🚀 go-pugleaf

On 01/11/2012 07:49 PM, Bill Sloman 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... :)
>>
>>>> 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. 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 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).
>

On-chip interconnects, even the fatwire levels, are all RC.  Once you 
get off the chip, you have to worry about transmission line effects, but 
the losses in chip wiring are so horrendous that you have to use 
multiple repeaters to go a couple of centimters. The delays in the 
repeaters, and the edge degradation due to RC rolloff, produce a net 
propagation speed of about c/10.  Of course my information is two or 
three years old at this point, but I wouldn't expect inductance to get 
more important anytime soon.

Cheers

Phil Hobbs


-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net