• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.854-859
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• 2001

An eigenvalue analysis of a tunable micro-mechanical actuator is presented. The actuator is modeled as a continuum structure. The eigenvalue modified by the tuning voltage is computed through the linearization of the relation between the electrostatic force and the displacement at the equilibrium. A staggered algorithm is employed to perform the coupled analysis of the electrostatic and elastic fields. The stiffness matrix of the actuator is modified at this equilibrium state. The displacement field is perturbed using an eigenmode profile of the actuator. The configuration change of the actuator due to perturbation modifies the electrostatic field and thus the electrostatic force. The equivalent stiffness matrix corresponding to the perturbation and the change in the electrostatic force is then added to stiffness matrix in order to explain natural frequency shifting. The numerical examples are presented and compared with the experiments in the literatures.

• Journal of Power Electronics
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• 제9권2호
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• pp.320-333
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• 2009

A Photovoltaic (PV) system's power output varies with the change of climate. Frequency deviations, tie line voltage swings are caused by the varying PV power when large PV power from several PV systems is fed in the utility. In this paper, to overcome these problems, a simple coordinated control method for smoothing the variations of combined PV power from multiple PV systems is proposed. Here, output power command is formed in two steps: central and local. Fuzzy control is used to produce the central smoothing output power command considering insolation, variance of insolation and absolute average of frequency deviation. In local step, a simple coordination is kept between the central power command and the local power commands by producing a common tuning factor. Power converters are used to achieve the same output power as local command power employing PI control law for each of the PV generation systems. The proposed method is compared with the method where conventional Maximum Power Point Tracking (MPPT) control is used for each of the PV systems. Simulation results show that the proposed method is effective for smoothing the output power variations and feasible to reduce the frequency deviations of the power utility.

• 한국소음진동공학회논문집
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• 제12권5호
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• pp.374-379
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• 2002

A new active muffler system has been developed and its superior performance on both noise reduction and engine torque increase is demonstrated with experiment. Main characteristic of the proposed muffler system is the use of destructive interference by transmission path difference of divided exhaust pipes to reduce major exhaust noise components thereby overcoming problems of other active exhaust noise control methods. The exhaust pipe is divided into two sections and joined again downstream. One divided pipe has a sliding mechanism to vary its length, which is controlled to make half wavelength transmission path difference for the major engine rpm frequency. In this system one divided pipe is used to control major rpm frequency and its Harmonics and another pipe is used to control noise component double the frequency of rpm. An after-market tuning muffler, which has very simple internal structure and minimal back pressure, is also installed to remove remaining wideband noise. To make the system to be small enough to be practical, conventional muffler is also installed and used in low rpm range and active muffler is only employed in high rpm range. Noise reduction of the proposed system is comparable to conventional passive muffler. The engine dynamo test has proved the proposed system can recover almost all the torque lost by conventional muffler.

• 한국광학회지
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• 제4권3호
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• pp.301-308
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• 1993

현상론적인 비 선형 이득 포화 효과가 연속 파장 가변시 다전극 DBR 레이저의 변조 특성에 미치는 영향을 이론적으로 분석하였다. 수동 부분에 전류 주입의 증가에 따라 FM 효율, 3dB 대역폭, 공명 주파수는 감소하지만, flat FM응답은 증가한다. 비 선형 이득 포화 효과는 FM/IM응답, 3dB 대역폭, 공명 주파수, chirping-to-modulation-power ratio 등 변조 특성에 커다란 영향을 미치지만, 연속 파장 가변에 의한 변조 특성에는 영향을 미치지 않는다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 심포지엄 논문집 정보 및 제어부문
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• pp.195-196
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• 2007

Since the digital TV signal band is very wide ($54{\sim}806MHz$), the VCO used in the frequency synthesizer must also have a wide frequency tuning range. Multiple LC VCOs have been used to cover such wide frequency band. However, the chip area increases due to the increased number of integrated inductors. In this paper, a scheme is proposed to cover the full band using only one VCO. The RF VCO block designed using a 0.18um CMOS process consists of a wideband LC VCO, five divide-by-2 circuits and several buffers. The simulation results show that the designed circuit has a phase noise at 10kHz better than -87dBc/Hz throughout the signal band and consumes 10mA from a 1.8V supply.

