Environmental Engineering Reference
In-Depth Information
8.3 NOISE MODELS OF CIRCUIT COMPONENTS
In the previous paragraph we modeled the noise of an input signal source
as a noise voltage associated to its series resistance. Actually, for noise
calculations it is advantageous to have noise models for each active and
passive circuit component. These models are derived in detail in standard
textbooks like [GM93], here we summarise some results useful for our
ensuing discussion.
Resistor
A resistance
R
generates thermal noise voltage whose PSD is given by
in which
k
is the Boltzmann's constant and
T
is the absolute temperature
In Fig. 8.4a this noise is modeled by a voltage
generator in series with the resistor. In some circuit configurations it is more
convenient to represent this noise by a parallel current generator (see Fig.
8.4b) whose PSD is
