Basics about Rapid Single-Flux Quantum (RSFQ) digital electronics

Kris Gaj, Quentin Herr, Victor Adler +3 more

Rapid single flux quantum (RSFQ) digital circuits have reached the level of medium- to large-scale of integration. At this level, existing design methodologies, developed specifically for RSFQ circuits, have become computationally inefficient. Applying mature semiconductor methodologies to the design of RSFQ circuits, one encounters substantial difficulties originating from the differences between both technologies. In this paper, a new design methodology aimed at large-scale RSFQ circuits is proposed. This methodology is based on a semiconductor semicustom design approach. An established design methodology for small-stale RSFQ digital circuits, based on circuit (junction-level) simulation and device parameter optimization, is used for the design of basic RSFQ cells. A library composed of about 20 basic RSFQ cells has been developed based on this approach. A novel design methodology for large-scale circuits, presented in this paper, is based on logic (gate-level) simulation and timing optimization. This methodology has been implemented around the Cadence integrated design environment and used successfully at the University of Rochester for the design of two large-scale digital circuits.

Gleb Krylov, Eby G. Friedman

Boyko Dimov, M. Khabipov, D Balashov +5 more

The Rapid Single Flux Quantum (RSFQ) technique is regarded as one of the most promising electronics due to its extremely high operating speed and low power consumption. Middle-scale RSFQ applications operating at multigigahertz frequency have recently been reported on. At such high operating frequencies, the on-chip interconnects start to play a limiting role for the performance of the densely packaged digital circuits. Our previous studies have theoretically investigated the parasitic coupling effects between superconductive microstrip transmission lines and conclusions have been drawn about the critical coupling levels of several typical microstrip geometries. Here, basic RSFQ structures are investigated experimentally, which contain a Josephson transmission line stage with large inductance and can either trap or pass SFQ pulses. These structures are incorporated in critical microstrip layouts, thus being subjected to parasitic coupling. The bias levels are monitored at which the structures start to pass the SFQ pulses with and without coupling influences. Thus, the conclusions of our previous theoretical investigations are verified experimentally.

Gleb Krylov, Tahereh Jabbari, Eby G. Friedman

Vinod Kumar Khanna

Vratislav Michal, Emanuele Baggetta, Mario Aurino +2 more

The Rapid Single-Flux-Quantum logic (RSFQ) presents an efficient way to achieve ultra fast digital operations. This logic uses the macroscopic effects which can be found in nano-structured superconductor devices such as the Josephson AC and DC effects, and the magnetic flux quantization. As the typical time of the Josephson junction quantized phase leap 2π is in the order of picoseconds, the RSFQ circuits can operate with clock frequencies in the order of hundreds of GHz. This invited paper focuses on basic principles of superconducting RSFQ logic as well as on typical applications, such as the signal conversion or petaflops computing systems. In addition we point out the benefits of the semi-metallic NbN-TaxN-NbN Josephson junction technology, which has been developed at CEA-INAC in Grenoble.