专业英语Lesson 3 Sampled-Data Signals.pptVIP

《电子信息工程专业英语教程》 Lesson 3 Sampled-Data Signals Backgrounds Text tour Language in use Vocabulary Structure Reading/writing techniques Backgrounds Terminology Digital electronics 数字电子 The Dirac function 迪拉克函数 Shifting property 移位算子 Time and frequency-domain 时域和频域 Spectral lines 谱线 DFT 离散傅里叶变换 FFT 快速傅里叶变换 Mapping 映射 　 Decaying oscillatory function 衰减振荡函数 Text tour Outline 3.1 Introduction 3.2 Mathematical Description Using the Dirac Function 3.3 Spectra of Sampled-data Signals 3.4 The z-transform 3.1 Introduction Sampled-data signals arise whenever continuous functions are measured or recorded intermittently and the interval between successive samples is sufficiently small 3.2 Mathematical Description Using the Dirac Function The definition of the Dirac function we make use of the so-called ‘shifting property’ of the Dirac function to evaluate that of the unit Dirac function. 3.2 Mathematical Description Using the Dirac Function Discussing the spectrum of a delayed Dirac pulse which occurs at some instant t=T. Clearly 3.3 Spectra of Sampled-data Signals 3.3.1 The Discrete Fourier Transform 3.3.2 The Fast Fourier Transform 3.3.1 The Discrete Fourier Transform The reasons that the Fourier transform of a sampled-data signal is generally referred to as a discrete Fourier transform (DFT) ⅰ) the signal itself is discrete ⅱ) The Fourier transform can only be estimated for a set of discrete values of The way of visualize the spectrum of a sampled-data signal form 3.3.1 The Discrete Fourier Transform Example Figure 3.1 Four signals and their spectra. The continuous and sampled version of the cosine and pulse waveforms have similar spectra in the region , but the sampled-data spectra repeat indefinitely at intervals in of 3.3.2 The Fast Fourier Transform The number of computer operations needed to evaluate the DFT of a signal consisting of N samples. The introduction of the fast Fourier transform (FFT) 3.4 The z-t