fg_06_07.m

英文书《Digital Signal Processing with Examples in MATLAB》附带的MATLAB实例

% fg_06_07  Analog Butterworth and Chebyshev power gain.
wc=1;
L=[2 4 6];
dB0=[-40 -80 -120];
w1=[10 10 10];
dBs=[-40 -80 -120];
txb=[7 6.5 6];
txc=[6.5 5.5 5.2];
w=linspace(0,w1(plt),500);
sp_fig(1,9,6);
for plt=1:3,
% Butterworth   
   PBut=1./(1+w.^(2*L(plt)));
   dBBut=10*log10(max(10^(dB0(plt)/10),PBut));
% Chebyshev.
   ws=wc*cosh((6.02-dBs(plt))/(8.69*L(plt)));
   VL0=cosh(L(plt)*acosh(ws/wc));
   VL=cosh(L(plt)*acosh(ws./max(1.e-20,w)));
   P=1./(1+(VL0^2)./(VL.^2));
   dBCheb=10*log10(max(10^(dB0(plt)/10),P));
% Plot.
   subplot(1,3,plt);
   axis([0 w1(plt) dB0(plt) 0]);
   set(gca,'fontsize',16);
   line(w,dBCheb,'color','r');
   line(w,dBBut,'color','b'); grid;
   if(plt==1)
      ylabel('Power gain in dB');
   elseif(plt==2)
      xlabel('Frequency in rad/s');
   end
   title(['L=',int2str(L(plt))]);
   h(1)=text(txb(plt),dBBut(round(500*txb(plt)/w1(plt))),'B');
   h(2)=text(txc(plt),dBCheb(round(500*txc(plt)/w1(plt))),'C');
   set(h,'fontsize',18);   
end