PRACTICAL MATLAB® FOR ENGINEERS PRACTICAL MATLAB

656 Practical MATLAB® Applications for Engineers

FIGURE 6.80
Twe n t y- fi fth-order normalized FIR/LPF using the MATLAB fi r1 function of Example 6.21.

0

0

1

magnitude0.5

1.5

0.1 0.2 0.3 0.4 0.5

Mag./FIR using fir1

frequency in rad

0.6 0.7 0.8 0.9 1

0

 25

 20

 15

 10

 5

0

phase in rad.

0.1 0.2 0.3 0.4 0.5

Phase/FIR using fir1

frequency in rad

0.6 0.7 0.8 0.9 1

MATLAB Solution

% Script file: revisit _ analog _ filters

% part (a)

% normalize low pass filters: Butt. and Cheby.

[z1,p1,k1] = buttap (4);

[num1,den1] = zp2tf(z1,p1,k1);

w =0:.01:6;

figure(1)

subplot(2,2,1);

H1= freqs(num1,den1,w);

plot(w,abs(H1));

ylabel(‘magnitude’)

title(‘Butt. norm. LPF’)

subplot(2,2,2);

plot(w,angle(H1)*180/pi)

ylabel(‘phase (deg)’)

title(‘Butt. LPF’)

[z2,p2,k2] = cheb1ap(4,2); % type 1,with 2 db passband

[num2,den2] = zp2tf(z2,p2,k2);

H2 = freqs(num2,den2,w);

subplot(2,2,3);

plot(w,abs(H2))

ylabel(‘magnitude’)

title(‘Cheb. norm. LPF’)

xlabel(‘frequency (rad/sec)’)

subplot(2,2,4);

plot(w,angle(H2)*180/pi)

ylabel(‘phase (deg)’)

title(‘Cheb. LPF’)

xlabel(‘frequency (rad/sec)’)