www.gusucode.com > MATLAB仿真技术与应用__的配套例题和习题的matlab源代码 > 第四章/example8.m

    MATLAB程序为：
% MATLAB program 4-8
% 3-order Analog filter design
clear all;
clc;
N=3; Rp=3; Rs=40;
[z1,p1,k1]=buttap(N);                         %Butterworth filter
[z2,p2,k2]=cheb2ap(N,Rs);                     %Chebyshev II filter
[z3,p3,k3]=ellipap(N,Rp,Rs);                   %Elliptic filter
[b1,a1]=zp2tf(z1,p1,k1);                       %零极点形式转换成状态空间形式
[b2,a2]=zp2tf(z2,p2,k2);
[b3,a3]=zp2tf(z3,p3,k3);
figure;
[h1,w1]=freqs(b1,a1); 
[h2,w2]=freqs(b2,a2); 
[h3,w3]=freqs(b3,a3); 
mag1 = 20*log10(abs(h1));
plot(w1,mag1);
grid;                             %绘频率响应图
figure;
mag2 = 20*log10(abs(h2));
plot(w2,mag2);
grid; 
figure;
mag3 = 20*log10(abs(h3));
plot(w3,mag3);
grid;