IIR数字滤波器的设计.doc

IIR数字滤波器的设计
clear;close all
t=1; fs=4000;
wpu=0.65*pi,wpl=0.45*pi;
wsu=0.75*pi,wsl=0.30*pi;
wpz=[0.45,0.65];
wsz=[0.30,0.75];
wp=2/t*tan(wpz/2);ws=2/t*tan(wsz/2);
rp=1;as=40;
[n,wc]=buttord(wp,ws,rp,as,'s'); %计算带通滤波器阶数N和3dB截止频率wc
[b,a]=butter(n,wc,'s'); %计算带通滤波器系统函数分子分母多项式系数向量b,a
[bz,az]=bilinear(b,a,fs);
[nd,wdc]=buttord(wpz,wsz,rp,as);
[bd,adz]=butter(nd,wdc);
hk=freqz(bd,adz)
subplot(2,2,1)
plot(abs(hk))
xlabel('Hz');
ylabel(' 幅度');
title('幅度函数曲线')
subplot(2,2,2)
plot(angle(hk))
xlabel('\omega/\pi');
ylabel('phi(omega)');
title('相频特性曲线')

FIR数字滤波器的设计
[n,wn,bta,ftype]=kaiserord([0.3 0.45 0.65 0.8],[0 1 0],[0.01 0.1087 0.01]);
h1=fir1(n,wn,ftype,kaiser(n+1,bta),'noscale');
[hh1,w1]=freqz(h1,1,256);
figure(1)
subplot(2,1,1)
plot(w1/pi,20*log10(abs(hh1)))
grid
xlabel('归一化频率w');ylabel('幅度/db');
subplot(2,1,2)
plot(w1/pi,angle(hh1))
grid
xlabel('归一化频率w');ylabel('相位/rad');