2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/105576We generalize a simple model for superlattices to include the effect of differential capacitance. It is shown that the model always has a stable steady-state solution (SSS) if all differential capacitances are positive. On the other hand, when negative differential capacitance is included, the model can have no stable SSS and be in a self-sustained current oscillation behavior. Therefore, we find a possible minimum toy model with both negative differential resistance and negative differential capacitance which can include the phenomena of both self-sustained current oscillation and $I-V$ oscillation of stable SSSs.6 pages, 3 figuresMaterials Sciencetext