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排序方式: 共有7941条查询结果,搜索用时 31 毫秒
61.
Luis Abraham Sánchez Gaspariano Clara Iliana Martínez Gómez José Miguel Rocha Pérez Jesús Ezequiel Molinar Solís Jesús Manuel Muñoz Pacheco Carlos Muñíz Montero Alejandro Díaz Sánchez 《Circuits, Systems, and Signal Processing》2013,32(2):415-431
In this paper, the synthesis, design, and implementation of a programmable phase shifter circuit for sinusoidal signals is presented. The proposed circuit, built-up herein with operational amplifiers (OPAMPs), high precision resistors and low voltage switches, consists of a digitally controlled amplitude attenuator in combination with a single-tone orthogonalizer. Experimental results agree with theoretical background: the attained phase range was 252° in 256 steps with a median step of 0.9°. The inaccuracy of the circuit was determined to be of 0.03 %. Contrary to other OPAMP approaches for sinusoidal signals reported in the literature and based on a first-order all-pass filter structure, the approximation suggested in this work is based on a different concept. The achieved results demonstrate the functionality of the system for the case of a sinusoidal signal with frequency of 1 kHz. Notwithstanding, the proposed architecture can be extended to operate at higher frequencies by using different building blocks with larger bandwidth. Furthermore, it can be extended as well to work out with other periodic input waveforms, like triangular shapes or square waves, with the use of an appropriate orthogonalizer. 相似文献
62.
Hussein Fakhoury Papy Ndungidi Carlos Valderrama 《Analog Integrated Circuits and Signal Processing》2011,67(3):273-284
A low-power, low-pass continuous-time sigma-delta A/D modulator with 1-MHz bandwidth is implemented in a 130-nm CMOS process. The circuit is targeted for an IEEE 802.15.4 direct conversion receiver operating in the 2.4-GHz band. It has a third-order feedforward single-loop filter and a 1-bit quantizer to minimize power consumption. Non-return-to-zero DAC pulse shaping is used to reduce sensitivity to clock jitter. Clocked at 64 MHz, the prototype chip achieves 62-dB peak SNR, −70-dB peak THD, 63-dB dynamic range with an oversampling ratio of 32. The built-in anti-alias filter provides alias attenuation greater than 57 dB, which improves coexistence of the receiver with other devices that operate in the 2.4-GHz band. The circuit dissipates 1.44 mW from the 1.2-V supply and the active die area is 0.1 mm2. 相似文献
63.
On the variability of manual spike sorting 总被引:3,自引:0,他引:3
Wood F Black MJ Vargas-Irwin C Fellows M Donoghue JP 《IEEE transactions on bio-medical engineering》2004,51(6):912-918
The analysis of action potentials, or "spikes," is central to systems neuroscience research. Spikes are typically identified from raw waveforms manually for off-line analysis or automatically by human-configured algorithms for on-line applications. The variability of manual spike "sorting" is studied and its implications for neural prostheses discussed. Waveforms were recorded using a micro-electrode array and were used to construct a statistically similar synthetic dataset. Results showed wide variability in the number of neurons and spikes detected in real data. Additionally, average error rates of 23% false positive and 30% false negative were found for synthetic data. 相似文献
64.
von Ellenrieder N Muravchik CH Nehorai A 《IEEE transactions on bio-medical engineering》2005,52(2):249-257
We present a numerical method to solve the quasistatic Maxwell equations and compute the electroencephalography (EEG) forward problem solution. More generally, we develop a computationally efficient method to obtain the electric potential distribution generated by a source of electric activity inside a three-dimensional body of arbitrary shape and layers of different electric conductivities. The method needs only a set of nodes on the surface and inside the head, but not a mesh connecting the nodes. This represents an advantage over traditional methods like boundary elements or finite elements since the generation of the mesh is typically computationally intensive. The performance of the proposed method is compared with the boundary element method (BEM) by numerically solving some EEG forward problems examples. For a large number of nodes and the same precision, our method has lower computational load than BEM due to a faster convergence rate and to the sparsity of the linear system to be solved. 相似文献
65.
von Ellenrieder N Muravchik CH Nehorai A 《IEEE transactions on bio-medical engineering》2005,52(7):1210-1217
We present a formulation for the magnetoencephalography (MEG) forward problem with a layered head model. Traditionally the magnetic field is computed based on the electric potential on the interfaces between the layers. We propose to express the effect of the volumetric currents in terms of an equivalent surface current density on each interface, and obtain the magnetic field based on them. The boundary elements method is used to compute the equivalent current density and the magnetic field for a realistic head geometry. We present numerical results showing that the MEG forward problem is solved correctly with this formulation, and compare it with the performance of the traditional formulation. We conclude that the traditional formulation generally performs better, but still the new formulation is useful in certain situations. 相似文献
66.
