Browsing by Author "Hsieh, CY"

Now showing 1 - 10 of 10

A 1-V 2.4-GHz cmos frequency synthesizer with current-match charge pump
(2004)
Wu, CY
;
Hsieh, CY
;
Chen, WM
;
電機學院
;
College of Electrical and Computer Engineering
A 1-V 2.4-GHz fully integrated frequency synthesizer for Bluetooth applications is proposed and designed in 0.25-mu m CMOS technology. An improved current-match charge pump circuit without the start-up problem is used to reduce the spur level. Moreover, a bandswitching VCO is used to reduce the Kvco and hence the spur level can be further reduced. The prescaler is designed in 1-V supply voltage without the supply-voltage boosting. The circuit is verified by both HSPICE and ADS simulations.
Crucial effects of polar alignment symmetry on the dynamical behaviors of quasi-homeotropic liquid crystal cells
(2002-08-01)
Hsieh, CY
;
Chen, SH
;
光電工程學系
;
Department of Photonics
We present an interesting transient electro-optical phenomenon including double optical bounce during the rising period of a quasi-homeotropic liquid crystal (QHLC) cell with an asymmetrical polar-alignment boundary condition. The unique optical behavior of the QHLC cell is produced by the flow effect together with the complicated alignment condition of the substrates, which is a combination of the deviation of azimuthal alignment and the asymmetrical polar alignment. We have found that the symmetrical characteristic of polar alignment plays a critical role in the dynamical behavior of the QHLC cell. Furthermore, our simulation results show that the double optical-bounce phenomenon appears even when the difference between the top and bottom tilt angles is only 0.1degrees. The experimental results and numerical calculation are described in this paper.
Donor states in a multi-layered quantum dot
(2000-10-09)
Hsieh, CY
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The ground and excited state energies of a hydrogenic impurity located at the centre of a multi-layered quantum dot (MLQD) are calculated in the framework of the effective-mass approximation. The MLQD consists of a spherical core (e.g. GaAs) and a coated spherical shell (e.g. Ga1-xAlxAs). The whole dot is then embedded inside a bulk material (e.g. Ga1-xAlyAs). We solve the Schrodinger equation exactly. The eigenfunctions of the impurity are expressed in terms of Whittaker function and Coulomb wavefunction. The state energies are expressed in terms of the shell thickness, core radius, total dot radius and the potential heights. Our calculation shows that, as the dot radius approaches infinity, the state energies of an impurity located at the centre of a multi-layered or a single-layered QD approach -1/n(2) Ry, where n is the principal quantum number, Ry = mue(4)/2 epsilon (2)h(2), mu and epsilon are the electronic effective mass and the dielectric constant of GaAs material. Thus it behaves like a three-dimensional free hydrogen atom. For very small dot radius, however, the state energy of the hydrogenic impurity of a MLQD behaves very differently from that of a single-layered QD. For a multi-layered QD with finite shell and bulk potential barrier heights, the state energies of the impurity are found to be dependent on the difference of the shell potential (V-2) and the bulk potential (V-3).
Dynamical behavior of a bistable chiral quasihomeotropic liquid crystal cell
(2003-08-11)
Hsieh, CY
;
Chen, SH
;
光電工程學系
;
Department of Photonics
The dynamical behavior of the directors in a bistable chiral quasihomeotropic (BCQH) liquid crystal cell has been investigated. This cell can be switched from the initial quasihomeotropic configuration state at zero field to two static twisted states at 14 V by different switching processes. We studied the dynamic behavior of the BCQH cell based on the general nematohydrodynamic theory, and the detailed dynamical mechanism was illustrated by analyzing the director and velocity profiles obtained from the numerical simulation. We found that, in addition to the flow effect, the asymmetric polar-alignment condition is another important factor to achieve the switching bistability of our BCQH cell. The experimental and numerical results are reported in this letter. (C) 2003 American Institute of Physics.
Electrically switching bistability of a chiral quasi-homeotropic liquid crystal device with low driving voltage
(2003-11-01)
Hsieh, CY
;
Chen, SH
;
光電工程學系
;
Department of Photonics
We report a new electrically switching bistable chiral quasi-homeotropic liquid crystal device with low driving voltage. This device is operated from the initial twisted-homeotropic state to either +90degrees or -270degrees twisted static state showing dark and bright transmittances, respectively, using different switching processes. The critical applied voltage to achieve the switching bistability of our device is only 4.3 V, which is approximately twice its threshold voltage for Freedericksz transition. In addition, the switching characteristics of this device with different driving waveforms are also investigated in this paper.
