Datasheet

AD8045
Rev. A | Page 18 of 24
OUTPUT NOISE
Figure 66 shows the contributors to the noise at the output of a
noninverting configuration.
R
G
R
F
V
OUT
R
S
+–
V
EN
V
RF
V
RG
V
RS
I
EN
+
I
EN
–
04814-0-011
Figure 66. Amplifier DC Errors
Ven ,
IN+
, and
IN−
are due to the amplifier. , , and
are due to the feedback network resistors. R
F
R
V
G
R
V
S
R
V
G
and R
F
, and
source resistor,
R
S
. Total output voltage noise,
ENOUT
V
_
, is the
rms sum of all the contributions.
=
ENOUT
V
_
()()() () ()
22
222
444
n
S
n
G
f
n
G
F
n
S
n
GkTRGkTRkTRG||RRINGRINVenG +++××−+××++×
where:
G
n
is the noise gain
⎟
⎠
⎞
⎜
⎝
⎛
+
G
G
F
R
RR
.
Ven is the op amp input voltage noise.
I
N
is the op amp input current noise.
Table 7 lists the expected output voltage noise spectral density
for several gain configurations.
Table 7. Noise and Bandwidth for Various Gains
Gain R
F
R
G
R
S
−3 dB
Bandwidth
1
Output
Noise
(nV/√Hz)
+1 0 − 100 1 GHz 3.3
[phone] MHz 7.4
[phone] MHz 16.4
[phone] MHz 31
−1 499 499 N/A 300 MHz 7.4
1
R
L
= 1 kΩ.