巴特沃斯低筒.rar_巴特沃斯滤波

% IIR Lowpass Use Butterworth % copyright by Etual clear; fs=20;fpass=4;fstop=5; Ap=0.5;As=10; wp=2*pi*fpass/fs;ws=2*pi*fstop/fs; omegap=tan(wp/2);omegas=tan(ws/2); ep=sqrt(10^(Ap/10)-1); es=sqrt(10^(As/10)-1); N=ceil(log(es/ep)/log(omegas/omegap)); omega0=omegap/ep^(1/N); K=floor(N/2); for i=1:K theta(i)=pi*(N-1+2*i)/(2*N); end for i=1:K G(i)=omega0^2/(1-2*omega0*cos(theta(i))+omega0^2); end for i=1:K a1(i)=2*(omega0^2-1)/(1-2*omega0*cos(theta(i))+omega0^2); end for i=1:K a2(i)=(1+2*omega0*cos(theta(i))+omega0^2)/(1-2*omega0*cos(theta(i))+omega0^2); end if K<(N/2) G0=omega0/(omega0+1);a0=(omega0-1)/(omega0+1); end w=0:pi/300:pi; Hw2=1./(1+(tan(w/2)/omega0).^(2*N)); plot(w/pi,Hw2); grid;