🚀 go-pugleaf

On 01/11/2012 10:38 PM, krw@att.bizzzzzzzzzzzz wrote:
> 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.
>

Probably so.  I've never designed repeaters myself, all of this stuff 
comes from palling around with some of the leading lights of the field.

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