Environmental Engineering Reference
In-Depth Information
The second basic case considered is that of a nonlinear amplifier followed
by a linear stage, as shown in Fig. 7.3b. Assuming, as usual, that the
incremental input voltage is a pure sinusoidal tone,
the
intermediate output is
where coefficients
are again given by (7.3)-(7.6) in which
have
to be used instead of constant values
Then, the output signal is
In the above equations the phase contribution of
to the
components
and that of
to
has been neglected. Finally, from (7.7) and (7.8) we
get
Comparing the above expressions with (7.7) we see that the harmonic
distortion factors are now multiplied by the ratio of the transfer function
magnitudes evaluated at the frequency of the considered harmonics and at
the fundamental frequency.
As a particular case, assume that coefficients
are constant, and that the
transfer function
has a single pole (the pole of the amplifier and also
of the loop gain)
Accordingly, (7.41) and (7.42) become
