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论述了过采样 Σ- ΔADC的基本原理及结构 ,分析了 Σ- Δ调制器的频域传输特性和系统的信噪比 ,给出了实现不同的 A/D转换精度必须满足的条件和用单片机实现 Σ- ΔADC的具体方法和电路 .实际使用表明 ,该方法测量结果可靠 ,具有实用价值 相似文献
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微格教学是现代教育技术中最早使用的一种教学方法,主要用于培训学生的专项技能,在师范院校应用比较广泛。微格教学经历了模拟时代、数字化时代,现在正处于网络化时代并逐步走向成熟。本文从微格教学的基本概念入手,分析了微格教学实验室建设的三个发展历程,并主要探讨了建设网络化的微格教学实验室的标志所在,以及建设网络化的微格教学实验室的益处和应注意的问题。 相似文献
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A Simple Route of Morphology Control and Structural and Optical Properties of ZnO Grown by Metal-Organic Chemical Vapour Deposition
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Employing the metal-organic chemical vapour deposition (MOCVD) technique, we prepare ZnO samples with different morphologies from the film to nanorods through conveniently changing the bubbled diethylzinc flux (BDF) and the carrier gas flux of oxygen (OCGF). The scanning electron microscope images indicate that small BDF and OCGF induce two-dimensional growth while the large ones avail quasi-one-dimensional growth. X-ray diffraction (XRD) and Raman scattering analyses show that all of the morphology-dependent ZnO samples are of high crystal quality with a c-axis orientation. From the precise shifts of the 20 locations of ZnQ (002) face in the XRD patterns and the E2 (high) locations in the Raman spectra, we deduce that the compressive stress forms in the ZnO samples and is strengthened with the increasing BDF and OCGF. Photoluminescence spectroscopy results show all the samples have a sharp ultraviolet luminescent band without any defects-related emission. Upon the experiments a possible growth mechanism is proposed. 相似文献
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