Datasheet

R
1
R
2
E
O
R
1
R
2
E
O
R
S
V
S
R
S
V
S
A)NoiseinNoninvertingGainConfiguration
B)NoiseinInvertingGainConfiguration
Noiseattheoutput:
E =
O
2
Wheree = Ö
S
4kTR
S
´ =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
4kTR
1
´ =thermalnoiseofR
1
2
1+
R
2
R
1
e = Ö
2 2
4kTR
2
=thermalnoiseofR
Noiseattheoutput:
E =
O
2
Wheree = Ö
S
4kTR
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 = Ö
1
4kTR
1
´ =thermalnoiseofR
1
e = Ö
2 2
4kTR =thermalnoiseofR
2
FortheOPA827seriesopampsat1kHz,e =4nV/ andi =2.2fA/ .Ö Ö
n
Hz Hz
n
OPA827
www.ti.com SBOS376H –NOVEMBER 2006–REVISED MAY 2012
Figure 42 illustrates both noninverting (A) and The feedback resistor values can generally be
inverting (B) op amp circuit configurations with gain. chosen to make these noise sources negligible. Note
In circuit configurations with gain, the feedback that low impedance feedback resistors will load the
network resistors also contribute noise. The current output of the amplifier. The equations for total noise
noise of the op amp reacts with the feedback are shown for both configurations.
resistors to create additional noise components.
Figure 42. Noise Calculation in Gain Configurations
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