Practical completion detection for 2-of-N delay-insensitive codes

There is increasing interest in using m-of-n delay-insensitive codes for robust asynchronous global communication, to support the design of coding-efficient and low-power channels. However, a fundamental obstacle in using these codes has been complex and expensive hardware support. This paper addresses this issue, introducing and evaluating practical completion detector units for 2-of-n codes. Designs are proposed for both return-to-zero (RZ) and non-return-to-zero (NRZ) codes. The RZ designs build on prior work of Piestrak [14]; this paper proposes a small modification to their work to provide a fully timing-robust (i.e. quasi-delay insensitive, or QDI) version. The main contribution of the paper is an efficient completion for NRZ 2-of-n codes. Both detector architectures are modular and simple, composed of basic cells in a binary tree. Initial simulation results were performed on several implementations of a 2-of-9 detector using Cadence's Spectre environment, after mapping to a 90nm standard cell library. The new RZ detector has 35% area reduction and comparable delays and energy to the earlier Piestrak design, but unlike the latter, ensures robust QDI operation. The new NRZ detector is shown to have negligible stabilization time between successive codewords (0.05–0.19 ns) when compared to a recent alternative approach.