Upper limit estimation on the conversion gain of a mixer

A simple method for estimating the theoretical limit on conversion gain of an active device operating as a mixer is presented. The analysis is based on two sets of small-signal S-parameters measured at different bias conditions. This analysis applies to both FETs and bipolar junction transistors (BJTs) in emitter(source)-injected or base(gate)-injected configuration. This information is particularly useful in receiver design where the gain of a mixer is always an unknown or difficult to predict in the design stage, and can be used as a figure of merit in comparing the mixing performances of different transistors