• JSTS:Journal of Semiconductor Technology and Science
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• 제14권3호
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• pp.313-321
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• 2014

A low-power low-cost polar transmitter for EDGE is designed in $0.18{\mu}m$ CMOS. A differential delta-sigma modulator (DSM) tunes a three-terminal voltage-controlled oscillator (VCO) to perform RF phase modulation, where the VCO tuning curve is digitally pre-compensated for high linearity and the carrier frequency is calibrated by a dual-mode low-power frequency-locked loop (FLL). A digital intermediate-frequency (IF) pulse-width5 modulator (PWM) drives a complementary power-switch followed by an LC filter to achieve envelope modulation with high efficiency. The proposed transmitter with 9mW power dissipation relaxes the time alignment between the phase and envelope modulations, and achieves an error vector magnitude (EVM) of 4% and phase noise of -123dBc/Hz at 400kHz offset frequency.

• Structural Engineering and Mechanics
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• 제43권5호
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• pp.691-709
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• 2012

This paper provides a variety of viewpoints to illustrate the mechanism of the deck-stay interaction with the appropriate initial shapes of cable-stayed bridges. Based on the smooth and convergent bridge shapes obtained by the initial shape analysis, the one-element cable system (OECS) and multi-element cable system (MECS) models of the Kao Ping Hsi Bridge in Taiwan are developed to verify the applicability of the analytical model and numerical formulation from the field observations in the authors' previous work. For this purpose, the modal analysis of the two finite element models are conducted to calculate the natural frequency and normalized mode shape of the individual modes of the bridge. The modal coupling assessment is also performed to obtain the generalized mass ratios among the structural components for each mode of the bridge. The findings indicate that the coupled modes are attributed to the frequency loci veering and mode localization when the "pure" deck-tower frequency and the "pure" stay cable frequency approach one another, implying that the mode shapes of such coupled modes are simply different from those of the deck-tower system or stay cables alone. The distribution of the generalized mass ratios between the deck-tower system and stay cables are useful indices for quantitatively assessing the degree of coupling for each mode. These results are demonstrated to fully understand the mechanism of the deck-stay interaction with the appropriate initial shapes of cable-stayed bridges.

• 한국전자파학회논문지
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• 제14권1호
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• pp.1-7
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• 2003

Davidenko 방법으로 정확하게 구하여진 정규화 복소 전파 상수로부터 원형 유전체 봉의 누설 모드를 조사하였다. 도파 모드의 차단 주파수 아래에서 nonphysical 영역, 안테나 모드 영역, Reactive 모드 영역, spectral gap영역 등의 독특한 주파수 영역이 관찰되었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.202-207
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• 2002

This paper deals with a novel shunted actuator, which has a capability to suppress multi-mode vibration amplitudes by using a pair of piezoceramic patches. In order to describe the characteristic behaviors of shunted dampers connected with a series and a parallel resistor-negative capacitive branch circuit, the stiffness ratio and loss factor with respect to the non-dimensional frequency are considered. To obtain a guideline model of a piezo/beam system connected with a series and a parallel resistor-negative capacitor branch circuit, the governing equations of motion is derived through Hamiltons principle and a piezo sensor equation as well as a shunt damping matrix is developed. The theoretical analysis shows that the shunted actuator developed in this study can significantly reduce multiple-mode vibration amplitudes simultaneously over the whole structural frequency range.

• Nuclear Engineering and Technology
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• 제50권7호
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• pp.1106-1111
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• 2018

Electromagnetic waves potentially have been used to heat overdense nuclear fusion plasmas through a double mode conversion from ordinary to slow extraordinary and finally to Electron Bernstein Wave (EBW) modes, OSXB. This scheme is efficient and has not any plasma density limit of electron cyclotron resonance heating due to cut-off layer. The efficiency of conversion depends on the isotropic launching angles of the microwaves with the plasma parameters. In this article, a two-step mode conversions of OSXB power transmission efficiency affected by the fast extraordinary (FX) loses at upper hybrid frequency are studied. In addition, the kinetic (hot) dispersion relation of a overdense plasma in a full wave analysis of a OSXB in Wendelstein 7X (W7-X) stellarator plasma has been numerically simulated. The influence of plasma dependent parameters such as finite Larmor radius, electron thermal velocity and electron cyclotron frequency are represented.

• 한국음향학회지
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• 제21권8호
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• pp.757-765
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• 2002

본 논문은 해석과 실험을 통하여 구형 압전 변환기의 점대칭 방사모드 진동 특성을 규명하는 것을 목적으로 한다. 반경 방향 좌표와 시간의 함수인 반경 방향 변위와 전기 퍼텐셜로 표현되는 지배방정식을 구성한다. 역학적 경계조건과 전기적 경계조건을 적용하여 방사 진동의 특성방정식을 유도한다. 이 식을 이용하여 압전 고유진동수를 계산하고, 그 결과를 측정 결과와 비교한다. 수치계산을 통하여 압전 공진과 탄성 공진의 차이, 구형 압전체의 반경 및 두께에 따른 고유진동수 등을 고찰한다. 그 결과 1차 방사모드의 고유진동수 크기는 압전현상으로 인해 작아지며 구형의 곡률 반지름이 커짐에 따라 지수함수적으로 작아지는 것을 알게 되었다.

