Browsing by Author "Wang, DY"

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Audio coding using sinusoidal excitation representation
(1997)
Chang, WW
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Wang, DY
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Wang, LW
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交大名義發表
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電信工程研究所
Most LPC-based audio coders employ simplistic noise-shaping operations to perform psychoacoustic control of quantization noise. In this paper, we report on new approaches to exploiting perceptual masking in the design of adaptive quantization of LPC excitation parameters. Due to its localized spectral sensitivity, sinusoidal excitation representation is preferred to spectrally flat signals for use in excitation modeling. Simulation results indicate that the proposed multisinusoid excited coder can deliver high quality audio reproduction at the rate of 72 kb/s.
Basic characteristics of Pt/SrBi2Ta2O9/HfO2/Si structure using layer-by-layer crystallization
(2005)
Wang, DY
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Chang, CY
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Layer-by-layer-crystallized SrBi2Ta2O9 (SBT) films were deposited by metallorganic decomposition on a 14-nm-thick HfO2 buffer layer. Experimental results indicate that the metal-ferroelectric-insulator-semiconductor (MFIS) stack with a layer-by-layer-crystallized SBT film exhibits ferroelectric hysteresis and a memory window of around 0.34 V at an operating voltage of 6.0 V. When postdeposition annealing was performed at 850 S C, the layer-by-layer-crystallized MFIS structure exhibited favorable switching characteristics with negligible degradations of the memory window and capacitance retention time. The retention time of this structure exceeded 10(4) s and the extrapolated time was about 105 s. (c) 2005 The Electrochemical Society. All rights reserved.
Direct measurement of electrical hysteresis of micron-sized Pb(Zr,Ti)O-3 capacitors using the constant current method
(2004-07-01)
Wang, DY
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Chang, CY
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
In this paper, we introduce a constant current method (CCM) for directly measuring the electrical hysteresis of micron-sized Pb(Zr,Ti)O-3 capacitors prepared on Pt/Ta/SiO2/Si substrates. The parasitic effect of the probing setup is found to possibly increase the maximum polarization as the capacitor's area is reduced. The CCM technique can be exploited to calculate the parasitic capacitance of the probe station and then easily construct the corrected hysteresis loops. Additionally, the dielectric constants of small capacitors were measured using an LCR meter, for comparison with the linear dielectric constant obtained from the high-field slope of the hysteresis loops with parasitic correction. Strong agreement was found between the measured dielectric constants and the results obtained from the hysteresis loops. These results indicate that the CCM technique represents an approach for investigating the ferroelectric characteristics of small ferroelectric capacitors.
High-performance Pt/SrBi2Ta2O9/HfO2/Si structure for nondestructive readout memory
(2003-09-01)
Chien, CH
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Wang, DY
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Yang, MJ
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Lehnen, P
;
Leu, CC
Metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with 390-nm-thick SrBi2Ta2O9 (SBT) ferroelectric film and 8-nm-thick hafnium. oxide (HfO2) layer on silicon substrate have been fabricated and characterized. It is demonstrated for the first time that the MFIS stack exhibits a large memory window of around 1.08 V at an operation voltage of 3.5 V. Moreover, the MFIS memory structure suffers only 18% degradation in the memory window after 10(9) switching cycles. The excellent performance is attributed to the formation of well-crystallized SBT perovskite thin film on top of the HfO2 buffer layer, as evidenced by the distinctive sharp peaks in X-ray diffraction (XRD) spectra. In addition to its relatively high kappa value, HfO2 also serves as a good seed layer for SBT crystallization, making the proposed Pt/SrBi2Ta2O9/HfO2/Si structure ideally suitable for low-voltage and high-performance ferroelectric memories.
Low-pressure crystallization of sol-gel-derived PbZr0.52Ti0.48O3 thin films at low temperature for low-voltage operation
(2003-05-01)
Wang, DY
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Chien, CH
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Chang, CY
;
Leu, CC
;
Yang, JY
The properties of sol-gel-derived 120-nm PbZr0.52Ti0.48O3 thin films crystallized in low-pressure O-2 ambient at 500degreesC have been investigated. it is found that PbZr0.52Ti0.48O3 films crystallized in low-pressure oxygen ambient exhibit higher remanent polarization as well as a lower coercive field, compared to those annealed in O-2 atmosphere. The remanent polarization (i.e., 2P(r)) for samples annealed in 60 mbar O-2 ambient is as high as 36 muC/cm(2), and the coercive field (2E(C)) is 99.9 kV/cm at an applied voltage of 2 V. The improvement of P-E hysteresis loops by low-pressure oxygen annealing is ascribed to less incorporation of oxygen and other residues in the resultant PbZr0.52Ti0.48O3 films, since the reductions in the amount of these residual species are beneficial for the complete transformation of the perovskite structure. The reductions in oxygen content and amounts of other residues such as CO2 and H2O are confirmed based on Auger depth profiles and thermal desorption spectra (TDS), respectively.
Perceptual quantisation of LPC excitation parameters
(1998-06-01)
Chang, WW
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Wang, DY
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電信工程研究所
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Institute of Communications Engineering
A new approach to wideband digital audio compression at 64 kbit/s is presented. This LPC coder features a sinusoidal excitation model and adaptive bit-allocation based on a mask-to-noise ratio perceptual measure. Owing to its localised spectral sensitivity, sinusoidal excitation representation can be shown to provide an ideal framework for incorporating an estimated masking threshold in the design of noise spectral shaping. Quantisation of LPC and excitation parameters is also examined. Simulation results indicate that sine waves are preferred to spectrally flat signals for use in excitation modelling, because in the former the estimated masking threshold can be more precisely implemented in the distribution of quantisation noise.
