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Analog-to-Digital Filter Transformations 431
1
0.8913
Magnitude Response
1
Phase Response
|H|
π units
0
0.1778
0
0 0.2 0.3 1
frequency in π units
−1
0 0.2 0.3 1
frequency in π units
0
1
Magnitude in dB
15
Group Delay
decibels
15
Samples
10
5
0 0.2 0.3 1
frequency in π units
0
0 0.2 0.3 1
frequency in π units
FIGURE 8.22
Digital Chebyshev-I lowpass filter using impulse invariance design
script follows:
>> % Digital Filter Specifications:
>> wp = 0.2*pi; % digital Passband freq in rad
>> ws = 0.3*pi; % digital Stopband freq in rad
>> Rp = 1; % Passband ripple in dB
>> As = 15; % Stopband attenuation in dB
>> % Analog Prototype Specifications: Inverse mapping for frequencies
>> T = 1; % Set T=1
>> OmegaP = wp / T; % Prototype Passband freq
>> OmegaS = ws / T; % Prototype Stopband freq
>> % Analog Chebyshev-1 Prototype Filter Calculation:
>> [cs,ds] = afd_chb2(OmegaP,OmegaS,Rp,As);
*** Chebyshev-2 Filter Order = 4
>> % Impulse Invariance transformation:
>> [b,a] = imp_invr(cs,ds,T); [C,B,A] = dir2par(b,a);
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