Browsing by Author "Chen, CH"

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4-(Dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran doped red emitters in organic light-emitting devices
(2003-09-22)
Liu, TH
;
Iou, CY
;
Wen, SW
;
Chen, CH
;
應用化學系
We have studied the device optimization of red 4-(Dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) dye doped Alq(3) emitters in organic light-emitting devices (OLED). By varying the hole injection materials, thickness of hole-transport layer and by evaporation with rubrene as co-dopant, efficiencies of 3.24 cd/A and near saturated CIE color coordinates of x = 0.643, y = 0.354 was achieved without needing additional doping of hole-trap with NPB. From experiments with film thickness variation, it is concluded that the improved electrofluorescent (EL) performance and color saturation are due to the synergistic effects of microcavity, device structural optimization as well as optimal doping of DCJTB with rubrene. We believe this luminance efficiency for red is by far one of the best ever reported for dye-doped electrofluorescent OLEDs. (C) 2003 Elsevier B.V. All rights reserved.
5.4GHz-127 dBc/Hz at 1MHz GaInP/GaAs HBT quadrature VCO using stacked transformers
(2005-08-04)
Meng, CC
;
Chen, CH
;
Chang, YW
;
Huang, GW
;
電信工程研究所
The first fully integrated GaInP/GaAs heterojunction bipolar transistor (HBT) quadrature voltage controlled oscillator (VCO) using the stacked-transformer LC tank is demonstrated at 5.43-5.31 GHz with low-phase-noise performance. The stacked-transformers are formed by two interconnect metal layers and possess good electrical properties at high frequencies because of the semi-insulating GaAs substrate. The quadrature VCO at 5.38 GHz has phase noise of -127.4 dBc/Hz at 1 MHz offset frequency, output power of -4 dBm and a figure of merit (FOM) -191 dBc/Hz.
A beamspace-time blind RAKE receiver for sectored CDMA systems
(2001-04-01)
Lee, TS
;
Tsai, TC
;
Chen, CH
;
電信工程研究所
;
友訊交大聯合研發中心
A beamspace-time (BT) RAKE receiver is proposed for multiple access interference (MAT) suppression and multipath diversity reception in sectored wireless CDMA communications. The scheme involves three stages. First, a set of adaptive beamformers encompassing a prescribed angular sector is constructed on an antenna array, each providing effective suppression of out-of-sector MAI and reception of in-sector signal. Second, a set of adaptive correlators is attached to each beam to combat in-sector MAI. Finally, the beamspace correlator output data are combined to capture the signal multipaths coherently. The above three-stage operation is performed in a blind mode in that no training signal is needed. The only information required is the signature, timing and a rough estimate of the angle of arrival (AOA) of the desired signal.
A dynamic model of mutual inductance for the compensation of current control utilizing the optimum searching strategy for switched reluctance motor drives
(2004)
Huang, WN
;
Teng, CC
;
Fang, CH
;
Chen, CH
;
電控工程研究所
A methodology to design the dynamic model taking the mutual inductance into account for the switched reluctance motor (SRM) drives is proposed in this paper. The overall consideration is focus on the current control compensation strategy that related to the practically existing unmodeled parameter, the mutual inductance, to improve the drives performance. A mutual inductance related expression is discussed and then an optimum searching method, chosen for ease-of-applying, is utilized for solving the key parameter owning on-line computational procedures potentials. By the presented model based on the motor characteristics analytical opinion, the relationship between the compensation current command and the neglected effect of the drives output can be established. The effectiveness of this model is demonstrated by the comparison with/without the dynamic model being involved.
A JPEG-like texture compression with adaptive quantization for 3D graphics application
(2002-02-01)
Chen, CH
;
Lee, CY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
DCT-based compression is widely used in video and image compression for a high compression ratio, but it suffers from random-access problem when applied to texture compression. In this paper we present a JPEG-Like DCT-based texture compression technique which is suitable for 3D graphics rendering system. We apply a simple adaptive quantization on an 8 x 8 bloc size texture, such that the length of the encoded bit stream of one block can be approximated to the target. A pre-defined quantizer scale is encoded with the bit stream with a small overhead. Our technique achieved a high compression ratio, quality control of true color texture, and random access of texture data.
