Infinite Impulse Response Filter Design - Digital Signal Processing: Fundamentals and Applications - page 332

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FIGURE 8.20

Frequency responses of the designed digital filter for Example 8.11.

b. MATLAB Program 8.7 is given for this example, and the corresponding frequency response plots are illustrated
in Figure 8.20 .

Program 8.7. MATLAB program for Example 8.11.

% Example 8.11
% Design of the digital bandpass Butterworth filter
format long
fs ¼ 8000;
[B A] ¼ lp2bp([1],[1 1],sqrt(5.7499*10^8),4088) % Complete step 2

[b a] ¼ bilinear(B,A,fs) % Complete step 3

% Plot the magnitude and phase responses j H(z) j
%b ¼ [0.0730 0 -0.0730]; numerator coefficients from MATLAB
%a ¼ [1 0.7117 0.8541]; denominator coefficients form MATLAB
freqz(b, a,512,fs);
axis([0 fs/2 -40 10])

EXAMPLE 8.12
Now let us examine the bandstop Butterworth filter design.
a. Design a digital bandstop Butterworth filter with the following specifications:
• Center frequency of 2.5 kHz
• Passband width of 200 Hz and ripple of 3dB