RHF350 STMICROELECTRONICS [STMicroelectronics], RHF350 Datasheet - Page 17

• Manufacturer Part Number: RHF350
• Description: Rad-hard 550 MHz low noise operational amplifier
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

RHF350
7
Active filtering
Figure 29. Low-pass active filtering, Sallen-Key
From the resistors R
inverting amplification configuration.
Equation 12
We assume the following expression is the response of the system.
Equation 13
The cut-off frequency is not gain-dependent and so becomes:
Equation 14
The damping factor is calculated by
Equation 15
IN
fb
and R
R1
G
=
Doc ID 15604 Rev 4
we can directly calculate the gain of the filter in a classic non-
T
1
-- -
2
j
c
R2
=
A
C
Equation 15:
Vout
---------------- -
V
1
Vin
c
R
=
=
1
C1
R
j
+
g
G
j
------------------------------------ -
C2
R1R2C1C2
C
=
=
1
R
1
---------------------------------------- -
1
2
+
1
+
+
+
_
R
--------
R
2
C
fb
g
2
---- -
j
g
R
c
R
fb
+
1
–
----------- -
j
C
c
2
1
2
R
1
g
OUT
AM00840
100
Active filtering
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