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Oversampling and sigma-delta strategies for data conversion

ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL 1998年第1期10卷 37-47页

作者： Stewart, RW Pfann, E Univ Strathclyde Dept Elect & Elect Engn Signal Proc Div Glasgow G1 1XW Lanark Scotland

This paper presents an introduction to oversampling techniques a nd the theory and advantages of sigma-delta (Sigma Delta) devices for digital-to-analogue conversion (DAC) and analogue-to-digital conversion (ADC) in digital signal processing (DSP) systems. It begins with a discussion of conventional Nyquist-sampling-rate DSP, which is followed by an overview of oversampling and decimation/interpolation techniques to reduce the anti-alias and reconstruction filter specifications. Oversampling strategies to increase the resolution of an N-bit ADC or DAC by reducing the baseband quantisation noise are then presented, and this is followed by a description of the use of Sigma Delta noise-shaping techniques and the design of Sigma Delta converters. The paper concludes with comments on a few of the application and research areas where Sigma Delta devices are having a major impact.

关键词： digital signal processing pulse code modulation PCM systems data conversion Nyquist-sampling-rate DSP Digital signal processing chips sigma-delta strategies quantisation (signal) digital-to-analogue conversion Digital signal processing digital signal processing chips Interpolation and function approximation (numerical analysis) modulation and coding methods baseband quantisation noise filtering theory decimation/interpolation oversampling techniques signal reconstruction A/D and D/A convertors digital-analogue conversion analogue-to-digital conversion reconstruction filter specifications research areas signal sampling interpolation DAC ADC ΣΔ noise-shaping techniques Signal processing and detection anti-alias reduction sigma-delta modulation ΣΔ converters design DSP systems signal resolution

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Electronic warfare systems

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IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES 2002年第3期50卷 633-644页

作者： Spezio, AE USN Res Lab Tactical Elect Warfare Div Elect Warfare Support Measures Branch Washington DC 20375 USA

Electronic warfare (EW) is an important capability that can advance desired military, diplomatic, and economic objectives or, conversely, impede undesired ones. In a military application, EW provides the means to counter, in all battle phases, hostile actions that involve the electromagnetic (EM) spectrum-from the beginning when enemy forces are mobilized for an attack, through to the final engagement. EW exploits the EM environment by sensing and analyzing an adversary's application of the spectrum and imposing appropriate countermeasures (CMs) to hostile spectrum use. EW sensors are one means by which the military gathers tactical intelligence from noncooperative forces. EW sensors, together with EW CMs, mitigate the effectiveness of an adversary's electrooptic/infrared, and radio frequency-controlled weapons. EW enhances the survivability of the host force through control and manipulation of the EM environment and denies or limits its use by an adversary. EM spectrum CMs to threat systems can be selectively applied on a time- and/or frequency-multiplexed basis so that host force use of the EM spectrum is uninhibited.

关键词： terms-circuit functions complex modulation cooperative sensors counter countermeasures countermeasures digital receiver technology electrooptic/infrared electromagnetic environment electromagnetic spectrum electronic attack electronic self-protection electronic support electronic surveillance electronic warfare filters high-gain antenna improved signal processing independent sensors isotropic antenna offboard countermeasures phased-array antennas pulse code modulation radar advancement response techniques sensor technology spectral selectivity subsystems sensors threat systems triangulation

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Experimental investigation and numerical comparison of the performance of a proton exchange membrane fuel cell at different channel geometry

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HEAT AND MASS TRANSFER 2015年第8期51卷 1177-1187页

作者： Khazaee, I. Shahid Beheshti Univ Fac Mech & Energy Engn AC Tehran Iran

In this study, the performance of a PEM fuel cell is investigated experimentally and numerically by changing the geometry of the channels. At first an experimental setup is used and three different fuel cells with rectangular, elliptical and triangular serpentine channels are constructed. The active area of each cell is 25 cm(2) that its weight is 1,300 g. The material of the gas diffusion layer is carbon clothes, the membrane is nafion 117 and the catalyst layer is a plane with 0.004 g cm(-2) platinum. Then a complete three-dimensional model for fuel cell is used to investigate the effect of using this channels geometry on the performance. The proposed model is a full cell model, which includes all the parts of the PEM fuel cell, flow channels, gas diffusion electrodes, catalyst layers and the membrane. Coupled transport and electrochemical kinetics equations are solved in a single domain;therefore no interfacial boundary condition is required at the internal boundaries between cell components. The results show that the predicted polarization curves by using this model are in good agreement with the experimental results. Also the results show that when the geometry of channel is rectangular the performance of the cell is better than the triangular and elliptical channel.

