"Chapter 1 - The Op Amp's Place in the World" - HTL Wien 10

Active Filter Design Techniques
Practical Design Hints
The difference between ideal and real response peaks with 0.35 dB at approximately 30
kHz, which is equivalent to an enormous 4.1% gain error can be seen.
|A| — Gain — dB
9
7.5
6
4.5
3
1.5
0
–1.5
–3
10 k
A1
A1R
A2
A2R
A3R
f — Frequency — Hz
Figure 16–51. Differences in Q and f C in the Partial Filters of an Eighth-Order Butterworth
Low-Pass Filter
|A| — Gain — dB
0.4
0
–0.4
–0.8
–1.2
–1.6
–2
–2.4
A – Real
A – Ideal
A3
A4R
A4
100 k
–2.8
1 k 10 k
f — Frequency — Hz
100 k
Figure 16–52. Modification of the Intended Butterworth Response to a
Tschebyscheff-Type Characteristic
16-51