RE: [SI-LIST] : even-odd mode influence

Weber Chuang (WeberChuang@via.com.tw)
Fri, 16 Jul 1999 10:37:11 +0800

Hey! Hey! Doug, you really got my point, though xtalk is one of my concern
since the swing is now smaller(1.5 Volt), while the edge rate seems to stay
the same or even get faster, however, what bothers me most is that when we
are designing PCB for PC133 , there are so many signals in a bus such that
we cannot avoid to put them in adjacent to each other(not widely separated),
here comes the problem, the difference of about 30 %(even higher if the
trace width:cleance is 1:1 or 1:1.5 and stackup not well arranged and 7
conductor considered) in impedance between even and odd mode will make the
termination scheme fail and the estimation of ISI jittering become very
difficult, besides, it will also be data pattern dependent. If I cannot
analyze(simulate) the ISI jittering correctly, I cannot do static timing
analysis correctly, that resides my problem. Thanks in advance for any
comment and discussions.

Best Regards

Weber Chuang(ChingFu Chuang)
Signal Integrity Engineer,
VIA Technologies, Inc. Taipei, Taiwan, ROC
TEL : 886-2-22185452 ext : 6522
mailto:weber@via.com.tw
http://www.via.com.tw
Very Innovative Architecture

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Douglas McKean
Sent: Friday, July 16, 1999 8:42 AM
To: si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] : even-odd mode influence

At 08:27 PM 7/15/99 +0100, Adrian Shiner wrote:
>You are right, but the real world is that you get both in some proportion
no matter how you think you have designed in one mode. Can't answer on the
tools.
>
>PCB scale, box scale, system scale, the fundamentls remain the same. The
engineering changes a bit. It strikes me that some younger guys out there
are relying on their college education & software tools too much. Get
reading and
>talking to the guys with grey and thin(ning hair)! Experience counts and
pride in one's education comes before a fall (to distort a well known
phrase or saying!).

Can't imagine someone trying to design for only one
mode. The question pertained to "effect". The other
effect are differences in impedance between even and
odd being almost 30%. Something to consider. Well,
maybe since no one has brought it up.

I didn't hear about even or odd mode impedances until
10 years after the university and that was over 15 years
ago. And I've got more than enough of the grey hair.

But thanks for trying to call me a "younger guy".

Much appreciated!!!

Regards, Doug McKean

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