Datasheet

Sallen-Key Low-Pass Filter
4-3
Example Circuits
4.2 Sallen-Key Low-Pass Filter
Figure 4–1 shows area 100 equipped with a dual operational amplifier
configured as a second-order Sallen-Key low-pass filter using dual-power
supplies.
Basic setup is done by proper choice of resistors R and mR, and capacitors
C and nC. The transfer function is:
V
OUT
V
IN
1
1
– f f
o
2
j Q f f
o
Where:
f
o
1
2 mnRC
And
Q
mn
m 1
Figure 4–1. Sallen-Key Low-Pass Filter with Dual Supply Using Area 100
C104 C105
C112 C113
V1+
V1–
V1+
GND1
V1–
Power Supply Bypass
+
–
14
1
4
3
2
V1+
V1–
R106
C115
R119
C106
R121
R110
R120
R109
R108
R118
C114
C107
A1OUT
1/2 Dual Op Amp
A101–
A102–
A103+
A104+
+
–
13
11
12
R104
C109
R113 C102
R103
R102
R112
R101
R111
R114
C110
C101
B1OUT
1/2 Dual Op Amp
B101–
B102–
B103+
B104+
R114
C
R
A
U102
R117
Voltage Reference
V1+
VREF1
U101a
U101b
R115
Jumper
+
–
mR R
nC
Jumper
Jumper
Not Used
Not Used
V
out
V
in
V
in
=
1
1– (f/fo)
2
+ (j/Q)(f/fo)
fo =
1
2π √mn RC
Q =
√mn
m+1
0.1 µ F10µ F
0.1 µ F10µ F
6
A1/SD
R107
A1 FLT
C108
9 B1/SD
R105
B1 FLT
C103
C111