untitled.m

试验三 ：用双线性变换法设计IIR数字滤波器

%x(n)的心电脉冲函数
x=[-4,-2,0,-4,-6,-4,-2,-4,-6,-6,-4,-4,-6,-6,-2,6,12,8,0,-16,-38,-60,-84,-90,-66,-32,-4,-2,-4,8,12,12,10,6,6,6,4,0,0,0,0,0,-2,-4,0,0,0,-2,-2,0,0,-2,-2,-2,-2,0];
subplot(2,2,1);
n=0:55;
stem(n,x,'.');
xlabel('n');
ylabel('x(n)');
title('x(n)的心电脉冲函数');
%通过滤波器H1(z)后的y1(n)函数
A=0.09036;
b1=[A,2*A,A];
a1=[1,-1.2686,0.7051];
h1=filter(b1,a1,x);
[H1,w]=freqz(b1,a1,100);
%通过滤波器H1(z)、H2(z)后的y2(n)函数
b2=[A,2*A,A];
a2=[1,-1.0106,0.3583];
h2=filter(b2,a2,h1);
[H2,w]=freqz(b2,a2,100);
%通过滤波器H1(z)、H2(z)、H3(z)后的y3(n)函数
b3=[A,2*A,A];
a3=[1,-0.9044,0.2155];
h3=filter(b3,a3,h2);
[H3,w]=freqz(b3,a3,100);
subplot(2,2,2);
stem(n,h3,'.');
xlabel('n');
ylabel('y(n)');
title('通过滤波器H1(z)、H2(z)、H3(z)后的y3(n)函数');
%通过滤波器H1(z)、H2(z)、H3(z)后的对数频率响应20log[Ha3(ejw)]函数
subplot(2,2,3);
H4=H1.*(H2);
H=H4.*(H3);
mag=abs(H);
db=20*log10((mag+eps)/max(mag));
plot(w/pi,db);
xlabel('w/п');
ylabel('20log[Ha3(ejw)]');
title('通过滤波器H1(z)、H2(z)、H3(z)后的对数频率响应20log[Ha3(ejw)]函数');
grid;