Environmental Engineering Reference
In-Depth Information
transresistance closed-loop gain is
The PSD of the output noise voltage
for the two circuits is respectively
Thus we get
Equations (8.14) and (8.16) although derived for a particular circuit, are
general in their essence. They show that the equivalent input noise voltage of
an amplifier is unmodified by the application of parallel-mixing feedback,
whilst the noise current of the feedback network is added directly to the
closed-loop input-referred noise current. Moreover, when the amplifier noise
voltage contributes to the equivalent closed-loop input noise current, this
contribution is usually negligible. Otherwise, correlation between
and
is introduced.
Consider now the circuit in Fig. 8.10 which shows a voltage amplifier
with series-mixing feedback at the input. Resistors noise is modeled via the
two voltage generators
and
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