[email protected] 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.


Optical stuff is still single-ended.  :)

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.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.




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