• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.329.1-329
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• 2002

To detect external vibration signals on the latticed fence structure, distributed fiber optic sensor using Sagnac interferometer was fabricated and tested. The latticed structure fabricated with dimension of 170cm in width and 180cm in height, the optical fiber, 50m in lengtn, distributed and fixed on the latticed structure. It was verified the sensitivity of the Sagnac interferometer using the PZT phase modulator. Fiber-optic external vibration signal applied to the latticed structure from 100㎐ to several ㎑. (omitted)

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.04a
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• pp.45-54
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• 2003

This paper deal with the GPS performance for determining the ocean tidal loading components(M$_2$, N$_2$, S$_2$, K$_2$) and the availability of permanent GPS stations(CHJU, KANR) established in Korea. We determined the ocean tidal loading components from GPS observation by spectrum analysis and compared to that from global ocean tidal models(GOT00.2, FES99, CRS4.0, NAO99). Through this study, we have a sense that amplitude and phase lags of ocean tidal loading components from observed GPS data was almost equal to value calculated in ocean tide models. The diurnal ocean tide loading constituents are not considered, because unmodeled troposhere effects increase the noise level near the diurnal frequency band and prevent us from obtaining significant results.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.160-168
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• 2001

The RPWM (Random· Pulse Width Modulation) is a switching technique to spread the voltage and current harmonics over a wide frequency area. By using randomly changing switching frequency of the inverter, the power spectrum of the electromagnetic acoustic noise can be spread to the wide-band area. The wide­band noise is much more comfortable and less annoying than the narrow-band one. So, the RPWM has been attracting interest as an excellent method for the reduction of acoustic noise on the inverter drive system. In this paper a new RPPWM (Random Position Space Vector PWM) is proposed and implemented. Each of three phase pulses is located randomly in each switching interval. Along with the randomization of PWM pulses, the space vector modulation is also executed in the C167 micro-controller. The experimental results show that the voltage and current harmonics are spread to a wide band area and that the audible switching noise is reduced by the proposed RPPWM method.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.3
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• pp.41-51
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• 1997

In this study, two types of the direct digital frequency synthesizers (DDFS) designed and implemented using 1.0.mu.m CMOS gatearray(SOG) technolgoies are interoduced. To analize the effect of the number of phase bits(L), address data bits(A), and DAC bits (D) on the output spectrums of the DDFSs, the NCO-based BCD-DDFS composed of L=24, A=14, and D=8, and the improved binary-DDFS composed of L=24, A=8, and D=10 have been studied. The chips have been designed with and without a noise shapper to reduce spurious noises due to phase truncation and reduced sine ROM in output spectrum.

• Journal of KSNVE
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• v.9 no.2
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• pp.409-417
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• 1999

A new method is proposed for the isolation of resonances from scattered waves for the isolaton of resonances from scattered waves for acoustic wave resonance scattering problems. The resonance scattering function consisting purely of resonance information is defined. Acoustic wave scattering from a variety of submerged bodies is numerically analyzed. The classical resonance scattering theory (RST) and the new method compute identical magnitudes of the resonances from each partial wave, however, the phases are significantly different. The exact $\pi$-radians phase shifts through the resonance and anti-resonance frequencies show that the proposed method properly extracts the vibrational resonance information of the scatterer. Due to the differences in phases of the resonances from each partial wave, the new method and RST generate different total resonance spectra.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.2
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• pp.187-195
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• 1999

A series feedback DRO operating at 3.2 GHz applicable to the spectrum analyzer as the second local oscillator, is designed and fabricated. We can obtain a low noise by utilizing the small signal S-parameter of the transistor and adjusting the reflection coefficient from the coupling coefficient between dielectric resonator and microstrip line. The results show that output power is 10.50 dBm, a stable low phase noise is -116 dBc/Hz at a 10 kHz offset frequency and a harmonic characteristic is 19.33 dBc.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.2 s.117
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• pp.213-218
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• 2007

