Environmental Engineering Reference
In-Depth Information
(
fundamental
component), and two other sinusoidal waveforms having a
frequency twice and three times greater than that of the input signal,
multiplied by the coefficients and respectively (
second
and
third
harmonic
components). To outline the weight of the harmonics, the
harmonic distortion factors are defined as given below [S70]
where the gain compression [MW95], which arises in term and is due to
coefficient have been neglected. It is worth noting that the harmonic
factors increase with the input amplitude.
In order to allow a simple comparison with the closed-loop cases that will
be developed in the following paragraphs, the harmonic distortion factors
can be also referred to the amplitude of the output fundamental component,
Of course, the two above equations can be used to compare the linearity
performance of two different amplifiers but at the same (fundamental) output
signal level.
Alternatively,
we
can
represent
the
input
signal
by
the
expression
and the output signal, through (7.1), becomes
Thus, to
obtain the same distortion factors as in (4) we have to define
and
As we will show this representation is useful to
characterise nonlinear systems in the frequency domain.
