Operation Limits for RTD-Based MOBILE Circuits

Resonant-tunneling-diode (RTD)-based monostable-bistable logic element (MOBILE) circuits operate properly in a certain frequency range. They exhibit both a minimum operating frequency and a maximum one. From a design point of view, it should be desirable to have gates with a correct operation from dc up to the maximum operating frequency (i.e., without the minimum bound). This paper undertakes this problem by analyzing how transistors and RTDs interact in RTD-based circuits. Two malfunctions have been identified: the incorrect evaluation of inputs and the lack of self-latching operation. The difficulty to study these problems in an analytical way has been overcome by resorting to series expansions for both the RTD and the heterojunction field-effect transistor I-V characteristics in the points of interest. We have obtained analytical expression linking representative device parameters and technological setup, for a MOBILE-based circuit to operate correctly.