A low power, fast-switching frequency synthesizer of 5.2GHz WLANs
(2004)
Cheng, KH
;
Chen, CH
;
Jou, CF
;
電信工程研究所
;
Institute of Communications Engineering
A 1.5V supply, low power consumption and fast switching integer-N frequency synthesizer is presented. The synthesizer consists of LC-tank VCO with quadrature output, D-type flip-flop (DFF) prescalar, swallow-counter, phase-frequency detector, charge pump and 4(th) order loop filter. A noble design procedure for loop filter is also presented with the aid of MATLAB program. The phase noise of VCO is -106dBc/Hz @1MHz offset. Total power consumption of synthesizer is 20.5mW. Settling time is 40us. The synthesizer is fabricated by TSMC 0.25um CMOS technology, and is suitable for HiperLAN II and IEEE 802.11a lower side-band applications.
A new yellow fluorescent dopant for high-efficiency organic light-emitting devices
(2006-02-21)
Wu, YS
;
Liu, TH
;
Chen, HH
;
Chen, CH
;
應用化學系
We describe the design and synthesis of a sterically hindered yellow dopant, tetra(l-butyl)rubrene (TBRb) which, when doped in either 1,4-bis[N-(1-naphthyl)-N'-phenylamino]-biphenyl or aluminum tris(8-hydroxyquinoline) (Alq(3)) as emitter, shows nearly 25% increase in luminance efficiency over that of the state-of-the-art rubrene (Rb) device without significantly effecting its corresponding color. At 5% doping in Alq3 and 20 mA/cm(2) current drive condition, the electroluminescence efficiency of TBRb reaches 8.5 cd/A and 2.8 1m/W with a yellow color of Commission Internationale de l'Eclairage chromaticity coordinates (CIEx,y)=[0.52,0.48], which is among the best ever reported for yellow electrofluorescence in organic light-emitting devices. (c) 2005 Elsevier B.V. All rights reserved.
A novel visual distortion sensitivity analysis for video encoder bit allocation
(2004)
Tang, CW
;
Chen, CH
;
Yu, YH
;
Tsai, CJ
;
資訊工程學系
A novel video bit allocation technique adopting a visual distortion sensitivity model for better rate-visual distortion coding control is proposed in this paper. Instead of applying complicated semantic understanding, the proposed automatic distortion sensitivity analysis process analyzes both the motion and the texture structures in the video sequences in order to achieve better bit allocation for rate-constrained video coding This analysis evaluates the tolerable perceptual distortions on a macroblock basis, and allocates fewer bits to regions permitting large perceptual distortions for rate reduction. The proposed algorithm can be incorporated into any existing video coding rate control schemes to achieve same Visual quality at greatly reduced bitrate. Experiments based on H.264 show that this technique achieves bit-rate saving of up to 40% with no perceptual quality degradations. The experiments also demonstrate the inadequacy Of using PSNR as a distortion measure in a video coding framework.
A numerical analysis of horizontal flame spread over a thin fuel in normal and elevated gravity regime
(1995)
Chen, CH
;
Chan, SC
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
A numerical model is developed to simulate flame spread over a thin solid fuel horizontally in a gravitational field. In this paper, the burning behaviors in normal and elevated gravity are analyzed. In normal gravity, the flame structures are investigated in detail in order to find the essential features of such spreading flame. The flame can be separated into an upper flame and a lower flame by the fuel plate. There are three high temperature regions: two of them are at the upper and lower flame fronts, respectively, and the other one is at the combustion plume, just behind the burnout point. The induced flow moves upward and forms a thermal plume above the fuel plate. An entrainment of air moves toward the flame, opposed to the upper spreading flame. Below the fuel plate, the induced flow moves concurrently with the lower spreading flame. From the reaction rate distribution, the characteristics of triple-reaction-zone is identified. The heat flux on the bottom side is more intensive and extends further upstream than that on top side, confirming that the controlling mechanism is determined by the spreading flame underneath the fuel plate. A qualitative comparison with experiments is given. A parametric study by elevating gravity is followed. A blowoff limit occurs at about g = 5.5. During the process, the horizontal flame spread rate is found to be slower than the downward one behind g = 2.5, where the lower flame is broken due to the up-rising induced flow. The variation in flame structures as a function of gravity is discussed.
