Interesting to see RF matters on the screen. Too seldom announced.
I'll ask Steve to hang a pic of an old
board on the Wall. You see only a small fraction of the board,
which is nearly one sq foot. There you can see both stubs and flags and couplers and other
fun things. Today, we put the main part of these things on the chip level and try
to minimize tuning on the board. Tuning by cutting stubs and soldering copper stripes are
nowadays more and more superseded by using intelligent software. I remember the days when
I tuned waveguide filters with up to 25 tuning screws. Took one hour to tune one single
filter...if you were skilled. Then you had to seal carefully all screws and paint the
whole thing with a nice grey enamel.
Ingemar Hernefjord
Ericsson Microwaves Systems
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Kanaiyalal Patel
Sent: den 8 juni 2005 17:47
To: [log in to unmask]
Subject: Re: [TN] stubbing in circuit design?
Thanks Bill. You cleared my question.
Re,
Ken Patel
--- "Brooks,Bill" <[log in to unmask]> wrote:
> 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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