7. Dynamic Single Flux Quantum Majority Gates

Among the major issues in modern large scale rapid single flux quantum circuits are the complexity of the clock network, tight timing tolerances, poor applicability of existing CMOS electronic design automation (EDA) techniques, and extremely deep pipelines, which reduce the effective clock frequency. In this chapter, asynchronous dynamic SFQ majority gates are proposed to solve some of these problems. The proposed logic gates exhibit high bias margins and do not require significant area or a large number of Josephson junctions as compared to existing RSFQ logic gates. These gates exhibit a tradeoff among the input skew tolerance, clock frequency, and bias margins. Asynchronous logic gates greatly reduce the complexity of the clock network in large scale RSFQ circuits, thereby alleviating certain timing issues while reducing the required bias currents. Furthermore, asynchronous logic allows existing EDA tools to utilize CMOS approaches for synthesis, verification, and testability. The adoption of majority logic in complex RSFQ circuits also reduces the pipeline depth, enabling higher clock speeds in large scale RSFQ circuits.