A Comparison of Clocking Schemes for SFQ Circuits

Sasan Razmkhah, Pascal Febvre

Naofumi Takagi, Masamitsu Tanaka

Recent advances of superconducting single-flux-quantum (SFQ) circuit technology make it attractive to investigate computing systems using SFQ circuits, where arithmetic circuits play important roles. In order to develop excellent SFQ arithmetic circuits, we have to design or select their underlying algorithms, called hardware algorithms, from different point of view than CMOS circuits, because SFQ circuits work by pulse logic while CMOS circuits work by level logic. In this paper, we compare implementations of hardware algorithms for addition by synchronous-clocking SFQ circuits. We show that a set of individual bit-serial adders and Kogge-Stone adder are superior to others.

T. Van Duzer

Junhyuk Choi, Juwon Hong, Junpyo Kim +6 more

Superconducting computing using single flux quantum (SFQ) technology has been recognized as a promising post-Moore's law era technology thanks to its extremely low power and high performance.Therefore, many researchers have proposed various SFQbased circuits (e.g., ALU, register file) and architectures (e.g., NPU, CPU) to exploit the potential.However, due to the absence of a reliable and high-frequency clocking scheme, general SFQ circuits cannot operate at high frequencies, making all architectural efforts for high-performance SFQ computing ineffective.In this paper, we propose SuperSFQ, a new design methodology for SFQ hardware that unlocks the high-frequency potential of SFQ technology by co-designing the clocking scheme, circuitry, and architecture.First, we propose SuperClocking, a new clocking scheme that enables high frequency in general SFQ hardware.Second, we implement an SFQ-based synchronizer to realize the reliable operation of SuperClocking.Finally, we provide two architectural design guidelines and corresponding solutions to ensure the functional correctness of SuperClocking in general SFQ devices.By applying our clocking scheme, synchronizer, and guidelines to the latest general-purpose SFQ CPU, SuperSFQ achieves up to 62.5 times higher frequency and improves single-thread and multithread performance by 17 and 62.5 times, respectively, compared to conventional designs, with only 34.4% Josephson junction overhead.In addition, to demonstrate the generality of SuperSFQ, we apply SuperSFQ to 48 different benchmark circuits, achieving 88.5 times higher frequency compared to conventional designs, on average.

Terabe Masayoshi, Sekiya Akito, Fujimaki Akira

Kazunori Miyahara, Shuichi Nagasawa, H. Hasegawa +3 more