• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.2
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• pp.27-35
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• 2016

A Low jitter dual output frequency synthesizer for smart audio devices is described in this paper. It has been fabricated in a 1.8 V Dongbu $0.18-{\mu}m$ CMOS process. Output frequency is controlled by 3 rd order Sigma-Delta Modulation and digital divider. The frequency synthesizer has a size of $0.6mm^2$, frequency range of 0.6-200 MHz, loop bandwidth of 350 kHz, and rms jitter of 11.4 ps-21.6 ps.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.301-306
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• 2014

We proposed a new PCB-type 'common-mode current($I_c$) and differential-mode current($I_d$) detector' working for fast detection of $I_c$ and $I_d$ from the differential-mode signaling, with miniaturization effect and possibility of cheaper fabrication. In order to realize this device, we suggest a branch-line-coupler balun having a composite right- and left-handed(CRLH) one-layer microstrip phase-shifting line as compact as roughly ${\lambda}_g/14$. The presented balun obviously is different from the conventional bent-&-folded delay lines or slits on the ground for coupling the lines on the top and bottom dielectrics. As we connect the suggested balun output ports of the differential-mode signal lines via the through-port named U and coupled-port named L, $I_c$ and $I_d$ will appear at port ${\Delta}$ and port ${\Sigma}$ of the present device, in order. The validity of the design scheme is verified by the circuit-and numerical electromagnetic analyses, and the dispersion curve proving the metamaterial characteristics of the geometry. Besides, the examples of the $I_c$ and $I_d$ indicator are observed as the even and odd modes in differential-mode signal feeding. Also, the proposed device is shown to be very compact, compared with the conventional structure.

• Journal of Welding and Joining
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• v.32 no.2
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• pp.48-53
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• 2014

This study was carried out to investigate the effect of postweld heat treatment(PWHT, 930, 1080, $1230^{\circ}C$) on the microstructure, phase formation, pitting corrosion and mechanical properties such as hardness, tensile strength and impact values of super duplex stainless steel(UNS S32750) multipass welds. Based on the microstructural examination and X-ray diffraction analysis, it was found that the ${\sigma}$ phase was formed in the welds heat treated at $930^{\circ}C$ in which the ferrite content greatly decreased into 5~10% in the welds. The secondary austenite was formed in the reheated zone of welds and redissolved into ferrite with increasing heat treatment temperatures. The tensile strength and impact values of welds heat treated at $930^{\circ}C$ were the lowest and revealed the brittle fracture surface. The weight loss by pitting corrosion increased with test temperatures. It was confirmed that pitting corrosion occurred mainly in secondary austenite of reheated zones. The postweld heat treatment temperature is recommended to be in the range of $1050{\sim}1150^{\circ}C$.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3452-3457
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• 2007

Experiments were carried out in an atmopheric pressure, lab-scale gas turbine combustor to see the effect of partial premixing on unstable flame structure and $NO_X$ emission characteristics. The swirl angle is 45 deg., fuel-air mixing degrees were varied 0, 50, and 100% respectively at equivalence ration ranging from 0.53 to 0.79. The evaluation of phased-locked OH chemiluminescence images were acquired with an ICCD. $NO_X$ emission characteristics were also investigated at each experimental condition. The effect of the fuel-air mixing degree on the flame structure was obtained from phase-locked $OH^*$ images. And it was obtained from local heat release characteristics that the information about the region which the combustion instability was amplified or damped. It also could be confirmed that ${\sigma}$ has greatly influence on $NO_X $emission characteristics at lean regimes. It would be expected that it could provide invaluable data for understanding the mechanism of combustion instability

• ETRI Journal
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• v.40 no.2
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• pp.167-179
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• 2018

This paper proposes an IEEE 802.15.4m compliant TV white-space orthogonal frequency-division multiplexing (TVWS)-(OFDM) radio frequency (RF) transceiver that can be adopted in advanced metering infrastructures, universal remote controllers, smart factories, consumer electronics, and other areas. The proposed TVWS-OFDM RF transceiver consists of a receiver, a transmitter, a 25% duty-cycle local oscillator generator, and a delta-sigma fractional-N phase-locked loop. In the TV band from 470 MHz to 698 MHz, the highly linear RF transmitter protects the occupied TV signals, and the high-Q filtering RF receiver is tolerable to in-band interferers as strong as -20 dBm at a 3-MHz offset. The proposed TVWS-OFDM RF transceiver is fabricated using a $0.13-{\mu}m$ CMOS process, and consumes 47 mA in the Tx mode and 35 mA in the Rx mode. The fabricated chip shows a Tx average power of 0 dBm with an error-vector-magnitude of < 3%, and a sensitivity level of -103 dBm with a packet-error-rate of < 3%. Using the implemented TVWS-OFDM modules, a public demonstration of electricity metering was successfully carried out.

