Dr Howard Johnson, this weeks guest on The Amp Hour

That Dr. Howard looks awfly familiar !

He also lives awfly close to us here in the PNW...

Also saw a link that shows your new videos.

Thx David !

boB

waveform...

"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.

-- Bill Sloman, Nijmegen

fame:

Yeah, his book is half nonsense. If you can tell which half is which, you don't need the book. His ideas on "return currents" and bypassing are absurd. And the writing is dreadful.

His articles in EDN (or ED, whatever) are horrible too. He ran out of material years ago, but he keeps writing.

I started highlighting the really bad, flat silly parts of "Black Magic" but gave up less then halfway through.

John

e-waveform...

Perhaps, it is time for the first ever 'conference' book written by a consortium of engineers/scientists.

Put my name in for proffreading. :)

fame:

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

Sure that will work out well... :)

--

John Devereux

fame:

Yep. I'm the only one that's armed ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

fame:

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

I haven't got the book handy, but I'll pick it up tomorrow or so. Do you mind expounding on why his "return currents" make no sense? Did he mean something different from image currents?

Jeroen Belleman

He says that a transmission-line pcb trace must always be "referenced" to the same "return current" plane it started with and shouldn't pass through vias to become referenced to a different plane, or else the return currents will get confused or go on strike or something. If that were true, 98% or the multilayer boards on Earth would quit working.

He also says that you should add bypass caps and stitching vias to conduct these return currents whenever a trace does via to a different "reference plane."

All silly.

John

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      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

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

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
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

Did you have to pay him? How much?

John

Ah, yes, I agree with you there. Mostly anyway. Capacitance between planes should be plenty to take care of that.

I *did* have this amplifier with a ridiculously high gain that wouldn't keep still with its output trace running over the V+ plane. The problem vanished when I made it run over a GND plane instead. Then again, there were a few other layout tweaks that may have contributed to fixing it.

Jeroen Belleman

Not completely silly. One of the more avoidable hold-ups in the development of the electron beam tester at Cambridge Instruments from

1988 to 1991 was when the drafting office sent out a six layer board for manufacture without specifying the order of the inner planes - they "knew" that the order didn't matter, despite the fact that I'd spelled it out, in detail, on the release note that I'd given them.

Almost all of the very high frequency connections - from GaAs logic outputs to GaAs logic inputs - were supposed to have been routed directly above the -2V plane (which should have been directly under the components), and the terminating resistors were returned to that plane (through a via at the relevant end of the resistor).

The board didn't work, and it took us a while to find out why. Whenever I walked past the engineer working on the board I'd remind him that he had the stuck of images of the various planes stuck together in the wrong order, and eventually this irritated him enough that he got out a drill and worked that he'd got them in the right order, which explained most of why the board wasn't working.

We did get it to work eventually, but all the high-frequency connections through the board ended up being routed through tacked-on lumps of sub-miniature coaxial cable.

The next board had the inner planes in the right order, amongst other changes, and worked a lot better.

-- Bill Sloman, Nijmegen

-- Bill Sloman, Nijmegen

No, he was not paid, non of our guests are. We invite them on and they graciously agree to give up their time to participate.

Dave.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

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

Of course the stackup and order matter, if not to get the DC connections right, then to get the impedances right. But the obsession with return currents and "reference planes" is mostly silly.

As is the admonition to never cross slits in planes, fr'instance running a trace above a plane that has multiple pour pours.

John

Did you mean "multiple poor pours."? :-)