Manolis T. Terrovitis’s research while affiliated with University of California, Berkeley and other places

Because of the periodically time-varying nature of some circuit blocks of a communication system, such as the mixers, the noise which is generated and processed by the system has periodically time-varying statistics. An accurate evaluation of the system output noise is not straightforward as in the case where all the circuit blocks are linear-time-invariant and the noise that they generate is time-independent. We qualitatively examine here, conditions under which we can treat the noise at the output of every circuit block of a practical communication system as if it were time-invariant, in order to simplify the noise analysis without introducing significant inaccuracy in the noise characterization of the overall communication system.

The nonlinearity behavior of CMOS current-switching mixers is investigated. By treating the mixer as a periodically-time-varying weakly nonlinear circuit, we study the distortion-causing mechanisms and we predict the mixer distortion performance. Normalized graphs are provided from which the designer can readily estimate the mixer nonlinearity for particular process and design parameters. A simple CMOS transistor model appropriate for our calculations, which also takes into account deviation from the square law is adopted. The significance of a physical transistor model for reliable distortion simulation is demonstrated. The prediction of our analysis is compared with simulation results and with experimental data

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