fff1.m

matlab 编写的FIR iir滤波器源程序

function [B,A] = fff1( ap,as,wp,ws ,fs)   %程序中fs为抽样频率，输出[A,B]为滤波器的系数
T=1/fs;
ws=2/T*tan(ws/2);                                                   %频率修正
wp=2/T*tan(wp/2);
N=ceil((log10((10^(as/10)-1)/(10^(ap/10)-1)))/(2*(log10(ws/wp))))   %计算模拟滤波器的阶数N
wc=ws/((10^(as/10)-1)^(1/(2*N)));                                   %计算模拟滤波器的截止频率
for k=1:N
    s(k)=wc*exp(j*(1/2+(2*k-1)/(2*N))*pi);                          %计算巴特沃思模拟滤波器的极点
end                                           
    b=wc^N;                                                         %分别算出分子、分母系数
a=real(poly(s));             
[B,A]=bilinear(b,a,fs);      %进行双线形z变换
w=[0:0.1:2];
H=freqz(B,A,w);              %计算频率响应
angH=angle(H);               %计算幅度响应
H=abs(H);
DB=20*log10(H);
subplot(2,2,1);plot(w/(2*pi)*1000,DB)   %绘图
axis([0,350,-25,0]);grid on;
subplot(2,2,2);plot(w/(2*pi)*1000,angH) 
grid on;
subplot(2,1,2);plot(w/(2*pi)*1000,H)
grid on;