Dr Howard Johnson, this weeks guest on The Amp Hour

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Pity about the brained.

-- Bill Sloman, Nijmegen

fame:

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

John

on

Our suppliers back then didn't do buried vias, and the boards weren't so tightly packed that we had any need of them, so the DC connections were going to be fine, independent of the stack-up, but the return current under the transmission-line tracks did end up following rather more convoluted routes than we'd had in mind.

Return current routing does matter, and you should keep it in mind. Half-baked rules of thumb aren't a good substitute for thinking about what is going on, but thye can be better than nothing.

It certainly changes the transmission line impedance in the vicinity of the slit, if the slit is long enough vis a vis the transition time of the edge travelling along the transmission line.

-- Bill Sloman, Nijmegen

fame:

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      |
| 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:

Post it and we'll see.

John

some-waveform...

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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

Rather like authors going on "signing tours" to get a bit more publicity for the books they have written.

Winfield Hill never seems to have done that in the past. Maybe he'll get sent on tour when the third edition finally comes off the press.

-- Bill Sloman, Nijmegen

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.

at

the whole ridiculous thing.

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
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

No, not at all. We liked him so invited him on the show, he did not approach us. He was kind enough to come on and be a guest without any agenda at all.

Dave.

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

You're just spoiled...

8-layer boards aren't cheap. Heck, four layer boards aren't cheap. If I can avoid it, I'll pick 2 layer whenever possible. Great proto prices and turn arounds. With two layers to choose from, you have no choice but to stitch like a carpet. You only have room for one ground plane as such. Heck, if you think you have room for two (maybe VCC and GND), you're being lazy and could get by with 1 layer. :)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

8's do get expensive, and you can't do serious stuff on 4, so we try to use 6 layers when we can. Routing a BGA FPGA to a BGA ARM and then to a lot of ADCs and such can be a challenge on 6 layers.

Having a solid ground layer is great for signal integrity, mandatory for fast stuff. And the power pours make nice heat sinks for voltage regulators and power opamps and things.

I haven't done a single-sided board in decades. We do do some doubles for adapters and breakouts, things like that.

But a bare board, 6 or 8 layers, is a per cent or two of our selling price. It makes more sense to pack on features and sell a few more.

John

These days even a house thermostat design requires a 432 pin BGA (plus scores of other parts), so 1 or 2 layer boards are not practical. 8-(

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Have you tried any of the FPGAs with an ARM core built in? Heard Altera is going to make a Cyclone SoC, which might be interesting to try on our next rev. Having an ~800MHz core puts a lot more power at your fingertips than an IP core, or a lot more bandwidth than pins allow. Your budget and demands, of course, allow for much flasher hardware, of which I'm sure there are lots available.

Having full VCC and GND planes is wonderful. The guys at our sister company said it would never work, the FPGA thing, LVDS, sensitive low voltage logic thresholds, blah blah. One prototype we built had the FPGA board about one inch from a whole stack of (noisy, prototype) power boards. Never a glitch attributed to board succeptability. Getting all the signals and supplies and bypasses underneath the chip looks a little funky, guidelines and dogma and all that, but you can't argue with results.

Yup. Fairly low inductance too, although that burned me on a prototype power board -- you still get a few nanohenries here and there, which as it turns out, matters when you surge a hundred amps across it. I opened a hole on that one to increase the supply inductance. Worked like a charm.

In somewhat one-offy stuff with big NRE and big margins like that, it's absolutely true. I'm not working anywhere near Joerg's every-SMT-is-a-threat domain, but we'll notice a few hundred bucks here and there on the books, so it's worth trying, especially on bigger boards.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

I stand corrected.

A track across a slit is an antenna. Unless there's another plane underneath covering the slit, in which case it probably doesn't matter.

Jeroen Belleman

Lucky him. There can't be all that many hosts who don't know how marginal his stuff actually is. Rather like Michelin's lowest grade of approval - useful in the area, at the price. His books aren't cheap, but they are cheaper than a google search or a couple of hours in a good technical library.

-- Bill Sloman, Nijmegen

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.

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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.

? Ralph Morrison on Grounding and sheilding? (the only Morrison on my shelf) Or someone else?

George H.

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