Browsing by Author "Chang, WJ"

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A novel TOA estimation method of broadband signal propagation in outdoor environment
(2004)
Chang, WJ
;
Tarng, JH
;
電信工程研究所
;
Institute of Communications Engineering
In high-speed wireless data transmission, severe frequency-selective fading of multipath channel causes inter-symbol interference (ISI) and leads to a significant problem of the systems. To ease the problem, precise modeling of the multipath time-of-arrival (TOA) is important and needed. In this paper, a novel method based on Turin's A-K model is proposed to estimate TOA of a broadband signal through the measured result of a narrow band signal in outdoor environments. Our method have been validated by the measurement result of 1.95 GHz and 2.44 GHz radio propagation in metropolitan and suburban areas. TOA of a 120MHz bandwidth signal can be effectively predicted by using our method with the measured results of a 15MHz bandwidth signal.
Discrete fuzzy covariance control for specified decay rate
(2005-03-15)
Chang, WJ
;
Shing, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper addresses the covariance control problem with decay rate for a class of nonlinear discrete stochastic systems using the Takagi- Sugeno ( T- S) fuzzy models. A methodology is developed to find the discrete fuzzy controllers for achieving individual state variance constraints of discrete T- S fuzzy stochastic models. The approach developed in this paper is based on the concept of parallel distributed compensation ( PDC) and covariance control. For each rule of the discrete T- S fuzzy model, it shows how to parameterize the static linear state feedback control gains to achieve a common covariance matrix and decay rate for each subsystem. Finally, a numerical example is provided to verify the effects of the proposed design method.
Effect of mechanical properties using different filler metals on wide-clearance activated-diffusion-brazed Ni-based superalloy
(2000-12-01)
Su, CY
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Chou, CP
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Chang, WJ
;
Liu, MH
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機械工程學系
The investigation of mechanical properties and failure mechanism of activated-diffusion-brazed (ADB) joints in IN-738 plate were conducted. Joints of this type, which had wide clearance, were formed using the brazing alloys Nicrobraz 150 and DF4B, The microstructural characterization showed that chromium borides with a blocky morphology were present in joints associated with the two brazing alloys. A major difference in matrix phase chemistry was observed, however, for the two brazing alloys, e.g., an Ni-B eutectic phase was observed in Nicrobraz 150, but DF4B exhibited a coarsened gamma prime (gamma) phase and an absence of a nickel boride matrix phase, Results of tensile test showed that ADB specimens using DF4B brazing alloy exhibited 95% nominal tensile strength of IN-738 base materials. Fracture cracks in the joint area mere initiated and confined to dispersed chromium boride sites. However, tensile test of ADB specimens using Nicrobraz 150 showed poor tensile properties at all testing temperatures, and their fractures were initiated at a brittle nickel boride site and propagated along the weak-bonded interface between the Ni-B eutectic phase and base materials.
Effect of radio bandwidth on multipath clustering
(2003)
Chang, WJ
;
Tarng, JH
;
電信工程研究所
;
Institute of Communications Engineering
Detail knowledge of time dispersion characteristics of radio multipath propagation channel is essential for successful design of Ultra-Wideband (UWB) systems. The multipath-clustering phenomenon, which is caused by the fact that scatterers tend to group together, may become one of the dominant factors affecting the delay spread especially in the long delay situation. In this paper, a method based on Turin's A-K model is proposed to investigate and estimate the effect of radio bandwidth on the multipath clustering. It is found that the signal of larger bandwidth will observe stronger multipath clustering phenomenon because more paths can be resolved due to a finer time resolution. Our finding has been validated by the measurement result of 1.95 GHz radio propagation in metropolitan and suburban areas. It is also proposed that the A-K process of a wider-bandwidth signal can determine that of a narrower-bandwidth signal.
Effects of compressive epitaxial strain on the magnetotransport properties of single-phase electron-doped La0.7Ce0.3MnO3 films
(2004-10-15)
Chang, WJ
;
Hsieh, CC
;
Juang, JY
;
Wu, KH
;
Uen, TM
Single-phase electron-doped manganite thin films with nominal composition of La0.7Ce0.3MnO3 (LCeMO) have been prepared on SrTiO3 (100) substrates by pulsed laser deposition. The conditions for obtaining purely single-phase LCeMO films lie within a very narrow window of substrate temperature (T(s)similar to720 degreesC) and laser energy density (E(D)similar to2 J/cm(2)) during deposition. In situ postdeposition annealing, mainly to relax the possible epitaxial in-plane tensile strain between the film and the substrate, leads to an increasing c-axis lattice constant accompanied by the formation of secondary CeO2 phase and higher metal-insulator transition temperature. This is indicative of a strong coupling between the electron and lattice degree of freedom. (C) 2004 American Institute of Physics.
