🚀 go-pugleaf

On Jan 12, 3:13 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Wed, 11 Jan 2012 16:49:18 -0800 (PST),BillSloman
>
> <bill.slo...@ieee.org> wrote:
> >On Jan 11, 8:22 pm, Phil Hobbs
> ><pcdhSpamMeSensel...@electrooptical.net> wrote:
> >> On 01/11/2012 01:43 PM, John Larkin wrote:
>
> >> > On Tue, 10 Jan 2012 18:02:50 -0800 (PST),BillSloman
> >> > <bill.slo...@gmail.com> wrote:
>
> >> >> On Jan 10, 4:55 pm, John Devereux<j...@devereux.me.uk> wrote:
> >> >>> Robert Macy<robert.a.m...@gmail.com> writes:
> >> >>>> On Jan 10, 2:28 am,BillSloman<bill.slo...@ieee.org> wrote:
> >> >>>>> On Jan 10, 7:47 am, "David L. Jones"<altz...@gmail.com> wrote:
>
> >> >>>>>> Just thought some might be interested in hearing our recent guest on
> >> >>>>>> our Amp Hour radio show, Dr Howard Johnson of "Handbook of Black
> >> >>>>>> Magic" fame:http://www.theamphour.com/2012/01/10/the-amp-hour-77-winsome-waveform...
>
> >> >>>>>> Lots of history of the book, signal integrity, Gigabit Ethernet
> >> >>>>>> development, 90 degree PCB bends, audiophoolery, and a whole bunch of
> >> >>>>>> other talk over almost 1 1/12 hours.
>
> >> >>>>> "Black Magic" is more notorious than famous. I own both it and it's
> >> >>>>> follow-up, and both have got some useful content but they are badly
> >> >>>>> organised and what useful content they do contain is hard to find.
>
> >> >>>>> The field is still waiting for a decent textbook on high speed circuit
> >> >>>>> design and layout.
>
> >> >>>>> This is one of the few matters on which John Larkin and I seem to
> >> >>>>> agree.
>
> >> >>>> Perhaps, it is time for the first ever 'conference' book written by a
> >> >>>> consortium of engineers/scientists.
>
> >> >>>> Put my name in for proffreading. :)
>
> >> >>> Great idea. Perhaps John Larkin, Jim Thompson andBillSlomancould
> >> >>> collaborate on it.
>
> >> >>> Sure that will work out well... :)
>
> >> >> I'm not sure what Jim Thompson might contribute. I've seen papers that
> >> >> worry about the characteristic impedance of connections on the silicon
> >> >> (or whatever) inside integrated circuits, but I don't have the feeling
> >> >> that Jim designs stuff that's big enough and fast enough for him to
> >> >> need to know much about it.
>
> >> > I get the impression that most interconnects inside ICs are primarily
> >> > distributed R-C things, not real transmission lines at all.
> >> > Propagation speed of interconnects is a big deal in routing fast logic
> >> > chips, but the speed of light isn't the issue.
>
> >> >> Motorola's ECL applications notes on board layout were rather useful,
>
> >> > Just don't trust their microstrip equation!
>
> >They looked okay in the range 50R to 75R.
>
> Yup. And they give silly, even negative, impedances for traces outside
> a narrow width zone.

Which is more or less what I went on to say in the next paragraph -
you seem to suffer from premature ejeculation.

> >Specialised textbooks give
> >longer and more complicated expressions that give rather different
> >results for microstrips and strip-line with higher and lower
> >characteristic impedances.
>
> >> Yup, all RC transmission lines with repeaters, speed roughly c/10.
>
> >I wonder what Dr. Hobbs thinks he is talking about
>
> The fact that on-chip interconnects are usually dominated by
> resistance and capacitance, and don't behave like the transmission
> lines you're used to. Since the risetime of a distributed R-C line
> degrades as length-squared or something horrible like that, it makes
> sense to insert active buffers in long runs.

Which didn't have much to do with the point that the Motorola ECL data
books used formulas for trace impedance that only worked well over a
narrow - if useful - range of trace impedances. It's entirely relevant
to the point that Jim Thompson doesn't have to know much about laying
out printed circuit boards for signals with short transition times,
but Phil didn't bother to make it clear that he was addressing that
particular question.

> I believe he has a bunch of direct experience in this area.

> > - the Motorola  ECL
> >application notes discussed proper microstrip and stripline
> >transmission lines, where the propagation delay is basically that of
> >electromagenetic waves in dielectric - something around two-thirds of
> >the speed of light in vacuum (depending on the dielectric constant of
> >the substrate).
>
> They also cautioned against sharp corners, a silly warning at ECL
> speeds.

At current ECLinPS speeds everything gets averaged over a few
millimetres of track. The extra capacitance implicit in a right-angle
bend on a 5OR track might be perceptible, but you can pretty much
eliminate it by chamfering the corner, or making two 45-degree bends
in quick succession.

--
Bill Sloman, Nijmegen