Power is measured in Watts and P = V x I = E x f

Gate current I = Static Current (leakage) + Dynamic Current.

Early CMOS (VCC 5 volts): negligible static current,

but today at VCC of 1.3 volts it's up to 30 percent of consumption.

Dynamic current = Short circuit current + Dynamic charge current.

Dynamic charge current computation: - All energy in a net/gates is wasted each time it goes from one to zero.
- The energy in a capacitor is E = CV^2/2.
- Dominant capacitance is proportional to net length.
- Gate input and output capacitance also contribute to C.
Activity ratio, a: percentage of clock cycles that see a transition from 0 to 1. The net toggle rate = Clock frequency x activity ratio = f x a. For leakage and short circuit power see cell library. |

Further details: »Power Management in CPU Design.

11: (C) 2008-13, DJ Greaves, University of Cambridge, Computer Laboratory. |