Juan Hernández-Serrano Juan Vera-del-Campo Josep Pegueroles Carlos Gañán 《Wireless Networks》2013,19(1):47-67
Wireless sensor networks (WSNs) are made up of large groups of nodes that perform distributed monitoring services. Since sensor measurements are often sensitive data acquired in hostile environments, securing WSN becomes mandatory. However, WSNs consists of low-end devices and frequently preclude the presence of a centralized security manager. Therefore, achieving security is even more challenging. State-of-the-art proposals rely on: (1) attended and centralized security systems; or (2) establishing initial keys without taking into account how to efficiently manage rekeying. In this paper we present a scalable group key management proposal for unattended WSNs that is designed to reduce the rekeying cost when the group membership changes. 相似文献
67.
Helder Fleury Pinheiro Attílio José Giarola Carlos Leônidas da Silva Souza Sobrinho 《Journal of Infrared, Millimeter and Terahertz Waves》1995,16(11):1965-1975
The formulation is developed in the frequency domain and the finite difference method is used for the numerical solution of the scalar wave equation, written in terms of the transverse components of the magnetic field. As a result a conventional eigenvalue problem is obtained without the presence of spurious modes due to the implicit inclusion of the divergence of the magnetic field equal to zero. The formulation is developed to include biaxial anisotropic dielectrics with an index profile varying arbitrarily in the cross section of the waveguide under analysis. This formulation is then applied to the analysis of the influence on the dispersion characteristics of the dimensions of asymmetric coupled rectangular uniaxial anisotropic dielectric waveguides. As expected, the reduction of the height or the width of one of the rectangular dielectric waveguides causes the dispersion curves to move towards higher frequencies. 相似文献
68.
69.
Manoj Kumar Singh Tolou Shokuhfar José Joaquim de Almeida Gracio António Carlos Mendes de Sousa José Maria Da Fonte Fereira Hamid Garmestani Said Ahzi 《Advanced functional materials》2008,18(5):694-700
The paper reports on a freeze‐granulation technique to prepare a novel nanocomposite of poly(methyl methacrylate) (PMMA)‐modified hydroxyapatite (HA) with multiwalled carbon nanotubes (MWCNTs) as reinforcement for a new generation biomedical bone cement and implant coatings. By using this technique it is possible to increase material homogeneity and also enhance the dispersion of MWCNTs in the composite matrix. The phase composition and the surface morphology of the nanocomposite material were studied using X‐ray diffraction, field‐emission scanning electron microscopy, and micro‐Raman spectroscopy. Additionally, nanomechanical properties of different concentrations of MWCNT‐reinforced nanocomposite were performed by a nanoindentation technique, which indicates that a concentration of 0.1 wt % MWCNTs in the PMMA/HA nanocomposite material gives the best mechanical properties. 相似文献
70.
Alberto Reyna Marco A. Panduro Carlos del Rio-Bocio Aldo L. Méndez 《Telecommunication Systems》2017,65(2):269-279
The synthesis of different planar geometries of antenna arrays for isoflux radiation is presented in this paper. This synthesis considers the reduction of the side lobe level and the isoflux radiation requirements for Geostationary Earth Orbit satellites. The behavior of the radiation is studied in three geometries of two-dimensional antenna arrays such as uniform planar arrays, aperiodic planar arrays (APA) and concentric ring arrays (CRA). The well-known methods of genetic algorithm and particle swarm optimization are utilized for the optimization problem. In this way, the designs of APA and CRA presented in this paper could provide an acceptable solution for reducing the antenna hardware and simplifying the power feeding even more than results presented previously in the literature. 相似文献