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1.
Direct digital synthesizer with jittered clock 总被引:5,自引:0,他引:5
Yih-Chyun Jenq 《IEEE transactions on instrumentation and measurement》1997,46(3):653-655
Since the direct digital synthesizer (DDS) can potentially be used as a flexible clock source, it is of interest to study its spectrum purity as well as jitter characteristic. In this paper, we investigate the jitter transfer characteristic of the DDS clock driven by a jittered digital-to-analog converter (DAC) clock. We first derive the dosed form expressions of the spectrum of the DAC output signal with jittered driving clock. These expressions are then used to investigate the spectral structure of the DDS clock. Equations are derived for the calculation of the SNR. For a small phase noise power in the driving clock, the DDS clock SNR is obtained in a simple closed form and is shown to be lower than that of the input driving clock by the amount of 20 log(fs/dd) dB, where fs is the nominal driving clock frequency and fd is the desirable DDS output clock frequency 相似文献
2.
Kwok Wa Leung Hoi Kuen Ng 《Antennas and Propagation, IEEE Transactions on》2005,53(5):1762-1769
The aperture-coupled hemispherical dielectric resonator antenna (DRA) with a parasitic patch is studied rigorously. Using the Green's function approach, integral equations for the unknown patch and slot currents are formulated and solved using the method of moments. The theory is utilized to design a circularly polarized (CP) DRA and a wide-band linearly polarized (LP) DRA. In the former, the CP frequency and axial ratio (AR) can easily be controlled by the patch location and patch size, respectively, with the impedance matched by varying the slot length and microstrip stub length. It is important that the AR will not be affected when the input impedance is tuned, and the CP design is therefore greatly facilitated. For the wide-band LP antenna, a maximum bandwidth of 22% can be obtained, which is much wider than the previous bandwidth of 7.5% with no parasitic patches. Finally, the frequency-tuning characteristics of the proposed antenna are discussed. Since the parasitic patch can be applied to any DRAs, the method will find applications in practical DRA designs. 相似文献
3.
Kuo‐Chung Huang Yi‐Heng Chou Lang‐chin Lin Hoang Yan Lin Fu‐Hao Chen Ching‐Chiu Liao Yi‐Han Chen Kuen Lee Wan‐Hsuan Hsu 《Journal of the Society for Information Display》2013,21(6):263-270
The optimal viewing distance was proposed as a parameter for designing a parallax barrier 3D display. It can be designed based on simple geometric method and by considering the pitches of image display pixels and parallax barrier, or even including the aperture ratios of the image display pixels and parallax barrier. It can be analyzed by using ray tracing method. By considering the optical refraction index of the cover glass, the angular behavior of the system becomes more realistic; however, the geometric method is difficult to be used. We propose a revised method for estimating the view distance and angular behavior. In this paper, we have demonstrated a designated eye position (DEP) for each view and shown that multiple DEPs make a circular curve around the center of the display. We prove the new concept by comparing the optical ray tracing calculations and optical measurement. 相似文献
4.
Jenq‐Lang Wu 《Asian journal of control》2009,11(3):295-301
A controller design method is provided to simultaneously stabilize a collection of nonlinear control systems in canonical form. It is shown that, under a mild assumption, any collection of nonlinear systems in canonical form can be simultaneously stabilized by one continuous state feedback controller. A constructive universal formula is presented explicitly. An illustrative example is given to demonstrate the validity of the method. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society 相似文献
5.
Aluminium nitride substrates were immersed in acid, basic solutions and deionized water for 1–120 h at room temperature. The corrosion rates are higher in basic solutions (NaOH and KOH) than those in acid solutions (CH3COOH, HCOOH, HNO3, HCl and H2SO4) and deionized water. The weight loss of AIN corroded in alkali aqueous reaches 70% and results in an increase in surface roughness ranging from 10 nm to 7 m after 3 days corrosion. However, the weight loss in acid solution is only 1/700 of the alkali case. Violent chemical reactions between AIN and basic solutions were observed. Na2O, or Na2Al2O4·6H2O, is the intermediate product, and NaOH is a catalytic agent of the reaction. The surface morphology of the AIN etched by alkaline solutions is coral-like in microscopic view and appears like hills. In contrast, only several atomic layers of AIN surface are etched off in acid solutions and in deionized water. The lightly etched surface is mirror-like and flat, and the shapes of the grains are visible under the microscope, as the corrosion rate of each AIN grain varies with different crystal orientations. Consequently, after etching in acid solutions, the resulting microscopic surface morphology looks like a map of a jigsaw puzzle. 相似文献
6.
Controlling Synergistic Oxidation Processes for Efficient and Stable Blue Thermally Activated Delayed Fluorescence Devices
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7.
Blue OLEDs: Controlling Synergistic Oxidation Processes for Efficient and Stable Blue Thermally Activated Delayed Fluorescence Devices (Adv. Mater. 35/2016)
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8.
In this paper, we first introduce the use of an interactive hidden Markov model (IHMM) for modeling and analyzing default
data in a sector. Under the IHMM, transitions of the hidden risk states of the sector depend on the observed number of bonds
in the sector that default in the current time period. This incorporates the feedback effect of the number of defaults on
the transitions of the hidden risk states. This feature seems to be more realistic and does not enjoy by the traditional HMMs.
We then develop a “dynamic” version of the binomial expansion technique (BET) modulated by the IHMM for modeling the occurrence
of defaults of bonds issued by firms in the same sector. Under the BET modulated by the IHMM, the number of bonds defaulting
in each time period follows a Markov-modulated binomial distribution with the probability of defaulting of each bond depending
on the states of the IHMM, which represent the hidden risk states of the sector. Efficient method will be presented for estimating
the model parameters in the BET modulated by the IHMM. We shall compare the hidden risk state process extracted from the IHMM-modulated
BET with that extracted from the BET modulated by HMM in order to illustrate the significance of the feedback effect using
real data. We shall also present the estimation results for the BET modulated by the IHMM and compare them with those for
the BET modulated by the HMM. 相似文献
9.
A Simultaneous Mixed LQR/H∞ Control Approach to the Design of Reliable Active Suspension Controllers
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Jenq‐Lang Wu 《Asian journal of control》2017,19(2):415-427
This paper is concerned with the synthesis of reliable controllers for quarter‐car active suspension systems. By a simultaneous mixed LQR/H∞ control approach, a static output feedback controller is derived for guaranteeing good suspension performance under possible sensor fault or suspension component breakdown. The considered simultaneous mixed LQR/H∞ control problem is a nonconvex optimization problem; therefore, the linear matrix inequality approach is not applicable. Based on the barrier method, we solve an auxiliary minimization problem to get an approximate solution for the simultaneous mixed LQR/H∞ control problem. Necessary conditions for the local optimum of the auxiliary minimization problem are derived. Moreover, a three‐stage solution algorithm is developed for solving the auxiliary minimization problem. The simulation shows that the obtained static output feedback suspension controllers can improve suspension performance in nominal mode and all considered failure modes. 相似文献
10.
A discrete-time control problem of a finite-state hidden Markov chain partially observed in a fractional Gaussian process is discussed using filtering. The control problem is then recast as a separated problem with information variables given by the unnormalized conditional probabilities of the whole path of the hidden Markov chain. A dynamic programming result and a minimum principle are obtained. 相似文献