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| OPA211-EP_15 Datasheet, PDF (18/26 Pages) Texas Instruments – 1.1nV/√Hz NOISE, LOW POWER, PRECISION OPERATIONAL AMPLIFIER | |||
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OPA211-EP
SBOS638 â JUNE 2012
Noise in Noninverting Gain Configuration
R2
R1
EO
RS
VS
www.ti.com
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
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 OPA211 series op amps at 1kHz, en = 1.1nV/ÃHz and in = 1.7pA/ÃHz.
Figure 48. Noise Calculation in Gain Configurations
R1
R2
Signal Gain = 1+ R2
R1
Distortion Gain = 1+ R2
R1 II R3
R3
OPA211
VOUT
Generator
Output
Analyzer
Input
Audio Precision
System Two(1)
with PC Controller
Load
SIG. DIST.
GAIN GAIN R1
1 101 ¥
R2
R3
1kW 10W
11 101 100W 1kW 11W
(1) For measurement bandwidth, see Figure 4, Figure 5, and Figure 6.
Figure 49. Distortion Test Circuit
18
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Copyright © 2012, Texas Instruments Incorporated
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