Logic design of a single-flux-quantum (SFQ) 2x2 unit switch for Banyan networks

We describe the logic design of a single-flux-quantum (SFQ) 2 x 2 unit switch. It is the main component of the SFQ Banyan packet switch we are developing that enables a switching capacity of over I Tbit/s. In this paper, we focus on the design of the controller in the unit switch. The controller does not have a simple "off-the-shelf" conventional circuit, like those used in shift registers or adders. To design such a complicated random logic circuit, we need to adopt a systematic top-down design approach. Using a graphical technique, we first obtained logic functions. Next, to use the deep pipeline architecture, we broke down the functions into one-level logic operations that can be executed within one clock cycle. Finally, we mapped the functions on to the physical circuits using pre-designed SFQ standard cells. The 2 x 2 unit switch consists of 59 logic gates and needs about 600 Josephson junctions without gate interconnections. We tested the gate-level circuit by logic simulation and found that it operates correctly at a, throughput of 40 GHz.