Noise in current-commutating CMOS mixers

A noise analysis of current-commutating CMOS mixers, such as the widely used CMOS Gilbert cell, is presented. The contribution of all internal and external noise sources to the output noise is calculated. As a result, the noise figure can be rapidly estimated by computing only a few parameters or by reading them from provided normalized graphs. Simple explicit formulas for the noise introduced by a switching pair are derived, and the upper frequency limit of validity of the analysis is examined. Although capacitive effects are neglected, the results are applicable up to the gigahertz frequency range for modern submicrometer CMOS technologies. The deviation of the device characteristics from the ideal square law is taken into account, and the analysis is verified with measurements