Treffer: 100-GHz Single-Flux-Quantum Bit-Serial Adder Based on 10-kA/cm2 Niobium Process
Yokohama National University, Yokohama 240-8501, Japan
Superconductivity Research Laboratory, ISTEC, Tsukuba 305-8501, Japan
Kyoto University, Kyoto 606-8501, Japan
CC BY 4.0
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Electronics
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This paper reports the design and test results of a single-flux-quantum (SFQ) bit-serial adder, which we designed with a target-clock frequency of 100 GHz, to investigate several techniques for producing ultra-high-speed computations using SFQ circuits. The bit-serial adder was designed based on a new cell library developed for the ISTEC Advanced Process, where the critical current density and McCumber-Stewart parameters of Josephson junctions were increased to 10 kA/cm2 and 2.0, respectively, to obtain higher operating frequencies. In addition, we adopted a circuit-design technique based on state transitions excluding a feedback loop in a typical bit-serial adder, and redesigned the NOR gate with the McCumber-Stewart parameter increased to 4.0 to improve performance. As a result, we experimentally obtained a sufficient dc bias margin of ±18% from low frequencies to 60 GHz, and verified the correctness of operations up to 93 GHz. We also demonstrated that the introduction of a higher bias voltage or large inductors in series with bias resistors is effective for achieving faster operation.