Design of a superconducting ALU with a 3-input XOR gate

In order to develop superconducting Digital Signal Processors (DSP´s), we have been studying a superconducting 1-bit Arithmetic Logic Unit (ALU). This ALU has the simplest function of AND, OR, ADD (addition), and SUB (subtraction). The ALU operates in a 3-stage pipeline. All logic functions such as AND, OR, and SUM (summation) can be executed within a single stage of the pipeline. In order to achieve the high-speed operation of the ALU, we proposed and designed a novel 3-input XOR gate, which can operate in only one logic stage. Our simulation study showed that all components of the ALU can operate up to 50 GHz. These ALU components were fabricated and tested at low speed. Large bias margins of more than ±37% were achieved. The designed ALU´s were laid out and fabricated with an Nb process. The ALU occupied the area of 1200 μm × 2600 μm, which contains 560 Josephson junctions (JJ´s).