www.ti.com

C2

R2

R1

C1

R1=R2=R

C1=C2=C

Q=PeakingFactor

(ButterworthQ=0.707)

_

+

S0288-01

3dB

1

f

2 RC

-

=

p

F

G

R

R

1

2

Q

=

æ

ö

-

ç

÷

è

ø

+

–

C1

THS6022

S0289-01

O

F

F

I

G

1

S

V

R

R C1

V

R

S

æ

ö

+

ç

÷

æ

ö

ç

÷

= ç

÷

ç

֍

÷

è

ø

ç

÷

è

ø

+

–

R2

R1

C1

THS6022

ForStableOperation:

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

Submit Documentation Feedback