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151.
This paper presents a 12-bit 100 MS/s CMOS pipelined analog-to-digital converter (ADC) with digital background calibration. A large magnitude calibration signal is injected into the multiplying digital-to-analog converter (MDAC) while the architecture of the MDAC remains unchanged. When sampled at 100 MS/s, it takes only 2.8 s to calibrate the 12-bit prototype ADC and achieves a peak spurious-free dynamic range of 85 dB and a peak signal-to-noise plus distortion ratio of 66 dB with 2 MHz input. Integral nonlinearity is improved from 1.9 to 0.6 least significant bits after calibration. The chip is fabricated in a 0.18μm CMOS process, occupies an active area of 2.3×1.6 mm~2, and consumes 205 mW at 1.8 V. 相似文献
152.
DWT-based joint antenna selection for correlated MIMO channels 总被引:1,自引:0,他引:1
Ehab Farouk Badran 《Signal, Image and Video Processing》2009,3(1):35-45
This paper proposes a new discrete wavelet transform (DWT)-based joint antenna selection scheme for spatially correlated multiple-input
multiple output (MIMO) channels. To reduce the severe performance degradation of the traditional antenna selection schemes
in correlated channels, a new scheme which employ joint antenna selection (JAS) at both link ends algorithm and embed DWT
operations in the receiver-end RF chains is proposed. Through extensive simulations it is demonstrated that the proposed DWT-based
joint antenna selection has significant improvement of the capacity for both i.i.d and correlated MIMO channels, while requiring
only a minor hardware overhead and low computational complexity for the DWT operations. Moreover, it is shown that the capacity
associated with DWT-based JAS is higher than the system employing DWT-based receive antenna selection (RAS) only. This is
achieved in i.i.d. and correlated MIMO channels. 相似文献
153.
This paper examines the use of quantity based fixed incentives to coordinate inventory decisions in a decentralized supply chain. We consider a two stage supply chain of autonomous supplier and distributor and prove that the optimal ordering policy for the newsvendor distributor under fixed incentives is an (s,S) type policy. We further show that external and internal quantity based incentives can restore channel coordination in single period and channel members can benefit through arbitrary splitting of the resulting additional chain profit. The single period results are extended to multiple periods and the impact of fixed incentives on the distributor’s optimal stocking policy and channel efficiency are examined under three different multi-period supplier strategies. Numerical examples are used to compare the multi-period strategies and to provide additional managerial insights. The results show that contrary to common belief, incentive plans developed and maintained based only on current inventory data perform poorly in long term and that such incentive plans must be periodically updated to enhance their efficiency. Furthermore, we show that high level of incentives designed to push too much inventory downstream of the supply chain can actually reduce the chain’s efficiency. 相似文献
154.
We study backbone colorings, a variation on classical vertex colorings: Given a graph G and a subgraph H of G (the backbone of G), a backbone coloring for G and H is a proper vertex k-coloring of G in which the colors assigned to adjacent vertices in H differ by at least 2. The minimal k∈N for which such a coloring exists is called the backbone chromatic number of G. We show that for a graph G of maximum degree Δ where the backbone graph is a d-degenerated subgraph of G, the backbone chromatic number is at most Δ+d+1 and moreover, in the case when the backbone graph being a matching we prove that the backbone chromatic number is at most Δ+1. We also present examples where these bounds are attained.Finally, the asymptotic behavior of the backbone chromatic number is studied regarding the degrees of G and H. We prove for any sparse graph G that if the maximum degree of a backbone graph is small compared to the maximum degree of G, then the backbone chromatic number is at most . 相似文献
155.
提出了一种采用倾斜脉冲的级联二阶非线性来实现超短激光脉冲压缩的方法. 对基于单块BBO晶体中基频光与倍频光群速度匹配的级联二阶非线性的脉冲压缩方案进行了理论分析. 对比研究了群速度匹配与失配情况下利用级联二阶非线性进行脉冲压缩的效果, 并模拟分析了基频光与倍频光的位相失配量、非线性晶体长度、 基频光初始峰值光强和初始脉宽等因素对脉冲压缩效果的影响. 结果表明, 基频光与倍频光的群速度匹配将会大幅度改善压缩脉冲的时间波形和频谱分布. 通过对位相失配量、晶体长度、初始光强等参数的优化和选取可获得较理想的压缩效果. 采用倾斜脉冲的级联二阶非线性的脉宽压缩方法, 针对中心波长800 nm、脉宽100 fs, 峰值光强为50 GW/cm2的基频光脉冲, 采用25 mm厚BBO晶体, 当基频光与倍频光位相失配量Δk=60 mm-1(对应失谐角1.98°), 晶体外部脉冲前沿倾斜角γ0=74°时, 计算获得了质量较好的20 fs剩余基频光, 并同时产生了14 fs的倍频光.
