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Adiabatic quantum-flux-parametron (AQFP) logic is a superconductor logic family that can operate with low switching energy due to adiabatic switching. In a previous study, we proposed a low-latency clocking scheme called delay-line clocking, in which the latency for each logic operation is determined by the propagation delay of the excitation current. We demonstrated several AQFP logic gates with delay-line clocking and demonstrated a phase skipping operation, in which some of the AQFP buffers for phase synchronization are removed to reduce the junction count and energy dissipation. In the present study, we design and demonstrate an AQFP 8-bit ripple carry adder with delay-line clocking to show that delay-line clocking and the phase skipping operation are applicable to large-scale AQFP circuits. The latency of this adder is 960 ps, which is 40% of that for a conventional design. Moreover, due to the phase skipping operation, the junction count is reduced to approximately 70% of that for the conventional design. We find that this adder can operate at up to 4 GHz. The above results indicate that large-scale AQFP circuits can operate with low latency and low junction count by using delay-line clocking and a phase skipping operation.

Adiabatic quantum-flux-parametron (AQFP) logic is a promising technology for future energy-efficient, high- performance information processing systems because it has significantly low power consumption due to the adiabatic switching of Josephson junctions. We are developing a high-performance field-programmable gate array (FPGA) using superconducting AQFP circuits to reduce its energy consumption. The all-AQFP FPGA consists of logic blocks, switch blocks, connection blocks, and memory using AQFP circuits. In particular, the memory is composed of AQFP buffer chains, enabling high-density and low-power memory. The switch blocks can perform data routing as well as several logic functions, including majority, and, and or functions, which increases the design flexibility of the all-AQFP FPGA. We fabricated a one-unit all-AQFP FPGA and demonstrated its reconfigurable operation at low speed. It was found that much lower power consumption can be achieved in the new FPGA than in the other superconducting FPGAs.