IIR数字滤波器的设计及软件实现

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附录（Ⅰ）：

原信号输出：

(a)s(t)的波形4020s(t)0-2000.0010.0020.0030.0040.0050.0060.0070.0080.009t/s(b) s(t)的频谱0.011幅度0.5002004006008001000f/HZ12001400160018002000

低通输出：

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(a) s(t)损耗函数曲线0-20-40-60-80幅度（dB）00.10.20.30.40.50.6?/?(b) s(t)的波形0.70.80.91y(n)100-1000.010.020.030.040.05t/s(c) s(t)的频谱0.060.071幅度0.5002004006008001000f/Hz12001400160018002000

带通输出：

(a) s(t)损耗函数曲线0-20-40-60-80幅度（dB）00.10.20.30.40.50.6?/?(b) s(t)的波形0.70.80.91y(n)100-1000.010.020.030.040.05t/s(c) s(t)的频谱0.060.071幅度0.5002004006008001000f/Hz12001400160018002000

高通输出：

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(a) s(t)损耗函数曲线0-20-40-60-80幅度（dB）00.10.20.30.40.50.6?/?(b) s(t)的波形0.70.80.91y(n)100-1000.010.020.030.040.05t/s(c) s(t)的频谱0.060.071幅度0.5002004006008001000f/Hz12001400160018002000

附录（Ⅱ）：

%主函数

%IIR数字滤波器设计及软件实现 clear all;

%调用信号产生函数mstg产生又三路抑制载波调幅信号相加构成的复合信号 syms st; syms t;

st=mstg; %低通滤波器设计与实现 Fs=10000;T=1/Fs;

n=800;Tp=n*T;k=0:n-1;f=k/Tp; fp=280;fs=450;

wp=2*fp/Fs;ws=2*fs/Fs;

rp=0.1;rs=60; ?指标;(低通滤波器的通阻带边界频率)

[N,wp0]=ellipord(wp,ws,rp,rs);%调用ellipod计算椭圆DF阶数N和通带截止频率wp [B,A]=ellip(N,rp,rs,wp0);%调用ellip计算椭圆带通DF系统函数系数向量B和A y1t=filter(B,A,st);%滤波器的软件实现 fyt=fft(y1t,n); %下面为绘图部分 figure(2);

subplot(3,1,1); myplot(B,A);

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yt='y_1(t)'; subplot(3,1,2); tplot(y1t,T,yt); subplot(3,1,3);

stem(f,abs(fyt)/max(abs(fyt)),'.'); grid;

title('(c) s(t)的频谱'); axis([0,Fs/5,0,1.2]);

xlabel('f/Hz');ylabel('幅度');

%带通滤波器的实现与设计

fpl=440;fpu=560;fsl=275;fsu=900; wp=[2*fpl/Fs,2*fpu/Fs]; ws=[2*fsl/Fs,2*fsu/Fs]; rp=0.1;rs=60;

[N,wp0]=ellipord(wp,ws,rp,rs); [B,A]=ellip(N,rp,rs,wp0); y2t=filter(B,A,st); fyt=fft(y2t,n); figure(3);

subplot(3,1,1); myplot(B,A); yt='y_1(t)'; subplot(3,1,2); tplot(y1t,T,yt); subplot(3,1,3);

stem(f,abs(fyt)/max(abs(fyt)),'.'); grid;

title('(c) s(t)的频谱'); axis([0,Fs/5,0,1.2]);

xlabel('f/Hz');ylabel('幅度');

%高通滤波器的实现与设计 fp=890;fs=600;

wp=2*fp/Fs;ws=2*fs/Fs; rp=0.1;rs=60;

[N,wp0]=ellipord(wp,ws,rp,rs); [B,A]=ellip(N,rp,rs,wp0,'high'); y3t=filter(B,A,st); fyt=fft(y3t,n); figure(4);

subplot(3,1,1); myplot(B,A); yt='y_1(t)';

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