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:
Wheree =
S
4kTR
S
4kTR
1
4kTR
2
=thermalnoiseofR
S
=thermalnoiseofR
1
=thermalnoiseofR
2
e =
1
e =
2
Noiseattheoutput:
E =
O
2
1+
R
2
R +R
1 S
R
2
R +R
1 S
2 22
Wheree =
S
4kTR
S
4kTR
1
4kTR
2
=thermalnoiseofR
S
=thermalnoiseofR
1
=thermalnoiseofR
2
e =
1
e =
2
R
2
R +R
1 S
2
1+
R
2
R
1
1+
R
2
R
1
2
R
2
R
1
2
e +e +
1 2
2 2
E =
O
2
e +
n
2
e
s
2
FortheOPA164xseriesopampsat1kHz,e =5.1nV/ Hz
n
Ö
e +e +
1 2
2 2
e
s
2
e +
n
2
OPA1641
OPA1642
OPA1644
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SBOS484B DECEMBER 2009REVISED AUGUST 2010
Figure 32 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. In general, output of the amplifier. The equations for total noise
the current noise of the op amp reacts with the are shown for both configurations.
feedback resistors to create additional noise
space
components. However, the extremely low current
noise of the OPA164x means that its current noise
space
contribution can be neglected.
Figure 32. Noise Calculation in Gain Configurations
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