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 RQL 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 (MCM) 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 at 4.2 K.
@article{arxiv.2109.01808,
title = {Isochronous Data Link Across a Superconducting Nb Flex Cable with 5 femtojoules per Bit},
author = {Haitao Dai and Corey Kegerreis and Deepal Wehella Gamage and Jonathan Egan and Max Nielsen and Yuan Chen and David Tuckerman and Sherman E. Peek and Bhargav Yelamanchili and Michael Hamilton and Rabindra Das and Anna Herr and Quentin Herr},
journal= {arXiv preprint arXiv:2109.01808},
year = {2022}
}