IIR 滤波器
N1=10000;%采样点数
Fs=10000;T=1/Fs;Tp=N1*T;%Tp 采样总时间
t=0:T:(N1-1)*T;k=0:N1-1;f=k/Tp;
f1=250;
f2=500;
xt1=sin(2*pi*f1*t);
xt2=sin(2*pi*f2*t);
st=xt1+xt2;%两路正弦信号的叠加
fxt=fft(st,N1);%快速傅里叶变换
subplot(2,1,1)
plot(t,st);grid;
xlabel('t');
ylabel('s(t)');
axis([0,0.02,min(st),max(st)]);
title('s(t)波形')
subplot(2,1,2)
stem(t,st, '.');
%stem(f,abs(fxt)/max(abs(fxt)), '.');%归一化
grid;
xlabel('T/s');
ylabel('幅度');
%axis([0,1000,0,2]);
axis([0,0.02,-2,2]);
title('s(t)采样');
%低通滤波器
wp=2*pi*280;
ws=2*pi*450;
Rp=1;
As=30;
[N,wc]=buttord(wp,ws,Rp,As,'s');%计算滤波器的阶数和 3dB 截止频率
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