Page 262 - Analog and Digital Filter Design
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Phase-Shift Neiworks (All-Pass Filters)
Equalizer Example: A Delay Equalized 7th Order Butterworth Filter
Frequency Range 1% to 200% of Cut-off
0 := 1,2.. 100
Seventh order Butterworth filter delay
w
Second Order Equalizer Delay
8:=0.18 Q:=0.615
R
Q:=- Q = 0.641
2.6
p = 0.384
Overall delay, filter + equalizer
Delay
% of cut-off frequency
Figure 9.13
Equalized Seventh-Order Response
A third-order equalizer could be used in the above example to reduce the group
delay ripple further. The first-order section would produce its maximum delay
at low frequencies. The delay from this section would add to the second-order
section delay; so, at higher frequencies where the second-order section peak
delay occurs, the overall peak would be raised too high. It would be necessary
