Synthesis of hazard-free asynchronous circuits based on characteristic graph

To synthesize hazard-free asynchronous circuits from Signal Transition Graphs (STGs), we present a new Characteristic Graph (CG) to encapsulate all feasible solutions of the original STG in reduced size, which compares favorably with the state graph approach. Based on CG, we are able to explore the design space, as well as develop a necessary and sufficient condition for hazard-free realization on a predefined general circuit model, which has not yet been reported. The exact optimization for synthesis is shown to be NP hard. A heuristic method is thus proposed which results in efficient solutions while requiring very little CPU time.