PRACTICAL MATLAB® FOR ENGINEERS PRACTICAL MATLAB

626 Practical MATLAB® Applications for Engineers

phase2=angle(h2)*180/pi;

plot (w, phase2)

title (‘Phase of LPF with wc=3’)

xlabel (‘w in rad/sec’)

ylabel (‘degrees’)

[Pz,Qz]=bilinear (Pa,Qa,1/T); % discrete transfer function

disp(‘******************************************’)

disp(‘**************RESULTS******************* ‘)

disp(‘*******************************************’)

disp(‘Digital filter /numerator coefficients of the transfer

function :’)

disp(Pz)

disp(‘ Digital filter / denominator coefficients of the transfer func-

tion :’)

disp(Qz)

disp(‘*******************************************’)

figure(3); zplane (Pz,Qz)

title (‘zero-pole plot of H(z)’)

figure(4);pzmap(Pa,Qa)

title (‘zero-pole plot of H(s)’)

figure(5)

[magz, phasez] = freqz (Pz, Qz, w*T/pi);

subplot (1,2,1) % digital filter

plot (w*T, magz)

xlabel (‘W in rad’); title(‘Mag.of digital filter H(Z)’)

ylabel (‘magnitude’);axis([-2 2 0.4 1.1]);

subplot(1,2,2)

plot(w*T,phasez*180/pi)

xlabel(‘W in rad’); ylabel(‘degrees’);

title(‘Phase of digital filter H(z)’)

Back in the command window, the script fi le analog_digital is executed and the results

are shown as follows (Figures 6.53 through 6.57):

>> analog _ digital

******************************************

**************RESULTS*******************

******************************************

Digital filter /numerator coefficients of the transfer function :

0.0380 0.1141 0.1141 0.0380

Digital filter / denominator coefficients of the transfer function :

1.0000 -1.3445 0.8215 -0.1727

*******************************************