Async FPGA ~2GHz

I'm guessing the third is due to the reduction in frequency.

Cheers,
Jon

Peter Alfke wrote:

>>>As you linearly decrease the voltage you get a cubic improvement in
>>>power consumption. So at 0.6-V we got 400-MHz performance on our
>>>prototype but with an 87 percent reduction in power consumption.
>>
> In my book it is f x C x Vsquared. Where does the third power come
> from?
> Physics is physics, even when it runs asynchronously.

Let's see:

1.93-GHz @ 1.2V
400-MHz  @ 0.6V

(0.4/1.93)*(0.6/1.2)*(0.6/1.2)= 0.052, or 5.2%.

He mentions 13%, but that value will include static Icc,
so it looks like, to a rough first iteration :

(5.2% Dynamic(calc) + 7.8% Static(inferred) = 13%(measured).

Assumed: Thermal equilibrium in their measurements.

However, because MHz has changed a better performance metric is energy.
( "cubic improvement in power consumption" is not the whole story,
as it does come at a cost.. )

ie at 400MHz, it will take 4.825x as long to complete
a multi cycle calculation (assumes a Burst/sleep scheme),
and their Static Icc content has reduced the energy ratio to 0.62725.

[An ideal device with no Static Icc, and following the Physics, would
have an energy ratio of 0.2509]

  If you transfer that energy back to a battery, then the regulator 
choice becomes important.

  Duty cycles and Idle.max ratios also matter, because that sets average
die temperatures and Static Icc will suffer with 'C, and also MHz drops
as well.

-jg

Peter Alfke schrieb:
>>>As you linearly decrease the voltage you get a cubic improvement in
>>>power consumption. So at 0.6-V we got 400-MHz performance on our
>>>prototype but with an 87 percent reduction in power consumption.
>>
> In my book it is f x C x Vsquared. Where does the third power come
> from?
> Physics is physics, even when it runs asynchronously.
> Peter Alfke

LOL.
f_max is a linear function of V. So you really get a cubic improvement
in thermal design power. But of course, you also get less performance.

Actually, who cares about the time the energy is spent in for dynamic
power? What really matters is Joule per operation which is C x V x V.
The number of operations depends on your algorithm. Once you know how
quickly you need a result you can select f to choose the amount of time
you want to spent that energy in.

Kolja Sulimma