• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.5
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• pp.621-627
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• 2011

In this paper, we analysed performance for on-wafer GaN HEMT using load-pull in X-band, and studied optimum impedance point based on analysis result. We suggested method of optimum performance device by analysis of optimum impedance for solid state device on-wafer condition before packaging. The measured device is gate length 0.25um, and gate width is 400um, 800um. device 400um is performed $P_{sat}$=33.16dBm, PAE=67.36%, Gain=15.16dBm, and device 800um is performed $P_{sat}$=35.91dBm, PAE=69.23%, Gain=14.87dBm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.11
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• pp.1034-1046
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• 2011

In this paper, a design and fabrication of 40 W power amplifier for the X-band using load-pull measurement of GaN HEMT chip are presented. The adopted active device for power amplifier is GaN HEMT chip of TriQuint company, which is recently released. Pre-matched fixtures are designed in test jig, because the impedance range of load-pull tuner is limited at measuring frequency. Essentially required 2-port S-parameters of the fixtures for extraction optimal input and output impedances is obtained by the presented newly method. The method is verified in comparison of the extracted optimal impedances with data sheet. The impedance matching circuit for power amplifier is designed based on EM co-simulation using the optimal impedances. The fabricated power amplifier with 15${\times}$17.8 $mm^2$ shows the efficiency above 35 %, the power gain of 8.7~8.3 dB and the output power of 46.7~46.3 dBm at 9~9.5 GHz with pulsed-driving width of 10 usec and duty of 10 %.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.1
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• pp.42-48
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• 2011

In this paper, a passive load-pull using a GaN HEMT (Gallium Nitride High Electron Mobility Transistor) bare-chip in X-band is presented. To obtain operation conditions that characteristic change by self-heating was minimized, pulsed drain bias voltage and pulsed-RF signal is employed. An accuracy impedance matching circuits considered parasitic components such as wire-bonding effect at the boundary of the drain is accomplished through the use of a electro-magnetic simulation and a circuit simulation. The microstrip line length-tunable matching circuit is employed to adjust the impedance. The measured maximum output power and drain efficiency of the pulsed load-pull are 42.46 dBm and 58.7%, respectively, across the 8.5-9.2 GHz band.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.261-262
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• 2020

본 논문은 DC/DC 위상천이 풀브릿지 컨버터의 과도상태 개선을 위한 듀얼모드 제어를 제안한다. 기존의 discontinuous conduction mode (DCM)과 continuous conduction mode (CCM)을 이용하여 운용하는 위상천이 풀브릿지 컨버터는 각 모드의 상이한 전압게인의 특성을 고려하지 않아 급격한 로드 변동시 출력 전압의 언더슈트 혹은 오버슈트가 크게 발생한다. 제안하는 듀얼모드 제어는 DCM과 CCM 각 모드 별개로 제어가 적용되고 출력 전류의 변화에 대응하는 적응형 feed-forward 제어가 적용되어 컨버터의 과도상태를 개선할 수 있다. 듀얼모드의 제어 방법의 성능과 타당성을 시뮬레이션을 통해 입증한다.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.8
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• pp.945-952
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• 2015

Power amplification device which is matched to $50{\Omega}$ in order to achieve a high efficiency of a power amplifier using a GaN power amplification device, since there is a limit of application frequency bands, output power, efficiency characteristics selection, in this study based on the measurement data through the source/load-pull test, high output power and to extract quantitative input and output impedance that matches the design objectives of high output power, high efficiency, an implementation of the high efficiency power amplifier. Implemented power amplifier is shows 25watt(44dBm), PAE of 66-76% characteristics in the frequency band of 2.7-3.1 GHz.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.411-415
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• 2003

In this paper, a reflector type frequency doubler for local oscillator at 24GHz is designed and fabricated with ne71300-N MESFET. Optimum source and load impedances are decided through a multiharmonic load pull simulation technique. A conversion gain ran be improved using the reflector and fundamental and third harmonics are well suppressed with open stub of λ/4 length. Measured results show output power at 0dBm of input power is -3.776dBm, conversion gain 0.736dB, harmonic suppression 41.064dBc, respectively.

• Journal of Navigation and Port Research
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• v.28 no.1
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• pp.37-41
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• 2004

In this paper, a reflector type frequency doubler for local oscillator at 24GHz is designed and fabricated with ne71300-N MESFET. Optimum source and load impedances are decided through a multiharmonic load pull simulation technique. A conversion gain can be improved using the reflector and fundamental and third harmonics are well suppressed with open stub of $\lambda$/4 length Measured results show output power at 0dBm of input power is -3.776dBm, conversion gain 0.736dB, harmonic suppression 41.064dBc, respectively.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.11a
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• pp.117-118
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• 2009

클러스터링 분야에서는 대규모 계산 및 처리, 저장 등의 작업을 하기 위해 다양한 정책과 효율적인 전략들이 기술적 사상으로써 적용되는 대표적인 분야 중 하나이다. 그 중에서도 대규모 처리(Load)시 처리자원으로의 효율적인 자원 분배(Balancing)를 하는 LoadBalancing에 관한 연구는 지속적으로 이루어지고 있다. 효율적인 로드밸런싱 기법에는 경제적인 계산 비용이 소요되는 서버풀내의 각 처리 서버들에 대한 연결 정보를 Queue에 넣고 FCFS 스케줄링 알고리즘등을 활용하는 방법들이 널리 쓰이고 있다. 그러나, 이 방법의 경우, 서버풀의 추가 및 삭제와 같은 변동상황 발생시 이를 처리하는데 많은 비용이 소요된다는 문제를 가지고 있다. 본 논문에서는 클러스터링 처리 환경에서 이중 구조 큐 순환을 이용한 서버풀 및 이에 속하는 각각의 처리서버에 대한에 부하 분산 기법을 소개하고자 한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.9
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• pp.987-994
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• 2010

In this paper, a simple and effective active load-pull method is proposed, and the method to improve the efficiency of X-band power amplifier using harmonic control circuit is presented. The proposed active load-pull system mainly consists of directional coupler, phase shifter, short circuit, and power amplifier, and allows a user to access reflection coefficients near the edge of the Smith chart($\Gamma$=1) easily. The device used in this paper is Mitsubishi's GaAs FET MGF1801, and the operating frequency of the power amplifier is 9 GHz, The amplifier had output power of 21.65 dBm and drain efficiency of 24.9 % at class-A, and had output power of 21.46 dBm and drain efficiency of 53.3 % at class-AB. Harmonic control circuit is designed only second and third harmonic components because of the bandwidth limitation of the microwave components. The drain efficiency is improved as much as 6.4 % compared with class-AB power amplifier.

• Journal of the Korea Society of Computer and Information
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• v.15 no.3
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• pp.81-89
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• 2010

The research on peer-to-peer streaming schemes has largely focused on tree-push and mesh-pull structures. However, the tree-push structure has a defect that the tree restructuring time is long, and the mesh-pull structure has long startup delay and lag time from source servers. In this paper, we propose a new peer-to-peer live streaming scheme based on a push-mesh structure that takes advantages of tree-push and mesh-pull structure simultaneously. This structure basically provides the mesh-pull mechanism for data transmission and utilizes peers with high network upload capacity. It also supports the push mechanism along with paths from a source server, super peers, and selected general peers. By NS-2 simulation experiments, we finally show that our proposed scheme can achieve shorter startup delay than the mesh-pull structure, similar lag time to tree-push structure and best playback continuity among the three schemes.