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

From: Adrian Shiner ([email protected])
Date: Thu Nov 04 1999 - 13:12:53 PST

Eric, the address box is empty looking from my den!

----- Original Message -----
From: Eric Bogatin <[email protected]>
To: <[email protected]>
Cc: eric <[email protected]>
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: [email protected]
> web: <http://www.bogatinenterprises.com/>
>
>
> > -----Original Message-----
> > From: [email protected]
> > [mailto:[email protected]]On Behalf Of Beal, Weston
> > Sent: Monday, November 01, 1999 11:22 AM
> > To: '[email protected]'
> > 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:[email protected]]
> > Sent: Sunday, 31 October, 1999 10:54 PM
> > To: '[email protected]'
> > 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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>
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