From the abstract: > The accepted wisdom is that combinational circuits must have acyclic (i.e., loop-free or feed-forward) topologies. ... In this dissertatio

From the abstract: > The accepted wisdom is that combinational circuits must have acyclic (i.e., loop-free or feed-forward) topologies. ... In this dissertation, 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. > On the theoretical front, we discuss lower bounds and we show that certain cyclic circuits are one-half the size of the best possible equivalent acyclic implementations. On the practical front, we describe an efficient approach for analyzing cyclic circuits, and we provide a general framework for synthesizing such circuits. On trials with industry-accepted benchmark circuits, we obtained significant improvements in area and delay in nearly all cases. Also: This was published in 2004.