Design and Demonstration of a 44 SFQ Network Switch Prototype System and 10-Gbps Bit-Error-Rate Measurement

Yoshio KAMEDA  Yoshihito HASHIMOTO  Shinichi YOROZU  

IEICE TRANSACTIONS on Electronics   Vol.E91-C   No.3   pp.333-341
Publication Date: 2008/03/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e91-c.3.333
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Special Section on Recent Progress in Superconductive Digital Electronics)
SFQ (Single-Flux-Quantum) circuit,  superconductive circuit,  network switch,  cryocooled system,  Ethernet switch,  

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We developed a 44 SFQ network switch prototype system and demonstrated its operation at 10 Gbps. The system's core is composed of two SFQ chips: a 44 switch and a 6-channel voltage driver. The 44 switch chip contained both a switch fabric (i.e. a data path) and a switch scheduler (i.e. a controller). Both chips were attached to a multi-chip-module (MCM) carrier, which was then installed in a cryocooled system with 32 10-Gbps ports. Each chip contained about 2100 Josephson junctions on a 5-mm5-mm die. An NEC standard 2.5-kA/cm2 fabrication process was used for the switch chip. We increased the critical current density to 10 kA/cm2 for the driver chip to improve speed while maintaining wide bias margins. MCM implementation enabled us to use a hybrid critical current density technology. Voltage pulses were transferred between two chips through passive transmission lines on the MCM carrier. The cryocooled system was cooled down to about 4 K using a two-stage 1-W cryocooler. We correctly operated the whole system at 10 Gbps. The switch scheduler, which is driven by an on-chip clock generator, operated at 40 GHz. The speed gap between SFQ and room temperature devices was filled by on-chip SFQ FIFO buffers or shift registers. We measured the bit error rate at 10 Gbps and found that it was on the order of 10-13 for the 44 SFQ switch fabric. In addition, using semiconductor interface circuitry, we built a four-port SFQ Ethernet switch. All the components except for a compressor were installed in a standard 19-inch rack, filling a space 21 U (933.5 mm or 36.75 inches) in height. After four personal computers (PCs) were connected to the switch, we have successfully transferred video data between them.