Why computer chips use low voltage high current supplies?

[usernam]

Why are computer chips now going towards lower voltage and higher current power supplies. It started of arnd 5V and nowadays it is 3.3 V and I think they want to reduce it still further.
Is there some advantage from using a lower voltage to supply the chips?

 

[checkmate]

Re: Why computer chips use low voltage high current supplies

The main reason is to reduce power consumption. For IC design, as we try to pack more and more transistors into a limited space, the heat density increases. My prof once mentioned that the core of modern processors have a heat density higher than that of the surface of the sun. So a lower Vdd is required to prevent meltdown.

 

[usernam]

But ultimately the processors need the same amount of power to operate. So reducing Vdd means we have to increase I to ensure that the processor's are working. So either way we still lose the same amount of power in the form of heat.
How does reducing Vdd make any difference.

 

[checkmate]

Re: Why computer chips use low voltage high current supplies

And whichever ultimate being gave you the idea that processors (transistors to be more exact) are constant power devices? Does it mean that P=VI is constant, therefore the new transistor law is V=P/I?

CMOS circuits are known to be low power as there is little leakage current when the transistor is in a high or low state. Most power dissipation occurs during the transition state, known as dynamic dissipation. It involves mostly the charging and discharging of gate capacitances. For a hypothetical capacitance C, changing at a frequency f, the power dissipated can be simplified as P=fCVdd^2. You can easily see that increasing operating frequency also increases power. That is why centrino processors are clocked lower for the purpose of longer battery lives. It is also obvious that increasing Vdd is even worse as it is squared.

And to answer your 2nd question, the reason why modern processors consume so much more power than before, is simply because they have more transistors packed in them.

On the other hand, transistors have threshold voltages. Reducing Vdd too much may bring operating voltages dangerously close to threshold voltages, and transistor switching would then be unreliable. That is why when geeks overclock PCs, increasing Vdd is one of the ways to maintain system stability. It's also one of the ways to fry an egg with a processor.

 

[mdcui]

Re: Why computer chips use low voltage high current supplies

to put it simple, high current in mordern processor is inevitable because of a couple of reasons

1. to make transistors fater, threshold should be lowered, and gate oxide is thinner to get high gm, which cause a big subthreshold current and gate lekage current
2. the amount of logic gates increased drastically, and clk frequency increased to giga Hz, which cause lots of parasitic cap charge/discharge curernt and short current (current through both P and N device during logic toggling)

since we can not void such big current, we have to lower voltage to reduce power, that is make every charge/discharge consumes less energy and let the leakage current smaller.

 

[SkyHigh]

Re: Why computer chips use low voltage high current supplies

usernam

Why are computer chips now going towards lower voltage and higher current power supplies. It started of arnd 5V and nowadays it is 3.3 V and I think they want to reduce it still further.
Is there some advantage from using a lower voltage to supply the chips?

Computer chips using CMOS don't use higher current power supplies. However saying computer chips using CMOS that uses low voltage is correct.

To others

Since when computer chip uses high current?
I am seeing many people here spouting nonsenses by dumping correct engineering principles about power consumption but incorrectly used to support nonsensical claims!

Top-notch researchers at leading institutes like IBM, Motorola, Intel, AMD, Infineon, Philips, STMicro, etc are not stupid! They know IR drop, non-ideal return path, common-mode radiation, Simultaneous Switching Noise and etc, therefore using high current is never practical.

Please! Stop using theoretical principles to support nonsensical claims. This is a mockery to Electrical and Electronic Engineering.

Luckily some of you here are not born to become surgeons or doctors, else I can't imagine what kind of casualties will happen.[/quote]

 

[yjkwon57]

Re: Why computer chips use low voltage high current supplies

Hi, there.

As semiconductor technologies evolves, critical dimensions of transistor and other components are continuously decreased. This is why they should use low voltages for Vdd. And, since requirements for chips is increased for a higher functionality, a higher performance, a lower system implementation, and a higher system reliability, the number of transistors in a single (high-end) chip is continuously increasing. Higher transistors in a chip, generally higher current required by the chip, which cause the current consumption of the chip higher. I think that's it.

 

[SkyHigh]

Re: Why computer chips use low voltage high current supplies

Nope.

Scaling of devices and scaling of supply voltage Vdd, not a doubt in VLSI and towards low power, but it doesn't mean high current. Current gets scaled indirectly due to the scaling of device dimension, interconnect dimension and supply voltage because of Id = (KW/2L)(Vgs-Vt)² in Saturation which is a voltage-controlled source, where K is µ.Cox and Cox is ε/tox.

Since tox, Vt, Vgs, W and L are scaled according, Id is indirectly scaled too. Since Vgs is switched either to 0V or Vdd, Vgs is scaled too. Vt is scaled to ensure low leakage. tox is scaled to prevent oxide breakdown.

Low power means electronics below 5V and less than 100mA, giving less than 500mW.

There is no such thing as current becomes larger or high current is used in VLSI. This is a joke made by those nonsensical claims trying to get away by quoting correct principles.

 

[yjkwon57]

Re: Why computer chips use low voltage high current supplies

High SkyHigh.

I said "Higher transistors in a chip, generally higher current required by the chip, which cause the current consumption of the chip higher."

You said "There is no such thing as current becomes larger or high current is used in VLSI. This is a joke made by those nonsensical claims trying to get away by quoting correct principles."

Say, the average energy consumptions per clock and per gate for a previous and current design rules and device parameters is Ep and Ec, respectively. Then, it is evident that Ec < Ep. Nowdays, there are two general trends for high-ends chips: one is the high integration rate and the other is the high clock rate. A current chip will have much more gates and require higher clock rate than a previous chip.

You know, an efficient worker having more things to work will be more tired than an inefficient worker having less things to work, accoding to the work amounts between two workers.

Do you still need some mathematical proof?