新建 文本文档 (2).txt

双线性iir数字滤波器的设计。。。。。。。

clear 
wp0=0.5*pi;wp1=0.4*pi;wp2=0.6*pi; 
Ap=3;ws2=0.7*pi;As=15;T=2;   %数字带通滤波器技术指标 
ws1=wp0-(ws2-wp0);      %计算带通滤波器的阻带下截止频率 
wc1=(2/T)*tan(wp1/2);wc2=(2/T)*tan(wp2/2); 
wr1=(2/T)*tan(ws1/2);wr2=(2/T)*tan(ws2/2); 
w0=(2/T)*tan(wp0/2);         %频率预畸变 
B=wc2-wc1;     %带通滤波器的通带宽度    
normwr1=(((wr1^2)-(w0^2))/(B*wr1)); 
normwr2=(((wr2^2)-(w0^2))/(B*wr2)); 
normwc1=(((wc1^2)-(w0^2))/(B*wc1)); 
normwc2=(((wc2^2)-(w0^2))/(B*wc2));    %带通到低通的频率变换 
if abs(normwr1)>abs(normwr2) 
  normwr=abs(normwr2) 
else normwr=abs(normwr1) 
end 
normwc=1;          %将指标转换成归一化模拟低通滤波器的指标 
N=buttord(normwc,normwr,Ap,As,'s'); %设计归一化的模拟低通滤波器阶数N和3db截止频率 
[bLP,aLP]=butter(N,normwc,'s');     %计算相应的模拟滤波器系统函数G(p) 
[bBP,aBP]=lp2bp(bLP,aLP,w0,B);     %模拟域频率变换，将G(P)变换成模拟带通滤波器H(s) 
[b,a]=bilinear(bBP,aBP,0.5);       %用双线性变换法将H(s)转换成数字带通滤波器H(z) 
w=linspace (0,2*pi,500); 
h=freqz(b,a,w); 
subplot(2,1,2); 
plot(w,abs(h)); 
grid on 
xlabel('w(rad)') 
ylabel('|H(jw)|') 
title('频谱函数') 
subplot(2,2,1); 
plot(w,20*log10(abs(h))); 
axis([0,2*pi,-120,20]); 
grid on 
xlabel('w(rad)') 
ylabel('20*lg|H(jw)|(db)') 
title('20*lg|H(jw)|--w')