User manual

Active Filter Demo Board Kit User’s Guide
DS51614A-page 14 © 2006 Microchip Technology Inc.
2.5.2 Sallen-Key, Low-pass Filter Sections
TABLE 2-1: IMPEDANCES FOR SALLEN-KEY, LOW-PASS FILTER
SECTIONS
FIGURE 2-7: Sallen-Key, Low-pass (modified) Filter Topologies.
Topology SK-LP1 SK-LP2 SK-LP1-K SK-LP2-K
Z
1
0Ω R11 0Ω R11
Z
2
R11 R12 R11 R12
Z
3
—C11—C11
Z
4
————
Z
5
C11 C12 C11 C12
Z
6
————
Z
7
——0Ω 0Ω
Z
8
————
Z
9
————
Z
10
——RaRa
Z
11
0Ω 0Ω Rb Rb
U
1
R11
C11
V
IN
V
OUT
V
DD
SK-LP1
U
1
R11
C11
V
IN
V
OUT
V
DD
SK-LP2
R12
C12
U
1
R11
V
IN
V
OUT
V
DD
SK-LP1-K
C11
Rb
SK-LP2-K
Rb
U
1
R11
C11
V
IN
V
OUT
V
DD
R12
C12
Ra
V
DD
/2
Ra
V
DD
/2