• Korean Journal of Materials Research
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• v.11 no.11
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• pp.915-922
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• 2001

Effects of thermal exposure and rejuvenation treatment on the microstructural evolution and the stress-rupture properties of IN738LC have been investigated. The role of precipitates on the stress-rupture properties has been analyzed through microstructural observations. Thermal exposure at $982^{\circ}C$ for 1000 hours gave rise to precipitation of $\sigma$ phase and coarsening of r'. The microstructural degradation with thermal exposure at $982^{\circ}C$ deteriorated stress rupture properties of the alloy. All the existing phases except MC carbides have completely dissolved into the matrix with homogenization treatment at $1200^{\circ}C$ for 2 hours. Microstructure and stress-rupture properties of the thermal exposed specimens have been successfully rejuvenated by the proposed treatment.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.1312-1315
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• 2002

This research describes the design of a fully integrated fractional-N frequency synthesizer intended for the local oscillator in IMT-2000 system using 0.18-$\mu\textrm{m}$ CMOS technology and 1.8-V single power supply. The designed fractional-N synthesizer contains following components. Modified charge pump uses active cascode transistors to achieve the high output impedance. A multi-modulus prescaler has modified ECL-like D flip-flop with additional diode-connected transistors for short transient time and high frequency operation. And phase-frequency detector, integrated passive loop filter, LC-tuned VCO having a tuning range from 1.584 to 2.4 ㎓ at 1.8-V power supply, and higher-order sigma-delta modulator are contained. Finally, designed frequency synthesizer provides 5 ㎒ channel spacing with -122.6 dBc/Hz at 1 ㎒ in the WCDMA band and total output power is 28 mW.

• Nuclear Engineering and Technology
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• v.49 no.2
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• pp.349-359
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• 2017

During the past 25 years, in the context of probabilistic safety assessment, efforts have been directed towards establishment of comprehensive pipe failure event databases as a foundation for exploratory research to better understand how to effectively organize a piping reliability analysis task. The focused pipe failure database development efforts have progressed well with the development of piping reliability analysis frameworks that utilize the full body of service experience data, fracture mechanics analysis insights, expert elicitation results that are rolled into an integrated and risk-informed approach to the estimation of piping reliability parameters with full recognition of the embedded uncertainties. The discussion in this paper builds on a major collection of operating experience data (more than 11,000 pipe failure records) and the associated lessons learned from data analysis and data applications spanning three decades. The piping reliability analysis lessons learned have been obtained from the derivation of pipe leak and rupture frequencies for corrosion resistant piping in a raw water environment, loss-of-coolant-accident frequencies given degradation mitigation, high-energy pipe break analysis, moderate-energy pipe break analysis, and numerous plant-specific applications of a statistical piping reliability model framework. Conclusions are presented regarding the feasibility of determining and incorporating aging effects into probabilistic safety assessment models.

• Korean Journal of Materials Research
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• v.11 no.10
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• pp.833-840
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• 2001

Effects of thermal exposure and rejuvenation treatment on the microstructural evolution and the stress-rupture properties of IN738LC have been investigated. The role of precipitates on the stress- rupture properties has been analyzed through microstructural observations. Thermal exposure at $982^{\circ}C$ for 1000 hours gave rise to precipitation of $\sigma$ phase and coarsening of ${\gamma}$'. The microstructural degradation with thermal exposure at $982^{\circ}C$ deteriorated stress rupture properties of the alloy. All the existing phases except MC carbides have completely dissolved into the matrix with homogenization treatment at $1200^{\circ}C$ for 2 hours. Microstructure and stress-rupture properties of the thermal exposed specimens have been successfully rejuvenated by the proposed treatment.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.735-741
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• 2011

In the early phase of vehicle development, CAE is conducted as tool for vehicle performance assessment. To maintain acceptable road noise performance, solution for reduced vehicle sensitivity is required. Chassis interface dynamic stiffness characteristics are key component to isolating vibration and noise of road from the vehicle interior. This research provide how to set up the optimized dynamic characteristics under noise effect through DFSS study. CAE-based DOE is performed to build prediction math model, CMS process involves DOE to achieve very fast run times while giving results very comparable. Minimized $95^{th}$ percentile of performance distribution is applied to minimize vehicle sensitivity and road noise levels variation during the optimization process. Finally, the results of optimization were reviewed for performance and robustness.