[SI-LIST] Re: High speed serial links over copper cables
- From: olaney@xxxxxxxx
- To: jhasson@xxxxxxxxxxxxxxxxxxx
- Date: Mon, 20 Jul 2009 09:04:18 -0700
"how come only video field seems to have developed high speed single
ended video transmission?"
Video has been with us since before WWII, and video often has to go long
distances. This is why the industry evolved using 75 ohm coax (lowest
loss point) which can be had for a reasonable cost. The ineluctable fact
of every technology transition in the video industry is the economic
incentive of using already installed cabling, so each new generation has
retained the 75 ohm standard of the previous one. Visit a studio and
you'll see massive bundles of coax running everywhere. The coax just
keeps getting better to handle higher bandwidths. All things considered
it is a very adequate standard and there is no incentive to change.
There are times I've designed in a balun function between a differential
driver and a coax line to take advantage of coax transmission over
distance. A great deal of balanced transmission seems driven by simple
extension of what's provided at the driver chip rather than measured
consideration of what is optimal for the system.
Orin Laney
On Mon, 20 Jul 2009 09:05:47 +0200 jhasson@xxxxxxxxxxxxxxxxxxx writes:
> Hi,
> I have been looking at the possibility of setting up a high speed
> (about
> 2.5Gbit/s) serial link over a 10 m copper cable. In order to reduce
> weight
> and number of cables, a focus was given to single ended options. The
>
> standard that comes up is SMPTE424M running at up to 2.97Gbit/s over
> a
> long (much more than 10 m) 1694A belden coaxial cable. I would like
> to be
> able to use the physical layer but not to transmit video. Is there a
>
> drawback in using chips for SPMTE424M while for instance using the
> 8B/10B
> encoding instead of SMPTE scrambling ? I would not encounter the
> pathological data (the standard DC blocking capacitor could be
> reconsidered) then but are there any tricks to consider that would
> impact
> the link ? As a more general question, how come only video field
> seems to
> have developped high speed single ended video transmission ?
>
> Best regards,
>
> JF
>
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