🚀 go-pugleaf

On Wed, 11 Jan 2012 22:14:16 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>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.

OK, sure, the limit is where the gain from the repeater equals the reduction
because of the l^2 issue.  IOW, the wiring itself obeys the l^2 rule but add
repeaters and it linearizes.  I'd think this "constant" speed would be a large
function of the repeater delay.