Multiple-valued logic buses for reducing bus energy in low-power systems

The viability of bus interconnection models is explored, using the multiple-valued logic (MVL) paradigm to reduce the cost and energy consumption of off-chip and on-chip address, data and instruction buses within system-on-a-chip platforms. Data can be transferred over the buses using ternary, balanced ternary or quaternary number systems, rather than binary. This allows more compact bus design with a fewer number of bus lines, which can result in lower input/output pin cost for off-chip buses. Reducing the number of bus lines also allows us to increase the distance between the adjacent bus lines using the same silicon area. This further reduces interwire capacitance and may lead to significant on-chip bus energy reduction for low-power embedded systems. First, a combinatorial probabilistic view of digit transition patterns in binary and MVL number systems is provided. This is followed by an empirical study conducted by running various applications to measure bus switching activities as well as total bus energy consumption of real-world applications. It is observed that the number of bus transitions in a multiple-valued bus, particularly in a quaternary bus, is significantly less than the number of bus transitions in a binary bus. Our experimental results show that MVL bus models, replacing the binary equivalent, can be viable interconnection structures and are able to provide up to 29, 29 and 30% reduction in energy consumption for off-chip address, data and instruction buses, respectively. These savings are 55, 53 and 62% for on-chip quaternary address, data and instruction buses, respectively using 0.25 μm technology.