🚀 go-pugleaf

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?