邬震宇-信号与系统 4.pptVIP

* Example 4.3.1 Determine the FT of impulse train Solution： can be expressed as 1 * 2 The FT is * Table of Fourier Transform Properties. P.328, Table 4.1 (2) Table of Fourier Transform Pairs. P.329, Table 4.2 * 4.5.1 The system response of a CT LTI system A CT LTI system can be written by Assume that LTI * Take FT to the Eq: Define that: is called the system function and is also called Frequency Response(频率响应) of the LTI system. (4.76) * :Magnitude-Frequency relation(幅频特性) :Phase-Frequency relation(相频特性) And Impulse response system function * LTI } So, * Example 4.5.1: A CT LTI system is described by Solution: Assume that * * -3/2 4 5/2 * Example 4.5.2 A CT LTI system impulse response and input are Determine: (1) The system frequency response. (2)The system differentiation equation. (3)The system response. Solution： (1) The system frequency response is (2) Because of the fact that (2)The differentiation equation * (3) So, 请用FS方法验证 * LTI By designing the , to change the shape of , or eliminate some frequency components in .The process of signal processing is called filtering. Often, the system for filtering is called filter. Filter: 4.6.1 The concept of filtering Filtering: * Filter ——The system described by or Filtering ——The process to finish * Frequency-shaping filter(频率成形滤波器) change the shape of . Frequency-selective filter(频率选择性滤波器) eliminate some frequency components in * (1) Ideal lowpass filter Cutoff angular frequency Impulse response * Filter is： RC lowpass filter * (2) Ideal highpass filter Impulse response Cutoff angular frequency * or Passband (3) Ideal bandpass filter Impulse response * (4) Ideal bandpstop filter * Example4.6.1 (例4.2.1) Input Lowpass filter * （1） Sketch the frequ