Datasheet

Sallen-Key High-Pass Filter
4-4
Example Circuits
4.3 Sallen-Key High-Pass Filter
Figure 4–2 shows area 200 equipped with a dual operational amplifier config-
ured as a second-order Sallen-Key high-pass filter using single-supply power
input.
Basic setup is done by proper choice of resistors R and mR, and capacitors
C and nC. Note that capacitors should be used for components R211 and
R212, and a resistor for C201. The transfer function for the circuit as shown
is:
V
OUT
V
IN
– f f
o
2
1 j Q f f
o
– f f
o
2
VREF 2
Where:
f
o
1
2
mnRC
And
Q
mn
n 1
The TL431 adjustable precision shunt regulator, configured as shown,
provides a low impedance reference for the circuit at about 1/2 V2+ in a 5 V
system. Another option is to adjust resistors R216 and R217 for the desired
VREF2 voltage. The formula for calculating VREF2 is:
VREF 2 2.50 V
R 216 R 217
R 217