关键词： membrane Cells Cellular Structures gas diffusion fuel batteries useful area Proton exchange membrane fuel cells geometry Triangular pulse code modulation Channel morphology mucin 1

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Acid resistant PVDF-co-HFP based copolymer proton exchange membrane for electro-chemical application

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JOURNAL OF MEMBRANE SCIENCE 2019年 573卷 485-492页

作者： Sharma, Prem P. Yadav, Vikrant Gahlot, Swati Lebedeva, Oksana V. Chesnokova, Alexandra N. Srivastava, Divesh N. Raskulova, Tatiana V. Kulshrestha, Vaibhav CSMCRI CSIR Gijubhai Badheka Marg Bhavnagar 364002 Gujarat India CSMCRI CSIR Acad Sci & Innovat Res Gijubhai Badheka Marg Bhavnagar 364002 Gujarat India Irkutsk Natl Res Tech Univ 83 Lermontov Str Irkutsk 664074 Russia Angarsk State Tech Univ 60 Tchaikovsky Str Angarsk 665835 Russia

Acid resistant proton exchange membranes (PEMs) are synthesized from aliphatic highly hydrophobic polyvinylidene-co-hexafluoropropylene (PVDF-co-HFP) and aromatic hydrophilic sodium-p-styrene sulfonate at nanostructure level modification. Synthesized copolymer PEMs are analyzed for their chemical structure to confirm the presence of functional groups. Electrochemical characterizations are carried out in terms ion-exchange capacity, ionic conductivity and water content. Maximum IEC value 1.91 meq/gm is observed for PDSt-40 copolymer PEM with 1.58x10(-2) S/cm proton conductivity and 29.1% of water content. Vanadium ion permeability is also checked for copolymer membranes in terms of applicability for vanadium redox flow batteries. PDSt-40 copolymer PEM shows lowest value of VO2+ ion permeability 2.87x10(-7) cm(2) min(-1), which is about 40% less compared to Nafion membrane. Further all synthesized PEMs are checked for charging-discharging performance for single cell VRFB. PDSt-40 PEM shows better performance in term of columbic and voltage efficiency. Copolymer membranes found to be stable thermally and mechanically and also in harass condition with 18M H2SO4 for 24 h. Results indicate that synthesized copolymer PEMs can be a good candidate for electrochemical energy systems as well as high temperature applications.

关键词： chemical structure Electrochemistry High temperature applications ENERGY SYSTEMS membrane hydrogen ions ion permeability Copolymers pulse code modulation mucin 1

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Fidelity of phase-conjugated beams in a four-wave mixing set-up using Bi12TiO20-crystals

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JOURNAL OF MODERN OPTICS 1996年第7期43卷 1525-1533页

作者： Kiessling, A Baade, T Wenke, L Institute of Applied Optics Friedrich-Schiller-Universitat Jena Max-Wien-Platz 1 07743 Jena Germany

The quality of the aberration compensation provided by phase-conjugating mirrors (PCMs) is important for applications in lensless imaging or interferometry. In many cases an accuracy of a tenth of the wavelength for the phase reversal is sufficient. It will be shown that both the Fourier fringe evaluation method and a lensless image projection technique are useful to characterize the fidelity of phase conjugation with BaTiO3. A quantitative evaluation of the fidelity is given for four-wave mixing in Bi12TiO20 and self-pumped PCM with BaTiO3.

关键词： Four wave mixing phase conjugation Deci interferometry Fidelity BEAM pulse code modulation Bismuth titanate

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APPLICATION OF DATA COMPRESSION TO AN EXPERIMENTAL 9.6 KBIT-S ADAPTIVE PCM DIGITAL SPEECH SYSTEM

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PROCEEDINGS OF THE INSTITUTION OF ELECTRICAL ENGINEERS-LONDON 1976年第2期123卷 109-114页

作者： TURNER, LF IMPERIAL COLL SCI & TECHNOL DEPT ELECTR ENGNEXHIBITION RDLONDON SW7 2BTENGLAND

The paper deals with an investigation that was carried out to determine whether simple data-compression techniques could be applied successfully to an experimental 9.6 kbit/s adaptive p.c.m. digital speech system: The main aim of the investigation was to ascertain whether compression factors of two or four could be achieved. In the paper, the results of the investigation are presented and it is shown that the adaptive p.c.m. system is converting speech into a 9.6 kbit/s digital form that appears to possess very little redundancy. The results of a statistical analysis of the data are given, and it is shown that a compression factor of two is unlikely to result in a speech quality that is commercially acceptable. The results of an experimental investigation that was carried out in support of the theoretical investigation are presented. The results of the experimental investigation show that although compression by a factor of two results in a speech quality that is commercially unacceptable, a 4/3 compression can be achieved without any serious degradation of the speech quality.

