• Journal of electromagnetic engineering and science
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• 제13권2호
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• pp.137-139
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• 2013

A compact metamaterial (MTM)-based tunable phase shifter consisting of four unit cells with a simple DC bias circuit has been designed at 2.4 GHz. The variable series capacitors and shunt inductors that are required to be loaded periodically onto a host transmission line are realized employing only chip variable capacitors (varactors). In addition, the proposed phase shifter requires only one DC bias source to control the varactors, with the matching condition of the MTM line automatically satisfied. The measured phase shifting range is $285.2^{\circ}$ (from $-74.2^{\circ}$ to $211^{\circ}$). The measured insertion loss is approximately 1.5 dB. The circuit/electromagnetic-simulated and measured results are in good agreement.

• 천문학회지
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• 제38권3호
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• pp.339-344
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• 2005

We present analysis results of the energy spectra of MCG-2-58-22 associated with occasional flares which appear in a long-term X-ray light curve. We measure an intrinsic power-law slope of this object to be ${\Gamma}=1.74{\pm}0.02$ in the energy range of ${\sim}1-5keV$ and find that this slope is little affected by flares. We confirm that there exists a broad excess emission above 5 keV to the power-law continuum. The excess emission is less variable compared with a flux variation of flare and tends to be relatively weak during flares. A soft X-ray spectrum is also found to change, implying the presence of a variable soft component. We discuss the implications of these spectral variations.

• ETRI Journal
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• 제26권5호
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• pp.486-492
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• 2004

The emergence of wide channel bandwidth wireless standards requires the use of a highly linear, wideband integrated CMOS baseband chain with moderate power consumption. In this paper, we present the design of highly linear, wideband active RC filters and a digitally programmable variable gain amplifier. To achieve a high unity gain bandwidth product with moderate power consumption, the feed-forward compensation technique is applied for the design of wideband active RC filters. Measured results from a $0.5{\mu}m$ CMOS prototype baseband chain show a cutoff frequency of 10 MHz, a variable gain range of 33 dB, an in-band IIP3 of 13 dBV, and an input referred noise of 114 ${\mu}Vrms$ while dissipating 20 mW from a 3 V supply.

• ETRI Journal
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• 제31권2호
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• pp.234-236
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• 2009

We present a novel operational amplifier preset technique for a switched-capacitor circuit to reduce the acquisition time by improving the slewing. The acquisition time of a variable gain amplifier (VGA) using the proposed technique is reduced by 30% compared with a conventional one; therefore, the power consumption of the VGA is decreased. For additional power reduction, a programmable capacitor array scheme is used in the VGA. In the 0.13 ${\mu}m$ CMOS process, the VGA, which consists of three-stages, occupies 0.33 $mm^2$ and dissipates 19.2 mW at 60 MHz with a supply voltage of 1.2 V. The gain range is 36.03 dB, which is controlled by a 10-bit control word with a gain error of ${\pm}0.68$ LSB.

• Journal of the Optical Society of Korea
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• 제8권1호
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• pp.17-20
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• 2004

An in-line variable attenuator has been proposed and demonstrated exploiting a side-polished single-mode (SM) fiber evanescently coupled with an index matched dielectric plate. The attenuation can be controlled by fine mechanical sliding of the index matched dielectric plate. We have achieved 49 ㏈ dynamic range and very low excess loss of 0.2 ㏈ at 1550 nm wavelength. The measured polarization dependent losses (PDL) were 0.1, 0.2, and 0.4 ㏈ at 10, 20, and 30 ㏈ attenuation, respectively. Wavelength sensitivity was measured to be -0.017/nm ㏈ at 20 ㏈ attenuation.

• 한국전자통신학회논문지
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• 제2권2호
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• pp.99-105
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• 2007

MANET(Mobile Ad-hoc network) have recently attracted a lot of attention in the research community as well as in industry. Although the previous research mainly focused on various of MANET in routing, we consider, in this paper, how to efficiently support applications such as variable geocasting basd on MANET. The goal of a geocasting protocol is deliver data packet to a group of nodes that are located within a specified geocasting region. Previous research that support geocast service in mobilie computing based on MANET have the non-optimization problem of data delivery path, overhead by frequent reconstruction of the geocast tree, and service disruption problem. In this paper, we propose the mobility pattern based geocast technique using variable service range according to the mobility of destination node and resource reservation to solve this problem. The experimental results show that our proposed mechanism has improved performance of Accessibility & Network Overhead than previous research.

• 한국정보통신학회논문지
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• 제7권8호
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• pp.1751-1758
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• 2003

본 논문에서는 V55 마이크로프로세서로 제어되는 반브릿지 인버터를 사용하여 영구 콘덴서형 단상유도 전동기의 가변속 구동에 대해 연구하였다. Patel의 알고리즘을 이용한 SHE(Selected Harmonic Elimination) PWM 구동방식에 의한 V/F 제어로 출력전압의 고조파분을 제거할 수 있으며, 속도의 제어 범위가 넓어짐을 알 수 있었다. 제안한 방법을 시뮬레이션과 실험의 결과로 입증하였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권5호
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• pp.253-257
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• 2004

In order to analyze the frequency dependance of ground impedance in grounding grids for lightning and surge protection, a novel method for measuring the ground impedance as a function of frequency were experimentally investigated. The experiments were carried out in rectangular grounding grids with $6{\times}8$ conductors of 22 $mm^2$ buried at a depth of 0.5 m. The test current was injected by the variable frequency inverter whose frequency is linearly controlled for the established period in the range of 5∼500 KHz. The amplitude and phase of ground impedance were calculated from the waveforms of the test current and ground potential rise measured by the band-pass filter tuned in a specific frequency. The frequency dependence of ground impedance was mainly caused by the inductive current flowing through grounding conductors over the frequency of 100 KHz. The proposed measurement method of ground impedance would be applicable to evaluate the transient response characteristics in lightning protection grounding systems.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 G
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• pp.3117-3119
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• 1999

In this paper, a new phase detector which can detect phase difference of variable input frequency and represent as a DC voltage is designed. The proposed phase detector has detection range from $-180^{\circ}$ to $180^{\circ}$. It is implemented by digital electronic circuit. It operates from 125 kHz to 4 MHz frequency of input signal and it's maximum phase error is $360/256^{\circ}$.

• 센서학회지
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• 제24권6호
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• pp.398-403
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• 2015

In this paper, the sine-wave and trigger pulse generator with capability of frequency high-resolution and time-variable trigger edge has implemented. It fulfills well the requirements for SS-OCT with frequency resolution of 1 Hz, frequency stability of ${\leq}{\pm}0.03Hz$ and time-variable trigger edge. Through its performance test applied to the wavelength swept laser, 90 nm, sweeping range and 10mW average optical power were obtained. This showes that the realized generator can replace the commercial high cost and high performance signal generators employed by current SS-OCT systems.