Common Mistakes in Adiabatic Logic Design and How to Avoid Them

Most so-called “adiabatic” digital logic circuit families reported in the low-power design literature are actually not truly adiabatic, in that they do not satisfy the general definition of adiabatic physical processes, as ones whose energy dissipation tends towards zero as their speed and/or parasitic interactions are decreased. Yet, the need for truly adiabatic design can be proven to be a key requirement for cost-efficient digital design for the majority of general-purpose computing applications in the long run, as technology advances and power dissipation becomes an increasingly stringent limiting factor on system performance. Although they may remain useful for some specialized applications, all of these only semi-adiabatic logic styles (as well as all non-adiabatic logics) are doomed to eventual irrelevance to the bulk of the computing market, most likely within only a few decades. It therefore behooves us to begin emphasizing today how to design truly adiabatic circuits. In this paper, I describe the most common departures from true adiabaticity in the logic designs that have been published to date, and discuss how these problems can be avoided in the future. The most common problems are: (1) use of diodes, (2) turning off transistors when there is nonzero current across them, (3) failure of the design style to accommodate arbitrarily much logical reversibility, which can be proven to be required to approach truly adiabatic operation, and (4) failure to accommodate the asymptotically most cost-efficient possible circuit algorithms, in terms of both hardware-