Cyclic combinational circuits

Speaker: Andrey Mokhov

31st October 2008 , 1pm , Merz Court M413

Abstract

A collection of logic gates forms a combinational circuit if the outputs can be described as Boolean functions of the current input values. Optimizing combinational circuitry, for instance, by reducing the number of gates (the area) or by reducing the length of the signal paths (the delay), is an overriding concern in the design of integrated circuits.

The accepted wisdom is that combinational circuits must have acyclic (i.e., loop-free or feed-forward) topologies. In fact, the idea that "combinational" and "acyclic" are synonymous terms is so thoroughly ingrained that many textbooks provide the latter as a definition of the former. And yet simple examples suggest that this is incorrect. In this presentation, we advocate the design of cyclic combinational circuits (i.e., circuits with loops or feedback paths). We demonstrate that circuits can be optimized effectively for area and for delay by introducing cycles.