Augmentation of SPICE for simulation of circuits containingresonant tunneling diodes

This paper describes the incorporation of an accurate physics-based model of the resonant tunneling diode (RTD) into Berkeley SPICE version 3F5 and addresses the related direct current (dc) and transient convergence problems caused by the negative differential resistance (NDR) and the exponential nature of the device characteristics. To circumvent the dc convergence problems, a new continuation technique using artificial parameter embedding and a current limiting algorithm are proposed. The studies made in this paper have shown that these techniques are superior to the in-built continuation methods of SPICE, such as Gmin-stepping and Source-stepping, for a large number of circuits of varying sizes. To improve transient convergence performance, the following three algorithms are added to SPICE: a modified forced-convergence algorithm, a new time-step adjustment algorithm, and a modified device voltage prediction algorithm.