REDUCED INPUT VOLTAGE NOISE =

2

2

2

=

1

N

1

N

2

=

N

N

=

1

N

10

1k

100k

10M

0.1

1

100

1000

1M

10k

100

10

LMP2234

SNOSAW4D – SEPTEMBER 2007 – REVISED MARCH 2013

www.ti.com

Figure 47. Total Input Noise

VOLTAGE NOISE REDUCTION

The LMP2234 has an input voltage noise of 60 nV/

√Hz . While this value is very low for micropower amplifiers,

this input voltage noise can be further reduced by placing multiple 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:

(2)

Figure 48 shows a schematic of this input voltage noise reduction circuit using the LMP2234. Typical resistor

18

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