Optimizing Adiabatic Quantum-Flux-Parametron (AQFP) Circuits using an Exact Database

Adiabatic Quantum-Flux-Parametron (AQFP) is a family of superconducting electronic (SCE) circuits exhibiting high energy efficiency. In AQFP technology, logic gates require splitters to drive multiple fanouts and both the logic gates and the splitters are clocked, requiring path balancing using buffers to ensure all fanins of a gate arrive simultaneously. In this work, we propose a new synthesis approach comprising of two stages: In the first stage, a database of optimum small AQFP circuit structures is generated. This is a one-time, network-independent operation. In the second stage, the input network is first mapped to a LUT network and then the LUTs are replaced with the locally optimum (area or delay) AQFP structures from the generated database in the topological order. Our proposed method simultaneously optimizes the resources used by 1) gates that compute logic functions and 2) buffers/splitters. Hence, it captures additional optimization opportunities that are not explored in the state-of-the-art methods where buffer-splitter optimizations are done after the logic optimizations. Our method, when using a delay-oriented (area-oriented) strategy, achieves over a 40% (35%) decrease in delay in the critical path (the number of levels) and a 19% (21%) decrease in area (the number of Josephson Junctions) as compared to existing work.