Logic Analysers

Tony Duell ard.p850ug1 at gmail.com
Fri Feb 3 13:43:58 CST 2017

On Fri, Feb 3, 2017 at 7:35 PM, Mouse <mouse at rodents-montreal.org> wrote:
>>> the propagation delay as the signal gets to each pin (remember a
>>> foot is about a nanosecond.  [...])
> Not really.  A foot is about a light-nanosecond, yes, but
> high-frequency signals in copper travel by skin effect, moving
> significantly more slowly - somewhere around .6c, I think it is.

It's not really the skin effect that matters here. It's the dielectric
medium that surrounds the conductors that effectively slows the
fields down.

But that's why I said 'about'. I am doing order-of-magnitude calculations,
not trying to design a delay line. I would estimate that between adjacent
ICs on the same board you'd get a delay measured in 10's or 100's of
picoseconds. That sort of order. So a 25MHz logic analyser, with an
effective time resolution of 40ns (if that) is not going to show it.

There is no way you're going to get delays of 40ns between adjacent
ICs on any reasonable PCB.

> It's still on the general order of c, mind you; for the purposes of
> this discussion, c and .5c - even .1c - are much the same.



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