cheblow1.m

自己做的： （一）用双线性变换法设计并用实验系统实现一个三阶的契比雪夫Ⅰ型低通数字滤波器

function[Fs,N,ai,bi]=chebulow1(fs,as)
Fs=8000;T=1/Fs;
fp=2000;Rp=1;
fs=input('请输入阻带临界频率fs=');
As=input('请输入阻带内衰减as=');
%频率预畸
wp=fp/Fs*2*pi;
ws=fs/Fs*2*pi;
OmegaP=(2/T)*tan(wp/2);
OmegaS=(2/T)*tan(ws/2);
%设计Chebyshev低通滤波器原型
ep=sqrt(10^(Rp/10)-1);
A=10^(As/20);
OmegaC=OmegaP;
OmegaR=OmegaS/OmegaP;
g=sqrt(A*A-1)/ep;
N=ceil(log10(g+sqrt(g*g-1))/log10(OmegaR+sqrt(OmegaR*OmegaR-1)));

[z,p,k]=cheb1ap(N,Rp);%获取零极点参数
a=real(poly(p));
aNn=a(N+1);
p=p*OmegaC;
a=real(poly(p));
aNu=a(N+1);
k=k*aNu/aNn;
b0=k;
B=real(poly(z)); 
b=k*B;

%双线性变换
[bi,ai]=bilinear(b,a,Fs);
%绘制结果
%freqz(bi,ai,200,Fs,'whole');
H=freqz(bi,ai,200,Fs,'whole');
plot(abs(H));

x1=[Fs N ai bi];
disp(x1(1:4));