FREQUENCY DOMAIN ANALYSIS OF PERIODICALLY SWITCHED NONLINEAR CIRCUITS - Computer Methods for Analysis of Mixed-Mode Switching Circuits - page 305

In a very like manner, one can show that

The total harmonic distortion, a measure of how closely the output
waveform resembles a pure sinusoid, is obtained from

1.2 Intermodulation Distortion
Intermodulation occurs when two sinusoids of different frequencies are
applied to nonlinear circuits. Consider the same nonlinear circuit. Let
the input be

It is trivial to show that the response of the circuit contains the fre-
quency components tabulated in Table 1.2
The second-order intermodulation is obtained from

Note that was assumed. The third-order inter-

modulation is computed from