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Sallen-Key High-Pass Filter
3-6
Example Circuits
3.6 Sallen-Key High-Pass Filter
Figure 3–5 shows area 200 equipped with a dual operational amplifier
configured 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 R201 and
R205, 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
VREF2
Where:
f
o
1
2 mn
RC
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 R211 and R213 for the desired
VREF2 voltage. The formula for calculating VREF2 is:
VREF2 2.50 V
R211 R213
R213