Browsing by Author "Lee, YY"

Now showing 1 - 14 of 14

A novel algorithm for computing the 2D split-vector-radix FFT
(2004-03-01)
Huang, HY
;
Lee, YY
;
Lo, PC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper presents a novel two-dimensional split-vector-radix fast-Fourier-transform (2D svr-FFT) algorithm. The modularizing feature of the 2D svr-FFT structure enables us to explore its characteristics by identifying the local structural property. Each local module is designated as a DFT (non-DFT) block if its output corresponds to DFT (non-DFT) values. The block attribute (DFT or non-DFT) directs the algorithm to construct the local module. We will show that the distribution of DFT blocks can be illustrated by the Sierpinski triangle-a class of fractals generated by IFS (iterated function system). The finding of the Sierpinski-triangle structural property enables us to actually implement the 2D svr-FFT algorithm. To the best of our knowledge, the 2D svr-FFT has never been realized in software. The computational efficiency of the proposed algorithm is considerably improved in comparison with that provided by Matlab. (C) 2003 Elsevier B.V. All rights reserved.
An efficient FFT algorithm based on building on-line butterfly sub-structure
(1998)
Lee, YY
;
Lo, PC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper presents a new method of implementing the fast Fourier transform (FFT), the "real-time FFT algorithm", which efficiently utilizes the computer time to perform the FFT computation while the data acquisition proceeds. The main idea is to build the local butterfly modules using the data points available. The algorithm is based on the decimation-in-time split-radix FFT (DIT sr-FFT) butterfly structure. The algorithm is superior to the conventional whole-block FET algorithm in synchronizing with the on-line process. The time delay is about 2/r that of the whole-block algorithm considering the FFT size N=2(r).
Applicability of phase-locked loop to tracking the rhythmic activity in EEGS
(2000)
Lo, PC
;
Lee, YY
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Conventional methods of spectral analysis are based on mathematical or numerical algorithms applied to digitized signals. This paper discusses the applicability of the phase-locked loop (PLL) approach for tracking electroencephalogram (EEG) rhythmic bands (delta, theta, alpha, or beta). The use of the PLL for frequency tracking should also aid the development of online EEG interpretation and screening based on frequency characteristics when the PLL is realized by hardware. As a result, two factors in the applicability of the PLL are: (1) translation of the EEG spectrum to a higher-frequency band by a single-sideband (SSB) modulation scheme, and (2) the narrowband spectral feature of the EEG-a small difference between two major frequencies. The PLL output is further quantized according to the EEG rhythmic bands. Our analysis shows that the integrated system is capable of tracking the EEG rhythmic patterns.
Categorization of EEG rhythmic patterns based on PLL approach
(2000)
Lee, YY
;
Lo, PC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper demonstrates a new approach based on phase-locked loop (PLL) model to categorizing the EEG (electroencephalogram) rhythmic band (delta, theta, alpha, or beta). The main idea is to translate the EEG spectrum to a higher frequency band by single-sideband (SSB) modulation scheme. A few factors determine the system performance in EEG analysis. According to the results of computer simulation, a satisfactory performance can be achieved by using the PLL model with a properly selected loop gain and loop-filter bandwidth.
Effects in carrier dynamics of Isolectronic In doped in GaN films grown by metalorganic vapor phase epitaxy
(2000)
Huang, HY
;
Shu, CK
;
Lin, WC
;
Liao, KC
;
Chuang, CH
Time-resolved photoluminescence spectra were used to characterize isoelectronically doped GaN:In films. Our results indicate that the recombination lifetime of donor-bound-exciton transition of pure GaN exhibits strong dependence on temperature. When In is doped into GaN, the recombination lifetime decreases sharply from 68 ps to 30 ps, irregardless of measured temperature and In doping concentration. The cause for this appearance is not clear at present. It might be related to the isoelectronic In impurity itself in GaN, which creates shallow energy levels that predominate the recombination process.
Isoelectronic As doping effects on the optical characteristics of GaN films grown by metalorganic chemical-vapor deposition
(2000-10-30)
Huang, HY
;
Lin, WC
;
Lee, WH
;
Shu, CK
;
Liao, KC
We have studied the As doping effects on the optical characteristics of GaN films by time-integrated photoluminescence and time-resolved photoluminescence. When As is incorporated into the film, the localized defect levels and donor-acceptor pair transition become less resolved. The recombination lifetime of neutral-donor-bound exciton (I-2) transition in undoped GaN increases with temperature as T-1.5. However, the I-2 recombination lifetime in As-doped GaN first decreases exponentially from 98 to 41 ps between 12 and 75 K, then increases gradually to 72 ps at 250 K. Such a difference is related to the isoelectronic As impurities in GaN, which generate nearby shallow levels that dominate the recombination process. (C) 2000 American Institute of Physics. [S0003-6951(00)01941-0].
Kinetics of the CH3S+O-3 reaction.
(1997-09-07)
Wang, NS
;
Chew, EP
;
Lin, JT
;
Lee, YY
;
Lee, YP
Kinetics of the CH3S+O-3 reaction.
