The generation of sum and difference frequencies which result from applying two AC wave forms 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.