Process and supply variations all have a large influence on current-mode signaling (CMS) circuits, limiting their application on the fields of high-speed low power communication over long on-chip interconnects. A variation-insensitive CMS scheme (CMS-Bias) was offered, employing a particular bias circuit to compensate the effects of variations, and was robust enough against inter-die and intra-die variations. In this paper, we studied in detail the principle of variation tolerance of the CMS circuit and proposed a more suitable bias circuit for it. The CMS-Bias with the proposed bias circuit (CMS-Proposed) can acquire the same variation tolerance but consume less energy, compared with CMS-Bias with the original bias circuit (CMS-Original). Both the CMS schemes were fabricated in 180 nm CMOS technology. Simulation and measured results indicate that the two CMS interconnect circuits have the similar signal propagation delay when driving signal over a 10 mm line, but the CMS-Proposed offers about 9% reduction in energy/bit and 7.2% reduction in energy-delay-product (EDP) over the CMS-Original. Simulation results show that the two CMS schemes only change about 5% in delay when suffering intra-die variations, and have the same robustness against inter-die variations. Both simulation and measurements all show that the proposed bias circuits, employing self-biasing structure, contribute to robustness against supply variations to some extent. Jitter analysis presents the two CMS schemes have the same noise performance.
High-Speed On-Chip signaling: Voltage or Current-Mode?