Environmental Engineering Reference
In-Depth Information
In order to evaluate the different weight between the nonlinearity of the
amplifier and that of the feedback network, it is useful to write the two
coefficients when the amplifier is linear (i.e., with
and
As expected, comparison of (7.34) and (7.35) with (7.16) and (7.17),
which refer to the case of nonlinear amplifier with linear feedback, shows
that the feedback path is more critical than the forward path. Indeed,
assuming the nonlinearity for both the amplifier and the feedback network to
be equal, which means and for the same output magnitude,
relationship (7.16) is lower than (7.34) by a factor and relationship
(7.17) is lower than (7.35) by about Moreover, it is worth noting that for
negative feedback, distortion due to the feedback network has an opposite
sign to that due to the amplifier.
A more compact and clear representation of the harmonic distortion in a
nonlinear amplifier with nonlinear feedback is
In conclusion, the second and third harmonic distortion terms can be
compactly represented by relationships (7.36) which are only a simple
function of the second and third harmonic distortion of the whole feedback
network evaluated in two particular cases:
a nonlinear amplifier with linearised feedback network
a linearised amplifier with nonlinear feedback network.
This consideration can be particularly interesting from a design point of
view, since other than allowing us to get more insight into the circuit
behaviour and its final performance, permits to evaluate all the harmonic
distortion factors through separate calculation (or simulation) of the two
couples of terms
and
[PP981].
