exa4_7.m

新版Matlab 7辅助信号处理技术与应用

% exa4-7_lp2bs for example4-7
% chebshev I analog lowpass filter prototype to bandstop filter 

clear all;
N=9;
Rp=3;
wl=200*pi;
wh=1000*pi;
% Chebyshev analog lowpass filter prototype
[z,p,k]=cheb1ap(N,Rp);
[b,a]=zp2tf(z,p,k);
% Find the center frequency and bandwidth
Wo=sqrt(wl*wh);
Bw=wh-wl;
% Design analog bandpass filter
[bt,at]=lp2bs(b,a,Wo,Bw);
[H,w]=freqs(bt,at);
semilogy(w/pi,abs(H));
axis([0 3000 1e-8 1.1]);
xlabel('Frequency(pi rad/s)');
ylabel('|H(jw)|');
grid on