I can't read this web page I am linking here too well (it's in some oriental
language) but it has a great illustration of a 'stub' in a RF circuit....
down quite a way on the page...
http://www.rfdh.com/bas_rf/begin/smith6.htm
I understand that Valor detects these features in the circuit and will
notify the CAM operator of their locations in the circuit... Some CAD
systems do this as well.
In Microwave circuits these are used to 'tune' the circuit... in High Speed
design they are typically avoided because of the trouble they cause with
signal integrity.
A stub is loosely defined as an un-terminated transmission line... or one
without a load at the end of it to be driven by a signal... They make great
signal reflectors and can cause havoc with digital signals...
But they are not ALL BAD...In Microwave circuits they can be used
effectively to match the impedance of a transmission line or act as a
printed component of the RF circuit.
I think the item you were reading about where they say to 'avoid stubs' was
related to the bad effects they can have on digital signal integrity.
Best regards,
Bill Brooks - KG6VVP
PCB Design Engineer, C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
Datron World Communications, Inc.
_______________________________________
San Diego Chapter of the IPC Designers Council
Communications Officer, Web Manager
http://dcchapters.ipc.org/SanDiego/
http://pcbwizards.com
-----Original Message-----
From: Dave Seymour [mailto:[log in to unmask]]
Sent: Wednesday, June 08, 2005 7:26 AM
To: [log in to unmask]
Subject: Re: [TN] stubbing in circuit design?
Ken,
When designing a PCB, the engineers talk about "Stubs" as a "T" in the
signal route.
o------------o------------o This is daisy chain.
o------------o-----------o
|
|
|
o This is a "Stub" or "T".
Depending on the frequency ( rising edge) of the signal, reflections could
create false triggering of the circuit.
Stubs are impossible to design out 100%, think about pin escapes, or
wire bonds
on the IC itself. However, the length of the stub is can be critical.
Do some google searches on signal integrity or high speed design.
Hope this helps,
Dave
Dave Simonik wrote:
>Could this be referencing the plated hole wall remaining above the Must Not
>Cut (MNC) layer after Back Drilling on back planes? This is normally
>referred to as the 'Stub'.
>
>Dave Simonik
>Sanmina SCI
>Owego NY Division
>
>-----Original Message-----
>From: Kanaiyalal Patel [mailto:[log in to unmask]]
>Sent: Wednesday, June 08, 2005 9:54 AM
>To: [log in to unmask]
>Subject: stubbing in circuit design?
>
>
>All,
>What is stubbing in PCB circuit design? Can some one
>send me a picture or link to visulize it?
>
>Re,
>Ken Patel
>
>
>
--
Dave Seymour, CID+
Catapult Communications Inc.
800 Perimeter Park Dr, Suite A
Morrisville, NC 27560
Direct: (919)653-4249
Main: (919)653-4180
Fax: (919)653-4297
[log in to unmask]
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