[SI-LIST] Re: risetime effects of plane breaks
- From: Doug Smith <doug@xxxxxxxxxx>
- To: Chris.Cheng@xxxxxxxxxxxx
- Date: Fri, 14 Jan 2005 22:17:31 -0800
Hi Chris,
The stack-up is:
signal
split plane
split plane
The experiment I did yesterday in class was (using tape to close one gap)
signal
split plane
solid plane
Doug
Chris Cheng wrote:
> Doug,
> Just try to understand your new stack up,
> is it :
> signal-splitplane-solid plane
> or
> splitplane-signal-solid plane ?
>
> -----Original Message-----
> From: Doug Smith [mailto:doug@xxxxxxxxxx]
> Sent: Friday, January 14, 2005 3:17 PM
> To: weirsp@xxxxxxxxxx
> Cc: emcesd2000@xxxxxxxxx; SI-List
> Subject: [SI-LIST] Re: risetime effects of plane breaks
>
>
> Wow! I didn't realize my little article would stimulate so many
> postings. Having a good discussion like this is good for us all.
>
> While teaching a seminar in San Diego yesterday I did a slight
> modification of the split plane board I used for my article this
> month. I covered the bottom plane split (opposite signal wire with
> copper tape and measured the ESD immunity via radiation from an ESD
> event. This was the first time for this setup and live for the class.
> I scoured the tape many times to make sure connection was made through
> the "conductive" adhesive.
>
> The immunity was significantly worst (0.5 Volts induced in path) than
> the path over solid plane (0.1 Volt) and better than the path where
> both planes were cut (1.5 Volts induced EMI).
>
> Doug
>
> For the 30 or so mil plane spacing of the board
>
> steve weir wrote:
>
>>Oscar, yes, it is quite a dramatic effect isn't it? I suspect that when
>>Lee says "it depends on how you do it" he has another contiguous plane, ie
>
>
>>ground underneath the split as opposed to a split on all planes as in
>>Doug's experiment. Assuming lots of decoupling between each of the
>
> islands
>
>>and the common ground plane the jump in coupling between lines would be
>>greatly suppressed.
>>
>>Regards,
>>
>>
>>Steve.
>>
>>At 11:00 AM 1/10/2005 -0800, Ahmad Fallah wrote:
>>
>>
>>>Hi Steve,
>>>
>>>I have repeated Doug's experiment with a modified fixture where an
>>>additional trace (victim) was added near (~1 cm) the "signal" line for
>>>X-talk measurements. I have measured a 10-fold increase in x-talk
>>>amplitude in going from Case 1 to Case 2.
>>>
>>>Case 1: the offending and victim lines are both drawn over a solid return
>>>plane.
>>>Case 2: the offending and victim lines are both drawn over the cut in the
>>>return plane
>>>
>>>Regards,
>>>
>>>Oscar
>>>
>>>
>>>
>>>steve weir <weirsp@xxxxxxxxxx> wrote:
>>>
>>>Lee, the 5cm is the length of the break. The break is only about 20-50mils
>>>wide. Hit the link and scroll to Figure 3. In Doug's test set-up, both of
>>>the two planes have been broken. Now, If one cares to do a crosstalk test,
>>>it looks like Doug could modify his fixture rather easily to do that. In
>>>the vicinity of the break, the multiple line coupling, including between
>>>members of a diff pair jumps.
>>>
>>>
>>>
>>>
>>>
>>>If you want to perform an entertaining experiment, take a diff pair, or
>>>just one active driver and a quiet line and route them over a narrow, and
>>>short break, say 0.25" by 0.02" and take four port S parameter
>>>measurements. Take another pair and do likewise, but keep extending the
>>>length of the slot, ie perpendicular to the traces by a factor of 2 with
>>>each test. Even though the width of the gap is short, by the time that
>>>slot becomes an inch or two long the band of frequencies where coupling is
>>>fairly strong will be pretty wide.
>>>
>>>http://emcesd.com/tt2005/tt010105.htm
>>>
>>>Regards,
>>>
>>>Steve
>>>
>>>
>>>At 04:30 PM 1/9/2005 -0800, Lee Ritchey wrote:
>>>
>>>
>>>>Just noticed that you call a 5 cm break relatively small. Does that mean
>>>>5 cm in width?
>>>>
>>>>Lee W. Ritchey
>>>>Speeding Edge
>>>>P. O. Box 2194
>>>>Glen Ellen, CA 95442
>>>>Phone- 707-568-3983
>>>>FAX- 707-568-3504
>>>>
>>>>I just used the energy it took to be angry to write some blues.
>>>>Count Basie
>>>>
>>>>
>>>>
>>>>
>>>>>[Original Message]
>>>>>From: Doug Smith
>>>>>To: SI-List
>>>>>Date: 1/8/2005 5:23:26 PM
>>>>>Subject: [SI-LIST] risetime effects of plane breaks
>>>>>
>>>>>I think most of us know not to route signals over plane breaks on PWBs
>>>>>as all kinds of bad things can happen when this occurs in a layout.
>>>>>But, how do you convince co-workers or your boss that a new design
>>>>>needs to avoid doing this even if added expense or project delay is
>>>>>required? Experimental data can be the key and this month my Technical
>>>>>Tidbit shows what happens to signal risetime if the signal crosses a
>>>>>plane break.
>>>>>
>>>>>Crossing Ground Plane Breaks - Part 4
>>>>>Risetime Effects on Signals
>>>>>
>>>>>Abstract: Signals that cross ground plane breaks on printed wiring
>>>>>boards (PWBs) experience degradation as well as cause EMI problems.
>>>>>Significant degradation of signal risetime is shown to occur, even
>>>>>with a relatively small ground break of five cm at risetimes on the
>>>>>order of 300 ps.
>>>>>
>>>>>The link to the article is the picture of the experimental test setup
>>>>>at the bottom of the home page at http://emcesd.com .
>>>>>
>>>>>Doug
>>>>>--
>>>>>-------------------------------------------------------
>>>>>___ _ Doug Smith
>>>>>\ / ) P.O. Box 1457
>>>>>========= Los Gatos, CA 95031-1457
>>>>>_ / \ / \ _ TEL/FAX: 408-356-4186/358-3799
>>>>>/ /\ \ ] / /\ \ Mobile: 408-858-4528
>>>>>| q-----( ) | o | Email: doug@xxxxxxxxxx
>>>>>\ _ / ] \ _ / Website: http://www.dsmith.org
>>>>>-------------------------------------------------------
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>>
>>
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>
>
--
-------------------------------------------------------
___ _ Doug Smith
\ / ) P.O. Box 1457
========= Los Gatos, CA 95031-1457
_ / \ / \ _ TEL/FAX: 408-356-4186/358-3799
/ /\ \ ] / /\ \ Mobile: 408-858-4528
| q-----( ) | o | Email: doug@xxxxxxxxxx
\ _ / ] \ _ / Website: http://www.dsmith.org
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