Dr Howard Johnson, this weeks guest on The Amp Hour - Page 2

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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
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Perhaps, it is time for the first ever 'conference' book written by a
consortium of engineers/scientists.

Put my name in for proffreading.  :)

Re: Dr Howard Johnson, this weeks guest on The Amp Hour

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Great idea. Perhaps John Larkin, Jim Thompson and Bill Sloman could
collaborate on it.

Sure that will work out well... :)


--

John Devereux

Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Tue, 10 Jan 2012 15:55:53 +0000, John Devereux

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Yep.  I'm the only one that's armed ;-)
        
                                        ...Jim Thompson
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Jan 10, 5:21A0%pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:
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Pity about the brained.

--
Bill Sloman, Nijmegen


Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Tue, 10 Jan 2012 17:38:43 -0800 (PST), Bill Sloman

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His switcher design is due before midnight. Should be fun.

John


Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Tue, 10 Jan 2012 17:46:03 -0800, John Larkin

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John Are you really that ignorant/narcissistic?  You know that what I
post will work.  Why don't you knock off the crap and grow up?  Or are
you intent in going down in history as just another Slowman...
worthless and limp-dicked by the time you reach "old age" ?:-)
        
                                        ...Jim Thompson
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Tue, 10 Jan 2012 18:56:35 -0700, Jim Thompson

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Post it and we'll see.

John


Re: Dr Howard Johnson, this weeks guest on The Amp Hour
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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.

Motorola's ECL applications notes on board layout were rather useful,
and date back to Jim's time with them, but he won't have written them,
any more than he wrote the rather comprehensive applications notes for
his MC4024/MC4044 precursors of the 4046, though he may have
supervised the people who did.

--
Bill Sloman, Nijmegen

Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Tue, 10 Jan 2012 18:02:50 -0800 (PST), Bill Sloman

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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.

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Just don't trust their microstrip equation!

John


Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Wed, 11 Jan 2012 10:43:15 -0800, John Larkin

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Written by clueless PhD's trying the publish or perish route :-)

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What a fundamental fathead you are, Slowman.  Even Larkin knows I've
designed quite a bit of PECL.

I have chips out there, commercial successes, running at 5GHz.

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                                        ...Jim Thompson
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Jan 11, 8:10A0%pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:
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The authors affiliations seemed to be with the semiconductor firms,
but that doesn't stop them from being clueless Ph.D.s.

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We all know that - you tell us about it at every possible opportunity.
None of its big enough that you are going to have start treating
interconnection on the chip as transmission lines.

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So what. 5GHz is 200psec and light travels about 6cm in that period -
I'd be surprised if any of your chips were as big as 1cm across. You
really don't have to worry about reflections from discontinuities in
the connections across you chips..

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Me too.

--
Bill Sloman, Nijmegen

Re: Dr Howard Johnson, this weeks guest on The Amp Hour
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Even large processors are all RC internally.  (Part of my previous job
was helping set IBM's optical interconnection strategy, so we went over
all that wire stuff in gory detail.)  There was a DARPA program a few
years back that tried pushing copper interconnects to much lower
speed/power points, but inductance never became a big factor.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
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Yup, all RC transmission lines with repeaters, speed roughly c/10.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Jan 11, 8:22A0%pm, Phil Hobbs
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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.

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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).

--
Bill sloman, Nijmegen

Re: Dr Howard Johnson, this weeks guest on The Amp Hour
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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
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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Jan 12, 2:56A0%am, Phil Hobbs
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It's an entirely valid point, but you inserted the comment a couple of
paragraphs further down the post than you should have - it looked as
if you were commenting on the limitations of the Motorola ECL
application notes (which were perfectly okay, though they should have
included a caution about the range of validity of the trace-impedance
expressions) rather than on the sort of experience Jim Thompson might
have had in laying out transmission lines (very little to none).

--
Bill Sloman, Nijmegen

Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Wed, 11 Jan 2012 16:49:18 -0800 (PST), Bill Sloman

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Yup. And they give silly, even negative, impedances for traces outside
a narrow width zone.


 Specialised textbooks give
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The fact that on-chip interconnects are usually dominated by
resistance and capacitance, and don't behave like the transmission
lines you're used to. Since the risetime of a distributed R-C line
degrades as length-squared or something horrible like that, it makes
sense to insert active buffers in long runs.

I believe he has a bunch of direct experience in this area.

 - the Motorola  ECL
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They also cautioned against sharp corners, a silly warning at ECL
speeds.

John


Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Jan 12, 3:13A0%am, John Larkin
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Which is more or less what I went on to say in the next paragraph -
you seem to suffer from premature ejeculation.

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Which didn't have much to do with the point that the Motorola ECL data
books used formulas for trace impedance that only worked well over a
narrow - if useful - range of trace impedances. It's entirely relevant
to the point that Jim Thompson doesn't have to know much about laying
out printed circuit boards for signals with short transition times,
but Phil didn't bother to make it clear that he was addressing that
particular question.

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At current ECLinPS speeds everything gets averaged over a few
millimetres of track. The extra capacitance implicit in a right-angle
bend on a 5OR track might be perceptible, but you can pretty much
eliminate it by chamfering the corner, or making two 45-degree bends
in quick succession.

--
Bill Sloman, Nijmegen


Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Thu, 12 Jan 2012 02:11:46 -0800 (PST), Bill Sloman

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of
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circuit
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You suffer from nostalgia for the times, decades ago, when you
actually did things... most of which didn't work.


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That's what the ancient Moto book said. It was stupid at 10K speeds
and it remains stupid at EclipsPlus speeds. I can barely discern a
right angle with a zoomed-up 30 ps TDR edge. The weave of the
fiberglass changes the impedance more than a sharp corner. Vias are
hugely more important than right angles.

John


Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Jan 12, 4:30A0%pm, John Larkin
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<snip>

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I do feel a certain amount of nostalgia for the times when I did
things - which all actually worked when management didn't cancel the
projects before we'd got to actual hardware. Management did frequently
decide that they couldn't sell the stuff that I was allowed to get
working.

All of this is entirely irrelevant to the observation that you went
off at half-cock, busily saying pretty much what I'd already posted,
but you couldn't find a way of justifying that, so you posted one more
of your inaccurate insults instead.

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<snip>

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Obviously.

I'm a bit surprised that you are bothering to do time domain
reflectometry on FR-4 boards. Rogers make a bunch of substrates that
work rather better at very high frequencies. A Cambridge Instruments
we made the outer layers of six layer boards for the GaAs parts with
isocyanate-resin-bounded Teflon cloth. The inner layers (that weren't
exposed to the GaAs signals) were regular FR-4 which kept the board as
a whole rigid - they were triple extended Eurocards and we didn't want
them flopping around.

Our printed circuit board supplier charged us extravagantly for the
boards - he had to buy a lot more of the isocyanate-resin-bonded
Teflon cloth substrate than he need to make up our first batch of
boards, and he knew we were pushing the state of the art, and - very
wisely - wasn't prepared to wait for us to order a production batch of
boards to cover the expenditure.

--
Bill Sloman, Nijmegen


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