TLV27L1

TLV27L2

SLOS378A – SEPTEMBER 2001 – REVISED JULY 2003

9

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APPLICATION INFORMATION

offset voltage

corresponding gains. The following schematic and formula can be used to calculate the output offset voltage:

V

OO +

V

IO

1

)

R

F

R

G

" I

IB

)

R

S

1

)

R

F

R

G

" I

IB–

R

F

+

–

VI

+

RG

RS

RF

IIB–

VO

IIB+

Figure 25. Output Offset Voltage Model

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 26).

VI

VO

C1

+

–

RG

RF

R1

f

–3dB +

1

2

pR1C1

V

O

V

I

+

1

)

R

F

R

G

1

1

) sR1C1

VDD/2

Figure 26. 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

VDD/2

Figure 27. 2-Pole Low-Pass Sallen-Key Filter