New nonlinear analysis of onset of oscillations

This paper presents a novel approach to analysis of onset of oscillations in circuits with many nonlinear elements. It includes a simple design algorithm implemented in HP HFDS. The method is applied to a 900 MHz digital pager´s local oscillator. Introduction Onset of oscillations from the quiescent point is a phenomenon both important and intrinsically difficult to analyze. This paper presents a simple new analysis of the phenomenon, and shows how to apply it in oscillator design. We combine small signal analysis with post-processing capabilities of modern software and obtain a simple geometrical algorithm, which describes the existence and stability, and also frequency and power of oscillations. Although the onset of oscillations was analysed in the past, the results were presented in the language of dynamical systems and were of little use to design engineers. The simplest formulation from engineering point of view was presented in [3] by Kudrewicz for single-feedback and in [1,2,4] Mees and Allwright (and generalized by Hente) for multiple-feedback systems. The recent development of CAE tools allows to apply the theoretical results to circuit design. This paper extends the results presented in [5] to circuits with many nonlinearities.