In this paper, we propose the design and fabrication on high frequency CMOS VCO for DS-UWB(Direct-Sequence Ultra-WideBand) applications using 0.18 ${\mu}m$ process. The complementary cross-coupled LC oscillator architecture which is composed of PMOS, NMOS symmetrically, is designed for improving the phase noise characteristic. The resistor is used instead of current source that reduce the 1/f noise of current source. The high-speed buffer is needed for measuring the output characteristic of VCO using spectrum analyzer, therefore the high-speed inverter buffer is designed with VCO. A fabricated core VCO size is $340{\mu}m{\times}535{\mu}m$. The VCO is tunable between 7.09 and 7.52 GHz and has a phase noise lower than -107 dBc/Hz at 1-MHz offset over entire tuning range. The measured harmonic suppression is 32 dB. The VCO core circuit draws 2.0 mA from a 1.8 V supply.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.12
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• pp.3235-3245
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• 1996

A DDFS(Direct Digital Frequency Synthesizer) used in spread spectrum communication systems must need fast switching speed, high resolution(the step size of the synthesizer), small size and low power. The chip has been designed with four parallel sine look-up table to achieve four times throughput of a single DDFS. To achieve a high processing speed DDFS chip, a 24-bit pipelined CMOS technique has been applied to the phase accumulator design. To reduce the size of the ROM, each sine ROM of the DDFS is stored 0-.pi./2 sine wave data by taking advantage of the fact that only one quadrant of the sine needs to be stored, since the sine the sine has symmetric property. And the 8 bit of phase accumulator's output are used as ROM addresses, and the 2 MSBs control the quadrants to synthesis the sine wave. To compensate the spectrum purity ty phase truncation, the DDFS use a noise shaper that structure like a phase accumlator. The system input clock is divided clock, 1/2*clock, and 1/4*clock. and the system use a low frequency(1/4*clock) except MUX block, so reduce the power consumption. A 107MHz DDFS(Direct Digital Frequency Synthesizer) implemented using 0.8.mu.m CMOS gate array technologies is presented. The synthesizer covers a bandwidth from DC to 26.5MHz in steps of 1.48Hz with a switching speed of 0.5.mu.s and a turing latency of 55 clock cycles. The DDFS synthesizes 10 bit sine waveforms with a spectral purity of -65dBc. Power consumption is 276.5mW at 40MHz and 5V.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.94-100
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• 2001

In October 1997, low-frequency reverberation was measured at an experimental site off the west coast of the Jeju island using the explosive charge, Signals Underwater Sound (SUS). Received signals were separated into the noise, the reflection, and the scattering region, and then were analyzed for the spectral and statistical characteristics of each region. In the analysis of the spectrum we verified that each region had a unique frequency band and statistical characteristics as well. The results of this analysis showed that the real and imaginary portions were shown to be both normal distributions in each frequency bin. The reverberation envelope had a Rayleigh distribution and the phase had a uniform distribution.

• Journal of Communications and Networks
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• v.6 no.2
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• pp.93-105
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• 2004

This paper discusses cyclostationary interference suppression for multiuser wired communication systems. Crosstalk interference from digital signals in multipair cables has been shown to be cyclostationary. Many crosstalk equalization or suppression techniques have been proposed which make implicit use of the cyclostationarity of the crosstalk interferer. In this paper, the convergence and steady-state behaviors of a fractionally spaced equalizer (FSE) in the presence of multiple cyclostationary crosstalk interference are thoroughly analyzed by using the equalizer's eigenstructure. The eigenvalues with multiple cyclostationary interference depend upon the folded signal and interferer power spectra, the cross power spectrum between the signal and the interferer, and tile cross power spectrum between the interferers, which results in significantly different initial convergence and steady-state behaviors as compared to the stationary noise case. The performance of the equalizer varies depending on the relative clock phase of the symbol clocks used by the signal and multiple interferers. Measued characteristics as well as analytical model of NEXT/FEXT channel are used to compute the optimum and worst relative clock phases among the signal and multiple interferers.