Isochronous data link across a superconducting Nb flex cable with 5 femtojoules per bit

• Published in: Superconductor science & technology Vol. 35; no. 4; pp. 45014 - 45020
• Main Authors: Dai, Haitao, Kegerreis, Corey, Wehella Gamage, Deepal, Egan, Jonathan, Nielsen, Max, Chen, Yuan, Tuckerman, David, Peek, Sherman E, Yelamanchili, Bhargav, Hamilton, Michael, Das, Rabindra N, Herr, Anna, Herr, Quentin
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.04.2022
• Subjects: digital; interconnect; packaging; SFQ
• ISSN: 0953-2048; 1361-6668
• DOI: 10.1088/1361-6668/ac5786

Abstract Interconnect properties position superconducting digital circuits to build large, high performance, power efficient digital systems. We report a board-to-board communication data link, which is a critical technological component that has not yet been addressed. Synchronous communication on chip and between chips mounted on a common board is enabled by the superconducting resonant clock/power network for Reciprocal Quantum Logic circuits. The data link is extended to board-to-board communication using isochronous communication, where there is a common frequency between boards but the relative phase is unknown. Our link uses over-sampling and configurable delay at the receiver to synchronize to the local clock phase. A single-bit isochronous data link has been demonstrated on-chip through a transmission line, and on a multi-chip module through a superconducting tape between driver and receiver with variable phase offset. Measured results demonstrated correct functionality with a clock margin of 3 dB at 3.6 GHz, and with 5 fJ bit −1 at 4.2 K.