The generation of sum and difference frequencies which result from applying
two AC waveforms to a non-linear circuit element.
In mixer applications, with a signal of frequency fRF applied to the RF port and
a signal fLO applied to the LO port, the resulting signal at the IF port will
consist of two carriers (or sidebands) of frequencies fRF + fLO and fRF - fLO
with internally-generated LO and RF harmonics and intermodulation products.