Cycle in a Conventional Combinational Circuit: A Comprehensive Survey

A Boolean Combinational circuit can be made of some wires and logic gates whose outputs at any time are determined directly from the present combination of inputs without any regard to previous input. Reduction of number of gates (area) and the length of the signal path (delay) to optimize a Boolean circuit is always an overriding concern in the design of digital integrated circuit. The accepted phenomena that combinational circuit is based only on acyclic (loop-free or feed-forward) topology no longer exist. Introducing cycles in combinational circuit we may have same acyclic operation with reduced area and delay of the circuit. Cyclic circuits that do not hold state or oscillate are often the most convenient representation for certain functions, such as arbiters. The main aim of cyclic circuit is to introduce structural feedback & to avoid the logical feedback in order to get combinational primary output. In this survey, we advocate the technological depth of cyclic circuit and their design methodologies with certain merits and demerits. It includes functional analysis i.e. to determine what values will appear and the timing analysis which determine when these values will appear.