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RE: Advantages of 3.3V Signaling??

> I am designing a new card, and of course, will use the Universal connector
> and
> make the card compliant with both 5V and 3.3V signaling.  But my question
> is,
> what is the advantage of 3.3V signaling?  Is the goal to eventually to
> also move
> to 3.3V power rails only, and eliminate the 5V power rails, or is that not
> even
> part of the plan?
There are, of course, the usual advantages of 3.3V vs. 5V which include less
power dissipation.

As IC processes continue to shrink, their ability to handle voltages on the
order of 5V and above (for overshoot) becomes severely limited.  Even 3.3V
is difficult if not prohibited in modern IC processes.  The current PCI spec
requires the 3.3V supply because corelogic chips were reaching the point
where they could no longer tolerate 5V levels.

The 3.3V PCI signaling levels are somewhat more optimized with respect to
symmetrical drive levels, noise margins, etc.

3.3V signal levels may be somewhat "quieter" for crosstalk and EMI/RFI,
compared to 5V rail-to-rail levels.

I have not heard of any plans, official or otherwise, to eliminate the 5V
power rail.  However, in five years time I wouldn't be surprised to find
that almost nothing in a PC uses a 5V supply, and there might be pressure
from PC manufacturers to remove that supply rail from their box.