OPA227 Datasheet, PDF (13/25 Pages) Burr-Brown (TI) – High Precision, Low Noise OPERATIONAL AMPLIFIERS

Noise in Noninverting Gain Configuration
R₂
R₁
E_O
R_S
V_S
Noise at the output:
( ) ( ) E_O2
=

¹
+
R₂
R₁


2
e
n
2
+
e₁₂
+
e
2
2
+
i_nR₂
2 _{+ eS2 +}
i_n R_S
2

¹
+
R₂
R₁
²

Where
e_S
=
√4kTR_S
•

¹
+
R₂
R₁


=
thermal
noise
of
R_S
e₁
=
√4kTR₁
•


R₂
R₁


= thermal noise of R₁
e₂ = √4kTR₂
= thermal noise of R₂
Noise in Inverting Gain Configuration
R₂
R₁
R_S
E_O
V_S
Noise at the output:
( ) E_O2
=

¹
+
R₂
R₁ + R_S


2
e
n
2
+
e₁₂ + e₂₂ +
i_nR₂
2 _{+ eS2}
Where
e_S
=
√4kTR_S
•


R₂
R₁ + R
S


= thermal noise of R_S
e₁
=
√4kTR₁
•


R₂
R₁ + R_S


= thermal noise of R₁
e₂ = √4kTR₂
= thermal noise of R₂
For the OPA227 and OPA228 series op amps at 1kHz, e_n = 3nV/√Hz and i_n = 0.4pA/√Hz.
FIGURE 5. Noise Calculation in Gain Configurations.
OPA227, 2227, 4227
OPA228, 2228, 4228
13
SBOS110A
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