Environmental Engineering Reference
In-Depth Information
Let us first evaluate the total output noise of the amplifier without feedback
(i.e., with
f =
0). This is
Then evaluate the total output noise in closed-loop conditions. We get
The output PSD noise voltage is lower in the latter case. Indeed, every
component is divided by the square of the loop gain. This is not
a surprising result since the closed-loop gain is smaller than the open-loop
gain by just the same quantity. Since the two systems have different gains,
the output noise cannot be used for meaningful comparison. Instead, we can
use the equivalent input noise for this purpose. It is found for the open- and
closed-loop configuration by dividing the output PSD noise by the square of
the system gain. We get the following results for the two cases
