Datasheet

OPA227, 2227, 4227
OPA228, 2228, 4228
13
SBOS110A
www.ti.com
FIGURE 5. Noise Calculation in Gain Configurations.
Where e
S
= √4kTR
S
• = thermal noise of R
S
e
1
= √4kTR
1
• = thermal noise of R
1
e
2
= √4kTR
2
= thermal noise of R
2
1
2
1
+






R
R
Noise at the output:
R
R
2
1






E
R
R
eeeiReiR
R
R
On nSnS
2
2
1
2
2
1
2
2
2
2
2
2
2
2
1
2
11=+






+++
()
++
()
+






Where e
S
= √4kTR
S
• = thermal noise of R
S
e
1
= √4kTR
1
• = thermal noise of R
1
e
2
= √4kTR
2
= thermal noise of R
2
Noise at the output:
R
RR
S
2
1
+






R
RR
S
2
1
+






E
R
RR
eeeiRe
O
S
nnS
2
2
1
2
2
1
2
2
2
2
2
2
1=+
+






+++
()
+
R
1
R
2
E
O
R
1
R
2
E
O
R
S
V
S
R
S
V
S
Noise in Noninverting Gain Configuration
Noise in Inverting Gain Configuration
For the OPA227 and OPA228 series op amps at 1kHz, e
n
= 3nV/√Hz and i
n
= 0.4pA/√Hz.