the antenna on a thin substrate, the impedance lowering of an antenna caused by the relative dielectric constant of the substrate was prevented and the end-fire radiation pattern which is the original radiation characteristic of the Yagi-Uda antenna could be obtained. We expect that the proposed Yagi-Uda antenna can achieve increased terahertz output power by improving the impedance mismatching problem with the photomixer.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.1
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• pp.109-116
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• 2014

This paper presents a high-efficiency digital class-D audio amplifier using a composite interpolation filter for portable audio devices. The proposed audio amplifier is composed of an interpolation filter, a delta-sigma modulator, and a class-D output stage. To reduce power consumption, the designed interpolation filter has an optimized composite structure that uses a direct-form symmetric and Lagrange FIR filters. Compared to the filters with homogeneous structures, the hardware cost and complexity are reduced by about half by the optimization. The coefficients of the digital delta-sigma modulator are also optimized for low power consumption. The class-D output stage has gate driver circuits to reduce shoot-through current. The implemented class-D audio amplifier exhibited a high efficiency of 87.8 % with an output power of 57 mW at a load impedance of $16{\Omega}$ and a power supply voltage of 1.8 V. An outstanding signal-to-noise ratio of 90 dB and a total harmonic distortion plus noise of 0.03 % are achieved for a single-tone input signal with a frequency of 1 kHz.

• International Journal of Highway Engineering
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• v.15 no.5
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• pp.203-215
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• 2013

PURPOSES : This study deals with first traffic violations occurred by novice drivers, which may be associated with traffic accidents. The objective of this study is to identify what kinds of drivers' characteristics influence on duration till the first traffic violation. METHODS : For the study, Survival Analysis and Cox proportional hazard model, that are usually used in the medical field, were employed. Survival Analysis was conducted to investigate whether there exist differences in survival duration by each covariate, whereas Cox proportional hazard model was used to identify significant factors that affect survival duration till novice drivers violate traffic regulations for the first time after getting a driver license. RESULTS : The results of Survival Analysis indicate that female, age (less than 21), low-frequency examinee of written exam, and non-crash involved drivers have longer duration till the first violation compared to male, greater than 21 years old, high-frequency examinee of written exam, and crash involved drivers, respectively. For the Cox proportional hazard model, license class 1 acquisitor was found to increase the survival duration till the first traffic violation was made, while male, age of 21-24, age of 25-34, age of 45-54, and crash involved drivers were more likely to reduce the survival duration. CONCLUSIONS : Absolutely, traffic violation is closely related to traffic accidents and all of the drivers should keep the traffic regulations to enhance highway safety. The results of this study might provide some insights to construct safe road environments by controlling the factors that reduce the traffic violation duration of novice drivers.

• Journal of Power Electronics
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• v.11 no.3
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• pp.271-278
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• 2011

This paper presents a LLC resonant controller IC for secondary side control without external active devices to achieve low profile and low cost LED back light units. A gate driving transformer is adopted to isolate the primary side and the secondary side instead of an opto-coupler. A new integrated dimming circuitry is proposed to improve the dynamic current control characteristic and the current density of a LED for the brightness modulation of a large screen LCD. A dual-slope clock generator is proposed to overcome the frequency error due to the under shoot in conventional approaches. This chip is fabricated using 0.35 ${\mu}m$ BCD technology and the die size is $2{\times}2\;mm^2$. The frequency range of the clock generator is from 50 kHz to 500 kHz and the range of the dead time is from 50 ns to 2.2 ${\mu}s$. The efficiency of the LED driving circuit is 97 % and the current consumption is 40 mA for a 100 kHz operation frequency from a 15 V supply voltage.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.416-419
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• 1995

An analysis of a new load resonant inverter considering stray inductance is given. There are several different types for load resonant inverters. They can offer zero turn-on as well as zero turn-off switching losses, yielding high efficiency at high power and high frequencies. However, they didn't consider the influences of stray inductance. In conventional topology using lossless snubber capacitor, stray inductances result in very high frequency resonant current. Especially, these influences can be problematic in high power system such as induction heating system with large current of some 10A associated with it. These currents increase EMI problem, give harmful effects in gate driver's operation and increase loss of dc-link capacitor as well as snubber capacitor. Therefore, the effect of stray inductances should be treated and reduced. This paper presents a new load resonant inverter topology, which can reduce the effect of stray inductances.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.9
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• pp.667-670
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• 2010

In this paper, a high voltage current sensing circuit for boost converter is designed and verified by Cadence SPECTRE simulations. The current mirror pair, power and sensing metal-oxide semiconductor field effect transistors (MOSFETs) with size ratio of K, is used in our on-chip current sensing circuit. Very low drain voltages of the current mirror pair should be matched to give accurate current sensing, so a folded-cascode opamp with a PMOS input pair is used in our design. A high voltage high side lateral-diffused MOS transistor (LDMOST) switch is used between the current sensing circuit and power MOSFET to protect the current sensing circuit from the high output voltage. Simulation results using 0.35 ${\mu}m$ BCD process show that current sensing is accurate and the pulse frequency modulation (PFM) boost converter using the proposed current sensing circuit satisfies with the specifications.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.4
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• pp.1908-1914
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• 2013

In this paper, we introduce a design method for a broadband planar quasi-Yagi antenna (QYA) for terrestrial digital television (DTV) reception. The coplanar strip line which feeds the driver dipole is connected to a microstrip line and is terminated by short circuit. By appending a wide strip-type rectangular director at a location close to the driver dipole, broadband impedance matching and gain enhancement in a high frequency region are obtained. The gain characteristics in a low frequency region are improved by adding a reflector formed by a truncated ground plane. To reduce the antenna size, the strip-type dipole and reflector are modified to half bow-tie (V)-shaped elements. The effects of various parameters on the antenna characteristics are examined. An antenna, as a design example for the proposed antenna, is designed for the operation in the frequency band of 470-806 MHz for terrestrial DTV. The optimized antenna is fabricated on an FR4 substrate and the experimental results show that the antenna has a good performance such as a frequency band of 450-848 MHz for a VSWR < 2, gain > 4.1 dBi, and front-to-back ratio > 10.4 dB.

• Journal of electromagnetic engineering and science
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• v.8 no.3
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• pp.91-95
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• 2008

This paper presents a direct-conversion I/Q up-mixer block, which supports $3{\sim}5$ GHz ultra-wideband(UWB) applications. It consists of a VI converter, a double-balanced mixer, a RF amplifier, and a differential-to-single signal converter. To achieve wideband characteristics over $3{\sim}5$ GHz frequency range, the double-balanced mixer adopts a shunt-peaking load. The proposed RF amplifier can suppress unwanted common-mode input signals with high linearity. The proposed direct-conversion I/Q up-mixer block is implemented using $0.18-{\mu}m$ CMOS technology. The measured results for three channels show a power gain of $-2{\sim}-9$ dB with a gain flatness of 1dB, a maximum output power level of $-7{\sim}-14.5$ dBm, and a output return loss of more than - 8.8 dB. The current consumption of the fabricated chip is 25.2 mA from a 1.8 V power supply.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.1
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• pp.23-31
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• 1994

The present works are the experimental results of the study to develope a damping flexible coupling which has a high performance of control for the torsional vibrations of power shafts in a large machinery. The damping flexible coupling is manufactured and is compared for dynamic characteristics with other type coupling which is the Geislinger coupling. The static coefficient of stiffness and the damping coefficient allows the control of excitation frequency through a cam driver. The experimental results obtained from the two couplings are compared with the theoretically results.