Bus encoding to prevent crosstalk delay

The propagation delay across long on-chip buses is increasingly becoming a limiting factor in high-speed designs. Crosstalk between adjacent wires on the bus may create a significant portion of this delay. Placing a shield wire between each signal wire alleviates the crosstalk problem but doubles the area used by the bus, an unacceptable consequence when the bus is routed using scarce top-level metal resources. Instead, we propose to employ data encoding to eliminate crosstalk delay within a bus. This paper presents a rigorous analysis of the theory behind "self-shielding codes", and gives the fundamental theoretical limits on the performance of codes with and without memory. Specifically, we find that a 32-bit bus can be encoded with 40 wires using a code with memory or 46 wires with a memoryless code, in comparison to the 63 wires required with simple shielding.