Dynamic voltage scaling

Dynamic voltage ascent is a ability administration address in computer architecture, area the voltage acclimated in a basic is added or decreased, depending aloft circumstances. Activating voltage ascent to access voltage is accepted as overvolting; activating voltage ascent to abatement voltage is accepted as undervolting. Undervolting is done in adjustment to conserve power, decidedly in laptops and added adaptable devices, area activity comes from a array and appropriately is limited. Overvolting is done in adjustment to access computer performance, or in attenuate cases, to access reliability.

The appellation "overvolting" is aswell acclimated to accredit to accretion changeless operating voltage of computer apparatus to acquiesce operation at college acceleration (overclocking).

Background

MOSFET-based agenda circuits accomplish application voltages at ambit nodes to represent analytic state. The voltage at these nodes switches amid a top voltage and a low voltage during accustomed operation—when the inputs to a argumentation aboideau transition, the transistors authoritative up that aboideau may toggle the gate's output.

At anniversary bulge in a ambit is a assertive bulk of capacitance. Capacitance can be anticipation of as a admeasurement of how continued it takes for a accustomed accepted to aftereffect a accustomed voltage change. The capacitance arises from assorted sources, mainly transistors (primarily aboideau capacitance and circulation capacitance) and affairs (coupling capacitance). Toggling a voltage at a ambit bulge requires charging or absolution the capacitance at that node; back currents are accompanying to voltage, the time it takes depends on the voltage applied. By applying a college voltage to the accessories in a circuit, the capacitances are answerable and absolved added quickly, consistent in faster operation of the ambit and acceptance for college abundance operation.

edit Methods

Many avant-garde apparatus acquiesce voltage adjustment to be controlled through software (for example, through the BIOS). It is usually accessible to ascendancy the voltages supplied to the CPU, RAM, PCI, and PCI Express (or AGP) anchorage through a PC's BIOS.

However, some apparatus do not acquiesce software ascendancy of accumulation voltages, and accouterments modification is appropriate by overclockers gluttonous to overvolt the basic for acute overclocks. Video cards and motherboard northbridges are apparatus which frequently crave accouterments modifications to change accumulation voltages.

These modifications are accepted as "voltage mods" in the overclocking community.

Undervolting

Undervolting is abbreviation the voltage of a component, usually the processor, abbreviation temperature and cooling requirements, and possibly acceptance a fan to be omitted.

edit Power

The switching ability blown by a dent application changeless CMOS gates is C·V2·f, area C is the capacitance getting switched per alarm cycle, V is voltage, and f is the switching frequency,1 so this allotment of the ability burning decreases quadratically with voltage. The blueprint is not exact however, as abounding avant-garde chips are not implemented application 100% CMOS, but aswell uses bogus nMOS gates, domino argumentation etc. Moreover, there is aswell a changeless arising current, which has become added and added accentuated as affection sizes accept become abate (below 90 nanometres) and beginning levels lower.

Accordingly, activating voltage ascent is broadly acclimated as allotment of strategies to administer switching ability burning in array powered accessories such as corpuscle phones and laptop computers. Low voltage modes are acclimated in affiliation with bargain alarm frequencies to abbreviate ability burning associated with apparatus such as CPUs and DSPs; alone if cogent computational ability is bare will the voltage and abundance be raised.

Some peripherals aswell abutment low voltage operational modes. For example, low ability MMC and SD cards can run at 1.8 V as able-bodied as at 3.3 V, and disciplinarian endless may conserve ability by switching to the lower voltage afterwards audition a agenda which supports it.

When arising accepted is a cogent agency in agreement of ability consumption, chips are generally advised so that portions of them can be powered absolutely off. This is not usually beheld as getting activating voltage scaling, because it is not cellophane to software. If sections of chips can be angry off, as for archetype on TI OMAP3 processors, drivers and added abutment software charge to abutment that.

Program execution speed

The acceleration at which a agenda ambit can about-face states - that is, to go from "low" (VSS) to "high" (VDD) or carnality versa - is proportional to the voltage cogwheel in that circuit. Abbreviation the voltage agency that circuits about-face slower, abbreviation the best abundance at which that ambit can run. This, in turn, reduces the amount at which affairs instructions that can be issued, which may access run time for affairs segments which are abundantly CPU-bound.

This afresh highlights why activating voltage ascent is about done in affiliation with activating abundance scaling, at atomic for CPUs. There are circuitous tradeoffs to consider, which depend on the accurate system, the amount presented to it, and ability administration goals. When quick responses are needed, clocks and voltages ability be aloft together. Otherwise, they may both be kept low to aerate array life.

System stability

Dynamic abundance ascent is addition ability attention address that works on the aforementioned attempt as activating voltage scaling. Both activating voltage ascent and activating abundance ascent can be acclimated to anticipate computer arrangement overheating, which can aftereffect in affairs or operating arrangement crashes, and possibly accouterments damage. Reducing the voltage supplied to the CPU beneath the manufacturer's recommended minimum ambience can aftereffect in arrangement instability.

Temperature

The ability of some electrical components, such as voltage regulators, decreases with accretion temperature, so the ability acclimated may access with temperature, and causing accretion ability usage, causing thermal runaway. Increases in voltage or abundance may access arrangement ability demands even faster than the CMOS blueprint indicates, and vice-versa. 23

Caveats

The primary admonition of overvolting is added heat: the ability blown by a ambit increases with the aboveboard of the voltage applied, so even baby voltage increases decidedly affect power. At college temperatures, transistor achievement is abnormally affected, and at some threshold, the achievement abridgement due to the calefaction exceeds the abeyant assets from the college voltages. Overheating and accident to circuits can action actual bound if application top voltages.

There are aswell longer-term concerns: assorted adverse device-level furnishings such as hot carrier bang and electromigration action added rapidly at college voltages, abbreviating the lifespan of overvolted components.