Rise time analysis of MOBILE circuit

Recently, high-speed circuit applications using resonant tunnel diodes (RTDs) have attracted much attention due to their fast switching speed and increased Boolean functionality. For example, high-speed operation up to 35 Gb/s of a flip-flop circuit has been demonstrated using a pair of series connected RTDs, called a mono-stable bistable transition logic element (MOBILE) (K. Maezawa et al, IEEE Electron Dev. Lett., vol. 19, no. 3, pp. 80-82, 1998). It has been noted, however, that the MOBILE-type circuit has a critical value for the rise time of the supplied clock pulse, T_R^C, which limits the operation speed (T.C.L.G. Sollner et al, Proc. Int. Semicond. Dev. Res. Symp., pp. 307-310, 1993). Several switching time analyses have been performed based on numerical simulation (K. Maezawa, Jpn. J. Appl. Phys. vol. 34, no. 213, pp. 1213-1217, 1995; Y. Ohno et al, IEICE Trans. Electron., vol. E79-C, no. 11, pp. 1530-1536, 1996). From the circuit design point of view, however, a closed form of an analytical expression of T_R^C is necessary. In this paper, analytical expressions of T_R^C as well as a minimum total transition time are derived. The circuit parameter dependence of the operating speed is also analyzed.