Simultaneous Bidirectional Signaling for Die-to-Die Links: Signal Integrity Challenges and Hybrid Circuits

This article reviews simultaneous bidirectional signaling and its unique signal integrity challenges for die-to-die links: the near-end echo signal and the hybrid circuit required to remove it, signal reflections, and the impact of timing. A few key works in the design of simultaneous bidirectional transceivers are covered, such as dynamic reference-switching, the replica driver, and the split-termination hybrid, followed by a survey of recent simultaneous bidirectional transceivers for die-to-die links. Finally, we present our own split-termination, passive hybrid simultaneous bidirectional transceiver as a low-power alternative for die-to-die links.