TLV2780, TLV2781, TLV2782, TLV2783, TLV2784, TLV2785, TLV278xA

FAMILY OF 1.8 V HIGHSPEED RAILTORAIL INPUT/OUTPUT

OPERATIONAL AMPLIFIERS WITH SHUTDOWN

SLOS245E − MARCH 2000 − REVISED JANUARY 2005

14

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APPLICATION INFORMATION

general configurations

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

required. The simplest way to accomplish this is to place an RC filter at the noninverting terminal of the amplifier

(see Figure 32).

VI

VO

C1

+

−

RG

RF

R1

f

–3dB +

1

2

pR1C1

V

O

V

I

+

1

)

R

F

R

G

1

1

) 2pfR1C1

Figure 32. 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. For best results, the amplifier should have a bandwidth that is 8 to 10 times the filter frequency bandwidth.

Failure to do this can result in phase shift of the amplifier.

VI

C2

R2

R1

C1

RF

RG

R1 = R2 = R

C1 = C2 = C

Q = Peaking Factor

(Butterworth Q = 0.707)

(

=

1

Q

2 −

)

RG

RF

_

+

f

–3dB +

1

2

pRC

Figure 33. 2-Pole Low-Pass Sallen-Key Filter