PRACTICAL MATLAB® FOR ENGINEERS PRACTICAL MATLAB

620 Practical MATLAB® Applications for Engineers

Example 6.5

Let Hs

Vs

Vs

as

as

o

i

()

()

()









2

2

1

1

be the transfer function of the active fi lter shown in Figure 6.47,

where s = jw, with the following time constants a 2 = R 2 C 2 = (^5) 10 −^2 s and a 1 = R 1 C 1 = (^3) 10 −^4 s.
Create the script fi le activefi lter that returns the following plots:
a. H(w) (in decibels) versus w
b. ∠H(w) (in degrees) versus w
c. Bode plots of H(w) (magnitude and phase)
d. Evaluation and plot the zero–pole of the transfer function H(w)
MATLAB Solution
% Script file: active filter
a1 = 3e-4;
a2 = 5e-2;
w = 1e1:1e3:1e8;
num = [a2 1];
den = [a1 1];
H = freqs(num,den,w);
mag = 20log10(abs(H));
figure(1)
subplot(2,1,1)
plot(w,mag);axis([1e2 1e4 0 50]);
ylabel(‘Magnitude’);xlabel(‘w in rad/sec’);
title(‘ Magnitude of H(w) vs. w’)
subplot(2,1,2);
phase=angle(H)180/pi;
plot(w,phase);
ylabel(‘Angle in degrees’);
axis([1e2 1e4 0 90]);
xlabel(‘w in rad/sec’)
FIGURE 6.47
Circuit diagram of Example 6.5.
C 2
Vi(s) C 1
Vo(s)
R 1
R 2

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