Growth of CdMnS films by pulsed laser evaporation
(1997-07-30)
Chuu, DS
;
Chang, YC
;
Hsieh, CY
;
電子物理學系
;
Department of Electrophysics
High orientation CdMnS thin films were grown on glass substrate by the pulsed laser evaporation (PLE) technique. Pulsed Nd:Yag laser was used as the evaporation source. During the deposition, various pulsed laser powers, substrate temperatures and different ratios of high purity CdS and MnS powder were used. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX) were employed to study the crystal structure, surface morphology and the Mn concentration of the as-deposited films. Absorption spectra were used to investigate the band gap of CdMnS films. It was found that the deviation of the band gap of CdMnS films from that of bulk CdS at room temperature depends on the concentration of Mn, The Raman spectra of our samples showed that the mixed mode behavior of transversal (longitudinal) frequency omega(T) (omega(L)) might exist in the CdMnS thin films. (C) 1997 Elsevier Science S.A.
Hydrogenic impurity in multilayered quantum wires
(2001-02-15)
Hsieh, CY
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The binding energy of the ground state of a hydrogenic impurity located at the center of a multilayered quantum wire (MLQW) is studied within the framework of the effective-mass approximation. The MLQW consists of a core wire (GaAs) coated by a cylindrical shell (Ga1-xAlxAs) and then embedded in the bulk (Ga1-yAlyAs). The calculation was performed by using a trial wave function. To make a comparison, the ground and excited states (1s, 2p, and 3d states) binding energies of a hydrogenic impurity located at the center of a single-layered quantum wire (QW) are also calculated. It is found for small wire radius, the ground-state binding energy of the hydrogenic impurity located at the center of a MLQW behaves very differently from that of a single-layered QW. (C) 2001 American Institute of Physics.
Improved field-emission properties of carbon nanotube field-emission arrays by controlled density growth,of carbon nanotubes
(2005-01-01)
Juan, CP
;
Chen, KJ
;
Tsai, CC
;
Lin, KC
;
Hong, WK
The density distribution of CNTs is one of the. crucial parameters determing the field-emission property of CNTs. To effectively control the density of CNTs, an inactive thin-film layer was deposited on a catalyst. The results showed that improved field emission property could be obtained with a thin SiO layer on the catalyst layer as the precursor. For 3.5 nm Fe and 3.5 nm SiO on 3.5 nm Fe as a catalyst, the turn-on field could be decreased from 3.7 V/mum. to 2.2 V/mum and the field-emission current density increased from 2.6 x 10(-8) A/cm(2) to 2.4 x 10(-4) A/cm(2) when the applied field was 4 V/mum.
Non-saturated binary image learning and recognition using the ratio-memory cellular neural network (RMCNN)
(2002)
Wu, CY
;
Hsieh, CY
;
Chen, SH
;
Hsieh, BCY
;
Chen, CR
dIn this paper, cellular neural network with ratio memory is proposed for non-saturated binary image processing. The Hebbien learning rule will be used to learn the weight of template A. The RMCNN system can recognize one non-saturated binary image and remove most of the noise added to the image pattern during the recognition period. The behavior of recognizing non-saturated binary images will be proved by mathematics equations. The effect will be simulated by Matlab software. With the method for non-saturated binary image processing, this theory can be easily implemented in hardware.
The optimization of compensation films for TNLCDs
(1999)
Hsieh, CY
;
Wu, YS
;
Wu, YA
;
Chen, SH
;
光電工程學系
The narrow viewing angle of the twisted nematic liquid crystal displays (TN LCDs) limits the display's performance especially on the desktop monitors or large size TVs. Recently, the compensation films have been extensively developed to improve the viewing angle of TN LCDs. We have investigated the compensation films for TN LCDs which combined O-plates and O-plates. The parameters of the compensation films have been optimized by computer simulation and these results showed that the films could minimize the oblique leakage light of the dark state and improve the viewing angle efficiently.