(1997-09-07)
Wang, NS
;
Chew, EP
;
Lin, JT
;
Lee, YY
;
Lee, YP
Quantification of the pseudo-periodicity in EEG
(2000-03-01)
Lo, PC
;
Lee, YY
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Some EEG signals possess pseudo-periodicity, which is difficult to identify, and quantify. This paper points out the problems and proposes a straightforward approach for analyzing this long-term, extra low-rate rhythmicity (the fundamental frequency). The effect of pseudo periodicity on the Fourier spectrum is investigated. To process the enormous number of data points often encountered in this kind of signal, we adopt the down-sampling scheme in the field of multi-rate signal processing. In addition, waveform rectification is introduced to enhance the capability in detecting the number of pseudo periods. The experimental results demonstrate that the Fourier analysis, in combination with the down-sampling and amplitude-rectified processes, is feasible for quantifying the fundamental frequency and pseudo period of the EEG.
Real-time FFT algorithm applied to on-line spectral analysis
(1999-01-01)
Lo, PC
;
Lee, YY
;
電控工程研究所
;
Institute of Electrical and Control Engineering
On-line running spectral analysis is of considerable interest in many electrophysiological signals, such as the EEG (electroencephalograph). This paper presents a new method of implementing the fast Fourier transform (FFT) algorithm. Our "real-time FFT algorithm" efficiently utilizes computer time to perform the FFT computation while data acquisition proceeds so that local butterfly modules are built using the data points that are already available. The real-time FFT algorithm is developed using the decimation-in-time split-radix FFT (DIT sr-FFT) butterfly structure. In order to demonstate the synchronization ability of the proposed algorithm, the authors develop a method of evaluating the number of arithmetic operations that it requires. Both the derivation and the experimental result show that the real-time FFT algorithm is superior to the conventional whole-block FFT algorithm in synchronizing with the data acquisition process. Given that the FFT size N = 2(r), real-time implementation of the FFT algorithm requires only 2/r the computational time required by the whole-block FFT algorithm.
Real-time FFT algorithm applied to on-line spectral analysis
(1999-01-01)
Lo, PC
;
Lee, YY
;
電控工程研究所
;
Institute of Electrical and Control Engineering
On-line running spectral analysis is of considerable interest in many electrophysiological signals, such as the EEG (electroencephalograph). This paper presents a new method of implementing the fast Fourier transform (FFT) algorithm. Our "real-time FFT algorithm" efficiently utilizes computer time to perform the FFT computation while data acquisition proceeds so that local butterfly modules are built using the data points that are already available. The real-time FFT algorithm is developed using the decimation-in-time split-radix FFT (DIT sr-FFT) butterfly structure. In order to demonstate the synchronization ability of the proposed algorithm, the authors develop a method of evaluating the number of arithmetic operations that it requires. Both the derivation and the experimental result show that the real-time FFT algorithm is superior to the conventional whole-block FFT algorithm in synchronizing with the data acquisition process. Given that the FFT size N = 2(r), real-time implementation of the FFT algorithm requires only 2/r the computational time required by the whole-block FFT algorithm.
Real-time implementation of the moving FFT algorithm
(1999-12-01)
Lo, PC
;
Lee, YY
;
電控工程研究所
;
Institute of Electrical and Control Engineering
An integrated algorithm for analyzing the real-time, running Fourier spectra is presented. When applying to the real-time analysis, the computational efficiency and synchronization ability are highly improved by integrating the recursive procedure with the real-time implementation strategy. Given the FFT (frame) size N = 2(r) and moving size M = 2(p), the algorithm implements the recursive procedure for updating the succeeding decomposed (into size N/M) DFTs at the (r - p)th stage, and thereafter constructs the sr-FFT (split-radix fast-Fourier-transform) butterfly modules in a real-time way. The recursive procedure highly reduces the number of complex arithmetic operations when the moving size M is small. The real-time implementation scheme enables the running spectral analysis to better synchronize with the data acquisition process. The computational complexity of the integrated algorithm is analyzed in detail, which shows the dependence of the number of complex arithmetic operations on the ratio N/M. The experimental result tested on Pentium 66 agrees with the analysis. (C) 1999 Elsevier Science B.V. All rights reserved.
Real-time implementation of the split-radix FFT - An algorithm to efficiently construct local butterfly modules
(1998-12-01)
Lo, PC
;
Lee, YY
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Time-resolved photoluminescence study of isoelectronic In-doped GaN films grown by metalorganic vapor-phase epitaxy
(2000-05-29)
Huang, HY
;
Shu, CK
;
Lin, WC
;
Chuang, CH
;
Lee, MC
Time-resolved photoluminescence spectra were used to characterize isoelectronically doped GaN:In films. Our results indicate that the recombination lifetime of the donor-bound-exciton transition of undoped GaN exhibits a strong dependence on temperature. When In is doped into the film, the recombination lifetime decreases sharply from 68 to 30 ps, regardless of the measured temperature and In source flow rate. These observations might be related to the isoelectronic In impurity itself in GaN, which creates shallow energy levels that predominate the recombination process. (C) 2000 American Institute of Physics. [S0003- 6951(00)02622-X].