SLVU006A Datasheet, PDF (20/28 Pages) Texas Instruments – UNIVERSAL OPERATIONAL AMPLIFIER EVALUATION MODULE

Sallen-Key Low-Pass Filter
3.2 Sallen-Key Low-Pass Filter
Figure 3–1 shows area 100 equipped with a dual operational amplifier
configured as a second-order Sallen-Key low-pass filter using dual-power
supplies.
Basic set up is done by proper choice of resistors R and mR, and capacitors
C and nC. The transfer function is:
Where:
ǒ Ǔ ǒ Ǔ ^VOUT
+ _{ń ) ǒ ń Ǔ ń VIN}
1
2
1 – f fo
j Q f fo
+ _Ǹ fo
1
2p m n RC
And
Q
+
m^Ǹm)
n
1
Figure 3–1. Sallen-Key Low-Pass Filter with Dual Supply Using Area 100
R118
C105
V1+
V1+
GND1
V1–
C104
0.1 µ F
C103
1µF
C109
0.1 µ F
C110
1µF
Power Supply Bypass ^V1–
A101–
A102–
A103+
A104+
+
Vin
–
R106
R107
R108
mR
R109
C112
R119
R
C111
R105
Jumper
V1+
Vout
Vin
=
1
1– (f/fo)2 + (j/Q)(f/fo)
2–
3+
8
1
4 ^U101a
A1OUT
1/2 Dual OP Amp
V1–
R117
fo
=
2π
1
√mn
RC
Q
=
√mn
m+1
C106
V1+
R101
VREF1
R114
C
R
A
R115
U102
Voltage Reference
Not Used
B101–
B102–
B103+
B104+
R103
R102
R101
R110
R112
C107
nC
C102
R104
Jumper
R111
6–
5+
7
B1OUT
U101b
1/2 Dual OP Amp
C108
R113
Not Used
C101
3-2
Example Circuits