离散时间信号处理（英文版）chp4-第2讲.pptVIP

4.4 Discrete-time Processing of Continuous-time Signals Question 1: 4.4.1 LTI discrete-time system 4.4.1 LTI discrete-time system Example 4.4 Ideal Lowpass Filter Example 4.4 Ideal Lowpass Filter Example 4.5 Example 4.5 Example 4.6 4.4.2 Impulse invariance 4.4.2 Impulse invariance Short verification Additional explanation Conclusion 4.5 Continuous-time Processing of  Discrete-time Signals Example 4.9 Noninteger delay Example 4.9 Noninteger delay Example 4.9 Noninteger delay Example 4.9 Noninteger delay Example 4.10 MA system with noninteger delay Summary Summary Homework 4.5, 4.25, 4.32 (a), (c) Class test 1) Solution Solution 3) The C/D and D/C converters may have different sampling rate. Given C/D : D/C : LTI D-T system: then If (no aliasing in C/D) Effective frequency response: then Conclusion: Furthermore, (4.38) is valid even if some aliasing occurs in the C/D converter, as long as does not pass the aliased components. If (no aliasing in C/D) LTI D-T system: Then If (no aliasing in C/D) If aliasing occurs in C/D, but can be removed by , Then, is also valid. 对于一个固定的离散时间低通滤波器，只要改变采样周期T，就可以实现不同截止频率的连续时间低通滤波器 当 时，截止频率为 的离散时间低通滤波器可以实现截止频率为 的连续时间低通滤波器 Conclusion: 设计一个离散时间系统，使 经过下面系统完成微分功能 Assume is bandlimited, and the Nyquist condition is met, it is sufficient that Let The expected result is: If Then (bandlimited) Question 2: Given realized by D-T system Question 3: What relationship between h[n] and hc(t)? Further requirement for T such that: If (requirement) compare (in fact) + + + + when , 因此，脉冲响应不变法提供了连续时间系统的离散时间实现的一种途径，也是数字滤波器设计的一种方法。 用离散时间系统实现连续时间系统时，只要满足： 则h[n]就是幅度加权的hc(t)的采样序列，即： 故称为脉冲响应不变法。 如果连续时间系统 非理想带限，则 频谱出现混叠；只要 在高频快速衰减，且采样频率足够高，则 混叠很小，可忽略不计，则： (Example 4.8) The system is not typically used to implement discrete-time system, but it provid