• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.6
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• pp.105-112
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• 2003

Diode rectifier which can't be controlled output voltage and phase control converter as AC/DC converter have low power factor and harmonics of lower order in the line current. In this paper, three phase PWM(Pulse Width Modulation) AC/DC boost converter is studied to solve these problems. The characteristics of a proposed converter are to control the phase of current without current sensor as a very simple control algorithm using circuit parameters only and to apply sinusoidal PWM method with fixed switching frequency due to a difficult design of input filter and switching device. We simulate for the proposed algorithm that high power factor is achieved and DC link voltage has fast dynamic response without ripple in rectifying and regenerating operation. As a result of experiment with circuit parameter(inductor, capacitor) decided in simulation, the proposed converter had high power factor and reduction of low order harmonics as against diode rectifier.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.1
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• pp.85-91
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• 2012

In this paper, we implemented a Ka-band frequency synthesizer for millimeter wave seeker. we designed for high frequency resolution and frequency hopping response time in the digital synthesis method which uses DDS(Direct Digital Synthesizer). but frequency bandwidth was limited low frequency because DDS output frequency was limited 1/2 by system clock. thus, frequency synthesizer was converted to Ka-band using the frequency multiplier ${\times}4$ and local oscillator. proposed frequency synthesizer was bandwidth 500MHz, frequency switching time was $0.7{\mu}s$, spurious level was suppressed below -52dBc. phase noise was -99dBc/Hz at offset 100kHz and flatness was ${\pm}1dB$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.4
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• pp.298-308
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• 2017

This paper presents a Interleaved Buck Converter(IBC) system with Random PWM to reduce electromagnetic noise by harmonics. Swithced mode power supply generally controlled by high switching frequency have a electromagnetic interference(EMI) issue due to the high-voltage/high-current switching to regulate the voltage in buck converter. To solve the problem. we present a novel IBC system with PRBS. IBC system has two active switches with 180 phase difference that controll the cicuit with two PWM signal. IBC system may be disadventageous for the cost due to the addtion of one set of switch, but it has adventages of power distribution, current ripple cancellation, fast transient response, and passive component size reduction. To verify the validity of study, simulation program has been bulit using PSIM and the experimental results of IBC system using RPWM was compared with the conventinal PWM and randomized PWM.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.54-57
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• 2007

Much researches have studied for seamless mobility service. Those focused on minimizing the delay time due to the handover. In this paper, we suggest seamless mobility service with the network-based preemptive operations. With these operations, if it's found that the MT(Mobile Terminal)'s handover using L2-trigger event, old access network buffers the delivering data. Therefore this can decrease the data drop rates. And also, this can deal with the ping-pong's phenomenon of MT. At the end of MT's movement, these operations can provide seamless mobility service sending buffered data after checking the MT's movement. This mechanism uses MPLS-LSP(MultiProtocol Label Switching-Label Switched Path) in core network for fast process.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.396-396
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• 2013

The resistive random access memory (ReRAM) has several advantages to apply next generation non-volatile memory device, because of fast switching time, long retentions, and large memory windows. The high mobility of monolayered graphene showed several possibilities for scale down and electrical property enhancement of memory device. In this study, the monolayered graphene grown by chemical vapor deposition was transferred to $SiO_2$ (100 nm)/Si substrate and glass by using PMMA coating method. For formation of metal-oxide nanoparticles, we used a chemical reaction between metal films and polyamic acid layer. The 50-nm thick BPDA-PDA polyamic acid layer was coated on the graphene layer. Through soft baking at $125^{\circ}C$ or 30 min, solvent in polyimide layer was removed. Then, 5-nm-thick indium layer was deposited by using thermal evaporator at room temperature. And then, the second polyimide layer was coated on the indium thin film. After remove solvent and open bottom graphene layer, the samples were annealed at $400^{\circ}C$ or 1 hr by using furnace in $N_2$ ambient. The average diameter and density of nanoparticle were depending on annealing temperature and times. During annealing process, the metal and oxygen ions combined to create $In_2O_3$ nanoparticle in the polyimide layer. The electrical properties of $In_2O_3$ nanoparticle ReRAM such as current-voltage curve, operation speed and retention discussed for applictions of transparent and flexible hybrid ReRAM device.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.469-470
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• 2008

