🚀 go-pugleaf

On Wed, 11 Jan 2012 16:49:18 -0800 (PST), Bill Sloman
<bill.sloman@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:
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>> > On Tue, 10 Jan 2012 18:02:50 -0800 (PST),BillSloman
>> > <bill.slo...@gmail.com> �wrote:
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>> >> 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 and Bill Sloman could
>> >>> collaborate on it.
>>
>> >>> Sure that will work out well... :)
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>> >> 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.
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>> > 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.


 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.

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.

John