Excitation of oscillations in nonlinear systems under static feedback

New conditions for oscillatority of a system in the sense of Yakubovich (1973) are proposed. These conditions are applicable to nonlinear systems decomposed into two nonlinear parts. Upper and lower bounds for oscillation amplitude are obtained. The relation between the oscillatority bounds and excitability indices for the systems with the input are established. An example illustrating the proposed results by computer simulation is given.