Re: Alternative Concept

Amit Kucheria
2007-03-20T14:26:00Z

On 3/20/07, David Brownell <david-b@pacbell.net> wrote:
> On Monday 19 March 2007 7:12 am, Scott E. Preece wrote:
> >
> > Could you guys present a clear definition of exactly what you mean by
> > "clock domain" and "power domain"? I can think of several different ways
> > to interpret the phrases, and I'd like to end up with the same meaning
> > that you are arguing from...
>
> A set of devices that use the same power supply or clock are
> in the same "power domain" or "clock domain" (respectively).
>
> The domains will often be hierarchical, e.g. a base clock
> rooting other clocks, derived from it by dividers, PLL,
> or clock gates.
>
> Sometimes domains overlap ... e.g. a controller that needs
> to use one logic level for on-chip logic and another for the
> external interface; or similarly, different clock rates.
>
> Simple chips may not have many domains. Nowadays I think
> most SOCs have at least a decent selection of clock domains,
> to eliminate the power drain involved in driving transistors
> through clock ticks. I understand it's more complicated to
> have multiple power domains, but the incentive to shrink the
> leakage current is strong. (So adding on-chip power domains
> involves tricks to constrain leakage, and not just an ability
> to operate without a given power rail.)

For the sake of completeness, there is also the Voltage domain. A
groups of modules supplied by the same regulator would belong to a
single Voltage domain. Multiple voltage domains allow independent
scaling of voltages to different domains.
--
Amit Kucheria, Nokia