Electronic structure and transport properties of La0.7Ce0.3MnO3
(2005-10-01)
Chang, WJ
;
Tsai, JY
;
Jeng, HT
;
Lin, JY
;
Zhang, KYJ
X-ray absorption spectroscopy (XAS), optical reflectance spectroscopy, and the Hall effect measurements were used to investigate the electronic structure in La0.7Ce0.3MnO3 thin films (LCeMO). The XAS results are consistent with those obtained from LDA+U calculations. In that the doping of Ce has shifted up the Fermi level and resulted in marked shrinkage of hole pockets originally existing in La0.7Ca0.3MnO3 (LCaMO). The Hall measurements indicate that in LCeMO the carriers are still displaying the characteristics of holes as LDA+U calculations predict. Analyses of the optical reflectance spectra evidently disapprove the scenario that the present LCeMO might have been dominated by the La-deficient phases.
ESD protection design of low-voltage-triggered p-n-p devices and their failure modes in mixed-voltage I/O interfaces with signal levels higher than VDD and lower than VSS
(2005-09-01)
Ker, MD
;
Chang, WJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Electrostatic discharge (ESD) protection design for mixed-voltage I/O interfaces with the low-voltage-triggered p-n-p (LVTp-n-p) device in CMOS technology is proposed. The LVTp-n-p, by inserting N+ or P+ diffusion across the junction between N-well and P-substrate of the p-n-p device, is designed to protect the mixed-voltage I/O interfaces for signals with voltage levels higher than VDD (over-VDD) and lower than VSS (under-VSS). The LVTp-n-p devices with different structures have been investigated and compared in CMOS processes. The experimental results in a 0.35-mu m CMOS process have proven that the ESD level of the proposed LVTp-n-p is higher than that of the traditional p-n-p device. Furthermore, layout on LVTp-n-p device for ESD protection in mixed-voltage I/O interfaces is also optimized in this work. The experimental results verified in both 0.35- and 0.25-mu m CMOS processes have proven that the ESD levels of the LVTp-n-p drawn in the multifinger layout style are higher than that drawn in the single-finger layout style. Moreover, one of the LVTp-n-p devices drawn with the multifinger layout style has been used to successfully protect the input stage of an asymmetric digital subscriber line (ADSL) IC in a 0.25-mu m salicided CMOS process.
ESD protection structure with embedded high-voltage p-type SCR for automotive vacuum-fluorescent-display (VFD) applications
(2005)
Ker, MD
;
Chang, WJ
;
Yang, M
;
Chen, CC
;
Chan, MC
A new ESD protection structure of HVPSCR embedded into the high-voltage PMOS device is proposed to greatly improve ESD robustness of the vacuum-fluorescent-display (VFD) driver IC for automotive electronics applications. By only adding the additional N+ diffusion into the drain region of HVPMOS, the 112 of output cell has been greatly improved form 0.07A to be greater than 6A within the almost same layout area. Such an ESD-enhanced VFD driver IC has been in mass production for automotive applications in car to sustain HBM ESD stress of up to 8kV.
Impact analysis of shear deformable laminated composite plates
(1995-09-01)
Kam, TY
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Chang, WJ
;
機械工程學系
;
Department of Mechanical Engineering
A method for investigating the dynamic response of shear deformable laminated composite plates subject to low-speed impact is presented. The equations of motion of the impactor and the plate are derived via a virtual work approach. The contact force between the impactor and the plate is calculated by using an experimentally established contact law. The effects of existing in-plane forces, plate aspect ratio, length-to-thickness ratio, fiber angles, and number of layer groups on the contact force with or without the consideration of ply failure are studied. Optimal fiber angles and number of layer groups for angle-ply plates with maximum first-ply failure impact velocity are determined based on the maximum stress criterion.
Impact analysis of shear deformable laminated composite plates
(1995-09-01)
Kam, TY
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Chang, WJ
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
A method for investigating the dynamic response of shear deformable laminated composite plates subject to low-speed impact is presented. The equations of motion of the impactor and the plate are derived via a virtual work approach. The contact force between the impactor and the plate is calculated by using an experimentally established contact law. The effects of existing in-plane forces, plate aspect ratio, length-to-thickness ratio, fiber angles, and number of layer groups on the contact force with or without the consideration of ply failure are studied. Optimal fiber angles and number of layer groups for angle-ply plates with maximum first-ply failure impact velocity are determined based on the maximum stress criterion.
Layout optimization on low-voltage-triggered PNP devices for ESD protection in mixed-voltage I/O interfaces
(2004)
Chang, WJ
;
Ker, MD
;
電機學院
;
College of Electrical and Computer Engineering
Layout optimization on low-voltage-triggered PNP (LVTPNP) devices for ESD protection in mixed-voltage I/O interfaces is proposed in this paper. The experimental results in both 0.35-mum and 0.25-mum CMOS processes have proven that the ESD levels of the LVTPNP drawn in the multi-finger layout style are higher than that drawn in the original layout style. Moreover, the LVTPNP device in multi-finger layout style has been implemented in a 0.25-mum salicided CMOS process to protect successfully the input stage of an ADSL IC with power-rail ESD clamp circuit.
