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| OPA827 Datasheet, PDF (13/24 Pages) Burr-Brown (TI) – Low-Noise, High-Precision, JFET-Input, OPERATIONAL AMPLIFIER | |||
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OPA827
www.ti.com ..................................................................................................................................... SBOS376E â NOVEMBER 2006 â REVISED SEPTEMBER 2008
Figure 42 illustrates both noninverting (A) and
inverting (B) op amp circuit configurations with gain.
In circuit configurations with gain, the feedback
network resistors also contribute noise. The current
noise of the op amp reacts with the feedback
resistors to create additional noise components.
The feedback resistor values can generally be
chosen to make these noise sources negligible. Note
that low impedance feedback resistors will load the
output of the amplifier. The equations for total noise
are shown for both configurations.
A) Noise in Noninverting Gain Configuration
R2
R1
EO
RS
VS
Noise at the output:
2
2
EO2 =
1+
R2
R1
en2 + e12 + e22 + (inR2)2 + eS2 + (inRS)2
1+
R2
R1
Where eS = Ã4kTRS ´
1+
R2
R1
= thermal noise of RS
e1 = Ã4kTR1 ´
R2
R1
= thermal noise of R1
e2 = Ã4kTR2 = thermal noise of R2
B) Noise in Inverting Gain Configuration
R2
R1
RS
EO
VS
Noise at the output:
2
EO2 =
1 + R2
R1 + RS
en2 + e12 + e22 + (inR2)2 + eS2
Where eS = Ã4kTRS ´
R2
R1 + RS
= thermal noise of RS
e1 = Ã4kTR1 ´
R2
R1 + RS
= thermal noise of R1
e2 = Ã4kTR2 = thermal noise of R2
For the OPA827 series op amps at 1kHz, en = 4nV/ÃHz and in = 2.2fA/ÃHz.
Figure 42. Noise Calculation in Gain Configurations
Copyright © 2006â2008, Texas Instruments Incorporated
Product Folder Link(s): OPA827
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