On 02/07/2012 05:58 AM, Hal Murray wrote:
mag...@rubidium.dyndns.org said:
Oh... nothing really beats "it's what customers traditionally asks for"
Squarewave out provides high slew-rate which reduces the effect of
additional noise.
Right. But if you have a single frequency you can easily filter out most of
the noise.
-----------
As clock speed has increased over the years, a new field has emerged. A good
name is signal integrity. That covers clock distribution, data distribution,
and power supply bypassing/regulation/decoupling. It's basically all the
analog stuff needed to make digital logic work in the real world.
The technology for distributing more bits is also useful for reducing
noise/jitter.
There are whole families of chips for clock distribution. Many include PLLs which can
correct for trace length, make other frequencies, and/or do the spread spectrum thing to
"reduce" EMI. The ones I'm familiar with are targeted at digital applications.
Jitter within a small fraction of a bit cell is fine. The target market doesn't care
about time-nut class super clean clocks.
There are other families of chips (or parts of big chips) for driving/receiving
clocks and data between boards/boxes. Most of those are now differential so I
assume twisted pair is cheaper than coax. SATA between your motherboard and
hard disk is a good example. It runs at 1.5, 3, or 6 gigabits/second. Wiki
says up to 1 meter.
If you want a good example of the technology in this area, check out gigabit
ethernet over CAT5. It's 5 level encoding (2 bits/baud) at 125 megabaud/sec
over 4 pair in both directions over each pair.
Twisting my pre and post emphasis and receiver equalizers on the
multi-gigabit links... yes. An upswing for TDR/TDTs as well.
Optical stuff is still single-ended. :)
Well, you do not access the carriers directly as with electrical
signals, but different polarity of signal still exists.
There are some very low cost optical links for distribution of audio. The key
idea is to use plastic rather than glass. Bandwidth is limited but cost is low.
Oh, those horrid links creates a bundle of reflections and dispersion,
causing a greater need of compensation, something which is never given
as treatment. A multimode glass fibre would be a better choice, as the
components are cheap now. Even single mode 1310 nm is fairly cheap now.
Cheers,
Magnus
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