Beyond Local Optimality of Buffer and Splitter Insertion for AQFP Circuits

Adiabatic quantum-flux parametron (AQFP) is an energy-efficient superconducting technology. Buffer and splitter (B/S) cells must be inserted to an AQFP circuit to meet the technology-imposed constraints on path balancing and fanout branching. These cells account for a significant amount of the circuit’s area and delay. In this paper, we identify that B/S insertion is a scheduling problem, and propose (a) a linear-time algorithm for locally optimal B/S insertion subject to a given schedule; (b) an SMT formulation to find the global optimum; and (c) an efficient heuristic for globalB/S optimization. Experimental results show a reduction of 4% on the B/S cost and 124× speed-up compared to the state-of-the-art algorithm, and capability to scale to a magnitude larger benchmarks.