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418 Chapter 8 IIR FILTER DESIGN
if Ws Wp = 0.2*pi; Ws = 0.3*pi; Rp = 1; As = 16;
>> Ripple = 10 ^ (-Rp/20); Attn = 10 ^ (-As/20);
>> % Analog filter design:
>> [b,a] = afd_chb2(Wp,Ws,Rp,As);
*** Chebyshev-2 Filter Order = 4
>> % Calculation of second-order sections:
>> [C,B,A] = sdir2cas(b,a)
C = 0.1585
B = 1.0000 0 6.0654
1.0000 0 1.0407
A = 1.0000 1.9521 1.4747
1.0000 0.3719 0.6784
>> % Calculation of Frequency Response:
>> [db,mag,pha,w] = freqs_m(b,a,0.5*pi);
>> % Calculation of Impulse response:
>> [ha,x,t] = impulse(b,a);
The specifications are satisfied by a 4th-order Chebyshev-II filter whose system
function is
0.1585 ( s 2 +6.0654 )( s 2 +1.0407 )
H a(s) =
(s 2 +1.9521s +1.4747) (s 2 +0.3719s +0.6784)
The filter plots are shown in Figure 8.17.
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