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IEEE Transactions on Applied Superconductivity

Component development for a 16 Gb/s RSFQ-CMOS interface system

Nobuyuki Yoshikawa, Toshio Abe, Yuichi Kato, H. Hoshina

Published Mar 1, 2001• 9 citations
Publisher

Abstract

We have been developing an RSFQ-CMOS interface system. The system consists of three modules: a 1 to 32 bit DDST demultiplexer which converts a 16 Gb/s SFQ data input into a 32-channel 500 Mb/s output, asynchronous stacked-SQUID amplifiers which amplify an SFQ data input into a 5 mV voltage level output, and 77 K CMOS amplifiers which amplify a 5 mV voltage level input into a 5 V output at 500 MHz. We have implemented the asynchronous stacked-SQUID amplifier and the 77 K CMOS amplifier using the HYPRES 1 kA/cm/sup 2/ Nb process and the ROHM 0.6 /spl mu/m CMOS process, respectively. It was demonstrated that the 24-stage asynchronous stacked-SQUID amplifier amplifies an SFQ data input into a 2.0 mV voltage level at 600 MHz. The 77 K CMOS amplifier was shown to amplify a 5 mV voltage level input into 5 V at 500 MHz from the simulation, and a 175 mV voltage input into 3.5 V at 90 MHz from the experiment.

DOI
10.1109/77.919450

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We have been developing an RSFQ-CMOS interface system. The system consists of three modules: a 1 to 32 bit DDST demultiplexer which converts a 16 Gb/s SFQ data input into a 32-channel 500 Mb/s output, asynchronous stacked-SQUID amplifiers which amplify an SFQ data input into a 5 mV voltage level output, and 77 K CMOS amplifiers which amplify a 5 mV voltage level input into a 5 V output at 500 MHz. We have implemented the asynchronous stacked-SQUID amplifier and the 77 K CMOS amplifier using the HYPRES 1 kA/cm/sup 2/ Nb process and the ROHM 0.6 /spl mu/m CMOS process, respectively. It was demonstrated that the 24-stage asynchronous stacked-SQUID amplifier amplifies an SFQ data input into a 2.0 mV voltage level at 600 MHz. The 77 K CMOS amplifier was shown to amplify a 5 mV voltage level input into 5 V at 500 MHz from the simulation, and a 175 mV voltage input into 3.5 V at 90 MHz from the experiment.
High-speed logic operation of an output interface circuit for a single-flux-quantum (SFQ) system was demonstrated at a data rate of 5 Gb/s. Using NEC's 2.5-kA/cm/sup 2/ Nb junction process, we designed, fabricated, and tested the interface circuit consisting of a 2-b SFQ demultiplexer and two Josephson latching drivers. We verified the proper operation of the demultiplexer. The interface can convert 5-Gb/s SFQ-pulse data into two-channel 2.5-Gb/s return-to-zero data with an amplitude of approximately 6 mV.
We have developed a data-driven self-timed (DDST) rapid-single-flux-quantum (RSFQ) demultiplexer (demux) for the interface between on-chip high-speed RSFQ circuits and off-chip low-speed circuits. In order to eliminate the timing issue in a synchronous clocking system we employed the DDST architecture, where a clock signal is localized within a 2-bit basic demux module and dual rail lines are used to transfer the timing information between the modules. A larger demux can be produced simply by connecting the 2-bit modules in a tree structure. The DDST demux was designed for 10 Gb/s operation with sufficient dc bias margin using HYPRES 1 kA/cm/sup 2/ Nb process. We have successfully tested operation of the 2-bit demux up to 18 GHz using the DDST on-chip high-speed test system which was developed in our group.
We have developed and demonstrated high bandwidth Josephson circuits to interface the output of RSFQ circuits to room temperature electronics. Asynchronous dc powered voltage driver circuits have been designed to amplify RSFQ signal levels to voltage outputs in the 2-4 mV range, in a wide bandwidth. These driver circuits have been characterized and tested for data rates up to 8 Gb/s. The bit error rate for one of these drivers has been measured up to 7 Gb/s for a (2/sup 31/-1) bit long pseudo-random bit sequence (PRBS). In order to match the data rate of Josephson circuits to slower room temperature electronics, we have developed clock-controlled shift registers which allow shift-in and shift-out of data at different frequencies. Complete functionality of these circuits integrated with the drivers has been demonstrated at low speed. Shift registers integrated with the voltage driver circuits have been tested at high-speed for data rates up to 6 Gb/s.
The high-speed operation of a one-channel output interface for a single-flux quantum (SFQ) system has been demonstrated. The interface consisted of a Josephson latching driver, a room-temperature semiconductor amplifier, and a decision circuit module. The Josephson latching driver was fabricated by using a 2.5-kA/cm/sup 2/ standard Nb junction process and used to amplify an SFQ pulse into a 5.5-mV level signal at 10 Gb/s. The interface converted the SFQ pulse signal into a nonreturn-to-zero signal having an amplitude of 1 V at 10 Gb/s.
We have developed and demonstrated high bandwidth Josephson circuits to interface the output of RsFQ circuits to room temperature electronics. Asynchronous dc powered voltage driver circuits have been designed to amplify RSFQ signal levels to voltage outputs in the 2-4 mV range, in a wide bandwidth. These driver circuits have been characterized and tested for data rates up to 8 Gb/s. The bit error rate for one of these drivers has been measured up to 7 Gbls for a (Z3l -1) bit long pseudo-random bit sequence (PPRBS). In order to match the data rate of Josephson circuits to slower room temperature electronics, we have developed clock-controlled shift registers which allow shift-in and shift-out of data at different frequencies. Complete functionality of these circuits integrated with the drivers has been demonstrated at low speed. Shift registers integrated with the voltage driver circuits have been tested at high-speed for data rates up to 6 Gb/s.
Superconductive Rapid Single Flux Quantum (RSFQ) logic and memory, in which ones and zeros are represented by the presence or absence within a timing window of quantized picosecond voltage pulse (/spl int/v(t)dt=h/2e=2.07 mV/spl middot/ps), corresponding to one SFQ, can be integrated into a digital computing system with an operating rate of several tens of GHz, based on the present Nb Josephson junction integrated circuit technology. It is the most promising technology beyond semiconductor transistors for low-power high-end computation. However, as the operating speed of circuits and systems increase, timing uncertainty from fabrication process variations makes global synchronization very hard. In this paper, we present a globally asynchronous, locally synchronous timing methodology for RSFQ digital design, which can solve the global synchronization problem. We also demonstrate the recent experimental results of some asynchronous circuits and systems implemented in RSFQ technology. Several key components such as a self-timed shift register, a self-timed demultiplexor, a Muller-C element, a completion detector, and a clock generator have been designed and tested. High speed operation has been confirmed up to 20 Gb/s for a prototype data buffer system, which consists two self-timed shift registers and an on-chip 5-38 GHz clock generator.