Single-Ended Signaling for Energy-Efficient Short-Reach Communication with High-Bandwidth Density: Invited Paper

This paper describes how a novel single-ended signaling method intended for short-reach signaling evolved from concept to production. The initial prototype demonstrated 20 Gbps signaling, using 28 nm CMOS technology, at ~0.5 pJ/bit, over a 4.5 mm long on-package channel, while the final version operated at 40 Gbps, using 5 nm CMOS technology, at 1.3 pJ/bit, over a significantly more complex 120 mm long off-package channel. The process of adding features to improve performance along with the differences between prototype, advanced development, and production designs are presented. Some of those features include: a single-ended transmitter with nearly constant current consumption, a high-bandwidth receiver optimized for recovering a near-ground signal, a clocking architecture with excellent power-supply induced jitter tracking, and a novel power supply regulation scheme that levels circuit speed and current consumption across PVT. We also discuss the challenges to high-bandwidth density, single-ended signaling.