alpf.m

IIR-butter低通滤波器设计

wp=0.3*pi;
ws=0.4*pi;
Rp=3;
As=30;
T=1;
Pf=(2/T)*tan(wp/2);
Sf=(2/T)*tan(ws/2);
%巴特沃思型滤波器阶数
N=ceil((log10((10^(Rp/10)-1)/(10^(As/10)-1)))/(2*log10(Pf/Sf)));
[z,p,k]=buttap(N);
[b,a]=zp2tf(z,p,k);
[h,w]=freqs(b,a);
subplot(2,2,1);
plot(w,abs(h));
axis([0,4,0,1.2]);
title('ALPF的幅频特性')
xlabel('W')
ylabel('|H(s)|')
grid on
subplot(2,2,2);
h1=20*log10(abs(h));
plot(w,h1);
axis([0,4,-50,10])
title('ALPF的幅频特性，单位dB')
ylabel('|H(s)|(分贝数)')
grid on
subplot(2,2,3);
zplane(b,a);
title('极点分布图')