Compact Superconducting Lookup Table Composed of Two-Dimensional Memory Cell Array Reconfigured by External DC Control Currents

摘要

We investigated the hardware implementation of an area-efficient superconducting lookup table (LUT) based on a single flux quantum (SFQ) logic by using a newly proposed small memory cell. The memory cell is composed of a nondestructive read-out (NDRO) flip-flop with input circuits that convert the input dc current to an SFQ pulse signal. The datum can be written to the selected memory cell in the 2-D memory cell array by applying both x- and y-directional dc control currents. The data stored in the memory cell array can he reset simultaneously by applying a dc current to a common reset line. By employing the new memory cell, wiring for reconfiguring the data and resetting the memory cell array can be drastically simplified compared to that of the conventional SFQ LUT. We implemented and tested the memory cell and confirmed the correct operation with wide dc bias and input-current margins. We designed the 16-b LUT using the designed memory cells. The circuit area and the number of Josephson junctions of the 16-b LUT is reduced by approximately 24 and 41%, respectively, compared to those of the LUT based on the conventional architecture. We experimentally obtained the correct operation and reconfiguration of the 4-b LUT that uses the new memory cells with a normalized bias margin of -22 to +7%.