OPA145 Datasheet, PDF (21/40 Pages) Texas Instruments – High-Precision, Low-Noise, Rail-to-Rail Output, 5.5-MHz JFET Operational Amplifiers

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Feature Description (continued)
OPA145, OPA2145, OPA4145
SBOS427 – JUNE 2017
(A) Noise in Noninverting Gain Configuration
R1
R2
GND
±
EO
+
RS
+
VS
±
Source
GND
Noise at the output is given as EO, where
:1;
'₁
=
l1
+
4_{2 p}
4₁
„
¨:A₅ ;²
+
:A₀ ;²
+
kA_41æ42 o²
+
:E₀
„
4₅ ;²
+
lE₀
„
d₄₄₁₁₊^{„ 4422}hp²
> 8_4/5 ?
8
:2; A₅ = Â¥4 „ G_$ „ 6(-) „ 4₅ d _¾*V h
Thermal noise of RS
:3;
A_{41 æ42}
=
¨4
„
G_$
„
6(-)
„
d ^{41 „ 42} h
4₁ + 4₂
8
d _¾*V h
:4;
G_$ = 1.38065 „ 10^F23
,
d_-h
:5; 6(-) = 237.15 + 6(°%) > - ?
Thermal noise of R1 || R2
Boltzmann Constant
Temperature in kelvins
(B) Noise in Inverting Gain Configuration
R1
R2
RS
+
VS _±
Source
GND
±
+
GND
Noise at the output is given as EO, where
:6;
'₁
=
l1
+
4_{2 p}
4₅ + 4₁
„
¨:_A0 ;²
+
kA_{41+45 æ42} o²
+
FE₀
„
H:^{45 + 41; „ 42}IG²
4₅ + 4₁ + 4₂
> 8_4/5 ?
EO
:7;
A_{41+45 æ42}
=
¨4
„
G_$
„
6(-)
„
H:^{45 + 41; „ 42}I
4₅ + 4₁ + 4₂
8
d _¾*V h
Thermal noise of (R1 + RS) || R2
:8;
G_$ = 1.38065 „ 10^F23
,
dh
-
:9; 6(-) = 237.15 + 6(°%) > - ?
Boltzmann Constant
Temperature in kelvins
Copyright © 2017, Texas Instruments Incorporated
(1) e_N is the voltage noise of the amplifier. For the OPAx145 series of operational amplifiers, e_N = 7 nV/√Hz at 1 kHz.
(2) i_N is the current noise of the amplifier. For the OPAx145 series of operational amplifiers, i_N = 0.8 fA/√Hz at 1 kHz.
(3) For additional resources on noise calculations visit TI's Precision Labs Series.
Figure 40. Noise Calculation in Gain Configurations
Copyright © 2017, Texas Instruments Incorporated
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Product Folder Links: OPA145 OPA2145 OPA4145