PRACTICAL MATLAB® FOR ENGINEERS PRACTICAL MATLAB

650 Practical MATLAB® Applications for Engineers

Back in the command window, the script fi le FIR_IIR is executed a nd t he resu lt is show n

in Figure 6.75.

Example 6.20

Design the following digital fi lters:

a. An 18th-order normalized LPF with a cutoff frequency at 0.3 rad using the function

fi r1, truncated by a Hamming window.

b. An 8th-order normalized BPF with a pass band between 0.3 and 0.6 rad using the

function fi r1.

c. Repeat part (b) using the remez exchange algorithm that employs the Park–McClellan

approach.

For each one of the preceding fi lters, return the coeffi cients of the polynomials that

make up the transfer function, their transfer functions, and their respective magnitude

and phase plots.

The solution is given by the script fi le designs as follows:

MATLAB Solution

% Script file : designs

% FIR/LPF design using fir1/part (a)

coeflp = fir1(18,.3); % 18 th..order FIR filter with cutoff of .3

Hlp = freqz(coeflp,1); % coef. of FIR filter

figure(1)

w1= 0:1/512:511/512 ;

subplot(1,2,1)

plot(w1,abs(Hlp));grid on;

xlabel(‘ frequency W in rad.’)

FIGURE 6.75
IIR and FIR fi lter’s plots of Example 6.19.

20

FIR IMPLEMENTATION FROM IIR

0

 20

 40

 60

 80

 100

0 0.1 0.2 0.3 0.4 0.5

W in rad

0.6 0.7 0.8 0.9 1

Magnitude in db

IIR FILTER

FIR FILTER