Browsing by Author "Chang, YJ"

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A behavior-level fault model for the closed-loop operational amplifier
(2000-09-01)
Chang, YJ
;
Lee, CL
;
Chen, JE
;
Su, CC
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電子工程學系及電子研究所
In this paper, a simple behavior-level fault model, which is able to represent the faulty behavior of the closed-loop operational amplifier (OP), is presented. The fault model, derived from the macro equivalent circuit of the OP but verified with transistor level simulation, consists of the offset fault and the limited-current fault. It can represent the faulty behavior of the dosed loop OP of all the transistor parametric (soft) faults and many of the catastrophic (hard) faults. Due to its simplicity, the proposed fault model (1) significantly reduces the complexity of fault simulation, and (2) makes closed-form analysis of the faulty behavior of the closed loop OP feasible when the closed loop OP is used as a basic building block of a complicated circuit. Although derived for DC, it can also be applied to AC fault analysis.
A low-cost electrical beam tilting base station antennas for wireless communication system
(2004-01-01)
Hwang, RB
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Chang, YJ
;
Lai, MI
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友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
A multifunctional feeding network is presented in this paper. It contains a one-to-eight Wilkinson-based power divider and eight microstrip lines backed with slot array. In addition, the moveable card printed with seven metal strips servs as a novel phase shifter. By dynamically moving the card, we can adjust the number and shielding area of the slot array and then alter the distribution of phase angle at each port of the feeding network accordingly. For example, in our application, we can have a progressive phase difference between the ports of feeding network and dynamically adjust them by changing the degree of perturbation on the slots array. The characteristic of beam tilting has been carefully examined by measuring the phase angle at each port and also by the far-field radiation pattern of the patch antenna array integrated with this novel phase shifter, in various perturbation conditions. The reliable, easily fabricated, and low-cost characteristics show its potential applications in the base-station antenna design.
A new quorum-based replica control protocol
(1997)
Wu, YT
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Chang, YJ
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Yuan, SM
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Chang, HK
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資訊工程學系
Data replication if an important issue in distributed systems. Many protocols are designed to achieve high availability, but some of them have restrictions on N, the number of nodes in the system. This motivates us to design a protocol suitable for arbitrary N. In this paper, we present a new quorum-based replica control protocol whose quorum size is O(root N), which is the same as that of the grid protocol. Moreover; the proposed protocol is almost symmetric, i.e., each node nearly bears the same responsibility. In particular, our protocol performs well in systems where read operations are requested more frequently than write ones.
Characteristics of air-water two-phase flow in a 3-mm smooth tube
(2000-10-01)
Wang, CC
;
Yang, KS
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Chang, YJ
;
Lu, DC
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機械工程學系
Two-phase flow pattern and friction characteristics for an air-water system in a 3.17 mm smooth tube are reported in this study. The range of mass flux is between 50 and 700 kg/m(2)s. The experimental data show that the two-phase friction multipliers are strongly related to the flow pattern. For a stratified-wavy flow pattern, a mass-flux dependence of the two-phase multipliers is seen. For a non-stratified flow pattern, the two-phase frictional multipliers are comparatively independent of mass flux. Correlations of the frictional multipliers are developed for stratified and non-stratified flow. To use the appropriate correlation in different regime, a simple criterion is proposed.
Characterization of two populations of mesenchymal progenitor cells in umbilical cord blood
(2006-06-01)
Chang, YJ
;
Tseng, CP
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Hsu, LF
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Hsieh, TB
;
Hwang, SM
Umbilical cord blood (UCB) is a valuable source for hematopoietic progenitor cell therapy. Moreover, it contains another subset of non-hematopoietic population referred to as mesenchymal progenitor cells (MPCs), which can be ex vivo expanded and differentiated into osteoblasts, chondrocytes and adipocytes. In this study, we successfully isolated the clonogenic MPCs from UCB by limiting dilution method. These cells exhibited two different morphologic phenotypes, including flattened fibroblasts (majority) and spindle-shaped fibroblasts (minority). Both types of MPCs shared similar cell surface markers except CD90 and had similar osteogenic and chondrogenic potentials. However, the spindle-shaped clones possessed the positive CD90 expression and showed a greater tendency in adipogenesis, while the flattened clones were CD90 negative cells and showed a lower tendency in adipogenesis. The high number of flattened MPCs might be linked to the less sensitivity of UCB-derived MPCs in adipogenic differentiation. (c) 2006 International Federation for Cell Biology. Published by Elsevier Ltd. All rights reserved.
