RE: [SI-LIST] : 90-45 crnrs - used to be MECL System Design Handbook

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From: Marc Humphreys (mhumphreys@axiowave.com)
Date: Fri May 11 2001 - 16:17:46 PDT


Not to say that routing edge coupled diff pairs (the new trend)
really gave the routers a run for their (our) money on keeping
those radiused corners evenly spaced. Usually resort to having to manualy
cut and paste arcs on the inside or outside corner, whichever
wasn't the length/radius default. We bagged it and stuck with 45's.

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Dunbar, Tony
Sent: Friday, May 11, 2001 1:08 PM
To: 'SI-List'
Subject: RE: [SI-LIST] : 90-45 crnrs - used to be MECL System Design
Handbook

Back in the days when one's heart rate was faster than any of the clocks on
a board, didn't 45deg corners come about mainly to address the problem of
"acid traps"? No 70s and Woodstock jokes, please!

And then in the early 80s, didn't the capability to do radiused corners in
general (note, I put 'general', not RF, etc.) layout CAD tools proliferate
because one vendor did it either as a gimmick or to win a particular
benchmark? Then all had to do it because it was considered trendy; it would
never be used because it clogged up the routing algorithms and didn't
provide any performance advantages, but it looked pretty.

Tony

-----Original Message-----
From: david_instone@uk.xyratex.com [mailto:david_instone@uk.xyratex.com]
Sent: Friday, May 11, 2001 10:33 AM
To: cadpro2k@dacafe.com
Cc: David Instone; si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] : MECL System Design Handbook

Mitch,
  Thanks, yes, I know allegro can do radiused corners, use it all the
time. What I was referring too was a sharp 90 on the inside of the bend
and the outside of the bend cut off at 45 deg. Means you can't plot
that trace all in one go.

Don't know about whether its necessary at gbaud frequencies but our PCB
guys have got so skilled at radii and curves they can layout edge
coupled differential traces with no problem at all.

Dave

cadpro2k@dacafe.com wrote:
>
> Hi all,
>
> David, allegro can do radius'd traces relatively easy. I've had the
> opportunity to do them once or twice, and didn't have a problem. The
> problem I do have with any cad tool is to do "chamfer'd" corners. But
> then, at what speed do I need them? Answer me that and I might buy your
> property in the everglades. :) The times I've done the radius'd corners
> was on analog boards where the engineer was incredibly finicky with the
> copper geometries, and I was sure not to let many people know how easy
> it was to do. Again, what speeds is this necessary? (Got more property
> in the everglades?) I've worked on boards (layout) running at 10Ghz and
> they still were doing 45 degree geometries. The boards running at 40Ghz
> had more problems than just copper geometries.
>
> Best of luck out there.
>
> Mitch
> (No, I'm not from Florida :)
>
> ---------Included Message----------
> > From: "David Instone" <david_instone@uk.xyratex.com>
> > Subject: Re: [SI-LIST] : MECL System Design Handbook
> >
> > Scott,
> > What CAD tools do you have in mind? As far as I know the
> > Cadence/Allegro PCB layout software for one does not, unless of
> course
> > there is a little known command to make it do so. Then of course
> you
> > are dependent on the layout to gerber conversion. Remember most
> lines
> (snip)
>
> > Scott McMorrow wrote:
> (snip)
> > > a little extra CAD effort. Radiused bends can be used, but
> they
> > > are extremely difficult to perform in most CAD systems. They
> should
> > > be avoided.
> _____________________________________________________________
> Tired of limited space on Yahoo and Hotmail?
> Free 100 Meg email account available at http://www.dacafe.com

-- 
Regards

Dave Instone. Compliance Engineer Storage Systems Development, MP24/22 Xyratex, Langstone Rd., Havant, Hampshire, P09 1SA, UK. Tel: +44 (0)23-92-496862 (direct line) Fax: +44 (0)23-92-496014 http://www.xyratex.com Tel: +44 (0)23-92-496000

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