TSH310

Noise Measurements

12/19

5 Noise Measurements

The noise model is shown in Figure 28, where:

The thermal noise of a resistance R is:

where

∆F is the specified bandwidth.

On a 1Hz bandwidth the thermal noise is reduced to

where k is the Boltzmann's constant, equal to 1,374.10-23J/°K. T is the temperature (°K).

The output noise eNo is calculated using the Superposition Theorem. However eNo is not the simple sum

of all noise sources, but rather the square root of the sum of the square of each noise source, as shown

in Equation 1:

Equation 1

Equation 2

Figure 28: Noise model

+

_

R3

R1

output

R2

iN-

iN+

HP3577

Input noise:

8nV/

√Hz

N1

N2

N3

eN

+

_

R3

R1

output

R2

iN-

iN+

HP3577

Input noise:

8nV/

√Hz

N1

N2

N3

eN

4kTR

4kTR

eNo

V 1

2

V2

2

V3

2

V4

2

V5

2

V6

2

+

+++

+

=

eNo

2

eN

2

g

2

iNn

2

R2

2

iNp

2

+

×

+

×

R3

2

×

g

2

×

R 2

R 1

-------

2

4kTR14kTR21

R2

R1

-------

+

2

4kTR3

×

++

×

+

=