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991.
本文对无速度传感器的软起动器进行了深入剖折,所研究的软起动器具备四种起动方式:电压斜坡起动、限流起动、转速斜坡起动和分级变频起动。提出了基于无速度传感器的分级变频高转矩异步电机软起动方案。研制出基于80C196KC单片机控制的无速度传感器的分级变频高转矩软起动器。该软起动器具有结构简单,起动转矩大,能实现速度闭环控制的优点,使软起动器控制技术提高了一步,并且有持续研究开发的前景,有望在较广泛的应用领域得到推广应用。 相似文献
992.
高速PCB的设计中,数模混合电路的PCB设计中的干扰问题一直是一个难题。尤其模拟电路一般是信号的源头,能否正确接收和转换信号是PCB设计要考虑的重要因素。文章通过分析混合电路干扰产生的机理,结合设计实践,探讨了混合电路一般处理方法,并通过设计实例得到验证。 相似文献
993.
LED(发光二极管)以高效、低耗、发光柔和见长。用它作照明是一个发展方向。LED的伏安特性决定了它最好采用恒流源供电;为方便操作、减小机械磨损、降低故障率采用触模式调光是一种不错的选择。为解决停电麻烦增加后备供电也是必要的,此时LED的低耗特性显示出巨大的优势。设计采用特殊的恒流电路、电源管理电路和触摸防抖动电路使LED扬长避短,工作稳定可靠。 相似文献
994.
Al2O3 and Y2O3 have been respectively chosen for additional dopants to investigate the influence on the ferromagnetism of Co doped CeO2 bulk. Results indicate that ferromagnetism (FM) of Co doped CeO2 decrease with additional Al3+. Accordingly, certain amount of Y3+ can readily be incorporated into the lattice of CeO2 with the decrease of its grain size as well as some pores formation, leading to an enhancement of FM with a positive correlation between magnetization and Y3+ doping content. This experimental result is helpful both in understanding FM origination in diluted magnetic oxide (DMO) as well as to improve the moments of DMO applicable in spintronic devices. 相似文献
995.
Wen C.-K. Wong K.-K. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2007,53(1):252-268
While the capacity of a single-user, point-to-point, multiple-input multiple-output (MIMO) channel has been well known, the achievable capacity of a MIMO channel in the presence of other co-channel users is much less understood. One such important scenario is the multiple-access (MA) channel where communication occurs from many uncoordinated mobile users to a common base station receiver (i.e., multipoint-to-point). Unlike previous studies whose emphases were on the idealized spatially uncorrelated channels with Gaussian signaling inputs from users, this paper derives a general analytical expression for the asymptotic (in the sense of large-system limit) sum-rate of a MIMO-MA system where the transmitters and the receiver can have different spatial correlations, and the users' inputs are not necessarily Gaussian. In addition to the sum-rate formula that assumes optimal joint decoding at the base station, we also derive the asymptotic sum-rate of a more practical system which performs separate decoding (multiuser detection followed by a bank of temporal error-correction decoders). Our analytic formulae are important in that they reveal the sum-rate one's system can achieve given the spatial correlation structures at the transmitters and receiver, and the input signal distributions. For special cases that users are homogeneous or users have Gaussian inputs, our results degenerate to previously published results. Furthermore, through computer simulations, we see that the proposed asymptotic solution gives good estimates for the ergodic sum-rate of the systems even with only a few antenna elements at each transmitter and receiver 相似文献
996.
The design of a four-valued decoder based on the negative-differential- resistance (NDR) circuit is demonstrated. The presented NDR circuit is composed of a Si-based metal-oxide-semiconductor field-effect- transistor (MOS) and a SiGe-based heterojunction bipolar transistor (HBT). The fabrication of the four-valued decoder using this MOS- HBT-NDR circuit is based on the standard 0.35 mum SiGe-based BiCMOS process. 相似文献
997.
Xiao-Yu Gao Yong Zhou Ying Cao Chong Lei Wen Ding Hyung Choi Jonghwa Won 《Electronics Packaging Manufacturing, IEEE Transactions on》2007,30(2):123-127
This paper reports on a technological process that combines copper as conductor, permalloy as magnetic core material, and polyimide as insulation material to complete a microinductor on glass with high inductance. The shape of the magnetic core scheme was rectangular, of which the width of the long side and short side were 1.4 and 0.6 mm, respectively. The dimensions of the inductor are 3.86 mm times 3.94 mm times 90 mum with coil width of 20 mum and space of 35 mum. The results show that the maximum inductance is 4 muH at 1 MHz, and the maximum quality factor (Q-factor) is 1.5 at 2 MHz. 相似文献
998.
He Wen Huan Jiang Xiaoping Zheng Hanyi Zhang Yili Guo 《Photonics Technology Letters, IEEE》2007,19(18):1377-1379
In this letter, we propose two methods to enhance the performance of multichannel wavelength conversion of return-to-zero differential phase-shift-keying signal in a semiconductor optical amplifier (SOA) based on four-wave-mixing effect. The first one is optimizing the relative time delay of the multichannel signal to reduce the crosstalk-induced penalty in SOA. The second one is using the synchronous clock pumping to raise the power of converted signal. The experiment on wavelength conversion of two channels at 10-Gb/s signal showed the power penalty was improved more than 1 dB in the first method and about 1.5 dB in the second method. 相似文献
999.
Sensor delay and observation uncertainty often occur in modern computer-based systems, e.g., when the measurement is transmitted
to a remote controller through a network medium. In this paper, we revisit the Kalman filter design problem for a stochastic
dynamic system with random one-step sensor delay, and derive the optimal unbiased state estimation algorithm. Both full- and
reduced-order filters are studied, and the results compare favorably with those of the existing algorithms in examples via
simulation. 相似文献
1000.
Jyh-Horng Wen Gwo-Ruey Lee Wen-Hui Kuan Cheng-Ying Yang 《Wireless Personal Communications》2007,43(4):1323-1331
Previously, the timing estimation in OFDM system employs cyclic prefix has been presented with the assumption of independent
identified distributed OFDM symbol. The information used to find the symbol synchronization depends on the length of cyclic
prefix. Actually, the data in the BPSK-OFDM modulated symbol, transferred by inverse fast Fourier transform, is with a complex
symmetry character. With this character, more information from the whole OFDM symbol could be provided for the symbol timing.
In this paper, the proposed algorithm uses the autocorrelation of the received signal to obtain the symbol timing. The simulation
of Beek’s algorithm and the proposed scheme are presented. The performances of these algorithms are evaluated based on the
missing symbol probability and the estimator mean square error. The simulation results show that the proposed algorithm is
suitable to achieve a better symbol synchronization. 相似文献