Stability of digitally emulated mem-elements

The paper analyzes the stability issue of a special emulator of memristive, memcapacitive and meminductive systems as well as higher-order elements from Chua´s periodical table, and other two-terminal devices. It is demonstrated that, in order to provide stable behavior, the analog port of the emulator must be implemented by the controlled voltage or current source depending on the type of the emulated two-terminal device. As a practical consequence, the emulator must contain both of the above analog interfaces in order to be universal.