Datasheet

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V
I
C2
R2R1
C1
R
F
R
G
R1=R2=R
C1=C2=C
Q=PeakingFactor
(ButterworthQ=0.707)
_
+
S0288-01
3dB
1
f
2 RC
-
=
p
F
G
R
R
1
2
Q
=
æ ö
-
ç ÷
è ø
+
–
C1
R
F
R
G
V
I
THS6022
S0289-01
V
O
O
F F
I G
1
S
V
R R C1
V R S
æ ö
+
ç ÷
æ ö
ç ÷
=
ç ÷
ç ÷
ç ÷
è ø
ç ÷
è ø
+
–
R
F
V
O
R
G
R2R1
C1
R
A
V
I
THS6022
ForStableOperation:
S0290-01
F
A G
R
R2
R1|| R R
³
F
G
O I
R
1
R
V V
sR1C1
æ ö
+
ç ÷
ç ÷
@
ç ÷
ç ÷
è ø
THS6022
SLOS225D – SEPTEMBER 1998 – REVISED JULY 2007
If a multiple-pole filter is required, the use of a Sallen-Key filter can work very well with CFB amplifiers. This is
because the filtering elements are not in the negative feedback loop and stability is not compromised. Because
of their high slew-rates and high bandwidths, CFB amplifiers can create very accurate signals and help minimize
distortion. An example is shown in Figure 63
Figure 62. Two-Pole Low-Pass Sallen-Key Filter
There are two simple ways to create an integrator with a CFB amplifier. The first one, shown in Figure 64 , adds
a resistor in series with the capacitor. This is acceptable because at high frequencies, the resistor is dominant
and the feedback impedance never drops below the resistor value. The second one, shown in Figure 65, uses
positive feedback to create the integration. Caution is advised because oscillations can occur because of the
positive feedback.
Figure 63. Inverting CFB Integrator
Figure 64. Noninverting CFB Integrator
33
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