iir_df_cf.m

切比雪夫滤波器 切比雪夫滤波器的幅频特性在同代或者在阻带有波动

function Hz_ejw=IIR_DF_CF(Ucd,Ap,Usd,As,t,sum)
% 切比雪夫低通滤波器
E=(10^(0.1*Ap)-1)^0.5;
V=(10^(0.1*As)-1)^0.5;
Wc=Ucd*t; Ws=Usd*t;
Ucd=Wc/t; Usd=Ws/t;
Uca=(2/t)*tan(Ucd*t/2); 
Usa=(2/t)*tan(Usd*t/2);
N=ceil(acosh(V/E)/acosh(Usa/Uca));;
A=1/E+(1/E^2+1)^0.5;
a=1/2*(A^(1/N)-A^(-1/N));
b=1/2*(A^(1/N)+A^(-1/N));
k=1:2*N;
Spk=-a*sin((2*k-1)/(2*N)*pi)+j*b*cos((2*k-1)/(2*N)*pi);
i=find(real(Spk)<0);
Sk(1:N)=Spk(i);
den=real(poly(Sk'));
k0=1;
disp('模拟切比雪夫低通滤波器的归一化统函数 Ha(s) 为')
tf(k0,den)
if (rem(N,2)==1)
for i=1:N
k0=k0*(-Sk(i));
end
elseif ((rem(N,2))==0)
k0=1;
for i=1:N
k0=k0*(-Sk(i));
end
end
if (rem(N,2)==0)
k0=10^(-0.05*Ap)*k0;
end
k0=real(k0);
syms s z T;
den_jU=1;
s=s/Uca;
for i=1:N
den_jU=s^(N-i+1)*den(i)+den_jU;
end
Ha_s=simple(1/den_jU);
H_z=subs(Ha_s,'s',(2/T)*((1-1/z)/(1+1/z)));
k=1:sum;w=(2*pi/sum)*k;
ejw=exp(j*w);
Hz_ejw=subs(H_z,{z,T},{ejw,t*ones(1,length(ejw))});
figure(1),plot(w,abs(Hz_ejw));grid on
title('切比雪夫低通滤波器')
axis([2*pi/sum,pi,-0.5,max(abs(Hz_ejw))])