Augmentation of SPICE for simulation of circuits containing resonant tunneling diodes

This paper describes the incorporation of an accurate physics-based model o f the resonant tunneling diode (RTD) into Berkeley SPICE version 3F5 and ad dresses the related direct current (dc) and transient convergence problems caused by the negative differential resistance (NDR) and the exponential na ture of the device characteristics. To circumvent the de convergence proble ms, a new continuation technique using artificial parameter embedding and a current limiting algorithm are proposed. The studies made in this paper ha ve shown that these techniques are superior to the in-built continuation me thods of SPICE, such as Gmin-stepping and Source-stepping, for a large numb er of circuits of varying sizes. To improve transient convergence performan ce, the following three algorithms are added to SPICE: a modified forced-co nvergence algorithm, a new time-step adjustment algorithm, and a modified d evice voltage prediction algorithm.