Infinite Impulse Response Filters - Introduction to Digital Signal Processing and Filter Design - page 235

Magnitude resopnse of a Chebyshev I bandpass filter

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 0

0.1 0.2 0.3 0.4 0.5

Normalized frequency

0.6 0.7 0.8 0.9 1

Figure 4.25 Magnitude response of a Chebyshev I (equiripple) bandpass filter.

[b,a]=cheby1(N,0.5,Wn)
[h,w]=freqz(b,a,256);
H=abs(h);
HdB=20*log10(H);
plot(w/pi,H);grid
title('Magnitude response of a Chebyshev I Bandpass filter')
ylabel('Magnitude')
xlabel('Normalized frequency')
%end

The order of this filter is found to be 12, and its magnitude response is shown
in Figure 4.25.

Example 4.13

%MATLAB script to design a Butterworth Bandstop filter
% with Wp1 = 0.18, Ws1 = 0.2, Ws2 = 0.205, Wp2 = 0.24,

% Rp = 0.5 and Rs = 50

Wp=[0.18 0.24];
Ws=[0.2 0.205];
[N,Wn]=buttord(Wp,Ws,0.5,50);