🚀 go-pugleaf

On 01/11/2012 10:10 PM, krw@att.bizzzzzzzzzzzz wrote:
> On Wed, 11 Jan 2012 21:02:07 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net>  wrote:
>
>> On 01/11/2012 08:26 PM, krw@att.bizzzzzzzzzzzz wrote:
>>> On Wed, 11 Jan 2012 14:22:11 -0500, Phil Hobbs
>>> <pcdhSpamMeSenseless@electrooptical.net>   wrote:
>>>
>>>> On 01/11/2012 01:43 PM, John Larkin wrote:
>>>>> On Tue, 10 Jan 2012 18:02:50 -0800 (PST), Bill Sloman
>>>>> <bill.sloman@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.
>>>>>>>
>>>>>>>>> --
>>>>>>>>> BillSloman, Nijmegen
>>>>>>>
>>>>>>>> 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!
>>>>>
>>>>> John
>>>>>
>>>>
>>>> Yup, all RC transmission lines with repeaters, speed roughly c/10.
>>>
>>> The routing delay scales roughly with the square of the length (not at all
>>> linear).  Yes, it's often faster to buffer the middle of a long line.  In the
>>> PPC970/G5, there were several nets with three and four repeaters.  Even
>>> numbers work better, though.  ;-)
>>
>> In the limit of long lines, that's true.  However, you can't build chips
>> in that limit, because the bandwidth goes down quadratically with length
>> as well.  To maintain speed, you have to use repeaters, and maintaining
>> 2-3 GHz clock rates with reasonable jitter requires spacing them at
>> something like 1 mm intervals on long lines.  In an optimized layout,
>> that turns out to produce a roughly constant propagation speed of c/10
>> or so.
>>
>> Cheers
>>
>> Phil "Former on-chip optical interconnect person" Hobbs
>
> Our on-chip delay models were pretty much l^2 (RC, where c ~ l*w and R~l).  A
> constant delay would imply an LC line, no?
>

No, it just implies a constant distance between repeaters.  The optimal 
spacing doesn't depend on how many hops you have, so N hops gives N 
times the delay of one hop.

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