Re: [SI-LIST] : Definition of Hi-Speed (UC)

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From: Jim Freeman (freeman@broadcom.com)
Date: Mon Nov 08 1999 - 11:05:12 PST


Hi Jack,
    I was pleased to pick up a tome by Clayton Paul on multiple transmissionlines(MLT's). It was recommended by Mike King and is very theoretical but can be a guide to the theoretical underpinnings of the layout communities
rules' of thumb.

Jim Freeman

Jack Olson wrote:

> Well, I can't answer a question like what "happened" to education for PCB
> layout, because I haven't seen much of it available.
> I have a "basic" electronics engineering degree and they didn't teach
> ANYTHING about layout! Since my job is 100% layout I've used just about
> every available way to learn more about it but it ain't easy. Even the
> supposed experts intersperse provable results with lore and rules of thumb
> of questionable or even detrimental value. You could spend ALL your time
> poring through these lists and reading books and magazines, but some of us
> have to get some WORK done and our learning time is limited. Then when you
> attend these conferences one guy teaches decoupling is a waste and then the
> next guy says you need 100 in parallel (just one example)
>
> onward thru the fog...
> Jack
> (but I'm not here to discuss philosophy, sorry for going off-grid)
>
> -----Original Message-----
> From: Adrian Shiner [mailto:adrian.shiner@virgin.net]
> Sent: Tuesday, November 02, 1999 11:56 AM
> To: si-list@silab.eng.sun.com
> Cc: eric
> Subject: Re: [SI-LIST] : Definition of Hi-Speed (UC)
>
> What has happened to the education sytems in various
> countries? ECL logic
> was in use in the late 1960's, complete with all these
> characteristic fast
> rise time issues!!
>
> From reading many inputs to theis excellent forum for
> discussion, I wonder
> if some of the PCB layout guys have the formal basic
> engineering knowledge
> of the relevant subjects which are needed in this endevour.
>
> Adrian
>
> ----- Original Message -----
> From: Eric Bogatin <eric@bogent.com>
> To: <si-list@silab.eng.sun.com>
> Cc: eric <eric@bogent.com>
> Sent: 01 November 1999 18:52
> Subject: RE: [SI-LIST] : Definition of Hi-Speed (UC)
>
> > The definition of High Speed I use in the classes I teach
> is that high
> speed
> > is when the interconnects are no longer transparent to the
> signals. In
> this
> > regime, the electrical effects of the interconnects will
> affect signal
> > quality and if you don't take the interconnects into
> account, system
> > performance will be degraded.
> >
> > As has been pointed out by many on this list, this
> criteria depends more
> on
> > the rise time of signals than on the clock frequency. In
> my last article
> on
> > ChipCenter (click on this link if you want to read it:
> > http://www.chipcenter.com/signalintegrity/ ), I wrote
> about the coming
> > crisis when even jelly bean parts soon will have sub 0.5
> nsec rise times,
> > even if they are used in circuits with only 10 MHz clocks.
> >
> > However, sometimes managers don't really understand about
> rise time, and
> > just think in terms of clock frequency. They just want a
> number and want
> you
> > to fill in the blank with your best guess.
> >
> > So, given the caveat of the importance of rise time over
> clock frequency,
> > here's the rule of thumb I sometimes use to pick a number:
> >
> >
> > The starting clock frequency for high speed is F > 200
> MHz/L, where L is
> the
> > longest length of the board, in inches.
> >
> >
> > If your product is a 10 inch board, like a PC mother
> board, high frequency
> > is any clock frequency above about 20 MHz. If your product
> is a PC card
> > (PCMCIA format), 4 inches in a side, high frequency is
> when the clock is
> 50
> > MHz and above.
> >
> >
> > Here are the assumptions behind this "rule of thumb":
> >
> > 1. the rise times of signals are about 1/10 the clock
> period
> >
> > 2. transmission line effects dominate (ie, the
> interconnect is not
> > transparent) when TD > 1/3 x rise time
> >
> > 3. the substrate is FR4 and the speed of a signal is about
> 6 inches/nsec.
> >
> >
> > Note, as with all rules of thumb, if you are trying to
> make a distinction
> > between is 25 MHZ or 35 MHz really the "onset" of high
> speed, you don't
> want
> > to use a rule of thumb. But, if you want to know is 10 MHz
> or 50 MHz high
> > speed, this rule of thumb is a pretty quick way of getting
> an answer.
> >
> > For those interested, I have added a paper I wrote on
> "Rules of Thumb I
> Have
> > Known and Loved" to my collection of downloads for
> November. You are
> welcome
> > to download a pfd version of this by visiting my web site
> at:
> > <http://www.bogatinenterprises.com/>
> >
> > --eric
> >
> > Eric Bogatin
> > BOGATIN ENTERPRISES
> > Training for Signal Integrity and Interconnect Design
> > 26235 W. 110th Terr.
> > Olathe, KS 66061
> > v: 913-393-1305
> > f: 913-393-1306
> > pager: 888-775-1138
> > e: eric@bogent.com
> > web: <http://www.bogatinenterprises.com/>
> >
> >
> > > -----Original Message-----
> > > From: owner-si-list@silab.eng.sun.com
> > > [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of
> Beal, Weston
> > > Sent: Monday, November 01, 1999 11:22 AM
> > > To: 'si-list@silab.eng.sun.com'
> > > Subject: RE: [SI-LIST] : Definition of Hi-Speed (UC)
> > >
> > >
> > > The best definition I've ever heard of High-Speed was
> from someone on
> this
> > > list. Speak up or I'll take the credit.
> > >
> > > High-Speed is any design that has faster edge rates or
> clock rates than
> > > you've designed before.
> > >
> > > It's new to you, so you need to study and analyze it.
> > >
> > > Regards,
> > > Weston
> > >
> > >
> > > -----Original Message-----
> > > From: Lum Wee Mei [mailto:lweemei@dso.org.sg]
> > > Sent: Sunday, 31 October, 1999 10:54 PM
> > > To: 'si-list@silab.eng.sun.com'
> > > Subject: [SI-LIST] : Definition of Hi-Speed (UC)
> > >
> > > Pardon me for asking this stupid question because I am
> at a
> > > loss of how
> > > to explain hi-speed to my boss. He thinks that hi-speed
> is
> > > as simple and
> > > straightforward as resistance = V/I and nothing else.
> > > Hi-speed should be
> > > some circuits that need to operate at xxMHz or more.
> > > Anything less than
> > > xxMhz is not hi-speed.
> > >
> > > I would appreciate anyone of you experts out there who
> can
> > > enlighten me
> > > in a simple and easy to understand definition so that my
> > > boss can
> > > understand.
> > >
> > > Regards.
> > >
> > >
> > >
> > >
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