Power Consumption of Fault Tolerant Busses

On-chip interconnects in very deep submicrometer technology are becoming more sensitive and prone to errors caused by power supply noise, crosstalk, delay variations and transient faults. Error-correcting codes (ECCs) can be employed in order to provide signal transmission with the necessary data integrity. In this paper, the impact of ECCs to encode the information on a very deep submicrometer bus on bus power consumption is analyzed. To fulfill this purpose, both the bus wires (with mutual capacitances, drivers, repeaters and receivers) and the encoding-decoding circuitry are accounted for. After a detailed analysis of power dissipation in deep submicrometer fault-tolerant busses using Hamming single ECCs, it is shown that no power saving is possible by choosing among different Hamming codes. A novel scheme, called dual rail, is then proposed. It is shown that dual rail, combined with a proper bus layout, can provide a reduction of energy consumption. In particular, it is shown how the passive elements of the bus (bottom and mutual wire capacitances), active elements of the bus (buffers) and error-correcting circuits contribute to power consumption, and how different tradeoffs can be achieved. The analysis presented in this paper has been performed considering a realistic bus structure, implemented in a standard 0.13-mum CMOS technology.