Dr Howard Johnson, this weeks guest on The Amp Hour - Page 3

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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Thu, 12 Jan 2012 09:58:42 -0800 (PST), Bill Sloman

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I was talking about a Motorola data book, and you responded with a
personal insult. You do that sort of thing a lot here. It's not
surprising that people tended to not hire/keep you.


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Probably the cost of the boards contributed to the overall project
failure. We do picosecond stuff on FR4 all the time. I do TDR and
other tests on boards so I can understand them and learn stuff, and
make sure my suppliers are doing the stackups right, and so that I can
separate what matters from the masses of hand-waving "theory" that
folks like HoJo sell.


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The only thing you were pushing the state-of-the-art on was expense.
The Moto ECL and GBL GaAs parts would work fine on FR4.

The exotic substrates seldom make sense for digital logic. If you have
a *lot* of layers, over 8 maybe, a lower Er is handy to keep the trace
widths and impedances practical.

RF stuff can sometimes justify exotic laminates, to keep filter Qs up
and noise figures down. High thermal conductivity laminates could be
interesting.

John


Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Jan 12, 8:36A0%pm, John Larkin
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Please identify the personal insult - I wasn't actually intending to
insult you at that point so it would be useful if you indicated which
of your hyper-sensitive toes I trod on.

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The machine was priced to recover its development costs, not it's
component costs. Being "state of the art" was one of things that
marketing liked about the machine. The bare printed circuit boards
were expensive, but loading them with components cost more than buying
the boards.

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We didn't buy HoJo's handwaving theory back then. IIRR he wasn't
peddling his stuff until the 1990s.  We got hold of rather more
reliable data from the microwave world.

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We had a few nasty experiences with with GaAs pulses that got
inadvertently routed over FR-4. The choice of the isocyanate resin-
bonded Teflon cloth substrate was driven more by a wish to minimise
potential risks than any deep analysis of what was going to happen to
the pulse shapes by the time they got to the other side of a big board
- one of the things that really screwed the project was an initial
desire to get it up and running fast, so design reviews were by-passed
to get boards out to layout as soon as possible, in the best English
tradition of not having enough time to do it right so you have to find
time to do it over.

Once we'd got the printed circuit department to get the boards made
with the buried layers in the right order, the boards materials didn't
give us any trouble.

The half-nanosecond wide pulse generator for generating the
stroboscopic flash of electrons inside the electron microscope was
actually built on an alumina-loaded Teflon daughter board - we'd
bought in a microwave consultant, and that was what he chosen. I'd got
a similar circuit working fine on a polyimide board a few years
earlier - HF transistors involve ran hot and the polyimide tolerated
it better than FR-4, which turned brown and worried the customers and
our service engineers - but it doesn't make sense to pay through the
nose for consultants (no matter how flakey) and ignore their advice.

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These boards were "mixed signal". We used essentially analog circuits
to interpolate between the 800MHz digital clock edges - the aim was to
determine when an external trigger had come in to about 10psec, and
generate our sampling pulses at controlled intervals after that
trigger edge, with a resolution of 10psec. The fact that we had a crap
clock with some 50psec of jitter and our sampling pulse was 500psec
wide didn't stop marketing from insisting on the 10psec resolution.

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We stuck individual heat sinks on most of the faster logic packages,
and blew a lot of air through the crate. When testing individual
sticking out of the crate on an extender card (which was fun to design
and get built) you had a big domestic fan blowing into your ear.

--
Bill Sloman, Nijmegen



Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Wed, 11 Jan 2012 14:22:11 -0500, Phil Hobbs

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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.  ;-)

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

--
Dr Philip C D Hobbs
Principal Consultant
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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Wed, 11 Jan 2012 21:02:07 -0500, Phil Hobbs

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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?


Re: Dr Howard Johnson, this weeks guest on The Amp Hour
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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
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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Wed, 11 Jan 2012 22:14:16 -0500, Phil Hobbs

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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.
 

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of
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circuit
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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
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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Wed, 11 Jan 2012 20:26:50 -0500, " snipped-for-privacy@att.bizzzzzzzzzzzz"

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Getcher inverter for free!

John


Re: Dr Howard Johnson, this weeks guest on The Amp Hour
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Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Tue, 10 Jan 2012 07:23:01 -0800 (PST), Robert Macy

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Jim Williams' two great books on analog design were like that, each
chapter by someone else. Pease tried to imitate that, but didn't do it
very well.

John



Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Mon, 9 Jan 2012 22:47:01 -0800 (PST), "David L. Jones"

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Howard Johnson?  Wasn't that a restaurant that you went to for clam
strips ?:-)
        
                                        ...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

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I think there are only two HJ's left in the whole country.  I ate at the one
in Lake Placid a few times.



Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Tue, 10 Jan 2012 19:36:11 -0500, "Michael Robinson"

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According to Wikipedia, there are three; Lake Placid NY, Lake George NY (I
knew I'd seen one recently), and Bangor ME.  




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

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I stand corrected.



Re: Dr Howard Johnson, this weeks guest on The Amp Hour
On Wed, 11 Jan 2012 02:25:01 -0500, "Michael Robinson"

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Actually, I was the one who was wrong.  Having just seen one recently, I
didn't think they were down to just a few fingers.  After checking (there is a
lesson here for AlwaysWrong, but he's too dim), you were right, give or take.

Re: Dr Howard Johnson, this weeks guest on The Amp Hour
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HJ has a mixture of good stuff and complete nonsense.

I hope you grilled him a bit about his less sensible stuff, like that
hilariously erroneous video where he attempts to use electrostatics to
demonstrate that ground currents want to flow under traces.  Of course,
the impedance levels are millions of times too high for inductance to be
a factor in that demo, but never mind.    Have a look at
http://www.sigcon.com/Pubs/news/8_08.htm for the whole ridiculous thing.

(The current path is determined by corona discharge at the sharp corners
of the metal squares--if you look at all closely, you'll see that the
discharges always want to go out the corners of the squares.)

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 10, 12:09A0%pm, Phil Hobbs
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That is pretty silly.
But certainly it's a good idea to keep a nice unbroken ground plane
under the signal(s) that you really care about.

George H.

Re: Dr Howard Johnson, this weeks guest on The Amp Hour
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athttp://www.sigcon.com/Pubs/news/8_08.htmfor the whole ridiculous thing.
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I don't disagree with you there.  But I have small respect for someone
who makes his living peddling that sort of cargo-cult stuff.  If he ever
corrected himself, or offered actual real-world data or simulations, I'd
pay attention.  As it is, his stuff is like an old time medicine
show--the willow bark tea works, the snake oil doesn't, no apparent
effort is expended to sort them out.

Remember the little boy in the story:  "Why do you keep snapping your
fingers, Bobby?" "To keep polar bears away."  "But there isn't a polar
bear within 2000 miles of here!"  "Works great, doesn't it?"

Read Morrison instead.

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 10, 9:47A0%pm, Phil Hobbs
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Grin,  I've never read any of Ho Jo's books.  I figured I don't know
enough to separate the chaff from the grain.
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? Ralph Morrison on Grounding and sheilding?  (the only Morrison on my
shelf) Or someone else?

George H.
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