Technology Legalization and Optimization for Adiabatic Quantum-Flux Parametron

Adiabatic quantum-flux parametron (AQFP) is an energy-efficient superconducting technology. Before physical design can be performed, AQFP technology mapping involves not only mapping logic into supported gate types but also legalizing the circuit to fulfill the technology-imposed constraints on path balancing and fanout branching by inserting buffer and splitter cells. These cells account for a significant amount of the circuit's area, delay, as well as for increasing energy consumption. In this article, we 1) identify that the AQFP legalization problem is a scheduling problem; 2) propose linear-time depth-optimal scheduling and irredundant buffer insertion algorithms; 3) present heuristic optimization algorithms to further reduce buffer count; and 4) suggest an unsupervised design space exploration approach for AQFP technology mapping, mixing, and interleaving logic optimization and technology legalization. Experimental results show that our design space exploration, utilizing the proposed technology legalization and optimization flow, achieves 44% improvement on the energy-delay product compared to the state of the art.