LMI-based fuzzy controller design with minimum upper bound input energy and state variance constraints for discrete fuzzy stochastic systems
(2004)
Chang, WJ
;
Shing, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, a fuzzy controller design problem is considered for the discrete-time Takagi-Sugeno (T-S) fuzzy stochastic systems. The main purpose of this paper is to provide a systematic fuzzy controller design procedure for the discrete-time nonlinear stochastic systems, which are modeled by the T-S type fuzzy systems. A methodology is developed to find the discrete-time fuzzy controllers for minimizing upper bound control input energy and achieving state variance constraints for discrete-time T-S fuzzy stochastic systems. It is shown that the present approach can be used to solve the linear feedback control gains for each rule of the T-S fuzzy controllers using the Linear Matrix Inequality (LMI) technique. Finally, we apply the proposed controller design method to control a truck-trailer system to show the utility of the present approach.
Low-voltage-triggered PNP devices for ESD protection design in mixed-voltage I/O interface with over-VDD and under-VSS signal levels
(2004)
Ker, MD
;
Chang, WJ
;
Lo, WY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
ESD protection design for mixed-voltage I/O interfaces with the low-voltage-triggered PNP (LVTPNP) devices is proposed in this paper. The LVTPNP, by inserting N+ or P+ diffusion across the junction between N-well and P-substrate of the PNP devices, is designed to protect the mixed-voltage I/O pads for signals with voltage levels higher than VDD (over-VDD) and lower than VSS (under-VSS). The experimental results in a 0.35-mum CMOS process have proven that the ESD level of the proposed LVTPNP is higher than that of the traditional PNP device.
Magnetoresistance of La0.7Ca0.3MnO3 thin film biepitaxial step junctions
(2003-08-01)
Chen, SF
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Chang, WJ
;
Liu, SJ
;
Juang, JY
;
Lin, JY
The biepitaxial La0.7Ca0.3MnO3 (LCMO) thin films grown on SrTiO3 substrates using a buffer layer of anatase TiO2 were fabricated. The magnetoresistance (MR) of biepitaxial step junction (BSJ) across the boundary layer of biepitaxial LCMO (0 0 1) and LCMO (I 10) film was investigated. The temperature and field dependence of MR for BSJ are qualitatively similar to those obtained in other type of artificial grain boundaries with a comparable MR ratio at low temperatures. However, the observed linear current-voltage characteristic across BSJ is in sharp contrary to the commonly reported non-ohmic characteristics. The results are consistent with features predicted by the model of spin-dependent transport across a depressed magnetic ordering and metallic-like junction layer. (C) 2003 Elsevier Science B.V. All rights reserved.
Spectroscopic evidence of electron doping in La0.7Ce0.3MnO3
(2004-11-01)
Lin, JY
;
Chang, WJ
;
Juang, JY
;
Wen, TM
;
Wu, KH
X-ray absorption near edge spectroscopy was used to investigate the hole states in the La0.7Ce0.3MnO (LCeMO). A substantial decrease in the spectral weight of the e. orbital was observed in LCeMO compared to that in the hole-doped La0.7Ca0.3MnO. This directly proves that electron doping occurs in LCeMO. (C) 2004 Elsevier B.V. All rights reserved.
Strong anisotrpoic maganetoresistance and magnetic interaction in La0.7Ce0.3Mn0.3/La0.7Ca0.3MnO3 p-n junction
(2005-05-15)
Chou, H
;
Hong, ZY
;
Sun, SJ
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Juang, JY
;
Chang, WJ
The p-n junction made by colossal magnetoresistance materials, such as La0.7Ce0.3MnO3/La0.7Ca0.3MnO3, has great interest for its potential applications. However, the physics of the magnetic state and transport properties of the interface still remains open. In this article, bilayer La0.7Ce0.3MnO3/La0.7Ca0.3MnO3/STO films with a nearly perfect interface were studied. The p-n interface possibly becomes an antiferromagnetion-insulating layer as their parent compound, LaMnO3, and confines the bias current flowing only on the top layer. The top and bottom layers interact with each other in a way that a strong anisotropy tin magnetoresistance measurements was observed. (c) 2005 American Institute of Physics.
Traceless and stereoselective synthesis of tetrahydro-beta-carbolinethiohydantoins by microwave irradiation
(2006-03-01)
Chang, WJ
;
Kulkarni, MV
;
Sun, CM
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應用化學系
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Department of Applied Chemistry