电子科大课堂讲义课堂版信号678章课件

1、Chapter 6Time and Frequency Characterizationof Signals and Systems1Chapter 61 Chapter 6 Time and Frequency CharacterizationTime-Domain:Frequency-Domain:6.1 The Magnitude-Phase Representation （ 幅度-相位） of the Fourier TransformMagnitude Energy-Density2 Chapter 6 Chapter 6 Time and Frequency Characteriz

2、ation6.2 The Magnitude-Phase Representation of the Frequency Response of LTI SystemsGain Phase Shift1. Linear Phase2. Nonlinear Phase3 Chapter 6 Chapter 6 Time and Frequency CharacterizationHomework: 6.5 6.234 Chapter 6 6.5 Consider a continuous-time ideal bandbass filter whose frequency response is

3、 Chapter 6 Problem SolutionIf is the impulse response of this filter, determine a function such that (b) As is increased, does the impulse response of the filterget more concentrated or less concentrated about the origin?Solution (b) It will get more concentrated about the origin.(a)56.5 Consider a

4、continuous-tim Chapter 6 Problem Solution6.23 Shown in Figure 6.23 is for a lowpass filter. Determine and sketch the impulse response of the filter for each of the following phase characteristics: (a) (b) , where T is a constant.6 Chapter 6 (c) Chapter 6 Problem Solution7(c) Chapter 6 Chapter 7 Samp

5、ling Chapter 7 Sampling8 Chapter 7 Chapter 7 SamplingSampling Theorem:Let be a band-limited signal withThen is uniquely determined by its samples if where9 Chapter 7 Chapter 7 SamplingHomework: 7.1 7.2 7.3 7.6 7.97.3 The Effect of Undersampling: Aliasing 欠采样 混叠10 Chapter 7 Chapter 7 Problem Solution

6、7.1 A real-valued signal is known to be uniquely determined by its samples when the sampling frequency is . For what values of is guaranteed to be zero?11 Chapter 7 Chapter 7 Problem Solution7.2 A continuous-time signal is obtained at the output of an ideal lowpass filter with cutoff frequency . If

7、impulse-train sampling is performed on ,which of the following sampling periods would guarantee that can be recovered from its sampled version using an appropriate lowpass filter? (a) T=0.510-3 (b) T=210-3 (c) T=10-4(a) and (c)Sampling interval12 Chapter 7 Chapter 7 Problem Solution7.3 Determine the

8、 Nyquist rate corresponding to each of the following signals:13 Chapter 7 Chapter 7 Problem Solution7.6 Determine the maximum sampling interval T such that is recoverable from through the use of an ideal LPF.Nyquist ratemaximum sampling interval14 Chapter 7 Chapter 7 Problem Solution7.9 Consider the

9、 signalwhich we wish to sample with a sampling frequency ofto obtain a signal with Fourier transform . Determinethe maximum value of for which it is guaranteed that15 Chapter 7 5例 在如图1所示系统中,输入信号 的频谱如图2所示。已知 ，要求： 画出图中信号 和 的频谱；确定T的取值范围，以使信号 能从 中恢复。-2T -T -T1 0 T1 T 2T t Chapter 7 Problem Solution165例

10、在如图1所示系统中,输入信号 Chapter 8 Communication Systems17 Chapter 8 17 Chapter 8 Communication SystemsModulation :The general process of embedding an information-bearing signal into a second signal.Extracting the information-bearing signal.Demodulation :Modulation :Amplitude Modulation (AM)Frequency Modulati

11、on (FM)Phase Modulation (PM)18 Chapter 8 Chapter 8 Communication SystemsHomework: 8.1 8.3 8.2219 Chapter 8 Chapter 8 Problem Solution8.1 Determine a signal such that Solution 20 Chapter 8 Chapter 8 Problem Solution8.3 Determine . LPF Solution Be out of the passband of LPF21 Chapter 8 8.22In Figure (

12、a) ,a system is shown with input and outputThe input signal has the Fourier transform shown in Figure (b)Determine and sketch . Chapter 8 Problem SolutionFigure (a)Figure (b)22 8.22 Chapter 8 -7W -5W -3W 0 3W 5W 7W -5W -3W 0 3W 5W -8W -6W -2W 0 2W 6W 8W -2W 0 2W Chapter 8 Problem Solution23-7W -5W -

13、3W 0 3例 如图所示的系统中，已知输入信号 的傅立叶变换 如图1所示，且 。要求：ABC1图1 画出图2中A、B、C各点的信号频谱； 说明这是一个做什么用的系统。 Chapter 8 Problem Solution24例 如图所示的系统中，已知输入信号 ABC例 如图所示系统中，若输入信号，试分别A、B、C各点信号的频谱。 Chapter 8 Problem Solution25ABC例 如图所示系统中，若输入信号，试分别A、B、CProblems for Fourier AnalysisExample 4 In Figure (a), a system is shown with in

14、put signal and output signal . If the following information are given.1. Determine 2. Determine the impulse response of the whole system .If the input signal , determine the output signal +-26Problems for Fourier AnalysisEProblems for Fourier Analysis27Problems for Fourier Analysis2Problems for Four

15、ier Analysis例 如图所示系统中，已知 ，且 ，概略画出 ， ， 和的波形。说明整个系统等价于一个带通滤波器，并用 和 确定带通滤波器的上、下截止频率28Problems for Fourier Analysis例Problems for Fourier Analysis Consider an LTI system with unit impulse response 2. If the input is determine the output 1. Determine the frequency response of the whole system. 29Problems

16、for Fourier Analysis Problems for Fourier AnalysisA period of Example 1 Determine the Fourier transform of30Problems for Fourier AnalysisAExample 2 A real continuous-time signal with Fourier transform , and If is even, determine .If is odd, determine .Problems for Fourier AnalysisIf is real ,even2. If is real ,odd31Example 2 A real continu