Re: [SI-LIST] : Matched Length Traces

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From: Ritchey Lee (leeritchey@earthlink.net)
Date: Fri Nov 24 2000 - 07:47:12 PST


What happens between segments of a serpentine structure results from the mutual
inductance that exists between any two wires or metal structures that are near
each other. One flavor of this is cross talk. That's basically what is at work
in this case.

If you want to explore this more, get a microwave engineering test and explore
how to create bandpass filters by placing segments side by side.

Hope helps.

Lee

Chan, Michael wrote:

> Lee:
> Can you explain what is the physic behind your second statement below
> even though it is true? Thanks.
>
> MChan
>
> -----Original Message-----
> From: Ritchey Lee [mailto:leeritchey@earthlink.net]
> Sent: Wednesday, November 22, 2000 11:38 AM
> To: Andrew W. Riley III
> Cc: SI LIST
> Subject: Re: [SI-LIST] : Matched Length Traces
>
> Traces that loop back on each other don't turn into antennas any more
> than traces that are straight. The antenna effect happens only when the
> underlyig plane is removed.
>
> The bigger issue with this serpentine routing is that the segments
> interact with each other resulting in an electrical length that is
> shorter than anticipated.
>
> Lee
>
> Andrew W. Riley III wrote:
>
> > Hello SI-LIST members,
> >
> > One issue that I am unclear on is all the turns in the traces shown in the
> attached file 'Layer3.jpg' and in the picture Mr. Riazi attached for
> reference to his post on "Plane Splits Inspection".
> >
> > We have our designs sent to another company for Layout. In a section of
> the layout instructions I specified net pairs to be of equal length with an
> extremely generous tolerance (I think) of 0.200" but ONLY if excessive
> bends were not added to the trace. The board is relatively small;
> approximately 2"x6", and densely packed.
> >
> > I also referred to UltraCAD's Design Note www.ultracad.com/t001.pdf under
> the Radiating Points section, which states;
> > "Right angle turns and "T's": A trace that extends in a straight line is
> relatively clean. One that extends straight and then turns 180 degrees back
> on itself looks just like an antenna (like those on a tall building!)"
> >
> > Layer3.jpg is a sample of what was sent back to me for review and is what
> I thought we were trying to avoid. Also, I was somewhat surprised to see
> similar routing in "Figure 1" attached to Mr. Riazi's initial post "Plane
> Splits Inspection". This style of routing will not present any problems?
> >
> > Am I wrong in thinking the routing shown in Mr. Riazi's and my picture are
> examples of the 'antennas' mentioned in UltraCAD's Design Note? And to that
> end, would someone be so kind as to explain why?
> > Any references supplied would be most helpful, too.
> >
> > I will do my best to clarify anything that I neglected if at all possible.
> >
> > ------------------------------------------------------------------------
> >
> > Name: Layer3.jpg
> > Layer3.jpg Type: JPEG Image (image/jpeg)
> > Encoding: base64
>
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