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Both dynamic and short-circuit power consumption are dependent on the clock frequency, while the leakage current is dependent on the CPU supply voltage. It has been shown that the energy consumption of a program shows convex energy behavior, meaning that there exists an optimal CPU frequency at which energy consumption is minimal for the work done.
In electronics, leakage is the gradual transfer of electrical energy across a boundary normally viewed as insulating, such as the spontaneous discharge of a charged capacitor, magnetic coupling of a transformer with other components, or flow of current across a transistor in the "off" state or a reverse-polarized diode.
Leakage current has become more and more important as transistor sizes have become smaller and threshold voltage levels are reduced. A decade ago, dynamic power accounted for approximately two-thirds of the total chip power. The power loss due to leakage currents in contemporary CPUs and SoCs tend to dominate the total power consumption.
The amount of power a CPU uses, and thus the amount of heat it dissipates, is the product of this voltage and the current it draws. In modern CPUs, which are CMOS circuits, the current is almost proportional to the clock speed, the CPU drawing almost no current between clock cycles. (See, however, subthreshold leakage.)
The current consumed in the state is commonly called Iddq for Idd (quiescent) and hence the name. Iddq testing uses the principle that in a correctly operating quiescent CMOS digital circuit , there is no static current path between the power supply and ground, except for a small amount of leakage.
The 167-processor AsAP 2 chip enables individual processors to make extremely fast (on the order of 1-2ns) and locally controlled changes to their own supply voltages. Processors connect their local power grid to either a higher (VddHi) or lower (VddLow) supply voltage, or can be cut off entirely from either grid to dramatically cut leakage power.
Specifically, leakage current and threshold voltage do not scale with size, and so the power density increases with scaling. This eventually led to a power density that is too high. This is the "power wall", which caused Intel to cancel Tejas and Jayhawk in 2004. [9] Since around 2005–2007 Dennard scaling appears to have broken down.
This results in balanced propagation delay along different paths converging at the receiving gate. Performance is maintained since it is determined by the time required by the critical path. A higher threshold voltage also reduces the leakage current of a path.