关键词:
倾斜波
级联二阶非线性
群速度失配
脉冲压缩 相似文献
156.
G. W. Arnold 《辐射效应与固体损伤》2013,168(1-4):15-19
A new method of producing a glass-ceramic surface layer on fused silica has been demonstrated using Li+-ion implantation and relatively low-temperature annealing. Infrared reflection spectroscopy (IRS) was used to study the effects of ion implantation on structural changes. Isochronal annealing of samples implanted with 250 keV Li+/cm2 brings about a dramatic change in the IRS spectra at 800°C in that it becomes identical with that of α-quartz. The dependence of the degree of crystallization on temperature, Li+-ion fluence, and silica type was studied. 相似文献
157.
158.
AbstractThe structure of Al, Ge, Mo-doped Higher Manganese Silicide (HMS) crystals with the general formulas Mn(Si0.99Ge0.01)1.75, Mn(Si0.995Ge0.005)1.75 and (Mn0.98Mo0.02)[(Si0.98Ge0.02)1.75]0.99Al0.01 was investigated by scanning and transmission electron microscopy, electron diffraction and X-ray energy dispersive spectrometry in a wide scale range from a few mm to several Å. Several secondary phases were identified in the Mn4Si7 matrix: Ge1?xSix (0.1 < x < 0.9) solid solution precipitates with Ge concentration ranging from 5 at. % up to 93 at.%, MoSi2 platelets, MnSi and Mn5Si3 precipitates. Their morphology, structure and crystallographic relationships with the HMS matrix were determined. Mostly local strains in the matrix and precipitates due to lattice misfits at interfaces derived from crystallographic relationships were found two orders of magnitude higher than deformation induced by thermal expansion mismatch. Only a few exceptions of specific relationships were found when the lattice misfit and thermal mismatch have close values. The largest misfit of about 22% was observed between MnSi and Mn4Si7 what led to big and numerous cracks in crystals. Therefore, doping can improve the material performance (1) by preventing the formation of MnSi precipitates with metallic properties and (2) by reduction of cracking and crack propagation because of larger MnSi /Mn4Si7 lattice misfit compared to Ge1?xSix /Mn4Si7 or MoSi2/Mn4Si7 misfits. 相似文献
159.
We consider a scale-free network of stochastic HH neurons driven by a subthreshold periodic stimulus and investigate how the collective spiking regularity or the collective temporal coherence changes with the stimulus frequency, the intrinsic noise (or the cell size), the network average degree and the coupling strength. We show that the best temporal coherence is obtained for a certain level of the intrinsic noise when the frequencies of the external stimulus and the subthreshold oscillations of the network elements match. We also find that the collective regularity exhibits a resonance-like behavior depending on both the coupling strength and the network average degree at the optimal values of the stimulus frequency and the cell size, indicating that the best temporal coherence also requires an optimal coupling strength and an optimal average degree of the connectivity. 相似文献
160.
时间延迟积分型面阵CMOS图像传感器MTF速度失配模型研究 总被引:3,自引:2,他引:1
研究了时间延迟积分型面阵互补金属氧化物半导体(CMOS)图像传感器调制传递函数(MTF)速度失配特性,在分析累加级数、像素尺寸、镜头放大倍数、行周期及电机运动速度失配等影响因素的基础上,建立了MTF速度失配模型。基于现场可编程门阵列(FPGA)开发板,搭建面阵CMOS图像传感器实现线阵时间延时积分(TDI)的CMOS测试系统。实验结果表明,在光强为3lx,速度失配M(ΔV/V)<2,8级时间延迟积分与面阵成像相比,MTF值提高50%;当累加级数为8级,速度失配满足M(ΔV/V)=2的速度失配容限时,奈奎斯特频率处的MTF值下降10%,当速度失配达到M(ΔV/V)=10时,MTF值下降35%。 相似文献