RE: gEDA-user: trace calculation[Scanned]

["Robert Thorpe" <Robert.Thorpe@xxxxxxxxxxxx>]

> -----Original Message-----
> From: owner-geda-user@xxxxxxxx 
> [mailto:owner-geda-user@xxxxxxxx] On Behalf Of Dave McGuire
> Sent: 06 January 2006 02:12
> To: geda-user@xxxxxxxx
> Subject: Re: gEDA-user: trace calculation[Scanned]
> 
> On Jan 5, 2006, at 4:27 PM, DJ Delorie wrote:
> >> Isn't tuning trace _lengths_ more important on pcbs than 
> what types 
> >> of corners you're using?
> >
> > On my AMD motherboard, the bus traces have s-shaped wiggles 
> in them to 
> > keep the lengths all the same.  Rounded corners, too.
> 
>    I have several boards from a Cray-1 supercomputer here; 
> they are chock full of such wiggles.  The processor modules 
> in the Cray J90 machines also have those wiggles.  If I can 
> find the motivation (or the
> caffeine) I may take a few pics of them.

If you have a system of transmission lines where the matches at each end
of the lines are very good these little swirls aren't necessary.  If the
matches are poor, then there will be a standing wave across the
transmission line.  This standing wave will change the impedances at the
beginning and end of the line.  Sometimes by varying the length of the
line it's possible to vary these impedances in a useful way.

ISI or filtering of pulse signals can be caused by the same problem.

At least that's my understanding of it.

Rob
Disclaimer: Today, I'm not speaking for anyone.