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141.
A. J. Kalkman H. P. M. Pellemans T. O. Klaassen W. Th. Wenckebach 《Journal of Infrared, Millimeter and Terahertz Waves》1996,17(3):569-577
The low temperature lifetime of electrons excited in the 2p?1 donor level of n-GaAs has been studied in a far-infrared pump-probe experiment. The measurement has been carried out using a pulsed far-infrared molecular gas laser working at a wavelength of 292µm, with the sample in a magnetic field of 5.1 T, resonant with the 1so?2p?1 transition. Two FIR pulses are sliced from one FIR-laser pulse by means of optical switching techniques using two Q-switched Nd:YAG lasers. The first pulse is used to saturate the transition, while the second pulse probes the return of the population in the excited state towards thermal equilibrium as a function of the time delay after the excitation pulse. The value of 350±50 ns found for the lifetime falls in line with CW saturation results on materials with other doping concentrations. 相似文献
142.
Winzker M. Gruger K. Gehrke W. Pirsch P. 《Solid-State Circuits, IEEE Journal of》1993,28(12):1354-1361
A chip set for 2D subband filtering of HDTV signals has been designed, fabricated and successfully tested. The two chips perform 10*14 quadrature mirror filtering for analysis filtering at the coder and synthesis filtering at the decoder. In order to achieve a very compact realization, the architectures utilize all a priori known properties of the filter algorithm. A 2D polyphase filter structure reduces the processing clock rate from the 72-MHz sampling rate to a moderate 18 MHz. The memory for vertical filtering is realized by on-chip parallel shift registers with multiphase clocking. A small silicon area for the filter arithmetic is achieved by application of carry save adder trees with fixed filter coefficients represented by canonical signed digits. A complete filterbank for luminance and chrominance signals consists of four identical chips, each with 450 000 transistors on 92 mm2 相似文献
143.
The tone sense multiaccess with partial collision detection (TSMA/PCD) protocol is particularly suitable for a packet satellite system serving an area with a dense population of earth stations. By incorporating a narrowband ground radio channel for broadcasting busy ones, the earth stations are able to avoid packet collisions by sensing for the absence of busy tones before transmitting packets. Partial collision detection capability can also be achieved. Single-tone TSMA/PCD gives 97% of the carrier-sense multiaccess with collision detection (CSMA/CD) throughput when N =10 tones are used, while for multitone and slot-by-slot announcement TSMA/PCD protocols only N =8 and N =2, respectively, are sufficient to drive the system to the CSMA/CD performance 相似文献
144.
Arithmetic coding for data compression 总被引:17,自引:0,他引:17
Howard P.G. Vitter J.S. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1994,82(6):857-865
Arithmetic coding provides an effective mechanism for removing redundancy in the encoding of data. We show how arithmetic coding works and describe an efficient implementation that uses table lookup as a first alternative to arithmetic operations. The reduced-precision arithmetic has a provably negligible effect on the amount of compression achieved. We can speed up the implementation further by use of parallel processing. We discuss the role of probability models and how they provide probability information to the arithmetic coder. We conclude with perspectives on the comparative advantages and disadvantages of arithmetic coding 相似文献
145.
146.
P Sallagoity F Gaillard M Rivoire M Paoli M Haond S McClathie 《Microelectronics Reliability》1998,38(2):700
This paper presents Shallow Trench Isolation (STI) process steps for sub-1/4 μ CMOS technologies. Dummy active areas, vertical trench sidewalls, excellent gap filling, counter mask etch step and CMP end point detection, have been used for a 0.18 μm CMOS technology. Electrical results obtained with a 5.5 nm gate oxide thickness show good isolation down to 0.3 μm spacing. Good transistor performances have been demonstrated. 相似文献
147.
148.
Arafa M. Fay P. Ismail K. Chu J.O. Meyerson B.S. Adesida I. 《Electron Device Letters, IEEE》1996,17(3):124-126
We report on the fabrication and characterization of high-speed p-type modulation-doped field-effect transistors (MODFETs) with 0.7-μm and 1-μm gate-lengths having unity current-gain cut-off frequencies (fT) of 9.5 GHz and 5.3 GHz, respectively. The devices were fabricated on a high hole mobility SiGe heterostructure grown by ultra-high-vacuum chemical vapor deposition (UHV-CVD). The dc maximum extrinsic transconductance (gm) is 105 mS/mm (205 mS/mm) at room temperature (77 K) for the 0.7-μm gate length devices. The fabricated devices show good pinch-off characteristics and have a very low gate leakage current of a few μA/mm at room temperature and a few nA/mm at 77 K 相似文献
149.
Yurii P. Kalmykov 《Liquid crystals》1991,10(4):519-537
The relationship between the complex dielectric permittivity tensor of a polar nematic liquid crystal and the autocorrelation matrix for the permanent dipole moment of a molecule is obtained. The theory is applicable to the whole frequency range which characterizes orientational relaxation in liquid crystals (up to ∼ 5 THz). The models of rotational diffusion and extended rotational diffusion in a mean field nematic potential are used to evaluate the dielectric absorption and dispersion in nematics. 相似文献
150.
W. Fallmann P. Hudek I. Kostic A. Neubauer D. Pum I. Rangelow K. Riedling F. Rüdenauer U. B. Sleytr G. Stangl 《e & i Elektrotechnik und Informationstechnik》1998,115(7-8):349-353
This contribution describes the preparation, based upon a chemically amplified novolak resist (CAR), electron beam lithography, and ECR plasma etching, of structures with a high aspect ratio (10∶1) and lateral dimensions in the sub-micrometer range (150nm–300nm) which may serve as collector surfaces for sub-μm dust particles in a space experiment. 相似文献