Characterization of IIP2 and DC-offsets in transconductance mixers

Envelope distortion in transconductance mixers is analyzed in this paper. The analysis consists of a simplified theoretical study, simulation results, and measurements about several implemented mixers. The studied mixers are active single-balanced and double-balanced structures. A theoretical mismatch analysis is carried out instead of a complex mixer nonlinearity analysis; this gives an intuitive sense of even-order nonlinearity in balanced mixers, and provides information about the fundamental restrictions of second-order input intercept point (IIP2) and the relations of different imbalances to actual performance. The analysis uses a number of simplifying assumptions, but without losing generality. The IIP2 is sensitive to any mismatch in a differential circuit topology. It will be shown that an excellent IIP2 can be achieved in slightly imbalanced conditions by a controllable mismatch device.