This paper presents the design of an ultra-high-speed, low-power arithmetic unit that supports variable bit-width operations with single flux quantum (SFQ) technology. Because of the high-speed nature of superconductor devices, we can achieve extremely high power-performance efficiency that cannot be achieved by state-of-the-art CMOS devices. To implement the complex function to support the variable bit-width feature, we introduce a novel circuit architecture to maintain the high-speed operation over 50GHz. Our prototype chip design successfully demonstrated 53.5GHz 1.59mW operations.

To overcome issues originating from the CMOS technology, a large-scale reconfigurable data-path (LSRDP) processor based on single-flux quantum circuits is introduced. LSRDP is augmented to a general purpose processor to accelerate the execution of data flow graphs (DFGs) extracted from scientific applications. Procedure of mapping large DFGs onto the LSRDP is discussed and our proposed techniques for reducing area of the accelerator within the design procedure will be introduced as well.

Single-flux quantum logic (SFQ) circuits, in which a flux quantum is used as an information carrier, have the possibility for opening the door to a new digital system operated at over 100-GHz clock frequency at extremely low power dissipation. The SFQ logic system is a so-called pulse logic, which is completely different from the level logic for semiconductors like CMOS, so circuit design technologies for SFQ logic circuits have to be newly developed. Recently, much progress in basic technologies for designing SFQ circuits and operating circuits at high speeds has been made. With advances in these design tools, large-scale circuits including more than several thousand junctions can be easily operated with the clock frequency of more than several tens of gigahertz. High-end routers and high-end computers are possible applications of SFQ logic circuits because of their high throughput nature and the low power dissipation of SFQ logic. In this paper, recent advances of SFQ circuit design technologies and recent developments of switches for high-end routers and microprocessors for high-end computers that are considered possible applications for SFQ logic will be described.