• 한국통신학회논문지
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• 제22권4호
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• pp.685-695
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• 1997

In this paper, a new CMOS continuous-time fully-differential current-mode integrator is proposed as a basic building block of the low-voltage high frequency current-mode active filter. The proposed integrator is composed of the CMOS complementary circuit which can extend transconductance of an integrator. Therefore, the unity gain frequency which is determined by a small-signal transconductance and a MOSFET gate capacitance can be expanded by the complementary transconductance of the proposed integrator. And also the magnitude of pole and zero are increased. The unity gain frequency of the proposed integrator is increased about two times larger than that of the conventional continuous-time fully-differential integrator with NMOS-gm. These results are verified by the small signal analysis and the SPICE simulation. As an application circuit of the proposed fully-differential current-mode integrator, the three-pole Chebyshev lowpass filter is designed using 0.8.$\mu$m CMOS processing parameters. SPICE simulation predicts a 3-dB bandwidth of 148MHz and power dissipation of 4.3mW/pole for the three-pole filter with 3-V power supply.

• 한국산학기술학회논문지
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• 제13권10호
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• pp.4745-4750
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• 2012

본 논문에서는 저전압 저전력 필터 설계에 적합한 전류모드 방식을 이용하여 고속 전력선통신(PLC)모뎀 수 신단의 1MHz~30MHz 차단주파수를 갖는 6차 대역통과 필터를 설계하였다. 3차 바터워스 고역통과 필터와 3차 체비세프 저역통과 필터를 종속연결로 구성하여 대역통과 필터를 설계하였다. 필터를 구성하기 위한 핵심로써 기존의 전류미러형 적분기에 비하여 증가된 이득 및 차단주파수를 가지는 새로운 전류모드 적분기를 설계하였다. 설계된 전류모드 적분기의 이득과 차단주파수는 각각 32.2dB 및 247MHz이였다. 설계된 6차 대역통과 필터의 차단주파수는 제어전압에 따라서 200KHz에서 50MHz까지 조정이 될 수 있으며 소비전력은 공급전압 1.8V에서 2.85mW이였다. 설계된 대역통과 필터는 1.8V, $0.18{\mu}m$ CMOS 공정파라메터를 사용하여 검증되었다.

• Journal of Biosystems Engineering
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• 제14권4호
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• pp.229-241
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• 1989

The purposes of this study were to develop an electronic-hydraulic draft control system for tractor implements, to investigate the control performance of the system and the possibility of adaptation to the conventional tractor. Experiments were carried out to investigate the responses of the system to the step and sinusoidal inputs in draft control. The effects of control mode, hydraulic flow rate, reference deadband, and proportional constant on control performance of the system were investigated. Moreover, the effects of filtering signals from draft sensor were also investigated. The following conclusions were derived from the study; 1. In draft control, there were hunting problems in controlling the implement without filtering the draft signals. Filtering was performed by a control program of electronic controller and the control performance and stability of the system were improved significantly. 2. For the draft control system operated on on-off control mode, draft was controlled within ${\pm}27-{\pm}55kg_f$ to the reference draft when the hydraulic flow rates were 5-15 l/min. For the draft control system operated on PWM control, draft was controlled within ${\pm}27kg_f$ to the reference draft regardless of hydraulic flow rates. 3. In the frequency responses of the draft control system, control performance on PWM control mode was not better than on on-off control mode because of characteristics of hydraulic valve and drafe sensor. As the hydraulic flow rates increased for the system operated on on-off control mode, the corner frequency of amplitude attenuation increased, but the corner frequency of phase-angle change remained nearly the same. But, the system was unstable beyond the frequency of 3.1 rad/s. 4. The electronic-hydraulic hitch control system developed in this study showed superior control performance, stability and convenience compared to conventional mechanical-hydraulic hitch control system. It is considered to be a superior replacement for the conventional mechanical-hydraulic hitch control system.

• Structural Engineering and Mechanics
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• 제84권3호
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• pp.413-421
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• 2022

Modal parameters are the main dynamic characteristics of bridge. This study aims to propose an innovative route to estimate the modal parameters for bridges by using a parked vehicle in which mode shapes with high accuracy and spatial resolution are identified by frequency measurement. Based on the theory of dynamic modification and modal identification, the mathematical formulation between the parked mass induced frequency variation and the modal parameters of a bridge is derived. Then this mathematical formulation is extended to a parked vehicle-bridge system. The arithmetic and processes for estimating the modal parameters based on the identified frequency variation of the vehicle-bridge systems when the vehicle locates at sequentially arranged positions are presented. Finally the proposed method is applied to several simulated bridges of different types. The results indicate that it can estimate the modal parameters with high accuracy and efficiency.