A composite circuit model for NDR devices in random access memory cells

Devices exhibiting negative differential resistance (NDR), such as resonant tunneling diodes and Esaki-type diodes, offer the promise of converting a dynamic random access memory (DRAM) cell to operate like a static random access memory cell with potentially lower dynamic power dissipation and faster READ and WRITE operations than a conventional DRAM. However, a circuit model that describes the operation of the resulting novel memory cell and is of use for both hand analysis and design, and circuit simulation as has yet been developed due to the non-analytical current-voltage curve of the two NDR devices in the cell. In this paper, we present a "composite" circuit model that describes the relationship between current and voltage at the common node of connection of the two NDR devices. The composite model is analytical and can easily be implemented in SPICE or any circuit simulator. It is also useful for hand analysis of the READ/WRITE performance metrics. Finally, comparisons of composite models are presented.