Datasheet

REDUCED INPUT VOLTAGE NOISE =
e
n1
+e
n2
+
2 2

+e
nN
2
=
1
N
1
N
Ne
n
2
=
N
N
e
n
=
1
e
n
N
10
1k 100k 10M
R
S
(:)
0.1
1
100
1000
1M
10k
100
10
e
ni
e
n
e
i
VOLTAGE NOISE DENSITY
(nV/
Hz)
e
t
LMP2232
SNOSB02C –JANUARY 2008–REVISED MARCH 2013 www.ti.com
Figure 47. Total Input Noise
VOLTAGE NOISE REDUCTION
The LMP2232 has an input voltage noise of 60nV/√Hz . While this value is very low for micropower amplifiers,
this input voltage noise can be further reduced by placing N amplifiers in parallel as shown in Figure 48. The total
voltage noise on the output of this circuit is divided by the square root of the number of amplifiers used in this
parallel combination. This is because each individual amplifier acts as an independent noise source, and the
average noise of independent sources is the quadrature sum of the independent sources divided by the number
of sources. For N identical amplifiers, this means:
Figure 48 shows a schematic of this input voltage noise reduction circuit. Typical resistor values are: R
G
= 10Ω,
R
F
= 1 kΩ, and R
O
= 1 kΩ.
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