Dynamic voltage scaling
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Dynamic voltage scaling is a power management technique in computer architecture, where a component is run at a less-than-maximum voltage in order to conserve power. Dynamic voltage scaling is most commonly used in laptops and other mobile devices, where energy comes from a battery and thus is limited.
The switching power dissipated by a chip using static CMOS gates is C·V2·f, where C is the capacitance being switched per clock cycle, V is voltage, and f is the switching frequency,[1] so this part of the power consumption decreases quadratically with voltage. The formula is not exact however, as many modern chips are not implemented using 100% CMOS, but also uses pseudo nMOS gates, domino logic etc. Moreover, there is also a static leakage current, which has become more and more accentuated as feature sizes has become smaller and threshold levels lower.
Dynamic frequency scaling is another power conservation technique that works on the same principles as dynamic voltage scaling. Both dynamic voltage scaling and dynamic frequency scaling can be used to prevent computer system overheating, which can result in program or operating system crashes, and possibly hardware damage.
The speed at which a digital circuit can switch states - that is, to go from "low" (VDD) to "high" (VSS) or vice versa - is proportional to the voltage differential in that circuit. Reducing the voltage means that circuits switch slower, reducing the maximum frequency at which that circuit can run. This, in turn, reduces the rate at which program instructions that can be issued, increasing program runtime.
The efficiency of some electrical components, such as voltage regulators, decreases with increasing temperature, so the power used may increase with temperature. Since increasing power use may increase the temperature, increases in voltage or frequency may increase system power demands even faster than the CMOS formula indicates, and vice-versa. [2][3]
[edit] References
- ^ J. M. Rabaey. Digital Integrated Circuits. Prentice Hall, 1996.
- ^ Mike Chin. Asus EN9600GT Silent Edition Graphics Card. Silent PC Review. Retrieved on 2008-04-21.
- ^ MIke Chin. 80 Plus expands podium for Bronze, Silver & Gold. Silent PC Review. Retrieved on 2008-04-21.
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