High-frequency harmonic distortion in feedback amplifiers: analysis and applications

An approach for the evaluation of high-frequency harmonic-distortion factors in feedback systems is proposed and the results obtained are applied to feedback amplifiers. Under the assumption that transistors are not driven out of their linear operating regions, small-signal analysis and conventional algebra are exploited to derive understandable and compact expressions highly improving the comprehension of harmonic-distortion generation. The impact of the frequency compensation utilized (namely, dominant-pole or Miller technique) on linearity performance is evaluated and the high-frequency distortion properties of closed-loop single-stage and two-stage amplifiers are analyzed and compared. The accuracy of the analysis, also in view of the given applications, is confirmed through extensive simulations with Spectre on idealized models as well as on CMOS transistor-level circuits. Despite the approximated nature of the analytical models, predicted data are found in very close agreement with simulations in nearly all the frequency range of interest.