Geronimo Stempovski wrote:
> Hi all,
> 
> I wonder what is curently state-of-the art in serial high-speed transmission
> and what are the prevailing data rates? I know about some SerDes in the
> gigabit-per-second range but I cannot imagine if 10 Gbps are really a
> challenge or the applied method or if it's 1 Gbps (or something in
> between)...?
> I recently heard about some 60 GHz in the mobile communication sector and 10
> Gbit Ethernet but as far as I know there are those multi-level modulation
> methods (like QAM for example) that are able to provide 10 Gbit bandwidth
> with a bitrate of some Mbps (is that correct?).
> I'm not interested so much in those higher modulation methods (nor in
> optical transmission) but in the baseband communication where bitrate =
> clockrate, i.e. the line rate. What can be efficiently transmitted today
> electrically (over wire or PCB)? What is the prevailing technology of those
> circuits, is it CMOS or are there alternatives?
> I am a senior electrical engineer and unfortunately did not manage to keep
> up-to-date. After googling all night I'm really depressed because I finally
> couldn't find an unambiguous answer.
> Maybe some guys in the silicon-business or practitioners know the anser and
> are willing to share there knoledge with me?
> 
> Best regards
> Geronimo
> 
> 

In terms of bitrates, then I designed a board with serial links at 5Gb/s 
*per pair* a couple of years ago. Before that I designed some switches 
and gateways with 2.5Gb/s pairs (lots and lots of them). PCI Express has 
just released the 5Gb/s signalling revision (within the last month or 
so, I believe). The things I designed a few years ago were Infiniband 
(my name is actually one of many on the latest spec).

Over FR4 (or other materials less than totally exotic) 5Gb/s is about 
the most you'll get except for _very_ short runs, and as Joel notes 
everything's a transmission line at those rates. I've seen 2.5Gb/s 
Infiniband on a 4x cable (4 pairs in each direction) achieve 10 metres 
within the signalling budget. At 5Gb/s things are more difficult.

10G ethernet is actually 4 signals, incidentally.

So state of the art in terms of practical, shipping and costs less than 
a trip to the moon is currently in the 5Gb/s per pair range.

Cheers

PeteS