Environmental Engineering Reference
In-Depth Information
Of course, the above equations adhere with (7.16), (7.17) and (7.19a)
found in the case of frequency-independent loop gain, or that is the same, for
low-frequency input signals, in the present case, distortion of a feedback
network in terms of the output fundamental is reduced of a quantity still
equal to the return ratio but evaluated at the
considered
harmonic.
It is useful to extend these results to a more general model in which we
put the nonlinear block between two linear blocks in the forward path, as
shown in Fig. 7.8a. This system includes as particular cases the closed-loop
version of both occurrences, depicted in Fig. 7.3a and 7.3b, in which
distortion appears after or before a linear stage.
To obtain distortion factors of the system in Fig. 7.8, we can follow the
same procedure described above. Let us first evaluate the nonlinear
coefficients that relate
to
The first-order coefficient is
where
