第十章（IIR滤波器）.pptVIP

第十章　无限脉冲响应滤波器 12.9 MATLAB设计IIR滤波器 MATLAB滤波器设计函数简介 IIR滤波器阶数选择 1.Buttord：巴特沃斯滤波器阶数选择 BUTTORD Butterworth filter order selection. [N, Wn] = BUTTORD(Wp, Ws, Rp, Rs) returns the order N of the lowest order digital Butterworth filter that loses no more than Rp dB in the passband and has at least Rs dB of attenuation in the stopband. Wp and Ws are the passband and stopband edge frequencies, normalized from 0 to 1 (where 1 corresponds to pi radians/sample). For example, Lowpass: Wp = .1, Ws = .2 Highpass: Wp = .2, Ws = .1 Bandpass: Wp = [.2 .7], Ws = [.1 .8] Bandstop: Wp = [.1 .8], Ws = [.2 .7] BUTTORD also returns Wn, the Butterworth natural frequency (or, the 3 dB frequency) to use with BUTTER to achieve the specifications. [N, Wn] = BUTTORD(Wp, Ws, Rp, Rs, s) does the computation for an analog filter, in which case Wp and Ws are in radians/second. When Rp is chosen as 3 dB, the Wn in BUTTER is equal to Wp in BUTTORD. See also BUTTER, CHEB1ORD, CHEB2ORD, ELLIPORD. 例子1： 低通： [n,wn]=buttord(0.1,0.2,3,30) n = 5 wn = 0.10277874241508 高通： [n,wn]=buttord(0.3,0.2,3,30) n = 8 wn = 0.29533078603161 带通： [n,wn]=buttord([0.2,0.7],[0.1,0.8],3,30) n = 7 wn = 0.19094597277816 0.71252809718804 带阻： [n,wn]=buttord([0.1,0.8],[0.2,0.7],3,30) n = 7 wn = 0.13768026121850 0.78873776610924 2. cheb1ord：切比雪夫I型滤波器阶数选择 CHEB1ORD Chebyshev Type I filter order selection. [N, Wn] = CHEB1ORD(Wp, Ws, Rp, Rs) returns the order N of the lowest order digital Chebyshev Type I filter that loses no more than Rp dB in the passband and has at least Rs dB of attenuation in the stopband. Wp and Ws are the passband and stopband edge frequencies, normalized from 0 to 1 (where 1 corresponds to pi radians/sample). For example, Lowpass: Wp = .1, Ws = .2 Highpass: Wp = .2, Ws = .1 Bandpass: Wp = [.2 .7], Ws = [.1 .8] Bandstop: Wp = [.1 .8], Ws = [.2 .7] CHEB1ORD a