基于MATLAB的数字下变频器的设计与仿真应用

文中应用软件无线电思想对数字下变频器中的几个关键技术进行了研究,对下变频各个模块所涉及到的CIC、HB、FIR等关键算法进行了讨论、提炼与总结,应用matlab软件设计了下变频器中的CIC、HB、FIR滤波器等核心模块,并将各模块融为一体从软件实现的角度完成了对系统的搭建和功能仿真。仿真结果表明,系统实现了对中频信号的下变频处理且无失真现象,大大减少了软件无线电系统数字信号处理的运算量和数据的存储量,极大地提高了系统的实时性。     

Dynamics and mode-selected reaction of NCO+H_2→HNCO+H

The reaction path of the reaction NCO+H2→HNCO + H has been traced by Fukui's theory and the ab initio method. On this basis, the dynamical properties along the reaction path, canonical variational theory (CVT) rate constants and vibrational-mode-selected rate constants have been computed. The results show that the effect of the electron correlation energy on the activation barrier is large, and tiros the correction by MP4 method is effective; the results also show that the recrossing and tunneling effects exist, and thus the corrections by the variational transition state theory (VTST) and the small curvature (SC) approximation method are also effective. In the reaction, the coupling and energy transfer between mode 8(7) and reaction path are strong, so the rate is effectively enhanced while these modes, especially H2 stretching, are vibrationally excited.     

基于CORDIC算法的数字下变频技术设计与实现

传统的基于查表法的数控振荡器耗费大量的FPGA片内资源。为了解决这一问题，提出了一种基于CORDIC（coordinate rotation digital compute，坐标旋转数值计算）算法的数控振荡器的设计方法，而且该算法使数控本振和数字混频两个功能合在一起完成，省去了两个乘法器。最后通过仿真证明了其有效性，具有较高的工程应用价值。     

基于NCO IP core的Chirp函数实现设计

首先分析Chirp函数在频域上的一般特性,并且分析Altrea公司提供的数控振荡器知识产权核(NCO IP core)的输入/输出特性,通过MegaCore环境确定其输入控制字,通过外围逻辑电路实时向NCO IP core调入控制频率控制字以达到改变输出频率的目的,并通过在示波器上观测FPGA的运行情况,验证了该设计具有很好的输出效果.     

Si（NCO）^＋2结构与稳定性的密度泛函理论研究

使用密度泛函（DFT）方法对Si(NCO)^ 2的可能异构体进行了计算研究,在UB3LYP／6－311G（d)理论级别下得到了6种异构体的能量和振动频率,结果表明,以2个NCO基团直接与Si^ 配位形成的异体最为稳定,理论计算得到一个以2个CO分子对称方式吸附于SiN^2 两侧而形成的络合物,这个络合物是否存在需进一步证实,在UB3LYP／6－311g(D) Ez级别下,反应Si^ 2NOC→Si(NCO)^ 2的焓变为－751．94kJ/mol,说明此反应在能量上相当有利。     

DFT modeling of the hydrolysis of isocyanic acid over the TiO2 anatase (1 0 1) surface: Adsorption of HNCO species

The nature of the interaction of isocyanic acid (HNCO) with the active centers at the ideal anatase TiO₂ (1 0 1) surface were studied using ab initio density functional theory (DFT) method with a cluster model. Two types of adsorption of isocyanic acid are found to be likely at (1 0 1) surface – dissociative and molecular adsorption. Only molecular adsorption of HNCO leads to the direct weakening and further splitting of the NC bond, which is a necessary step for the hydrolysis of isocyanic acid. During molecular adsorption of HNCO, an energetically stable intermediate surface complex is created with an adsorption energy of −1.33 eV, in which the HNCO skeleton is changing due to new strong bonds between C–O_s and N–Ti_s. Based on the existence of this intermediate complex a probable reaction pathway for the hydrolysis of HNCO over the ideal anatase (1 0 1) surface was developed. A surface oxygen vacancy was formed after the decomposition of the intermediate complex and CO₂ desorption. Afterwards, water adsorbs at the oxygen vacancy site and NH₃ is successively formed. The HNCO hydrolysis over TiO₂ was found to be energetically favorable with global energy gain of about −2.08 eV.     

基于DSP Builder的NCO优化设计

首先介绍了数控振荡器（NCO,Numerically Controlled Oscillator）的原理和特点,研究了用DSP Builder实现数控振荡器的传统设计方法,并在此基础上提出了一种使用1/4周期存储的优化方法,并将其与整周期存储方法进行仿真比较。相对于传统整周期存储,采用1/4周期存储方法可以在不增加额外只读存储器（ROM,Read Only Memory）存储空间的情况下提高了频率分辨率。该方法在Matlab/Simulink中得以实现,在ModelSim中进行了功能仿真之后将设计模型下载到FPGA进行硬件仿真。     

基于CORDIC算法的NCO设计

该文介绍了坐标旋转数字计算方法(Coordinate Rotation Digital Computer,CORDIC)的基本原理及其典型应用,并指出传统CORDIC算法在应用方面的不足;在此基础上,针对数字控制振荡器(numerical controlled oseillator,NCO)的设计,对其进行了改进,解决...     

基于FPGA的正交数控振荡器(NCO)的设计与实现

在研究数控振荡器NCO工作原理的基础上,通过分析对比几种不同的NCO设计方法,采用了算法简单、节省资源的基于ROM查找表的设计方法。针对正交数控振荡器NCO的主要部件正余弦存储表、可变模计数器进行了算法设计和电路设计,并在Altera公司的FPGA上进行了验证,波形仿真结果表明了电路设计的正确性。采用查找表的方法可以有效提高系统功能的可扩展性和系统的可集成性,使得NCO功能模块可以通过配置存储表、频率控制字来满足多种应用场合下的NCO设计需要,可以广泛地应用于各种现代通信系统中。