Logical irreversibility will be an important factor to consider in nanocircuits, which reach gate density and operating frequency in the regime of the recently experimentally proven Landauer's Principle. The resulting heat density will limit the performance of classical digital circuits implemented with nanoscale components, when other heat factors are minimized, as in the predicted highly energy-efficient emerging technologies. We demonstrate this effect by calculating the expected logic and heat densities of various computer arithmetic units proposed for quantum-dot cellular automata, which is a computing paradigm offering molecular implementations and ultra-high signal energy conservation. The predicted worst case maximum operating frequencies are one or two orders of magnitude lower than the inherent technology switching rate of the molecular implementations, but increasing the degree of logical reversiblity may alleviate the problem. These results confirm that circuit design for the emerging technologies must account for irreversibility and the Landauer's Principle, which governs all high density and high energy-efficency post-CMOS technologies.
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