• 한국통신학회논문지
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• 제21권9호
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• pp.2362-2372
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• 1996

This paper deals with the design and development of an Injection-Locking Coupled Oscillators(ILCO), which functions like phase-shifter in the Active Intergrated Phased Array Antenna(AIPAA). This linear array 2-element ILCO consists of two Injection Locking Hair-pin Resonator Oscillators(ILHRO) and an unilateral amplifier. The first and second elements of the ILCO have same frequency tuning range but locking bandwidths of 11.5MHz and 14MHz respectively. A phase shift of .DELTA..PHI.=158.4.deg.(-78.0.deg. to 80.4.deg.) could be obtained inthe second element of ILCO when the first elementof the ILCO was in the reference locking mode(.DELTA..PHI.=0.deg.). When the ILCO is applied to the AIPAA, the predicted beam scanning angle value will be 38.4.deg.. Each ILCO gives good frequency stability and lower AM, FM, and PM noise charactheristics in the mutual coupling lockingmode. The ILCO can not only play a part as the phase shifter for the AIPAA but it can also be usedas the power combining device in the mm-wave frequency range and as a part of a T/R MMIC module.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 D
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• pp.3181-3183
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• 2000

As the fact that the simple data of text and sound in early year have been changed to be high quality images and sounds. PLL(Phase-Locked Loop) system plays an important role in communication system. VCO(Voltage Controlled Oscillator) is the most important part in PLL system because it can have critical effects on operation of PLL. Recently, it has been raised the necessity of high speed and high accuracy circuit application. In this paper, a new differential voltage clamped VCO using negative-skewed path is suggested. Using a dual-delay scheme to implement the VCO, higher operation frequency and wider tuning are achieved simultaneously. The dual-delay scheme means that both the negative skewed delay paths and the normal delay paths exist in the same ring oscillator. The negative skewed delay paths decrease the unit delay time of the ring oscillator below the single inverter delay time. As a result, higher operation frequency can be obtained. The whole characteristics of VCO are simulated by using HSPICE. Simulation results show that the resulting operating frequencies are 50% higher than those obtainable from the conventional approaches.

• 한국전자파학회논문지
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• 제21권3호
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• pp.223-228
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• 2010

본 논문에서는 온도 센서와 OP-AMP를 이용하여 X-밴드용 전압제어 발진기를 위한 온도 보상 회로를 구현하였다. 온도 변화에 대해 선형적인 특성을 갖는 온도 센서의 출력 전압을 튜닝 전압에 더해서 전압제어 발진기에 인가함으로써 온도에 따른 주파수 이동을 보상할 수 있었다. -30~+$60^{\circ}C$의 온도 범위에서 9.95~10.05 GHz의 대역에 대해 온도 보상을 한 결과, 전체 대역폭에서 출력 주파수는 온도 보상 전 71~73 MHz가 변화했으나, 온도보상 후에는 6.6~4.4 MHz의 변화를 보였다.

• 전기학회논문지
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• 제60권2호
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• pp.446-450
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• 2011

Tunable SC(Switched Capacitor) bandpass ${\Sigma}-{\Delta}$(Sigma-Delta) modulator used in wireless system receiver occurs a signal attenuation according to tuning of center frequency in signal bandwidth. In this paper, tunable bandpass 4th order SC bandpass ${\Sigma}-{\Delta}$ modulator with novel structure is proposed for rejection of signal attenuation in signal bandwidth. The existing structure uses a ten variable coefficient values for rejection of signal reduction in the modulator. But the proposed structure only use a two variable coefficient values for rejection of signal attenuation in the modulator. Also, an adder and comparator is replaced with a comparator having 4 inputs in the modulator. Therefore, the existing structure has one more OP-AMP. The purposed modulator was designed in $0.18\;{\mu}m$ CMOS technology. The resolution of the modulator within 310 kHz bandwidth and 40 MHz sampling frequency under 6.67 MHz, 10 MHz and 13.33 MHz intermediate frequency are over 10 bit.

• 전력전자학회논문지
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• 제7권1호
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• pp.48-54
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• 2002

본 논문에서는 간접 유도가열 되는 DPH시스템과 주파수 범위가 20kHz에서 50kHz사이에서 작동되는 전압형 직렬공진 고주파인버터를 이용하여 열 기체를 발생시키는 전압형 공진형 인버터에 관하여 설명하였다. 얇은 스텐레스 판재가 서로 스폿 용접되어 연결되어 있고 미세한 많은 구멍을 갖고있는 적층형 충진발열테로 특수하게 설계된 유도 가열기는 외부에 워크 코일로 감겨져 있는 불소수지계의 절연용기 안에 삽입되어 있다. 이 워크 코일은 공진형 인버터와 연결되어 있으며 유도가열기를 통해 흐르는 관 유체를 1단가열부에서 저압의 포화증기를 2단가열부에서 열방사성 증발유체를 생성하는 본 DPH시스템의 성능 및 효용성을 실용적인 측면에서 논의하고 평가 할 것이다.