Method and circuit for achieving frequency conversion

Abstract

A frequency conversion method and a frequency conversion circuit which enlarge the frequency difference between the upper and lower sidebands of the output signal so as to enable the undesired sideband to be easily eliminated by a filter even in a case where the frequency of the input signal is low. First, a first excitation signal having a first excitation frequency (Fp) is modulated by an input signal (a) of a predetermined frequency (F1) to produce two sidebands and thereby generate a first intermediate signal (b). Next, a second excitation signal having a second excitation frequency (Fq) lower than the first excitation frequency (Fp) by exactly a frequency twice the frequency of the input signal (a) is modulated by the input signal (a) to produce two sidebands and thereby generate a second intermediate signal (c). Further the first intermediate signal (b) and the second intermediate signal (c) are added so that the lower sideband of the first intermediate signal (b) and the upper sideband of the second intermediate signal (c) are cancelled by each other to thereby generate an output signal (d) composed of the upper sideband of the first intermediate signal (b) and the lower sideband of the second intermediate signal (c). By this, the space between the upper sideband and the lower sideband is widened and thereby the lower band erasing filter can easily erase the lower sideband.