Crosstalk fault detection for interconnection lines based on path delay inertia principle
(2005)
Wu, MS
;
Lee, CL
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Chang, YJ
;
Wu, WC
;
電子工程學系及電子研究所
The crosstalk fault becomes more and more important in the deep submicron SoC and its detection involves sophisticated timing measurement. In this paper a new test scheme to detect the crosstalk fault, based on the path delay inertia, for interconnection lines in SoC is proposed. The scheme, without using timing measurement, applies a transition on the aggressor line and a critical width pulse, CWP to the victim line and detects the propagation of the CWP at the output of the victim line. The scheme is simple and simulation analysis and experiments show that it is effective in detecting crosstalk faults.
DSP implementation of successive interference cancellation (SIC) receiver for 3GPP WCDMA uplink transmission
(2003-09-01)
Chang, YJ
;
Lin, YN
;
Lin, DW
;
電子工程學系及電子研究所
;
電信研究中心
The 3GPP WCDMA is a widely accepted third-generation cellular system standard. By using nonorthogonal codes for different users. the Multiple access interference (MAI) can be a limiting factor for system performance, as for other CDMA systems. Multiuser detection (MUD) is known to reduce MAI and improve CDMA system performance. but many Such techniques have high complexity. Successive interference cancellation (SIC) is an effective MUD technique with relatively low complexity. We consider the software implementation of an SIC receiver for WCDMA uplink transmission on a commercially available general-purpose multi digital signal processor (DSP) platform. This also goes in line with the recent interest in software-defined radio. Issues addressed in this work include job partitioning and signal routing for multiprocessor implementation, design of SIC components (especially the channel estimator and the si mal regenerator), determination of the precision of fixed-point computations. consideration of the receiver's error performance and analysis of the implementation's complexity and efficiency. These issues are tightly coupled with the 3GPP WCDMA specifications. Because the employed platform only contains four DSPs, the implementation only considers up to three users. But this is sufficient for Lis to appreciate various DSP implementation issues of an SIC receiver. Moreover, by the nature of SIC, it is easy to extend the implementation to handle more users with an enlarged platform. Our present implementation achieves real-time speed in the RAKE receiver part of the complete receiver. Due to the complexity in signal regeneration, the overall SIC receiver still falls short of the real-time requirement when interference cancellation is activated. In fact, the platform employed presently cannot support real-time processing when the number of multipaths is four or more, unless either the system architecture or the SIC algorithm is redesigned. Such and other ways of improvement are relegated to potential future work. Copyright (C) 2003 John Wiley Sons, Ltd.
Edge quantum yield in n-channel metal-oxide-semiconductor field-effect transistor
(2004-08-01)
Kang, TK
;
Su, KC
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Chang, YJ
;
Chen, MJ
;
Yeh, SH
The quantum yield of impact ionization is performed on an n-channel metal-oxide-semiconductor field-effect transistor (n-MOSFET) by a carrier separation measurement. When the n-MOSFET is biased in accumulation, the carrier separation measurement demonstrates that the gate current mainly originates from the electrons injected into the underlying drain/source overlap regions. The measured substrate current is due to excess holes originating from the impact ionization of the injected electrons in the overlap regions. Therefore, the quantum yield in the overlap regions can be determined by the ratio of the substrate current to the gate current. It is well matched with the theoretical calculation of quantum yield. (C) 2004 American Institute of Physics.
Forward gated-diode measurement of filled traps in high-field stressed thin oxides
(2000-08-01)
Chen, MJ
;
Kang, TK
;
Huang, HT
;
Liu, CH
;
Chang, YJ
The forward gated-diode monitoring technique can find its potential applications in assessing the filled traps in MOSFET thin oxides, which are subjected to high-field stressing and then followed by hot-electrons filling scheme. Our measurement of the gate voltage shift associated with the forward current peak produces a power lan relation between the filled trap density and the electron stress fluence, indeed in close agreement with that obtained by MOSFET threshold voltage shift.
Growth rate regulation of lac operon expression in Escherichia coli is cyclic AMP dependent
(2003-10-23)
Kuo, JT
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Chang, YJ
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Tseng, CP
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生物科技學系
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Department of Biological Science and Technology
In contrast to the ribosomal RNA gene expression increasing with growth rate, transcription of the lac operon is downregulated by cell growth rate. In continuous culture, growth rate regulation of lac promoter was independent of carbon substrate used and its location on the chromosome. Since the lac operon is activated by cyclic adenosine monophosphate (cAMP), which decreases with increasing cell growth rate, expression of plac-lacZ reporter fusion was analyzed in cya mutant under various growth conditions. The results demonstrated that expression of plac-lacZ in cya mutant was both lower and growth rate independent. In addition, ppGpp (guanosine tetraphosphate) was not involved in the mechanism of growth rate regulation of the lac promoter. Thus, the results of this study indicate that cAMP mediates the growth rate-dependent regulation of lac operon expression in Escherichia coli. (C) 2003 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.