A numerical analysis of ignition to steady downward flame spread over a thin solid fuel
(2003-05-01)
Wu, KK
;
Chen, CH
;
機械工程學系
;
Department of Mechanical Engineering
A numerical analysis using an unsteady combustion model is presented to study the ignition and subsequent downward flame spread over a thermally thin solid fuel in a gravitational field. The solid-fuel temperature rises gradually in the heat-up stage and the pyrolysis becomes more intense. Ignition, including the induction period and thermal runaway, occurs as soon as a flammable mixture is formed and the gas-phase temperature, heated by the solid fuel, becomes high enough. During the induction period, the reactivity and temperature in the gas phase are mutually supportive. The thermal runaway consists of a burning premixed flame as the flow moves with the flame front. This is followed by a transition from a premixed flame into a diffusion flame. The flame front extends along and toward the upstream virgin fuel as the diffusion flame is formed. Finally, steady flame spread takes place as burnout appears. The ignition delay time is found to be controlled mainly by the time required to form the flammable mixture and is almost independent of the gravity level and the ambient oxygen index. The ignition delay time increases nearly linearly with an increase in solid-fuel thickness within the range of 0.005 cm less than or equal to (τ) over bar less than or equal to 0.02 cm and is proportional to ((Q) over bar (max))(-1.11) within 2W/cm(2) less than or equal to (Q) over bar (max) less than or equal to 8 W/cm(2). The steady downward flame-spread rate decreases with increases in the gravity level or fuel thickness and with decreases in the ambient oxygen index but is independent of the incident peak heat flux. The blowoff limit is around 6.7 (g) over bar (e) and the extinction limit is found to be Y (Oinfinity) = 0.131.
A potential-based generalized cylinder representation
(2004-12-01)
Chuang, JH
;
Ahuja, N
;
Lin, CC
;
Tsai, CH
;
Chen, CH
Generalized cylinder (GC) is a class of parametric shapes that is very flexible and capable of modeling many different types of real-world objects, and have subsequently been the focus of considerable research in the vision community. Most of the related works proposed previously have dealt with the recovery of 3D shape description of objects based on the GC representation from one or more 2D image data. Different from the objective of the previous works, in this paper, we will propose a new approach to obtain a GC-based shape description of 3D objects. The proposed approach of deriving the GC axis is a further extension of the potential-based skeletonization approach presented in (IEEE Trans. Pattern Anal. Mach. Intell. 22(11) (2000) 1241). Simulation results demonstrate that the derived GC representation will yield better approximation of object shape than that based on simpler subclasses of GC since there is, in principle, no restriction on the topology of the GC axis and the shape of the cross-sections. (C) 2004 Elsevier Ltd. All rights reserved.
A study of meandered microstrip coupler with high directivity
(2003)
Wang, SM
;
Chen, CH
;
Chang, CY
;
電信工程研究所
;
Institute of Communications Engineering
A novel design technique to improve the directivity of a microstrip direction coupler by a meandered structure is proposed in this paper. Increasing of even-mode phase velocity by the proposed meandering method is reported for the first time. An analytical method to obtain closed-form equations of even-mode phase velocity is developed. The proposed structure is verified by experiments. More than 40 dB measured directivity improvement comparing to conventional microstrip coupler is achieved.
Ab initio molecular orbital study of 1,3,5-triazine derivatives for phosphorescent organic light emitting devices
(2005-10-24)
Chu, TY
;
Ho, MH
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Chen, JF
;
Chen, CH
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電子物理學系
Novel triplet host materials 2,4,6-tris(diarylamino)-1,3,5-triazine derivatives (TRZ1-TRZ4) have been reported and from which TRZ2 as a host for Ir(ppy)(3) was particularly useful in producing high efficiency phosphorescent organic light emitting diodes (OLEDs). This Letter reports the molecular orbital and energy level of these derivatives determined by ab initio calculation. The calculated triplet bandgap energy of TRZ1 has been found to be larger than that of TRZ2 and the TRZ1 molecules and has the lowest dipole moment which infers the highest carrier mobility. Therefore, TRZ1 has the potential to be a superb triplet host material and electron transport material. (c) 2005 Elsevier B.V. All rights reserved.
Adaptive rate-distortion optimization using perceptual hints
(2004)
Tsai, CJ
;
Tang, CW
;
Chen, CH
;
Yu, YH
;
資訊工程學系
A novel video coding approach that performs adaptive rate-distortion optimization guided by perceptual hints is proposed in this paper The key idea is to adaptively adjust the Lagrange multipliers of the RDO coder control module based on visual attention analysis. The observation is that human vision is sensitive to movement of well structured objects while tolerates large distortion in moving areas with random structure (texture-wise and motion-wise). The proposed algorithm analyzes permissible perceptual distortions and, accordingly, assigns larger Lagrange multipliers to regions that are perceptually less sensitive to distortion so that rate-reduction is weighted more than distortion reduction in these regions. Experiments show that this scheme achieves bit-rate saving of 5-7% with virtually same perceptual quality and is very promising for practical systems.
