Datasheet

R
1
R
2
E
O
R
1
R
2
E
O
R
S
V
S
R
S
V
S
NoiseinNoninvertingGainConfiguration
NoiseinInvertingGainConfiguration
Noiseattheoutput:
E =
O
2
Wheree = Ö
S S
4kTR ´ =thermalnoiseofR
S
2
1+
R
2
R
1
e +e
n
1 2
n
2 S S
+e +(i R ) +e +(i
n
R )
2 2 2 2 2 2
1+
R
2
R
1
R
2
R
1
e = Ö
1 1
4kTR ´ =thermalnoiseofR
1
2
1+
R
2
R
1
e = Ö
2 2 2
4kTR =thermalnoiseofR
Noiseattheoutput:
E =
O
2
Wheree = 4kTRÖ
S S
´ =thermalnoiseofR
S
2
1+
R
2
R +R
1 S
e +e
n 1 2 n 2 S
+e +(i R ) +e
2 2 2 2 2
R
2
R +R
1 S
R
2
R +R
1 S
e = 4kTRÖ
1 1
´ =thermalnoiseofR
1
e = 4kTRÖ
2 2 2
=thermalnoiseofR
OPA1611
OPA1612
SBOS450B –JULY 2009–REVISED JULY 2011 www.ti.com
Figure 32 illustrates both inverting and noninverting The current noise of the op amp reacts with the
op amp circuit configurations with gain. In circuit feedback resistors to create additional noise
configurations with gain, the feedback network components. The feedback resistor values can
resistors also contribute noise. generally be chosen to make these noise sources
negligible. The equations for total noise are shown for
both configurations.
For the OPA161x series op amps at 1kHz, e
n
= 1.1nV/√Hz and i
n
= 1.7pA/√Hz.
Figure 32. Noise Calculation in Gain Configurations
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