R

G

R

F

R

2

R

1

C

2

V

IN

V

OUT

1

2pRC

f

=

-

3 dB

C

1

R

R = R

C

C = C

Q = Peaking factor

(Butterworth Q = 0.707)

1

1

2

2

=

=

R

(

(

R

F

2 -

1

Q

R

G

R

F

R

1

C

1

V

IN

V

OUT

= 1 +

V

V

OUT

IN

R

R

F

G

1

1 + sR C

1

1

(

((

(

1

2pR C

1

1

f

=

-

3 dB

OPA313

OPA2313

OPA4313

www.ti.com

SBOS649C – SEPTEMBER 2012 – REVISED MARCH 2013

APPLICATION EXAMPLES

GENERAL CONFIGURATIONS

When receiving low-level signals, limiting the bandwidth of the incoming signals into the system is often required.

The simplest way to establish this limited bandwidth is to place an RC filter at the noninverting terminal of the

amplifier, as Figure 37 shows.

Figure 37. Single-Pole Low-Pass Filter

If even more attenuation is needed, a multiple pole filter is required. The Sallen-Key filter can be used for this

task, as Figure 38 shows. For best results, the amplifier should have a bandwidth that is eight to 10 times the

filter frequency bandwidth. Failure to follow this guideline can result in phase shift of the amplifier.

Figure 38. Two-Pole Low-Pass Sallen-Key Filter

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