64-GHz Datapath Demonstration for Bit-Parallel SFQ Microprocessors Based on a Gate-Level-Pipeline Structure

We successfully demonstrated an 8-bit-wide, bit-parallel datapath composed of an arithmetic logic unit and register files for high-throughput oriented SFQ microprocessors based on a gate-level-pipeline structure. Achieving high-speed operation in the bit-parallel datapath is difficult because of feedback paths. We used concurrent-flow clocking and counter-flow clocking in combination to solve the timing problem at the feedback path in the datapath, and we optimized the number of JJs and pipeline stages in the register file for solving the timing issue. We designed the datapath with the cell library for the AIST 10 kA/cm
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Advanced Process. The total number of pipeline stages, Josephson junctions, and circuit area of the designed datapath were 52, 18448, and 3.81 mm × 4.05 mm, respectively. We obtained a relatively wide bias margin of the designed datapath at the target clock frequency of 50 GHz, and it operated up to 64 GHz in on-chip high-speed testing.