The current-transfer processes in circuits composed of nonlinear semiconductor elements with negative differential conductivity of the N type and their response to external harmonic and large-amplitude noise perturbation are experimentally investigated. Ambiguities are found on the current branches and portions with absolute negative conductivity of the I - V characteristics of these circuits. Under the noise action of a certain spectral composition and intensity, the N portions of the current branches on the I - V characteristics of the circuits are completely smoothed. In view of application, the obtained result can be used to remove the firing mode in excited neural networks.