dlpf.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)));
fprintf('\n***巴特沃思型滤波器阶数=%2.0f \n',N)
Pf=(2/T)*tan(wp/2);
Sf=(2/T)*tan(ws/2);
[z,p,k]=buttap(N);
[b,a]=zp2tf(z,p,k);
[bb,aa]=lp2lp(b,a,Pf*10000)
[B,A]=bilinear(bb,aa,10000)
w=0:0.01:pi;
H=abs(freqz(B,A,w))
subplot(2,1,1);
plot(w/pi,H);
axis([0,1,0,1.2]);
title('DLPF的幅频特性')
grid;
subplot(2,1,2);
H1=20*log10(abs(H));
plot(w/pi,H1);
axis([0,1,-50,0]);
grid;
title('DLPF的幅频特性，单位dB')