Quality enhancement of sinusoidal transform vocoders
(1998-12-01)
Chang, WW
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Wang, DY
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電信工程研究所
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Institute of Communications Engineering
The authors present quality enhancement of sinusoidal transform coders (STCs) via the development of parametric models. The benefits of the Bark spectrum are explored for use in the design of perceptual coding of the sine-wave amplitudes. According to the results, the proposed approach provides a uniform perceptual fit across the spectrum. To enhance the accuracy of phase representation, noncausal all-pole modelling of the vocal system is also discussed. Experimental results indicate that the use of the developed new parametric models allows the STC to improve the phase accuracy as well as the synthetic speech quality.
Robust vector quantization for wireless channels
(2001-07-01)
Chang, WW
;
Tan, TH
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Wang, DY
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電信工程研究所
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Institute of Communications Engineering
This study focuses on two issues: parametric modeling of the channel and index assignment of codevectors, to design a vector quantizer that achieves high robustness against channel errors. We first formulate the design of a robust zero-redundancy vector quantizer as a combinatorial optimization problem leading to a genetic search for a minimum-distortion index assignment. Performance is further enhanced by the use of the Fritchman channel model that more closely characterizes the statistical dependencies between error sequences. This study also presents an index assignment algorithm based on the Fritchman model with parameter values estimated using a real-coded genetic algorithm. Simulation results indicate that the global explorative properties of genetic algorithms make them very effective in estimating Fritchman model parameters, and use of this model can match index assignment to expected channel conditions.
Switching current study: Hysteresis measurement of ferroelectric capacitors using current-voltage measurement method
(2005-04-01)
Wang, DY
;
Chang, CY
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this study, we utilize the current-voltage (I-V) measurement method for investigating the ferroelectric characteristics of ferroelectric capacitors, such as hysteresis loops, switching current characteristics, retention properties and depolarization characteristics. By applying triangular voltage wave forms without sweeping and measuring delay, the hysteresis switching current characteristic was determined and the polarization-voltage (P-V) loop could be obtained using an integral calculus. Additionally, two kinds of poling measurement were utilized to investigate the full-switching and nonswitching current characteristics. A strong agreement was found between nonvolatile polarization (Delta P) obtained from P-V loops and that obtained by poling measurements. Moreover, modified poling measurements were utilized to study the retention property of ferroelectric capacitors. A dynamic switching current characteristic was found in retention duration and an increased coercive voltage was also observed in its half-hysteresis loops as remaining time increased. Furthermore, another modified poling profile was utilized to investigate the depolarization characteristics of ferroelectric films.
Techniques for improving sinusoidal transform vocoders
(1998)
Chang, WW
;
Wang, DY
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電信工程研究所
;
Institute of Communications Engineering
This paper presents quality enhancement of sinusoidal transform coders (STC) via the development of new parametric models. First explored are the benefits of Bark spectrum for use in the design of perceptual coding of the sine-wave amplitudes. According to our results, the proposed approach provides a uniform perceptual fit across the spectrum. To enhance the accuracy of phase representation, noncausal all-pole modeling of the vocal system is also discussed. Experimental results indicate that the use of new parametric models allows the STC to improve the phase accuracy as well as the synthetic speech quality.
Triangular current: Method for measuring hysteresis loops of ferroelectric capacitors
(2004-09-01)
Wang, DY
;
Chang, CY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this paper, we present a triangular current (TC) method for measuring the hysteresis loops of Pb(Zr,Ti)O-3 capacitors prepared on Pt/Ta/SiO2/Si substrates. Like the constant current (CC) method, this method is a current source mode method for obtaining hysteresis loops. By applying a triangular charging current to a specimen, a measured voltage profile, which is almost noiseless and smooth in the high-field region, is obtained and its hysteresis curve can be determined using integral calculus to convert the charging current to charge. Under various charging conditions, the similarity of the obtained hysteresis curves implies that the step charging current and number of steps do not affect the measured results. Moreover, the parasitic effect of the probe setup is found to possibly increase the maximum polarization of the ferroelectric capacitor as the area of the capacitor is reduced. The TC method can be utilized to determine the parasitic capacitance of the probe setup and then can easily determine the corrected hysteresis loops of small capacitors. These findings reveal that the TC method constitutes a new method for measuring the hysteresis loops of ferroelectric capacitors.
Using agents and simulation to develop adequate thinking styles
(2005)
Wang, DY
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Wu, ZH
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Sun, CT
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Lin, SSJ
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資訊工程學系
Reinforcement learning theory encourages the use of agents for stimulating and assisting learners in their efforts to develop thinking styles. In this study the authors looked at a similar scenario of human-environmental interaction using Internet-mediated simulations as learning environments. One hundred and forty-nine vocational high schools students participated in this study to see if they can develop adequate thinking style when they learned in a simulation environment with help from agents. The results show that the judicial thinking style was best suited to the system we designed for this project-that is, we observed the greatest amount of development for this particular thinking style. Our results indicate that it is possible to establish and support thinking styles via Internet-mediated simulations.