A frequency-domain stability criterion for periodically driven varactor circuits

Abstract

In this paper we show how input-output stability theory bears on the problem of obtaining a frequency-domain stability criterion that can be used to design periodically driven varactor circuits with guaranteed stability. The design criterion requires that the locus of j/spl omega/Z(j/spl omega/) for -/spl infin/</spl omega/</spl infin/ avoids a critical disk in the complex plane, where Z(j/spl omega/) is the Thevenin equivalent driving-point impedance presented to the varactor at frequency /spl omega/. The location and size of the disk is a function only of the minimum and maximum incremental capacitance of the varactor. We present an example of how a varactor frequency doubler with guaranteed stability may be designed using this criterion.