Estimating the power consumption of CMOS adders

Six types of adders are examined in an attempt to model their power dissipation. It is shown that the use of a relatively simple model provides results that are qualitatively accurate, when compared to more sophisticated models and to physical implementations of the circuits. The main discrepancy between the simple model and the physical measurements seems to be the assumption that all gates will consume the same amount of power when they switch, regardless of their fan-in or fanout. Because the carry lookahead adder has several gates with a fan out and fan-in higher than two, the simple model underestimates its power dissipation