Circuit Controlled Current Instabilities in ``S‐Shaped'' Negative Differential Conductivity Elements

We compare the results of our theoretical analysis of an ``S‐shaped'' negative differential conductivity (NDC) element in a circuit containing a capacitor in parallel with the NDC element in series with an inductor, with the results of our experiments on PNPN and Ovonic diodes. All the major features of the experimental results are accounted for by the theory. These include, for the PNPN diode, switching to stable points in the DNC region and the appearance of damped chirps in response to a voltage ramp; for the Ovonic diode, voltage tunable relaxation oscillations. The theory provides a framework within which one can categorize and characterize the various modes of behavior observed in all S‐shaped NDC elements.