关键词： digital communication systems data compression compression factors statistical analysis Telephony voice communication speech quality pulse-code modulation experimental 9.6 kbit/s adaptive digital speech system pulse code modulation

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LOGARITHMIC AMPLITUDE-code CONVERTER

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INSTRUMENTS AND EXPERIMENTAL TECHNIQUES 1981年第1期24卷 104-108页

作者： VOLCHENKO, VI

A scheme is described for a logarithmic pulse-amplitude to code converter with a dynamic range of 50 dB. The sensitivity of the converter is 250 uv and its conversion frequency is 1 MHz. The temperature instability of the threshold is less than equivalent to 0. 1% over the temperature range plus 15 to plus 50 degree C. The differential nonlinearity of the converter is 3%. A method is given for measuring the differential nonlinearity of logarithmic converters.

关键词： pulse code modulation

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Investigation of Al doping on Ge₅₅Te₄₅ for phase change memory application

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JOURNAL OF APPLIED PHYSICS 2013年第23期113卷 234312-1-234312-5页

作者： Ren, Kun Rao, Feng Song, Zhitang Wu, Liangcai Xia, Mengjiao Liu, Bo Feng, Songlin Chinese Acad Sci Shanghai Inst Microsyst & Informat Technol State Key Lab Funct Mat Informat Lab Nanotechnol Shanghai 200050 Peoples R China Chinese Acad Sci Grad Univ Beijing 100080 Peoples R China

Al-doped Ge55Te45 materials are proposed for phase change memory application. Al incorporated in Ge55Te45 increases the crystallization temperature, band gap and 10-year data retention significantly. However, the crystallization speed of the Al-doped Ge55Te45 material will be lowered by excessive Al doping. The crystallization of the Al-doped Ge55Te45 film is observed to be growth-dominant, beginning with a random formation of spherical crystalline clusters. The 10-year data retention and crystallization speed of Al1Ge55Te45 are 117 degrees C and 5 ns, respectively, which makes the Al1Ge55Te45 a promising candidate for high speed PCM application. The 10-year data retention of 132 degrees C and good cyclic ability of similar to 2 x 10(3) cycles of the Al2Ge55Te45 based PCM have shown its application potential in automotive fields. (C) 2013 AIP Publishing LLC.

关键词： Crystallization doping (materials) Phase change memory aluminium pulse code modulation

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THRESHOLD EXTENSION IN PCM BY OPTIMUM ENERGY ALLOCATION

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INFORMATION SCIENCES 1994年第1-2期81卷 31-36页

作者： SOUFIZADEH, D STATE UNIV LIEGE B-4000 LIEGEBELGIUM

The problem of optimum energy allocation for a seven-digit PCM system and DPSK signaling is solved for two different cases: (1) For white noise, Rayleigh fading channel, and occurrence of only errors in a character and (2) for white noise and nonfading Gaussian channel for the case of the occurrence of doublet errors in a character.

关键词： pulse code modulation

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RATE-DISTORTION PERFORMANCE OF DPCM SCHEMES FOR AUTOREGRESSIVE SOURCES

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IEEE TRANSACTIONS ON INFORMATION THEORY 1985年第3期31卷 402-418页

作者： FARVARDIN, N MODESTINO, JW RENSSELAER POLYTECH INST DEPT ELECT COMP & SYST ENGN TROY NY 12180 USA

An analysis of the rate-distortion performance of differential pulse code modulation (DPCM) schemes operating on discrete-time auto-regressive processes is presented. The approach uses an iterative algorithm for the design of the predictive quantizer subject to an entropy constraint on the output sequence. At each stage the iterative algorithm optimizes the quantizer structure, given the probability distribution of the prediction error, while simultaneously updating the distribution of the resulting prediction error. Different orthogonal expansions specifically matched to the source are used to express the prediction error density. A complete description of the algorithm, including convergence and uniqueness properties, is given. Results are presented for rate-distortion performance of the optimum DPCM scheme for first-order Gauss-Markov and Laplace-Markov sources, including comparisons with the corresponding rate-distortion bounds. Furthermore, asymptotic formulas indicating the high-rate performance of these schemes are developed for both first-order Gaussian and Laplacian autoregressive sources.

关键词： pulse code modulation

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