We describe recent topics of rapid-single-flux-quantum (RSFQ) circuits. Much higher integration and higher-speed operation are required for commercializing the RSFQ circuits in any application. To satisfy this requirement, we measure several kinds of time fluctuations that possibly limit the integration level and operating speed, and introduce the flexible passive transmission line technology including a multicasting transmitter. In addition, we describe our ongoing applications. A multiple-detectors-system is expected to open a new application field of an RSFQ-based analog-to-digital converter and a digital signal processor. As for a microprocessor application, increased number of arithmetic logic units may be effective for enhancing the computing performances.
We describe recent topics of rapid-single-flux-quantum (RSFQ) circuits. Much higher integration and higher-speed operation are required for commercializing the RSFQ circuits in any application. To satisfy this requirement, we measure several kinds of time fluctuations that possibly limit the integration level and operating speed, and introduce the flexible passive transmission line technology including a multicasting transmitter. In addition, we describe our ongoing applications. A multiple-detectors-system is expected to open a new application field of an RSFQ-based analog-to-digital converter and a digital signal processor. As for a microprocessor application, increased number of arithmetic logic units may be effective for enhancing the computing performances.
I describe the fundamental technologies concerning the single flux quantum (SFQ) logic circuits. Recent remarkable progress in the computer-aided-design (CAD) tool, which is based on the cell-based design technique, enables us to make SFQ integrated circuits. Although the circuit demonstrated so far has 2, 300 Josephson junctions at most, this number will increase because the CAD tool is advancing. The on-chip test system has also been developed to test the high-speed nature of the SFQ circuit. For example, the shift-register employed as a circuit under test operates correctly at 55GHz. I also describe the potential applications of the SFQ circuits. An analog-to-digital converter utilizing the high-speed nature and high sensitivity in the SFQ circuits will be applicable to the front end of the future base stations, which require broad band width, high sensitivity, and flexibility. Packet switches used in the future high-end router need high throughput and functionality. Only SFQ-based packet switches can meet these requirements. Another potential application is a high-end server. We have studied micro-architectures of a processor executing the Java Byte Codes directly and a multiprocessor system constructed by connecting the processors and memories via the ultra-broad-band SFQ network switches. Throughout the study, we employ the concept of the complexity-reduction (CORE), in which the high-speed nature of the SFQ circuits is used for the reduction of the circuit scale or simplification of the micro-architecture; the multiprocessor system has high performances. These clear applications promote rapid technological progress in the SFQ technology, though we must make every endeavor to find new application fields.
The recent trend and perspectives for high-performance microprocessors based on superconductor single-fluxquantum (SFQ) logic families are described. The rapid single-flux-quantum (RSFQ) and its energy-efficient derivatives are promising as a next-generation digital circuit technology for very-large-scale integration in the post-Moore's era because of the capability of ultrahigh-frequency operation over 100 GHz and low energy consumption. Several ongoing research projects as well as results reported, including several demonstrations of SFQ-based microprocessors and their components, are reviewed.
Rapid Single Flux Quantum (RSFQ) Josephson-junction technology is capable of processing digital data at sub-terahertz frequencies while dissipating almost negligible power. At the present time one can routinely simulate, optimize, design, manufacture, and test an elementary RSFQ logic/memory cell consisting of dozens of Josephson junctions. Furthermore, a number of relatively complex (few hundred to few thousand Josephson junctions) digital circuits were designed and successfully tested. Moreover we know how to implement several RSFQ systems (including analog-to-digital and digital-to-analog converters, digital SQUIDs for supersensitive magnetometry, and digital autocorrelator for radioastronomy) which would far outperform their currently available and even prospective semiconductor counterparts. In order to implement more complex RSFQ systems, including high-performance digital signal processors and general purpose computers there are a number of technical problems to solve. The issues include making full use of on-chip sub-terahertz processing in conditions when inter-chip data/clock exchange speed is bound by bandwidth of the order of a few Gbps/pin. I present the current know-how of the field, and formulate the questions that need to be solved before the RSFQ technology becomes a major workhorse of high-performance computation.
The reduction of the critical current density in rapid single-flux quantum (RSFQ) circuits enables new application fields, like quantum computing and photonic detector readout. The low current density fabrication process creates new design challenges, such as lower stability against thermal fluctuations, violation of the lumped elements condition for microstrip inductances and increased sensitivity to the technological spread. To overcome these issues, we suggest a passive phase shifter as a promising alternative technique for superconductive phase dropping in the RSFQ electronics. Here, we study experimentally their applicability in high-speed RSFQ digital circuits. Conclusions are drawn about the impact of the passive phase shifters on the complexity, the speed and the bit error rate of the investigated RSFQ circuits. We demonstrate the successful operation of different circuits with implemented passive phase shifters at low and high speeds.
Rapid Single-Flux-Quantum (RSFQ) logic is a superconductor IC technology that, with only a modest number of researchers worldwide, has produced some of the world's highest performance digital and mixed-signal circuits. This achievement is due, in part, to a constellation of characteristics that manifest themselves at the circuit level – namely, high-speed digital logic at low-power, ideal interconnects, quantum accuracy, scalability, and simplicity of fabrication. A necessary key to translating these advantages to the system-level involves understanding the I/O, synchronization, and packaging issues associated with a cryogenic technology. The objective of this paper is to review the status of current RSFQ circuit-level infrastructure components and their potential impact on system-level applications.
Recent developments concerning the rapid single-flux-quantum (RSFQ) circuit family are reviewed. Elementary cells in this circuit family can generate, pass, memorize, and reproduce picosecond voltage pulses with a nominally quantized area corresponding to transfer of a single magnetic flux quantum across a Josephson junction. Functionally, each cell can be viewed as a combination of a logic gate and an output latch (register) controlled by clock pulses, which are physically similar to the signal pulses. Hand-shaking style of local exchange by the clock pulses enables one to increase complexity of the LSI RSFQ systems without loss of operating speed. The simplest components of the RSFQ circuitry have been experimentally tested at clock frequencies exceeding 100 GHz, and an increase of the speed beyond 300 GHz is expected as a result of using an up-to-date fabrication technology. This review includes a discussion of possible future developments and applications of this novel, ultrafast digital technology.>