Antiresonant reflecting optical waveguide surface plasmon resonance sensors
(2001)
Huang, YT
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Chang, WZ
;
Hsu, SH
;
Chen, CH
;
Chen, JC
An ARROW-B (antiresonant reflecting optical wavegnide, type B) surface plasmon resonance (SPR) sensor operating in aqueous environment is proposed. The characteristics, design, and optimization of the Au-coated ARROW-B SPR sensor are discussed. The operating range of the sensor can be shifted by adding a dielectric overlay. The detectable changes of the refractive index down to the order of 10(-5) can be achieved. The design of an ARROW SPR sensor on Si substrates for detecting hydrogen molecules with palladium as the metal film will also be discussed.
Assessment of fire protection performance of water mist applied in exhaust ducts for semiconductor fabrication process
(2005-09-01)
Shu, YL
;
Jeng, WJ
;
Chiu, CW
;
Chen, CH
;
機械工程學系
Fume exhaust pipes used in semiconductor facilities underwent a series of fire tests to evaluate the performance of a water mist system. The parameters considered were the amount of water that the mist nozzles used, the air flow velocity, the fire intensity and the water mist system operating pressure. In order to make a performance comparison, tests were also performed with a standard sprinkler system. The base case served as a reference and applied a single water mist nozzle (100 bar operating pressure, 7.31/min water volume flux and 200 pin mean droplet size) installed in the pipe (60 cm in diameter) subjected to a 350 degrees C air flow with an average velocity of 2 m/s. In such a case, the temperature in the hot flow dropped sharply as the water mist nozzle was activated and reached a 60 degrees C saturation point. Under the same operating conditions, four mist nozzles were applied, and made no further contribution to reducing the fire temperature compared with the case using only a single nozzle. Similar fire protection performances to that in the base case were still retained when the exhaust flow velocity increased to 3 m/s and the inlet air temperature was increased to 500 degrees C due to a stronger input fire scenario, respectively. Changing to a water mist system produced a better performance than a standard sprinkler. With regard to the effect of operating pressure of water mist system, a higher operating pressure can have a better. performance. The results above indicate that the droplet size in a water-related fire protection system plays a critical role. Copyright (c) 2005 John Wiley & Sons, Ltd.
Beam-propagation-dominant instability in an axially pumped solid-state laser near degenerate resonator configurations
(2001-08-01)
Chen, CH
;
Wei, MD
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
Propagation-dominant instabilities and chaos were found under so-called good-cavity conditions in an axially pumped solid-state laser operated near the 1/3-degenerate cavity configuration that had not previously been studied numerically. By using the generalized Huygens integral together with rate equations, we obtained a V-shaped configuration that depends on a quasi-periodic threshold. We call the propagation dominant because the laser behaves as a conservative system governed by beam propagation. Although it had previously been predicted that chaos would be impossible under nearly degenerate conditions, we have recognized that the laser is transformed into chaos as a result of the interplay of beam propagation and gain dynamics as the cavity is tuned close to degeneracy. (C) 2001 Optical Society of America.
Bottle beam from a bare laser for single-beam trapping
(2004-11-10)
Chen, CH
;
Tai, PT
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We demonstrate that a laser beam converging from a specific transverse mode is a bottle beam, as described in J. Opt. Soc. Am. B 20, 1220 (2003). To our knowledge, this is the first time that a bottle beam has been generated directly from a laser. By calculating the radiation forces on a dielectric Rayleigh sphere in the bottle beam, we show that the single beam can trap high-refractive-index particles at the multiple axial sites of intensity maxima, and it can confine low-index particles on a transverse plane within the bottle regions. Such a novel laser beam may have other applications. (C) 2004 Optical Society of America.
Cavity-configuration-dependent instability in a tightly focused end-pumped solid-state laser
(2004-11-01)
Chen, CH
;
Tai, PT
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We experimentally studied the cavity-configuration-dependent instability in an end-pumped Nd:YVO4 laser in the vicinity of the degenerate resonator configuration Of g(1)g(2) = 1/4 with small pump size. We found that the laser instability occurs in a narrow range of cavity tuning on each side of the degeneracy, which shows periodic, period-doubling, and chaotic time evolutions. By using Collin's integral together with rate equations and taking into account the thermal lens effect, we show that the simulation is consistent with the experiments. The observed instabilities are new and, as far as we know, this is the first report that discusses the relationship between the instability and the thermal lens effect. (C) 2004 Elsevier B.V. All rights reserved.
Characterization and optimization of NO-nitrided gate oxide by RTP
(1995)
Sun, SC
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Chen, CH
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Yen, DLW
;
Lin, CJ
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奈米中心