122 Chapter
6
Noise sources are characterized by their noise spectral density. All noise
spectral densities S
v
and S
i
(voltages and currents respectively) are in
squared units (V
2
/Hz and A
2
/Hz for spectral density).
In the case of a noise source the relation between spectral noise density
S(f) and the root mean square (effective value) V
eff
is given by
stop
f
start
f
eff
df
f
S
V
)
(
2
f
start
and f
stop
are the limits of the frequency range that has to be taken into
consideration to describe the noise source. In the case of constant spectral
density S it follows
f
S
f
f
S
V
start
stop
eff
)
(
2
The spectral density S
A
of a random waveform that results from a source
with spectral density S
E
is given by the squared transfer function times
S
E
, see Figure 6-62 (
f
2
).
S
A
j
S
E
j
H j
S
A
(j ) = |H(j )|
2
* S
E
(j )
Figure 6-62. Calculation of spectral noise densities
The spectral densities of uncorrelated noise contributions are added (see
also [Std99], Section 12.8).
In a simulation engine noise analysis is done in a specified frequency
range.
Summary :
In the case of constant spectral density S it follows f S f f S V start stop eff ) ( 2 The spectral density S A of a random waveform that results from a source with spectral density S E is given by the squared transfer function times S E , see Figure 6-62 ( f 2 ).
Tags :
spectral,noise,density,start,source,eff,stop,densities,figure,range,gien,squared,see