We have studied electro-optic characteristics as a function of splay elastic constants ($K_{11}$) in the fringe-field switching (FFS) mode using the LC with positive dielectric anisotropy. When $K_{11}$ is increased from 7.7pN to 11.7pN, a maximum transmittance is slightly increased and rising time become a little bit fast. However, operating voltage and threshold voltage is independent. In opposition to rising time, decay time is not affected by $K_{11}$. We already know that $K_{11}$ affects tilt angle of liquid crystals. Therefore, on the occasion of high $K_{11}$, liquid crystals are mainly affected by twist deformation because the higher $K_{11}$, the less tilt angle. In the FFS device, high $K_{11}$ is favorable to reduce tilt angle in on state and thus improve rising response time.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.8
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• pp.1099-1106
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• 2018

In this paper, we developed and then analyzed the specifications of the frequency synthesizer which was applied to long range MFR (Multi-function Radar). These specifications were able to guarantee the functions and performance of MFR. MFR was the radar system that used phase array for electronically scanning. This frequency synthesizer made various frequency signals including to STALO (Stable Local Oscillator) for MFR. By analyzing the MFR requirements, we choose the optimal frequency synthesis method and then we got the best performance and functionality including to physical size for this system. We designed and fabricated DDS (Direct Digital Synthesizer)-driven Offset-PLL (Phase Locked Loop) synthesizer to meet the requirements which were low phase noise, fast switching time and low spurious. This synthesizer had less than -131dBc/Hz@100kHz phase noise and less than $4.1{\mu}s$ switching time, respectively.

• The Transactions of the Korea Information Processing Society
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• v.1 no.4
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• pp.469-478
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• 1994

In this paper, a high speed, high resolution information processing digital- analog converter was designed for high definition color graphic, digital image signal processing, HDTV. For high speed operation, matrix type current cell array, latch which is not use pipelined, and two dimensional structure decoder using transmission gate were designed. It is adopted to fast-conversion, low-power implementation and exhibited high performance at linearity and accuracy. To reduce silicon area and to maintain resolution, current cell array composed of weighted and non-weighted current cells. In this paper, deglitching current cell design for high accuracy, new switching algorithm assert to reduce switching error. It's This circuit dissipates 130W with a 5-V power supply, and operate above 100MHz with 10 bit resolution.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.2116-2118
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• 2000

In the technique of Q-switching, very fast electronically controlled optical shutters can be made by using the electro-optic effect in crystals or liquids. The driver for the Pockels cell must be a high-speed, high-voltage switch which also must deliver a sizeable current. Common switching techniques include the use of vacuum tubes, cold cathode tubes, thyratrons, SCRs, and avalanche transistors. Semiconductor devices such as SCRs, avalanche transistors, and MOSFETs have been successfully employed to drive Pockels cell Q-switch. In this study, a simple driver for the Pockels cell Q-switch was developed by using SCRs, pulse transformer and TTL ICs. The Pockels cell Q-switch which was operated by this driver was employed in pulsed Nd:YAG laser system to investigate the operating characteristics of this Q-switch. And we have investigated the output characteristics of this Q-switch as a function of the Q-switch delay time to Xe flashlamp current on.

• The KIPS Transactions:PartC
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• v.9C no.6
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• pp.847-856
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• 2002

Cellular network applications are growing drastically and this requires a fast and efficient transport method between the base station and the mobile switching center. One possible solution is to use ATM links. The low data rate and small-sized packets in the typical cellular applications imply that significant amount of link bandwidth would be wasted, if this small sized packet is carried by one ATM cell. For efficient operation for such cellular and low bit rate applications, a new type of ATM Adaptation Layer, AAL Type 2, has been proposed. In this paper, the principles of AAL Type 2 are briefly described along with the introduction of other alternatives which have formed the basis for this new AAL. The result from the simulation to study the performance of the AAL Type 2 is discussed from the view point of packet delay and ATM cell use efficiency. Due to the variable size of packets in this application, the fairness issue in serving variable sized packets is also discussed along with the effect of fair queueing algorithm implemented at AAL Type 2.