OPA1662
OPA1664
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SBOS489 –DECEMBER 2011
A) Noise in Noninverting Gain Configuration
Noise at the output:
R2
2
2
2
R2
R2
R1
R2
2
EO
2
en
2
2
e12 + e2
1 +
+ es
R1
1 +
=
+
R1
R1
EO
4kTRS
4kTR1
4kTR2
Where eS =
e1 =
= thermal noise of RS
= thermal noise of R1
= thermal noise of R2
RS
VS
e2 =
B) Noise in Inverting Gain Configuration
Noise at the output:
R2
2
2
2
R2
EO2 = 1 +
R2
R2
2
2
2
en
+
e12 + e2
+
es
R1
R1 + RS
R1 + RS
R1 + RS
EO
RS
4kTRS
4kTR1
4kTR2
Where eS =
e1 =
= thermal noise of RS
= thermal noise of R1
= thermal noise of R2
VS
e2 =
Note: For the OPA166x series of op amps at 1 kHz, en = 3.3 nV/√Hz.
Figure 46. Noise Calculation in Gain Configurations
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