Mixer circuit to reduce local oscillator leakage signal

摘要

An automatic balancing circuit 50 for a radio frequency mixer, which reduces LO to IF signal leakage, as well as minimising second order harmonic distortion products. The circuit couples to in phase and out of phase signal lines 58, 59 originating from the mixer 52, and comprises a differential gain network 62, a differential phase shift network 64 and a combiner 66. The networks operate under the control of a microprocessor (90, fig. 3) which adjusts the networks so that the LO leakage signals, when combined, are almost completely eliminated. The circuit may be used in a spectrum analyser.