数字滤波器matlab的程序

数字滤波器matlab的源代码

function lvbo(Ua,Ub,choise)

%参考指令：lvbo(2*pi,10*pi,1/0/-1)

U1=min(Ua,Ub);

U2=max(Ua,Ub);

Us=16*U2;

T=2*pi/Us;

T_sum=4*max(2*pi/Ua,2*pi/Ub);

sum=T_sum/T;

t=T:T:T_sum;

x=sin(U1*t)+0.8*sin(U2*t);

X=DFT(x);

figure(1); subplot(221)

U=Us/sum:Us/sum:Us;

stem(U,abs(X));grid on

axis([Us/sum,Us/2,0,1.2*max(abs(X))])

title('原模拟信号采样频谱图')

Ucd=U1+(U2-U1)*1/5;Usd=U2-(U2-U1)*1/5;

switch choise

case 1

Hz_ejw=IIR_DF_BW(Ucd,1,Usd,30,T,sum);

case -1

Hz_ejw=IIR_DF_CF(Ucd,1,Usd,30,T,sum);

case 0

Hz_ejw=FIR_DF_HM(U1,U2,T,sum);

otherwise

Hz_ejw=IIR_DF_BW(Ucd,1,Usd,30,T,sum);

end

Y=X.*Hz_ejw;

y=1/sum*conj(DFT(conj(Y)));

figure(1); subplot(224)

plot(t,real(y)); title('模拟信号滤波后');grid on axis([0,T_sum,-max(real(y))*1.5,max(real(y))*1.5]) subplot(222);

plot(t,x); hold on

axis([0,T_sum,-max(x)*1.2,max(x)*1.2])

x=sin(U1*t);

plot(t,x,':r');grid on

title('模拟信号滤波前')

function Hz_ejw=IIR_DF_BW(Ucd,Ap,Usd,As,t,sum)

% 巴特沃思滤波器

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(log10(V/E)/log10(Usa/Uca));

k=[1:2*N];

Spk=exp(j*(pi/2+(2*k-1)/(2*N)*pi));

i=find(real(Spk)<0);

Sk(1:N)=Spk(i);

den=real(poly(Sk'));

k0=polyval(den,0);

disp('模拟巴特沃思滤波器的归一化统函数 Ha(s) 为')

tf(k0,den)

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); subplot(223)

plot(w,abs(Hz_ejw)); grid on

title('巴特沃思低通滤波器')

axis([2*pi/sum,pi,-0.2,1.2*max(abs(Hz_ejw))]) 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;