RE: [SI-LIST] : RF Design Question

Kowal, Keith (kowal@cabletron.com)
Fri, 9 Jul 1999 07:39:55 -0400

dave,
I had been involved in some RF designs that every little thing changes
the
EMC profile and other designs that teardropping is a standard practice
(under
125mhz)...
I don't think that a global statement (or rules of thumb) is the right
way to
understand the issue(s). The board construction is extremely important
along
with how the traces are routed. Vias contribute about 1pf or less ( in
my experience )
and should be minimized (if not eliminated) on high freq. clock runs, etc.
So,
anaylize each run and draw you own conclusion. Good clean signals and
lowering
the energy of signal current helps also. Series terminations are usually
better from
the EMC standpoint than AC terminations. There is alot to consider...!
good luck,
keith kowal

> -----Original Message-----
> From: Dave Hoover [SMTP:dhoover@mccurdy.com]
> Sent: Thursday, July 08, 1999 4:55 PM
> To: 'si-list@silab.eng.sun.com'
> Subject: [SI-LIST] : RF Design Question
>
> Hello,
> I'm fairly new to this group and really enjoy
> absorbing as much as I can from here. Being as
> I'm from the PCB fab side, I'm always tantalized
> (YANKED) into the electrical properties side
> of circuits/PCBs. Now I have a question.
> I have a customer (phone card manufacturer) who
> indicates that teardropping trace to pad junctions
> increases the the capacitance enough to completely
> change his EMC characteristics of the trace.
> Can this be so? (Sanity Check time)
> Next, there was ground pours around pads that had
> an octagon shape. We contourized the clearance which
> made it circular. Can this do the same EMC impact?
> In an industry where I've always been told that for
> reliability reasons we should always do the above
> mentioned for DFM. Now......in an RF environment the
> same reliability things change the designed in
> characteristics? I'm lost..........
> Any and all responses will be greatly appreciated.
>
> David Hoover
> Field Application Engineer
>
> McCurdy Circuits
> (714) 974-0401 ext 34
> (714) 974-3596 fax
> dhoover@McCurdy.com
> http://www.mccurdy.com
>
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