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460 Chapter 8 IIR FILTER DESIGN
1
0.8913
Magnitude Response
1
Phase Response
phase in π units
0.5
0
−0.5
0
0 0.3 0.4 0.6 0.75 1
frequency in π units
−1
0 0.3 0.4 0.6 0.75 1
frequency in π units
0
Magnitude in dB
40
Group Delay
30
samples
20
40
0 0.3 0.4 0.6 0.75 1
frequency in π units
10
0
0 0.3 0.4 0.6 0.75 1
frequency in π units
FIGURE 8.33 Digital elliptic bandpass filter in Example 8.29
□ EXAMPLE 8.30 Finally, we will design a Chebyshev-II bandstop filter whose specifications are
given in the following MATLAB script.
>> % Digital Filter Specifications: % Type: Chebyshev-II Bandstop
>> ws = [0.4*pi 0.7*pi]; % Dig. stopband edge frequency
>> wp = [0.25*pi 0.8*pi]; % Dig. passband edge frequency
>> Rp = 1; % Passband ripple in dB
>> As = 40; % Stopband attenuation in dB
>> % Calculations of Chebyshev-II Filter Parameters:
>> [N,wn] = cheb2ord(wp/pi,ws/pi,Rp,As);
>> % Digital Chebyshev-II Bandstop Filter Design:
>> [b,a] = cheby2(N,As,ws/pi,’stop’);
>> % Cascade Form Realization:
>> [b0,B,A] = dir2cas(b,a)
b0 = 0.1558
B = 1.0000 1.1456 1.0000
1.0000 0.8879 1.0000
1.0000 0.3511 1.0000
1.0000 -0.2434 1.0000
1.0000 -0.5768 1.0000
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