Low-frequency noise in n-channel metal-oxide-semiconductor field-effect transistors undergoing soft breakdown
(2001-01-01)
Chen, MJ
;
Kang, TK
;
Lee, YH
;
Liu, CH
;
Chang, YJ
For 3.3-nm thick gate oxide n-channel metal-oxide-semiconductor field-effect transistors subject to a stress gate voltage of 5.5 V, three distinct events are encountered in the time evolution of the gate current: stress-induced leakage current (SILC), soft breakdown (SBD), and hard breakdown (HBD). The localization of SBD and HBD paths, as well as their developments with the time, is determined electrically, showing random distribution in nature. At several stress times, we interrupt the stressing to measure the drain current low-frequency noise power S-id. As expected, S-id follows up the spontaneous changes at the onset of SBD and HBD. The S-id spectra measured in fresh and SILC mode are reproduced by a literature model accounting for the carrier number and surface mobility fluctuations in the channel, and, as a result, both preexisting and newly generated trap densities are assessed. The post-SBD S-id does originate from current fluctuations in the SBD percolation paths, which can couple indirectly to drain via underlying channel in series, or directly to drain if the SBD path is formed close to drain extension. In particular, a fluctuation in S-id itself in the whole SBD duration is observed. This phenomenon is very striking since it indeed evidences the dynamic percolation origin concerning the trapping-detrapping processes in and around the SBD paths. The subsequent HBD duration remarkably features a flat S-id, indicating the set-up of a complete conductive path prevailing over the trapping-detrapping processes. (C) 2001 American Institute of Physics.
Numerical confirmation of inelastic trap-assisted tunneling (ITAT) as SILC mechanism
(2001-10-01)
Kang, TK
;
Chen, MJ
;
Liu, CH
;
Chang, YJ
;
Fan, SK
This paper presents a quite comprehensive procedure covering both the stress-induced leakage current (SILC) and oxide breakdown, achieved by balancing systematically the modeling and experimental works. The underlying model as quoted in the literature features three key parameters: the tunneling relaxation time tau, the neutral electron trap density N-t, and the trap energy level E-t. First of all, 7-nm thick oxide MOS devices with wide range oxide areas are thoroughly characterized in terms of the optically induced trap filling, the charge-to-breakdown statistics, the gate voltage developments with the time, and the SILC I-V. The former three are involved together with a percolation oxide breakdown model to build N-t explicitly as function of the stress electron fluence. Then the overall tunneling probability is calculated, with which a best fitting to SILC I-V furnishes tau of 4.0 x 10(-13) s and E-t of 3.4 eV. The extracted tau is found to match exactly that extrapolated from existing data. Such striking consistencies thereby provide evidence that inelastic trap-assisted tunneling (ITAT) is indeed the SILC mechanism. Differences and similarities of the involved physical parameters between different studies are compared as well.
Oxide thinning percolation statistical model for soft breakdown in ultrathin gate oxides
(2000-07-24)
Chen, MJ
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Kang, TK
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Liu, CH
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Chang, YJ
;
Fu, KY
An existing cell-based percolation model with parameter correlation can find its potential applications in assessing soft-breakdown (BD) statistics as long as the oxide thinning due to the localized physical damage near the SiO2/Si interface is accounted for. The resulting model is expressed explicitly with the critical trap number per cell n(BD) and the remaining oxide thickness t(ox)(') both as parameters. Reproduction of time-to-bimodal (soft- and hard-) breakdown statistical data from 3.3-nm-thick gate-oxide samples yields n(BD) of 3 and 4 for soft and hard breakdown, respectively. The extracted t(ox)(') of 1.0 nm for soft breakdown, plus the transition layer thickness of 0.5 nm in the model, is fairly comparable with literature values from current-voltage fitting. The dimension and area of the localized physically damaged region or percolation path (cell) are quantified as well. Based on the work, the origins of soft and hard breakdown are clarified in the following: (i) soft breakdown behaves intrinsically as hard breakdown, that is, they share the same defect (neutral trap) generation process and follow Poisson random statistics; (ii) both are independent events corresponding to different t(ox)(') requirements; and (iii) hard breakdown takes place in a certain path located differently from that for the first soft breakdown. (C) 2000 American Institute of Physics. [S0003-6951(00)02130-6].
Switched Beam System for low-tier wireless communication systems
(2001)
Chang, YJ
;
Hwang, RB
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
In this paper, we present a switched-beam antenna including a 4 by 4 Butler matrix and novel, compact, broadband CPW-fed uniplanar monopole array antennas at ISM band that were all fabricated with FR4 substrate. The lost cost and fairly good performance undoubtedly confirm its promising application in the low-tier wireless communication system such as PHS, DCS and Wireless LAN.