A stability criterion for feedback systems with one nonlinear element

The paper investigates the stability of feedback systems with one nonlinear element whose input-output characteristic is contained within a sector of the input-output plane. The results are applicable to any nonlinearity within a given sector and the conditions for global asymptotic stability are necessary if the exact analytic description of the nonlinearity is not available. The conditions for asymptotic stability are related to the Routh-Hurwitz and Nyquist stability criteria for linear systems.