A STUDY OF NONLINEAR NEGATIVE CAPACITANCE

Abstract

Abstract : An analytical study is made of the behavior of a certain class of RLC networks which contain a theoretical nonlinear negative capacitance along with various possible combinations of constant parasitic elements that are certain to be present in any physical realization of this type of capacitance. The theoretical capacitor is defined in terms of its charge-voltage relationship. This study is directed toward an evaluation of the usefulness of a nonlinear negative capacitance in a network to accomplish either amplification or oscillation or switching. In order for a network to be useful as an amplifier, its small-signal model must be stable. Therefore, for this part of the study the nonlinear capacitor is represented by a linear, negative capacitance. Singular point analysis discloses that any of the defined networks may have two stable equilibrium points. This is the basic criterion for a bistable device, so the conclusion is that nonlinear capacitance, like nonlinear resistance, can be used effectively to construct a switching circuit. It is proven by phase plane methods that none of the second order systems can support a sustained oscillation. A nonlinear negative capacitance has been realized by means of a transistor negative impedance converter circuit.