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370 Chapter 7 FIR FILTER DESIGN
Actual Impulse Response
Magnitude Response in dB
0.4
0
h(n)
0.2
0
−0.2
Decibels
60
−0.4
0 30
n
1
Amplitude Response
0 0.2 0.35 0.65 0.8 1
frequency in π units
×
Weighted Error
10−3
1.0575
Hr(w)
Hr(w)
0
0
0 0.2 0.35 0.65 0.8 1
frequency in π units
−1.0575
0 0.2 0.35 0.65 0.8 1
frequency in π units
FIGURE 7.36 Plots for equiripple bandpass FIR filter in Example 7.24
The optimal value of M was found to be 29. The time- and the frequency-domain
plots of the designed filter are shown in Figure 7.36.
□
□ EXAMPLE 7.25 Design a highpass filter that has the following specifications:
ω s =0.6π,
ω p =0.75π,
A s =50dB
R p =0.5 dB
Solution
Since this is a highpass filter, we must ensure that the length M is an odd
number. This is shown in the following MATLAB script.
>> ws = 0.6*pi; wp = 0.75*pi; Rp = 0.5; As = 50;
>> [delta1,delta2] = db2delta(Rp,As);
>> [N,f,m,weights] = firpmord([ws,wp]/pi,[0,1],[delta2,delta1]); N
N = 26
>> h = firpm(N,f,m,weights);
>> [db,mag,pha,grd,w] = freqz_m(h,[1]);
>> delta_w = 2*pi/1000; wsi=ws/delta_w; wpi = wp/delta_w;
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