91 信号与系统 周建华 光电学院教学课件

1、第一章 部分习题讲解,Then,1.15 (a),1.21 (e),1.21 (f),1.22 ( c ),1.22 ( d ),1.22 ( h ),1.23 ( c ),1.24 ( a ),1.25 (d),Periodic. T=0.5.,Solution:,So, T=0.5,1.25 (e),Solution:,So, it is aperiodic.,1.25 (f),1.26 (c),1.31,第二章 部分习题讲解,2.4,(n-4)2 ，that is n6, yn=0.,3(n-4)8 ，that is 7n12，,(n-4)8 and (n-15)3,that is 12n18,yn=6,(n-4)8 and 3(n-15)8，that is 18n23,(n-15)8,that is n23, yn=0,1),2),3),4),5),2.5,then, N=4.,so, (-N+4)0, that is N4;,so,(-N+14)9,that is N5;,2.7 (a),2.7 (b),。

2、10.7 Analysis and characterization of LTI systems using z-transform,System function:,10.7 analysis and characterization of LTI system usingz-transform,10.7.1 Causality,a discrete-time LTI system is causal if and only if the ROC of its system function is the exterior of a circle, including infinity.,10.7 analysis and characterization of LTI system usingz-transform,A discrete-time LTI system with a rational system function H(z) is causal if and only if:(a) the ROC is the exterior of a circle out。

3、,6 Time and frequency characterization of S&S,本章要求: 了解LTI系统频率响应的幅度相位表示.了解理想频率选择滤波器的时域特性,6 Time and frequency characterization of S&S,6.1 The Magnitude-phase Representation of the Fourier Transform,For signal x(t) :,6 Time and frequency characterization of S&S,provides us with the information about the relative magnitudes of the complex exponentials that make up x(t).,provides us with the information concerning the relative phases of these complex exponentials .。

4、most periodic signals have the Fourier series representations:,How can do the aperodic signals?,4 The continuous time Fourier transform,4 The continuous time Fourier transform,Emphases in this chapter: The Fourier transform of the continuous-time aperiodic signal.The Fourier transform of the continuous-time periodic signal. The properties of Fourier transform. Basic Fourier transform pairs.Fourier inverse transform.analyze LTI systems in frequency domain.,4.1 The continuous time Fourier trans。

5、,3 Fourier Series Representation of Periodic Signals,In chapter 2: The analysis of LTI systems is based on representing input signals as linear combinations of shifted impulses.,The response of LTI system to the input signal isthe same linear combination of the individual response to each of the shifted impulses.,3 Fourier Series Representation of Periodic Signals,In the chapter, represent periodic signals as linear combinations of harmonically related complex exponentials.,The response of LTI。

6、,5 The discrete-time Fourier transform,Requirement in this chapter:Know about the Fourier transform of discrete-time signals.,5 The discrete-time Fourier transform,5 The discrete-time Fourier transform,5.1 the discrete-time Fourier Transform of aperiodic signal,Fourier series of periodic signal :,5 The discrete-time Fourier transform,Define:,5 The discrete-time Fourier transform,5 The discrete-time Fourier transform,5 The discrete-time Fourier transform,The Fourier transform of discre。

7、,7 Sampling,Emphases in this chapter: Impulse-train sampling.sampling theorem.the effect of undersampling: aliasingreferring to:figure 7.2 7.3 7.4 formula 7.17.6,7 Sampling,7.1 Representation of a Continuous-time Signal by its Samples: The Sampling Theorem,7. Sampling,7 Sampling,7 Sampling,7.1.1 Impulse-train Sampling,(1) Sampling,We wish to sample x(t).,a. Time domain:,7 Sampling,p(t): sampling function T: sample period s=2/T: Sample frequency,Figure 7.2,b. Frequency domain:,7 Samplin。

8、,1 Signal and System,Emphases in this chapter: 1) How to confirm a signals energy and power? 2) How to judge a signal is periodic or aperiodic signal? 3) The properties of complex exponential and sinusoidal signals. 4) How to do time-shifting, time-reversal and time-scaling? 5) The properties of unit impulse and unit step functions. 6) How to confirm whether a system is memory, invertible,causal, stable, time-invariant or linear or not?,1 Signal and System,1.1 Continuous-time and discrete-time。

9、Chapter 2 Linear Time-Invariant Systemsanalyze systems in time domain Chapter 4 The Continuous-Time Fourier Transformanalyze continuous-time systems in frequency domain Chapter 5 The Discrete-Time Fourier Transformanalyze discrete-time systems in frequency domain,Chapter 9 The Laplace Transformanalyze continuous-time systems in complex frequency domain Chapter 10 The Z-Transformanalyze discrete-time systems in complex frequency domain,2 Linear Time-Invariant Systems (LTI),Emphases in。

10、,8 Communication systems,Emphases in this chapter: Amplitude modulation with a sinusoidal carrier.demodulation for sinusoidal AM. Referring to: Figure 8.4 8.6 8.8 Formula 8.11 8.9 8.10 8.12 8.13,8 Communication systems,8. Communication Systems,8 Communication systems,The frequency of voice signal: 200Hz4kHz For microwave communication: 300MHz300GHz For satellite communication: a few hundred MHz40GHz,8 Communication systems,The source information,Transmitter or modulator,Communication cha。

11、,10.1 The z-Transform,10. The z-Transform,10.1 The z-Transform,LTI,(1) Definition,10.1 The z-Transform,10.1 The z-Transform,10.1 The z-Transform,a. Especially, when z=ej， above equation becomes The Fourier transform of signal xn:,So, the relationship between the Fourier transformand the z-transform is:,(2) The relationship between Z-transform and the Fourier transform of xn,b. On the other hand,10.1 The z-Transform,(2) Region of Convergence ( ROC ),ROC: Range of z for X(z) to conver。

12、9.7 Analysis and characterization of LTI systems using the Laplace transform,9 The Laplace Transform,9 The Laplace Transform,9.7.1 Causality,The ROC associated with the system functionfor a causal system is a right-half plane.,For a system with a rational system function,causality of system is equivalent to the ROC being the right-half plane to the right of the right-most pole.,Example 9.17 9.18 Find the ROC of the following systems and its causal property.,(a),(b),9 The Laplace Transform,Ex。

13、In chapter 4 and in chapter 5, we consider s=j and z= ej in the Fourier transform. Now , well consider s=+ j in the Laplace transform. And z= rej in the Z-transform.,本章 要求 ： 正确理解拉普拉斯变换及其定义式、熟练掌握由信号时域特点判断其拉氏变换收敛范围的定性分析方法（包括：有限持续期信号、左边信号、右边信号以及双边信号）。牢记常用典型信号的拉氏变换、正确理解拉氏变换的基本性质（特别注意单边拉氏变换和双边拉氏变化的区别、必须弄清楚初值定理和终值定理的使用条件）。熟练掌握从基本变换对出发、灵活运。